An electric baking oven includes an open mesh vertically oriented baking basket to hold food while the food is baked in air by a programmed combination of radiant and convective and conductive energy transfer. An electrical programming control controls the energy from vertically oriented toaster heating elements located juxtaposed to the large vertical faces of the basket and from at least one elongated heating member located below the vertical baking basket with the axis of the elongated heating member oriented nominally horizontal and parallel to the longer horizontal axis of the vertically oriented baking basket.

Parent U.S. Pat. No. 6,267,044 describes a toaster which contains heating elements optimally designed and positioned for toasting and provides the means to preheat the toasting elements to optimal thermal conditions for toasting before introducing the bread or other material to be toasted into the toasting environment. The novel toaster design disclosed in that patent includes also added means to create the optimal conditions for baking, warming, defrosting or a combination thereof. The design geometry, size and thermal environment of the relatively ubiquitous conventional toasters have not proven satisfactory for quality baking, defrosting or warming. By contrast this toaster will perform these functions faster and better than conventional baking ovens common to virtually all kitchens.
Conventional baking ovens that have been used for centuries are designed with horizontal shelves to cook food in horizontal containers that are slowly raised to elevated temperatures by heated air. Food in those containers is heated primarily by contact with the hot horizontal container or by contact with adjacent food in turn heated by contact with the container.
In more recent times motor driven fans have been introduced in ovens to circulate the air around the containers and over the top of foods in horizontal containers or horizontal shelves. Large electrical heaters have been added on the ceiling, floors and side walls of ovens to heat the air more rapidly. Horizontal shelves are provided universally as the means to hold food containers and in some cases to position bread or other foods horizontally in close proximity to a horizontal mounted heater that will toast or broil one side at a time. The efficiency of the toasting operations is very poor taking many minutes to toastxe2x80x94leaving a dry relatively unappetizing product. Large ovens of that sort take 10 or more minutes just to reach baking temperatures and substantial time to complete the baking because of inefficient heat transfer to the food. No provision is made in such ovens to insure intimate and direct contact with all surfaces of the food when that food is particulate or simultaneously with both sides of the food if the food is planer such as steaks, patties, and waffles. An exception to that is the rotisserie that secures larger foods on skewers and rotates them before the heated air, flames, or heated elements.
The present invention is directed to techniques for optimal baking cycles in the unique toaster of parent U.S. Pat. No. 6,267,044.
This invention describes the means and mechanism to hold particulate food within a toaster so that there is direct and intimate contact between heated air and virtually all the foods surface area to insure rapid and uniform heating of the food by naturally convective transfer from hot air at baking temperatures in combination with programmed temperature radiant energy from toasting elements and at least one auxiliary heater operating at optimum temperatures which are different from those that must be employed in an optimal toasting cycle. This programmed combination of heating by the hot air and radiation provides optimum baking rates without overheating the exposed surfaces of the food in such a manner as to create excessive or burning of the food surface. By this new methodology and by the close proximity of the heating system and the toasting elements it is possible to optimize the baking conditions for the effective baking of hundreds of uncooked or xe2x80x9cprecooked but not brownedxe2x80x9d foods available for quick bake-and-serve dishes. Unlike conventional ovens and toasters which cook slowly and unevenly, the means disclosed here bakes rapidly and uniformly simultaneously on virtually all surfaces of particulate foods creating tasty uniform temperature foods as a result.
Many ovens and so called toaster-ovens can be used for toasting but the toasted food lies flat and must be turned over to complete the toasting or to achieve relatively uniform toasting on each side. Those heater elements are not optimized for toasting. In the baking mode in conventional ovens there is little motion of the air over or through the food, rather the air is relatively quiescent. Convection ovens with fans generate a general air flow within the oven but these are not designed to circulate air through a bed of particulate foodxe2x80x94such as frozen french fries. Conventional toasters are used today in an attempt to xe2x80x9ccookxe2x80x9d many of the frozen xe2x80x9cprecooked but not brownedxe2x80x9d foods by simply repeating the toasting cycle several times. The results are very disappointing creating overcooked and undercooked areasxe2x80x94sometimes burnt before getting sufficiently warm on the interior. Good baking requires less intense heat in order that the interior can be warmed sufficiently before the surface is overheated or burnt.
No provision is made in such ovens for vertical open baskets to hold the food and to allow air to pass through a bed of particulate foodxe2x80x94such as frozen french fries.
There have been attempts to offer toasters that combine the toasting and baking functions such as U.S. Pat. No. 2,862,441 by W. A. Schmall (Dec. 2, 1958) assigned to General Electric. This describes a combination unit which uses movable mirrors to redirect radiant energy upward for toasting or downward to a separate baking compartment. That baking function can not be particularly effective since the heat was applied only by the mirrors to one side of the food.
In contrast to prior art the subject baking appliance is designed first as an optimal toaster Baking is accomplished in the same space with the use of an auxiliary air heater mounted below the baking space and with the use of sophisticated electrical and electronic control of the toasting elements to equalize air temperatures and to generate natural convection currents of the heated air through and around vertically configured open mesh basket that contains the particulate food. The relative amounts of heat provided by the toasting elements and by the auxiliary air heater are electronically controlled to optimize the baking rate while avoiding excessively localized heating of the food surface by either the localized air temperature or the radiation from toasting elements. The toasting elements are segmented so that they can be heated individually or together and thus temperature is controlled so as to optimize the air temperature along the vertical face of the vertical open mesh basket which holds the food to be baked.
U.S. Pat. No. 6,267,044, the details of which are incorporated herein by reference thereto, describes many of the novel aspects of this new batch toaster in particular means for retaining the food to be toasted remote from the toasting zone until the thermal conditions in the toasting zone are optimal for toasting. By that means the bread or other food to be toasted is when entered into the toasting zone, toasted rapidly avoiding unnecessary drying of the food that would otherwise take place before the ambient thermal conditions are optimal for toasting of the food surface. Consequently the toasted foods loses less internal water and can be crisp on its exterior surface while retaining more of its internal moisture. The food to be toasted is placed on a carrier of some sort and transported either manually or automatically into the toasting zone when that zone is thermally optimal for toasting.
For toasting to occur rapidly, and thus reduce the loss of moisture from the food, it is best that heat transfer be largely by radiation and less by a combination of hot air conduction and convection where heat transfer is inherently slower limited by the thin layer of air in the boundary layer adjacent the food surface. Heat transfer through such boundary layers is inherently slower while radiation can pass literally at the speed of light uninhibited from the radiant source onto the food surface. When toasting this speed is advantageous. When baking one has to monitor and control carefully the amount of radiant energy so as to avoid burning the surface of the food before the interior is adequately baked. For the interior of the food to be baked sufficiently, heat must be first transferred to the surface of the food, whence heat must travel by conduction to the middle of the food thickness. The latter takes time because the thermal conductivity of food is poor and the amount of heat transferred is driven only by the elevated surface temperature of the food. The higher the surface temperature the better up to the point where the surface is overheated and begins to burn or overcook. Consequently the surface temperature must be carefully controlled and limited to avoid burning but it must be hot enough to drive effectively the heat below the food surface where it is needed to evaporate excess water and to dehydrate and crosslink the food proteins or break chemical bonds.
Toasting a surface phenomenon, can be forced to occur rapidly. By contrast baking rates are limited by the slow transfer of heat through the full thickness of foods. Baking cannot be rushed without danger of burning the surface. This is why toasters are notoriously poor for baking. The intensity of toasting elements must be moderated if they are used during extended baking to assist in heating the surface of foods. Radiation from toasting elements will not shine onto all food surfaces within a bed of particulate food. Shadowing effects limit the effectiveness of direct radiation. Heat for the surface of interior particulate surfaces can be well provided by convective and conductive transfer from hot air circulating around and between the particulate food.
From the above it is clear that a thermal environment ideal for toasting is not suitable for quality baking. Similarly the environment optimal for baking is totally unsatisfactory for toasting. What this inventor has discovered is that it is possible to bake efficiently and rapidly in the toasting space by using segmented electrical toasting elements operating at reduced temperature as auxiliary heaters to supplement a remote efficient heating means to elevate the air temperature within the enclosure and to generate natural convection current around and through a bed of particulate food adjacent to the toasting elements. The baking process can be optimized by programming independently the temperature of the segmented toasting elements and the remote heating means throughout the baking cycle. In the relatively short initial heat-up phase of the baking cycle (approximately 1xc2xd minutes) both the upper and lower toasting segments are powered to an elevated temperature equal to or slightly lower than their temperature when toasting. This provides an initial burst of radiant and convective heat transfer that elevates the temperature of the food surface and hastens the overall temperature rise of the enclosed air, the oven walls and the baking basket. In the initial phase the remote heater also operates at or close to full power to hasten the heat-up process. Temperature within the baking space is monitored to determine when it has reached the desired baking temperature. After that time usually less than 2 minutes, the toaster elements are operated at reduced temperature and the power applied to the remote heater and to the toaster element is controlled to maintain the oven temperature at the desired temperature.
Any of a variety of electrical control means can be used to program during each portion of the baking cycle the appropriate amount of power to the toasting elements and to the remote heating means. A solid state relay controlled by an oven temperature sensing means proved particularly effective for controlling power to the various heating elements.
This inventor has found that the uniformity and speed of baking of particulate foods is enhanced significantly if the food is held in an elongated vertically oriented mesh basket of cross section sufficiently small that heated air can readily pass by naturally convective means through the basket thus contacting efficiently the surfaces of the particulate food held therein. Using a specific arrangement of heating elements and by employing a vertical basket of approximately 1xc2xe to 3 inch thickness (between the large vertical mesh faces) natural convection of the heated air passes rapidly through such a basket insuring that the particulate food is uniformly heated and baked throughout the basket.
A vertical configuration of the baking basket is optimal and it is consistent with the toasting geometry optimal for toasting as described herein and in parent U.S. Pat. No. 6,267,044. The elongated vertical orientation of the baking basket allows toasting heating elements of similar orientation to be used effectively to aid in the heating process and to apply heat uniformly to the face of the elongated vertical baking basket.
By using an elongated relatively high power heater (approximately 600-1000 watts) under the basket, air heated by this means rises naturally by virtue of its reduced density along the vertical faces of the mesh basket. By physically offsetting the heater slightly, on the order of a quarter inch or so from the long center line of the baking basket it was found that there is greater air flow up one side of the basket creating enough pressure difference between the faces of the basket to force a significant fraction of the hot air through the thickness of the mesh and across the surfaces of the cooler particulate food. It was found convenient to use a high temperature elongated source such as a cal-rod or a quartz-enclosed conventional hot wire heater. Because of the high temperature required for efficient heat transfer to air by such a source it may be hot enough to radiate significant energy. In that event the bottom of the mesh basket is best shielded from the direct radiation emitted by the heating source. One way to prevent the direct radiation from shining on the food basket is to locate that source in a relatively open but roofed compartment below the food basket. The mesh baking basket can be supported by, but spaced above an integral solid metal base. The bottom of the open mesh basket should optimally be positioned at least xe2x85x9cxe2x80x3 above any such base. By these means hot air can ascend up through the mesh bottom of the basket. Either the metal base or the roof of the heater compartment will shield the food from direct radiation from the lower heater.
More than one air heater can be used below the baking basket and their positioning can be arranged to provide greater air flow up one face of the basket and then pass the other to create a pressure difference across the faces of the basket and flow through the basket.
The elongated vertical configuration for the baking basket has proven ideal because it conforms directly with the planar geometry of the toasting heater boxes and it allows air heated from below to pass uniformly upward along and across the entire large faces of the baking basket and through the particulate food. The advantages of this arrangement can be readily visualized in comparison to the use of conventional horizontal pans, horizontal trays or open mesh shelving. None of these conventional baking configurations offer the possibility simultaneously for the symmetry and proximity of auxiliary planar heaters such as the toaster elements adjacent both major faces of the basket as described here nor do they offer opportunity for simultaneously creating uniform naturally convective air currents along both sides of the food basket and through its food bed.
The effectiveness of the natural convective hot air currents through the cool food was demonstrated by detailed temperature measurements of the food temperature and the air temperature adjacent to the baking basket. It was observed when the long axis of the lower heater was offset xc2xc inch or so from the lower center line of the basket, convective air currents through the food increased sufficiently to equalize the air temperature adjacent to the food to that of the rising main air stream. When the lower heater was centered the air temperature adjacent the cool food dropped below the temperature of the air above and below the food level reflecting much less convective circulation through the food. When the heater was set off center the food cooked (reached ultimate temperature faster) and it was cooked more uniformly throughout the food bed.
This unique toaster and baker is designed to optimize separately its performance for each of these two functions. None of the known batch toasters preheat the toasting element and toasting environments before toasting to create the crispy yet moist texture. None of the known batch toasters are effective for baking. Toaster ovens are available that offer the ability to either toast or bake. They do not offer means to optimize the toasting environment before introducing the bread. Neither do they offer optimal means to bake in a vertical basket by combining the heating advantages offered by precise and programmed control of adjacent planer toasting elements and a remote heater to generate efficient heated air convection currents past and through a bed of particulate food.

High speed baking in novel toasting apparatus


A process for producing solid dosage forms by a) producing a plastic mixture which comprises at least one active ingredient and at least one polymeric binder, and b) shaping the plastic mixture to the solid dosage forms in a molding calender with two counterrotating molding rolls, wherein one molding roll has at least one annular groove running along its periphery and the other molding roll has at least one ring, running along its periphery, of teeth extending radially outward and able to engage in the annular groove is described.

The present invention relates to a process for producing solid dosage forms by producing a plastic mixture which comprises at least one active ingredient and at least one polymeric binder, and shaping the plastic mixture to the solid dosage forms in a molding calender with two counterrotating forming rolls.
A process of this type is disclosed, for example, in U.S. Pat. No. 4,880,585. In this process, a composition containing active ingredient and binder is plasticized using an extruder, and the resulting melt is subjected to a shaping in a molding calender. The molding rolls of the molding calender have on their surface depressions with mutually corresponding outlines. The depressions on the surfaces of the molding rolls briefly meet at the contact line of the molding rolls to form molds for the active ingredient-containing melt and then, as rotation of the molding rolls continues, diverge again to release the molded dosage forms. This process has certain disadvantages. Thus, the depressions on the surface of the molding rolls must exactly coincide with their outlines during the shaping of the plastic mixture in order to achieve complete closure of the mold. Even tiny relative displacements of the depressions, e.g. in the region of a few micrometers, immediately lead to a detectable mismatch of the upper side and lower side of the dosage form. On the one hand this requires high precision in producing the molding rolls and, on the other, there must be exactly synchronous movement of the molding rolls in the calender toward one another. This is possible only with elaborately designed machinery. The production of the molding rolls is complicated and costly because cavities with a three-dimensional structure must be provided in the roll surfaces. This particularly applies when more complicated geometries, e.g. divisible tablets with a score are desired. Because of the need for the two molding rolls to be accurately aligned in the known molding calendering processes, no segmentation of the molding rolls into individual roll disks which each comprise only one or a few lanes of depressions, and can be combined to a multilane roll as required, is possible because the individual segments easily become twisted due to the molding pressure occurring during the calendering. However, this twisting leads to the upper and lower halves of the tablet molds not being exactly coincident on rotation. Segmentation of the molding rolls is, however, desirable in order for it to be necessary, for example if individual cavities are damaged, to replace only one roll disk and not the entire roll, or for it to be possible to combine diverse molds in one roll as desired.
It has already been proposed to combine a molding roll having depressions on its surface with a second roll which contains no depressions (smooth roll). In this case there is no need for accurate alignment of the two rolls. However, the disadvantage in this case is that elaborate production of at least one of the two rolls is still necessary. In addition, there are very limited possibilities for the shape of the tablet molds with this combination.
It is an object of the present invention to provide a simple and cost-effective process for producing solid dosage forms in which no problems relating to mismatch of upper and lower halves of the dosage forms occur.
We have found that this object is achieved when the molding rolls are designed on their surface so that they are able to intermesh.
The present invention therefore relates to a process for producing solid dosage forms by
a) producing a plastic mixture which comprises at least one active ingredient and at least one polymeric binder, and
b) shaping the plastic mixture to the solid dosage forms in a molding calender with two counterrotating molding rolls, wherein one molding roll has at least one annular groove running along its periphery and the other molding roll has at least one ring, running along its periphery, of teeth extending radially outward and able to engage in the annular groove. The teeth are shaped so that, on maximum engagement in the annular groove, they essentially completely fill the cross-section of the annular groove, i.e. the annular groove and the teeth are essentially complementary in cross-section profile.
The intermeshing of the molding rolls makes it unnecessary to align the two individual rolls accurately, because only one roll of the pair of rolls has an angle-dependent surface structure. It is therefore possible to select considerably simpler designs of machinery for the calenders accomodating the molding rolls.
Molding rolls to be used according to the invention are known as xe2x80x9cprism rollsxe2x80x9d from compaction technology. In this connection, reference is made to B. Pietsch, Aufbereitungs-Technik 3 (1970) pp. 128-138. The use of such rolls for compacting free-flowing materials to granules is described therein. Problems of a possible mismatch between upper and lower half of the compacts formed are not mentioned in this connection.
Pairs of rolls to be used according to the invention make it possible, despite the simple design of the rolls, for the solid dosage forms produced in this way to have a considerable variety of shapes. The possible variations relate primarily to the design of the annular groove and the design of the interstice between consecutive teeth in a ring. Thus, the annular groove may have a series of different cross-section profiles (projection onto a plane containing the axis of the roll). The annular groove may have a rectangular, triangular, rounded or any other cross-section. It is generally preferred for the annular groove to have a rounded cross-section profile for easier demolding of the shaped dosage forms.
The longitudinal profile of the interstices between consecutive teeth in a ring (i.e. the projection of the interstice onto a plane perpendicular to the axis of the roll) is likewise subject to variation. Thus, the interstices may have triangular, parallelogram-shaped, rounded or another longitudinal profile. However, it is generally preferred for the interstices between consecutive teeth in a ring to have a rounded longitudinal profile.
The resulting dosage forms may have in this way, for example, a prism shape, truncated prism shape, tetrahedral shape or saddle shape, and the saddle shape is preferred.
In a preferred embodiment of the process according to the invention, a circulating bar is present on the base of the annular groove and the teeth have a corresponding recess. It is possible in this way to produce divisible tablets having a score on one side of their surface.
It is likewise possible for a bar which does not extend up to the outer surface of the roll to be present between consecutive teeth in a ring. It is likewise possible in this way to produce divisible tablets with a score.
In order to facilitate demolding of the formed dosage forms from the annular groove and the interstices between the teeth, it is possible to keep the contact pressure between the two molding rolls low, or to provide a small spacing between the molding rolls, e.g. 0.1-1 mm. This results in a xe2x80x9ctablet ribbonxe2x80x9d in which the individual dosage forms are still connected together by narrow flashes. The individual dosage forms can, especially when the plastic mixture shows increased brittleness after complete cooling, easily be separated from one another. It may be appropriate then to deflash the resulting dosage forms.
After the molding process, the drug forms are allowed to cool and solidify, e.g. on a cooling belt.
The present process for producing solid dosage forms comprises the production of a plastic mixture. This usually takes place by mixing and melting at least one pharmacologically acceptable polymeric binder, at least one active pharmaceutical ingredient and, where appropriate, conventional pharmaceutical additives in the presence or absence of a solvent. These process steps can be carried out in known manner.
The components can first be mixed and then be melted and homogenized. However, it has proven to be preferred, especially on use of sensitive active ingredients, first for the polymeric binder to be melted and premixed where appropriate together with conventional pharmaceutical additives, operating the stirred vessels, agitators, solids mixers etc. where appropriate alternately, and then for the sensitive active ingredient(s) to be mixed in (homogenization) in xe2x80x9cintensive mixersxe2x80x9d in the plastic phase with very short residence times. The active ingredients) can be employed in solid form or as solution or dispersion.
The melting and mixing take place in an apparatus customary for this purpose. Extruders or heatable containers with an agitator, e.g. kneaders (such as the type mentioned below), are particularly suitable.
It is also possible to use as mixing apparatus the devices employed for mixing in plastics technology. Suitable devices are described, for example, in xe2x80x9cMischen beim Herstellen und Verarbeiten von Kunststoffenxe2x80x9d, H. Pahl, VDI-Verlag, 1986. Particularly suitable mixing apparatuses are extruders and dynamic and static mixers, and stirred vessels, single-shaft stirrers with stripper mechanisms, especially paste mixers, multishaft stirrers, especially PDSM mixers, solids mixers and, preferably, mixer/kneader reactors (e.g. ORP, CRP, AP, DTB supplied by List or Reactotherm supplied by Krauss-Maffei or Ko-kneader supplied by Buss), trough mixers and internal mixers or rotor/stator systems (e.g. Dispax supplied by IKA).
In the case of sensitive active ingredients, it is preferable first for the polymeric binder to be melted in an extruder and then for the active ingredient to be admixed in a mixer/kneader reactor. On the other hand, with less sensitive active ingredients, a rotor/stator system can be employed for vigorously dispersing the active ingredient.
The mixing device is charged continuously or batchwise, depending on its design, in a conventional way. Powdered components can be introduced in a free feed, e.g. via a weigh feeder. Plastic compositions can be fed in directly from an extruder or via a gear pump, which is particularly advantageous if the viscosities and pressures are high. Liquid media can be metered in by a suitable pump unit.
The mixture obtained by mixing and melting the binder, the active ingredient and, where appropriate, the additive(s) ranges from pasty to viscous (thermoplastic) and is therefore extrudable. The glass transition temperature of the mixture is below the decomposition temperature of all the components present in the mixture. The binder should preferably be soluble or swellable in a physiological medium. Examples of suitable binders are:
polyvinylpyrrolidone (PVP), copolymers of N-vinylpyrrolidone (NVP) and vinyl esters, especially vinyl acetate, copolymers of vinyl acetate and crotonic acid, partially hydrolyzed polyvinyl acetate, polyvinyl alcohol, poly(hydroxyalkyl acrylates), poly(hydroxyalkyl methacrylates), polyacrylates and polymethacrylates (Eudragit types), copolymers of methyl methacrylate and acrylic acid, cellulose esters, cellulose ethers, especially methylcellulose and ethylcellulose, hydroxyalkylcelluloses, in particular hydroxypropylcellulose, hydroxyalkylalkylcelluloses, in particular hydroxypropylethylcellulose, cellulose phthalates, in particular cellulose acetate phthalate and hydroxypropylmethylcellulose phthalate, and mannans, especially galactomannans. The K values (according to H. Fikentscher, Cellulose-Chemie 13 (1932), pages 58-64, 71, 74) of the polymers are in the range from 10 to 100, preferably 12 to 70, in particular 12 to 35, for PVP greater than 17, in particular 20 to 35.
Preferred polymeric binders are polyvinylpyrrolidone, copolymers of N-vinylpyrrolidone and vinyl esters, poly(hydroxyalkyl acrylates), poly(hydroxyalkyl methacrylates), polyacrylates, polymethacrylates, alkylcelluloses and hydroxyalkylcelluloses. The polymeric binder must soften or melt in the complete mixture of all the components in the range from 50 to 180xc2x0 C., preferably 60 to 130xc2x0 C. The glass transition temperature of the mixture must therefore be below 180xc2x0 C., preferably below 130xc2x0 C. If necessary, it is reduced by conventional pharmacologically acceptable plasticizing auxiliaries. The amount of plasticizer does not exceed 30% by weight, based on the total weight of binder and plasticizer, in order to form drug forms which are stable on storage and show no cold flow. However, the mixture preferably contains no plasticizer.
Examples of such plasticizers are:
long chain alcohols, ethylene glycol, propylene glycol, glycerol, trimethylolpropane, triethylene glycol, butanediols, pentanols such as pentaerythritol, hexanols, polyethylene glycols, polypropylene glycols, polyethylene/propylene glycols, silicones, aromatic carboxylic esters (e.g. dialkyl phthalates, trimellitic esters, benzoic esters, terephthalic esters) or aliphatic dicarboxylic esters (e.g. dialkyl adipates, sebacic esters, azelaic esters, citric and tartaric esters), fatty acid esters such as glycerol monoacetate, glycerol diacetate or glycerol triacetate or sodium diethyl sulfosuccinate. The concentration of plasticizer is generally from 0.5 to 15, preferably 0.5 to 5, % of the total weight of the mixture.
Conventional pharmaceutical auxiliaries, whose total amount can be up to 100% of the weight of the polymer, are, for example, extenders and bulking agents such as silicates or diatomaceous earth, magnesium oxide, aluminum oxide, titanium oxide, stearic acid or its salts, e.g. the magnesium or calcium salt, methylcellulose, sodium carboxymethylcellulose, talc, sucrose, lactose, cereal or corn starch, potato flour, polyvinyl alcohol, in particular in a concentration of from 0.02 to 50, preferably 0.20 to 20, % of the total weight of the mixture.
Lubricants such as aluminum and calcium stearates, talc and silicones, in a concentration of from 0.1 to 5, preferably 0.1 to 3, % of the total weight of the mixture.
Flowability agents such as animal or vegetable fats, especially in hydrogenated form and those which are solid at room temperature. These fats preferably have a melting point of 50xc2x0 C. or above. Triglycerides of C12, C14, C16 and C18 fatty acids are preferred. It is also possible to use waxes such as carnauba wax. These fats and waxes may be admixed advantageously alone or together with mono- and/or diglycerides or phosphatides, especially lecithin. The mono- and diglycerides are preferably derived from the abovementioned fatty acid types. The total amount of fats, waxes, mono-, diglycerides and/or lecithins is from 0.1 to 30, preferably 0.1 to 5, % of the total weight of the composition for the particular layer;
dyes such as azo dyes, organic or inorganic pigments or dyes of natural origin, with preference for inorganic pigments in a concentration of from 0.001 to 10, preferably 0.5 to 3, % of the total weight of the mixture;
stabilizers such as antioxidants, light stabilizers, hydroperoxide destroyers, radical scavengers, stabilizers against microbial attack.
It is also possible to add wetting agents, preservatives, disintegrants, adsorbents, release agents and blowing agents (cf., for example, H. Sucker et al., Pharmazeutische Technologie, Thierne-Verlag, Stuttgart 1978).
Auxiliaries include for the purpose of the invention substances for producing a solid solution of the active ingredient. Examples of these auxiliaries are pentaerythritol and pentaerythritol tetraacetate, polymers such as polyethylene oxide and polypropylene oxide and their block copolymers (poloxamers), phosphatides such as lecithin, homo- and copolymers of vinylpyrrolidone, surfactants such as polyoxyethylene 40 stearate, and citric and succinic acids, bile acids, sterols and others as indicated, for example, in J. L. Ford, Pharm. Acta Helv. 61 (1986) pp.69-88.
Pharmaceutical auxiliaries are also regarded as being additions of bases and acids to control the solubility of an active ingredient (see, for example, K. Thoma et al., Pharm. Ind. 51 (1989) 98-101).
The only precondition for the suitability of auxiliaries is adequate temperature stability.
Active ingredients mean for the purpose of the invention all substances with a pharmaceutical effect and minimal side effects as long as they do not decompose under the processing conditions. The amount of active ingredient per dose unit and the concentration may vary within wide limits depending on the activity and the release rate. The only condition is that they suffice to achieve the desired effect. Thus, the concentration of active ingredient can be in the range from 0.1 to 95, preferably from 20 to 80, in particular 30 to 70, % by weight. It is also possible to employ active ingredient combinations. Active ingredients for the purpose of the invention also include vitamins and minerals, as well as plant treatment agents and insecticides. The vitamins include the vitamins of the A group, the B group, which are meant besides B1, B2, B6 and B12 and nicotinic acid and nicotinamide to include also compounds with vitamin B properties such as adenine, choline, pantothenic acid, biotin, adenylic acid, folic acid, orotic acid, pangamic acid, carnitine, p-aminobenzoic acid, myo-inositol and lipoic acid, and vitamin C, vitamins of the D group, E group, F group, H group, I and J groups, K group and P group. Active ingredients for the purpose of the invention also include therapeutic peptides.
The process according to the invention is suitable, for example, for processing the following active ingredients:
acebutolol, acetylcysteine, acetylsalicylic acid, acyclovir, alfacalcidol, allantoin, allopurinol, alprazolam, ambroxol, amikacin, amiloride, aminoacetic acid, amiodarone, amitriptyline, amlodipine, amoxicillin, ampicillin, ascorbic acid, aspartame, astemizole, atenolol, beclomethasone, benserazide, benzalkoniumhydrochloride, benzocaine, benzoic acid, betamethasone, bezafibrate, biotin, biperiden, bisoprolol, bromazepam, bromhexine, bromocriptine, budesonide, bufexamac, buflomedil, buspirone, caffeine, camphor, captopril, carbamazepine, carbidopa, carboplatin, cefachlor, cefadroxil, cefalexin, cefazolin, cefixime, cefotaxime, ceftazidime, ceftriaxone, cefuroxime, chloramphenicol, chlorhexidine, chlor-pheniramine, chlortalidone, choline, cyclosporin, cilastatin, cimetidine, ciprofloxacin, cisapride, cisplatin, clarithromycin, clavulanic acid, clomipramine, clonazepam, clonidine, clotrimazole, codeine, cholestyramine, cromoglycic acid, cyanocobalamin, cyproterone, desogestrel, dexamethasone, dexpanthenol, dextromethorphan, dextropropoxiphene, diazepam, diclofenac, digoxin, dihydrocodeine, dihydroergotamine, dihydroergotoxin, diltiazem, diphenhydramine, dipyridamole, dipyrone, disopyramide, domperidone, dopamine, doxocyclin, enalapril, ephedrine, epinephrine, ergocalciferol, ergotamine, erythromycin, estradiol, ethinylestradiol, etoposide, Eucalyptus globulus, famotidine, felodipine, fenofibrate, fenoterol, fentanyl, flavin-mononucleotide, fluconazole, flunarizine, fluorouracil, fluoxetine, flurbiprofen, folinic acid, furosemide, gallopamil, gemfibrozil, gentamicin, Gingko biloba, glibenclamide, glipizide, clozapine, glycyrrhiza glabra, griseofulvin, guaifenesin, haloperidol, heparin, hyaluronic acid, hydrochlorothiazide, hydrocodone, hydrocortisone, hydromorphone, ipratropium-hydroxide, ibuprofen, imipenem, indomethacin, iohexol, iopamidol, isosorbide-dinitrate, isosorbide-mononitrate, isotretinoin, ketotifen, ketoconazole, ketoprofen, ketorolac, labetalol, lactulose, lecithin, levocarnitine, levodopa, levoglutamide, levonorgestrel, levothyroxine, lidocaine, lipase, imipramine, lisinopril, loperamide, lorazepam, lovastatin, medroxyprogesterone, menthol, methotrexate, methyldopa, methylprednisolone, metoclopramide, metoprolol, miconazole, midazolam, minocycline, minoxidil, misoprostol, morphine, multivitamin mixtures or combinations and mineral salts, N-methylephedrine, naftidrofuryl, naproxen, neomycin, nicardipine, nicergoline, nicotinamide, nicotine, nicotinic acid, nifedipine, nimodipine, nitrazepam, nitrendipine, nizatidine, norethisterone, norfloxacin, norgestrel, nortriptyline, nystatin, ofloxacin, omeprazole, ondansetron, pancreatin, panthenol, pantothenic acid, paracetamol, penicillin G, penicillin V, pentoxifylline, phenobarbital, phenoxymethylpenicillin, phenylephrine, phenylpropanolamine, phenytoin, piroxicam, polymyxin B, povidone-iodine, pravastatin, prazepam, prazosin, prednisolone, prednisone, propafenone, propranolol, proxyphylline, pseudoephedrine, pyridoxine, quinidine, ramipril, ranitidine, reserpine, retinol, riboflavin, rifampicin, rutoside, saccharin, salbutamol, salcatonin, salicylic acid, selegiline, simvastatin, somatropin, sotalol, spironolactone, sucralfate, sulbactam, sulfamethoxazole, sulfasalazine, sulpiride, tamoxifen, tegafur, teprenone, terazosin, terbutaline, terfenadine, tetracycline, theophylline, thiamine, ticlopidine, timolol, tranexamic acid, tretinoin, triamcinolone-acetonide, triamterene, trimethoprim, troxerutin, uracil, valproic acid, vancomycin, verapamil, vitamin E, zidovudine.
Preferred active ingredients are ibuprofen (as racemate, enantiomer or enriched enantiomer), ketoprofen, flurbiprofen, acetylsalicylic acid, verapamil, paracetamol, nifedipine or captopril.
It is possible in particular for solid solutions to be formed. The term xe2x80x9csolid solutionsxe2x80x9d is familiar to the skilled worker, for example from the literature cited at the outset. In solid solutions of active pharmaceutical ingredients in polymers, the active ingredient is in the form of a molecular dispersion in the polymer.
The resulting mixture is preferably solvent-free, i.e. it contains neither water nor an organic solvent. The resulting mixture is subsequently introduced into a molding calender discussed above.
The solid pharmaceutical forms which can be produced using the process according to the invention can finally also be provided in a conventional way with film coatings which control the release of active ingredient or mask the taste. Suitable materials for such coatings are polyacrylates such as the Eudragit types, cellulose esters such as the hydroxypropylmethylcellulose phthalates, and cellulose ethers such as ethylcellulose, hydroxypropylmethylcellulose or hydroxypropylcellulose.
It is thus possible with the process according to the invention to produce drug forms with particularly accurate dimensions. Surprisingly, this process is low-cost, permits very large numbers of item per unit time to be achieved and avoids all waste.


A fluid level sensor and a method of operating the oil level sensor to measure the fluid level and dielectric strength of the fluid substantially simultaneously. The fluid level sensor having a compensator capacitor normally fully submerged within the fluid and a linear capacitor variably submerged as a function of fluid level. Oscillators convert the capacitance of the linear and compensator capacitors into a first and second frequency respectively. A processor uses the two frequencies and calibration data stored in a memory to calculate the fluid level and dielectric strength substantially simultaneously. The dielectric strength calculation may be based upon an offset from the second frequency from a known frequency of a known dielectric strength. The fluid level calculation may be based upon a ratio of a numerator to a denominator where the numerator is a difference between the second frequency and a second focal point frequency, and the denominator is a difference between the first frequency and a first focal point frequency.

The present invention is related to the field of capacitive based fluid sensors used to measure fluid levels and a dielectric strength of the fluids using a ratiometric algorithm.
Operation of capacitive based fluid sensors is based upon a measurable change in capacitance of the sensor caused by a difference in the dielectric strength of air as compared to the dielectric strength of a fluid or oil being measured. As fluid levels rise and fall between vertical plates of the sensor, the effective dielectric strength between the plates changes, resulting in an increase or decrease in total capacitance of the sensor. Since the total capacitance is proportional to a product of the dielectric strength and the area of the plates, then given a known constant dielectric strength of the fluid or oil being measured allows the depth of the plates covered by the fluid or oil to be calculated. If the sensor is totally submerged in the fluid, then the measured capacitance can be used to calculate the actual dielectric strength of the fluid.
Capacitive based fluid sensors have found practical applications in engines, transmissions and gear boxes for machines in which the level and quality of the fluid or oil is crucial to the operation and wear of the moving parts. As level sensors, the capacitive based fluid sensors provide a real time indication of the amount of fluid or oil available. The rate at which the fluid or oil level changes can be used to distinguish between normal operational losses and a leak in the system. If the fluid or oil level drops below a predetermined level, automatic alarms or self-preservation routines can be implemented in the machinery to prevent severe damage.
When used to measure dielectric strength, the capacitive based fluid sensors can provide an indication when the fluid or oil is losing its effectiveness, and may indicate a failure in the system. Thermal breakdown of the oil over time generally results in an increase in the dielectric strength of the oil. A combination of time and change in the measured dielectric strength can be used to determine when the oil requires to be changed. Premature or sudden changes in the dielectric strength of the oil can indicate the presence of impurities in the oil. This may indicate severe problems such as engine coolant or fuel leaking around a faulty seal or gasket.
The basic design of many capacitive based fluid sensors limit their accuracy when measuring fluid levels and dielectric strengths. For example, many designs assume a constant dielectric strength when measuring fluid level. If the dielectric strength of the fluid changes with temperature and time, or if a different brand of fluid having a different dielectric strength is substituted for the original fluid, then the measured fluid level changes even though the actual fluid level remains constant. In another example, some sensor designs do not compensate for the effects of temperature on the fluid""s characteristics. The dielectric strength of many fluids is dependent upon the temperature of the fluid. As fluid temperature increases, the dielectric strength increases resulting in a higher measured capacitance. Further, the volume of the fluid may also be dependent upon the temperature. When the fluid is confined in a container, a thermally induced increase in volume will result in an increase in the fluid level in the container. In yet another example, many sensor designs cannot account for the geometry of the container holding the fluid. Many containers have non-uniform shapes causing a non-linear relationship between the level of the fluid and the actual volume of fluid present in the container.
Some capacitive based fluid sensors utilize two active capacitors to mitigate the effects of changing dielectric strength on the accuracy of the fluid level measurements. U.S. Pat. No. 5,929,754 issued to Park et al. on Jul. 27, 1999 is an example of such a dual capacitor sensor. Park""s sensor has a level/deterioration (dielectric) sensing capacitor plus a reference capacitor. The reference capacitor is disposed near the bottom of the sensor so that it is fully submerged in the oil during normal operation. Electronics embedded within the sensor housing use the reference capacitor to partially compensate for variations in dielectric strength over time, for dielectric strength variations between different oil brands, and for geometric changes in the sensor material due to thermal expansion. A temperature sensor is included in the design to help compensate for temperature changes.
The electronics in the Park sensor measure the capacitance of the level/deterioration capacitor and the reference capacitor and output a voltage that is proportional to the difference between the two capacitances divided by the sum of the two capacitances. Trim resistors and other fixed capacitors are used to adjust the output voltage depending upon the use of the sensor for measuring level or oil deterioration. In one embodiment, the electronics toggle the two capacitors between two sets of electronic circuits, one electronic circuit is trimmed for level, the other electronic circuit is trimmed for deterioration. One limitation of this arrangement is that an accurate deterioration (dielectric) measurement can only be made while the level/deterioration capacitor is completely submerged in the oil, and useful level measurements require the level/deterioration capacitor to be only partially submerged.
The present invention is a capacitive based fluid sensor that is capable of generating output signals proportional to a fluid or oil level above a predetermined level and a dielectric strength of the fluid or oil within a container substantially simultaneously. (From this point forward, the fluid or oil will be referred to only as an oil.) The sensor has a compensator capacitor that is disposed within the container and fully submerged within the oil. A linear capacitor of the sensor is disposed within the container so that it initially engages the oil when the oil is at a predetermined level. Both capacitors have openings that allow the oil to flow between capacitive plates of the capacitors. An electronic circuit is electrically connected to both capacitors to measure their respective capacitances. The electronic circuit calculates a dielectric strength based upon the capacitance of the compensator capacitor and an oil level based upon the capacitance of both capacitors. The calculations are performed substantially simultaneously. A temperature sensor may also be positioned to provide an oil temperature signal to the electronic circuit for use in the calculations. An engine speed signal may be provided to the electronic circuit from an external source for use in the calculations.
The capacitors are formed as coaxially cylindrical plates. An inner surface of a hollow housing forms an outer capacitive plate common to both the linear capacitor and the compensator capacitor. A first inner capacitive plate disposed adjacent to the outer capacitive plate completes the linear capacitor. A second inner capacitive plate disposed adjacent the outer capacitive plate completes the compensator capacitor. The first and second inner capacitive plates are held in position by a circuit board assembly that runs the length of the housing. The circuit board assembly is held in position by guides disposed on the inner surface of the housing. In an alternative embodiment, the first inner capacitive plate may include circumferential groves to assist the oil in wetting the plate in predetermined increments.
The housing has one or more openings of suitable size to allow the oil to enter the hollow interior of the housing. A curved section may be included in the housing to allow the sensor to fit into tight locations.
In one embodiment, the electronic circuit includes two oscillators, with one oscillator connected to each of the linear capacitor and the compensator capacitor respectively. The frequency of the oscillators are inversely proportional to the capacitance of the respective capacitors. An advantage of using one oscillator for each capacitor is that both capacitor/oscillator combinations are electrically isolated from each other. A failure of one capacitor/oscillator combination does not necessarily disrupt operation of the other capacitor/oscillator combination. A processor, generally a microprocessor or microcontroller, connected to the outputs of the two oscillators calculates the dielectric strength and oil level. Programming pins connected to the processor, and a memory may be used to load calibration and other characteristics into the electronic circuit for use in the calculations. One or more digital to analog converters may be connected to the processor to convert the dielectric strength and oil level from digital form to analog form. Alternatively, the dielectric strength and oil level may be output in parallel or serial digital form.
Calculation of the oil level and dielectric strength are based upon a plot of the sensor""s characteristics curves using the frequency associated with the linear capacitor (called a first frequency) as the X-axis and the frequency associated with the compensator capacitor (called a second frequency) as the Y-axis. Each curve of the sensor""s characteristic curves intersect at a focal point where the dielectric strength has a value of one. Near this focal point the individual oil level curves are approximately straight lines, each with a unique slope. Each point of the characteristic curve represents an oil level and a dielectric strength. After measuring the first frequency and the second frequency, then the oil level and dielectric strength can be determined from the characteristic curves.
In an alternative embodiment, the oil level calculation determines a difference between the focal point and the first frequency to produce a denominator, and a difference between the focal point and the second frequency to produce a numerator. Calculating a ratio of the numerator to the denominator produces a measured slope that indicates the oil level.
In another alternative embodiment, the dielectric strength calculation is based upon the difference between the second frequency and a known characteristic of a known dielectric strength. A scale factor and offset may be included in the calculation as necessary.
Diagnostics may be performed by the processor to detect, signal and compensate for failures of the capacitors, wiring and some of the electronics. One error detection is accomplished by checking the first frequency and the second frequency against valid frequency bands. A second error detection is accomplished by checking the denominator for a zero value prior to calculating the ratio of the numerator to the denominator. A third error detection is accomplished by checking the calculated ratio against a valid ratio range. If any one or more errors are detected, an error signal may be generated by the processor. Error detection filtering may be applied to minimize spurious errors.
Accordingly, it is an object of the present invention to provide a capacitive based oil sensor that is capable of measuring and reporting the level of the oil and the dielectric strength of the oil substantially simultaneously.
Another object of the present invention is to provide a method of calculating the oil level and dielectric strength using a ratiometeric algorithm.

Device which measures oil level and dielectric strength with a capacitance based sensor using a ratiometric algorithm


The invention relates to a wind-driven power-plant comprising a rotor (100) which is fitted with at least one rotor blade and which is connected directly or indirectly to a generator for power generation, further including an electrical assembly made up of different electrical sub-assemblies including electronic, electrical and/or electromechanical and/or sensor elements and/or electrotechnical safety elements, where, depending on their purposes, all elements/components of one or more electrical sub-assemblies or specific elements of the electrical sub-assembly are combined into one or more function modules that implement at least one function in relation to the generation of electric power, where a parallel module is associated with at least one function module, and the parallel module is able to implement the same or nearly the same function as the function module in normal operation.

The objective of the present invention is to create a wind-driven power-plant comprising an electric assembly compensating for defects as they occur so that the power-plant remains ready to operate, and unnecessary periods of interrupted operation and their entailed costs are averted in this manner.
The wind-driven power-plant of the invention comprises a rotor fitted with at least one blade and connected directly or indirectly to an electric power generator, further it comprises an electric assembly composed of different electrical sub-assemblies that are fitted with electronic, electric and/or electromechanical and/or detecting elements/components and/or electrotechnical safety devices.
In the present invention, all or specific elements/components of an electric sub-assembly are combined in relation to their purposes into one or more function modules (250, 250′), such function module(s) implementing at least one function in conjunction with the generation of electrical power generation, at least one parallel module being present for at least one function module, said parallel module implementing, or being able to implement, during typical power-plant operation, an identical or analogous function of the function module, the function module and the parallel module being connected or connectable to each other in such a way that, in the event of operational malfunction affecting a functional or a parallel module, the remaining still operational parallel or operational modules shall maintain, at least in part, the generation of electrical power.
In the present invention, specific or all elements/components of the sub-assemblies are combined into function modules. The function modules so created are configured in a way that they implement specific functions relating to the power-plant's generation of electricity. At least one parallel module is provided for one function module, the purpose of the parallel module(s) being to maintain electric power generation.
Using the parallel module makes it possible to delay replacing a defective function module until the weather improves or until the next scheduled maintenance operation. This feature offers the advantage, in particular, as regards offshore power-plants that travel to said plants shall be limited substantially to regularly scheduled maintenance and thereby repair costs may be lowered.
The parallel module, and in part also the function module, may be designed differently to solve this problem.
On one hand, the parallel module may be designed to carry out the same operation as does the function module. In the process the parallel module may carry out that function simultaneously with the function module, namely, the electric power generation is carried out simultaneously by the two modules, whereby, in the event of operational malfunction in either parallel or function module, the power generation of the remaining, effective module will continue and in this manner continuous operation, even though restricted, is advantageously attained for the power-plant.
One particular configuration of generator technology has long been known. In this configuration and for economic reasons, the generator assembly was split into two to four parallel generators, for instance two 750 kw generators for one 1.5 Mw power-plant or four 250 kw generators for 1 Mw power-plant. These designs however only addressed the problem that the larger generators could not be manufactured at all, or when, then at substantially higher costs than a larger number of smaller generators, in other words, at the time the goal was to reduce capital costs. The gear units of this machinery indeed were not suitable to continue generating power in the event of failure of one of the generators because the resultant asymmetrical loading would have damaged the gearing.
The German patent document DE 100 40 273.9 A1 discloses a generator configuration comprising at least two stators besides one rotor, each stator being associated with at least one converter. However substantial additional costs are incurred when one generator is fitted with at least two stators.
Even in the embodiment of the present invention, capital costs are initially increased on account of the more complex design, though to a lesser extent than for one generator with at least two stators. Relative to the state of the art, the lesser additional costs of the invention offer the prime advantage that amortizing said additional costs is attained more rapidly on account of the higher reliability of power generation over the 20-year life of the wind-driven power-plant.
The parallel module moreover may be designed in a manner that it shall operate similarly to the function module, where however this similar operation does or may contribute to power generation just as does the function module. Illustratively the parallel module may be more compact than the function module and hence be produced more cheaply.
Again the parallel module may be configured in a way that it shall operate jointly with the function module.
The design of a wind-driven power-plant comprising two control computers in the conventional master-slave configuration is known. The first (master) control computer is illustratively used for override operation and for matching the power-plant to the electrical public power, in particular to match the generated power to predetermined input parameters of the public power network. The second control computer (slave) assumes recording and analyzing sensor data and controlling and regulating the power-plannt during short term operational procedures.
In the present invention, the two computers may be designed in a manner that if one fails, the other may assume its operations. The two computers also may be over-sized so that the computer remaining operative may operate instead of and for both in the case of failure of one. Economically, however, over-sizing should be minimized to just ensure essential maintenance of power generation even in the face of the drawback that the still viable computer no longer can carry out some operations, for instance optimizing power or compensating for extreme ambiences (extreme wind gusts, extreme incidents in the public power network such as voltage or frequency notches.
The invention also allows the parallel module to be passive during normal power-plant operation while being activated only upon failure of the function module and in this manner at least partly maintain power generation.
Illustratively, the detecting elements measuring ambient effects such as wind speed, temperature etc. may be combined into one function module called "sensors". In this respect a parallel module might include the same detectors. If the "sensors" function module were to fail, then the "sensors" parallel module would be activated and would assume the former's assignment.
In one advantageous embodiment mode of the present invention, the parallel module furthermore may be designed in a manner that upon failure of the function module, the latter's operation may be completely taken over by former. This design offers the advantage that the parallel module operates virtually as a replacement module and that, in the event of function module failure, electric power generation may be maintained in full and no economic losses are incurred.
In a further advantageous embodiment of the invention, the wind-driven power-plant comprises at least two function modules implementing identical or similar operations and at least one parallel module that preferably completely assumes operations of one function module after it fails.
The feature of a minimum of two function modules jointly carrying out one function for electric power generation offers the advantage that the parallel module in turn need only be half size to completely maintain power generation in the event of an element/component failure. Increasing the number of function modules lowers the size of the required parallel module commensurately. Depending on the probability of malfunction and the costs of said function module, the economically optimal configuration may be determined individually.
However in another further advantageous embodiment mode of the present invention, the parallel module for instance may be selected smaller and hence more advantageously, whereby it shall only partly assume the operations of the function module. This design variation offers the advantage of maintaining at least partial electric power generation in economic manner.
The above discussed control system redundancy entails difficulties in diagnosing which of two modules is malfunctioning when there is discrepancy between the performances of two modules. Accordingly, elements especially susceptible to malfunctioning may be used advantageously in triplicate. This feature allows diagnosing properly a defective or malfunctioning module by using two coinciding results over one deviating from them as long as only one module shall deviate. In the event of two malfunctioning modules, diagnosis still may be properly carried out using a control program based on the plausibility test (knowledge based expert system).
In another advantageous embodiment mode of the present invention, an electrical sub-assembly may include a control device optimizing electric power generation and itself comprising at least one operations managing computer.
In yet another advantageous embodiment mode of the present invention, the wind-driven power-plant may include at least one feed module feeding electric power to said control device, said feed module in a still further and advantageous embodiment mode of the invention being designed to be independent of the public electric power supply.
Preferably at least two feed modules feeding the control device shall be independent of the public power supply in order to assure power to the control device even when the public power supply fails. Redundancy of the control power independent of public power is especially important as regards a wind-driven power-plant because control failure would entail emergency braking and thereby highly loading all power-plant elements/components and high wear.
In an especially advantageous manner, redundancy shall be implemented using different physical principles. The commercial, battery based systems (also called USV's or UPS'S) of the state of the art incur the practical drawback of being susceptible—and very susceptible at low temperatures—to malfunctions. Accordingly, the combination of two supplies of different intrinsic operation is an explicit part of the present invention. An especially appropriate design feature is the combination of an economical battery storage with the highly reliable, if expensive, capacitive storage (UltraCaps). To make possible feeding the control device for an extended time interval in the case of public power failure, the control device may be combined with a solar cell or with a small windmill or the like or with both to attain high supply reliability. The solar cell or the small windmill may be mounted advantageously at the top of the generator pod, underneath the rotor, to the side of the tower or, as regards offshore wind-driven power-plants, to a platform affixed to the tower. The attitude should be toward the wind's lee and/or windward sides to assure maximum supply reliability.
In yet another advantageous embodiment mode of the present invention, at least one more control device may be available, the first control device serving as the operational module and the second as the parallel module. This design offers the advantage of power generation always being maintained even if the control device malfunctions totally or only partly.
In still another advantageous embodiment mode of the present invention, at least one replacement element/component may be present for at least one of the electronic, electrical and/or electromechanical basic elements/components, where the basic elements/components and the replacement elements/components are mutually configured in such a way that, upon operational malfunction in a basic element/component, its function shall be assumed by the replacement element/component.
It is known to keep a replacement element/component in reserve for basic elements/components in the form of sensors such as a wind-speed measuring anemometer. However, these features so far have been used only for those sensors of which the defective display entails significant jeopardy to all or parts of the power-plant.
Keeping replacement elements/components in reserve offers the advantage that continuous operation of the wind-driven power-plant is assured even when a basic element/component fails.
Not every basic element/component requires the presence of a replacement element/component. A judicious pre-selection of basic elements/components would be advantageous with respect to selecting a replacement component. Illustratively, such preselection may relate to basic elements/components in which a malfunction would at once shut down the power-plant. However said preselection also may relate to basic elements/components which are empirically known to be subjected to special loads in wind-driven power-plants. Desirably again basic elements/components of known malfunctioning profiles should be present in duplicate.
In a further embodiment mode of the present invention, the wind-driven power-plant is designed for maintenance from a remote monitoring station.
Furthermore, the remote monitoring station may also be designed that it may act on the wind-driven power-plant's control device.
As a rule the control device of a modern wind-driven power-plant is designed that it may be parameterized by means of so-called control parameters, that is that it shall be adjustable for instance to be appropriate for the particular kind of power-plant or the particulars of the site.
Also parameters relating to ambience and powerplant are fed to the control device, the power-plant ambience parameters for instance being air temperature, air pressure and wind speed. As a rule, the ambience parameters are measured by the power-plant sensors and the measurement data are transferred to the control device. Special parameters such as the requirements from the power network operator at a particular time however also may be fed externally for instance through data lines to the power-plant control devices.
Power-plant parameters relate to said power-plant and may be measured during operation at the power-plant and be communicated to the control device. These parameters, for instance, are the magnitude of the electric power, rotor rotational speed, generator rotational speed, blade attitude, power-plant temperature or the temperature of specific elements/components, modules or sub-assemblies, hydraulic pressures, data regarding electric currents or voltages etc.
Remote maintenance of a wind-driven power-plant using a remote monitoring system on one hand offers the advantageous ability to check said plant remotely. For instance the plant operator may inquire by means of the remote monitoring system about the power test results. However, operational malfunction in said power-plant also may be displayed by the remote monitoring system, and, in an advantageous embodiment mode of the present invention, said remote monitoring system illustratively also may be designed to let an expert carry out a complete defect diagnosis via the remote monitoring system in order to identify the cause(s) of malfunction.
Remote monitoring access to the control device furthermore offers the advantage that changes in control, ambience and power-plant parameters may be fed to said device. In this manner the present invention also allows transmitting for instance a new operations software by means of the remote monitoring system to the operational control computer of the drive device and to activate it.
Remote maintenance by means of the remote monitoring system moreover makes it possible—following power-plant defect diagnosis—to remedy the defect using said system and thereby keeping power-plant operation uninterrupted.
When the wind-driven power-plant is one of several power-plants in a wind park, the remote monitoring system may be integrated with or linked to the park control apparatus. Frequently, the total power outputs of the several wind-driven power-plants of a wind park may be fed jointly into the electric power network. To match the power-plant's total power output to power line requirements, this design of park control via the remote monitoring system makes it accessible to the power-plant and to accordingly modify latter's output.
In another advantageous embodiment mode of the present invention, the wind-driven power-plant may be designed in a manner that the control device shall manage operation by means of the ambience and power-plant parameters. In this respect the terminology "operations management" denotes both controlling/regulating the power-plant during operation to optimize power generation and the overriding operational management by means of the regulating and controlling operations that do not directly relate to power generation such as wind tracking, lubrication etc. and safety monitoring and any monitoring of the constituent sub-assemblies (diagnosis).
In general operations management of a wind-driven power-plant is designed in a manner that it shall be operated within the permissible limits of the ambience and plant parameters, said limits being defined by design parameters which in particular may be special control parameters. Illustratively, these design parameters may predetermine that the said plant shall be operating only within a given plant temperature range and that the generator output shall be reduced when this temperature range is exceeded in order that the power-plant temperature be lowered.
The design parameters moreover may require that the wind-driven power-plant be started very slowly if the external temperature should be very low, in the extreme case over a matter of hours, in order to allow thereby very uniform heating of all constituents/parts before the power-plant shall be operated under full load.
In another illustration, the design parameters may specify that at very turbulent wind conditions (gusts) the nominal rotational speed of the wind-driven power-plant shall be lowered in order to preclude the power-plant from running at excessively high speeds caused by strong gusts.
In typical operation for instance, the design parameters may be in the form of standard design parameters present in the operations managing computer of the control device, or else they may be computed from other data in the control device using the operations managing computer.
In one advantageous embodiment mode of the present invention, the operations managing computer may access temporary design parameters in the event of operational malfunction. The temporary design parameters may be stored in the operations managing computer for specific cases of malfunction, for instance failure of a basic function module. However, the operations managing computer also may generate/compute the temporary design parameters corresponding to such a failure, where called for, on the basis of data fed, for instance manually, to the operations managing computer.
By means of the temporary design parameters, the operations managing computer defines the temporary ranges, which match operations management, of permissible ambience and power-plant parameters, allowing maintaining the electric power output.
Illustratively, in this manner, if there is an operational malfunction in a total of four basic function modules in parallel, the nominal power output can be maintained in the frequency converter range provided that a desirable but not mandatory request to the public power operator be forsaken (for instance cos(p compensation), and/or the admissible external temperature is below a limit value (for instance 15° C., in order to especially effectively cool the frequency converter) and/or the generator rotational speed range is restricted (for instance ±10% of the rotational speed range instead of ±30% in nominal operation (to restrict the frequency converter's frequency matching).
The above described feasible design of the present invention offers the advantage that in spite of occurrence of malfunction, a response in the form of commensurately modifying the operational ranges of the ambience and power-plant parameters allows electrical power generation which preferably shall correspond to that of said plant in nominal operation.
Possibly, the modification of the operational ranges is permissible only over a given time interval, for instance because higher mechanical or thermal loads on an element/component would shorten life if extended longer. The present invention provides that such time limitations may be part of the temporary design parameters and that the control device shall shut off the power-plant when the limit value is exceeded or shall reduce its output power.
In a further embodiment mode, the operations managing computer may be programmed in a manner that it shall resort to the temporary design parameters until nominal power-plant operation has been restored.
The above cited designs make it possible to continuously operate a wind-driven power-plant, essentially by means of redundancies in elements/components, modules or sub-assemblies of the electrical assembly.
As regards the electrical assembly, in particular with respect to monitoring and control devices, the elements/components, modules and sub-assemblies amount to a highly developed network, as a result of which the redundancy in elements/components, modules and sub-assemblies entails a more than commensurately rising expenditure for connecting lines and switching devices. Furthermore electrical assemblies are in jeopardy of electrical shorts in a component entailing by means of said connections to consequential damages in other elements/components.
Accordingly, and in one advantageous embodiment mode of the present invention, the connection between at least two of the redundant elements/components and/or modules and/or sub-assemblies may be implemented exclusively or partly by at least one system of buses. In an especially advantageous embodiment the hooked-up elements/components are also conductively de-coupled by appropriately selecting the physical transmission medium (for instance in an optical medium using light guides). In an especially advantageous embodiment mode, the connecting lines of the bus system also may be redundant.
A bus system consists of bus users (for instance bus actuators, bus sensors, operations managing computer), a transmission medium (for instance bus cables or wireless links) and also a special software mounted on one of the bus users, in general the operations managing computer. The bus users comprise special bus hookup assemblies hooking up to the bus and assuring frictionless communication on the bus. The bus hookup assemblies consist of a processor (controller), a software and of a hookup unit ("transceiver") implementing signal transposition to the transport medium. The bus sensors are the power-plant's sensor elements which are also used for element/component monitoring, whereas the bus adjusting elements represent the elements/components and basic function modules through which the commands can be carried out. The transport medium in this design may be a conventional wire cable or in the form of optical fibers. When used in a wind-driven power-plant, the optical version offers the advantage of electromagnetic compatibility and being safe from lightning because signal lines frequently must be laid in close proximity to power cables over long distances.
The design of the present invention concerning the bus system applies to any kind of bus system, for instance CAN-Bus, in particular CANopen-Bus, Ethernet, Profibus, DP/FMS, Interbus, TTP, FlexRay.
Advantageously, the bus system is used both to transmit all signals required regarding control and operations management and to monitoring and activating the redundant design of the present invention. Obviously, the present invention also covers embodiment modes wherein signal transmission regarding control and operations management shall be entirely separate from the signal transmission regarding monitoring and activating redundant modules.
Accordingly, the invention's advantageous design offers a way to recognize, especially using a correspondingly programmed operations managing computer and the bus system, a defect in an element/component/module/sub-assembly, thereupon the replacement element/component being activated for signal transmission without incurring the need for switching connection lines, as a result of which power-plant operation is maintained. An additional monitoring device might also be used.
However, depending on the kind of element/component/module/sub-assembly, additional connection lines might require switching to transmit the power.
In this respect, the bus system is preferably implemented in the form of a network, whereby all essential function modules may communicate with one another even in the event of failure of individual communication paths. In that case each essential function module must be designed as a bus user, the higher costs so incurred, however, being compensated by the higher reliability of power generation.
In another advantageous further embodiment mode of the present invention, further smart bus users are operative besides the operations managing computer. This feature can be implemented either by means of additional smart nodes or by individual function modules connected to the bus system and fitted with their own "smart" microprocessors. These bus users, which are generally called smart bus function modules, are programmed in a manner to carry out individual tasks. Illustratively the smart bus function module assumes its own independent monitoring of part of the bus system and of the hooked-up elements/components and it shall introduce steps to switch over to parallel modules (smart bus system) in the event of failures.
Excellent reliability is attained for instance by using an error-tolerant bus system which for instance in the event of a bus user defect or an interruption of a connection line undertakes reconfiguring the entire network and thereby saves the entire bus system from operational failure.
Accordingly, using a smart bus system offers on one hand the advantage of automatically recognizing and eliminating defects without thereby affecting the capacities of the control computer and on the other hand the need to shut off only a considerably smaller portion of the bus system in the event of failure in a smart bus system having several smart branch off sites than in a system containing only one smart bus function module (as a rule the operations managing computer).
In a further advantageous embodiment mode of the present invention, the minimum of one rotor blade may be mounted in angularly adjustable manner relative to the rotor. This design offers the advantage that the application of wind energy/power to the rotor is variable due to changing the blade's angular position so that electric power generation also may be maintained in the presence of strong winds without the power-plant being unduly loaded. Furthermore, power generation can be regulated by adjusting the rotor blade angle in such a manner that said power shall match the electric network requirements.
In an especially advantageous design of the present invention, the wind-driven power-plant may comprise an electric assembly containing a further sub-assembly in the form of a blade adjusting device regulating the angular position of the rotor blade(s).
In a further advantageous embodiment mode of the present invention, the hook-up of the generator to the electric network is designed in a manner that the generator may be run at least at two different rotational speeds at the network, said device moreover in an especially advantageous embodiment of the present invention allowing to operate the generator within a variable speed range.
The above embodiments relate both to hookup devices for pole-reversing generators and to hookup devices that comprise, due to electromechanical, electric or electronic elements/components a speed range limited by an upper and lower speed limit, said lower speed limit also including 0 rpm, to vary generator speed between said limits.
Furthermore, a converter sub-assembly is provided in an advantageous embodiment mode of the present invention to match the generator power to the particulars of the electric network by means of several active switches such as thyristors, GTOs, IGCTs or IGBTs.
In a further advantageous embodiment mode of the present invention, the above active switches can be driven by a conversion control which is configured in the converter sub-assembly and which illustratively is connected to the control device.
According to one embodiment mode of the present invention, a function module may be designed in a manner that it comprises at least the active switches or some of the active switches of the converter sub-assembly. Several function modules that include active switches in relation to their switching needs also may be used
An especially preferred embodiment mode of the present invention uses an AC generator. Such generators are characterized by high reliability and are especially economical.
A converter sub-assembly hooking up such a generator to the electrical network may be designed according to a further embodiment mode in a way that it comprises an AC rectifier (diode rectifier or conversion element with active switch) near the generator to which it is connected and rectifying AC current at least partly into DC current or DC voltage. The converter sub-assembly also may comprise a DC current intermediate circuit or a DC voltage intermediate circuit connecting a generator-side AC rectifier to a DC inverter at the network-side. The network-side DC inverter is hooked up to the network and is used to convert the DC current or voltage generated by the generator-side AC rectifier into the electric power matching the electrical network. Also, electromechanical safety elements protecting the power-plant and filters limiting, for instance, the steepness of applied voltage at the generator-side and improving network quality at the network-side may be present in the converter sub-assembly.
In especially advantageous manner, the generator-side AC rectifier is fitted with active switches to allow a power flow in the converter sub-assembly in both directions and furthermore making possible reactive power. In this manner, generator excitation and reactive power generation may be controlled, as a result of which the generator may be designed to be especially economical.
In an especially preferred embodiment of the present invention, a function module may be designed in a way that it comprises at least the generator-side AC rectifier, the current or voltage intermediate circuit and the network-side DC inverter. Said function module however may also contain further elements such as the electrical safety elements or the filters.
This configuration is highly advantageous because allowing to hook together extant converters into very high power output aggregates so that development times may be shortened with a view toward the explosively increasing bulks of wind-driven power-plants.
Another very advantageous embodiment mode of the present invention comprises at least one parallel module for the above stated embodiments of the converter's function modules, the function module(s) and the parallel module(s) being connected by separable connectors directly or indirectly to the generator and directly or indirectly (for instance by an intermediate transformer unit) to the electrical network.
The above especially advantageous embodiment mode of the present invention is based on the insight that the active switches of a converter sub-assembly are especially susceptible to malfunctioning. In view of their substantial numbers, their integration in the manner of the invention by means of function modules into the electric assembly offers a simple and effective way to isolate any damaged/failing module by opening the separable connectors/hook-ups and in this manner to maintain power generation entirely or at least in a more limited way by means of the remaining operational function and parallel modules.
The preferably complete isolation of the failed function module is important in that otherwise one or more modules adjoining the one that failed for instance due to a short might in turn be damaged.
One advantageous embodiment mode of the present invention implements the separable hookups in the form of switching elements. One of the advantages offered by this design is that it allows even less skilled personnel to open, even manually, the separable hookup, no prior know-how being required as long as the switching elements are unambiguously marked.
In an especially advantageous manner and in particular for offshore power-plants in the planning stage, a further development of the present invention provides that the switching elements be operable by the remote monitoring device. In that case no technician at all need be on site for the purpose of keeping up power generation, at least partly, following function module malfunction.
In further advantageous embodiment modes, the switching elements also may be driven automatically for instance by means of the control device and/or the remote monitor.
A further and very advantageous embodiment mode of the present invention provides that at least one separable hookup comprise two series switching elements, one of which is a power switch and the other an active switch (for instance a thyristor). This invention is based on the insight that a power switch in addition to just switching also acts as a safety element by tripping at overload down to a limit current. On the other hand, a power switch is appropriate only for a very limited number of switching cycles, as a result of which higher rates of switching are taken over by the series contactor that, however, offers no safety function. In this simple and effective manner a configuration of function module and parallel module of similar function is being created whereby, if a malfunction arises in one of the modules, the other shall take over almost entirely the first one's function.
Further features, aspects and advantages of the present invention are disclosed in part by the text below and are partly made clear by the specification or result when reducing the present invention to practice. One embodiment mode of the present invention is discussed in detail below. It should be understood that other embodiment modes may be used and may be modified without thereby transcending the present invention. The comprehensive discussion below therefore must be viewed broadly and the invention's scope is best defined by the appended claims.