Method for operating power electronics for controlling an electric three-phase machine

Abstract

The invention relates to a method for operating power electronics (10) for controlling an electric three-phase machine (12), in particular a steering system (14), wherein the electric three-phase machine (12) can be operated in motor mode and in generator mode and is provided in motor mode for the provision of a drive torque. It is proposed that the power electronics (10) limit energy recuperation during generator operation, at least temporarily for a defined time interval (t). K ) is short-circuited.

Description

State of the art

[0001] The invention relates to a method for operating power electronics for controlling an electric three-phase motor, in particular a steering system, according to the preamble of claim 1. Furthermore, the invention relates to a control unit for carrying out such a method, a steering system with such a control unit, and a vehicle with such a steering system.

[0002] Various methods for operating power electronics to control an electric three-phase motor are known in the prior art, in which the electric three-phase motor is operated as an actuator in motor mode and as a generator in generator mode. For example, an electric three-phase motor of a vehicle's steering system is designed to provide drive torque in the form of steering torque in motor mode and is actively controlled in this case to move a steering actuator, for example in the form of a rack and pinion, to a predetermined position or to set a requested wheel steering angle. Energy is drawn from the vehicle or a vehicle power supply system in this process. Simultaneously, corresponding driving maneuvers and / or potholes in the road surface can exert a feedback torque on the electric three-phase motor.This causes the electric motor to operate in generator mode, feeding energy back into the vehicle or the power supply system. Generator operation, or energy recuperation, can cause problems, especially if the vehicle lacks a regenerative power supply system, particularly in the form of a suitable vehicle battery and / or a suitable DC-DC converter, as this increases the vehicle's electrical system voltage. This condition is undesirable or only permissible for a limited time at certain voltage levels, as otherwise damage to the vehicle's electronics and / or steering system may occur.

[0003] Furthermore, methods for operating a steering system are known in which power electronics for controlling an electric three-phase motor are deliberately short-circuited in the event of a malfunction and / or fault. In this context, reference is made, for example, to DE 10 2012 105 143 A1, DE 10 2015 108 691 and / or DE 10 2020 207 857 A1.

[0004] The object of the invention is, in particular, to provide a method for operating power electronics with improved operational reliability, especially during trouble-free normal operation. This object is achieved by the features of claims 1, 8, 9, and 10, while advantageous embodiments and further developments of the invention can be found in the dependent claims. Disclosure of the invention

[0005] The invention relates to a method for operating power electronics for controlling an electric three-phase motor, wherein the electric three-phase motor can be operated in motor mode and in generator mode, and is designed to provide a drive torque in motor mode. In the present case, the electric three-phase motor is thus operated as an actuator in motor mode.

[0006] It is proposed that the power electronics be short-circuited, at least temporarily for a defined time interval, to limit energy feedback during generator operation. In generator mode, the three-phase electric machine thus operates as a generator. To limit energy feedback and, in particular, to protect the electronic components, the power electronics are selectively short-circuited temporarily, more precisely, for a short period during generator operation, and not for the entire duration of generator operation. During the remaining time of generator operation, the power electronics are not short-circuited and, in particular, operate normally, i.e., in such a way that the three-phase electric machine is controlled.The defined time interval during which the power electronics are short-circuited is advantageously at least 1 ms, and particularly advantageously at least 5 ms and / or at most 30 ms, and particularly advantageously at most 20 ms. The defined time interval is selected such that no uncontrollable behavior occurs in the three-phase electric motor and / or any assembly interacting with the three-phase electric motor. This design improves operational reliability, especially during normal, trouble-free operation. In particular, it also prevents or at least reduces system voltage increases in systems without a regenerative power supply. Furthermore, by appropriately selecting the defined time interval, any impact on the efficiency and / or performance of the three-phase electric motor can be minimized.

[0007] The three-phase electric machine is preferably designed as a synchronous machine, and ideally as a permanent magnet synchronous machine. Furthermore, the three-phase electric machine is advantageously designed as a multiphase machine. For example, the three-phase electric machine could be designed as a six-phase, nine-phase, or twelve-phase machine. However, the three-phase electric machine is preferably designed as a three-phase machine. In addition, the power electronics are preferably designed as an inverter unit, in particular as a power stage and / or as a B6 bridge circuit, and are provided for supplying power to and / or energizing the three-phase electric machine.The power electronics can advantageously comprise several half-bridges, particularly advantageously at least three half-bridges, each with a high-side circuit breaker and a low-side circuit breaker, wherein each phase of the three-phase electric motor is assigned one of the half-bridges. Furthermore, a control unit is preferably provided, which is designed to control the power electronics and, in particular, to carry out the method for operating the power electronics. In this context, a "control unit" is understood to mean, in particular, an electronic unit that has an information input, information processing, and information output.Advantageously, the control unit further comprises at least one processor, at least one operating memory, at least one input and / or output device, at least one operating program, at least one control routine, at least one calculation routine, and / or at least one short-circuit routine. In particular, the control unit is designed, at least temporarily, and especially by means of the short-circuit routine, to selectively short-circuit the power electronics to limit energy recuperation during generator operation for a defined time interval. Furthermore, the control unit can be designed, especially by means of the control routine, to control the three-phase electric motor during the remaining time period of generator operation and / or during motor operation in such a way that a drive torque is provided by means of the three-phase electric motor.The term "intended" should be understood to mean specifically programmed, designed, and / or equipped. The fact that an object is intended for a specific function should be understood to mean, in particular, that the object fulfills and / or executes this specific function in at least one application and / or operating state.

[0008] Preferably, the three-phase electric motor, the power electronics, and the control unit are part of a vehicle, and particularly preferably part of the vehicle's steering system, and are powered by at least one energy supply system, for example, the vehicle's electrical system. Preferably, the three-phase electric motor is configured as a steering motor and, in motor mode, is intended to provide steering torque. Furthermore, in this case, the control unit can be configured to control the power electronics in such a way as to achieve field-oriented control and / or field-oriented regulation of the three-phase electric motor. The vehicle is, in particular, a motor vehicle, and preferably a hybrid and / or electric vehicle, and includes, in particular, an energy supply system (optionally non-regenerative) with a vehicle battery and / or a DC / DC converter.The steering system can be designed as a conventional steering system, in particular as an electric power steering system, and include a mechanical linkage, or as a steer-by-wire steering system, in which a steering input, in particular from the driver, is advantageously transmitted purely electrically to the vehicle wheels. In this case, an increase in the vehicle's electrical system voltage can be avoided or at least reduced, especially in vehicles without a regenerative energy supply system, in particular in the form of a corresponding vehicle battery and / or a corresponding DC / DC converter.

[0009] It is also preferably proposed that the power electronics be repeatedly short-circuited, in particular several times and preferably for a defined time interval, to limit energy regeneration during generator operation. This allows for particularly advantageous adjustment and control of maximum energy regeneration. The individual time intervals could have different durations, so that the duration during which the power electronics are short-circuited can be varied, and, for example, at least two time intervals with different durations could be used alternately. Using such control, the short-circuit time could, for example, be advantageously adjusted as a function of a specific energy regeneration value.However, according to a preferred embodiment, it is proposed that the time intervals in which the power electronics are short-circuited have an identical duration, which in particular simplifies the control algorithm. Furthermore, it is proposed that the time interval between any two consecutive short-circuited time intervals also have an identical duration. In this case, the time intervals in which the power electronics operate normally also have an identical duration, so that, in particular, control via a fixed frequency can be implemented and a particularly simple control algorithm can be provided.

[0010] In principle, it is conceivable to short-circuit all high-side power switches of the power electronics to limit energy regeneration during generator operation. However, it is preferred that all low-side power switches of the power electronics be short-circuited to limit energy regeneration during generator operation, which would further improve operational reliability.

[0011] In a further embodiment, it is proposed that the power electronics, to limit energy regeneration during generator operation, are only short-circuited when a voltage threshold, particularly a predefined one, is exceeded, especially in the event of an overvoltage in the power supply system or at a DC-DC converter within the power supply system. This advantageously allows high voltage values ​​during energy regeneration to be absorbed. Furthermore, it provides a high level of protection for the electronic components while simultaneously minimizing the impact on the efficiency and / or performance of the three-phase electric motor.

[0012] The method for operating the power electronics is not limited to the application and embodiment described above. In particular, the method for operating the power electronics may, to achieve a functionality described herein, include a different number of individual elements, components, and units than the number specified herein. Drawings

[0013] Further advantages become apparent from the following description of the drawings. The drawings illustrate an embodiment of the invention.

[0014] They show: Fig. 1a-b an exemplary vehicle with a steering system designed as a steer-by-wire system in a simplified representation, Fig. 2 an electric three-phase motor, power electronics and a steering system control unit, Fig. 3a-b Diagrams of various signals during operation of the steering system and Fig. 4 An exemplary flowchart with main process steps of a method for operating the power electronics for controlling the electric three-phase machine. Description of the exemplary embodiment

[0015] The following embodiment relates, by way of example, to a vehicle steering system. However, the invention is not fundamentally limited to use in a steering system and could, for example, also be used in other areas of a vehicle, such as a wiper system, a window regulator system and / or a drive system, and / or in other electronic systems, for example in the field of household appliances and / or machine tools.

[0016] The Fig. 1a and Fig. Figure 1b shows a simplified representation of a vehicle 40, designed as a passenger car, with several wheels 42. The vehicle 40 is designed as an electric vehicle, more precisely as a battery electric vehicle (BEV), and includes a drive system with an electric drive motor (not shown). The vehicle 40 also includes a power supply system 36 with a vehicle battery 44 and a DC-DC converter 34. In this case, the power supply system 36 is not designed to allow regenerative energy recovery. This means that the vehicle battery 44 cannot absorb energy recuperation and / or the DC-DC converter 34 does not have a regenerative energy recovery capability. In principle, however, a vehicle could also be designed as a hybrid vehicle with an electric drive motor and an internal combustion engine, or as a conventional internal combustion engine vehicle.Furthermore, an energy supply system could in principle include an energy source different from a vehicle battery and / or be designed to be capable of regenerative braking.

[0017] Furthermore, the vehicle 40 includes a steering system 14, which is known per se. The steering system 14 is designed to provide steering functionality for steering the vehicle 40. In this case, the steering system 14 is configured as a steer-by-wire system, so that a steering input is transmitted electrically to the vehicle wheels 42 in at least one operating state. In principle, however, a steering system could also be configured as a conventional steering system with a mechanical linkage and electric power steering.

[0018] The steering system 14 has a control unit 46, which is known per se. The control unit 46 comprises a steering handle 48, for example in the form of a steering wheel, and a feedback actuator 50 mechanically coupled to the steering handle 48 for generating steering resistance and / or a restoring torque on the steering handle 48. Alternatively, a steering handle could also be designed as a joystick, a steering lever, and / or a steering ball or the like. Furthermore, it is also possible, in principle, to dispense with a control unit altogether.

[0019] Furthermore, the steering system 14 includes a wheel steering angle actuator 52. The wheel steering angle actuator 52 is mechanically separate from the control unit 46 and connected to it purely electrically. In this case, the wheel steering angle actuator 52 is designed as a central actuator. However, a steering system could also include several wheel steering angle actuators, particularly those designed as individual wheel actuators. The wheel steering angle actuator 52 has an operative connection with at least two of the vehicle wheels 42, in particular two front wheels, and is designed to translate the steering input into a steering movement of the vehicle wheels 42. For this purpose, the wheel steering angle actuator 52 includes a steering actuating element 54, in particular in the form of a rack and pinion, and a steering actuator 56 that interacts with the steering actuating element 54.

[0020] The steering actuator 56 comprises a three-phase electric motor 12. In this case, the three-phase electric motor 12 is configured as a steering motor, more precisely as a permanent magnet synchronous motor. The three-phase electric motor 12 is also multiphase, in this example, three-phase. The three-phase electric motor 12 can be operated in motor mode and in generator mode. In motor mode, the three-phase electric motor 12 is operated as an actuator and is designed to provide a drive torque, in this case, in particular, a steering torque.

[0021] Furthermore, the vehicle 40 has a control unit 58. In this case, the control unit 58 is designed as a steering control unit and is therefore part of the steering system 14. The control unit 58 has an electrical connection to the operating unit 46. The control unit 58 also has an electrical connection to the wheel steering angle actuator 52, in particular the steering actuator 56. The control unit 58 is intended at least for controlling the operation of the steering system 14. In this case, the control unit 58 is intended at least for controlling the electric three-phase motor 12 and thus, in particular, for adjusting the drive torque or steering torque. In principle, however, a control unit could also be different from a steering control unit and, for example, be designed as a single, central vehicle control unit.Furthermore, it is conceivable to provide separate control units for a wheel steering angle actuator and for a control unit, and to connect these to each other in a communicating manner.

[0022] The control unit 58 comprises a control unit 38. The control unit 38 comprises at least one processor (not shown), for example in the form of a microprocessor, and at least one operating memory (not shown). Furthermore, the control unit 38 comprises at least one operating program stored in the operating memory.

[0023] Furthermore, the control unit 58 includes a power electronics unit 10, known per se, for supplying energy to the three-phase electric motor 12 (see in particular also Fig. 2) The power electronics 10 has an operative connection with the control unit 38 and is connected downstream of it for control purposes. Furthermore, the power electronics 10 has an operative connection with the power supply system 36 and the three-phase electric motor 12. The power electronics 10 is arranged in the circuit between the power supply system 36 and the three-phase electric motor 12. The power electronics 10 is also designed as an inverter unit and, in this case, comprises several half-bridges 16, 18, 20, which are, in particular, identical to one another, with each phase of the three-phase electric motor 12 being assigned one of the half-bridges 16, 18, 20. Each of the half-bridges 16, 18, 20 comprises two circuit breakers, which are, in particular, identical to one another, specifically a high-side circuit breaker 22, 24, 26 and a low-side circuit breaker 28, 30, 32.Each of the half-bridges 16, 18, 20 is designed to convert a pulsating rectified voltage from the power supply system 36 into a phase current and supply it to the three-phase electric motor 12, in particular to exactly one phase of the three-phase electric motor 12. In principle, power electronics could of course also be designed separately and / or independently of a control unit.

[0024] In motor mode, the three-phase electric motor 12 is actively controlled to move the steering actuator 54 to a predetermined position or to set a requested wheel steering angle. Energy is drawn from the vehicle 40, or more precisely, from the power supply system 36. Simultaneously, appropriate driving maneuvers and / or potholes in the road surface can exert a return torque on the three-phase electric motor 12. This causes the three-phase electric motor 12 to operate in generator mode, during which energy is fed back into the vehicle 40, or more precisely, the power supply system 36. A typical steering maneuver generally consists of alternating between motor and generator modes of the three-phase electric motor 12. The generator mode, orEnergy regeneration can lead to problems, especially if the vehicle 40, as in the present case, does not have a regenerative energy supply system 36, since the vehicle's electrical system voltage increases in this case. This condition is undesirable or only permissible for a limited time at certain voltage levels, as otherwise damage to the electronic components can occur. The requirement, therefore, is to limit or eliminate this regenerative energy regeneration.

[0025] A method for operating the power electronics 10 is described below. The control unit 38 is designed to execute this method and includes, in particular, a computer program with corresponding program code.

[0026] According to the invention, the power electronics 10 are used to limit energy feedback during generator operation, at least temporarily for a defined time interval t. K short-circuited (see also Fig. 3a and Fig. 3b). Preferably, all low-side circuit breakers 28, 30, 32 can be short-circuited for this purpose. However, short-circuiting the low-side circuit breakers 28, 30, 32 also means that the three-phase electric motor 12 cannot be controlled, and therefore, in this case, the position of the steering actuator 54 cannot be regulated. For this reason, the defined time interval t Kselected such that no uncontrollable behavior occurs in the three-phase electric motor 12 and / or in any assembly interacting with the three-phase electric motor 12, in particular in the steering actuator 54. When applying the presented functionality in the steering system 14, the defined time interval t K for example, between 5 ms and 20 ms, and preferably around 10 ms.

[0027] To better control the energy recuperation, the power electronics 10 can also be repeatedly short-circuited, i.e., several times, preferably for the time intervals t K , in which the power electronics 10 are short-circuited, an identical duration and a time interval T N between any two consecutive time intervals t KThe time intervals during which the power electronics 10 is short-circuited have an identical duration. In the latter case, the time intervals during which the power electronics 10 operates normally are also identical. This has the advantage that control via a fixed frequency can be implemented and a particularly simple control algorithm can be provided. In principle, however, the individual time intervals during which the power electronics 10 is short-circuited or normally operated could also have different durations and, for example, be varied depending on the current value of an energy recuperation.

[0028] During the time intervals t KDuring the periods in which the power electronics 10 are short-circuited, the backflow current due to the short circuit is 0 amperes. During the time intervals in which the power electronics 10 are operated normally, or between the short circuits, either a positive battery current is present, as the position of the steering actuator 54 is actively controlled, or a negative battery current is present, but for a significantly shorter period compared to conventional control without a short circuit.

[0029] Furthermore, it is conceivable to short-circuit the power electronics 10 to limit energy feedback in generator operation only when a predefined voltage threshold is exceeded, for example in the event of an overvoltage at the DC voltage converter 34 of the power supply system 36, thereby improving operational reliability and minimizing the impact on the efficiency and / or performance of the three-phase electric machine 12.

[0030] The Fig. 3a and Fig. 3b shows exemplary diagrams of various signals during the operation of the steering system 14.

[0031] Each ordinate axis represents quantity, while each abscissa axis represents time. Curve 60 shows a section of the time course of a supply voltage. Curve 62 shows a section of the time course of a current input or output. Curve 64 shows a section of the time course of an energy input or output.

[0032] In Fig. 3a further indicates a first area 66 in the middle graphic as a motor operation, a second area 68 in the middle graphic as a generator operation and a third area 70 in the middle graphic again as a motor operation.

[0033] In Fig. 3b additionally, two of the time intervals t K , in which the power electronics 10 are short-circuited, as well as two time intervals T N hinted at.

[0034] In particular, based on Fig. 3b shows a control of the power electronics 10 according to the invention, wherein it is repeatedly short-circuited.

[0035] Fig. Figure 4 shows an exemplary flowchart with the main process steps of the procedure for operating the power electronics 10.

[0036] In process step 80, it is determined whether regenerative operation is present.

[0037] If generator-safe operation is detected, the power electronics 10 are switched off in a process step 82 to limit energy feedback, at least temporarily for a defined time interval t. K short-circuited.

[0038] The flowchart in Fig.Section 4 merely describes an exemplary method for operating the power electronics 10. In particular, individual process steps can vary or additional process steps can be added. For example, it is conceivable to repeatedly short-circuit the power electronics and / or to consider a voltage threshold when controlling the power electronics 10, so that the power electronics 10 is only short-circuited to limit energy recuperation in generator mode, for example, when the voltage threshold is exceeded. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2012 105 143 A1

[0003] DE 10 2015 108 691

[0003] DE 10 2020 207 857 A1

[0003]

Claims

[1] Method for operating power electronics (10) for controlling an electric three-phase machine (12), in particular a steering system (14), wherein the electric three-phase machine (12) is operable in motor mode and in generator mode and is intended to provide a drive torque in motor mode, characterized by , that the power electronics (10) limit energy recuperation in generator mode at least temporarily for a defined time interval (t K ) is short-circuited. [2] Method according to claim 1, characterized by , that the defined time interval (t K ) is at least 1 ms and / or at most 30 ms. [3] Method according to claim 1 or 2, characterized by , that the power electronics (10) are repeatedly short-circuited to limit energy feedback during generator operation. [4] Method according to claim 3, characterized by, that the time intervals (t K ), in which the power electronics (10) is short-circuited, have an identical duration. [5] Method according to claim 3 or 4, characterized by that a time interval (T N ) between any two consecutive time intervals (t K ), in which the power electronics (10) is short-circuited, have an identical further duration. [6] Method according to any one of the preceding claims, characterized by , that the power electronics (10) comprises several half-bridges (16, 18, 20) each with a high-side power switch (22, 24, 26) and a low-side power switch (28, 30, 32), wherein each phase of the three-phase electric machine (12) is assigned one of the half-bridges (16, 18, 20), and wherein all low-side power switches (28, 30, 32) are short-circuited to limit energy regeneration in generator operation. [7] Method according to any one of the preceding claims, characterized by , that the power electronics (10) to limit energy regeneration in generator operation is only short-circuited when a voltage threshold is exceeded, in particular in the event of an overvoltage at a DC voltage converter (34) of a power supply system (36). [8] Control unit (38) for carrying out a method according to any of the preceding claims. [9] Steering system (14) comprising at least one three-phase electric motor (12), at least one power electronics (10) for controlling the three-phase electric motor (12) and a control unit (38) according to claim 8. [10] Vehicle (40), in particular electric vehicle, with a steering system (14) according to claim 9.

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