Method for dynamic current sharing in a multi-motor drive system

Abstract

Method for dynamic current distribution in a multi-motor drive system (10), wherein the multi-motor drive system (10) comprises a first electric motor (5) and a second electric motor (6), wherein the method comprises a query process (P2) in the context of which it is continuously queried which torque each of the two electric motors (5, 6) could deliver if it were provided with a certain electric current, characterized in that the query process (P2) is carried out at least partially during a switching operation.

Description

Technical FieldThe invention relates to a method for dynamic current division according to the preamble of claim 1.Prior ArtElectric vehicles typically include drive systems having at least one, but frequently a plurality of electric motors. The plurality of electric motors can be arranged differently in the drive system, for example each electric motor alone or also, for example, in each case two electric motors connected via a common transmission.In such multi-motor drive systems, it may occur that the different electric motors are subjected to different loads and thus each differ in terms of their current performance. For example, it is possible that in the case of two electric motors which are connected via a common transmission, one of the electric motors can deliver a greater torque than the other electric motor at a specific point in time. It is also possible that at a certain point in time one of the electric motors can draw a greater current than the other electric motor, or else can feed a greater current back into the drive system than the other electric motor. Such problems arise, for example, during shifting processes, during the scope of which the transmission carries out a shift from one gear to another gear. In such cases, it is possible that, for example, one of the electric motors continues to provide a torque during the shifting process, whereas the other electric motor does not provide a torque, but rather carries out a synchronization to a new rotational speed. In such shifting operations, there is the risk that, if the two electric motors do not coordinate, an unpleasant driving behavior will occur, for example if the drive system cannot temporarily deliver a power requested by the driver, because one electric motor or several electric motors cannot absorb the required currents at a specific time and / or cannot deliver the desired torques.DE 10 2011 119 207 A1 discloses a method for controlling the operation of an arrangement of at least two electric machines which are motion-coupled to different wheels of a motor vehicle and are connected to a battery.DE 10 2015 117 464 A1 discloses an electrically operated motor vehicle and a method for operating the electrically operated motor vehicle.DE 10 2013 013 953 A1 discloses a vehicle controller for an at least partially electrically driven vehicle.DE 10 2021 130 360 A1 discloses a method for distributing electrical power to electric motors in an electric drive train, in which the electric motors are electrically connected to a common power supply.DE 10 2012 219 026 A1 discloses a battery protection device for protecting a battery of a vehicle.GENERAL DESCRIPTION OF THE INVENTIONThe object of the invention is to eliminate or at least reduce the disadvantages of the prior art.The object is achieved by a method for dynamic current distribution in a multimotor drive system, wherein the multimotor drive system comprises a first electric motor and a second electric motor, wherein the method comprises a query process in the scope of which it is continuously queried which torque each of the two electric motors could deliver if it were to provide a specific electric current.A "dynamic current distribution" is understood here to mean a current distribution between the first electric motor and the second electric motor, which is not the same (i.e. static) at any point in time of the operation of the multimotor drive system, but during which the current components, which are distributed in each case to the first electric motor and the second electric motor, can continuously change or at least change during the course of the method. The two electric motors are typically connected to one another via a transmission. In typical embodiments, the multi-motor drive system includes an inverter for each electric motor. Thus, the first electric motor is typically connected to a first electric motor and the second electric motor is typically connected to a second inverter. In advantageous embodiments, the multimotor drive system additionally comprises a control device, also referred to as a superimposed control device, which typically communicates with the electric motors via the corresponding inverters and which also typically communicates with the transmission, which connects the two electric motors to one another. The interrogations which are carried out in the interrogation process within the scope of the method are typically carried out by the superimposed control device, in particular in a cooperation with the respective inverters of the two electric motors. In advantageous embodiments, the interrogation process comprises a question sub-process, in the scope of which a question or a plurality of questions is / are sent to the inverter or inverters by the superimposed control device. In addition, in advantageous embodiments, the interrogation process comprises a response sub-process, within the scope of which the inverter or inverters responds / respond to the question(s) of the overlaid control unit.In advantageous embodiments, the interrogation process asks which torque each of the two electric motors could deliver if it were to provide the specific electric current for a specific period of time, for example one second. In typical embodiments, the interrogation process asks which torque each of the two electric motors could deliver if it were to provide the specific electric current at a specific point in time, for example one second after the question has been received.The inventors have found that with the aid of such a query process, in the scope of which fictitious current supplies are sent to the two electric motors and their respective inverters, a particularly advantageous current distribution between the two electric motors can be achieved. One reason for this is that loops between the superimposed control device and one of the inverters can be prevented in this way, in which no current is provided to the respective inverter because no torque is currently being requested. Namely, such problems may occur in multi-motor drive systems.In typical embodiments, the method comprises a current division process, within the scope of which an available electric current is divided between the first electric motor and the second electric motor, wherein results of the interrogation process are continuously taken into account in the current division process. The available electric current is typically an electric current which a battery, in particular a high-voltage battery, of the multi-motor drive system can make available at the present time or in the near future. The current distribution between the first electric motor and the second electric motor is typically dynamic. In other words, therefore, the same current is not distributed to a respective electric motor at any point in time, but rather the portions of the available electric current for the two electric motors continuously change over time of the method, in particular depending on the results of the interrogation process.In typical embodiments, the method comprises a battery state determination process, within the scope of which a maximum charging current and / or a maximum discharging current of a battery of the multi-motor drive system is / are determined continuously. In this way, it is made possible, for example, to request each of the two inverters for a specific maximum discharge current, how much percent of this maximum discharge current the respective electric motor could absorb and what torque it could deliver for this specific electric current. Continuously interrogating the maximum charging current has the further advantage that knowing this maximum charging current in principle also makes it possible to run the method backward to some extent, i.e. in particular in such a way that it is determined in the interrogation process how much electric current a specific electric motor could deliver at which point in time, so that it is possible to calculate on the basis of this information how the torques of the two electric motors must be coordinated in order not to overload the battery.In advantageous embodiments, a split factor is continuously calculated within the scope of the method, wherein the split factor preferably has a value between 0 and 1, and / or wherein the split factor preferably indicates which part of the maximum discharge current is made available to the first electric motor and / or which part of the maximum discharge current is made available to the second electric motor. In typical embodiments, the split factor is calculated dynamically, for example at fixed intervals, for example every 1 to 100 ms, preferably every 5 to 50 ms, preferably about every 10 ms. The term "about" in this specification is to be understood as describing a tolerance of + / - 20%, or a tolerance of + / - 15%, or a tolerance of + / - 10%. In typical embodiments, the split factor calculation is performed in the controller based on information provided by the inverters by the controller. In typical embodiments, each inverter provides specific information to the control device at specific intervals, in particular, for example, every 125 μs to every 1 ms. Based on this information, the controller then dynamically calculates the split factor.The interrogation process is performed at least partially during a shift. In advantageous embodiments, the current sharing process is performed at least partially during the shift operation and / or the battery state determination process is performed at least partially during the shift operation and / or the split factor is determined during the shift operation. The inventors have found that, in particular during shifting operations, that is to say during periods in which the transmission which connects the first electric motor and the second electric motor changes from one gear to the other gear, carrying out the abovementioned processes and / or calculations and / or ascertainments is advantageous, in particular in order to improve driving comfort. In principle, however, it is also possible to have the method run outside of shifting operations, in particular in addition to running during shifting operations.In advantageous embodiments, a first fictive split factor is continuously calculated within the scope of the method, which is used in the interrogation process in order to determine the determined electric current for the first electric motor, wherein the determined electric current for the first electric motor preferably corresponds to a product of the maximum discharge current of the battery and the first fictive split factor. In advantageous embodiments, a second fictive split factor is continuously calculated within the scope of the method, which is used in the interrogation process in order to determine the determined electric current for the second electric motor, wherein the determined electric current for the second electric motor preferably corresponds to a product of the maximum discharge current of the battery and the second fictive split factor. The first fictitious split factor and / or the second fictitious split factor typically has / have a value between 0 and 1.The object is furthermore achieved by a system comprising means for at least partially carrying out a method according to at least one of the aforementioned embodiments.Such a system typically includes at least two motor-inverter components, each motor-inverter component including an inverter (also referred to as an inverter) and an electric motor that is powered by the inverter. In addition, such a system typically includes a transmission that connects the two electric motors. In addition, such a system typically includes a superimposed controller and a battery.In advantageous embodiments, the system is suitable for at least partially carrying out and / or coordinating and / or controlling a method according to at least one of the aforementioned embodiments. For this purpose, the system advantageously comprises suitable components, for example a query component which is suitable for carrying out the query process and / or an upstream split component which is suitable for carrying out the current split process and / or a battery state determination component which is suitable for carrying out the battery state determination process and / or a split factor calculation component which is suitable for calculating the split factor. In advantageous embodiments, the system comprises a fictitious split factor calculation component for calculating the first fictitious split factor and / or the second fictitious split factor. In advantageous embodiments, the system comprises a shift-process detection component which is suitable for detecting a shift process of the transmission which is taking place or is imminent. In advantageous embodiments, the system comprises a control component which is suitable for controlling the method. In typical embodiments, the superimposed control device comprises the control component.In advantageous embodiments, the system is a multi-motor drive system, which is suitable for carrying out a method according to at least one of the methods described above or below, at least partially.Advantageously, at least some of the aforementioned components are implemented in the system by means of computer program code. In advantageous embodiments, the system, in particular at least some of the aforementioned components, is at least partially part of a vehicle controller and / or a cloud. In typical embodiments, the system comprises a digital control unit and / or a display and / or means for data input and / or means for data output.In one embodiment of the invention, a vehicle is suitable for carrying out a method according to at least one of the aforementioned embodiments and / or comprises a system according to one of the aforementioned embodiments. For this purpose, the vehicle typically comprises means for carrying out a method according to at least one of the aforementioned embodiments.In one embodiment of the invention, a computer program comprises instructions which, when the computer program is executed by a computer, cause the computer program to execute one of the aforementioned methods. The computer program can also be referred to as a computer program product.In one embodiment of the invention, a computer-readable medium comprises computer program code for carrying out one of the aforementioned methods. The term "computer-readable medium" is to be understood here in particular, but not exclusively, as hard disks and / or servers and / or memory sticks and / or flash memories and / or DVDs and / or Bluerays and / or CDs. In addition, the term "computer-readable medium" is also to be understood as meaning a data stream, as arises, for example, when a computer program and / or a computer program product is downloaded from the Internet.Brief Description of the DrawingsThe invention is briefly explained below with reference to drawings, in which: FIG. 1 : shows a schematic illustration of a method according to the invention in a first embodiment, FIG. 2 : shows a schematic illustration of a method according to the invention in a second embodiment, FIG. 3 : shows a system according to the invention in a first embodiment in schematic illustration, FIG. 4 : a visualization of the mode of operation of a system according to the invention in an embodiment as a schematic illustration, and FIG. 5 shows a schematic illustration of a vehicle according to the invention in one embodiment.DESCRIPTION OF PREFERRED EMBODIMENTSFIG. 1 shows a schematic representation of a method according to the invention in a first embodiment as a flow chart. Specifically, a battery state determination process P 1, a polling process P 2, and a current sharing process P 3 are shown in FIG. 1. These processes P 1, P 2, P 3 are carried out in an endless loop in the exemplary embodiment shown in FIG. 1. In the battery state determination process P 1, a maximum charging current for a battery of a multi-motor drive system (not illustrated in FIG. 1 ) and a maximum discharging current of this battery are determined. In some embodiments, it is also possible that in the battery state determination process P 1 only a maximum discharge current of the battery of the multi-motor drive system is determined. The maximum discharge current (and the maximum charging current, if it has been determined) are then transferred to the interrogation process P 2. In the framework of the interrogation process P 2, two electric motors (not shown in FIG. 1 ) of the multi-motor drive system are requested, which could deliver torque to each of these two electric motors if it were to provide a specific electric current. The determined electric current for which the two electric motors are requested can correspond, for example, to the maximum discharge current of the battery. Alternatively, for each of the two electric motors, a certain electric current for which the request is sent may be determined based on the maximum discharge current. Subsequently, in the current sharing process P 3, an available electric current, typically the maximum discharge current, is shared between the first electric motor and the second electric motor, taking into account results of the polling process P 2. In other words, based on results of the inquiry process P2 in the current division process P3, the current available in the multimotor drive system for driving the electric motors is divided so as to take into account findings obtained in the inquiry process P2.FIG. 2 shows a schematic illustration of a method according to the invention in a second embodiment. In particular, FIG. 2 again shows a battery state determination process P 1, a query process P 2 and a current division process P 3. These three processes P 1, P 2, P 3 do not run in an endless loop, however, in contrast to the exemplary embodiment shown in FIG. 1, but rather essentially simultaneously and in parallel. Information flows between the individual processes P 1, P 2, P 3 are illustrated in FIG. 2 as dashed arrows. The query process P 2 comprises a first fictitious split factor determination sub-process S 1 and a second fictitious split factor determination sub-process S 2. The current division process P 3 includes a split factor determination sub-process S 3. Within the framework of the interrogation process P 2, a first fictitious split factor is predefined for the first electric motor (again not shown in FIG. 2 ) by the first fictitious split factor ascertainment sub-process S 1 and interrogated by the first electric motor which torque this first electric motor could deliver in the case of such a first fictitious split factor and predefined maximum discharge current of the battery. Analogously, in the second fictitious split factor ascertainment sub-process S 2, the second electric motor (again not shown in FIG. 2 ) queries which torque this second electric motor could deliver at a predefined maximum discharge current and the second fictitious split factor. The two electric motors then supply the desired information to the interrogation process P 2. The query process P2 passes this information on to the stream splitting process P3. Within the scope of the current division process P 3, it is decided which current distribution makes the most important at the current point in time, for example in order to achieve maximum driving comfort during a switching operation or else maximum energy efficiency. This optimal current distribution is used within the scope of the split factor determination sub-process S 3 to determine the split factor. In typical embodiments, the split factor has a value between 0 and 1 and indicates, for example, how much percent of the maximum available discharge current is to be supplied to the first electric motor. If, for example, a split factor of 0.3 thus results, this means that 30% of the maximum discharge current is to be made available to the first electric motor and 70% of the maximum discharge current is to be made available to the second electric motor. However, other definitions of the split factor are also possible. It is decisive that the split factor is calculated dynamically, in particular on the basis of the findings which are continuously determined within the scope of the battery state determination process P 1 and the interrogation process P 2, whereby a dynamic current distribution in the multi-motor drive system for the two electric motors is made possible.FIG. 3 now shows a system according to the invention in a first embodiment in schematic representation. In particular, FIG. 3 shows a battery 1, a control device 2, a first electric motor inverter component 8 and a second electric motor inverter component 9. The first motor-inverter component 8 includes a first inverter 3 and a first motor 5. the second motor-inverter component 9 includes a second inverter 4 and a second motor 6. the first motor 5 and the second motor 6 are connected by a transmission 7. Information flows, or in other words data flows, are represented in FIG. 3 by dashed arrows. A charging current info 12 and a discharging current info 13 are continuously transmitted from the battery 1 to the control unit 2. With the aid of the charging current info 12 and the discharging current info 13, the battery 1 continuously notifies the control device 2 with which current quantity it could currently be charged and which current quantity it can currently output. Between the control device 2 and the first electric motor inverter component 8, a first query data packet 14 and a first response data packet 15 are continuously exchanged. In typical embodiments, the first query data packet 14 comprises, for example, information about a current maximum discharge current for the battery 1, advantageously in conjunction with a first fictitious split factor. The first response data packet 15 typically comprises information about a maximum available torque, in particular for the information which was requested by the control device 2 in the first query data packet 14. The first question data packet 14 and the first answer data packet 15, which are typically continuously exchanged between the control device 2 and the first electric motor inverter component 8 in the course of a method according to the invention, establish a question answer process which enables the control device 2 to have an exact idea at any point in time of the method of which torque the first electric motor 5 could currently deliver if a specific current were made available to it. Analogously to this question-answer process between the control device 2 and the first electric motor-inverter component 8, a question-answer process runs between the control device 2 and the second electric motor-inverter component 9. This question-answer process is implemented by a continuous exchange of the second question data packet 16 and the second answer data packet 17. All the statements made with respect to the first query data packet 14 and the first response data packet 15 analogously also apply to the second query data packet 16 and the second response data packet 17. In order to avoid repetitions, reference is therefore made to the statements previously with respect to the first electric motor inverter component 8 for the information exchange between the control device 2 and the second electric motor inverter component 9. Thus, the control device 2 also knows at any point in time during the course of the method which torque the second electric motor 6 could be available if it were given a specific electric current. The control unit 2 is also capable of transmitting servomotor commands 18 to the transmission 7. The control device 2 also receives vehicle request data 19 from the vehicle, not shown in FIG. 3, in which the system shown in FIG. 3 is arranged. This vehicle request data 19 can comprise, for example, an accelerator pedal position or brake data.FIG. 4 shows a visualization of the mode of operation of a system according to the invention in an embodiment as a schematic illustration. In particular, FIG. 4 shows a control device 2 and a first inverter 3, which supplies a first electric motor, not shown in FIG. 4, with current. In the embodiment shown in FIG. 4, the sampling process P 2 and the current sharing process P 3 are executed in the first inverter 3. For this purpose, the interrogation process P 2 and the current division process P 3 are continuously supplied by the control unit 2 with a multiplicity of data, such as data relating to maximum discharge current or maximum charging current of a battery, not shown in FIG. 4, and / or data relating to specific electrical currents and / or data relating to required torques. This input data of the first inverter 3 is shown by wide dashed arrows in FIG. 4. Based on this input data, values are continuously determined in the first inverter 3 as part of the interrogation process P 2 and the current division process P 3, for example torque values, current values or the like, which are continuously fed back to the control device 2. This output data of the first inverter 3, which is made available continuously to the control device 2 as input data, is again shown in FIG. 4 as a thick dashed arrow.FIG. 5 now shows a schematic illustration of a vehicle 11 according to the invention in an embodiment of the invention. The vehicle 11 includes a multi-motor drive system 10. the multi-motor drive system 10 includes a battery 1 connected to a control device 2. The control device 2 includes an interrogation component 20, an upstream division component 21, and a battery state determination component 22, and these components 20, 21, 22 are each capable of executing the interrogation process P 2, the current division process P 3, and the battery state determination process P 1 described above. On the output side, the control device 2 is connected to a first inverter 3 and a second inverter 4. The first inverter 3 is connected to a first electric motor 5 and the second inverter 4 is connected to a second electric motor 6. The first electric motor 5 and the second electric motor 6 are connected to one another via a transmission 7. The vehicle 11 according to the invention thus comprises a multi-motor drive system 10 according to the invention, which is suitable for carrying out a method according to the invention for dynamic current distribution.The invention is not limited to the described exemplary embodiments. The scope of protection is defined by the claims.In principle, all methods described in the description or in the claims can be carried out by apparatuses which comprise means for carrying out the respective method steps of these methods.Reference numerals denote reference numerals1 Battery 2 Control device 3 First inverter 4 Second inverter 5 First electric motor 6 Second electric motor 7 Transmission 8 First electric motor inverter component 9 Second electric motor inverter component 10 Multimotor drive system 11 Vehicle 12 Charging current Info 13 Discharging current Info 14 First question data packet 15 First response data packet 16 Second question data packet 17 Second response data packet 18 Servomotor commands 19 Vehicle request data 20 Query component 21 Upstream split component 22 Battery state determination component P 1 Battery state determination process P 2 Query process P 3 Current split process S 1 First fictitious split factor determination sub-process S 2 Second fictitious split factor determination sub-process S 3 Split Factor Determination Sub-Process

Claims

Method for dynamic current distribution in a multimotor drive system (10), wherein the multimotor drive system (10) comprises a first electric motor (5) and a second electric motor (6), wherein the method comprises a interrogation process (P2), in the scope of which it is continuously interrogated which torque each of the two electric motors (5, 6) could deliver if it were to provide a specific electric current, characterized in that the interrogation process (P2) is carried out at least partially during a switching process.Method according to Claim 1, characterized in that the method comprises a current division process (P3), within the scope of which an available electric current is divided between the first electric motor (5) and the second electric motor (6), results of the interrogation process (P2) being taken into account continuously in the current division process.Method according to one of the preceding claims, characterized in that the method comprises a battery state determination process (P1), within the scope of which a maximum charging current and / or a maximum discharging current of a battery (1) of the multimotor drive system (10) is / are determined continuously.Method according to one of the preceding claims, characterized in that a split factor is calculated continuously within the scope of the method, - wherein the split factor preferably has a value between 0 and 1, and / or - wherein the split factor preferably specifies which part of the maximum discharge current is made available to the first electric motor (5) and / or which part of the maximum discharge current is made available to the second electric motor (6).Method according to one of Claims 2 to 4, characterized in that the current splitting process (P3) is carried out at least partially during the shifting process and / or in that the battery state determination process (P1) is carried out at least partially during the shifting process and / or in that the split factor is determined during the shifting process.Method according to one of the preceding claims, characterized in that, within the scope of the method, - a first fictitious split factor is calculated continuously, which split factor is used in the interrogation process (P2) in order to determine the determined electric current for the first electric motor (5), wherein the determined electric current for the first electric motor (5) preferably corresponds to a product of the maximum discharge current of the battery (1) and the first fictitious split factor, and / or - a second fictitious split factor is calculated continuously, which split factor is used in the interrogation process (P2) in order to determine the determined electric current for the second electric motor (6), wherein the determined electric current for the second electric motor (6) preferably corresponds to a product of the maximum discharge current of the battery (1) and the second fictitious split factor.A system (10) comprising means for at least partially performing a method according to any one of claims 1 to 6.Vehicle (11) suitable for carrying out a method according to one of Claims 1 to 6 and / or comprising a system (10) according to Claim 7.A computer program comprising instructions which, when the computer program is executed by a computer, cause the computer program to carry out the method of any one of claims 1 to 6.A computer readable medium, characterized in that the computer readable medium comprises computer program code for performing a method according to any one of claims 1 to 6.

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