Method for determining a load angle of a synchronous motor and synchronous motor

Abstract

The invention relates to a method for determining a load angle (LW) of a synchronous motor (10; 110), having the following steps: actuating a winding system (14) of the synchronous motor (10; 110) in order to set a defined working point of the synchronous motor (10; 110), recording a winding voltage curve (Uw) of the winding system (14), interrupting the actuation process of the winding system (14), determining an electromotive force fundamental component (Uemk) by evaluating a section (A2) of the winding voltage curve (Uw), said section being recorded after the actuation was interrupted, determining an actuation voltage fundamental component (Ua) by evaluating a section (A1) of the winding voltage curve (Uw), said section being recorded prior to interrupting the actuation, and determining the load angle (LW) on the basis of a phase angle (φemk) of the electromotive force fundamental component (Uemk) and a phase angle (φa) of the actuation voltage fundamental component (Ua). The invention additionally relates to a synchronous motor (10) comprising motor electronics (22) which are designed to: carry out the method according to the invention in order to determine a load angle (LW) and actuate the winding system on the basis of the determined load angle (LW).

Description

[0001] DESCRIPTION

[0002] Method for determining a load angle of a synchronous motor and synchronous motor

[0003] The present invention relates to a method for determining a load angle of a synchronous motor, in particular an electronically commutated synchronous motor. The present invention further relates to a synchronous motor comprising: a permanent magnet motor rotor, an electromagnetic motor stator with a winding system having at least one winding, and motor electronics configured to control the winding system to drive the motor rotor.

[0004] The load angle, also called the rotor angle, of a synchronous motor indicates the angle at which the magnetic field of the permanent magnet motor rotor, also called the rotor, lags behind the rotating magnetic field generated by the electromagnetic motor stator. Knowing the load angle is crucial for ensuring reliable and efficient operation of the synchronous motor.

[0005] US 2021 / 0336573 A1 discloses a generic synchronous motor and a method for determining a load angle of the synchronous motor. Here, a winding system of the synchronous motor is controlled to drive the motor rotor, a control voltage and an alternating rotor magnetic field generated by the rotating motor rotor are detected, and the load angle is determined based on a phase angle of the control voltage and a phase angle of the rotor magnetic field. However, to detect the rotor magnetic field, the synchronous motor must necessarily have a magnetic field sensor, which results in relatively high manufacturing costs for the synchronous motor.

[0006] Against this background, the task is to enable a relatively cost-effective synchronous motor.

[0007] This object is achieved by a method for determining a load angle of a synchronous motor, having the features of claim 1, and by a synchronous motor having the features of claim 7.

[0008] In the method according to the invention for determining a load angle of a synchronous motor, a winding system of the synchronous motor is controlled in such a way that a defined operating point of the synchronous motor, i.e., a defined speed of a permanent-magnet motor rotor of the synchronous motor, is set. Typically, the winding system is controlled by means of special power electronics comprising several semiconductor switches, via which individual windings of the winding system can be selectively connected to a supply voltage.Typically, an effective supply voltage provided to the respective windings is varied by means of so-called pulse width modulation (PWM), whereby the semiconductor switches assigned to the respective winding are alternately switched on and off at a relatively high frequency and the effective supply voltage can be adjusted via a ratio between the on-time and off-time during a defined period.

[0009] In the method according to the invention, at least one winding voltage curve of the winding system, i.e., the voltage curve at at least one winding of the winding system, is recorded. Typically, a temporal sequence of winding voltage values ​​is recorded and stored in a corresponding data memory.

[0010] In the method according to the invention, the control of the winding system is interrupted at a defined point in time, thus stopping the motor rotor of the synchronous motor from being actively driven. Typically, all semiconductor switches of the power electronics are switched to high impedance to electrically disconnect the winding system from the supply voltage. However, due to inertia, the motor rotor continues to rotate after the control is interrupted, so that the alternating rotor magnetic field generated by the rotating permanent magnet motor rotor continues to induce the so-called electromotive force (EMF) in the winding system.

[0011] In the method according to the invention, an EMF fundamental oscillation is determined by evaluating a section of the winding voltage curve recorded after the interruption of the control, i.e., by evaluating a section of the winding voltage curve in which the winding voltage is substantially equal to the EMF. Furthermore, a control voltage fundamental oscillation is determined by evaluating a section of the winding voltage curve recorded before the interruption of the control, i.e., by evaluating a section of the winding voltage curve in which a control voltage is applied to the winding system.

[0012] The fundamental EMF oscillation and the drive voltage oscillation can each be defined either by an amplitude, a frequency, and a phase angle, or by a complex fundamental oscillation space vector with a magnitude and a phase angle. Methods for determining the fundamental oscillation or a corresponding fundamental oscillation space vector based on a recorded voltage waveform are well known in the art and will therefore not be explained in detail here.

[0013] In the method according to the invention, the load angle is determined based on the phase angle of the EMF fundamental and the phase angle of the drive voltage fundamental. Since the speed of the motor rotor shortly after the interruption of the drive approximately corresponds to the speed of the motor rotor during the drive, the load angle for the operating point set before the interruption of the drive can be determined with a good approximation from the difference between the phase angle of the EMF fundamental and the phase angle of the drive voltage fundamental.

[0014] The method according to the invention enables the determination of the load angle without the need for a magnetic field sensor and thus enables the realization of a relatively cost-effective synchronous motor.

[0015] Furthermore, the method according to the invention also enables simple and cost-effective characterization of a synchronous motor in the laboratory. For example, load angle characteristic maps for a map-controlled synchronous motor can be determined in a simple manner using the method according to the invention. Furthermore, synchronous motor prototypes can also be characterized relatively simply and cost-effectively using the method according to the invention, thereby reducing the development costs for a synchronous motor. Preferably, the fundamental EMF oscillation and the fundamental control voltage oscillation are each determined using a Fourier analysis of the corresponding section of the winding voltage curve. Particularly preferably, a so-called discrete Fourier transformation (DFT) or a so-called fast Fourier transformation (FFT) is carried out here.Fourier analysis allows a fundamental oscillation to be determined easily and efficiently from a recorded signal waveform. Fourier analysis therefore enables the determination of the fundamental EMF oscillation and the drive voltage oscillation using a relatively simple and therefore relatively inexpensive computing unit.

[0016] Typically, the winding system of a synchronous motor comprises a plurality of separate windings, which may have slightly different electromagnetic properties due to manufacturing tolerances and / or slightly different material properties. Therefore, advantageously, for each

[0017] For each winding of the winding system: a winding-specific winding voltage curve is recorded, a winding-specific fundamental EMF and a winding-specific fundamental control voltage are determined by evaluating the corresponding sections of the recorded winding-specific winding voltage curve, and a winding-specific load angle is determined based on a phase angle of the winding-specific fundamental EMF and a phase angle of the winding-specific fundamental control voltage. This enables, on the one hand, particularly precise characterization of the synchronous motor in the laboratory and, on the other hand, particularly precise control of the synchronous motor during operation. Preferably, an overall load angle is determined based on the winding-specific load angles. For example, the overall load angle can be easily determined as the mean or median of all winding-specific load angles.Determining the total load angle enables relatively precise and at the same time relatively simple control of the synchronous motor.

[0018] In particular, when using the method according to the invention in regular operation of the synchronous motor, the control of the winding system is preferably suspended for a maximum of two periods of a control signal in order to avoid significant braking of the motor rotor during the suspension and thus "unsmooth" running of the synchronous motor.

[0019] In particular, to determine a load angle characteristic map, for example, for a map-controlled synchronous motor, the previously described method steps can be performed for at least one additional operating point of the synchronous motor in order to determine at least one additional load angle. Typically, the described method steps are each performed for a plurality of operating points, thus determining a plurality of operating-point-specific load angles. This allows a relatively comprehensive load angle characteristic map to be determined in a relatively simple manner.

[0020] The synchronous motor according to the invention comprises a permanent-magnet motor rotor, an electromagnetic motor stator with a winding system having at least one winding, and motor electronics configured to control the winding system to drive the motor rotor. In the synchronous motor according to the invention, the motor electronics are further configured to carry out the previously described inventive method to determine a load angle and to control the winding system based on the determined load angle. For this purpose, the motor electronics in particular have means for detecting the winding voltage and for storing and evaluating the winding voltage curve. The motor electronics typically comprise a microcontroller for evaluating the winding voltage curve.

[0021] The motor electronics of the synchronous motor according to the invention are thus configured to determine the load angle by carrying out the method according to the invention - as described above - without the need for a magnetic field sensor, so that the synchronous motor according to the invention can be manufactured relatively inexpensively.

[0022] Embodiments of the present invention are described below with reference to the accompanying figures. Herein:

[0023] Figure 1 is a schematic representation of a synchronous motor according to the invention,

[0024] Figure 2 shows an exemplary image recorded during the execution of a method according to the invention

[0025] Winding voltage curve of a winding system of the synchronous motor from Figure 1 (top), as well as a fundamental electromotive force oscillation determined from the winding voltage curve (middle) and a fundamental electromotive force oscillation determined from the winding voltage curve

[0026] Drive voltage fundamental oscillation (below), Figure 3 a space vector representation of the electromotive force fundamental oscillation and the drive voltage fundamental oscillation from Figure 2, and

[0027] Figure 4 is a schematic representation of an arrangement for characterizing a synchronous motor by means of a method according to the invention.

[0028] Fig. 1 shows a synchronous motor 10 comprising an electromagnetic motor stator 12 with a winding system 14 and a permanent magnet motor rotor 16. In the present embodiment, the winding system 14 comprises three windings 18, wherein one winding end of each winding 18 can be electrically contacted via a contact element 20 and the other winding end is electrically connected to a so-called star point.

[0029] The synchronous motor 10 comprises motor electronics 22 with a control unit 24, with a detection unit 26, with a data memory 28, and with an evaluation unit 30.

[0030] The control unit 24 is electrically connected to the contact elements 20 of the three windings 18. The control unit 24 is configured to read a load angle parameter and other control parameters from the data memory 28 and to control the windings 18 based on the load angle parameter and the other control parameters in order to drive the motor rotor 16 at a defined speed. The control unit 24 is configured to interrupt, i.e., temporarily suspend, the control of the windings 18 at predefined times in order to enable the evaluation unit 30 to determine a current load angle LW. The detection unit 26 is electrically connected to the three contact elements 20.The detection unit 26 is configured to detect a winding voltage applied to the respective contact element 20 and to record a respective winding-specific winding voltage curve Uw, i.e. to store a respective temporal sequence of the detected values ​​of the winding voltage in the data memory 28.

[0031] The evaluation unit 30 is configured to read out and evaluate the winding-specific winding voltage curves Uw from the data memory 28 at predefined times after the interruption of the control of the windings 18. In particular, the evaluation unit 30 is configured to determine a winding-specific fundamental EMF oscillation Uemk for each winding 18 by means of Fourier analysis of a section A2 of the corresponding winding-specific winding voltage curve Uw recorded after the interruption of the control, and to determine a winding-specific fundamental control voltage oscillation Ua for each winding 18 by means of Fourier analysis of a section A1 of the corresponding winding-specific winding voltage curve Uw recorded before the interruption of the control.

[0032] The evaluation unit 30 is configured to determine a winding-specific load angle LW for each winding 18 based on a phase angle cpemk of the winding-specific fundamental EMF oscillation Uemk and a phase angle cpa of the winding-specific fundamental control voltage oscillation Ua. The evaluation unit 30 is configured to determine an overall load angle by calculating the mean value of all winding-specific load angles LW and to write a load angle parameter corresponding to the overall load angle into the data memory 28. Fig. 2 shows an exemplary winding voltage curve Uw recorded by the acquisition unit 26, as well as the corresponding fundamental EMF oscillation Uemk determined by the evaluation unit 30 and the corresponding fundamental control voltage oscillation Ua determined by the evaluation unit 30.

[0033] Between a time toff and a time ton, the control of the winding system 14 by the control unit 24 was interrupted. The duration of the interruption is approximately 1.75 periods of the fundamental control voltage oscillation Ua, with the period of the fundamental control voltage oscillation Ua corresponding to the period of a control signal. Thus, the control of the winding system 14 is interrupted for less than two periods of the control signal.

[0034] Section A1 of the winding voltage curve Uw recorded before time toff, i.e., during activation, is evaluated by the evaluation unit 30 using Fourier analysis to determine the corresponding fundamental control voltage oscillation Ua. Section A2 of the winding voltage curve Uw recorded between time toff and time ton, i.e., during the cessation of activation, is evaluated by the evaluation unit 30 using Fourier analysis to determine the corresponding fundamental EMF oscillation Uemk.

[0035] The phase shift between the specific EMF fundamental oscillation Uemk and the specific drive voltage fundamental oscillation Ua, which is shown in Fig. 2 as an example by the shift of the zero crossings of the EMF fundamental oscillation Uemk and the

[0036] The fundamental control voltage Ua defines the corresponding load angle LW. Fig. 3 shows a so-called space vector representation of the fundamental EMF Uemk and the

[0037] Control voltage fundamental oscillation Ua from Fig. 2. Here, the load angle LW can be read directly from the difference between the phase angle cpemk of the EMF fundamental oscillation Uemk and the phase angle cpa of the control voltage fundamental oscillation Ua.

[0038] Fig. 4 shows an arrangement 100 for characterizing a synchronous motor 110. The synchronous motor 110 corresponds in its basic structure to the synchronous motor 10 from Fig. 1, but does not include motor electronics.

[0039] In addition to the synchronous motor 110, the arrangement 100 comprises a characterization device 102 with a control unit 124, with a detection unit 126, with a data memory 128, and with an evaluation unit 130.

[0040] The control unit 124 is connected, analogously to the control unit 24 of Fig. 1, to the contact elements 20 of the three windings 18 of the synchronous motor 110 and is configured to control the winding system 14 of the synchronous motor 110 in order to set predetermined operating points.

[0041] Analogous to the detection unit 26 of Fig. 1, the detection unit 126 is electrically connected to the three contact elements 20 of the synchronous motor 110 and configured to record the winding-specific winding voltage curve Uw for each winding 18 of the synchronous motor 110. The evaluation unit 130 is configured to specify an operating point for the control unit 124 and to provide the control unit 124 with a signal for controlling the winding system 14. The evaluation unit 130 is further configured to provide the control unit 124 with a signal to suspend the control at a defined time.

[0042] The evaluation unit 130 is configured to evaluate the winding-specific winding voltage curves Uw at predefined times after the interruption of the control of the windings 18 in order to determine the winding-specific load angle LW and the corresponding total load angle for the currently set operating point—analogous to the functionality of the evaluation unit 30 in Fig. 1. The evaluation unit 130 is further configured to enter at least the determined total load angle as a load angle parameter for the current operating point in a load angle characteristic map stored in the data memory 128.

[0043] The evaluation unit 130 is configured - as previously described - to determine the winding-specific load angle LW as well as the corresponding total load angle for a plurality of predetermined additional operating points and to enter them as load angle parameters for the respective operating point in the load angle characteristic map stored in the data memory 128.

[0044] List of reference symbols

[0045] 10 Synchronous motor

[0046] 12 Motor stator

[0047] 14 Winding system

[0048] 16 Motor rotor

[0049] 18 windings

[0050] 20 contact element

[0051] 22 Engine electronics

[0052] 24 control unit

[0053] 26 Recording unit

[0054] 28 data storage

[0055] 30 evaluation unit

[0056] All Section

[0057] A2 Section

[0058] LW load angle toff time tein time

[0059] Ua control voltage fundamental

[0060] Uernk Electromotive force fundamental oscillation

[0061] Uw Winding voltage curve cpa Phase angle of the control voltage fundamental cpemk Phase angle of the electromotive force fundamental

[0062] 100 arrangement

[0063] 102 Characterization device

[0064] 110 Synchronous motor

[0065] 124 control unit

[0066] 126 Recording unit 128 Data storage

[0067] 130 Evaluation unit

Claims

PATENT CLAIMS Method for determining a load angle (LW) of a synchronous motor (10;110), comprising the following method steps: - Controlling a winding system (14) of the synchronous motor (10;110) to set a defined operating point of the synchronous motor (10;110), - Recording a winding voltage curve (Uw) of the winding system (14), - Discontinuation of the control of the winding system (14), - Determining an electromotive force fundamental oscillation (Uemk) by evaluating a section (A2) of the winding voltage waveform (Uw) recorded after the cessation of the drive, - Determining a fundamental drive voltage frequency (Ua) by evaluating a section (Al) of the winding voltage waveform (Uw) recorded before the drive was discontinued, and - Determining the load angle (LW) based on a phase angle (cpemk) of the fundamental oscillation of the electromotive force (Uemk) and a phase angle (cpa) of the fundamental oscillation of the control voltage (Ua). Method according to claim 1, wherein the fundamental oscillation of the electromotive force (Uemk) and the fundamental oscillation of the control voltage (Ua) are each determined by means of a Fourier analysis of the corresponding section (A1,A2) of the winding voltage waveform (Uw). Method according to one of the preceding claims, wherein for each winding (18) of the winding system (14) respectively: - a winding-specific winding voltage curve (Uw) is recorded, - a winding-specific electromotive force fundamental oscillation (Uemk) and a winding-specific control voltage fundamental oscillation (Ua) are determined by evaluating the corresponding sections (A1,A2) of the recorded winding-specific winding voltage curve (Uw), and - a winding-specific load angle (LW) is determined based on a phase angle (cpemk) of the winding-specific fundamental electromotive force (Uemk) and a phase angle (cpa) of the winding-specific fundamental control voltage (Ua). Method according to claim 3, wherein an overall load angle is determined based on the winding-specific load angles (LW). Method according to any one of the preceding claims, wherein the control of the winding system (14) is suspended for a maximum duration of two periods of a control signal. Method according to any one of the preceding claims, wherein the previously described method steps are each carried out for at least one further operating point of the synchronous motor (110) in order to determine at least one further load angle (LW). Synchronous motor (10) comprising: - a permanent magnet motor rotor (16), - an electromagnetic motor stator (12) with a winding system (14) having at least one winding (18), and - a motor electronics unit (22) configured to control the winding system (14) for driving the motor rotor (16), characterized in that the motor electronics unit (22) is further configured as follows: - to carry out a method according to any one of claims 1 to 6 to determine a load angle (LW), and - the winding system based on the specific load angle (LW) to be targeted.