阅读说明：本技术 消除轮毂电机转矩脉动的控制绕组补偿电流快速整定方法 (Control winding compensation current rapid setting method for eliminating torque pulsation of hub motor ) 是由 王子辉 卢琴芬 于 2019-10-21 设计创作，主要内容包括：本发明公开了一种消除轮毂电机转矩脉动的控制绕组补偿电流快速整定方法,包括以下步骤：步骤S1,采集转矩信号；步骤S2,提取转矩谐波；步骤S3,整定电流频率和相位：根据转矩谐波中的频率和相位特征,精确计算得到补偿电流的频率和相位；步骤S4,整定电流幅值：以转矩中特定频率的谐波幅值为控制对象,采用二次曲线拟合的电流幅值自适应迭代法,以跟踪真实的转矩-电流曲线,对电流幅值进行微调,使目标谐波转矩幅值趋向于0；步骤S5,输出补偿电流。本发明基于单相补偿绕组结构以及电机电磁原理的频率/相位直接求解方法,具有计算量小、精度高的优点,基于二次曲线拟合算法的电流幅值整定方法具有收敛快速以及对电机未知参数不敏感的鲁棒性优势。(The invention discloses a control winding compensation current rapid setting method for eliminating torque pulsation of a hub motor, which comprises the following steps of: step S1, collecting a torque signal; step S2, extracting a torque harmonic; step S3, setting current frequency and phase: accurately calculating the frequency and the phase of the compensating current according to the frequency and phase characteristics in the torque harmonic; step S4, setting the current amplitude: the harmonic amplitude of a specific frequency in the torque is taken as a control object, a current amplitude self-adaptive iteration method of quadratic curve fitting is adopted to track a real torque-current curve, and the current amplitude is finely adjusted to make the target harmonic torque amplitude tend to 0; in step S5, the compensation current is output. The frequency/phase direct solving method based on the single-phase compensation winding structure and the motor electromagnetic principle has the advantages of small calculated amount and high precision, and the current amplitude setting method based on the quadratic curve fitting algorithm has the advantages of quick convergence and robustness and insensitivity to unknown parameters of the motor.)

1. A control winding compensation current rapid setting method for eliminating torque pulsation of a hub motor is controlled by a hub motor harmonic torque compensation system, the hub motor harmonic torque compensation system comprises a control winding, a speed measurement encoder, a torque sensor, a signal acquisition circuit, a core control unit and a drive circuit, wherein the hub motor is an outer rotor permanent magnet synchronous motor with an inner stator, the control winding is arranged on the inner stator, the drive circuit is provided with a drive bridge arm, the drive bridge arm is connected with the control winding in series, the speed measurement encoder or the torque sensor is connected with the outer rotor of the hub motor in a coupling mode, the signal acquisition circuit is connected with the speed measurement encoder, and the drive circuit is connected with the core control unit.

Step S1, collecting a torque signal: the instantaneous rotating speed of the motor is measured by a speed measuring encoder, the core control unit calculates to obtain the output electromagnetic torque of the hub motor, or the output torque is directly measured by a torque sensor, and the core control unit receives a torque signal;

step S2, extracting a torque harmonic: analyzing the motor torque by using an FFT (fast Fourier transform) method, extracting harmonic components in the torque according to frequency, and calibrating the frequency, amplitude and phase;

step S3, setting current frequency and phase: based on the electromagnetic principle of the motor and the control winding structure, the frequency and the phase of the compensation current are accurately calculated according to the frequency and the phase characteristics in the torque harmonic;

step S4, setting the current amplitude: the harmonic amplitude of a specific frequency in the torque is taken as a control object, a current amplitude self-adaptive iterative method of quadratic curve fitting is adopted to track a real torque-current curve, the effect of quickly weakening the torque amplitude is realized, the target torque is continuously tracked after weakening, and the current amplitude is finely adjusted to make the target harmonic torque amplitude tend to 0;

step S5, outputting a compensation current: and the core control unit takes a compensation current expected value as an input quantity by a current closed loop according to the frequency, the phase and the amplitude of the compensation current obtained by setting, takes the real-time current of the control winding acquired by the signal acquisition circuit as a closed-loop control signal, outputs a PWM (pulse width modulation) driving signal to the driving bridge arm, and performs closed-loop control on the compensation current of the control winding.

2. The method for rapidly setting the control winding compensating current for eliminating the torque ripple of the in-wheel motor according to claim 1, wherein the calculation formula of the electromagnetic torque output by the in-wheel motor calculated by the core control unit in the step S1 is as follows:

wherein omega is the mechanical rotating speed of the motor, J is the moment of inertia, B is the friction coefficient, T_LIs the load torque.

3. The method for rapidly setting the control winding compensating current for eliminating the torque ripple of the in-wheel motor according to claim 1, wherein after the fast fourier transform in the step S2, only the frequency, amplitude and phase characteristics of the torque harmonics, except for 0-th order effective electromagnetic torque, with order lower than 10-th order, are calibrated.

4. The method for rapidly setting the control winding compensation current for eliminating the torque ripple of the in-wheel motor according to claim 1, wherein the calculation formula of the characteristic parameter of the control winding compensation current in the step S3 is as follows:

wherein n, A_n，θ_nOrder, amplitude and phase, k, A, of the n-th order harmonics obtained for the fast Fourier transform in said step S2_k，θ_kTo compensate for the order, magnitude and phase of the current, the law of the current change with time t can be expressed as

I＝I_kcos(kpωt+θ_k) (3)

Wherein p is the number of pole pairs of the motor.

5. The method for rapidly setting the control winding compensating current for eliminating the torque ripple of the in-wheel motor according to claim 1, wherein the step S4 comprises the following steps:

s41: initial current injection, wherein the core control unit and the driving circuit inject three times of test current into the control winding, and the injection rule is expressed as follows:

I_P+1＝I_P+λ₁ΔI (4)

wherein I is the amplitude of the compensation current, P is the test frequency, lambda 1 is a step coefficient with a value of 1, and delta I is the change step of the adjacent two test currents,

wherein, I_sRated current for fundamental frequency of motor, A₀，A_nThe amplitudes of the torque direct current quantity and the n-th-order torque harmonic wave are respectively; the amplitude values of the tertiary current are arranged from small to large and are marked as I_P1，I_P2，I_P3；

S42: solving the harmonic torque gradient, repeating the steps S1-S2, and obtaining the residual harmonic torque amplitude after the third test current injection by using FFT Fourier transform, wherein the residual harmonic torque amplitude is marked as A_P1，A_P2，A_P3According to the gradient formula between two adjacent points:

judging whether the condition is satisfied

s43: fitting a quadratic curve, and recording the last three test currents as I_P1，I_P2，I_P3And fitting the relation between the torque and the current by using a quadratic equation, wherein the relation is expressed as follows:

solving the coefficients a, b and c of the fitted curve, and obtaining the extreme value coordinate points of the quadratic curve, which are expressed as:

s44: judging a convergence condition, and comparing the current amplitude I calculated in the step S43_P4Injecting a control winding, repeating the steps S1-S2 to obtain the torque harmonic amplitude A_P4Judging whether an iterative convergence condition I is satisfied_P4-I_P2< ε; if not, returning to the step S43 for iteration again, and if yes, entering the step S45;

s45: current trimming with I_P4For the initial value of iteration, the amplitude of the compensation current is finely adjusted, and the relation is expressed as:

I_P+1＝I_P+λ₂ΔI (7)

wherein λ is₂For fine-tuning the step-size coefficient and satisfying lambda₂＝λ₁Then, the current amplitude I calculated in the formula (7) is used_P5Injecting a control winding, repeating the steps S1-S2 to obtain the torque harmonic amplitude A_P5Judging whether or not the condition A is satisfied_P5＜A_P4；

If not, let λ₂＝-λ₂Returning to step S45 for reiteration; if satisfied, maintaining λ₂And returning to the step S45 for reiteration without change.

6. The method for rapidly setting the compensation current of the control winding for eliminating the torque ripple of the in-wheel motor according to any one of claims 1 to 5, wherein the compensation winding is composed of two groups of single-phase coils which are connected in parallel and have the same number of turns, the inner stator comprises a stator core, the stator core is provided with two groups of stator slots in the vertical direction, one group of single-phase coils is nested in each group of stator slots, and the two groups of single-phase coils are arranged in the same direction.

Technical Field

The invention relates to the technical field of electric automobiles driven by hub motors, in particular to the field of hub motor drive control.

Background

The adoption of distributed hub motor driving is the future development direction of light electric automobiles. The hub motor of the electric automobile belongs to an outer rotor permanent magnet synchronous motor, has simple structure and flexible control, but dynamic loads (such as vehicle body bumping) are directly applied to vehicle wheels and the motor during driving, so that obvious motor torque fluctuation is caused, and the driving comfort and safety are influenced.

At present, the published patent achievement in the aspect of controlling the torque ripple of the outer rotor hub motor of the electric automobile is less, and the prior technical scheme is divided into two types aiming at the torque ripple control of the conventional inner rotor permanent magnet synchronous motor: the first type is motor body structure optimization, such as stator/rotor skewed slot or skewed pole, magnetic pole shape optimization, fractional slot structure, pole arc coefficient combination optimization and the like (such as CN201910334884.7, CN201810301554.3), and the method is suitable for modifying the physical structure of the motor in the design stage so as to weaken specific static torque harmonic waves, and once the structure is designed and shaped, other dynamic torque harmonic waves (such as eccentricity caused by the manufacturing process, deformation eccentricity under external force impact, asymmetric stator current and the like) cannot be weakened. The second category is to suppress torque ripple using a motor control strategy, i.e., by controlling the voltage or current waveform applied to the stator windings. For example, patent CN201110054889.8 discloses a method for suppressing torque ripple of a permanent magnet motor based on direct torque control, which directly injects an additional harmonic current based on a given electromagnetic torque for a positioning harmonic torque existing in a motor body structure, so that the amplitude of the additional harmonic torque is equal to that of a fundamental component and a higher harmonic component in the positioning torque, the phases of the additional harmonic current are opposite, and the additional harmonic current and the higher harmonic component cancel each other out, thereby achieving suppression of torque ripple. Patent cn201910127436.x discloses a torque ripple suppression method and system for a permanent magnet generator, which uses torque ripple as a control target, automatically adjusts the injection current harmonic given quantity through a current closed loop, and superposes the injection current harmonic given quantity on a current loop of a controller to realize compensated current tracking, thereby suppressing the torque ripple of a motor. In addition, CN201511006191.3, a hub-side electromagnetic damping control method for an electric vehicle driven by a hub motor, and CN201710815905.8, a method for eliminating electromagnetic torque ripple of a hub motor for an electric vehicle, which have been published and authorized, also belong to a scheme for suppressing torque ripple by using a motor control strategy.

Further, the voltage or current compensation injection manner in the second scheme can be divided into main winding injection or additional winding injection. The main winding current injection scheme does not need to modify a motor winding structure, but the signal noise coupling problem exists because the harmonic current signal needs to be filtered and extracted from the main current signal, the signal processing process is easily influenced by the operating condition, and the anti-interference capability is limited. The scheme of additional winding current injection needs to add an additional control winding in the motor stator, the current extraction and control processes are independent relative to the main winding, the control algorithm is simple, the robustness is strong, and the torque suppression effect is better.

As described above, the first type is a torque ripple suppression scheme based on structural optimization of a motor body, and is suitable for weakening specific static torque harmonics in a motor design stage, once the motor structure cannot be changed after design and sizing, dynamic torque harmonics cannot be weakened, flexibility is not strong, requirements on a motor processing process are high, and manufacturing cost is increased. The second type of torque ripple suppression scheme based on the control strategy has strong flexibility, does not increase the design and manufacturing cost of the motor, but has more complex control process, higher requirement on the performance of the controller and certain influence on the running efficiency of the motor. In general, the second method is superior to the first method.

However, the current setting method adopted in the electromagnetic damping control method on the hub side of the electric vehicle driven by the hub motor of CN201511006191.3 has the following defects: and extracting the torque harmonic measured value through FFT spectral characteristics, carrying out differential operation on the obtained amplitude and the expected value 0, and outputting the expected value of the compensation current required by the compensation winding through a PI regulator with negative feedback characteristics. The method does not consider duality of FFT amplitude-frequency conversion, namely harmonic torque still represents the same amplitude-frequency characteristic as under-compensation under the over-compensation condition, so that the PI regulator works in a positive feedback state (namely the larger the compensation current amplitude is, the larger the absolute amplitude of negative harmonic torque is, the larger the current output by the regulator is), and finally the effect of stably converging to a 0 expected value cannot be realized. Therefore, the tuning method of the patent is only suitable for a slow adjustment control process under the condition of torque under-compensation, cannot realize convergence control after over-compensation, and has large system robustness limitation.

Disclosure of Invention

The invention aims to solve the technical problem of providing a control winding compensation current quick setting method for eliminating the torque pulsation of a hub motor, injecting a setting current into a control winding, optimizing the setting process of the frequency, the phase and the amplitude of the control current, realizing the instantaneous setting of the current frequency/phase, and realizing a current amplitude setting mechanism with under/over modulation bidirectional convergence characteristics, so that the electromagnetic torque pulsation phenomenon of the hub motor can be quickly eliminated, and the control robustness is good.

In order to solve the technical problems, the invention adopts the following technical scheme: a control winding compensation current rapid setting method for eliminating torque pulsation of a hub motor is controlled by a hub motor harmonic torque compensation system, the hub motor harmonic torque compensation system comprises a control winding, a speed measurement encoder, a torque sensor, a signal acquisition circuit, a core control unit and a drive circuit, wherein the hub motor is an outer rotor permanent magnet synchronous motor with an inner stator, the control winding is arranged on the inner stator, the drive circuit is provided with a drive bridge arm, the drive bridge arm is connected with the control winding in series, the speed measurement encoder or the torque sensor is connected with the outer rotor of the hub motor in a coupling mode, the signal acquisition circuit is connected with the speed measurement encoder, and the drive circuit is connected with the core control unit.

Step S1, collecting a torque signal: the instantaneous rotating speed of the motor is measured by a speed measuring encoder, the core control unit calculates to obtain the output electromagnetic torque of the hub motor, or the output torque is directly measured by a torque sensor, and the core control unit receives a torque signal;

step S2, extracting a torque harmonic: analyzing the motor torque by using an FFT (fast Fourier transform) method, extracting harmonic components in the torque according to frequency, and calibrating the frequency, amplitude and phase;

step S3, setting current frequency and phase: based on the electromagnetic principle of the motor and the control winding structure, the frequency and the phase of the compensation current are accurately calculated according to the frequency and the phase characteristics in the torque harmonic;

step S4, setting the current amplitude: the harmonic amplitude of a specific frequency in the torque is taken as a control object, a current amplitude self-adaptive iterative method of quadratic curve fitting is adopted to track a real torque-current curve, the effect of quickly weakening the torque amplitude is realized, the target torque is continuously tracked after weakening, and the current amplitude is finely adjusted to make the target harmonic torque amplitude tend to 0;

step S5, outputting a compensation current: and the core control unit takes a compensation current expected value as an input quantity by a current closed loop according to the frequency, the phase and the amplitude of the compensation current obtained by setting, takes the real-time current of the control winding acquired by the signal acquisition circuit as a closed-loop control signal, outputs a PWM (pulse width modulation) driving signal to the driving bridge arm, and performs closed-loop control on the compensation current of the control winding.

The invention has the beneficial effects that:

the invention is matched with a corresponding control winding and an independent power supply, firstly, the frequency spectrum characteristics of the electromagnetic torque of the motor are analyzed, then, the compensation current is quickly set according to the amplitude-frequency characteristics of the torque harmonic wave, so that the generated compensation torque is equal to the original higher harmonic wave component in amplitude and opposite in phase, and the compensation torque and the original higher harmonic wave component are mutually offset, thereby realizing the effect of inhibiting torque pulsation.

The frequency/phase direct solving method based on the single-phase compensation winding structure and the motor electromagnetic principle has the advantages of small calculated amount and high precision, and the current amplitude setting method based on the quadratic curve fitting algorithm has the advantages of rapid convergence and robustness and insensitivity to unknown parameters of the motor.

In addition, the method can simultaneously solve and track a plurality of control currents with different frequencies, provides a current closed-loop control signal with optimal phase and amplitude under various frequencies, realizes synchronous and rapid compensation of harmonic torques with various frequencies, and has obvious speed advantages and effect advantages compared with the conventional successive compensation scheme.

The specific technical effects of the present invention will be further explained in the detailed description.

Drawings

The invention is further described below in conjunction with the appended drawings and the detailed description:

FIG. 1 is an electrical diagram of a torque compensation system;

FIG. 2 is a signal flow diagram of a torque compensation system;

FIG. 3 is a flowchart illustrating the operational steps of the torque compensation system;

FIG. 4 is a flow chart of current amplitude setting steps;

FIG. 5 is a schematic diagram of a current magnitude curve fitting process;

FIG. 6 is a cross-sectional view of the in-wheel motor with the compensating winding installed;

reference numerals:

1-vehicle power supply, 1 a-storage battery pack, 1 b-power converter;

2-a motor controller, 2 a-a signal acquisition circuit, 2 b-a core control unit, 2 c-a drive circuit,

3-hub motor, 31-hub motor outer rotor, 31 a-permanent magnet, 32-air gap, 33-hub motor inner stator, 34-bearing, 35-motor shaft;

4-a compensation winding;

5-speed measuring encoder/moment sensor.

Detailed Description

The following detailed description of embodiments of the invention refers to the accompanying drawings.

As shown in fig. 1, an electric vehicle is provided with a vehicle-mounted power supply 1, which can supply power to a hub motor, and the vehicle-mounted power supply 1 includes a battery pack 1a and a power converter 1 b.

As shown in fig. 6, the hub motor 3 with the compensation winding installed thereon includes an outer rotor 31, an inner stator 33, a bearing 34, a motor shaft 35 and an end cover 36, the inner stator 33 is disposed on the inner periphery of the outer rotor 31, the end cover 36 is fixedly connected with the outer rotor 31, the inner stator 33 is fixedly connected with the motor shaft 35, the bearing 34 is disposed on the end cover 36, the motor shaft 35 is cooperatively connected with the bearing 34, a permanent magnet 31a is disposed on the inner peripheral surface of the outer rotor 31, the hub motor 3 is an outer rotor permanent magnet synchronous motor with the inner stator, an air gap 32 is provided between the inner peripheral surface of the outer rotor 31 and the outer peripheral surface of the inner stator 33, and when a vertical load of the vehicle body weight is applied to the bearing, the deformation of the bearing 34 causes the inner stator 33 and.

To compensate for the electromagnetic torque ripple caused by the air gap field distortion, the present embodiment employs an additional winding current injection scheme, adding an additional control winding 4 in the motor stator. The inner stator comprises a stator core, the stator core is provided with two groups of stator slots in the vertical direction, a group of single-phase coils are nested in each group of stator slots, and the two groups of single-phase coils are arranged in the same direction. Because the two groups of single-phase coils are arranged in the vertical direction of the stator core, the two groups of single-phase coils can generate compensation torque with the same amplitude and the opposite phase as the harmonic electromagnetic torque after being electrified, and the compensation of torque pulsation is realized.

In order to realize the rapid setting of the compensation current of the control winding, a hub motor harmonic torque compensation system is adopted, and as shown in fig. 1 and fig. 2, the hub motor harmonic torque compensation system comprises a speed measurement encoder/torque sensor 5, a signal acquisition circuit 2a, a core control unit 2b and a drive circuit 2c, wherein the drive circuit is provided with a drive bridge arm, the drive bridge arm is connected with the control winding in series, the speed measurement encoder or the torque sensor is coupled with an outer rotor of the hub motor, the signal acquisition circuit is connected with the speed measurement encoder, and the drive circuit is connected with the core control unit.

In order to improve the circuit integration and reduce the circuit volume, the signal acquisition circuit 2a, the core control unit 2b and the drive circuit 2c are preferably integrated into a whole to form the motor controller 2, the storage battery 1a is connected with the drive circuit 2 through a direct current bus to output high-voltage direct current, the power converter 1b acquires high-voltage direct current voltage from the direct current bus of the drive circuit 2 and then reduces the voltage to low-voltage direct current, the output end of the power converter 1b is connected with the signal acquisition circuit 2a, the core control unit 2b and the drive circuit 2c, according to the rated voltage requirements of the signal acquisition circuit 2a, the core control unit 2b and the drive circuit 2c, the power converter 1b adopts a voltage reduction device of the DC-DC power converter to convert high-voltage direct current into low-voltage direct current of 15V and 5V to supply power to the signal acquisition circuit 2a, the core control unit 2b and the drive circuit 2 c.

In order to further improve the circuit integration efficiency, the rotating speed and the torque of the hub motor 3 are also controlled by the motor controller 2, the driving circuit 2c is provided with a three-phase bridge arm, the hub motor 3 is provided with a three-phase incoming line end, the three-phase bridge arm is correspondingly connected with the three-phase incoming line end of the hub motor 3, the core control unit 2b is connected with the three-phase bridge arm to output three paths of PWM driving signals to control the rotating speed and the torque of the hub motor 3, and the current sensor is also connected with the three-phase incoming line end of the hub motor 3.

In order to accurately control the intensity of the compensation current of the compensation winding 4, the driving circuit 2c is a PWM power driving module and is provided with a driving bridge arm, the driving bridge arm is electrically connected with the compensation winding 4, in order to improve the switching response speed of the driving bridge arm, the driving bridge arm preferably adopts IGBT or MOSFET as a switching device, the signal acquisition circuit 2a and the driving circuit 2c are respectively connected with the core control unit 2b, the core control unit 2b adopts a microprocessor formed by a single chip microcomputer or a DSP chip, the signal acquisition circuit 2a acquires the current of the hub motor 3 and the current of the compensation winding 4 and sends the acquired signals to the core control unit 2b, the signal acquisition circuit 2a comprises a current sensor and a conditioning circuit, the current sensor acquires the current of the hub motor 3 and the current of the compensation winding 4, the conditioning circuit conditions the signals of the current sensor and then outputs the conditioned signals to, the core control unit 2b outputs a PWM driving signal to the driving bridge arm according to the received current collecting signal to control the current of the compensation winding 4 in a closed-loop manner, the driving bridge arm is provided with a power element, the power element controls the output current through the PWM driving signal, and controls the compensation torque excited by the compensation winding 4 through controlling the current of the compensation winding 4, so that the torque pulsation is reduced, the vertical characteristic of the electric vehicle is improved, and the running smoothness of the vehicle is improved.

Referring to fig. 3, the method for rapidly setting the compensation current of the control winding for eliminating the torque ripple of the hub motor is controlled by a harmonic torque compensation system of the hub motor, and comprises the following steps:

step S1, collecting a torque signal: the instantaneous rotating speed of the motor is measured by a speed measuring encoder, the core control unit calculates to obtain the output electromagnetic torque of the hub motor, or the output torque is directly measured by a torque sensor, and the core control unit receives a torque signal;

step S2, extracting a torque harmonic: analyzing the motor torque by using an FFT (fast Fourier transform) method, extracting harmonic components in the torque according to frequency, and calibrating the frequency, amplitude and phase;

step S3, setting current frequency and phase: based on the electromagnetic principle of the motor and the control winding structure, the frequency and the phase of the compensation current are accurately calculated according to the frequency and the phase characteristics in the torque harmonic;

step S4, setting the current amplitude: the harmonic amplitude of a specific frequency in the torque is taken as a control object, a current amplitude self-adaptive iterative method of quadratic curve fitting is adopted to track a real torque-current curve, the effect of quickly weakening the torque amplitude is realized, the target torque is continuously tracked after weakening, and the current amplitude is finely adjusted to make the target harmonic torque amplitude tend to 0;

step S5, outputting a compensation current: and the core control unit takes a compensation current expected value as an input quantity by a current closed loop according to the frequency, the phase and the amplitude of the compensation current obtained by setting, takes the real-time current of the control winding acquired by the signal acquisition circuit as a closed-loop control signal, outputs a PWM (pulse width modulation) driving signal to the driving bridge arm, and performs closed-loop control on the compensation current of the control winding.

Further, in step S1, the calculation formula of the electromagnetic torque of the in-wheel motor calculated by the core control unit is as follows:

where ω is the mechanical rotation speed of the motor, J is the moment of inertia, B is the coefficient of friction, T_LIs the load torque.

Further, after the fast fourier transform in step S2, only the frequency, amplitude and phase characteristics of the torque harmonics with order lower than 10, such as the second and sixth harmonics with significant amplitude, except the 0 th order effective electromagnetic torque, are calibrated.

Further, the calculation formula of the compensation current characteristic parameter of the control winding in step S3 is as follows:

wherein n, A_n，θ_nOrder, amplitude and phase, k, A, of the n-th order harmonics obtained for the fast Fourier transform in said step S2_k，θ_kTo compensate for the order, magnitude and phase of the current, the law of the current change with time t can be expressed as

I＝I_kcos(kpωt+θ_k) (3)

Wherein p is the number of pole pairs of the motor.

Under actual operation condition, flux linkage parameter psi in formula (2)_fSince the amplitude of the compensation current directly calculated by equation (2) has a large error with the change of the saturation level of the magnetic field of the motor, the optimal current amplitude is searched by an iterative method, and further, as shown in fig. 4 and 5, the step S4 includes the following steps:

s41: initial current injection, wherein the motor controller injects three times of test current into the control winding, and the injection rule is expressed as:

I_P+1＝I_P+λ₁ΔI (4)

where I is the amplitude of the compensation current, P is the number of tests, λ₁The step coefficient is preferably 1, Δ I is the change step of two adjacent test currents, and the amplitude is preferably:

wherein I_sRated current for fundamental frequency of motor, A₀，A_nThe amplitudes of the torque direct current and the n-th order torque harmonic are respectively. Three testsThe current amplitudes are arranged from small to large and are marked as I_P1，I_P2，I_P3；

The amplitude values of the tertiary current are arranged from small to large and are marked as I_P1，I_P2，I_P3；

S42: solving the harmonic torque gradient, repeating the steps S1-S2, and obtaining the residual harmonic torque amplitude after the third test current injection by using FFT Fourier transform, wherein the residual harmonic torque amplitude is marked as A_P1，A_P2，A_P3According to the gradient formula between two adjacent points:

determine whether condition ▽ is satisfied₁▽₂Less than 0; if not, returning to S41, continuing to iterate the next test current according to the formula (4), and if the condition is met, entering the step S43;

s43: fitting a quadratic curve, and recording the last three test currents as I_P1，I_P2，I_P3And fitting the relation between the torque and the current by using a quadratic equation, wherein the relation is expressed as follows:

solving the coefficients a, b and c of the fitted curve, and obtaining the extreme value coordinate points of the quadratic curve, which are expressed as:

s44: judging a convergence condition, and comparing the current amplitude I calculated in the step S43_P4Injecting a control winding, repeating the steps S1-S2 to obtain the torque harmonic amplitude A_P4Judging whether an iterative convergence condition I is satisfied_P4-I_P2< ε; if not, returning to the step S43 for iteration again, and if yes, entering the step S45;

s45: current trimming with I_P4For the iterative initial value, the amplitude of the compensation current is finely adjusted,the relation is expressed as:

I_P+1＝I_P+λ₂ΔI (9)

wherein λ₂For fine-tuning the step-size coefficient and satisfying lambda₂＝λ₁Then, the current amplitude I calculated in the formula (9) is used_P5Injecting a control winding, repeating the steps S1-S2 to obtain the torque harmonic amplitude A_P5Judging whether or not the condition A is satisfied_P5＜A_P4(ii) a If not, let λ₂＝-λ₂Returning to step S45 for reiteration; if satisfied, maintaining λ₂And returning to the step S45 for reiteration without change.

The foregoing has been a description of the preferred embodiments of the present invention and is not to be construed as limiting the claims. The present invention is not limited to the above embodiments, and the specific structure thereof is allowed to vary, and those skilled in the art can make various changes and modifications according to the present invention within the scope defined by the appended claims without departing from the spirit of the present invention.