CN114710068A - Permanent magnet synchronous motor control device and method - Google Patents

Abstract

The invention discloses a permanent magnet synchronous motor control device, comprising: the device comprises a permanent magnet synchronous motor, a rotary transformer, an angle calculation unit and a controller; and applying voltage and current to the permanent magnet synchronous motor through the controller to obtain the relative angle between each antipole zero point of the rotary transformer and the permanent magnet on the rotor of the permanent magnet synchronous motor, thereby identifying each antipole of the rotary transformer. The counter pole of the resolver can be accurately positioned so that the signal output from the resolver can be corrected using the stored error data of the resolver or the amplitude and angle of the specific frequency obtained by the frequency analyzing section to suppress the periodic error due to the assembly error, the shape error, or the like of the resolver with high accuracy.

Description

Permanent magnet synchronous motor control device and method

Technical Field

The invention relates to the field of control, in particular to a permanent magnet synchronous motor control device. The invention also discloses a control method of the permanent magnet synchronous motor.

Background

The permanent magnet synchronous motor has the advantages of simple structure, small volume, light weight, small loss and high efficiency. Compared with a direct current motor, the motor has no defects of a commutator, an electric brush and the like of the direct current motor; compared with an asynchronous motor, the asynchronous motor does not need reactive exciting current, so that the efficiency is high, the power factor is high, the moment-inertia ratio is large, the loss of stator current and stator resistance is reduced, the rotor parameter can be measured, and the control performance is good; compared with the common synchronous motor, the synchronous motor omits an excitation device, simplifies the structure and improves the efficiency. The system for dragging the permanent magnet synchronous motor can realize high-precision, high-dynamic performance and large-range speed regulation or positioning control, so that the permanent magnet synchronous motor is widely applied to a motor dragging system. Unlike asynchronous motors, the position of the permanent magnets on the rotor of a permanent magnet synchronous motor needs to be determined in advance or detected by a motor controller to operate properly. The controller of the permanent magnet synchronous motor generally records the angle of the permanent magnet of the rotor or automatically learns the angle of the permanent magnet after powering on every time when the power is off. The permanent magnet synchronous motor has corresponding electrical parameters according to the installation mode and the number of the rotor permanent magnets: the number of pole pairs is assumed to be M, that is, the mechanical angle changes from 0 to 360 degrees for 1 period every time the rotor rotates 1 circle, but the corresponding electrical angle of the rotor permanent magnet changes from 0 to 360 degrees for M periods.

Since the resolver has strong mechanical properties and excellent environmental resistance, it is widely used for detecting the rotation angle of the motor. However, in general, in the resolver, errors depending on the periodic variation of the rotational position are caused due to eccentricity or shape errors of the rotor, and these errors cause errors in the calculated angle. The resolver may be classified into 1-pair, 2-pair, 3-pair, … …, or N-pair resolver according to the number of cycles of the output signal. Generally, the more the number of pole pairs, the smaller the error of the periodic variation, and the higher the accuracy. In order to reduce the cost, more and more manufacturers select a few numbers of resolver pairs, and these periodically varying errors need to be overcome so as not to adversely affect the driving performance of the system. Therefore, various methods have been proposed to realize high-precision driving by suppressing the error described above on the control device side.

Japanese patent laid-open No. 11-27973 discloses the following technique: in addition to the detector for drive control, a high-precision detector is prepared, and a position detected by the detector for drive control and a position detected by the high-precision detector are compared in advance, and a detection error is calculated and stored in the control device. A rotation command is given to the motor to drive the motor to rotate, and the position detected by the detector is corrected with the stored detection error. Further, in this patent, as a method which is not suitable for a case where a high-precision detector is applied to calculate a detection error, the following technique is disclosed: a technique of rotating a motor at a sufficient speed that cannot be followed by a speed loop characteristic for controlling the motor, and calculating a detection error based on a detection signal in this state; and a technique of opening a speed loop, that is, rotating the motor without using a signal of the detector, and calculating a detection error based on a detection signal in this state.

The above patent shows a technique for recording a periodic error of a detector used for drive control for correcting a signal of the detector to realize high-precision driving. If the resolver has the number of pole pairs of 1, the angle calculated according to sine and cosine signals output by two phase output coils of the resolver corresponds to the mechanical angle one by one, the recorded periodic error also corresponds to the mechanical angle one by one, and error data needing to be corrected can be directly found from the stored error data according to the position calculated according to the sine and cosine signals output by the two phase output coils of the resolver.

If the pole pair number of the rotary transformer is not 1, but N pairs of poles (N is a positive integer not equal to 1), the angle (0-360 degrees) calculated according to sine and cosine signals output by two-phase output coils of the rotary transformer changes by N periods every 1 rotation of the rotor of the rotary transformer, and the N periods do not correspond to mechanical angles one by one. That is, if the control device is powered on or reset after power off, the mechanical angle of the rotor cannot be directly calculated according to the sine and cosine signals output by the two-phase output coils, and the stored error data corresponding to the mechanical angle one by one cannot be used for correction.

CN10720690A discloses an angle error correction device for a position detector, in which a frequency analysis unit performs frequency analysis on a detected motor current to obtain an amplitude and an angle of a specific frequency component corresponding to an angle error, and then corrects a rotational position based on the detected rotational position and the amplitude and the angle of the specific frequency obtained by the frequency analysis unit. In the case of the resolver, the position detector in this patent must position the counter electrode of the resolver in advance to correct the amplitude and angle of the specific frequency obtained by the frequency analyzer.

The simple solution to this problem is to add an extra switch, which is activated once per revolution of the resolver. The mechanical angle of the resolver during the switching operation is stored in advance, and the stored resolver periodic error data or the amplitude and angle of the specific frequency obtained by the frequency analysis unit are used to correct the resolver signal. However, this solution increases the cost of the control device and is not cost effective.

Disclosure of Invention

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a permanent magnet synchronous motor control apparatus capable of accurately positioning the counter electrode of a resolver so as to correct a signal output from the resolver using stored resolver error data or amplitude and angle of a specific frequency obtained by a frequency analyzing unit, thereby suppressing a periodic error caused by an assembly error, a shape error, or the like of the resolver with high accuracy.

In order to solve the above technical problem, the present invention discloses a permanent magnet synchronous motor control device, including: a permanent magnet synchronous motor including a rotor; the rotary transformer is arranged on a rotor shaft of the permanent magnet synchronous motor; the rotary transformer is used for outputting sine and cosine signals; the angle calculation unit is used for acquiring sine and cosine signals output by the rotary transformer and outputting angle signals corresponding to a permanent magnet synchronous motor rotor; the controller is used for receiving the angle signal output by the angle calculation unit and outputting voltage and current to control the speed and the torque of the permanent magnet synchronous motor so as to drive the rotor of the permanent magnet synchronous motor to rotate; and applying voltage and current to the permanent magnet synchronous motor through the controller to obtain the relative angle between each antipole zero point of the rotary transformer and the permanent magnet on the rotor of the permanent magnet synchronous motor, thereby identifying each antipole of the rotary transformer.

Preferably, the resolver includes: the excitation coil and the sine detection coil are used for detecting the rotary transformer rotor; the cosine detection coil is used for detecting the rotor of the rotary transformer; the resolver drives the excitation coil by an alternating-current excitation voltage, thereby outputting a sine signal amplitude-modulated according to the angle of the resolver rotor at an output terminal of the sine detection coil, and outputting a cosine signal amplitude-modulated according to the angle of the resolver rotor at an output terminal of the cosine detection coil.

Preferably, the number of pole pairs M of the permanent magnet synchronous motor and the number of pole pairs N of the resolver satisfy a relationship that M, 2M, 3M, … …, and (N-1) M are not divisible by N, and M and N are positive integers.

Preferably, the angle control unit includes: an excitation circuit for driving the excitation coil; the differential amplifier is used for differentially amplifying the voltage between the output ends of the sine detection coil and the voltage between the output ends of the cosine detection coil and outputting signals; the A/D converter is used for collecting the output signal of the differential amplifier and outputting a sine signal and a cosine signal; and the angle calculator is used for acquiring the sine signal and the cosine signal output by the A/D converter and outputting a pulse signal to the controller.

Preferably, the controller counts the pulse signals and forms a pulse count value corresponding to a mechanical angle of a rotor of the resolver.

Preferably, the permanent magnet synchronous motor control device further includes: and a detector for recording error data between the rotor position output by the resolver and the rotor position output by the detector.

Preferably, the detector is a high precision encoder.

Preferably, the angle calculation unit and the controller are two separate parts, or the angle calculation unit and the controller are integrated into one part.

The invention also discloses a control method of the permanent magnet synchronous motor, which is characterized by comprising the following steps:

carrying out frequency analysis on the current of the permanent magnet synchronous motor or the signal output by the rotary transformer through a controller to obtain the amplitude and the phase angle of specific frequency;

randomly appointing a zero point of a certain pair of poles as a starting point for recording periodic errors or frequency analysis, simultaneously learning the magnetic pole angle of the zero point of the pair of poles, presetting the angle as an angle theta, and storing the angle theta;

when the controller is powered off and then powered on or reset, magnetic pole learning is carried out on the output voltage and current of the permanent magnet synchronous motor, the motor is driven to rotate, and the magnetic pole angle of each antipodal zero point of the rotary transformer can be determined according to the learned magnetic pole angle;

and comparing the magnetic pole angle of each antipodal zero point of the rotary transformer with the stored angle theta, wherein the closest angle is the specified antipodal zero point before power failure or reset, and the antipodal positioning of the rotary transformer is also finished.

According to the invention, the controller applies voltage and current to the permanent magnet synchronous motor to obtain the relative angle between each pair of pole zero points of the resolver and the permanent magnet on the permanent magnet synchronous motor rotor, so that each pair of poles of the resolver is identified.

Drawings

Fig. 1 is a block diagram of an embodiment of a permanent magnet synchronous motor control device according to the present invention.

Fig. 2 is a waveform diagram of waveforms of respective coils of the resolver of fig. 1.

Fig. 3 is a corresponding relationship diagram of each signal of the angle calculating unit in fig. 1.

Fig. 4 is a block diagram showing a second configuration of the permanent magnet synchronous motor control device according to the present invention.

Fig. 5 is a comparison graph of the count values of the resolver and the detector output a signal or B signal in the second embodiment of the permanent magnet synchronous motor control apparatus according to the present invention.

Fig. 6 is a graph of deviation error data of the count value 1 and the count value 2 in fig. 4 recorded by one rotation of the rotary transformer in the second embodiment of the permanent magnet synchronous motor control device according to the present invention.

Fig. 7 is a magnetic pole angle diagram of a zero point of a certain counter pole corresponding to an error data start point learned by magnetic pole learning in the second embodiment of the permanent magnet synchronous motor control device according to the present invention.

Description of the reference numerals

1 rotary transformer 2 field coil

3 cosine detection coil and 4 sine detection coil

5 exciting circuit 6 differential amplifier

7 angle calculating unit 8A/D converter

9 resolver rotor 10 angle calculator

11 controller 12 permanent magnet synchronous motor

13 Detector

Detailed Description

Hereinafter, an embodiment of the control device according to the present invention will be described in detail with reference to the drawings. The present invention is not limited to the present embodiment.

Example one

Fig. 1 is a block diagram showing a configuration of a first embodiment of the present invention. In the figure, a resolver 1 is composed of an excitation coil 2, a sine detection coil 4 that detects a resolver rotor 9, and a cosine detection coil 3 that detects the resolver rotor 9. By driving the excitation coil 2 with an ac excitation voltage indicated by a curve (a) in fig. 2, a sine signal amplitude-modulated by the angle of the resolver rotor 9 shown in (c) in fig. 2 is output to the output terminal of the sine detection coil 4, and a cosine signal amplitude-modulated by the angle of the resolver rotor 9 shown in (b) in fig. 2 is output to the output terminal of the cosine detection coil 3. Here, the horizontal axis in fig. 2 represents the mechanical angle of the resolver rotor 9.

Next, a method of processing the signal output from the resolver 1 will be described. In fig. 1, an exciting coil 2 of a rotary transformer 1 is driven by an exciting circuit 5 with an ac voltage signal shown in fig. 2 (a). The voltage between the two output terminals of the sine detection coil 4 and the voltage between the two output terminals of the cosine detection coil 3 of the resolver 1 are differentially amplified by a differential amplifier 6 and output to an a/D converter 8 (i.e., an analog-digital converter). The a/D converter 8 (i.e., an analog-to-digital converter) collects peak points of the sine value and the cosine value represented in fig. 2 (c) and fig. 2 (b), and obtains sine and cosine signals as shown in D and e in fig. 3.

The angle calculator 10 in fig. 1 outputs an a signal, a B signal, and a Z signal corresponding to the pulse signal a1, the pulse signal B2, and the pulse signal Z3 shown in fig. 3, based on the sine signal and the cosine signal output from the a/D converter 8. The controller 11 counts the a signal and the B signal to form a pulse count value f like a sawtooth wave as shown in fig. 3, and corresponds to the mechanical angle of the resolver rotor 9, and also corresponds to the mechanical angle of the permanent magnet synchronous motor rotor because the resolver rotor and the permanent magnet synchronous motor rotor are coaxially mounted.

As shown in fig. 1, the shape of the rotor 9 of the rotary transformer in the present embodiment has 4 waveforms, which indicates that the rotary transformer is 4 pairs of poles, and the signals output by the sine coil 4 and the cosine coil 3 in fig. 1 will change for 4 cycles per rotation, such as the peak values of the waveforms shown in fig. 2 (b) and fig. 2 (c), and the sine and cosine waveforms output by the a/D converter 8 in the angle calculation unit 7 in fig. 1 will also change for 4 cycles. The pulse signal Z3 in fig. 3 has 4 pulses, each pulse corresponding to the zero point of the sinusoidal waveform d in fig. 3 and also corresponding to the zero point of the pulse count value f in fig. 3, the 4 zero points corresponding to the zero points of the respective poles of the resolver. If any Z signal is designated as the zero position of the 1 st antipode, the Z phase signals of the 2 nd, 3 rd and 4 th antipodes follow, and when the Z phase signals run in the reverse direction, the Z phase signals of the 4 th, 3 rd and 2 nd antipodes follow. Such a Z signal changes 4 times per revolution, and so on.

The angle calculation unit 7 and the controller 11 of the present embodiment are two separate components, but may be integrated, and the present invention is not limited thereto.

In this embodiment, taking an example in which the resolver is an N-pair pole and the permanent magnet synchronous motor is an M-pair pole, N cannot be divided by M, 2M, 3M, … …, and (N-1) M. If the zero point of a certain antipole of the rotary transformer is aligned with the permanent magnet field of the rotor of the permanent magnet synchronous motor, namely the angle of the magnetic pole of the zero point of the antipole is 0 degree, the subsequent N-1 pairsThe angle of the magnetic pole at the pole zero point is respectively

Since M, 2M, 3M, and … … (N-1) M cannot divide N evenly, the magnetic pole angles of the N pole zero points are different from each other. Under the condition, when measuring the periodic error of the rotary transformer or analyzing the amplitude and the angle of a specific frequency, the zero point of a certain pair of poles is arbitrarily designated as the starting point for recording the periodic error or analyzing the frequency, and the magnetic pole angle of the zero point of the pair of poles is learned, assumed to be theta, and stored. The magnetic pole angles of the subsequent N-1 antipodal zero points are respectively

When the controller is powered off and then powered on or reset, firstly, magnetic pole learning is carried out on the output voltage and current of the permanent magnet synchronous motor, the motor is driven to rotate, the magnetic pole angle of each antipode zero point of the rotary transformer can be determined according to the learned magnetic pole angle, the magnetic pole angle is compared with the stored angle theta, the closest angle is the appointed antipode zero point before power off or reset, the antipode positioning of the rotary transformer is completed, and then the stored periodic error data or the amplitude and the angle of a specific frequency can be used for calibrating the signal of the rotary transformer so as to restrain the periodic error generated by the assembly error or the shape error of the rotary transformer.

Example two

Fig. 4 is a block diagram of a second structure of an embodiment of a control device of a permanent magnet synchronous motor, where 12 is the permanent magnet synchronous motor, a resolver 1 is installed on a rotor shaft of the permanent magnet synchronous motor 12, an angle calculation unit 7 outputs an angle signal corresponding to a rotor of the permanent magnet synchronous motor 12 by collecting sine and cosine signals output by the resolver and outputs the angle signal to a controller 11, and the controller 11 outputs a voltage to control the speed and the torque of the permanent magnet synchronous motor 12 and drive the rotor to rotate. To satisfy the principle that M, 2M, 3M, … …, and (N-1) M cannot divide N, the present embodiment selects a 4-pole resolver and a 9-pole permanent magnet synchronous motor, so that 9, 2 × 9, and 3 × 9 cannot divide 4.

In order to record the error of the resolver 1 caused by the eccentricity or the shape error of the rotor, which depends on the periodic variation of the rotational position, a high-precision detector 13, such as a photoelectric encoder, is additionally provided on the rotor shaft of the permanent magnet synchronous motor 12 in this example. Of course, the detector 13 does not necessarily need to be mounted on the same shaft as the resolver 1, and may be any detector as long as it can accurately detect the rotor angle of the permanent magnet synchronous motor 12.

For comparison, the angle calculating unit 7 is configured to output 2048 a signals and B signals for each pair of poles of the resolver, 8192 a signals and B signals for each turn of 4 pairs of poles, and the detector 13 is a high-precision encoder, for example, a photoelectric encoder that outputs 8192 a signals and B signals for each turn.

The controller 11 drives the rotor of the permanent magnet synchronous motor 12 to rotate, the counting value of the A signal or the B signal output by the resolver 1 and the detector 13 is compared as shown in fig. 5, the counting value g is the counting value of the output pulse of the detector 13 in fig. 4, one circle of 8192 pulses, the counting value h is the counting value of the output pulse of the angle calculation 7 in fig. 4, 2048 pulses are output for each pair of poles, and 8192 pulses are output for one circle. The counting value h corresponding to the output signal of the resolver 1 in fig. 4 has a significant fluctuation relative to the counting value g due to the eccentricity or the shape error of the rotor.

And (3) randomly finding the zero point of a certain antipode as a starting point for recording error data, rotating the rotary transformer for one turn, and recording the deviation value of the count value g and the count value h in the graph 4, such as the graph 6. In order to improve the accuracy, several more circles may be recorded, and the error data may be averaged for each angle. These error data need to be saved, and the detector 13 in fig. 4 can be removed after the error data is saved.

Next, magnetic pole learning is entered. In fig. 4, the rotor of the resolver 1 is coaxially mounted with the rotor of the permanent magnet synchronous motor 12, and the relative positions of the rotor thereof and the permanent magnets on the rotor of the permanent magnet synchronous motor 12 are determined if the resolver 1 is not replaced any more. Learning the magnetic pole angle theta of the zero point of a certain antipode corresponding to the initial point of the error data through magnetic poles, as shown in fig. 7, outputting a count value i of pulses for the resolver, wherein each pair of poles corresponds to 2048 pulses, each ring of 8192 pulses, the magnetic pole angle j of the permanent magnet synchronous motor is 9 antipodes, the magnetic pole angle of each ring changes from 0 to 360 degrees for 9 times, the magnetic pole angle corresponding to the zero point of the first antipode of the resolver is theta, the magnetic pole angles corresponding to the zero points of the other 3 antipodes are respectively 90 degrees + theta, 180 degrees + theta and 270 degrees + theta, and the magnetic pole angles corresponding to the 4 antipode zero points are different from each other.

After the system is powered on or reset after power failure, the controller 11 cannot recognize the corresponding relationship between the Z signal output by the detector and the zero point of the opposite pole determined during the last magnetic pole learning, and cannot correct the resolver signal by using the stored periodic error data to eliminate the periodic error. At this time, the magnetic pole learning mode needs to be entered again, the motor is driven to rotate, after the magnetic pole learning is completed, the magnetic pole angle of each antipode zero point can be directly calculated and compared with theta, the Z signal with the minimum deviation with the theta is the starting point of the last recorded error data, and antipodes corresponding to the other Z signals are determined.

After the order of the opposite poles is determined, the stored error data of the rotary transformer can be applied to compensate signals of the rotary transformer, and the running performance of the elevator is improved.

The magnetic pole learning of the permanent magnet synchronous motor is to utilize the saturation effect of the permanent magnet of the rotor to output voltage and current to the stator coil and determine the position of the permanent magnet on the rotor, and then the speed and the torque of the permanent magnet synchronous motor can be controlled.

In this embodiment, a detector 13 is additionally provided on the rotor of the permanent magnet synchronous motor 12 to record error data between the position of the rotor output from the resolver 1 and the position of the rotor output from the detector 13. Of course, the detector 13 may not be added, and the controller 11 may perform frequency analysis on the current of the permanent magnet synchronous motor 12 or the signal output by the resolver 3 to obtain the amplitude and the phase angle of a specific frequency, and the determination method of the starting position point is the same as that of the aforementioned arbitrary zero point of a certain antipole. Those skilled in the art will appreciate that the present invention is not so limited.

The foregoing embodiments illustrate and describe the principles and general features of the present invention and its advantages. It will be understood by those skilled in the art that the present invention is not limited by the embodiments described above, which are given by way of illustration of the principles of the invention and are not to be taken as limiting the scope of the invention in any way, and that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

Claims (9)

1. A permanent magnet synchronous motor control apparatus, comprising:

a permanent magnet synchronous motor including a rotor;

the rotary transformer is arranged on a rotor shaft of the permanent magnet synchronous motor; the rotary transformer is used for outputting sine and cosine signals;

the angle calculation unit is used for acquiring sine and cosine signals output by the rotary transformer and outputting angle signals corresponding to a permanent magnet synchronous motor rotor;

the controller is used for receiving the angle signal output by the angle calculation unit, outputting voltage and current to control the speed and the moment of the permanent magnet synchronous motor and driving a rotor of the permanent magnet synchronous motor to rotate;

and applying voltage and current to the permanent magnet synchronous motor through the controller to obtain the relative angle between each antipole zero point of the rotary transformer and the permanent magnet on the rotor of the permanent magnet synchronous motor, thereby identifying each antipole of the rotary transformer.

2. The permanent magnet synchronous motor control apparatus of claim 1, wherein the resolver comprises:

an excitation coil is provided on the outer surface of the casing,

the sine detection coil is used for detecting the rotary transformer rotor;

the cosine detection coil is used for detecting the rotor of the rotary transformer;

the resolver drives the excitation coil by an alternating-current excitation voltage, thereby outputting a sine signal amplitude-modulated according to the angle of the resolver rotor at an output terminal of the sine detection coil, and outputting a cosine signal amplitude-modulated according to the angle of the resolver rotor at an output terminal of the cosine detection coil.

3. The control device of a permanent magnet synchronous motor according to claim 1, wherein a pole pair number M of said permanent magnet synchronous motor and a pole pair number N of said resolver satisfy a relationship that M, 2M, 3M, … …, and (N-1) M are not divisible by N, and M and N are positive integers.

4. The permanent magnet synchronous motor control device according to claim 1, wherein the angle control unit includes:

an excitation circuit for driving the excitation coil;

the differential amplifier is used for differentially amplifying the voltage between the output ends of the sine detection coil and the cosine detection coil and outputting signals;

the A/D converter is used for collecting the output signal of the differential amplifier and outputting a sine signal and a cosine signal;

and the angle calculator is used for acquiring the sine signal and the cosine signal output by the A/D converter and outputting a pulse signal to the controller.

5. The permanent magnet synchronous motor control apparatus of claim 4, wherein the controller counts the pulse signals and forms a pulse count value corresponding to a mechanical angle of a rotor of the resolver.

6. The permanent magnet synchronous motor control apparatus of claim 1, further comprising:

and a detector for recording error data between the rotor position output by the resolver and the rotor position output by the detector.

7. The permanent magnet synchronous motor control apparatus of claim 6, wherein the detector is a high precision encoder.

8. The permanent magnet synchronous motor control apparatus of claim 1, wherein the angle calculation unit and the controller are two separate parts or the angle calculation unit and the controller are integrated into one part.

9. A permanent magnet synchronous motor control method using the permanent magnet synchronous motor control apparatus according to one of claims 1 to 8, characterized by comprising the steps of:

carrying out frequency analysis on the current of the permanent magnet synchronous motor or the signal output by the rotary transformer through a controller to obtain the amplitude and the phase angle of specific frequency;

randomly appointing a zero point of a certain pair of poles as a starting point for recording periodic errors or frequency analysis, simultaneously learning the magnetic pole angle of the zero point of the pair of poles, presetting the angle as an angle theta, and storing the angle theta;

when the controller is powered off and then powered on or reset, magnetic pole learning is carried out on the output voltage and current of the permanent magnet synchronous motor, the motor is driven to rotate, and the magnetic pole angle of each antipodal zero point of the rotary transformer can be determined according to the learned magnetic pole angle;

and comparing the magnetic pole angle of each antipodal zero point of the rotary transformer with the stored angle theta, wherein the closest angle is the specified antipodal zero point before power failure or reset, and the antipodal positioning of the rotary transformer is also finished.

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