Title of Invention: DEVICE AND METHOD FOR LIMITING LEAKAGE CURRENTS
Abstract: 
A device including a mechanism detecting a position of a neutral of a power supply source for an electrical energy apparatus, such as a battery charger of an electric or hybrid motor vehicle, and a mechanism connecting a capacitor for limiting leakage currents between the neutral and an electrically conducting structure in which the apparatus is placed. The device can be used to limit leakage current during recharging of an electric or hybrid traction motor vehicle.

Detailed Description: 

The invention relates to the limiting of leakage currents of an electrical apparatus and more particularly the limiting of the leakage currents likely to occur within the chassis of an electric or hybrid motor vehicle when a battery charger is connected.
The chargers used in certain electric motor vehicles are not isolated. Each element of the charger has a common-mode capacitor relative to the chassis. On connection to an electrical power distribution network, the voltages applied to these various elements will, through these capacitors, cause leakage currents to ground.
These leakage currents to ground may, when they occur, trigger differential protections of residual current that are capable of interrupting the charging process.
If a user touches the chassis of the electric vehicle during charging, the leakage currents to ground become what are known as “touch” currents if there is a grounding fault of the vehicle. These touch currents are potentially dangerous and are limited by international standard 6 185 1-21 to 3.5 mA.
It is therefore necessary to limit these leakage currents. Accordingly, it has been proposed to use a transformer creating a galvanic isolation between the distribution network and the battery.
The transformers used are bulky elements the size of which increases with the charging power, or with the current passing through them. This solution therefore has the drawback of incurring an additional cost and an increase in the volume of the device, which greatly penalizes the electric motor vehicle.
Moreover, it is possible to connect current chargers to single-phase or three-phase networks in order to obtain a higher charging power. During a connection to a three-phase network, the stresses on the transformers used are therefore increased.
In light of the foregoing, the object of the present invention is to limit the leakage currents of an electrical apparatus.
Another object of the invention is to limit the leakage currents for several types of supply network.
According to a first aspect, a device is therefore proposed for limiting the leakage currents for an electrical apparatus, such as a battery charger installed onboard a motor vehicle with electrical or hybrid drive.
This device comprises means for detecting the position of the neutral of a source for supplying the apparatus with electrical power and means for connecting a capacitor for limiting the leakage currents between the neutral and an electrically conductive structure in which the apparatus is placed.
Thus, the capacitor placed between the neutral and the electrically conductive structure makes it possible to partly divert to neutral the leakage currents of the electrical apparatus. This solution can be applied to any type of non-isolated charger.
Advantageously, the device comprises a voltage sensor for each phase of the supply source.
Voltage sensors make it possible to determine the type of supply (single-phase, three-phase), and to detect the position of the various phases and of the neutral.
The supply source may be a three-phase or single-phase supply network.
The device may comprise three capacitors, the first electrodes of said three capacitors being connected together and to a first switch capable of connecting the three capacitors to said structure, the second electrodes of said three capacitors being respectively connected to each of the three phases of the supply source.
On connection to a three-phase supply network with no neutral, it is possible to reconstitute the neutral by connecting the three phases to the capacitors. The switch makes it possible to connect the electrically conductive structure to the neutral thus reconstituted.
Moreover, at least two phases are respectively connected to switches capable of connecting at least one of the two phases to a capacitor connected to said structure.
On connection to a single-phase supply network, these two phases are used. The switches make it possible to connect to said structure the phase on which the neutral is detected.
According to another aspect, a method is proposed for limiting leakage currents for an electrical apparatus such as a battery charger installed onboard a motor vehicle with electrical or hybrid drive.
According to a general feature of the method, the position of the neutral of a source for supplying the apparatus with electrical power is detected and a capacitor for limiting the leakage currents between the neutral and an electrically conductive structure in which the electrical apparatus is placed is connected.
Advantageously, the neutral is formed from the phases of a three-phase supply source.
The electrical apparatus is not supplied with power if the neutral has not been detected and connected to the electrically conductive structure of the electrical apparatus or if the neutral has not been formed.
Thus, the method according to the invention makes it possible to prevent at least a portion of the electrical apparatus from functioning if the limitation of the leakage currents cannot be applied.



Other advantages and features of the invention will become apparent on studying the following description, taken as a nonlimiting example and illustrated by the appended drawings in which:
FIG. 1 illustrates the occurrence of leakage current in a battery charger of an electric motor vehicle;
FIG. 2 shows schematically the general principle of limiting leakage current according to the invention;
FIG. 3 illustrates one embodiment of a limiting device according to the invention; and
FIGS. 4, 5 and 6 illustrate the operation of the device of FIG. 3.



FIG. 1 shows the principle of generating leakage currents known as “touch” currents in an electric vehicle to which a battery charger is connected that is not isolated galvanically.
It will be noted however that this principle applies to any type of apparatus, of the battery charger or other type, notably for a motor vehicle with an electric or hybrid drive train in which touch currents are likely to occur after connection of the apparatus when the bodywork of the vehicle is touched.
In this figure, reference number 1 designates the vehicle in its entirety and reference number 2 designates an electrically conductive structure of the vehicle, in this instance the bodywork of the vehicle.
As shown, the electric motor vehicle 1 is in this instance furnished with a charger 3 and also comprises an assembly of batteries and of non-isolated electric drive train.
Naturally, the vehicle 1 may also be fitted with many additional members that have not been shown in the figure for reasons of simplification.
During charging, the charger 3 is connected to the supply network by several electrical connections 4a, 4b. The electrical connection 4a may comprise several phases, and the connection 4b corresponds to the neutral.
When the charger 3 is connected to an electrical network, interference capacitors between the charger 3 and the structure 2 (symbolized by an interference capacitor 5), are sources of leakage current.
If a user 6, illustrated here by his resistive impedance, touches the structure 2, the latter is traversed by a touch current created through the interference capacitor 5.
FIG. 2 shows schematically the limitation of the leakage currents generated during the connection of the vehicle to a recharging terminal. As can be seen, a capacitor 7 is connected between the neutral 4b and the structure 2.
The leakage currents are thus at least partly diverted toward the neutral through the capacitor 7 so that the user 6 is protected, by being traversed by a lesser current than in the case described in FIG. 1.
FIG. 3, in which the architecture of a leakage current limiting device according to the invention is shown in detail, illustrates a vehicle 1 comprising three electrical connections 4a, 4b and 4c providing the connection of the vehicle to a three-phase or single-phase network.
The device 1 in this instance comprises three capacitors 9a, 9b and 9c of which the first electrodes are connected together and to a first switch I1 capable of connecting the three capacitors 9a, 9b and 9c to the electrically conductive structure 2. The second electrodes of the capacitors 9a, 9b and 9c are respectively connected to each of the three electrical connections 4a, 4b and 4c. 
The two electrical connections 4a and 4b are respectively connected to two switches I2 and I3 capable of connecting at least one of the two electrical connections 4a and 4b to a capacitor 10 connected to the structure 2.
A processing unit 11 is used to control the switches I1, I2 and I3. This processing unit is also connected to the charger 3 and to three voltage sensors 12a, 12b and 12c. 
The processing unit 11 is also connected to the charger 3.
Thus, the voltage sensors 12a, 12b and 12c make it possible to indicate the type of supply network to which the vehicle 1 has been connected, then the processing unit can actuate one of the switches I1, I2 or I3 in order to connect, through a capacitor, the neutral to the structure.
FIG. 4 illustrates an example of use of a device according to the invention. The vehicle 1 is in this instance connected to a three-phase supply network 13.
In a first step, the processing unit 11 prevents the charger 3 from being supplied with power.
The three electrical connections 4a, 4b and 4c respectively convey each of the phases, and the three voltage sensors 12a, 12b and 12c indicate to the processing unit 11 that the vehicle 1 is connected to a three-phase supply network.
The processing unit 11 closes the switch I1 so as to reconstitute the neutral which will be connected to the structure 2 through the three capacitors 9a, 9b and 9c. 
The processing unit 11 then allows the charger 3 to be supplied with power.
FIG. 5 illustrates another method of use of a device according to the invention in which the vehicle 1 is connected to a single-phase supply network 14.
In a first step, the processing unit 11 prevents the charger 3 from being supplied with power.
The voltage sensor 12a detects the position of the phase and the voltage sensor 12b detects the neutral.
The processing unit therefore closes the switch I3 so as to connect the neutral to the structure 2 through the capacitor 10.
The processing unit 11 then allows the charger 3 to be supplied with power.
It will be noted that, on connection to a single-phase supply network, the phase can be situated on the electrical connection 4b and the neutral on the electrical connection 4a. The processing unit 11 will then close the switch I2.
FIG. 6 gives details of the various steps used within a device for limiting leakage currents according to the various methods of use envisaged above.
These steps are in this case applied within an electric motor vehicle 1 comprising a charger 3. A step not shown here comprises the connection of the vehicle 1 to an electric supply network and the prevention of charging of the battery.
A first step E1 is implemented by means of the three sensors 12a, 12b and 12c. These sensors 12a, 12b and 12c respectively measure the voltages V1, V2 and V3. The values measured are then supplied to the processing unit 11 where they are compared.
If the three measured voltages V1, V2 and V3 are equal (step E2), then it is considered that the vehicle has been correctly connected to a three-phase supply network 13. The next step E3 is then implemented. It corresponds to the formation of the neutral from the three phases of the three-phase supply 13 and to the closure of the switch I. This step is also carried out by the processing unit 11. Charging is then allowed (step E4).
If the voltage V1 has a root-mean-square value equal to 230V, and if the voltage V2 has a zero value (step E5), then it is considered that the vehicle 1 has been correctly connected to a single-phase supply network 14, and that the electrical connection 4a conveys the phase, while the electrical connection 4b corresponds to the neutral. The switch I3 is therefore closed during step E6 in order to connect the neutral to the structure 2 through the capacitor 10. The step E7 corresponds to allowing charging.
Steps E8, E9 and E10 are similar to steps E5, E6 and E7 in the situation in which the phase and the neutral are reversed.
If the voltage V1 is equal to the voltage V2 but differs from the voltage V3 (step E11), then the vehicle is connected to a supply network in which the neutral is not determined and cannot be reconstituted. The step E12 of preventing charging is then implemented.
By virtue of the invention, the user benefits from a device that can be used in any type of electrical apparatus comprising a non-isolated electrical member. The invention allows users to be protected and a simplified use of the items of electrical apparatus of which the operation will not be interrupted due to leakages of currents to ground.
Moreover, the invention makes it possible to limit the leakage currents within items of electrical apparatus connected to single-phase or three-phase supply networks.



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