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

Abstract

The present invention relates to a method for determining a load angle (LW) of a synchronous motor (100), comprising: actuating a winding system (1.1) of the synchronous motor (100) in order to set a defined operating point, recording a winding voltage profile (Uw-t), suspending the actuation of the winding system (1.1), determining an EMF phase angle profile (φEMK-t) by evaluating a section (A2) of the winding voltage profile (Uw-t) recorded after the suspension of the actuation, determining a model (M, M') for describing the EMF phase angle profile (φEMK-t) within an oscillation period (P), determining an EMF phase angle (φEMK-t.v) for a comparison time (t.v), which lies before the suspension of the actuation, by extrapolating the EMF phase angle profile (φEMK-t) by means of the model (M, M'), determining an actuation voltage phase angle (φA-t.v) for the comparison time (t.v) by evaluating a section (A1) of the winding voltage profile (Uw-t) recorded before the suspension of the actuation, and determining the load angle (LW) on the basis of the EMF phase angle (φEMK-t.v) determined for the comparison time (t.v) and the actuation voltage phase angle (φA-t.v) determined for the comparison time (t.v). The present invention further relates to a synchronous motor (100) comprising a motor electronics unit (3) which is designed to carry out a method according to the invention in order to determine a load angle (LW), and to actuate the winding system (1.1) on the basis of the determined load angle (W).

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] WO2023 / 143714 A1 discloses a synchronous motor and a method of the type mentioned above, wherein the control of the winding system of the synchronous motor is suspended, and the load angle is determined by evaluating a section of a winding voltage curve recorded before the suspension and a section of the winding voltage curve recorded after the suspension. The present invention is based on the object of enabling a relatively cost-effective and reliable synchronous motor.

[0006] This object is achieved according to the invention 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 8.

[0007] 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.

[0008] 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.

[0009] 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.

[0010] Since the synchronous motor typically drives some kind of tool or mechanism, the motor rotor decelerates to a greater or lesser extent after the interruption of the control. This results, on the one hand, in a continuous reduction in the oscillation amplitude of the winding voltage curve recorded after the interruption of the control, and, on the other hand, in a continuous increase in the oscillation period of the winding voltage curve recorded after the interruption of the control.

[0011] In the method according to the invention, an EMF phase angle curve, i.e., a temporal curve of a phase angle of the EMF, 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 essentially equal to the EMF. Methods for deriving a phase angle from a recorded voltage curve are well known in the prior art and are therefore not explained here.

[0012] Furthermore, according to the invention, a model is determined to describe the specific EMF phase angle curve within an oscillation period, i.e., within a range in which the phase angle lies between n and -n. The model can, for example, comprise a fitting function, also called an adaptation function, or another type of algorithm for mathematically describing the EMF phase angle curve within the oscillation period. In principle, however, the model can be implemented in any manner known from the prior art. In any case, the model is suitable for interpolating or extrapolating corresponding EMF phase angle values ​​for given points in time.

[0013] By means of the determined model, an EMF phase angle, i.e. a single EMF phase angle value, is then determined according to the invention for a comparison time prior to the interruption of the control by extrapolating the EMF phase angle curve.

[0014] By modeling and extrapolating the EMF phase angle curve according to the invention, the effects of deceleration of the motor rotor can be calculated relatively easily and with sufficient accuracy. This makes it possible to determine a relatively precise EMF phase angle for the comparison point in time prior to the interruption of the control.

[0015] In the method according to the invention, a drive voltage phase angle, i.e. a single drive voltage phase angle value, is further determined for the comparison time point in a known manner by evaluating a section of the winding voltage curve recorded before the interruption of the drive, i.e. by evaluating a section of the winding voltage curve in which a drive voltage is applied to the winding system.

[0016] In the method according to the invention, the load angle is then determined based on the EMF phase angle determined for the comparison time and the control voltage phase angle determined for the comparison time.

[0017] The method according to the invention enables a relatively exact determination of the load angle even when the motor rotor is braked relatively strongly after the interruption of the control, without the need for an additional magnetic field sensor, and thus enables the realization of a relatively cost-effective and reliable synchronous motor.

[0018] Preferably, the determined EMF phase angle profile comprises a complete oscillation period, where a complete oscillation period is understood to be the range between a phase angle of n and a phase angle of -n. A complete oscillation period therefore starts at a phase angle of n or -n and ends at a phase angle of -n or n, respectively. This allows a particularly accurate model and thus a particularly accurate EMF phase angle to be determined for the comparison time.

[0019] Particularly preferably, the determination of the EMF phase angle curve is started immediately after the interruption of the control, and the determination of the EMF phase angle curve is terminated as soon as the determined EMF phase angle curve encompasses a complete oscillation period, so that the determined EMF phase angle curve encompasses exactly one complete oscillation period. This enables a particularly accurate determination of the EMF phase angle for the comparison time with a relatively short interruption of the control.

[0020] Preferably, the EMF phase angle curve and / or the drive voltage phase angle curve are determined using a so-called Fourier analysis of the corresponding section of the winding voltage curve. Particularly preferred is a so-called discrete Fourier transformation (DFT) or a so-called fast Fourier transformation (FFT). Using Fourier analysis, a phase angle can be determined from a recorded signal curve in a simple and efficient manner. Fourier analysis therefore enables the EMF phase angle curve and / or the drive voltage phase angle curve to be determined using a relatively simple and therefore relatively inexpensive computing unit.

[0021] 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, for each winding of the winding system, the following are preferably recorded: a winding-specific winding voltage curve; a winding-specific EMF phase angle curve is determined by evaluating the corresponding section of the recorded winding-specific winding voltage curve; a winding-specific model is determined to describe the determined winding-specific EMF phase angle curve within an oscillation period; a winding-specific EMF phase angle is determined for a comparison time prior to the interruption of the control;by extrapolating the determined winding-specific EMF phase angle curve using the determined winding-specific model, a winding-specific drive voltage phase angle for the comparison time is determined by evaluating the corresponding section of the recorded winding-specific winding voltage curve, and a winding-specific load angle is determined based on the winding-specific EMF phase angle for the comparison time and the winding-specific drive voltage phase angle for the comparison time. This enables particularly precise control of the synchronous motor during operation.

[0022] Preferably, a total load angle is determined based on the winding-specific load angles. For example, the total 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.

[0023] Preferably, the control of the winding system is suspended for a maximum duration of two oscillation period lengths 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.

[0024] 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.

[0025] The motor electronics of the synchronous motor according to the invention are thus configured to determine the load angle relatively precisely by carrying out the method according to the invention - as described above - even in the case of a motor rotor that is braked relatively strongly after the control has been interrupted, without the need for a magnetic field sensor, so that the synchronous motor according to the invention can be manufactured relatively inexpensively and operates relatively reliably.

[0026] An embodiment of the present invention is described below with reference to the accompanying figures. Herein:

[0027] Fig. 1 is a schematic representation of an inventive

[0028] synchronous motor, and

[0029] Fig. 2 shows an exemplary image recorded during the execution of a method according to the invention

[0030] Winding voltage curve of a winding system of the synchronous motor from Fig. 1 (top) and a voltage curve determined by evaluating the winding voltage curve

[0031] Phase angle curve (below).

[0032] Fig. 1 shows a synchronous motor 100 with an electromagnetic motor stator 1, a permanent magnet motor rotor 2 and motor electronics 3.

[0033] The motor stator 1 comprises a winding system 1.1 having three windings 1.2, wherein one winding end of each winding 1.2 can be electrically contacted via a contact element 1.3 and the other winding end is electrically connected to a so-called star point (not shown here).

[0034] The engine electronics 3 comprises a control unit 3.1, a recording unit 3.2, a data memory 3.3 and an evaluation unit 3.4.

[0035] The control unit 3.1 is electrically connected to the contact elements 1.3 of the three windings 1.2 and is configured to read a load angle parameter and further control parameters from the data memory 3.3 and to control the windings 1.2 based on the load angle parameter and the further control parameters in order to drive the motor rotor 2 at a defined speed.

[0036] The control unit 3.1 is further configured to suspend, i.e. temporarily interrupt, the control of the windings 1.2 at predefined times t.off in order to enable the evaluation unit 3.4 to determine a current load angle LW.

[0037] The detection unit 3.2 is electrically connected to the three contact elements 1.3 and is configured to detect a winding voltage applied to the respective contact element 1.3 and to record a winding-specific winding voltage curve Uw-t, i.e. to store a time sequence of the detected winding voltage values ​​in the data memory 3.3.

[0038] The evaluation unit 3.4 is configured to continuously read and evaluate the winding-specific winding voltage curves Uw-t from the data memory 3.3 after the control of the windings 1.2 has been interrupted.

[0039] The evaluation unit 3.4 is specifically designed to determine a winding-specific phase angle curve cp-t for each winding 1.2 by means of Fourier analysis of the corresponding winding-specific winding voltage curve Uw-t and, if appropriate, suitable filtering, wherein the phase angle curve cp-t determined for a section A1 extending until the control is interrupted corresponds in each case to a control voltage phase angle curve cpA-t and the phase angle curve cp-t determined for a section A2 beginning immediately after the control is interrupted corresponds in each case to an EMF phase angle curve cpEMK-t.

[0040] The evaluation unit 3.4 is set up to read out and evaluate the winding-specific winding voltage curves Uw-t until the winding-specific EMF phase angle curves cpEMK-t determined by evaluating section A2 each comprise exactly one complete oscillation period P.

[0041] The evaluation unit 3.4 is further configured to determine winding-specific models for describing the determined winding-specific EMF phase angle curves cpEMK-t within the complete oscillation period P and, by extrapolating the winding-specific EMF phase angle curves cpEMK-t using the winding-specific models, to determine for each winding 1.2 a winding-specific EMF phase angle cpEMK-tv for a comparison time tv which is before the interruption of the control, i.e. which is less than or equal to the time t.aus of the start of the interruption of the control.

[0042] The evaluation unit 3.4 is further configured to determine a winding-specific control voltage phase angle cpA-t.v for each winding 1.2 based on the determined winding-specific control voltage phase angle curves cpA-t for the comparison time tv.

[0043] The evaluation unit 3.4 is further configured to determine a winding-specific load angle LW for each winding 1.2 based on the respective winding-specific EMF phase angle cpEMK-tv for the comparison time tv and the respective winding-specific control voltage phase angle cpA-t.v for the comparison time tv.

[0044] The evaluation unit 3.4 is further configured to determine a total load angle by calculating the mean value of all winding-specific load angles LW and to write a load angle parameter corresponding to the total load angle into the data memory 3.3.

[0045] The evaluation unit 3.4 is further configured to provide the control unit 3.2 with a signal to terminate the suspension of the control as soon as the load angle parameter has been written to the data memory 3.3. Fig. 2 shows an example of a winding voltage curve Uw-t recorded by the acquisition unit 3.2, as well as the corresponding phase angle curve cp-t determined by the evaluation unit 3.4.

[0046] Between the time t.off and the time t.on, the control of the winding system 1.2 by the control unit 3.2 was suspended, whereby the control of the winding system 1.2 was suspended for less than two oscillation period lengths of a control signal.

[0047] The phase angle curve cp-t determined by evaluating the section Al of the winding voltage curve Uw-t recorded before the time t.off, i.e. during the control, forms the control voltage phase angle curve cpA-t and the phase angle curve cp-t determined by evaluating the section A2 of the winding voltage curve Uw-t recorded between the time toff and the time tein, i.e. during the interruption of the control, forms the EMF phase angle curve cpEMK-t.

[0048] The section A2 evaluated by the control unit 3.2 ends at a time t.end at which the determined EMF phase angle curve cpEMK-t comprises exactly one complete oscillation period.

[0049] The model determined by the control unit 3.2 to describe the EMF phase angle curve cpEMK-t within an oscillation period is depicted in Fig. 2 by a modeling function M shown as a dashed line. The comparison time tv is preferably set to the time t.off, i.e., the time at which the interruption of the control begins, as shown in Fig. 2.

[0050] In the illustration of Fig. 2, the control voltage phase angle cpA-tv for the comparison time tv corresponds to the intersection point of the control voltage phase angle curve cpA-t with the vertical auxiliary line drawn at the comparison time tv and the EMF phase angle cpEMK-tv for the comparison time tv corresponds to the intersection point of the modeling function M with the vertical auxiliary line drawn at the comparison time tv.

[0051] In the illustration of Fig. 2, the load angle LW, which results from the difference between the control voltage phase angle cpA-tv for the comparison time tv and the EMF phase angle cpEMK-tv for the comparison time tv, corresponds to the vertical distance between the control voltage phase angle cpA-tv for the comparison time tv and the EMF phase angle cpEMK-tv for the comparison time tv

[0052] If an amount of the load angle LW is greater than 2TT, the load angle LW is preferably reduced in amount by 2TT, which is indicated in Fig. 2 by a modeling function M' shifted by 2TT as well as the resulting EMF phase angle cpEMK-tv' for the comparison time tv and the resulting load angle LW'.

[0053] List of reference symbols

[0054] 100 synchronous motor

[0055] 1 motor stator

[0056] 1.1 Winding system

[0057] 1.2 Winding

[0058] 1.3 Contact element

[0059] 2 Motor rotor

[0060] 3 Engine electronics

[0061] 3.1 Control unit

[0062] 3.2 Recording unit

[0063] 3.3 Data storage

[0064] 3.4 Evaluation unit

[0065] All Section

[0066] A2 Section

[0067] LW load angle

[0068] LW' load angle

[0069] M modeling function

[0070] M' shifted modeling function

[0071] P Oscillation period t.off Time of start of suspension of control t.end Time of end of evaluation t.on Time of end of suspension of control tv Comparison time

[0072] Uw-t Winding voltage curve cp-t Phase angle curve cpA-t Control voltage phase angle curve cpA-tv Control voltage phase angle for the

[0073] Comparison time tv cpEMK-t EMF phase angle curve cpEMK-tv EMF phase angle for the comparison time tv cpEMK-tv' EMF phase angle for the comparison time tv

Claims

PATENT CLAIMS 1. Method for determining a load angle (LW) of a synchronous motor (100), comprising the following method steps: - controlling a winding system (1.1) of the synchronous motor (100) to set a defined operating point of the synchronous motor (100), - Recording a winding voltage curve (llw-t) of the winding system (1.1), - Suspension of the control of the winding system (1.1), - Determining an electromotive force phase angle curve (cpEMK-t) by evaluating a section (A2) of the winding voltage curve (llw-t) recorded after the interruption of the control, - determining a model (M, M') to describe the determined electromotive force phase angle curve (cpEMK-t) within an oscillation period (P), - Determining an electromotive force phase angle (cpEMK-t. v) for a comparison time (tv) prior to the interruption of the control by extrapolating the electromotive force phase angle curve (cpEMK-t) using the determined model (M, M'), - determining a control voltage phase angle (cpA-tv) for the comparison time (tv) by evaluating a section (Al) of the winding voltage curve (llw-t) recorded before the interruption of the control, and - Determining the load angle (LW) based on the electromotive force phase angle (cpEMK-t. v) determined for the comparison time (tv) and the control voltage phase angle (cpA-tv) determined for the comparison time (tv).

2. The method according to claim 1, wherein the determined electromotive force phase angle curve (cpEMK-t) comprises a complete oscillation period (P).

3. The method according to claim 2, wherein the determination of the electromotive force phase angle curve (cpEMK-t) is started immediately after the interruption of the control, and wherein the determination of the electromotive force phase angle curve (cpEMK-t) is terminated as soon as the determined electromotive force phase angle curve (cpEMK-t) comprises a complete oscillation period (P).

4. Method according to one of the preceding claims, wherein the electromotive force phase angle curve (cpEMK-t) and / or the drive voltage phase angle (cpA-tv) is determined by means of a Fourier analysis of the corresponding section (A2, A1) of the winding voltage curve (Uw-T).

5. Method according to one of the preceding claims, wherein for each winding (1.2) of the winding system (1.1): - a winding-specific winding voltage curve (Uw-t) is recorded, - a winding-specific electromotive force Phase angle curve (cpEMK-t) is determined by evaluating the corresponding section (A2) of the recorded winding-specific winding voltage curve (Uw-t), - a winding-specific model (M, M') for describing the specific winding-specific electromotive force phase angle curve (cpEMK-t) within one oscillation period (P) is determined, - a winding-specific electromotive force phase angle (cpEMK-t. v) for a comparison time (tv) prior to the interruption of the control is determined by extrapolating the determined winding-specific electromotive force phase angle curve (cpEMK-t) using the determined winding-specific model (M, M'), - a winding-specific control voltage phase angle (cpA-tv) for the comparison time (tv) is determined by evaluating the corresponding section (Al) of the recorded winding-specific winding voltage curve (Uw-t), and - a winding-specific load angle (LW) is determined based on the winding-specific electromotive force phase angle (cpEMK-t. v) for the comparison time (tv) and the winding-specific control voltage phase angle (cpA-tv) for the comparison time (tv).

6. The method according to claim 5, wherein a total load angle is determined based on the winding-specific load angles (LW).

7. Method according to one of the preceding claims, wherein the control of the winding system (1.1) is suspended for a maximum duration of two oscillation period lengths of a control signal.

8. Synchronous motor (100) comprising: - a permanent magnet motor rotor (2), - an electromagnetic motor stator (1) with a winding system (1.1) with at least one winding (1.2), and - motor electronics (3) which are designed to control the winding system (1.1) for driving the motor rotor (2), characterized in that the motor electronics (3) are further designed: - to carry out a method according to one of claims 1 to 7 to determine a load angle (LW), and - to control the winding system (1.1) based on the determined load angle (LW).

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