Method for sensorless control of an electric motor and drive system

Abstract

The invention relates to a method for sensorless control of an electric motor (1), in particular a permanent magnet synchronous motor, with a stator and a rotor rotatable relative to the stator, wherein the electric motor (1) is controlled by an inverter (14) with several voltage signals which are superimposed with a periodic injection signal to estimate a position and / or speed of the rotor, characterized by the fact that the inverter (14) is designed as a multilevel inverter and the voltage signals each have at least three different voltage levels.

Description

[0001] The invention relates to a method for the sensorless control of an electric motor, in particular a permanent magnet synchronous motor, having a stator and a rotor rotatable relative to the stator. Furthermore, the invention relates to a drive system comprising an inverter and an electric motor controlled by the inverter, which has a stator and a rotor rotatable relative to the stator.

[0002] Electric motors with a permanent magnet rotor are also known as permanent-magnet electric motors and are increasingly used in the automotive industry, particularly in the form of permanent-magnet synchronous motors. Controlling such electric motors requires knowledge of the position of the permanent magnet rotor. Conventionally, this position is determined using a position sensor, but its use involves additional costs and space requirements. Therefore, there is a need for sensorless alternatives for controlling such machines.

[0003] In sensorless operation of electric motors, current sensor signals and measured or estimated phase voltages are used to determine the rotor position and speed of the electric motor using a mathematical model. At low speeds, and especially when the rotor is stationary, it is necessary to feed in so-called injection signals, which enable the identification of the rotor position and speed. These injection signals often have a frequency in the audible range, which can lead to acoustic interference. The use of injection signals must therefore be carefully considered and is often only considered if the drive system will not be operated near people or is acoustically shielded.

[0004] WO 2022 / 233 384 A1 presents an exemplary method for sensorless control of an electric induction motor. This method is enabled by injecting an injection signal. The injection frequency is selected so high that this injection signal has no negative acoustic properties. Current measurement is performed at a much lower frequency. The necessary information can be determined by subsampling the signal. Unfortunately, this method significantly increases the power loss in the inverter because injecting the injection signal requires a much higher frequency of the fundamental oscillation of the voltage signals supplied to the electric motor (PWM frequency). This results in a much higher number of switching operations within a given time period than in a comparable system with a conventional low PWM frequency.

[0005] Against this background, the task arises to enable sensorless control of an electric motor without acoustic impairment and without a significant increase in power loss.

[0006] The object is achieved by a method for the sensorless control of an electric motor, in particular a permanent magnet synchronous motor, with a stator and a rotor rotatable relative to the stator, wherein the electric motor is controlled by an inverter with several voltage signals which are superimposed with a periodic injection signal to estimate a position and / or speed of the rotor, wherein the inverter is designed as a multilevel inverter and the voltage signals each have at least three different voltage levels.

[0007] By superimposing a periodic injection signal on the voltage signals, it is possible to control the electric motor sensorless, i.e. without measuring the rotor position or speed, and without the need for a mathematical motor model. According to the invention, instead of a conventional inverter, which generates voltage signals with exactly two different voltage levels, a multilevel inverter is used to control the electric motor. This multilevel inverter controls the electric motor with voltage signals having at least three different voltage levels. In this respect, the multilevel inverter generates voltage signals with more voltage levels than conventional inverters. This increased number of voltage levels allows the desired sinusoidal signal to be better approximated at the input of the electric motor. Consequently, losses in the electric motor are reduced.Compared to a conventional inverter, the multilevel inverter can also operate at a significantly higher PWM frequency without increasing inverter losses. The significantly higher PWM frequency allows the electric motor to be operated sensorlessly using the injection method without any audible interference, as the injection frequency can be selected to exceed 20 kHz.

[0008] According to an advantageous embodiment of the invention, the frequency of the periodic injection signal is greater than 20 kHz. By selecting the frequency in this range, noises that are audibly perceptible to humans can be avoided. The PWM frequency is preferably greater than the frequency of the periodic injection signal, for example, a multiple of the frequency of the periodic injection signal. For example, it is conceivable that the PWM frequency is twice or four times the frequency of the periodic injection signal.

[0009] According to an advantageous embodiment of the invention, the voltage signals have exactly three different voltage levels. In this respect, a multilevel inverter designed as a 3-level inverter can be used in the method. Such multilevel inverters require fewer components and less space than higher-order multilevel inverters and can therefore be implemented with comparatively little effort. Alternatively, the voltage signals can have exactly five, seven, nine, eleven, or more different voltage levels.

[0010] According to an advantageous embodiment of the invention, it is provided that no sensor measuring the position and / or speed of the rotor is used.

[0011] According to an advantageous embodiment of the invention, it is provided that the voltage signals are superimposed with the periodic injection signal in an entire speed range in which the electric motor is operated.

[0012] To solve the problem mentioned above, a drive system with an inverter and an electric motor controlled by the inverter is also proposed, which has a stator and a rotor rotatable relative to the stator, wherein the drive system is configured to superimpose a periodic injection signal on the voltage signals for estimating a position and / or speed of the rotor; wherein the inverter is designed as a multilevel inverter and is configured to control the electric motor with a plurality of voltage signals, each of which has at least three different voltage levels.

[0013] With the drive system according to the invention, the same technical effects and advantages can be achieved as have already been explained in connection with the method according to the invention.

[0014] According to an advantageous embodiment of the invention, the frequency of the periodic injection signal is greater than 20 kHz. As already mentioned, selecting a frequency in this range can prevent human-perceivable noise.

[0015] According to an advantageous embodiment of the invention, the voltage signals have exactly three different voltage levels. This allows the use of a multilevel inverter designed as a 3-level inverter.

[0016] According to an advantageous embodiment of the invention, it is provided that the drive system is free of a sensor measuring the position and / or speed of the rotor.

[0017] Further details and advantages of the invention will be explained below with reference to the exemplary embodiment illustrated in the drawings. Herein: Fig. 1 shows a drive system with a device for the sensorless determination of the angular frequency and / or position of a permanent magnet rotor of a brushless electric machine according to an embodiment of the invention; and Fig. 2 example curves of voltage signals for controlling an electric motor with exactly two, exactly three and exactly nine voltage levels.

[0018] The representation in Fig. Figure 1 shows a drive system that can be used, for example, in the automotive industry. The drive system comprises an electric motor 1 with a stator 2 and a permanent magnet rotor, for example, a brushless synchronous motor. A control device 10 is provided to control the position and angular frequency of the rotor of the electric motor 1, which implements field-oriented control (vector control).

[0019] The control device 10 comprises two controllers 11.1, 11.2, via which a d-voltage u d and a q-voltage u q in the rotor-related qd coordinate system. These stresses u d and u q are fed to a transformation unit 12, in which a transformation from the rotor-related dq coordinate system into the stator-related α,β coordinate system is carried out. The stator-related voltages u obtained at the output of the transformation unit 12 αand u β are fed to a space vector modulation (SVM) unit 13, which controls a converter 14 using pulse width modulation. This inverter 14 provides three voltage signals for the winding of the stator 2 of the electric motor 1.

[0020] Two phase currents i1 and i2 of stator 2 are measured by current sensors 15 and fed to further transformation units 16, 17, which transform the phase currents into the rotor-related d,q coordinate system. The actual currents i are obtained. d and i q . These actual flows i d , i q are fed to a notch filter 18, which has a blocking frequency ω c which corresponds to a carrier frequency used in an injection process, which will be explained further below. The filter 18 can remove high-frequency components in the actual currents i generated by the injection process. d , iq filtered out so that they do not affect the control. The filtered actual currents i d , i q are then fed to the controllers 11.1, 11.2 as actual values. Further input signals of the controllers 11.1, 11.2 are the setpoint currents id*.iq*.

[0021] For the sensorless determination of the angular frequency and position of the permanent magnet rotor, an injection method (blocks 30, 31, 32) is used in the drive system according to the exemplary embodiment. This method provides an indication of the angular frequency ω and the position φ of the rotor of the electric motor 1 from block 40. In addition, a low-pass filtered angular frequency ω f provided.

[0022] To implement the injection process, the drive system comprises an injection block 30, a demodulation block 31 and an injection tracking controller 32.

[0023] In the injection block 30, a high-frequency d-test signal voltage u0sin(ω c t) with a given carrier frequency ω c which is applied to the d-voltage u d is imprinted.

[0024] The demodulation block 31 receives as input signals the unfiltered actual currents i d , i q and determines a demodulated current i q,dem . The demodulated current i q,dem is combined with the proportional element k kor (load correction) weighted, filtered q-actual current i qf fed to the injection tracking controller 32. The injection tracking controller 32 implements a difference formation of demodulated current i q,dem and weighted, filtered q-actual current i qfThe difference is fed to a proportional-integral controller (PI), which outputs the injection angular frequency. The injection tracking controller 32 thus determines an angular frequency, which is also referred to here as the injection angular frequency.

[0025] The determined electrical angle φ is forwarded to the controller 10, in particular the transformation units 12, 17, and is taken into account there in the transformation from the stator-related to the rotor-related coordinate system or vice versa.

[0026] In the drive system according to the exemplary embodiment, the inverter 14 is designed as a multilevel inverter and is configured to control the electric motor 1 with three voltage signals, each of which has at least three different voltage levels. Preferably, the inverter 14 is a 3-level inverter configured to control the electric motor 1 with three voltage signals, each of which has exactly three different voltage levels.

[0027] The frequency of the periodic injection signal u0sin(ω c t) is preferably selected to be greater than 20 kHz, so that acoustically perceptible noises are avoided. Preferably, the PWM frequency used in inverter 14 is greater than the frequency of the periodic injection signal u0sin(ω c t), for example double or quadruple the frequency of the periodic injection signal u0sin(ω c t).

[0028] The representation in Fig.Figure 2 shows exemplary waveforms of voltage signals u(t) for controlling an electric motor 1 with exactly two (a), exactly three (b), and exactly nine (c) voltage levels. It can be seen that the desired sinusoidal voltage signal is better approximated with an increasing number of voltage levels. QUOTES CONTAINED IN THE DESCRIPTION

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

[0000] WO 2022 / 233 384 A1

[0004]

Claims

[1] Method for the sensorless control of an electric motor (1), in particular a permanent magnet synchronous motor, with a stator and a rotor rotatable relative to the stator, wherein the electric motor (1) is controlled by an inverter (14) with a plurality of voltage signals which are superimposed with a periodic injection signal to estimate a position and / or speed of the rotor, characterized by , that the inverter (14) is designed as a multilevel inverter and the voltage signals each have at least three different voltage levels. [2] Method according to claim 1, characterized by that a frequency of the periodic injection signal is greater than 20 kHz. [3] Method according to one of the preceding claims, characterized by that the voltage signals have exactly three different voltage levels. [4] Method according to one of the preceding claims, characterized by that no sensor measuring the position and / or speed of the rotor is used. [5] Method according to one of the preceding claims, characterized by that the voltage signals are superimposed with the periodic injection signal in an entire speed range in which the electric motor (1) is operated. [6] Drive system with an inverter (14) and an electric motor (1) controlled by the inverter (14), which has a stator and a rotor rotatable relative to the stator, wherein the drive system is configured to superimpose a periodic injection signal on the voltage signals for estimating a position and / or speed of the rotor; characterized by , that the inverter (14) is designed as a multilevel inverter and is configured to control the electric motor (1) with a plurality of voltage signals, each of which has at least three different voltage levels. [7] Drive system according to claim 6, characterized by that a frequency of the periodic injection signal is greater than 20 kHz. [8] Drive system according to one of claims 6 or 7, characterized by that the voltage signals have exactly three different voltage levels. [9] Drive system according to one of claims 6 to 8, characterized by that the drive system is free of a sensor measuring the position and / or speed of the rotor.

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