Method and motor control for controlling an electric drive motor

Abstract

Method (100) for controlling an electric motor (M), comprising the following steps: Reading (102) a characteristic map for the electric motor (M) from a memory, which maps a control current associated with a specific torque applied to a motor shaft of the electric motor (M) or a speed at a specific rotor temperature, Decide (104) whether a determination of the rotor temperature should be carried out, - when a determination of the rotor temperature is to be carried out, measuring (106) the torque applied to the motor shaft or the speed and the control current, as well as Determining (108) an updated rotor temperature based on the characteristic map, Storing (110) the updated rotor temperature for further use, when a determination of the rotor temperature is not to be carried out, i.e. when the rotor temperature is known Receiving (112) a target torque or a target speed to be set, Determining (114) a control current required for the target torque or the target speed at the known rotor temperature based on the characteristic map, and Applying (116) the control current to the electric motor (M).

Description

[0001] The present invention relates to drives of a motor vehicle, in particular the control of electric machines for setting a desired torque.

[0002] To set a target speed and / or a target torque of electric drive motors of hybrid and electric vehicles, control circuits provide corresponding currents.

[0003] The speed and torque of a drive motor can be measured using appropriate sensors on the motor shaft and fed back to the control circuit as a controlled variable, where any deviation from the reference variable, which specifies the setpoint, is applied to a controller as a control deviation. The controller outputs a corresponding drive current as the manipulated variable.

[0004] Depending on the type and design of the controller, this conventional control can result in oscillations, or the setpoint may be reached more slowly than actually possible, for example, in an overdamped system. This can lead to unsatisfactory performance, particularly in the drive systems of sports vehicles, so there is a great need for methods and devices for the precise and rapid adjustment of a setpoint torque or speed of an electric drive motor.

[0005] Like almost all technical systems, a temperature dependence between the drive current and the speed and torque can be observed in electric drive motors. This is also the case with permanent magnet excited electric motors, where the field strength of the permanent magnets decreases above a certain temperature until they become only paramagnetic after reaching the Curie temperature. Even at temperatures below the Curie temperature, in the presence of an opposing magnetic field, such as can occur in the event of a fault, a local demagnetization of the permanent magnets can occur. This demagnetization is not fully reversible without further measures, causing permanent damage to the electric motor, which will prevent it from achieving its rated properties even after a reduction in temperature.

[0006] The temperature of the electric drive motor, especially of the rotor, is usually not precisely known, and the use of inexpensive temperature sensors on the rotor has not yet been satisfactorily solved due to the high mechanical loads.

[0007] In order to at least partially compensate for the temperature dependence, computational models are used that take into account the temperature dependence of the motor parameters, especially the torque, on the motor temperature—in this case, especially the rotor temperature—when generating control signals. Therefore, there is also a great need for methods and devices that enable improved determination of the rotor temperature, thus ultimately contributing to the precise and rapid setting of a target torque or speed of an electric drive motor.

[0008] DE 10 2020 215 124 A1 discloses a method for operating an electric machine, in which a characteristic map for the electric machine is read from a memory, which characteristic map limits the torque of the electric machine to a maximum torque depending on the temperature of a stator winding. The target torque is determined based on the temperature of the stator winding, and a drive current for the electric machine is determined based on the target torque. The drive current is applied to the electric machine.

[0009] DE 10 2012 200 199 A1 and EP 2 787 588 A2 disclose further methods for operating an electric motor. Depending on the motor load or motor speed, the temperature of the electric motor is determined from a mathematical temperature model.

[0010] It is therefore an object of the present invention to propose a method and a motor controller for controlling an electric drive motor, which improve the control of electric drive motors while taking the rotor temperature into account. Furthermore, a corresponding computer program product and computer-readable medium are to be provided.

[0011] This object is achieved by the method specified in claim 1, the engine control specified in claim 7, the computer program product according to claim 9 and the computer-readable medium according to claim 10.

[0012] Advantageous embodiments and further developments are specified in the dependent claims.

[0013] According to the invention, a characteristic map of a particular engine or, for an engine model, across a plurality of engines of the same series is first determined, which maps the curve of the control currents required for a specific torque at different temperatures. This characteristic map is stored in a readable memory of an engine control unit.

[0014] During motor operation, the torque, speed, and drive current can be measured relatively easily and precisely. This makes it easy to determine the rotor temperature at any time during motor operation without requiring a temperature sensor in the electric motor itself. Since the rotor temperature changes relatively slowly, this temperature determination only needs to be performed periodically, with the periodicity being dynamically adjusted depending on the motor power drawn after each measurement. Alternatively or additionally, the periodicity can be adjusted depending on the most recently determined rotor temperature, for example, to perform more frequent measurements in temperature ranges close to a permissible maximum value.

[0015] In this way, on the one hand, a control current adapted to the rotor temperature can be set at any time, at which a desired target torque or speed is immediately achieved with only minor deviations. On the other hand, even before a critical temperature range is reached, in which the motor could be damaged, the motor control can be limited to control currents that prevent further approach to the critical temperature range.

[0016] The method according to the invention also makes it possible to more quickly correct any remaining deviation of a measured actual torque from the target torque or of a measured actual speed from the target speed, since the control range can be selected to be smaller and a controller can be designed with a smaller reserve and corresponding dynamics.

[0017] In one or more embodiments, the method further comprises updating the rotor temperature depending on the magnitude of the deviation of the measured actual torque from the measured target torque or the actual speed from the target speed. This embodiment can provide at least an approximate current rotor temperature based on the characteristic map, even with longer temperature determination intervals.

[0018] For vehicles with independent wheel drive, the more precisely adjustable torque achieved with this method offers the advantage that, for example, a torque vector control system can be designed closer to the physical system limits to improve driving dynamics without compromising safety. A differential function can also be implemented more simply and precisely.

[0019] A motor controller for an electric motor according to the invention comprises a microprocessor, volatile and non-volatile memory, one or more sensor inputs, and one or more control outputs. The aforementioned elements are connected to one another via one or more data or control lines or buses. The non-volatile memory contains a characteristic map adapted to the electric motor to be controlled and computer program instructions which, when executed by the microprocessor in the volatile memory, configure the motor controller to implement embodiments of the method described above.

[0020] The control output can provide the drive current for the electric motor directly or a control signal for a power stage. The control output can preferably implement pulse width modulation (PWM).

[0021] The computer program instructions constitute a standalone computer program product. The computer program product may be stored on a computer-readable medium or data carrier. The medium or data carrier may be physically embodied, e.g., as a hard disk, CD, DVD, flash memory, or the like, but the medium or data carrier may also comprise a modulated electrical, electromagnetic, or optical signal that can be received by a computer using a corresponding receiver and stored in the computer's memory.

[0022] The invention is described below by way of example with reference to the figures of the drawing. Fig. 1 a flowchart of an exemplary method according to the invention, Fig. 2 a block diagram of a system with an electric motor and a motor control, and Fig. 3 a schematic block diagram of an engine control according to the invention.

[0023] In the figures, identical or similar elements may be referenced with the same reference numerals.

[0024] Fig. 1 shows a flowchart of an exemplary method 100 according to the invention for controlling an electric motor M. In step 102, a characteristic map for the electric motor M is first read from a memory, which maps a control current associated with a specific torque applied to a motor shaft of the electric motor M or a speed at a specific rotor temperature. In step 104, a decision is first made as to whether the rotor temperature should be determined, e.g., after a specific time has elapsed since the last temperature determination. If the answer is yes (“yes” branch from step 104), the torque applied to the motor shaft or a speed as well as the currently applied control current are measured in step 106, and in step 108 the rotor temperature is determined based on the characteristic map. In step 110, the updated rotor temperature is saved for future use.If the decision in step 104 is negative (“no” branch of step 104), a target torque or a target speed to be set is received in step 112, and in step 114, a control current required for the target torque or the target speed at the known rotor temperature is determined based on the characteristic map, which control current is applied to the electric motor M in step 116. Following steps 110 or 116, the process is repeated.

[0025] Fig. Figure 2 shows a block diagram of a system 10 with an electric motor M and a motor controller 200. The motor controller 200, supplied with electrical energy from an electrical energy source 400, e.g., a battery, controls the electric motor M either directly or via an intermediate power stage 300, which is also supplied with electrical energy from the electrical energy source 400. Optional elements are shown in the figure with dashed lines.

[0026] Fig.3 shows a schematic block diagram of an engine control unit 200 configured to carry out the method 100 according to the invention. A microprocessor 202, volatile 204 and non-volatile 206 memory, sensor inputs 208, and control outputs 210 are communicatively connected to one another via one or more data lines or buses 212. The non-volatile memory 206 contains a characteristic map adapted to the electric motor as well as computer program instructions which, when executed by the microprocessor 202 in the volatile memory 204, configure the engine control unit 200 to receive sensor data from a power controller, torque sensor, and / or speed sensor (not shown in the figure) via the sensor inputs 208 and configure the engine control unit 200 to carry out the method according to the invention, in particular to control the electric motor or a power stage (not shown in the figure) via the control outputs 210. LIST OF REFERENCE SYMBOLS 10 systems 100 procedures 102 Reading the map 104 Measure / Adjust? 106 Measuring torque / speed, current 108 Determining the rotor temperature 110 Updating the rotor temperature 112 Receive target torque / speed 114 Determine the control current 116 Apply control current 200 Engine control 202 microprocessor 204 volatile memory 206 non-volatile memory 208 sensor inputs 210 control outputs 212 data lines / buses 300 power level 400 electrical energy source

Claims

[1] Method (100) for controlling an electric motor (M), comprising the following steps: Reading (102) a characteristic map for the electric motor (M) from a memory which represents a control current corresponding to a specific torque applied to a motor shaft of the electric motor (M) or a rotational speed at a specific rotor temperature, Decide (104) whether to carry out a determination of the rotor temperature, - then, if a determination of the rotor temperature is to be carried out, measure (106) the torque applied to the motor shaft or the speed and the control current, as well as Determining (108) an updated rotor temperature using the characteristic map, Saving (110) the updated rotor temperature for later use, that is, when a determination of the rotor temperature is not to be carried out, i.e., when the rotor temperature is known. Receiving (112) a target torque or target speed to be set, Determine (114) a control current required for the target torque or speed at the known rotor temperature using the characteristic map, and Applying (116) the control current to the electric motor (M). [2] Method (100) according to claim 1, further comprising: Measuring the actual torque or speed applied to the motor shaft after applying the previously determined control current, and Compensation for deviations from the target torque or actual speed by adjusting the control current accordingly. [3] Method (100) according to claim 2, further comprising: Updating the rotor temperature depending on the size of the deviation of the actual torque from the target torque or the actual speed from the target speed, based on the characteristic map. [4] Method (100) according to any one of the preceding claims, further comprising: Limiting a maximum control current, a maximum torque applied to the motor shaft, or a maximum rotational speed depending on a current rotor temperature. [5] Method according to one of the preceding claims, wherein the rotor temperature is determined periodically. [6] Method according to claim 5, wherein the periodicity is dynamically adjustable depending on the magnitude of the control current applied to the electric motor (M) since the last determination of the temperature and / or the last determined rotor temperature. [7] Motor control (200) of an electric motor (M) comprising a microprocessor (202), volatile (204) and non-volatile (206) memory, one or more sensor inputs (208) and one or more control outputs (210) which are interconnected via one or more data or control lines or buses (212), wherein the non-volatile memory (206) contains a characteristic map adapted to the electric motor (M) as well as computer program instructions which, when executed by the microprocessor (202) in the volatile memory (204), configure the motor control (200) to execute the method according to any one of claims 1 to 6. [8] Motor control (200) according to claim 7, wherein one or more control outputs (210) directly provide the control current for the electric motor (M) or control a power stage. [9] Computer program product comprising computer program instructions executable by a microprocessor which, when the computer program instructions are executed by a motor controller (200) of an electric motor (M) according to one of claims 7 or 8, configure or cause the motor to execute the method (100) according to one of claims 1 to 6. [10] Computer-readable medium comprising computer program instructions which, when executed by a motor control (200) of an electric motor (M) according to one of claims 7 or 8, configure or cause the motor to execute the method (100) according to one of claims 1 to 6.

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