Controller for an inverter of an electric motor

Abstract

The invention relates to a controller (3) for an inverter (4) of an electric motor (5), wherein the electric motor (5) has a rotor, wherein the controller (3) is designed to determine, depending on a speed of the rotor, a control signal to be output from the controller (3) to the inverter (4) by means of either space vector modulation or synchronous optimal pulse width modulation.

Description

[0001] Hanover, September 18, 2024 IP. Jauch, T&S 304103-DE-NP EM 304103

[0002] Control unit for an inverter of an electric motor

[0003] The present disclosure relates to a control system for an inverter of an electric motor, a system comprising the control system, the inverter and the electric motor, and a control method for the inverter.

[0004] In the control of an electric motor, pulse-width modulated (PWM) control signals for an (optionally 2-stage) inverter are conventionally determined by a space vector modulation (SVM) algorithm, where an SVM sector is determined by a-β voltage requirements.

[0005] To better utilize the available voltage and output power, either bus clamping or six-step operation is conventionally employed. Furthermore, depending on the configuration of the current sensors (e.g., in systems with a single current sensor), limitations may arise for the PWM signal, further restricting the utilization of the available voltage. Therefore, SVM-based control algorithms are conventionally used.

[0006] EP 1 525 655 B1 concerns a drive system for a three-phase brushless AC motor. The drive system is designed to optimize the transistor circuit pattern to improve output power while simultaneously enabling current measurement in all phases using a single sensor. This is achieved by defining voltage requirement vectors x where more than two states are needed to achieve a minimum state time determined by the single-sensor method, and by calculating three or more state vectors that generate the required vector x while also enabling single current measurement. Various methods for optimizing the PWM pattern to achieve maximum output power using a single current measurement are also described. Traditionally, bus clamping is required to maximize output power.Bus clamping is typically used in situations where the power electronic switches of an inverter are almost constantly on. Bus clamping prevents the switches from being switched off and then on again shortly afterward, thus enabling higher output power than with the modulation strategy used to switch between different voltage demand vectors with shorter duty cycles. Furthermore, it reduces the losses from switching power electronic devices and the resulting heat generation.

[0007] At high voltage requirements, bus clamping can lead to lower quality voltage and current waveforms, particularly through the introduction of higher-frequency harmonics. These lower-quality waveforms can result in higher losses, which in turn leads to thermal problems and reduced output power. Poor waveform quality can also cause greater fluctuation in motor torque as the rotor rotates, which can propagate to other parts of the system to which the motor is mechanically coupled, causing increased vibration or audible noise. Another disadvantage of conventional methods is the switching from one waveform to another, i.e.,The switch from a high-quality waveform to a lower-quality waveform occurs at a specific point in time, which may be perceptible from the outside due to the additional noise and resulting vibrations.

[0008] Against the background of this prior art, one objective of the present disclosure is to specify a device and / or a method which are each suitable to enrich the prior art, optionally to overcome the disadvantages of the prior art described above.

[0009] A possible specific objective of the disclosure can be seen as achieving high efficiency of the power electronic circuitry across the entire speed range of the motor, combined with good waveform quality and a smooth transition between the inverter's operating modes. This objective is achieved by the features of the independent claims. The dependent and subordinate claims each contain optional further developments of the disclosure.

[0010] The task is then solved by a controller for an inverter of an electric motor. The electric motor has a rotor. The controller is designed to determine a control signal to be output to the inverter, depending on the rotor speed, either by means of space vector modulation or by means of synchronous optimal pulse width modulation.

[0011] Space vector modulation is generally known to those skilled in the art (see, for example, https: / / de.wikipedia.org / wiki / Raumzeigermodulation). In power electronics, space vector modulation (SVM) (also known as space vector control) refers to a method for controlling rotating electrical machines, in this context referred to as electric motors, based on pulse-width modulation. SVM is a common technique in field-oriented control for asynchronous motors and permanent magnet synchronous motors (PMSM). SVM is responsible for generating pulse-width modulated signals to control the switches or transistors of an inverter, which then generates the required modulated voltage to drive the electric motor at the desired speed or torque. Specifically, in two-stage pulse inverters, there are exactly two... A3 = 8 switching states. These can be specified by the corresponding voltage space vectors. With six of the voltage space vectors, each shifted by 60° 0When the voltage space vectors are rotated relative to each other, a voltage can be applied to the load. The seventh and eighth voltage space vectors sum the voltages at the load to zero. Therefore, in a two-stage pulse inverter, only eight different voltage space vectors can be shifted. In contrast, with space vector modulation, setpoint space vectors with arbitrary values ​​or time profiles are specified within the hexagon spanned by the first to sixth space vectors. These are then approximated by successively switching three adjacent voltage space vectors for suitable time periods. Synchronous optimal pulse width modulation (SOPWM) or synchronous optimized pulse pattern (OPP) is also fundamentally known to those skilled in the art (see BM Saur et al. Applying DBFC with Integrated Optimized Pulsed Pattern to Maximize Voltage Utilization with Low Distortion in Automotive Traction Drives. In Conf. Proc. EPE23 ECCE Europe, 2023).In detail: Pulse-width modulated signals have a pattern of successive pulses. When the arrangement and duration of the pulses are determined based on a cost function and boundary conditions, this is referred to as synchronous optimal pulse-width modulation (OPP).

[0012] In general, the control system can be used for all types of mechatronic systems with electric drives, such as in wind turbines, electric power steering systems, and / or electrified turbomachinery. It is particularly advantageous for use in motor vehicles.

[0013] The control system can, for example, be an electronic control unit (ECU). The electronic control unit can be an intelligent, processor-controlled unit that can communicate with other modules via a central gateway (CGW) and may form the vehicle's electrical network via fieldbuses such as CAN bus, LIN bus, MOST bus, FlexRay, and / or Automotive Ethernet, for example, together with telematics control units and / or environmental sensors.

[0014] The control unit can be designed for various electric motors. For example, the control unit can be located (from a circuit perspective) in the powertrain of a motor vehicle between a (high-voltage) battery and the electric motor.

[0015] Among other things, power electronics can convert direct current from the battery into alternating current for use in the electric machine or electric motor.

[0016] The part of the power electronics responsible for this conversion can also be called an inverter. The inverter can comprise several transistors or switches that turn on and off at controllable intervals. When switched on, the transistors each conduct the battery current to or from the electric motor. Together, these (high-frequency) switching operations can produce a sinusoidal voltage waveform for the current supplied to the electric motor, which serves as its driving energy.

[0017] An electric motor can consist of a rotor, the rotating part of the motor, and an armature, which is stationary or static. The rotating rotor can drive the wheels of a vehicle via the drivetrain.

[0018] The control system can be designed to control the transistors and thus the switching operations of the inverter by means of the control signal output to the inverter, which in turn influences the voltage curve of the (battery) current supplied to the electric motor.

[0019] The revelation describes a solution that enables smooth transitions and high efficiency across a wide operating range of the electric motor.

[0020] More precisely, SVM can generate a sinusoidal motor current waveform with only a few harmonics of the fundamental frequency. However, this requires the switching frequency to be significantly higher than the fundamental frequency of the generated sine wave. Therefore, as the motor speed increases, the switching frequency must also be increased to maintain the quality of the motor current waveform. Increasing the switching frequency also increases the electrical losses that occur during switching when both the switching current and voltage are non-zero. This power loss, which is dissipated as heat, must be dissipated by the equipment to prevent damage and ensure that the maximum operating temperature of the equipment is not exceeded. A purely harmonic motor current waveform also helps to minimize electrically generated heat losses in the motor.An optimized pulse-pattern modulation (OPP) strategy contains significantly fewer switching operations than standardized modulation (SVM) at high motor speeds. With a suitable number of pulses, this results in a better current curve and lower motor losses compared to SVM. The OPP strategy also leads to lower inverter switching losses at higher rotor speeds compared to SVM. Therefore, to leverage the advantages of both strategies, SVM can be used at lower rotor speeds, while switching to OPP at higher speeds.

[0021] Instead of switching between different modulation methods and the bus clamping, switching is therefore only possible between SVM and OPPs, according to the disclosure.

[0022] Therefore, a low voltage distortion can be achieved across the entire operating range of the electric motor.

[0023] In other words, to achieve low voltage and current distortion at high voltages, OPPs can be used for large modulation indices. By appropriately switching between SVMs and OPPs, the disadvantages of OPPs at low voltages or small modulation indices can be compensated for.

[0024] The integration of the control system into the drivetrain for traction is just one example of how the disclosed solution can be used. It is also conceivable, for instance, that the control system could be used for an air compressor in a fuel cell. The electric motor, or rather its rotor for the air compressor, typically rotates at high speed, and the operating points are more stable compared to traction drives. Therefore, the disclosed solution offers an advantageous, and simple, implementation for such a system. Other exemplary applications include, among others, actuators and / or power steering systems.

[0025] The following section describes in detail optional training courses for the disclosed control system. In particular, it describes the conditions under which switching between SVM and OPPs is possible.

[0026] It is conceivable that the control system is designed to switch between space vector modulation and synchronous optimal pulse width modulation depending on a ratio of a switching frequency of the space vector modulation and an average switching frequency of the synchronous optimal pulse width modulation that depends on the speed of the rotor.

[0027] In other words, the selection of SVM mode or OPP mode can be based on a number Q, which is determined by the quotient of the switching frequency f. s of the SVM and the average switching frequency favg.opp of the OPP, which depends on the actual rotor speed. This can be expressed as follows:

[0028] The control system can be designed to determine the average switching frequency of the synchronous optimal pulse width modulation as a function of the rotor speed. Since the number of pulses of a synchronous pulse pattern or OPP per period is constant, but the period duration is variable, an average switching frequency is obtained with respect to the pulses. This is defined by equation (2).

[0029] The control system can be configured to determine the average switching frequency of the synchronous optimal pulse width modulation (OPP) as a function of a number of switching angles per predetermined sub-interval of 2TT ZU. A switching angle on the OPP defines the position or angle at which a transition from 1 to -1 or from -1 to 1 occurs.

[0030] In other words, the average frequency favg.opp in equation (1) can be determined by a rotor speed Q and the specific structure of the OPP. The structure of the OPP can be defined by the number of switching angles per specific sub-interval of 2 TT. For example, if the number of switching angles per quarter-wave is TT / 2 n, then the average frequency can be determined as follows: where in equation (2) a rotor speed Q is specified in rpm and z p corresponds to a number of pole pairs.

[0031] It is conceivable that the control system is designed to use space vector modulation to determine the control signal when the ratio is greater than a predetermined limit. It is also conceivable that the control system is designed to use synchronous optimal pulse width modulation to determine the control signal when the ratio is less than the predetermined limit.

[0032] In other words, a threshold value d can be defined. If the quotient Q is above the threshold value d, SVM can be used. As soon as the quotient Q falls below the threshold value d, OPP can be used.

[0033] It is conceivable that the predetermined limit is greater than or equal to one.

[0034] This means that one possibility for the threshold value d is d = 1. OPP can then be used as soon as the average frequency favg.opp is greater than or equal to the switching frequency f. s of the SVM. At low speeds, where Q » 1, SVM can then be used.

[0035] It is conceivable that the predetermined limit includes a hysteresis band of a predetermined size, resulting in a predetermined upper limit and a predetermined lower limit. It is conceivable that the controller is designed to use space vector modulation to determine the control signal when the ratio is greater than the predetermined upper limit. It is conceivable that the controller is designed to use synchronous optimal pulse width modulation to determine the control signal when the ratio is less than the predetermined lower limit. The size of the hysteresis band can be less than or equal to 0.1.

[0036] As another option to avoid velocity noise, a hysteresis band of size 2E can be added for the threshold d. This could mean that SVM is used when the quotient Q is above a threshold d + E. Once the quotient Q is below a threshold d - E, OPP can be used. It is conceivable that the control system could be designed to continue using either space vector modulation or synchronous optimal pulse width modulation to determine the control signal when the ratio is within the hysteresis band.

[0037] In other words, a hysteresis range can be defined. If the ratio of the two frequencies (see equation (2)) is above this range, SVM is used; if it is below, OPP is used. If the ratio is within the range, the mode used remains unchanged.

[0038] This means that the hysteresis or hysteresis band can represent the range around the setpoint by which the actual value may fluctuate without switching between SVM and OPP, thus preventing constant switching between SVM and OPP.

[0039] Furthermore, the disclosure relates to a system comprising an electric motor, optionally for a motor vehicle, an inverter and the control described above, wherein the electric motor has a rotor.

[0040] A motor vehicle can also be provided with the system. This motor vehicle can be a passenger car, in particular an automobile, or a commercial vehicle, such as a truck.

[0041] What has been described with regard to the control system also applies analogously to the system and vice versa.

[0042] Furthermore, the disclosure relates to a control method for an inverter of an electric motor comprising a rotor. The control method includes determining a control signal for the inverter as a function of a rotor speed, either by means of space vector modulation or by means of synchronous optimal pulse width modulation.

[0043] The control procedure can be a computer-implemented procedure, i.e., one, several or all steps of the procedure can be at least partially carried out by a computer or a data processing device, optionally the control device.

[0044] A computer program comprising commands that, when executed by a computer, cause it to at least partially carry out the procedure described above can be provided.

[0045] The program code of a computer program can be in any type of code, especially code suitable for controlling motor vehicles.

[0046] The program can be developed, compiled, downloaded, and stored in a (semiconductor) memory, such as an EPROM, within the electronic control unit (ECU) on a computer. This means the computer program can be written, for example, in a high-level language like C and / or a graphical programming language. This can be done on a laptop or desktop computer equipped with suitable software. This program can then be cross-compiled into object code for the microcontroller in the ECU. The program can then be downloaded or otherwise transferred to the non-volatile memory of the ECU. This means the program can be permanently stored in the ECU and is available every time the system is used. All of the aforementioned forms and development steps are encompassed by the term "computer program."

[0047] A computer-readable medium, in particular a computer-readable storage medium, can be provided. The computer-readable medium comprises instructions which, when executed by a computer, cause it to at least partially execute the procedure described above.

[0048] This means that a computer-readable medium containing a computer program as defined above can be provided. The computer-readable medium can be any digital data storage device, such as a USB flash drive, a hard drive, a CD-ROM, an SD card, an SSD card (or SSD drive / SSD hard drive), or semiconductor memory. The computer program does not necessarily have to be stored on such a computer-readable storage medium to be made available to the computer; it can also be obtained via the internet or from other external sources.

[0049] What has been described with regard to the control system and the electric motor also applies analogously to the control procedure and vice versa.

[0050] Insofar as this refers to taxation, it can be understood as taxation without feedback as well as taxation with feedback, i.e., rules.

[0051] An optional embodiment is described below with reference to Figures 1 to 5.

[0052] Fig. 1 shows schematically and by way of example a system with a control system according to the disclosure for an inverter of an electric motor,

[0053] Fig. 2 shows a schematic and exemplary flowchart of a tax procedure in accordance with the disclosure,

[0054] Fig. 3 shows schematically and by way of example a (approximately sinusoidal) current waveform over an interval of 2 TT, which is achieved by the sole use of space vector modulation,

[0055] Fig. 4 schematically and exemplarily shows a (approximately sinusoidal) current waveform over an interval of 2 TT, which is achieved with the control method according to the disclosure, here by the use of synchronous optimal pulse width modulation, and

[0056] Fig. 5 schematically and by way of example shows the power loss of the electric motor achieved by space vector modulation, compared to the power loss of the electric motor achieved with synchronous optimal pulse width modulation at an exemplary speed where the mean switching frequency of the synchronous optimal pulse width modulation is lower than the switching frequency of the space vector modulation. The system 1 shown schematically in Fig. 1 comprises a vector control 2 (which can also be referred to as field-oriented control), a controller 3 for an inverter 4, the inverter 4 itself, an electric motor 5, which can be used, for example, for an air compressor (not shown) of a fuel cell within a motor vehicle, and a measuring device 6.

[0057] Vector control 2 receives as input data a target torque of the electric motor 5. Vector control 2 also receives as input data the actual position of a (not shown) rotor of the electric motor 5, measured or determined by the measuring device 6. Vector control 2 also receives as input data actual D / Q currents (where Q stands for quadrature and D for direct) determined or measured by the measuring device 6. Based on this, vector control 2 determines target D / Q values ​​(i.e., VD, VQ, V). a and Vß, where a and ß represent orthogonal two-phase parameters and V stands for voltage) and outputs these to the control unit 3.

[0058] The controller 3 takes the target D / Q values ​​together with the actual rotor speed determined or measured by the measuring device 6 as input data and processes this data to determine a control signal for the inverter 4. This control signal consists of edges that close or open (not shown) transistors or switches of the inverter 4. A separate control signal is output for each of the three phases of the electric motor 5, so that a corresponding voltage (i.e., Va, Vb, V) is supplied via the inverter 4. c with a, b, and c for the three phases) is supplied to the electric motor 5.

[0059] The edges or control signals are determined by the controller 3 either by means of space vector modulation or by means of synchronous optimal pulse width modulation, depending, among other things, on the speed of the rotor. How this is done is described in detail below with reference to Figure 2.

[0060] In a first step 101 of the disclosed control method 100, the control 3 determines an average switching frequency of the synchronous optimal pulse width modulation as a function of the speed of the rotor and a number of switching angles per predetermined sub-interval of 2TT of the synchronous optimal pulse width modulation.

[0061] In a second step 102 of the procedure 100, the control 3 determines a ratio of a switching frequency of the space vector modulation and the average switching frequency of the synchronous optimal pulse width modulation.

[0062] In a third step 103 of the procedure 100, the controller 3 determines, based on the determined ratio, whether to switch between space vector modulation and synchronous optimal pulse width modulation, or whether to use space vector modulation or synchronous optimal pulse width modulation to generate the control signal.

[0063] Space vector modulation is used to determine the control signal when the ratio is greater than a predetermined threshold, and synchronous optimal pulse width modulation is used to determine the control signal when the ratio is less than the predetermined threshold. The predetermined threshold is greater than or equal to one.

[0064] The predetermined limit can encompass a hysteresis band of a predetermined size, resulting in a predetermined upper limit and a predetermined lower limit. Controller 3 can then use space vector modulation to determine the control signal when the ratio is greater than the predetermined upper limit. Synchronous optimal pulse width modulation can be used to determine the control signal when the ratio is less than the predetermined lower limit. Space vector modulation or synchronous optimal pulse width modulation can still be used to determine the control signal when the ratio lies within the hysteresis band.

[0065] The effects achievable with the solution as revealed can be seen in Figures 3 to 5.

[0066] Figure 3 shows the normalized current waveform over 2TT, which is approximately sinusoidal when using a conventional control method (i.e., using only space vector modulation). Figure 4 similarly shows the current normalized over an electrical cycle of 2TT using synchronous optimal pulse-width modulation. In this example, Figure 3 shows 15 switching operations and Figure 4 shows 14. In both cases, the waveforms are essentially sinusoidal, but as can be seen from Figure 4, the current has lower residual ripple and fewer higher-order harmonics. This is a speed at which synchronous optimal pulse-width modulation is preferable to space vector modulation.

[0067] A comparison of Figures 3 and 4 already shows that the disclosed method results in a different current profile than the conventional method. As can be seen in Figure 5, this leads to a lower loss in the disclosed method (right bar in Figure 5) compared to the conventional method (left bar in Figure 5).

[0068] Reference symbol (part of the description) System Vector control Control Inverter Electric motor of the fuel cell compressor Measuring device Control method Determine average frequency of the OPP Determine ratio of the average frequency of the OPP to the (conversion)

[0069] Switching frequency of the SVM: compare ratio with limit value

Claims

Patent claims 1. Control (3) for an inverter (4) of an electric motor (5), wherein the electric motor (5) has a rotor, characterized in that the control (3) is designed to determine, as a function of a speed of the rotor, a control signal to be output by the control (3) to the inverter (4) either by means of a space vector modulation or by means of a synchronous optimal pulse width modulation.

2. Control (3) according to claim 1 , characterized in that the control (3) is designed to switch between space vector modulation and synchronous optimal pulse width modulation depending on a ratio of a switching frequency of the space vector modulation and an average switching frequency of the synchronous optimal pulse width modulation which depends on the speed of the rotor.

3. Control (3) according to claim 2, characterized in that the control (3) is designed to determine the average switching frequency of the synchronous optimal pulse width modulation as a function of the speed of the rotor.

4. Control (3) according to claim 3, characterized in that the control (3) is designed to additionally determine the average switching frequency of the synchronous optimal pulse width modulation as a function of a number of switching angles per predetermined partial interval of 2TT ZU.

5. Control (3) according to one of claims 2 to 4, characterized in that the control (3) is designed to: - to use space vector modulation to determine the control signal when the ratio is greater than a predetermined limit, and - to use synchronous optimal pulse width modulation to determine the control signal when the ratio is smaller than the predetermined limit.

6. Control (3) according to claim 5, characterized in that the predetermined limit value is greater than or equal to one.

7. Control (3) according to claim 5 or 6, characterized in that: - the predetermined limit value includes a hysteresis band of predetermined size, optionally less than or equal to 0.1, such that a predetermined upper limit value and a predetermined lower limit value result, and - the control (3) is designed to: - to use space vector modulation to determine the control signal when the ratio is greater than the predetermined upper limit, and - to use synchronous optimal pulse width modulation to determine the control signal when the ratio is smaller than the predetermined lower limit.

8. Control (3) according to claim 7, characterized in that the control (3) is designed to further use either the space vector modulation or the synchronous optimal pulse width modulation to determine the control signal when the ratio lies within the hysteresis band.

9. System (1), characterized in that the system (1) comprises an electric motor (5) with a rotor, an inverter (4) and the control system (3) according to one of claims 1 to 8.

10. Control method (100) for an inverter (4) of an electric motor (5) having a rotor, characterized in that the control method (100) comprises determining (103) a control signal for the inverter (4) as a function of a speed of the rotor either by means of a space vector modulation or by means of a synchronous optimal pulse width modulation.

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