1. A wireless power transfer system, comprising:
an auxiliary coil positioned in proximity to at least one of a power source and a power receiver;
a detector positioned in proximity to at least one of the power source and the power receiver, wherein the detector is configured to generate an electrical signal in response to a change in a magnetic field; and
control electronics coupled to the auxiliary coil and to the detector, wherein the control electronics are configured to;
activate at least one of the power source and the auxiliary coil to generate a magnetic field at a position of the detector;
measure the electrical signal generated by the detector in response to the magnetic field; and
determine whether debris is positioned in proximity to at least one of the power source and the power receiver by comparing baseline information to the measured electrical signal,wherein the baseline information comprises information about an electrical signal generated by the detector when no debris is positioned in proximity to the power source and the power receiver; and
wherein the control electronics are configured to compare the baseline information to the measured signal by determining mean and covariance matrices for the baseline information and determining whether debris is positioned in proximity to at least one of the power source and the power receiver based on the mean and covariance matrices.
1 Assignment
The disclosure features apparatus, methods, and systems for wireless power transfer that include a power source featuring at least one resonator, a power receiver featuring at least one resonator, a first detector featuring one or more loops of conductive material and configured to generate an electrical signal based on a magnetic field between the power source and the power receiver, a second detector featuring conductive material, and control electronics coupled to the first and second detectors, where during operation, the control electronics are configured to measure the electrical signal of the first detector and compare the measured electrical signal of the first detector to baseline electrical information for the first detector to determine information about whether debris is positioned between the power source and the power receiver.
No References
SYSTEM AND METHODS FOR INDUCTIVE CHARGING, AND IMPROVEMENTS AND USES THEREOF
SAFETY FEATURE FOR WIRELESS CHARGER
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Battery charger with wind tunnel cooling
Illinois Tool Works Inc.
Non-contact charger capable of wireless data and power transmission and related battery pack and mobile device
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Chun-Kil Jung
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COIL UNIT AND ELECTRONIC INSTRUMENT
Powering cell phones and similar devices using RF energy harvesting
Cooling Device for Electrical Apparatus Mounted on Vehicle
Charging circuit, charging system and charging method
NON-CONTACT POWER TRANSMISSION DEVICE, POWER TRANSMISSION DEVICE AND ELECTRONIC APPARATUS USING THE SAME
COIL UNIT AND ELECTRONIC APPARATUS USING THE SAME
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Power transmission device and electronic instrument
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National Institute of Advanced Industrial Science and Technology
Methods and apparatus for stationary object detection
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BAUMER ELECTRIC AG HUMMELSTRASSE 17 8500 FRAUENFELD SWITZERLAND
SYSTEM FOR TRANSFERRING ENERGY WIRELESSLY
Telecom Italia SPA
BATTERY ASSEMBLY WITH COOLING
Samsung SDI Company Limited, Robert Bosch GmbH
INDUCTIVE POWER TRANSFER
DEVICE FOR INDUCTIVE TRANSMISSION OF ELECTRICAL ENERGY
Conductix-Wampfler GmbH
Environmental control system and method for a battery in a vehicle
Ford Global Technologies LLC
ANTENNA ALIGNMENT AND VEHICLE GUIDANCE FOR WIRELESS CHARGING OF ELECTRIC VEHICLES
Power transmission control device, power transmitting device, non-contact power transmission system, and secondary coil positioning method
Chamiraux Management LLC
Power transmission control device, power transmission device, power reception control device, power reception device, electronic apparatus, and contactless power transmission system
Power reception device, non-contact power transmission system, and electronic instrument
RESONANCE-TYPE NON-CONTACT POWER SUPPLY SYSTEM
Ibaraki Toyota Jidosha Kabushiki Kaisha, Kabushiki Kaisha Toyota Jidoshokki
Power transmission control device, power transmission device, power reception control device, power reception device, and electronic apparatus
NONCONTACT CHARGER SYSTEM
WIRELESS POWER SYSTEM WITH CAPACITIVE PROXIMITY SENSING
2. The system of claim 1, wherein the control electronics are configured to calculate a likelihood value that debris is positioned in proximity to at least one of the power source and the power receiver based on the mean and covariance matrices.
3. The system of claim 2, wherein the control electronics are configured to calculate a probability value between 0 and 1 that debris is positioned in proximity to at least one of the power source and the power receiver, based on the likelihood value.
4. The system of claim 2, wherein the control electronics are configured to determine whether debris is positioned in proximity to at least one of the power source and the power receiver by comparing the likelihood value to a threshold likelihood value.
5. The system of claim 1, wherein the control electronics are configured to obtain the baseline information by:
retrieving the information from an electronic storage unit;
oractivating at least one of the power source and the auxiliary coil to generate a magnetic field at a position of the detector with no debris in proximity to the power source and the power receiver to generate a magnetic flux at the detector, and measuring the electrical signal generated by the detector in response to the magnetic flux.
6. The system of claim 5, wherein the control electronics are configured to activate the power source and to measure the electrical signal of the detector without power transfer occurring between the power source and the power receiver.
7. The system of claim 6, wherein the baseline information comprises information about electrical signals generated by the detector that correspond to different operating states of the system, and wherein the different operating states correspond to at least one of different energy transfer rates between the power source and the power receiver, different alignments between the power source and the power receiver, and different spacings between the power source and the power receiver measured along a direction orthogonal to a plane defined by the auxiliary coil.
8. The system of claim 7, wherein the control electronics are configured to generate mean and covariance matrices that correspond to each of the different operating states, and to compare the measured signal to a portion of the baseline information that corresponds to the operating state of the system.
9. The system of claim 8, wherein the control electronics are configured to determine the operating state of the system by comparing the measured electrical signal of the detector to the mean and covariance matrices corresponding to each of the different operating states.
10. The system of claim 1, wherein the power source is a component of a vehicle charging station, and the power receiver is a component of a vehicle.
11. The system of claim 1, wherein the auxiliary coil comprises one or more loops of conductive material arranged to form a planar coil defining a first plane, and wherein the detector comprises one or more loops of conductive material each positioned in a second plane approximately parallel to the first plane.
12. The system of claim 11, wherein the detector comprises multiple loops of conductive material spaced from one another in the second plane.
13. The system of claim 12, wherein a magnetic flux density generated by the power source in a first region of the second plane is larger than a magnetic flux density in a second region of the second plane, and wherein an area of the detector loops is smaller in the first region of the second plane than an area of the detector loops in the second region of the second plane.
14. The system of claim 11, wherein when the auxiliary coil is activated by the control electronics, the auxiliary coil generates a magnetic dipole oriented in a direction perpendicular to the first plane.
15. The system of claim 1, further comprising the power source and the power receiver, wherein the power source comprises a source resonator coil comprising a plurality of loops of conductive material defining a third plane, and wherein the power receiver comprises a receiver resonator coil comprising a plurality of loops of conductive material defining a fourth plane.
16. The system of claim 14, wherein the third and fourth planes are approximately parallel.
17. The system of claim 14, wherein when the power source is activated by the control electronics, a source resonator of the power source generates a magnetic dipole oriented in a direction perpendicular to the third plane.
18. The system of claim 1, wherein the detector is positioned closer to the power source than to the power receiver, and wherein the control electronics are configured so that if debris is positioned in proximity to at least one of the power source and the power receiver, the control electronics at least one of interrupts wireless power transfer between the power source and the power receiver, reduces an energy transfer rate between the power source and the power receiver, and provides a warning indicator to a user of the wireless power transfer system.
19. A method, comprising:
activating an auxiliary coil, separate from a power source and from a power receiver of a wireless power transfer system, to generate a magnetic field at a position of a detector positioned in proximity to at least one of the power source and the power receiver;
measuring an electrical signal generated by the detector in response to the magnetic field; and
determining whether debris is positioned in proximity to at least one of the power source and the power receiver by comparing baseline information to the measured electrical signal,wherein the baseline information comprises information about an electrical signal generated by the detector when no debris is positioned in proximity to the power source and the power receiver; and
wherein comparing the baseline information to the measured signal comprises determining mean and covariance matrices for the baseline information and determining whether debris is positioned in proximity to at least one of the power source and the power receiver based on the mean and covariance matrices.
This application is a continuation of and claims priority to U.S. patent application Ser. No. 14/059,094, filed on Oct. 21, 2013, which claims priority to: U.S. Provisional Patent Application No. 61/716,432, filed on Oct. 19, 2012; U.S. Provisional Patent Application No. 61/866,703, filed on Aug. 16, 2013; and U.S. Provisional Patent Application No. 61/877,482, filed on Sep. 13, 2013. The entire disclosures of the above listed applications are incorporated by reference into this application.
This disclosure relates to wireless energy transfer and methods for detecting foreign object debris (FOD) on wireless power transmission systems.
Energy or power may be transferred wirelessly using a variety of known radiative, or far-field, and non-radiative, or near-field, techniques as detailed, for example, in commonly owned U.S. patent application Ser. No. 12/613,686 published on May 6, 2010 as US 2010/010909445 and entitled “Wireless Energy Transfer Systems,” U.S. patent application Ser. No. 12/860,375 published on Dec. 9, 2010 as 2010/0308939 and entitled “Integrated Resonator-Shield Structures,” U.S. patent application Ser. No. 13/222,915 published on Mar. 15, 2012 as 2012/0062345 and entitled “Low Resistance Electrical Conductor,” U.S. patent application Ser. No. 13/283,811 published on Oct. 4, 2012 as 2012/0248981 and entitled “Multi-Resonator Wireless Energy Transfer for Lighting,” the contents of which are incorporated by reference.
In general, in a first aspect, the disclosure features wireless power transfer systems that include a power source featuring at least one resonator, a power receiver featuring at least one resonator, where the power receiver is configured to receive electrical power transmitted wirelessly by the power source, a first detector featuring one or more loops of conductive material, where the first detector is configured to generate an electrical signal based on a magnetic field between the power source and the power receiver, a second detector featuring conductive material, and control electronics coupled to the first and second detectors, where during operation of the system, the control electronics are configured to: measure the electrical signal of the first detector, compare the measured electrical signal of the first detector to baseline electrical information for the first detector to determine information about whether debris is positioned between the power source and the power receiver; measure an electrical signal of the second detector, where the electrical signal of the second detector is related to a capacitance of the second detector; and compare the measured electrical signal of the second detector to baseline electrical information for the second detector to determine information about whether a living object is positioned between the power source and the power receiver.
Embodiments of the systems can include any one or more of the following features.
The power source can be a component of a vehicle charging station. The power receiver can be a component of a vehicle.
The electrical signal generated by the first detector can include at least one of a voltage and a current. The electrical signal of the second detector can include at least one of a voltage and a capacitance.
The baseline electrical information for the first detector can correspond to an electrical signal of the first detector when no debris is positioned between the power source and the power receiver. The baseline electrical information for the second detector can correspond to an electrical signal of the second detector when no living objects are positioned between the power source and the power receiver.
Determining information about whether debris is positioned between the power source and the power receiver can include comparing a likelihood value that debris is positioned between the power source and the power receiver to a threshold value. The control electronics can be configured to determine the likelihood value by calculating mean and covariance matrices for the baseline electrical information for the first detector, and determining the likelihood value based on the mean and covariance matrices. Determining information about whether a living object is positioned between the power source and the power receiver can include comparing the measured electrical signal of the second detector to a threshold value.
The first detector can include multiple loops of conductive material positioned in at least a first plane between the power source and the power receiver. The second detector can include a length of conductive material positioned in at least a second plane between the power source and the power receiver. The first and second planes can be parallel. The first and second planes can be the same plane.
A magnetic field generated by the power source in the second plane can have a full width at half maximum cross-sectional distribution, and a circular perimeter of minimum size that encircles the second detector in the second plane has an enclosed area that is 100% or more (e.g., 110% or more, 120% or more, 130% or more, 140% or more, 150% or more, 175% or more, 200% or more) of the full width at half maximum cross-sectional distribution.
The length of conductive material can form a serpentine pathway in the second plane. The length of conductive material can include a plurality of segments extending substantially in a common direction, and a spacing between at least some of the segments can vary in a direction perpendicular to the common direction. A magnetic flux density generated by the power source in a first region of the second plane can be larger than a magnetic flux density in a second region of the second plane, and a spacing between successive segments in the first region can be smaller than in the second region.
The first detector can include a plurality of loops spaced from one another in the first plane, and a spacing between adjacent loops can vary. A magnetic flux density generated by the power source in a first region of the first plane can be larger than a magnetic flux density in a second region of the first plane, and the spacing between adjacent loops can be smaller in the first region than in the second region. The first and second planes can be positioned closer to the power receiver than to the power source.
A total cross-sectional area of the at least one resonator of the power receiver can be 80% or more (e.g., 90% or more, 100% or more, 120% or more, 140% or more, 150% or more, 175% or more) of a full-width at half maximum cross-sectional area of a magnetic field generated by the power source at a position of the power receiver.
The power source can be configured to transfer 1 kW or more (e.g., 2 kW or more, 3 kW or more, 4 kW or more, 6 kW or more, 8 kW or more, 10 kW or more, 15 kW or more, 20 kW or more) of power to the power receiver.
The power source can be configured to transfer power at multiple different energy transfer rates to the power receiver. The control electronics can be configured to: adjust the power source to transfer power at a selected one of the multiple different energy transfer rates; and obtain baseline electrical information that corresponds to the selected energy transfer rate.
Obtaining the baseline electrical information can include retrieving the information from an electronic storage unit. The control electronics can be configured to measure the baseline electrical information by: activating the power source with no debris in the vicinity of the power source to generate a magnetic flux through the first detector; and measuring the electrical signal of the first detector in response to the magnetic flux. The control electronics can be configured to activate the power source and to measure the electrical signal of the first detector with the power source and the power receiver at least partially aligned. The control electronics can be configured to activate the power source and to measure the electrical signal of the first detector without power transfer occurring between the power source and the power receiver.
The power source can be configured to generate a magnetic flux of at least 6.25 μT (e.g., at least 7 μT, at least 8 μT, at least 10 μT, at least 15 μT, at least 20 μT, at least 30 μT, at least 50 μT) at a position between the power source and the power receiver.
The first detector can include multiple loops, and the control electronics can be configured to measure electrical signals generated by at least some of the multiple loops to determine information about misalignment between the power source and the power receiver based on the measured electrical signal. The at least some of the multiple loops can be positioned adjacent to an edge of the power source. The control electronics can be configured to determine the information about misalignment by comparing electrical signals generated by the at least some of the multiple loops.
The control electronics can be configured so that if the likelihood value corresponding to whether debris is positioned between the power source and the power receiver exceeds the threshold value, the control electronics interrupt wireless power transfer between the power source and the power receiver. The control electronics can be configured so that if the likelihood value corresponding to whether debris is positioned between the power source and the power receiver exceeds the threshold value, the control electronics reduce an energy transfer rate between the power source and the power receiver. The control electronics can be configured so that if the likelihood value corresponding to whether debris is positioned between the power source and the power receiver exceeds the threshold value, the control electronics provide a warning indicator to a user of the wireless power transfer system.
The control electronics can be configured so that if the measured electrical signal of the second detector exceeds the threshold value, the control electronics interrupt wireless power transfer power the power source and the power receiver. The control electronics can be configured so that if the measured electrical signal of the second detector exceeds the threshold value, the control electronics reduce a magnitude of a magnetic field generated by the power source. The control electronics can be configured so that if the measured electrical signal of the second detector exceeds the threshold value, the control electronics provide a warning indicator to a user of the wireless power transfer system.
Each resonator in the power source can be an electromagnetic resonator having a resonant frequency f=ω/2π, an intrinsic loss rate Γ, and a Q-factor Q=ω/(2Γ), and the Q-factor for at least one of the resonators in the power source can be greater than 100. Each resonator in the power source can have a capacitance and an inductance that define the resonant frequency f. The Q-factor for at least one of the resonators in the power source can be greater than 300.
Each resonator in the power receiver can be an electromagnetic resonator having a resonant frequency f=ω/2π, an intrinsic loss rate Γ, and a Q-factor Q=ω/(2Γ), and the Q-factor for at least one of the resonators in the power receiver can be greater than 100. Each resonator in the power receiver can have a capacitance and an inductance that define the resonant frequency f. The Q-factor for at least one of the resonators in the power receiver can be greater than 300.
Embodiments of the systems can also include any of the other features disclosed herein, in any combination, as appropriate.
In another aspect, the disclosure features methods that include measuring an electrical signal generated by a first detector featuring one or more loops of conductive material positioned between a power source and a power receiver in a wireless power transfer system, comparing the measured electrical signal generated by the first detector to baseline electrical information for the first detector to determine information about whether debris is positioned between the power source and the power receiver, measuring an electrical signal generated by a second detector featuring conductive material, where the electrical signal of the second detector is related to a capacitance of the second detector, and comparing the measured electrical signal generated by the second detector to baseline electrical information for the second detector to determine information about whether a living object is positioned between the power source and the power receiver.
Embodiments of the methods can include any one or more of the following features.
The power receiver can be a component of a vehicle, and the methods can include using the power source to transfer electrical power to the vehicle. The baseline electrical information for the first detector can correspond to an electrical signal of the first detector when no debris is positioned between the power source and the power receiver. The baseline electrical information for the second detector can correspond to an electrical signal of the second detector when no living objects are positioned between the power source and the power receiver.
Determining information about whether debris is positioned between the power source and the power receiver can include comparing a likelihood value that debris is positioned between the power source and the power receiver to a threshold value. The methods can include determining the likelihood value by calculating mean and covariance matrices for the baseline electrical information for the first detector, and determining the likelihood value based on the mean and covariance matrices. Determining information about whether a living object is positioned between the power source and the power receiver can include comparing the measured electrical signal of the second detector to a threshold value.
The methods can include using the power source to transfer 1 kW or more (e.g., 2 kW or more, 3 kW or more, 4 kW or more, 6 kW or more, 8 kW or more, 10 kW or more, 15 kW or more, 20 kW or more) of power to the power receiver.
The power source can be configured to transfer power at multiple different energy transfer rates to the power receiver, and the methods can include adjusting the power source to transfer power at a selected one of the multiple different energy transfer rates, and obtaining baseline electrical information that corresponds to the selected energy transfer rate. Obtaining the baseline electrical information can include retrieving the information from an electronic storage unit.
The methods can include activating the power source with no debris in the vicinity of the power source to generate a magnetic flux through the first detector, and measuring the electrical signal of the first detector in response to the magnetic flux to obtain the baseline electrical information for the first detector. The methods can include activating the power source and measuring the electrical signal of the first detector with the power source and the power receiver at least partially aligned. The methods can include activating the power source and measuring the electrical signal of the first detector without power transfer occurring between the power source and the power receiver.
The methods can include generating a magnetic flux of 6.25 μT or more (e.g., 7 μT or more, 8 μT or more, 10 μT or more, 15 μT or more, 20 μT or more, 30 μT or more, 50 μT or more) between the power source and the power receiver.
The methods can include measuring electrical signals generated by multiple loops of the first detector, and determining information about misalignment between the power source and the power receiver based on the measured electrical signals. The methods can include determining the information about misalignment by comparing electrical signals generated by the multiple loops.
The methods can include interrupting wireless power transfer between the power source and the power receiver if the likelihood value corresponding to whether debris is positioned between the power source and the power receiver exceeds the threshold value. The methods can include reducing an energy transfer rate between the power source and the power receiver if the likelihood value corresponding to whether debris is positioned between the power source and the power receiver exceeds the threshold value. The methods can include providing a warning indicator if the likelihood value corresponding to whether debris is positioned between the power source and the power receiver exceeds the threshold value.
The methods can include interrupting wireless power transfer between the power source and the power receiver if the measured electrical signal of the second detector exceeds the threshold value. The methods can include reducing an energy transfer rate between the power source and the power receiver if the measured electrical signal of the second detector exceeds the threshold value. The methods can include providing a warning indicator if the measured electrical signal of the second detector exceeds the threshold value.
The methods can also include any of the other steps and/or features disclosed herein, in any combination, as appropriate.
In a further aspect, the disclosure features an apparatus for detecting debris and living objects, the apparatus including a first detector featuring one or more loops of conductive material, where the first detector is configured to generate an electrical signal based on a magnetic field between a power source and a power receiver of a wireless power transfer system, a second detector featuring conductive material, and control electronics coupled to the first and second detectors, where during operation of the wireless power transfer system, the control electronics are configured to: measure the electrical signal of the first detector; compare the measured electrical signal of the first detector to baseline electrical information for the first detector to determine information about whether debris is positioned between the power source and the power receiver of the wireless power transfer system; measure an electrical signal of the second detector, where the electrical signal of the second detector is related to a capacitance of the second detector; and compare the measured electrical signal of the second detector to baseline electrical information for the second detector to determine information about whether a living object is positioned between the power source and the power receiver of the wireless power transfer system.
Embodiments of the apparatus can include any of the features disclosed herein, including any of the features disclosed herein in connection with any of the systems, in any combination, as appropriate.
In another aspect, the disclosure features a wireless power transfer system, including a power source featuring at least one resonator, a power receiver featuring at least one resonator, where the power receiver is configured to receive electrical power transmitted wirelessly by the power source, a detector positioned between the power source and the power receiver, where the detector is configured to generate an electrical signal based on a magnetic field between the power source and the power receiver, and control electronics coupled to the power source and detector, where the control electronics are configured to: activate the power source to generate a magnetic field between the power source and the power receiver; measure the electrical signal of the detector; and determine whether debris is positioned between the power source and the power receiver by comparing baseline information to the measured electrical signal, where the baseline information includes information about an electrical signal generated by the detector when no debris is positioned between the power source and the power receiver, and where the control electronics are configured to compare the baseline information to the measured signal by determining mean and covariance matrices for the baseline information and determining whether debris is positioned between the power source and the power receiver based on the mean and covariance matrices.
The control electronics can be configured to calculate a likelihood value that debris is positioned between the power source and the power receiver based on the mean and covariance matrices. The control electronics can be configured to calculate a probability value between 0 and 1 that debris is positioned between the power source and the power receiver, based on the likelihood value. The control electronics can be configured to determine whether debris is positioned between the power source and the power receiver by comparing the likelihood value to a threshold likelihood value.
The control electronics can be configured to obtain the baseline information. The control electronics can be configured to obtain the baseline information by retrieving the information from an electronic storage unit. The control electronics can be configured to obtain the baseline information by activating the power source with no debris in the vicinity of the power source to generate a magnetic flux through the detector, and measuring the electrical signal of the detector in response to the magnetic flux. The control electronics can be configured to activate the power source and to measure the electrical signal of the detector with the power source and the power receiver at least partially aligned. The control electronics can be configured to activate the power source and to measure the electrical signal of the detector without power transfer occurring between the power source and the power receiver.
The baseline information can include information about electrical signals generated by the detector that correspond to different operating states of the system. The different operating states can correspond to different energy transfer rates between the power source and the power receiver. The different operating states correspond to different alignments between the power source and the power receiver. The different operating states can correspond to different spacings between the power source and the power receiver measured along a direction orthogonal to a plane defined by the at least one resonator of the power source.
The control electronics can be configured to obtain the baseline information by measuring the electrical signal of the detector multiple times in response to the magnetic flux, and the mean and covariance matrices can include contributions from the multiple measurements of the electrical signal. The control electronics can be configured to generate mean and covariance matrices that correspond to each of the different operating states. The control electronics can be configured to determine the operating state of the system by comparing the measured electrical signal of the detector to the mean and covariance matrices corresponding to each of the different operating states.
The electrical signal generated by the detector can include at least one of a voltage and a current. The detector can include multiple loops of conductive material positioned between the power source and the power receiver. The multiple loops can be spaced from one another in the plane, and a spacing between adjacent loops can vary.
A magnetic flux density generated by the power source in a first region of the plane can be larger than a magnetic flux density in a second region of the plane, and the spacing between adjacent loops can be smaller in the first region than in the second region.
The detector can be positioned closer to the power receiver than to the power source. A total cross-sectional area of the at least one resonator of the power receiver can be 80% or more (e.g., 90% or more, 100% or more, 120% or more, 140% or more, 150% or more, 175% or more) of a full-width at half maximum cross-sectional area of a magnetic field generated by the power source at a position of the power receiver.
The power source is configured to transfer 1 kW or more (e.g., 2 kW or more, 3 kW or more, 4 kW or more, 6 kW or more, 8 kW or more, 10 kW or more, 15 kW or more, 20 kW or more) of power to the power receiver.
The control electronics can be configured to compare the measured signal to a portion of the baseline information that corresponds to the operating state of the system.
The power source can be configured to generate a magnetic flux of 6.25 μT or more (e.g., 7 μT or more, 8 μT or more, 10 μT or more, 15 μT or more, 20 μT or more, 30 μT or more, 50 μT or more) between the power source and the power receiver.
The detector can include multiple loops of conductive material each configured to generate an electrical signal when the power source generates a magnetic field, and the control electronics can be configured to measure the electrical signals generated by at least some of the multiple loops and to determine information about misalignment between the power source and the power receiver based on the measured electrical signals. The at least some of the multiple loops can be positioned adjacent to an edge of the power source. The control electronics can be configured to determine the information about misalignment by comparing electrical signals generated by the at least some of the multiple loops. The control electronics can be configured so that if debris is positioned between the power source and the power receiver, the control electronics interrupt wireless power transfer between the power source and the power receiver.
The control electronics can be configured so that if debris is positioned between the power source and the power receiver, the control electronics reduce an energy transfer rate between the power source and the power receiver. The control electronics can be configured so that if debris is positioned between the power source and the power receiver, the control electronics provide a warning indicator to a user of the wireless power transfer system.
Each resonator in the power source can be an electromagnetic resonator having a resonant frequency f=ω/2π, an intrinsic loss rate Γ, and a Q-factor Q=ω/(2Γ), and the Q-factor for at least one of the resonators in the power source can be greater than 100. Each resonator in the power source can have a capacitance and an inductance that define the resonant frequency f.
The Q-factor for at least one of the resonators in the power source can be greater than 300.
In a further aspect, the disclosure features methods that include activating a power source to generate a magnetic field between the power source and a power receiver of a wireless power transfer system, measuring an electrical signal generated by a detector positioned between the power source and the power receiver, and determining whether debris is positioned between the power source and the power receiver by comparing baseline information to the measured electrical signal, where the baseline information includes information about an electrical signal generated by the detector when no debris is positioned between the power source and the power receiver, and where comparing the baseline information to the measured signal includes determining mean and covariance matrices for the baseline information and determining whether debris is positioned between the power source and the power receiver based on the mean and covariance matrices.
The methods can include determining a likelihood value that debris is positioned between the power source and the power receiver based on the mean and covariance matrices. The methods can include determining a probability value between 0 and 1 that debris is positioned between the power source and the power receiver, based on the likelihood value. The methods can include determining whether debris is positioned between the power source and the power receiver by comparing the likelihood value to a threshold likelihood value.
The methods can include obtaining the baseline information by retrieving the information from an electronic storage unit. The methods can include obtaining the baseline information by activating the power source with no debris in the vicinity of the power source to generate a magnetic flux through the detector, and measuring the electrical signal of the detector in response to the magnetic flux. The methods can include activating the power source and measuring the electrical signal of the detector with the power source and the power receiver at least partially aligned. The methods can include activating the power source and measuring the electrical signal of the detector without power transfer occurring between the power source and the power receiver.
The baseline information can include information about electrical signals generated by the detector that correspond to different operating states of the system. The different operating states can correspond to at least one of different energy transfer rates between the power source and the power receiver, different alignments between the power source and the power receiver, and different spacings between the power source and the power receiver measured along a direction orthogonal to a plane defined by the at least one resonator of the power source. The methods can include obtaining the baseline information by measuring the electrical signal of the detector multiple times in response to the magnetic flux, where the mean and covariance matrices include contributions from the multiple measurements of the electrical signal.
The methods can include generating mean and covariance matrices that correspond to each of the different operating states. The methods can include determining the operating state of the system by comparing the measured electrical signal of the detector to the mean and covariance matrices corresponding to each of the different operating states.
The methods can include using the power source to transfer electrical power to a power receiver in a vehicle. The methods can include using the power source to transfer 1 kW or more (e.g., 2 kW or more, 3 kW or more, 4 kW or more, 6 kW or more, 8 kW or more, 10 kW or more, 15 kW or more, 20 kW or more) of power to the power receiver.
The methods can include comparing the measured signal to a portion of the baseline information that corresponds to the operating state of the system.
The methods can include using the power source to generate a magnetic flux of 6.25 μT or more (e.g., 7 μT or more, 8 μT or more, 10 μT or more, 15 μT or more, 20 μT or more, 30 μT or more, 50 μT or more) between the power source and the power receiver.
The methods can include interrupting wireless power transfer between the power source and the power receiver if debris is positioned between the power source and the power receiver. The methods can include reducing an energy transfer rate between the power source and the power receiver if debris is positioned between the power source and the power receiver. The methods can include providing a warning indicator if debris is positioned between the power source and the power receiver.
Embodiments of the methods can also include any of the other steps or features disclosed herein, in any combination, as appropriate.
In another aspect, the disclosure features apparatus for detecting debris, the apparatus including a detector, where the detector is configured so that when the detector is positioned between a power source and a power receiver of a wireless power transfer system, the detector generates an electrical signal based on a magnetic field between the power source and the power receiver, and control electronics coupled to the detector, where the control electronics are configured to: measure the electrical signal of the detector in response to a magnetic field between the power source and the power receiver; and determine whether debris is positioned between the power source and the power receiver by comparing baseline information to the measured electrical signal, where the baseline information includes information about an electrical signal generated by the detector when no debris is positioned between the power source and the power receiver, and where the control electronics are configured to compare the baseline information to the measured signal by determining mean and covariance matrices for the baseline information and determining whether debris is positioned between the power source and the power receiver based on the mean and covariance matrices.
In accordance with exemplary and non-limiting embodiments, a foreign object debris detection system may measure perturbations in the electromagnetic field around the resonators of a wireless energy transfer system using magnetic field sensors and/or gradiometers. The sensors and/or gradiometers may be positioned in the electromagnetic field of a wireless energy transfer system. The sensors and/or gradiometers may be positioned to substantially cover an area over which FOD should be detected. In an embodiment for a wireless power transfer system of a vehicle, an area over which FOD should be detected may include a region of the underside of a vehicle, or the entire underside of a vehicle, or a region larger than the underside of a vehicle, or a region that may not be under the underside of a vehicle. The sensors and/or gradiometers may include loops of wire and/or printed conductor traces forming loops, figure-8 loops, and/or structures including one loop or multiple loops that generate an electrical signal proportional to the amount of magnetic flux crossing the surface area enclosed by the loop and/or loops. The loop and/or loops may be connected to high-input-impedance readout circuitry. The readout circuitry may measure the voltage and/or the current and/or the relative phase of the voltages and/or currents in the loops. In embodiments, a system may include multiple layers of loops to increase the detection probability of FOD. In embodiments, the loops may be designed to operate without significantly affecting characteristics of a wireless power transfer system such as the perturbed quality factors of the resonators, the efficiency of the energy transfer, the amount of power transferred, the amount of heat generated by the system, and the like.
In this disclosure, it is understood that a gradiometer is a type of sensor. A gradiometer may include one or more detectors. For example, the one or more detectors can be used to detect a magnetic field flux around the detector.
In accordance with exemplary and non-limiting embodiments, a foreign object debris detection system may measure perturbations in the electric field around the resonators of a wireless energy transfer system using electric field sensors and/or gradiometers. The sensors and/or gradiometers may be positioned in the electromagnetic field of a wireless energy transfer system. The sensors and/or gradiometers may include lengths of wire and/or printed conductor traces and/or any type of conducting path and they may include a single or multiple conducting paths. The conducting path or paths may be constructed to substantially cover the area where FOD may need to be detected. In an embodiment, an electric field sensor may be a single conducting path that travels back and form across the FOD surface and in another embodiment there may be multiple substantially straight conducting paths that traverse the FOD surface and are sensed individually or after a parallel electrical connection and/or in a multiplexed manner. The electric field sensors and/or gradiometers may be connected to high-input-impedance readout circuitry. The readout circuitry may measure the voltage and/or the current and/or the relative phase of the voltages and/or currents in the sensors. In embodiments, a system may include multiple layers of sensors to increase the detection probability of FOD. In embodiments, sensors may be designed to operate without significantly affecting characteristics of a wireless power transfer system such as the perturbed quality factors of the resonators, the efficiency of the energy transfer, the amount of power transferred, the amount of heat generated by the system, and the like.
In accordance with exemplary and non-limiting embodiments, there is provided a wireless energy transfer system that may include at least one foreign object debris detection system. The system may include at least one wireless energy transfer source configured to generate an oscillating magnetic field. The foreign object debris may be detected by a field sensor positioned in the oscillating electromagnetic field. The voltages and/or currents of the field sensors may be measured using readout circuitry and a feedback loop based on the readings from the sensors may be used to control the parameters of the wireless energy source.
In this disclosure, FOD is used to refer to foreign object debris. It is understood that detecting FOD may be referred as foreign object detection and/or living object detection (LOD). In the industry, it is becoming more common to refer to detecting living objects as LOD, rather than FOD, but it is also generally recognized that FOD include a wide variety of materials and objects. In this disclosure, it is understood that foreign objects may include living objects. Accordingly, although the terms “FOD” and “LOD” are both used, it is understood that LOD may be considered as detecting FOD. Techniques disclosed in relation to detecting FOD are applicable to LOD, and vice versa. For example, an FOD sensor may be used as an LOD sensor, and methods for using an FOD sensor are applicable to an LOD sensor. Further, in this disclosure, a “living object” is an object that is composed, at least partially, of living organic tissue, e.g., cells. A living object can be an entire organism (e.g., a human, an animal, a plant). A living object can also be a portion of an organism (e.g., one or more limbs or body parts of a human, animal, or plant). A living object can also include an object (or a portion thereof) composed, at least partially, of organic tissue that was once living, but is now dead (e.g., a limb of a tree, a body of an animal).
FIG. 1 is a schematic diagram that shows a side view of a resonator with a resonator cover providing passive FOD mitigation.
FIG. 2 is a schematic diagram that shows two loops of wire that may be used as individual field sensors and that may be fashioned into a gradiometer that senses the difference in the magnetic flux captured by the two individual field loops.
FIG. 3A is a schematic diagram that shows a two-lobe configuration of two small conductor loops arranged to have opposed magnetic dipoles, (such a structure may be referred to as a magnetic quadrupole); FIG. 3B is a schematic diagram that shows a 4-lobe configuration of aligned magnetic quadrupoles; FIG. 3C is a schematic diagram that shows a 4-lobe configuration of opposed quadrupoles, sometimes referred to as an octupole; and FIG. 3D is a schematic diagram that shows a 4-lobe configuration extending in a linear dimension. The “+” and “−” signs indicate the direction of the magnetic dipole of each loop, in a relative reference frame.
FIG. 4A is a schematic diagram that shows a FOD detector array including loops with a substantially square shape to achieve high area-fill factor; and FIG. 4B is a schematic diagram that shows an embodiment with two offset arrays, an arrangement that may be used to eliminate blind spots.
FIG. 5 is a schematic diagram that shows an exemplary FOD detector connected to a readout circuit.
FIG. 6 is a schematic diagram that shows an array of exemplary FOD detectors connected to readout circuitry.
FIG. 7 is a schematic diagram that shows an array of FOD detectors connected to readout circuitry and a synchronization or reference loop.
FIG. 8 is a schematic diagram that shows an example embodiment of FOD detector loops.
FIGS. 9A-9C are graphs that show voltage measurement curves from a figure-8 gradiometer sensor.
FIG. 10 is a schematic diagram that shows a block diagram of an exemplary EV charger system.
FIGS. 11A-C are schematic diagrams that show asymmetrical sensors with different shapes.
FIG. 12 is a schematic diagram that shows a symmetric arrangement of FOD sensors.
FIG. 13 is a schematic diagram that shows an asymmetric arrangement of FOD sensors.
FIG. 14 is a schematic diagram that shows another asymmetric arrangement of FOD sensors.
FIG. 15 is a schematic diagram that shows a further asymmetric arrangement of FOD sensors.
FIG. 16 is a schematic diagram that shows an exemplary layout of a FOD detection sensor board.
FIG. 17 is a schematic diagram that shows an exemplary layout of a FOD detection sensor board with shielding traces.
FIGS. 18A-18F are schematic diagrams that show different arrangements of sensors.
FIGS. 19A-19E are schematic diagrams that show different arrangements of sensors.
FIGS. 20A-20C are schematic diagrams that show different arrangements of sensors.
FIGS. 21A-21D are schematic diagrams that show different arrangements of sensors.
FIG. 22 is a schematic diagram that shows an arrangement of FOD sensors.
FIG. 23 is a flow chart that shows a series of steps for detecting high fields using field sensors.
FIG. 24 is a flow chart that shows a series of steps for stand-alone FOD detection.
FIG. 25 is a flow chart that shows a series of steps for implementing different modes of operation of a FOD detection system.
FIG. 26 is a schematic diagram of an embodiment of a combined foreign object debris and living object debris detection system.
FIG. 27 is a schematic diagram of an embodiment of control electronics that include a computer system for detecting foreign object debris and/or living object debris.
FIG. 28 is a schematic diagram showing example arrangement of wireless power transfer systems.
FIG. 29 is a schematic diagram showing example alignments between a source coil and a device coil.
FIG. 30 are plots of simulation results obtained by a FOD sensor board.
FIG. 31 are plots of simulation results shown in FIG. 30 subtracted by a baseline pattern.
FIG. 32 are plots of simulation results with rescaled color bars.
FIG. 40 is a schematic diagram of a wireless power transfer system 4000.
FIG. 42 is a schematic diagram of a source.
FIG. 43A is a schematic diagram of a LOD sensor arrangement.
FIG. 43B are schematic diagrams of LOD sensors.
FIG. 44 is a schematic diagram of plots graphing an example measurement of two sensors.
It is understood that the figures show exemplary embodiments even if it is not explicitly stated to be exemplary.
Wireless power transfer systems that rely on an oscillating magnetic field between two coupled resonators can be efficient, non-radiative, and safe. Non-magnetic and/or non-metallic objects that are inserted between the resonators may not substantially interact with the magnetic field used for wireless energy transfer. In some embodiments, users of wireless power transfer systems may wish to detect the presence of these “foreign objects” and may wish to control, turn down, turn off, alarm, and the like, the wireless power transfer system. Metallic objects and/or other objects inserted between the resonators may interact with the magnetic field of the wireless power transfer system in a way that causes the metallic and/or other objects to perturb the wireless energy transfer and/or to heat up substantially. In some embodiments, users of wireless power transfer systems may wish to detect the presence of these “foreign objects” and may wish to control, turn down, turn off, alarm, and the like, the wireless power transfer system. In certain embodiments, a user may detect heating of a wireless power transfer system and control, turn down, turn off, set an alarm of the system for safe operation. Techniques for wireless power transfer, detecting the presence of foreign objects or detecting heating of a wireless power transfer system are described, for example, in commonly owned U.S. patent application Ser. No. 13/608,956 filed on Sep. 10, 2012 and entitled “Foreign Object Detection in Wireless Energy Transfer Systems,” U.S. provisional application 61/532,785 filed on Sep. 9, 2011 and entitled “Foreign Object Detection in Wireless Energy Transfer Systems,” U.S. patent application Ser. No. 12/899,281 filed on Oct. 6, 2010 and entitled “Vehicle Charger Safety System and Method,” and U.S. patent application Ser. No. 12/567,716 field on Sep. 25, 2009 and entitled “Wireless Energy Transfer Systems,” the contents of which are incorporated by reference.
Foreign Object Debris (FOD) positioned in the vicinity of wireless power transfer systems can be benign and/or may interact with the fields used for energy transfer in a benign way. Examples of benign FOD may include dirt, sand, leaves, twigs, snow, grease, oil, water, and other substances that may not interact significantly with a low-frequency magnetic field. In embodiments, FOD may include objects that may interact with the fields used for wireless power transfer in a benign way, but that may be restricted from the region very close to the resonators of the wireless transfer systems because of perceived danger, or out of a preponderance of caution. A common example of this type of FOD is a cat that may wish to sleep between the resonators and/or the resonator coils of a wireless vehicle charging system. Although unlikely, some may perceive a possibility of a human, especially a child, positioning themselves between the resonators in a high-power system where the human exposure effects may exceed certain exposure guidelines and regulations. In some cases, humans, animals, organic material, and the like may be a type of FOD in a wireless power transfer system. In some embodiments, the detection of living objects such as cats and people may be referred to as living object detection (LOD). In embodiments, some FOD may interact with the magnetic field in a way that may perturb the characteristics of the resonators used for energy transfer, may block or reduce the magnetic fields used for energy transfer, or may create a fire and or burning hazard. In some applications, special precautions may be necessary to avoid combustible metallic objects becoming hot enough to ignite during high-power charging. Some metallic objects can heat up and have enough heat capacity to cause a burn or discomfort to a person who might pick them up while they are still hot. Examples include tools, coils, metal pieces, soda cans, steel wool, food (chewing gum, burgers, etc.) wrappers, cigarette packs with metal foil, and the like.
Thus what are needed are methods and designs for detecting or mitigating the effects of FOD in the vicinity of a wireless power transfer system.
Methods for mitigating FOD risks can be categorized as passive mitigation techniques and active mitigation techniques. Passive mitigation techniques may be used to prevent FOD from entering or remaining in the regions of high electromagnetic fields (e.g., magnetic, electric fields). Passive mitigation techniques may lower the likelihood of FOD interacting hazardously with electromagnetic fields. Active mitigation techniques may be used detect and react to the presence of FOD.
In this disclosure, “wireless energy transfer” from one coil (e.g., resonator coil) to another coil (e.g., another resonator coil) refers to transferring energy to do useful work (e.g., mechanical work) such as powering electronic devices, vehicles, lighting a light bulb or charging batteries. Similarly, “wireless power transfer” from one coil (e.g., resonator coil) to another resonator (e.g., another resonator coil) refers to transferring power to do useful work (e.g., mechanical work) such as powering electronic devices, vehicles, lighting a light bulb or charging batteries. Both wireless energy transfer and wireless power transfer refer to the transfer (or equivalently, the transmission) of energy to provide operating power that would otherwise be provided through a connection to a power source, such as a connection to a main voltage source. Accordingly, with the above understanding, the expressions “wireless energy transfer” and “wireless power transfer” are used interchangeably in this disclosure. It is also understood that, “wireless power transfer” and “wireless energy transfer” can be accompanied by the transfer of information; that is, information can be transferred via an electromagnetic signal along with the energy or power to do useful work.
In some embodiments, a wireless power transfer system may utilize a source resonator to wirelessly transmit power to a receiver resonator. In certain embodiments, the wireless power transfer may be extended by multiple source resonators and/or multiple device resonators and/or multiple intermediate (also referred as “repeater” resonators.) The resonators can be electromagnetic resonator which are capable of storing energy in electromagnetic fields (e.g., electric, magnetic fields). Any one of the resonators can have a resonant frequency f=ω/2π, an intrinsic loss rate Γ, and a Q-factor Q=ω/(2Γ) (also referred as “intrinsic” Q-factor in this disclosure), where ω is the angular resonant frequency. A resonant frequency f of a resonator, for example, in a power source or power receiver of the system, can have a capacitance and inductance that defines its resonant frequency f.
In some embodiments, any one of a source, receiver, repeater resonator can have a Q-factor that is a high Q-factor where Q>100 (e.g., Q>100, Q>200, Q>300, Q>500, Q>1000). For example, the wireless power transfer system can include a power source having one or more source resonators, and at least one of the source resonators having a Q-factor of Q1>100 (e.g., Q1>100, Q1>200, Q1>300, Q1>500, Q1>1000). The wireless power transfer system can include a power receiver having one or more receiver resonators, and at least one of the receiver resonators having a Q-factor of Q2>100 (e.g., Q2>100, Q2>200, Q2>300, Q2>500, Q2>1000). The system can include at least one receiver resonator having a Q-factor of Q3>100 (e.g., Q3>100, Q3>200, Q3>300, Q3>500, Q3>1000). Utilizing high Q-factor resonators can lead to large energy coupling between at least some or all of the resonators in the wireless power transfer system. The high Q factors can lead to strong coupling between resonators such that the “coupling time” between the resonators is shorter than the “loss time” of the resonators. In this approach, energy can be transferred efficiently between resonators at a faster rate than the energy loss rate due to losses (e.g., heating loss, radiative loss) of the resonators. In certain embodiments, a geometric mean √{square root over (QiQj)} can be larger than 100 (e.g., √{square root over (QiQj)}>200, √{square root over (QiQj)}>300, √{square root over (QiQj)}>500, √{square root over (QiQj)}>1000) where i and j refer to a pair of source-receiver resonator, source-repeater resonator or repeater-receiver resonators (e.g., i=1, j=2, or i=1, j=3, or i=2, j=3.) Any one of the resonators can include coils described in the following sections. Techniques for utilizing high-Q resonators are described, for example, in commonly owned U.S. patent application Ser. No. 12/567,716 field on Sep. 25, 2009 and entitled “Wireless Energy Transfer Systems,” the contents of which are incorporated by reference.
Passive Mitigation Techniques
Passive mitigation techniques may be used to keep FOD from entering the regions between resonators or specific regions of high electromagnetic field, thereby preventing the interaction of the FOD with the electromagnetic fields.
By way of additional exemplary embodiments, the design of a resonator cover in a wireless power transfer system may provide a passive FOD mitigation technique. In embodiments the enclosure of a source and/or device and/or repeater resonator may be shaped to prevent FOD from coming close to the areas of the resonators and/or the resonator coils where the electromagnetic field may be large. In embodiments, a resonator enclosure may be thick enough to keep external objects from getting closer than a specified distance from the resonator or resonator coil. For example, the enclosure may include extra enclosure material and/or an air gap and/or potting materials and/or other objects and/or materials between the resonator coil and the outside surface of the resonator. In embodiments, the distance from the resonator coil surface to the enclosure surface may be 0.5 mm, 1 mm, 5 mm and the like. In embodiments, the distance between the top resonator coil surface and the top enclosure surface and the bottom resonator coil surface and the bottom enclosure surface may be different. In embodiments, the resonator coil may be positioned substantially in the middle of the thinnest dimension of the resonator enclosure. In other embodiments, the resonator coil may be positioned substantially offset from the middle of the thinnest dimension of the resonator enclosure. In embodiments, a resonator coil may be positioned substantially away from a surface that may be exposed to FOD. In embodiments, the resonator enclosure may include a keep-out zone providing for a minimum distance between FOD and the resonator components. The keep-out zone may be sufficiently large to ensure that the fields at the outside of the keep-out zone are sufficiently small to not cause safety or performance concerns.
A resonator enclosure may be designed to be curved, angled, or shaped to force any FOD on the enclosure to roll off the surface of the enclosure or cover and away from the resonator and/or high electromagnetic fields. The resonator enclosure may be shaped or positioned to allow gravity to pull objects away from the resonators. In some embodiments, the enclosures and position of the resonators may be designed to use other natural or omnipresent forces to move FOD away. For example, the force of water currents, wind, vibration, and the like may be used to prevent FOD from accumulating or staying in unwanted regions around resonators. In embodiments, the resonator surfaces where FOD may accumulate may be arranged to be substantially perpendicular to the ground so that objects may not naturally rest and accumulate on the resonators.
An example resonator cover providing a degree of passive FOD protection is shown in FIG. 1. A magnetic resonator 104 of a wireless power transfer system may be surrounded with or enclosed by or placed under a shaped cover 102. The cover 102 may be shaped to force FOD 106 to roll down the cover 102 due to the force of gravity. The shape of the cover 102 may prevent FOD 106 from accumulating on top of the cover 102 and/or in the vicinity of the resonator 104 by forcing any FOD to the sides of the resonator and/or away from the regions surrounding the resonator where the magnitude of the electromagnetic fields is high enough to cause a hazardous condition due to heating of or interaction with the FOD. In embodiments, the FOD may be forced far enough away from the high field regions to no longer pose a risk of being heated and/or ignited by the fields and/or of interacting negatively with the fields. In some embodiments, the cover may include portions shaped as cones, pyramids, mounds, ovals, spheres, and the like. In some embodiments, the cover may include materials that are slippery, such as Teflon, for example, to make it difficult for FOD to remain situated between the source and device resonators.
In other exemplary and non-limiting embodiments, a passive FOD technique may include sizing the resonators and/or resonator components to reduce the maximum electromagnetic field density (e.g., magnetic field density, electric field density) anywhere in the region of wireless power exchange below a desired limit. In some embodiments, relatively large resonator coils may be used to mitigate a subset of FOD risks. For a fixed level of power transfer the use of larger resonator coils may reduce the electromagnetic field strength per unit area required to transfer a certain amount of power wirelessly. For example, the maximum electromagnetic field strength generated by a source may be reduced below a threshold where heating or other hazards may be known to occur. Passive mitigation techniques may not always be possible or practical or sufficient. For example, reducing a FOD hazard by increasing a resonator size may not be practical owing to the system cost or weight constraints or to the desire to integrate a resonator into a system of a specified volume. However, even in applications where a completely passive technique may not be possible, practical and/or sufficient, passive mitigation techniques may be used to at least partially reduce the FOD risk and may be complementary to active mitigation techniques. In some applications, only active mitigation techniques may be utilized.
Active Mitigation Techniques
In accordance with exemplary and non-limiting embodiments, an active mitigation technique for FOD may include a detection system that may detect certain objects, certain types of objects, metallic objects, organic objects, hot objects, perturbations in resonator parameters, and/or perturbations in magnetic field distributions.
In accordance with exemplary and non-limiting embodiments, FOD, such as metallic objects, may be of sufficient size, extent, and/or material composition to perturb the efficiency or power transfer capabilities of a wireless energy transfer system. In such cases, the presence of said FOD may be determined by examining the change in one or more of the voltage, current, and/or power associated with a source resonator and/or device resonator and/or repeater resonator of a wireless power system. One or more of the source, device, or repeater resonators may have an intrinsic quality factor of at least 100 (e.g., at least 200, at least 500). Some FOD may perturb the parameters of the resonators used for energy transfer and/or may perturb the characteristics of the energy transfer. A FOD may change the impedance of a resonator for example. In accordance with exemplary and non-limiting embodiments, these perturbations may be detected by measuring the voltage, current, power, phase, impedance, frequency, and the like of the resonators and the wireless energy transfer. Changes or deviations from expected or predicted values may be used to detect the presence of FOD. In an exemplary embodiment, dedicated FOD sensors may not be needed to detect and react to FOD in a wireless power system.
In accordance with exemplary and non-limiting embodiments, FOD may only weakly perturb the wireless energy transfer and may not be substantially detectable by monitoring electrical parameters of the resonators and/or the characteristics of the wireless energy transfer. Such objects can still create a hazard, however. For example, FOD that only weakly interacts with the magnetic field may still heat up substantially. The FOD may heat up due to the magnetic field or electric field generated during the wireless energy transfer. An example of a FOD that may only weakly interact with the electromagnetic field but that may experience significant heating is a metal-foil-and-paper wrapper such as is often found in chewing gum and cigarette packages and as is often used to wrap food from fast food establishments such as Burger King and Kentucky Fried Chicken. When placed between the resonators of a 3.3-kW wireless energy vehicle charging system, a chewing gum wrapper may not be detectable by examining the electrical parameters associated with the resonators and/or the energy transfer system. However, said wrapper may still absorb enough power to rapidly heat and for the paper backing to eventually burn.
In accordance with exemplary and non-limiting embodiments, an active mitigation system for FOD may include temperature sensors to detect hot spots, hot areas, and/or hot objects on and/or near-by a wireless energy transfer system. A system may include any number of temperature sensors, infrared detectors, cameras, and the like to detect a heat source, heat gradient and the like in and around a wireless energy transfer system. In embodiments, hot object sensing may be used alone or in addition to other active and/or passive mitigation techniques and can be used to further improve the detectability of heated FOD and/or reduce the false-alarm rate of other active FOD detection systems.
In accordance with exemplary and non-limiting embodiments, an active mitigation system for FOD objects that only weakly perturb the electromagnetic field between two resonators may include sensors for measuring small changes in the magnetic field in the proximity of the FOD objects. For example, a metal-foil-and-paper chewing gum wrapper may not substantially alter the magnetic flux between two resonators, but it might substantially alter the magnetic flux through a smaller sensor coil or loop or sensor or gradiometer if it covered and/or blocked any portion of the coil or loop area or sensor or gradiometer. In embodiments, local disturbances in the magnetic field caused by the presence of FOD may be detected by measuring magnetic field changes, variations, gradients, and the like, in the vicinity of the FOD.
In accordance with exemplary and non-limiting embodiments, a FOD sensor may be realized using a small wire loop 202 as shown in FIG. 2. Such a sensor may be placed on or near the resonators used for wireless energy transfer. During operation, a wireless energy transfer system may generate a magnetic field that may pass through the loop. The loop may develop a voltage proportional to the amount of magnetic flux threading the inside of the loop 208. In some embodiments, a voltage induced in a loop may be less than 5V. In another embodiment, a voltage induced in a loop may be less than by. If, for example, a chewing gum wrapper is placed so that it partially covers the loop and/or or deflects and/or absorbs magnetic flux near the loop, then the voltage developed by the loop may change and the change in voltage may be detected and determined to indicate the presence of FOD. In embodiments, a conducting loop may be used to indicate the presence of FOD in a wireless power transfer system.
In accordance with exemplary and non-limiting embodiments, a FOD sensor may be realized using two small wire loops 202, 204 as shown in FIG. 2. Such a sensor may be placed on or near the resonators used for wireless energy transfer. During operation, a wireless energy transfer system may generate a magnetic field that may pass through the two loops. Each individual loop may develop a voltage proportional to the amount of time-varying magnetic flux threading the inside of each loop 206, 208. The difference between the voltages developed by the two loops may be, to first order, proportional to the gradient of the magnetic field in proximity to the loops. If the two loops are placed in a region of substantially uniform field and the loops are substantially similar, then the difference between the magnitudes of the voltages developed by the two loops may be very small. If, for example, a chewing gum wrapper is placed so that it partially covers one of the loops but not the other, then the difference in voltage developed by the two loops may be larger than when the wrapper was not present because the metallic foil of the gum wrapper may deflect or/or absorb some of the magnetic flux that would have normally passed through that loop. In some embodiments, the magnetic flux passing through a loop may be less than 6*10−6 T·m−2.
In embodiments, the output signals developed by the two loops may be subtracted from each other so that the structure formed by the combination of the loops produces a small signal when the sensed field is substantially uniform, and a measurably larger signal when there is a gradient in the field between the two loops. When the loops and/or coils are configured to generate a signal in the presence of a field gradient and/or a non-uniform or substantially non-uniform field, they may be referred to as being arranged as a gradiometer. Note the signals from different loops may be subtracted using analog circuitry, digital circuitry, processors, comparators, and the like. Note that the loops may be connected together in a specific configuration, such as in a figure 8 configuration, so that the voltage induced by the magnetic field crossing the surface area of one of the loops is approximately equal and opposite to the voltage induced by the magnetic field crossing the area of one of the other loops in the sensor. The sensitivity of the sensor and/or gradiometer may be related to the magnitude and/or phase of the voltage difference between the two loops.
Note that a so-called “figure 8” conducting loop may be formed by taking one large conducting loop, pinching it in the middle so that the one large loop forms two approximately equal-sized smaller loops, and then twisting one loop relative to the other by 180 degrees, or an odd multiple of 180 degrees. In embodiments, the figure 8 conducting loops may be realized using any type of conducting traces including, but not limited to, wire, Litz wire, conducting tubing, PCB traces, conducting inks, gels, paints, ribbons and the like.
In accordance with exemplary and non-limiting embodiments, the sensitivity of the loop and/or coil and/or sensor and/or gradiometer may be adjusted to preferentially detect objects of a given size, or above a given size. The sensitivity may be adjusted to reduce false detection rates, to lower the noise of a detection system, and/or to operate over a range of frequencies. In embodiments, the size and shape of the loops may be adjusted to adjust the sensitivity of the sensor. For example, the loops of a sensor may be smaller to lower background signals and to improve sensitivity to smaller FOD. However, if the sensor loops are too small, some FOD may completely cover all the loops of the sensor, so that a signal may not be produced by the FOD. Such scenarios may be mitigated by using multiple FOD sensors and positioning them throughout the region where FOD should be detected. Then, even when one FOD sensor does not detect the FOD, it is likely that at least one other sensor will. In the example given above, the larger FOD may completely cover some sensors, but only partially cover others. The sensors that are partially covered may detect the FOD, and the system can be programmed to react appropriately. In embodiments, the loops may be adjusted to include more turns and/or to include additional loops, such as four loops, or eight loops for example. In embodiments, the loops may be positioned to have rotational symmetry or they may be arranged in a linear arrangement or they may be shaped to fill a region of any size and shape. In embodiments, the loops may be substantially two dimensional and in other embodiments that may be extended in a third dimension to improve performance. For example, loop sensors may be realized on a printed circuit board (PCB) and multiple loop sensors may be realized on one layer (or two to form the figure 8), or multiple loops sensors may be realized on more than two layers of a PCB.
In embodiments where the magnetic field density may be non-uniform in the locations where gradiometers may be placed and/or where other gradiometer and/or loop designs may be implemented, the presence of metallic objects may result in amplitude and/or phase changes in waveforms corresponding to the difference between the two loop voltages. In embodiments, the loops may have a plurality of turns. In accordance with exemplary and non-limiting embodiments, the loop areas 206, 208 may be sized according to the magnetic field strength of a wireless energy transfer system, the desired sensitivity of the detection method, the complexity of the system and the like. If the metallic FOD is substantially smaller than the loop area, only a weak signal may arise when the FOD is present. This weak signal may risk being overwhelmed by noise or interfering signals. If the loop is sized to be on the order of (e.g. within a factor of 3) of the minimum FOD size to be detected, then the signal may be sufficiently large for detection with low false-alarm rate. In embodiments, a FOD sensor and/or gradiometer may include one or more loops of different sizes, shapes and/or arrangements. In embodiments, a FOD sensor may include regions with one sensor, more than one sensor or no sensor.
In an exemplary and non-limiting embodiment, an arrangement of FOD sensors may be optimized via an algorithm, computing systems, user or market feedback data, testing, etc.
In accordance with exemplary and non-limiting embodiments, another way to measure a field gradient in the vicinity of a metallic object may be to create a coil (also referred to as a loop) in a fashion that directly outputs a voltage that may be proportional to the local gradient in the magnetic field. Such a coil may serve the purpose of the two coils depicted in FIG. 2, but may require only one voltage measurement. If, for example, one were to double the area of one of the loops depicted in FIG. 2 and then twist it into a figure-8 shape where each lobe of the figure-8 had approximately equal area, but the voltage induced in each lobe by the local magnetic field is opposite in sign, then the voltage developed across its two terminals can be proportional to the difference in magnetic flux between the two lobes. If the magnetic flux passing through both loops is substantially equal, then the output signal from the sensor may be substantially zero. FIGS. 3A-3D depict some exemplary configurations of twisted loops that may be capable of directly creating a voltage that may be proportional to a local gradient in the strength and/or density of the magnetic field.
The two loops shown in FIG. 2 may be referred to as magnetic dipoles and the loops in FIG. 3A may be referred to as gradiometers and/or magnetic quadrupoles and the loops in FIG. 3B may be referred to as gradiometers and/or octupoles. The quadrupole configuration may develop a voltage proportional to the magnetic field gradient in the left-to-right orientation. The 4-lobe configurations can be configured to measure field gradients (FIG. 3B), and gradients of field gradients (FIG. 3C). FIG. 3D is representative of embodiments where multiple lobes may extend along a linear dimension to cover a FOD detection area that is rectangular, for example. Multiple sensors configured as shown in FIG. 3D may be configured in arrays to cover FOD detection areas of any shape and size. In embodiments, higher-order multipoles with an even number of lobes can also be configured to measure spatial perturbations to the magnetic field. In embodiments, the lobes depicted in FIG. 3A-3D may use multiple turns of a conductor, a wire, a conducting trace and the like.
Each of these configurations can accomplish the goal of measuring magnetic field perturbations due to the presence of FOD. The configurations with multiple lobes may cover more area (detect FOD in more locations) without substantially reducing the likelihood of detecting FOD of similar characteristic size to the lobes.
The loop configurations in FIG. 2 and FIGS. 3A-3D are depicted as circular but loops of any shape and size may be utilized. If it is desirable that multi-loop configurations produce as close to zero net current and/or net voltage when FOD is not present, then the cross-sectional area of each of the loops should be designed to capture equal amounts of flux. In substantially uniform magnetic fields, the loop areas may be substantially equal. If the loops are placed in substantially non-uniform magnetic fields, then the loop areas may be adjusted to be smaller where the field is stronger and larger where the field is weaker so that the voltage induced in each loop is substantially equal in magnitude and opposite in sign.
In embodiments, a sensor array may be calibrated and the signal output from the sensor may be processed in order to improve the performance of the sensor array. For example, if a FOD detection algorithm utilizes a change in a sensor output as a control signal, the sensor can be configured to have its output signal when no FOD is present to be as close to zero as possible. As mentioned above, the output signal may be very close to zero if the signals on the individual sensor lobes substantially cancel each other out. This may increase the dynamic range of the sensor. If the signals developed by the sensors when no FOD is present are not substantially zero, then they may be said to have a “background offset” and the signals may be processed in the detection circuitry and the offsets may be removed. In embodiments, different sensors in an array may have different background offsets. In embodiments, the background offsets may be determined in a calibration procedure
Shapes other than circles may be well suited for arrays with high-area fill factor. Examples include squares, rectangles, hexagons, and other shapes that tile with little interstitial space in between them. FIG. 4A shows an example of square-shaped coils where the array is assumed to extend further than shown and to have an equal number of plus and minus loops.
The purpose of the “+” and “−” signs in the figure is to indicate the relative signs of the induced voltages on the loops. Thus, a figure 8 sensor in a uniform field will be represented by two connected lobes, one marked as plus and the other minus because the lobes are configured so that the signal induced by the field in one loop substantially cancels the signal induced by the field in the other. That is, the plus and minus signs indicate a relative sign of the induced voltages at a given moment in time. Note that in an oscillating magnetic field, the sign of the induced voltages in a single loop or lobe is changing at the same frequency as the magnetic field oscillation. That is, if an induced voltage is positive, i.e. in the “plus” direction, at one point in time, the induced voltage is of opposite sign one half a cycle (tc/2) later (tc=1/f=2π/ω=λ/c). Therefore, the purpose of the “plus” and “minus” signs in the figure is to indicate that the instantaneous voltages induced in a set of loops have either the same relative sign, as would be the case for two “plus” loops and/or two “minus” loops, or have opposing signs, as would be the case for a “plus” and “minus” loop.
In this disclosure, it is understood that a “blind spot” can refer to an area where one or more sensors may not be able to detect a piece of FOD (e.g., debris) due to the arrangement of the one or more sensors. For the configuration shown in FIG. 4A, a symmetrical piece of FOD can be placed in certain positions between adjacent loops so that the field perturbation may not generate a detectable magnetic field gradient. An example of such a so-called “blind spot” is depicted in FIG. 4A. In accordance with exemplary and non-limiting embodiments, a second layer of arrayed loops may be placed above and/or below a first layer and may be translated laterally as shown in FIG. 4B. The amount of translation may be chosen so that the “blind spots” of the first layer of sensors may correspond to locations of maximum detectability or at least adequate detectability for the second layer. In embodiments, the translation may be any translation than improves the likelihood of detection of the FOD relative to the single array detection probability. In this way, the likelihood of having substantial blind spots where a piece of FOD may not be detectable may be reduced. Similar schemes of one or more translated arrays can achieve roughly the same advantage in reducing blind spots. The orientations of the loops in multiple arrays may also be changed to handle non-uniform magnetic fields.
In embodiments, layers of arrayed loops may have similar sized and/or shaped loops. In other embodiments, layers of arrayed loops may have different sized and/or shaped loops. In embodiments with layers of arrayed loops with different sizes and/or shapes, it may not be necessary to translate the arrayed loops in order to reduce the impact of “blind spots” and/or improve the likelihood of detection of the FOD.
In embodiments the individual loops or lobes of the dipoles, quadrupoles, octupoles, and the like may be of multiple sizes and/or of non-uniform sizes. In embodiments where the gradiometer may cover areas of non-uniform magnetic field the loops may be sized to ensure a minimal voltage at the output of the gradiometer loops when no FOD is present. The loops may be sized such that a larger loop is positioned in an area of weaker magnetic field and the smaller loops are positioned in the areas of higher magnetic field. In embodiments the loops may be sized such that a larger loop is positioned in an area of more uniform magnetic field and a smaller loop is positioned in an area of less uniform magnetic field. In embodiments, the size of the gradiometers in a sensor array may vary. In embodiments, smaller gradiometers may be positioned in areas of less uniform magnetic fields. In embodiments, smaller gradiometers may be positioned in areas of larger magnetic field strength to provide detection capability of smaller FOD items, and larger gradiometers may be placed in areas of smaller magnetic field strength where it may only be desired to detect larger items of FOD.
FIGS. 11A, 11B, 11C show several asymmetrical FOD sensor designs. The sensors may be shaped and sized to provide for a substantially zero voltage signal during normal operation when positioned in a non-uniform magnetic field. In an array of sensors 1202 on a board or across a region designed for FOD detection, FOD sensors 1204 may be arranged symmetrically throughout the region as shown in FIG. 12. In some embodiments the FOD sensors may be arranged asymmetrically as shown in FIGS. 13, 14 and 15. In embodiments the sensors may be positioned closer together in areas of high magnetic field and spaced further apart in areas of low magnetic field. For example, it may be desirable to have more sensors and/or higher sensitivity sensors in regions of highest field where FOD is most likely to be heated or to interact negatively with the field. In embodiments, there may be no reason to reduce the amount and/or type of sensors in the lower field regions. In some embodiments, it may be desirable to reduce the number of FOD sensors in an array. For example, if the sensors take up space that may be utilized for other circuitry, or if the sensors require components that add expense to a system, or for any such practical consideration, then it may be preferable to design a FOD system that includes multiple individual FOD sensors whose individual designs and placement within the array are specially designed. While some examples of such uniform and non-uniform arrays are described herein, they are just a few of many examples within the scope of the disclosed techniques.
In accordance with exemplary and non-limiting embodiments, an array of FOD sensors may include multiple types of sensors. In embodiments, a FOD sensor may include single loop sensors and/or dipole loop sensors/gradiometers and/or quadrupole loop sensors/gradiometers and/or octupole loop sensors/gradiometers and so on. Some areas of the FOD sensor may include no sensors and/or gradiometers. A FOD sensor may include temperature sensors, organic material sensors, electric field sensors, magnetic field sensors, capacitive sensors, magnetic sensors, inductive sensors, motion sensors, weight sensors, pressure sensors, water sensors, vibration sensors, optical sensors, and the like, and any combination of sensors.
In accordance with exemplary and non-limiting embodiments, an active mitigation system for FOD that only weakly perturb the electromagnetic field between two resonators may include sensors for measuring small changes in the capacitance of capacitive elements in the proximity of the FOD. For example, an object (e.g., organic, metallic material) placed on or near a wireless power transfer system may not substantially alter the magnetic flux between two resonators, but it might substantially alter the self-capacitance and/or mutual-capacitance of a length of conducting material in its vicinity. In general, when two objects—such as a length of conductive material and an organic or metallic object—approach one another (but remain separated by a dielectric material such as air), the capacitance of both objects changes, an effect referred to as “mutual capacitance”. Sensitive capacitance detectors can be used to detect changes in the capacitance of either object (i.e., as a voltage change, or a direct capacitance measurement), thereby detecting the approach of the objects to one another. Using such methods, in certain embodiments, local disturbances to the capacitive value of a capacitive element caused by the presence of FOD may be detected by detecting capacitance changes, variations, gradients, and the like, in the vicinity of the FOD. Such methods are particularly useful for detecting organic objects (e.g., living objects), which typically do not significantly perturb magnetic fields.
In accordance with exemplary and non-limiting embodiments, a FOD sensor may be realized using a length of wire 1802 as a capacitive element as shown in FIG. 18. The length of wire may have a different capacitance when there is no object in its proximity than when there is an object (e.g., organic, metallic material). If the length of wire 1802 is integrated with a circuit that can measure and/or react to its change in capacitance in the proximity of the object, then the length of wire may be referred to as a capacitive sensor. If the length of wire is placed in an area and/or region of a wireless power transfer system, then its capacitance changes may be used to indicate the presence of certain types of FOD in that area and/or region of wireless power transfer. In embodiments, a length of conductive material with a capacitance that is related to the proximity of certain materials may be used to indicate the presence of FOD in a wireless power transfer system.
In embodiments, any type of material and/or structure that has a capacitance value that may be related to the proximity of certain types of materials may be used in the capacitive sensors envisioned here. A length of wire or any type of conducting path may be attractive because it may be designed to have a sensing area of almost any size and shape and because its performance should not be degraded in the presence of the electromagnetic fields of a wireless power transfer system. Also, the wire/conducting trace'"'"'s capacitance may be changed when material such as organic material is near-by but not necessarily touching the sensor. In embodiments, a wire/conducting trace sensor may detect organic material that is not in physical contact with a resonator or resonator enclosure of a wireless power transfer system. In embodiments, wires/traces for use in a capacitive sensor may be integrated into circuits, PCBs, housings, modules, subsystems, and the like, of a wireless power transfer system.
In this disclosure, it is understood that a wire is an exemplary embodiment and that any type of conducting material, including but not limited to, solid wire, stranded wire, conducting tubing, printed circuit board traces, conducting inks, gels, paints, epoxies, and the like, are also suitable capacitive elements for the disclosed techniques described herein.
In embodiments, a capacitive sensor may include one or more capacitive elements. FIGS. 18A-F show several examples of capacitive elements. FIG. 18A shows an embodiment where a capacitive element 1802 may be of an asymmetrical and/or irregular shape. FIG. 18B shows an embodiment where a capacitive element 1804 may be of a sinusoidal shape and may be arranged to cover a region 1806 over which FOD should be detected. FIG. 18C shows an embodiment in which a capacitive element 1804 is arranged over FOD sensors 1204. FIGS. 18D through 18F show embodiments of an organization of one or more capacitive elements. For example, data from the one or more capacitive elements may be measured at one or more points and may be processed in one or more levels. FIG. 18D shows an embodiment where data measured at points 1808, 1810, 1812, and 1814 may be processed at a central or primary level of processing 1824. FIGS. 18E and 18F show an embodiment where data measured at points 1808, 1810, 1812, 1814, and 1815 may be processed at a primary (processor 1824) and/or secondary (processors 1816 to 1822) levels of processing. In some embodiments, the data from some points may be averaged and compared with others. For example, FIG. 18E shows an embodiment where points 1808 and 1810 may be averaged to be compared to the average of points 1812 and 1814 and may be further compared to point 1815.
The size of the capacitive elements can generally be selected as desired to permit detection of living objects. In some embodiments, for example, a power source generates a magnetic field that extends through a plane in which the capacitive elements are positioned. The field has a cross-sectional field intensity distribution with a full-width at half maximum in the plane. The capacitive elements can be positioned in the plane so that a circular perimeter of minimum size in the plane that encircles the capacitive elements has an enclosed area in the plane that is 100% or more (e.g., 110% or more, 120% or more, 130% or more, 140% or more, 150% or more, 175% or more, 200% or more) of the full-width at half maximum of the cross-sectional field distribution. In particular, by positioning some or all of the capacitive elements near the edges of the field distribution (e.g., near the edges of the power source and/or the power receiver), the capacitive elements can be used to detect living objects before the objects enter the region between the power source and the power receiver.
In general, both the power receiver and the power source can include one or more resonators, each of which can include one or more coils. In some embodiments, a total cross-sectional area of the resonators of the power receiver can be 80% or more (e.g., 100% or more, 120% or more, 140% or more, 150% or more, 175% or more, 200% or more) of a full-width at half maximum cross-sectional area of the magnetic field generated by the power source at the position of the power receiver.
To transfer power to the power receiver, the power source generates a magnetic field (i.e., a flux of magnetic field lines) between the power source and power receiver. In some embodiments, the power source is configured to generate a magnetic flux of at least 6.25 μT (e.g., 7 μT, 8 μT, 9 μT, 10 μT, 12 μT, 15 μT, 20 μT, 30 μT, 40 μT, 50 μT) between the power source and the power receiver (i.e., at one or more points between the power source and the power receiver).
Referring for example to FIG. 18C, in some embodiments, FOD sensors 1204 are positioned in a first plane between a power source and power receiver, and capacitive elements 1804 are positioned in a second plane between the power source and power receiver. The first and second planes can be the same or different planes. Either or both planes can be positioned closer to the power source, closer to the power receiver, or equidistant between the source and receiver in the region between the source and receiver.
FIG. 19 shows other exemplary and non-limiting embodiments of capacitive elements. In FIG. 19A, the boxed area 1902 may represent an exemplary area or region over which FOD should be detected. In this embodiment, a capacitive element 1802 may be realized by a single wire that meanders back and forth across the FOD detection area, e.g., forming a serpentine pathway. FIGS. 19B and 19C show alternate embodiments. FIG. 19D shows a similar embodiment to 19A, but the spacing between the wire paths is smaller while the spacing shown in FIG. 19E is larger. As in the case of the magnetic FOD sensor described above, the size, shape, arrangement, and placement of the sensors may impact the sensitivity of the FOD sensors. For example, a small block of organic material placed over the sensor shown in FIG. 19D may be detected everywhere in the region 1902, whereas that same material placed over the sensor in FIG. 19E may not be detected in the areas highlighted by the dashed circles. In some embodiments, it may be desirable to detect very small pieces of FOD and the sensor design of FIG. 19D may be preferable. In some embodiments, it may be desirable to detect only larger pieces of FOD, and using a detector that detects smaller FOD or that has higher sensitivity to other types of FOD may cause detection errors or false positives, so a sensor design more similar to that shown in FIG. 19E may be preferable.
One way to describe the features of a capacitive sensor is by the spacing between wires or wire segments across the length of the FOD array, the width of the FOD array and the height (for 3-D arrangements) of the FOD array. In FIG. 19A, the wire pattern that forms the capacitive element shows substantially equal spacing between the segments of the sensor along the length (ΔL) and along the width (ΔW). If the sensor included segments that went out of the plane shown as the FOD region 1902, the sensor may be described as having height segment spacing (ΔH). The capacitive elements shown in FIG. 19 are arranged to substantially fill the FOD detection region and may give similar sensitivity throughout the FOD region. Depending on the application, it may be preferable to have regions in the FOD area where the sensors are more sensitive and there may be regions where FOD detection is not required. Exemplary embodiments of those types of sensors are shown in FIG. 20.
In embodiments, a capacitive element may have segments with varying spacing along the length, width, and height of a FOD sensor. FIG. 20 shows several examples of the FOD sensor. Sensor 1802 shown in FIG. 20A may have higher sensitivity to small pieces of FOD on either side than at the center of the FOD region 1902. Sensor 1802 in FIG. 20B may have higher sensitivity to small pieces of FOD in the center than at the sides of the FOD region 1902. Sensor 1802 in FIG. 20C may have higher sensitivity to small pieces of FOD in the corners than at the center of the FOD region 1902. Sensors shown in FIGS. 20A-C may be described as having more than one segment spacing and/or as having variable segment spacing. In embodiments, capacitive elements for a FOD detector may have at least two width segment spacings (ΔW1, ΔW2, . . . , ΔWn). In embodiments, capacitive elements for a FOD detector may have at least two length segment spacings (ΔL1, ΔL2, . . . , ΔLn). In embodiments, capacitive elements for a FOD detector may have at least two height segment spacings (ΔH1, ΔH2, . . . , ΔHn). In embodiments, capacitive elements for a FOD detector may have any combination of constant and varied segment spacing.
As in the magnetic field sensors described above, the capacitive elements may be arranged in substantially a two-dimensional (2D) plane (i.e., the same plane or a different plane as a plane containing one or more loops of conductive material, as discussed above) or they may be arranged in 3D. FIG. 21 shows exemplary embodiments of capacitive elements 1802 that traverse an area 1902 in two different directions. In embodiments, the conductors of these capacitive elements may preferably be isolated from each other so that circulating currents may not be induced by the electromagnetic field of a wireless power transfer system. Therefore, such elements might be realized using insulated wires that are stacked on top of each other and/or they may be realized by fabricating the elements of different layers of a printed circuit board.
In embodiments, capacitive and inductive sensors may operate in the absence of an oscillating wireless power transfer electromagnetic field. For example, the capacitive sensors described above may operate in a similar manner in the presence of an oscillating electromagnetic field used for wireless power transfer and in the absence of the oscillating electromagnetic field. The sensors may be used to detect FOD in wireless power transfer regions where the electromagnetic fields are not large but where there may still be a desire to detect FOD. FIG. 22 shows an embodiment of a capacitive sensor 1802 that may be arranged around the edges and/or extending beyond the enclosure 2202 of the resonator of a wireless power system. The capacitive sensor 1802 may be used to detect objects and/or materials as they approach a resonator and/or before they enter the region of strongest field between the resonators. In an exemplary embodiment, an animal such as a cat walking towards a resonator enclosure may pass over a capacitive sensor 1802 and cause a capacitive change that may be detected and used to lower or shut down the power on a resonator coil. In embodiments, a capacitive sensor may be used to detect objects moving towards a wireless power transfer system and may send control signals to a wireless power system that a live object is entering a certain space, region, volume, area, and the like, of the wireless power transfer system.
In some embodiments, a capacitive sensor may be adversely affected by the oscillating magnetic fields generated during wireless energy transfer. Fields may impact the sensitivity of the readings or change the readings. Capacitive sensors may preferably be positioned and/or oriented to reduce their interaction with the fields. In some embodiments, for example, it may be preferable to orient conductors of a capacitive sensor to be parallel to the dipole moment of the resonators. FIGS. 21A-21D show possible orientations of conductors for LOD. The conductors 1802 of the detection area 1902 may be aligned with the dipole moment of the resonator as shown in FIGS. 21A-21C. In some embodiments, conductors may be arranged in multiple orientations as shown in FIG. 21D. Conductors in the orientation with a smaller interference may be automatically selected by the system.
In embodiments, a gradiometer as described above may generate its own magnetic field rather than using the magnetic field generated by a wireless power transfer system. The gradiometer may detect changes in its own magnetic field. In an exemplary embodiment, oscillating currents and or voltages may be applied to inductive sensors in the gradiometer. Changes to the oscillating currents and/or voltages detected in the presence of FOD may be signals used to indicate the presence of FOD. Oscillating currents and voltage signals may be used to directly drive the gradiometer. In some embodiments, an oscillating current signal is induced on the FOD sensor by the wireless power transfer field.
In some embodiments, the frequency of the oscillating currents and/or voltages used to directly drive a FOD sensor may be selected to make the sensor particularly sensitive or insensitive to particular types of FOD. In certain embodiments, the frequency, magnitude, and/or phase of the oscillating signals on the magnetic sensors may be varied to perform object and/or material characterization, identification and/or classification. In some embodiments, the frequency, magnitude and or phase of the induced FOD signal over a range of frequencies, magnitudes and/or phases, may be used to identify FOD and to determine whether a wireless power transfer system should react to the presence of that FOD. For example, a FOD detection system may be driven at a frequency that may evoke a reflection unique to a type, size, material, and/or location of a FOD. In another example, a FOD detection system may be driven with a broadband signal for which the reflection signature may also be unique to a type, size, material, and/or location of a FOD. In some embodiments, a FOD detection system may be driven at a frequency different than a frequency driving the wireless power transfer system. This may allow a FOD detection system and a wireless power transfer system to operate independently.
In some embodiments, a FOD sensor may include both inductive and capacitive sensors. In an example embodiment, the variable capacitance of the capacitive sensor may be integrated with a detection circuit of a magnetic field sensor. Such an embodiment has the advantage that the capacitive sensing function can be easily switched on and off, and may even be added on to a FOD detection system that was not originally designed to accept input signals from such a sensor.
In certain embodiments, a FOD detection system may include multiple sensor types. In some FOD detection systems, at least some of the different sensor types may be close together, may share the same space, and/or may detect FOD in similar or the same regions. In some embodiments, at least some of the different FOD may be apart from each other and/or may monitor different regions. In an exemplary embodiment, inductive sensors of a FOD system may be substantially separated from the capacitive elements of a magnetic resonator of the wireless power transfer system.
Active FOD Detection Processing
The loop, dipole, quadrupole, octupole, and the like coil sensor/gradiometer configurations described above may output oscillating voltages/currents/signals in the presence of oscillating electromagnetic fields. In embodiments, the oscillating electromagnetic field may be the desired measurement signal. In other embodiments, where the signals from multiple loops may be meant to substantially cancel each other out, the oscillating signals may be due to imperfect sensor and/or coil designs, imbalanced gradiometer designs and/or non-uniformities in the electromagnetic field, owing to the resonator designs, resonator positions, the presence of FOD, and the like. In accordance with exemplary and non-limiting embodiments, a read-out amplifier may be connected to a given coil, loop, sensor, gradiometer, and the like, and may have a high input impedance. This arrangement may prevent a substantial circulating current from developing in the sensor coil, loop, lobe, sensor, gradiometer and the like, which could, in turn, spoil and/or perturb the Q-factor of the resonators used for wireless energy transfer. In some embodiments, the loops, lobes, coils, gradiometers and the like may be connected to amplifiers and/or filters and/or analog-to-digital converters and/or operational amplifiers, and/or comparators, and/or processors, and/or any electronic component that may be arranged to have high input impedance. In certain embodiments, a FOD sensor may include a conducting loop and a high input impedance electronic component. In exemplary embodiments, signals induced in the loops, lobes, coils, sensors and the like may be small enough that processing circuitry of any input impedance may be used to process the FOD signal. Signal processing may include, but is not limited to, detecting the signal, amplifying the signal, combining the signal, converting the signal (from AC to DC and or from DC to AC), clamping the signal, comparing the signal, filtering the signal, storing the signal, analyzing the signal on a processor, and the like may be utilized. For example, a drive frequency for a FOD detection system may be chosen to be susceptible to a certain type of FOD. In some embodiments, the drive frequency may be lower than the frequency of a wireless power transfer system. For example, a drive frequency may be at 10 kHz because some metals create more loss at 10 kHz than at 145 kHz. In another exemplary and non-limiting embodiment, a broadband signal may be used to drive the FOD sensor and then spectral analysis may be performed on the measured and/or reflected signal to determine the presence of FOD. Different FOD may be associated with different reflection signatures. A system may include a learning algorithm that may characterize and store the reflected FOD signatures. A system may then determine the type of FOD based on its “known FOD” database.
In some embodiments, conditioning circuitry may be utilized to subtract unwanted offset signals, constant signals and/or oscillating signals from the sensors and gradiometers. Oscillating signals may be generated using any type of capture coil in the oscillating electromagnetic field, or by using a crystal oscillator and/or a processor. The magnitude and/or phase of the oscillating signal may be generated, conditioned and manipulated using any known electronic signal processing techniques. In embodiments, removing constant offsets and/or oscillating signals produced from the sensors in the absence of FOD may yield improved sensitivity and may reduce background noise and in some cases, false positive outputs from the sensors.
In accordance with exemplary and non-limiting embodiments, at least one conductor from at least one coil (loop, sensor, gradiometer) in an array may be connected to a readout amplifier and/or an analog-to-digital converter as shown in FIG. 5. A loop conductor 502 may be connected to an amplifier 506 and/or an analog-to-digital converter 508 and may produce an output 504 that may be used by other elements of a wireless energy transfer system or as an input to a processing element (not shown) such as a microprocessor to store and analyze the output of the coil, loop, sensor and/or gradiometer.
In certain embodiments, the voltage on certain or all coils, loops, sensors, gradiometers and the like, in an array may be measured in sequence or may be multiplexed in a way that allows fewer read-out amplifiers or analog-to-digital converters to sample the array such as in an exemplary embodiment shown in FIG. 6. In an exemplary embodiment, an array of gradiometers 602, 604, 606 may be connected to a multiplexed amplifier 608 and may be connected to one or more digital-to-analog converters 610. The output of the one or more digital-to-analog converters 612 may be used by other elements of the wireless energy transfer system or as an input to a processing element (not shown) such as a microprocessor to store, process, convert, report, analyze, and the like, the output of the coil, loop, sensor and/or gradiometer.
In some embodiments, conductors of a sensor and/or gradiometer loop may be connected to active and/or passive filter circuitry to provide a high terminating impedance at high or low frequencies. In certain embodiments, conductors of a sensor and/or gradiometer loop may be connected to active and/or passive filter circuitry to provide a high terminating impedance at very high or very low frequencies.
In some embodiments, a voltage on a coil, loop, sensor, gradiometer and the like may be sampled at increments that allow a processor to determine the amplitude and phase of the waveform induced on the coil, loop, sensor, gradiometer, and the like, relative to a reference waveform. In certain embodiments, a voltage may be sampled at least twice per period of oscillation (i.e. at or above the Nyquist rate). In embodiments, a voltage may be sampled less frequently (i.e. in higher-order Nyquist bands). A voltage waveform may be filtered or conditioned before sampling. A voltage signal may be processed to improve the signal-to-noise ratio or to reduce the harmonic content of the signals being sampled. A voltage waveform may be digitally filtered or conditioned after sampling.
In some embodiments, a current on a coil, loop, sensor, gradiometer and the like may be sampled at increments that allow a processor to determine the amplitude and phase of the waveform induced on the coil, loop, sensor, gradiometer, and the like, relative to a reference waveform. In certain embodiments, a current may be sampled at least twice per period of oscillation (i.e. at or above the Nyquist rate). In some embodiments, a current may be sampled less frequently (i.e. in higher-order Nyquist bands). A current waveform may be filtered or conditioned before sampling. A current signal may be processed to improve the signal-to-noise ratio or to reduce the harmonic content of the signals being sampled. A current waveform may be digitally filtered or conditioned after sampling.
In embodiments, a time-sampled electrical signal from coils, loops, sensors, gradiometers, and the like of the FOD detector may be processed to determine the amplitude and phase with respect to a reference signal. The reference signal may be derived from the same clock used to excite the resonators used for wireless energy transfer. In embodiments, the reference signal may be derived from the signal used to drive the coils, loops, sensors, gradiometers and the like of the FOD detector. In exemplary embodiments, signals from coils, loops, sensors, gradiometers, and the like may be processed by a FOD detection system at a rate of less than 5 samples per second or less than 10 samples per second.
In some embodiments, a FOD detection system may include a separate frequency, field magnitude, and/or phase sampling loop 704 and electronics 702 to synchronize the sensor and/or gradiometer readings to the oscillating magnetic fields of a wireless energy transfer system as shown in FIG. 7.
In embodiments, the reference signal may be from a different oscillator at a different frequency.
An example of processing a figure-8 quadrupole configuration (FIG. 3A) for FOD detection may be as follows:
1. With no FOD present, collect a time-sampled voltage waveform from one of the figure-8 loops
2. Determine the amplitude and/or phase of the fundamental frequency component (or of its harmonics)
3. Store the amplitude and/or phase as a baseline reference value
4. With FOD present, collect a voltage waveform from the same figure-8 loop
5. Determine the amplitude and/or phase of the fundamental (or its harmonics)
6. Compare the amplitude and/or phase to the reference value
7. If the difference between the signal and the reference exceeds a predetermined threshold, declare a detection of FOD.
In some embodiments, the amplitude and phase of the voltage/current waveforms with and without FOD present may be compared and/or evaluated on a polar plot and/or in amplitude/phase space. In embodiments using polar plots and/or amplitude/phase space, if the distance (e.g., a distance determined by least squares method) between a measured signal and a reference signal exceeds a predetermined threshold, it may be determined that FOD is present on the sensor.
In certain embodiments, the processing of a signal may be performed using analog electronic circuits, digital electronics or both. In some embodiments, the signals from multiple sensors may be compared and processed. In certain embodiments, FOD sensors may reside on only one, or all, or some of the resonators in a wireless power transfer system. In some embodiments, the signals from FOD sensors on different resonators may be processed to determine the presence of FOD and/or to give control information to a wireless power system. In certain embodiments, FOD detection may be controllably turned on and off In some embodiments, FOD detection and processing may be used to control the frequency of a wireless power transfer system, the power level transferred by a wireless power system, and/or the time period when wireless power transfer is enabled and/or disabled. In certain embodiments, the FOD detectors may be part of a reporting system that may report to a system user that FOD is present and/or that may report to higher level systems that FOD is present or is not present. In some embodiments, a FOD detection system may be capable of utilizing a “learning capability” that may be used to identify certain types of FOD and that may include system identification and/or system feedback to categorize types of FOD as harmless, in danger of heating, not allowed for other reasons, and the like. In an exemplary embodiment, a FOD detection system may require less than 5 W or less than 10 W or less than 20 W of power to operate.
In accordance with exemplary and non-limiting embodiments processing capabilities may be embedded into a FOD detection system and/or subsystem and/or sensor data may be sent to a remote and/or central processor. The processing may compare collected voltage waveforms to reference waveforms and look for statistically significant changes. The processing may compare collected current waveforms to reference waveforms and look for statistically significant changes. Those skilled in the art will understand that the waveforms can be compared in amplitude and phase, I or Q components, sine or cosine components, in the complex plane, and the like.
In embodiments, FOD calibration and/or reference and/or calculated and/or determined baseline information may be stored in a memory element of a FOD subsystem. In embodiments, FOD sensors may include printed circuit board traces and a FOD system may include a microcontroller residing on a printed circuit board. In embodiments, the memory element of a FOD system may be on the same printed circuit board as the FOD sensors. In other embodiments, the memory element for a FOD system may be remote from the FOD system. For example, the signals from a FOD system may be communicated to a controller/processor/ASIC/PIC/DSP and the like, and/or a memory unit included by a wireless power source resonator, device resonator, repeater resonator or any type of source, device and/or repeater electronics control unit. In some embodiments, the signals from a FOD system may be communicated to a computer. In certain embodiments, the signals from a FOD system may be used to control the operation of a wireless power transfer system.
Specific and non-limiting embodiments of FOD detection systems are described below. Data have been collected from the embodiments that show them working as FOD detectors.
In the first embodiment a stranded wire was formed into a figure-8 loop forming a quadrupole as shown in FIG. 8 with a longer wire between the two loops (gradiometer 1). The second embodiment was designed as shown as gradiometer 2 in FIG. 8. The figure-8 loops were approximately 5 cm long, with each lobe approximately 2.5 cm in diameter. FIG. 9A-9C show sample voltage waveforms collected from the two sensors placed on top of a wireless energy source resonator that was configured to deliver 3.3 kW to a load attached to a device resonator. FIG. 9A shows the small residual voltage (˜30 mVrms) on the two gradiometers pictured FIG. 8. The residual voltage may be due to a combination of non-uniform magnetic field, slight variations in lobe area, and electrical interference. Results from gradiometers #1 and #2 are plotted as curve 904 and curve 902, respectively. When a metallic chewing gum foil is placed on the right lobe of gradiometer #2, at least some flux through that lobe is blocked and the gradiometer becomes more imbalanced. In that scenario, a substantial amplitude increase and slight phase shift is observable as shown in FIG. 9B, curve 902. When the foil is moved to the left lobe of gradiometer #2, the gradiometer is again imbalanced, resulting in a similar change in amplitude to when the right lobe was blocked but with the phase changed by approximately 180° as shown in FIG. 9C. In some embodiments, these changes in phase and/or amplitude readings of a FOD sensor or gradiometer may be used to detect the presence of FOD on the sensors. In certain embodiments, these changes in phase and/or amplitude readings of a FOD sensor or gradiometer may be used to detect the position of FOD on the sensors.
An embodiment of the figure-8 sensors was also fabricated using printed-circuit board (PCB) techniques to realize the sensor coils or loops. This embodiment may have advantages including low cost, higher fill factor (since the loops can be made into any shape and easily tiled using standard PCB processing techniques), higher uniformity, higher reproducibility, smaller size and the like. A higher-fill factor was obtained using tiled rectangular loops for a 16-channel array of individual figure-8 sensors. The printed loops were highly uniform resulting in smaller (and flatter) baseline readings from the sensors when no FOD was present.
In some embodiments, the sensors and/or gradiometer sensors described above can be combined with other types of FOD sensors to improve detection likelihood and lower false alarms (system detects FOD when no FOD is present). For example, a single or an array of temperature sensors can be integrated into a resonator assembly. If a piece of FOD begins to heat up it may disturb the normally expected temperature measurement and/or spatial temperature distribution. That deviation can be detected and used to send an alarm to a system controller. In embodiments, a temperature sensor may be used alone or in combination with a metal object sensor and/or it may be used as a backup or confirming sensor to the metallic object sensor.
The presence of living objects such as humans and/or animals in the vicinity of wireless power may be detected and may cause a wireless power transfer system to turn down and/or shut down and/or produce an alarm or warning (e.g., a visual and/or auditory signal) if FOD is present between the source and receiver and/or if the living objects intrude into magnetic fields of certain field strengths. The tolerable, acceptable, permitted and the like, field strength limits may be frequency dependent and may be based on regulatory limits, safety limits, standards limits, public perception limits, and the like. In certain embodiments, a dielectric sensor may measure changes in the fringe capacitance from a conductor such as a long wire and may be used to detect the proximity of living beings. In some embodiments, this type of sensor may be used during diagnostic testing, prior to wireless energy transfer, and during wireless energy transfer. In embodiments, this type of sensor may be used alone or in combination with any type of FOD detector. In certain embodiments, FOD detectors may detect human beings, living organisms, biological matter, and the like.
Vehicle Charging Applications
Detection of FOD may be an important safety precaution in many types of wireless energy transfer systems. As an example, detection of FOD by a 3.3 kW car charging system is discussed below.
A block diagram of an exemplary EV Charger System is shown in FIG. 10. The system may be partitioned into a Source Module and a Device Module. The Source Module may be part of a charging station and the Device module may be mounted onto an electric vehicle. Power may be wirelessly transferred from the Source to the Device via the resonators. Closed loop control of the transmitted power may be performed through an in-band and/or out-of-band RF communications link between the Source and Device Modules.
A FOD detector system (not shown) can be integrated into the system in a variety of places. In some embodiments, FOD systems may be integrated into the Source Module, into the source resonator, into the housings or enclosures of the source resonator and the like. In certain embodiments, FOD systems may be integrated on the device side of the system. In some embodiments, FOD systems may be implemented on both the source and device sides of the wireless power transmission system. In certain embodiments, a FOD detection system may include multiple sensors and a processor with a discrimination algorithm. The processor can be connected to an interface that functions as an interlock in the Source control electronics. Other FOD detector systems may be connected to the charger systems through an additional interface or through an external interface. Local I/O (input/output) at each module may provide an interface for system level management and control functions in a wireless power system utilizing FOD detection.
The source resonator in a high power (3.3 kW or more) vehicle charging system may have its highest magnetic field density near the boundaries of the windings and, optionally, any magnetic material. In the areas of high magnetic field, a sensor array that includes multiple double-figure 8 coils with rectangular-shaped lobes can protect against inadvertent heating of metallic FOD. The array may be fabricated on a PCB and may have integrated filtering and signal conditioning included on the board. A second PCB of equivalent design may be positioned slightly above or below the first PCB and translated laterally in the manner described in FIG. 4B. Alternatively, a multilayer PCB may be used that contains both (or more) sets of arrays on a single board. An algorithm like that described above may run in an on-board processor whose output may be transmitted to a system controller. The system controller can compare the output of the metallic FOD detector to the outputs of additional FOD detectors, such as those measuring temperature profiles or dielectric changes. The system can then decide whether to turn down or shut down the system if FOD is detected.
Some possible operation modes of a FOD detection system are as follows:
Low-power diagnostic tests can be performed without the vehicle present to check health and status of the charging station and to check for FOD prior to a vehicle driving over the source.
After the vehicle arrives and is positioned over the source module, but prior to high-power charging, the FOD detector may verify that the source and/or a region around the source is still free of FOD.
After the vehicle arrives and is positioned over the source module, but prior to high-power charging, a FOD detector may verify that the device is free of FOD.
During high-power charging, one or more FOD detector(s) can verify that no additional FOD has moved onto the resonator coil or into the vicinity of the resonator coil.
If FOD is detected during low power diagnostics, a communication signal may be set to a vehicle, a charge station, a central processor and the like to indicate that FOD is present at a certain source location. In some embodiments, FOD sensors may include a communication facility. The communications may be in-band and/or out-of-band and may be part of the electric vehicle communication system or it may be a separate network. In certain embodiments, a source may provide an indication to a user or driver that it has FOD on it or in its vicinity. In some embodiments, a source may provide a visible indicator, and audible indicator, a physical indicator, a wireless indicator and the like, to alert a user to the presence of FOD. In certain embodiments, a resonator may include a mechanism for removing FOD from itself and/or its vicinity and may actuate such a mechanism when FOD is detected. In some embodiments, users may have equipment designed to remove FOD from resonators and may use such equipment to clear FOD from system resonators such as source resonators and/or device resonators and/or repeater resonators.
In certain embodiments, equipment designed to remove FOD may include magnets that may be used to attract certain FOD such as pieces of metal, conductors and/or magnetic materials. In some embodiments, equipment designed to remove FOD may include brushes, brooms, swiffers, rags, mops, sweeping materials, and the like that may be used to remove FOD. In certain embodiments, equipment designed to remove FOD may include vacuums, suction cups, tweezers, pinchers, sticky rollers, blowers, fans, and the like that may be used to remove FOD.
Processing of Sensor Data
In embodiments the readings from multiple FOD sensors in an array may be processed separately and compared to a baseline or expected and/or measured readings from other sensors, sensor arrays, reference readings, stored readings, look-up values and the like. In other embodiments, readings from multiple sensors may be used and analyzed together to analyze and compare the behavior of the whole array of sensors. Processing and analyzing readings from multiple sensors at the same time may provide for improved sensitivity, FOD discrimination, and the like. In this disclosure, it is understood that the processing and analyzing may be done at similar times. Processing multiple sensor readings together may provide more information due to the higher dimensionality of the data. Capturing and processing data from multiple sensors may capture effects like the inter-relation of adjacent sensors, trends and differences in complete sensor systems, and other effects that may not be captured if each sensor is analyzed separately. Some challenges with processing data from multiple sensors together may include ensuring that the data is processed efficiently and that possible information from the data is not lost during processing. A multidimensional data set may be difficult to store and analyze while data is continuing to be detected while maintaining the ability to detect small changes in the FOD sensors.
In some embodiments, readings from multiple sensors may be processed and analyzed together to calculate one or more numerical values that can be used as distinguishers or alarms for abnormal system state or the presence of FOD. The data processing methods may calculate one or more correlation, covariance, and means matrices from the multiple sensors that may be used as baseline values for comparing the readings of the system. Once a baseline is established readings from the sensors may be compared with the baseline using efficient matrix operation calculations to generate a probability or likelihood that the new readings are comparable to the baseline readings. The details of these exemplary steps are outlined below.
(i) Calculating Sensor Baseline
In some embodiments, to determine a no-FOD-present baseline, readings from at least two sensors in a sensor array may be used to calculate the mean and covariance matrix. The mean and covariance matrices may be used as a comparison for measured data during operation of a FOD detection system.
In an exemplary embodiment, a FOD system with j sensors, the amplitude ri and phase θi of the substantially sinusoidal signal from each sensor i may be captured from each sensor. The phase θi may be defined by a reference value or signal. A user may determine the reference value or signal. In some embodiment, the reference signal may be generated from a reference clock circuit. In some embodiments, where the signals produced by FOD sensors are not substantially sinusoidal, signal processing may be performed to substantially isolate and detect the fundamental component of the signal. In certain embodiments, where the signals produced by FOD sensors are not substantially sinusoidal, signal processing may be performed to substantially isolate and detect at least one harmonic component of the signal. In some embodiments, any combination of fundamental and harmonic components of the sensor signal may be measured and utilized in a FOD detection scheme. The phase θi may be calculated with respect to one or more reference signals for all sensors. For j sensors, the ri, θi of each sensor provide 2j data points. The ri, θi data may be represented in an array form x according to equation 1 (Eq. (1)), shown below:
x = [ r 1 θ 1 ⋮ r j θ j ] . ( 1 )
In some embodiments, there may more than one reference signal for comparison. Multiple reference signals may be generated via multiple reference coils in a FOD detection system. In some embodiments, an arrangement of reference coils may be dependent on the magnetic field of a wireless power transfer system. For example, for magnetic fields that are radial in shape and perpendicular to the plane of a resonator coil of a wireless power transfer system, reference coils may be arranged in a circle so that its field may be uniform from reference coil to reference coil. In another example, for magnetic fields that are parallel to the plane of a resonator coil of a wireless power transfer system, reference coils may be arranged in columns or rows, as shown in FIG. 12. Reference signals or sets of reference signals from reference coils may be compared to each other, to signals from FOD sensors, etc. A reference signal or a set of reference signals may be utilized based on the location, size, type, and/or material of detected FOD.
In certain embodiments, the readings of amplitude and phase from at least one sensor may be processed and/or modified by a function, by circuitry, by calculation and the like and the processed data may be represented in an array. In some embodiments, various functions may be used to process measured data. In certain embodiments, the function used to process and/or modify the original sensor data may not reduce the dimensionality of the data. For example, one function may be to take the sine and cosine of the phase of each reading which results in the following array x according to Eq. (2), shown below:
x = [ r 1 ⁢ cos ⁢ ⁢ θ 1 r 1 ⁢ sin ⁢ ⁢ θ 1 ⁢ ⋮ r j ⁢ cos ⁢ ⁢ θ j r j ⁢ sin ⁢ ⁢ θ j ] . ( 2 )
In some embodiments, each data column of x may be optionally normalized by a normalization factor such as the value
∑ i = 1 j ⁢ r i 2 ⁢ .
In an exemplary embodiment, to build the no-FOD-present baseline mean and covariance matrices, the system may acquire multiple sets, say p sets, of readings of the sensors to generate multiple data matrices, x, for various operating points of the system (power transfer levels, relative positions of the source and device modules, and the like). The multiple readings of the sensors may preferably represent a useful, common, specified, expected, and the like range of operation of the system and sensor readings. With the p sets of data (optionally normalized) the mean, μ, and covariance, σ, matrices may be calculated according to Eqs. (3) and (4), shown below:
μ = 1 p ⁢ ∑ l = 1 p ⁢ ⁢ x l ( 3 ) σ = 1 p ⁢ ∑ l = 1 p ⁢ ⁢ ( x l - μ ) ⁢ ( x l - μ ) T . ( 4 )
In this exemplary embodiment, the covariance matrix σ may be a 2j×2j matrix. The mean and covariance matrices may be saved by the system as a baseline for comparison against sensor readings during normal operation. The mean and covariance matrices may be used to calculate the FOD likelihood during operation.
(ii) FOD Likelihood Calculation
In an exemplary embodiment, during normal operation, the system may collect readings from the FOD sensors and compare the readings to the calibration baseline of the mean and covariance matrices to determine if FOD is present. The comparison may be based on a function that produces one or more easily analyzable or comparable numbers or likelihoods. In one embodiment, if x is the array of 2j data points from the j FOD sensors, the likelihood, y, may be computed as Eq. (5), shown below:
y=(x−μ)Tσ−1(x−μ). (5)
A probability, Ψ, may be computed as Eq. (5.5), shown below:
Ψ = ( 2 ⁢ ⁢ π ) - p 2 ⁢  σ  - 1 2 ⁢ e - 1 2 ⁢ ( x - μ ) T ⁢ σ - 1 ⁡ ( x - μ ) . ( 5.5 )
In embodiments, the inverse of the stored covariance matrix σ may be pre-computed. The likelihood, y, may be used as an indicator of FOD. In embodiments a threshold value may be assigned to a value of y above or below which the sensor readings are assumed to detect an abnormal state in the system such as the presence of FOD.
In this exemplary processing technique and method, the behavior of multiple sensor readings may be used together in an efficient manner to determine the likelihood of an abnormal state of the system with relatively small data storage requirements for storing baseline or calibration readings.
In an example embodiment, a system comprising one wireless source resonator and one wireless device resonator includes a FOD detection system. The FOD detection system includes a 7 by 7 array of figure-8 sensors (49 sensors total) positioned between the source and device resonators. The figure-8 sensors are positioned in the magnetic field of the source resonator. When the source resonator generates an oscillating magnetic field, the magnetic fields generate a small oscillating voltage in the 49 FOD sensors. The voltage in the FOD sensors may be dependent on the magnetic field distribution around the sensors and therefore may function as magnetic field gradiometers during operation of the system.
During normal operation of a wireless energy transfer system, the signals from or readings of the FOD sensors may change or drift due to changes in the magnetic field distribution caused by temperature changes, changes in offsets, power levels, presence of other resonators, and the like. The sensor readings may change or drift during normal operation of a wireless energy transfer system even when no FOD is present. The system may require a calibration step to determine a baseline range of sensor readings or a range of normal sensor readings. The baseline readings may be used to compare FOD sensor readings during system operation (system stand-by, start-up, power transfer, maintenance, and the like) to detect FOD, or abnormal system states that might manifest in a FOD sensor reading different from the baseline.
For the example system, the baseline may be established during a calibration procedure. The baseline may include mean and covariance matrices calculated based on one or more of the system FOD sensor readings. To determine a baseline the system may capture the amplitude and phase of the sensor readings for one or more system states (98 data points). The sensor readings for each state may be used to calculate the mean and covariance matrix as outlined above.
As described previously, suppose p measurements are performed for the purpose of calibration. Each measurement of the sensor data contains 98 values. Each measurement of sensor data xi can thus be represented as a column matrix of size 98 according to Eq. (6), shown below:
x i = [ r 1 ⁢ cos ⁢ ⁢ θ 1 r 1 ⁢ sin ⁢ ⁢ θ 1 ⋮ r 49 ⁢ cos ⁢ ⁢ θ 49 r 49 ⁢ sin ⁢ ⁢ θ 49 ] . ( 6 )
The p measurements of sensor data may preferably represent data produced over a range of operating points of the system over which the FOD may be detected. With the p measurements of data (optionally normalized) the mean μ and covariance σ matrix may be calculated according to Eqs. (7) and (8), shown below:
μ = 1 p ⁢ ∑ l = 1 p ⁢ x l ( 7 ) σ = 1 p ⁢ ∑ l = 1 p ⁢ ( x l - μ ) ⁢ ( x l - μ ) T . ( 8 )
Once the system is calibrated and the mean and covariance matrix saved and computed the system may periodically or continuously take measurement of the FOD sensors during operation of the system. For each set of readings from each sensor in the FOD system the system may compute the likelihood based function, y, of FOD being present near the system according to Eq. (9), shown below:
The likelihood y and probability Ψ may be used to determining the FOD likelihood. The largest likelihood y corresponds to the smallest value of Ψ.
Based on an input, calculated, measured, or predetermined threshold for y, the system may categorize calculated values as above the threshold to mean that FOD is present and mitigate or investigate the risk of FOD using other parts of the