Permanent magnet synchronous motor torque ripple suppression method based on high-frequency square wave injection

Abstract

The invention relates to the technical field of permanent magnet synchronous motor control, in particular to a permanent magnet synchronous motor torque ripple suppression method based on high-frequency square wave injection, and aims to solve the derived torque problem while keeping the advantages of high-frequency square wave injection position detection through the collaborative design of high-frequency injection and harmonic suppression. According to the method, the vicious cycle of precision improvement-torque fluctuation is broken through, double targets of high-precision control without a position sensor and low-torque ripple stable operation are achieved, fifth and seventh harmonic currents are converted into direct current components in a corresponding rotating coordinate system through Park conversion, pure direct current components are extracted in combination with a low-pass filter, and the direct current components in the rotating coordinate system are extracted. Finally, reverse compensation voltage is calculated and injected based on a compensation voltage equation, the influence of fifth and seventh harmonic currents can be directly counteracted, and the stability of the output torque of the permanent magnet synchronous motor and the control precision of the motor can be effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of permanent magnet synchronous motor control, in particular to a permanent magnet synchronous motor torque ripple suppression method based on high-frequency square wave injection. BACKGROUND

[0002] The output torque of the permanent magnet synchronous motor is unstable, which will cause vibration and noise during the operation of the permanent magnet synchronous motor, and affect the stability and control accuracy of the permanent magnet synchronous motor. In the prior art, a high-frequency square wave is usually injected into the d-axis winding of the permanent magnet synchronous motor, and the saturation salient pole effect of the rotor of the permanent magnet synchronous motor is used to generate a high-frequency response signal in the current that can reflect the position of the rotor, thereby improving the accuracy of the speed control of the permanent magnet synchronous motor.

[0003] However, when the high-frequency square wave is continuously injected into the d-axis winding, the electromagnetic coupling between the high-frequency signal and the stator winding of the motor will cause a large amount of 5th and 7th harmonic currents in the stator current. The two types of harmonic currents are typical low-order harmonics. The 5th harmonic current will generate a counter-rotating magnetic field inside the motor, and the 7th harmonic current will generate a forward-rotating but abnormal-speed magnetic field. The combined effect of the two will cause serious distortion of the stator current waveform, and the current distortion will directly cause periodic fluctuations in the electromagnetic torque, i.e. torque ripple. Since the frequency of the ripple is related to the harmonic frequency, and the amplitude increases with the increase of the harmonic current, the output torque of the motor will eventually become unstable. This not only reduces the effect of the high-frequency square wave injection method on the speed accuracy, but also further aggravates the vibration and noise of the motor, forming a vicious cycle of "accuracy improvement-torque fluctuation-performance decline", which affects the stability and control accuracy of the permanent magnet synchronous motor. Therefore, the present application proposes a permanent magnet synchronous motor torque ripple suppression method based on high-frequency square wave injection. SUMMARY

[0004] The purpose of the present application is to provide a permanent magnet synchronous motor torque ripple suppression method based on high-frequency square wave injection to solve the problems raised in the background.

[0005] To achieve the above-mentioned purpose, the present application provides a permanent magnet synchronous motor torque ripple suppression method based on high-frequency square wave injection, comprising the following steps: Sensing the physical quantities of the permanent magnet synchronous motor, transforming the physical quantities in the three-phase stationary coordinate system of the permanent magnet synchronous motor to the dq rotating coordinate system, and establishing the dq rotating coordinate system; constructing a basic stator voltage equation based on the back electromotive force of the permanent magnet synchronous motor and the parameters of the stator winding of the motor; based on the dq-axis currents in the stator winding, the magnetic fluxes generated in the d-axis and q-axis directions, respectively, constructing a dq-axis magnetic flux equation, and combining the stator voltage equation and the magnetic flux equation to output the stator voltage equation A; Inject a high-frequency voltage into the d-axis of the permanent magnet synchronous motor, substitute the high-frequency voltage into the stator voltage equation A, output the stator voltage equation B, solve the stator voltage equation B by integration, obtain the d-axis high-frequency current, receive the d-axis high-frequency current, and calculate the rotor position angle. Receive rotor position angle to calculate electric angular velocity, receive permanent magnet synchronous motor parameters to calculate electromagnetic torque and load torque, output motor motion equation and state space model equation, construct observation model equation to calculate observation state vector, introduce gain matrix into observation model equation, and output error feedback observation model. The system senses the 5th and 7th harmonic currents, converts them into their corresponding DC components through the dq rotating coordinate system, obtains the harmonic voltage, suppresses the AC component using a low-pass filter, extracts the DC component, outputs the compensation voltage formula based on the stator voltage equation, calculates the voltage compensation value, overlaps the harmonic voltage with the voltage compensation value, and outputs the dq axis voltage command of the permanent magnet synchronous motor.

[0006] Preferably, the physical quantities in the three-phase stationary coordinate system are transformed by a transformation matrix, and the basic stator voltage equation is established based on the fundamental frequency of the permanent magnet synchronous motor. The flux linkage equation is established based on the basic stator voltage equation, and the flux linkage equation is substituted into the basic stator voltage equation to output the stator voltage equation A.

[0007] Preferably, the high-frequency voltage is substituted into the stator voltage equation A to output the stator voltage equation B. The stator voltage equation B includes the high-frequency current and the high-frequency angular frequency. The specific working steps are as follows: By integrating and solving the stator voltage equation B, the high-frequency current along the d-axis is obtained, and the high-frequency angular frequency is... The discrete Fourier transform method is used to convert the high-frequency current signal from the time domain to the frequency domain, and the spectrum corresponding to the high-frequency current signal is obtained. Receive and sense the angular frequency of high-frequency voltage signals and the number of pole pairs of permanent magnet synchronous motors. Based on the salient pole effect of permanent magnet synchronous motors, analyze the maximum amplitude of the characteristic frequency of high-frequency voltage in the spectrum and determine the characteristic frequency distribution range. The high-frequency voltage signal angular frequency is received again to generate sine and cosine signals. The high-frequency current is multiplied by the sine and cosine signals respectively to obtain the amplitude of the low-frequency and high-frequency signals. The characteristic frequency components related to the rotor position are separated by a bandpass filter. The amplitudes of the two low-frequency signals after synchronous adjustment and the number of pole pairs of the permanent magnet synchronous motor are multiplied with the sinusoidal and cosine signals of the same frequency and phase in the injected high-frequency signal to obtain the intermediate signal. The rotor position angle in the intermediate signal is calculated using the four-quadrant arctangent function, and the rotor position angle is converted into the mechanical rotor position angle to obtain the real-time rotor position.

[0008] Preferably, the electric angular velocity is calculated by the derivative of the rotor position angle with respect to time, and the electromagnetic torque is calculated by receiving the permanent magnet flux linkage, the number of pole pairs of the permanent magnet synchronous motor, the dq-axis inductance, and the dq-axis current. The moment of inertia and viscous friction coefficient of the permanent magnet synchronous motor are sensed, and the derivative of the electric angular velocity with respect to time is calculated to obtain the acceleration of the electric angular velocity and calculate the load torque. Receive the load torque and electric angular velocity, as well as the motor parameters, subtract the load torque from the electromagnetic torque, then subtract the motor viscous friction coefficient, multiply by the electric angular velocity, and output the motor motion equation; The load torque and electric angular velocity are combined from state variables into state vector and input vector, and state space equations are constructed based on the state vector and input vector. The state vector and input vector are consistent with the dynamic characteristics of the permanent magnet synchronous motor, and the actual state space model equations are established.

[0009] Preferably, the observation model equations are constructed and dynamically corrected. The specific steps are as follows: Copy the actual state-space model, receive the system output matrix, and since the input vector is consistent with the actual state-space model, construct the observation model equation to obtain the observation state vector; Multiply the observed state vector by the system output matrix in the system matrix to obtain the predicted output value, and then subtract the predicted output value of the observation model from the output vector to obtain the output error; By introducing a gain matrix, the output error is multiplied by the gain matrix to obtain the feedback value. The feedback value is then fed back into the observation model equation, and combined with the output error, an error feedback observation model is established. Based on the sign of the poles of the gain matrix, we can determine how quickly the observed state vector converges to 0. The faster the convergence, the smaller the output error; conversely, the slower the convergence, the larger the output error.

[0010] Preferably, the 5th and 7th harmonic current distortion is suppressed, and the specific working steps are as follows: By using the conversion formula, the three-phase current of the permanent magnet synchronous motor is converted into two-phase static current. Then, the two-phase static current is converted into the dq rotating coordinate system through the Park transformation to obtain the DC components of the 5th and 7th harmonic currents. By suppressing the AC component in the harmonic current through a low-pass filter and extracting the DC component, the fundamental voltage equation of the harmonic current in the dq rotating coordinate system is constructed. Inject a compensation voltage and combine it with the basic voltage equation to construct the compensation voltage equation; The DC components of the 5th and 7th harmonics, the magnetic flux of the 5th and 7th harmonics, and the rotational angular frequencies of the 5th and 7th harmonics are received and substituted into the compensation voltage equation to obtain the voltage compensation values ​​corresponding to the 5th and 7th harmonic currents, respectively.

[0011] Preferably, the voltage compensation value is converted to the dq rotating coordinate system, the 5th and 7th harmonic voltage compensation values ​​in the dq rotating coordinate system are calculated, and control commands for the d-axis and q-axis of the permanent magnet synchronous motor are generated.

[0012] Preferably, the high-frequency current is equal to the DC component of the d-axis high-frequency current plus the AC component of the d-axis current, and the q-axis high-frequency current is 0 when there is no high-frequency current component initially. The bandpass filter suppresses high-frequency signals in the high-frequency current and retains low-frequency signals, including rotor position. The rotor position angle is obtained by dividing the rotor position angle by the number of pole pairs.

[0013] Preferably, two-thirds of the number of pole pairs of the permanent magnet synchronous motor is defined as the first value; The product of the permanent magnet flux linkage multiplied by the q-axis current, plus the difference between the d-axis inductance and the q-axis inductance, and multiplied by the difference by the d-axis current and the q-axis current, is defined as the second value. Multiplying the first value by the second value yields the electromagnetic torque in the dq rotating coordinate system; The load torque is obtained by subtracting the product of the moment of inertia and the electric angular velocity acceleration from the electromagnetic torque, and then subtracting the product of the electric angular velocity and the coefficient of viscous friction.

[0014] Preferably, the total voltage satisfies the condition that the sum of the fundamental voltage on the d-axis and the compensation voltage on the d-axis is 0, and the sum of the fundamental voltage on the q-axis and the compensation voltage on the q-axis is also 0.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. While existing high-frequency square wave injection methods can extract position signals by leveraging the rotor saturated salient pole effect and improve speed accuracy under sensorless control, they can also cause distortion of the 5th and 7th harmonic currents, leading to increased torque pulsation and vibration noise. This invention, through a collaborative design of "high-frequency injection + harmonic suppression," retains the advantages of high-frequency square wave injection for position detection while specifically addressing the resulting torque problem, breaking the vicious cycle of "accuracy improvement - torque fluctuation," and achieving the dual goals of "high-precision control without position sensors" and "smooth operation with low torque pulsation."

[0016] 2. The three-phase current is converted into two-phase static current through Clark transformation, and then the 5th and 7th harmonic currents are converted into DC components in the corresponding rotating coordinate system through Park transformation. The pure DC components are extracted by combining a low-pass filter. Finally, the reverse compensation voltage is calculated and injected based on the compensation voltage equation, which can directly cancel the influence of the 5th and 7th harmonic currents. Actual verification shows that the 5th harmonic component decreased from 5.216% to 0.6024%, the 7th harmonic component decreased from 2.08% to 0.6322%, the total harmonic distortion (THD) decreased from 9.29% to 3.66%, and the sinusoidal sine of the current waveform was significantly improved, thereby reducing the interference of current distortion on torque from the source.

[0017] 3. By constructing a state-space model consistent with the dynamic characteristics of the motor, and introducing a gain matrix to establish an error feedback observation model, the deviation between the observed state vector and the actual state vector can be corrected in real time (such as when the load torque changes suddenly). When the load suddenly increases from low load to high load (such as the load disturbance scenario in the text), the speed fluctuation is only about ±50 r / min, and it can recover to the set value within 0.1s. This effectively avoids speed instability and sudden torque change caused by sudden load changes, and ensures that the motor can still operate stably under the condition of frequent load fluctuation (such as electric vehicle drive and lifting equipment). Attached Figure Description

[0018] Figure 1 This is a system control block diagram of the present invention; Figure 2 This is a comparison diagram of the A-phase current before and after the invention's suppression of torque pulsation; Figure 3 This is a comparative FFT analysis of the A-phase current before and after the present invention's suppression of torque pulsation; Figure 4 This is a diagram illustrating the sudden change in rotational speed during operation, as presented in this invention. Figure 5 This is a diagram illustrating the load mutation condition analysis of the present invention. Figure 6 This is a flowchart illustrating the overall technical logic of the present invention. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Unless otherwise stated, the terms used herein (including technical terms) have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.

[0021] Reference Figures 1 to 6This invention addresses the issue that instability in the output torque of a permanent magnet synchronous motor (PMSM), which is determined by the q-axis current and the magnetic field by the d-axis current, can cause vibration and noise during operation, affecting the smoothness and control accuracy of the PMSM. Existing technologies typically employ a high-frequency square wave injection method, injecting a given high-frequency square wave into the d-axis winding of the PMSM. Utilizing the saturated salient pole effect of the PMSM rotor, a high-frequency response signal reflecting the rotor position is generated in the current, thus improving the speed control accuracy. However, when the high-frequency square wave is injected into the d-axis of the PMSM, it may generate a large number of harmonics (5th and 7th harmonic currents), causing distortion in the PMSM current and resulting in periodic fluctuations (torque pulsation) in the output torque. This further exacerbates the instability in the output torque, affecting the smoothness and control accuracy of the PMSM.

[0022] Because the rotor of a permanent magnet synchronous motor (especially a rotor with built-in permanent magnets or a salient pole structure) has spatial anisotropy (i.e., the inductance, reluctance and other parameters of the d-axis and q-axis are different), and the dq coordinate system is a coordinate system that rotates synchronously with the rotor, where the d-axis is in the same direction as the magnetic flux of the rotor permanent magnet and is the axis of the magnetic flux, and the q-axis leads the d-axis by 90° electrical angle and is the torque axis perpendicular to the magnetic flux. However, because the stator winding of the permanent magnet synchronous motor is in a three-phase stationary coordinate system (abc coordinate system), its inductance, voltage and other parameters change periodically with time. Therefore, transforming the physical quantities (current, voltage, etc.) in the three-phase stationary coordinate system (abc coordinate system) to the dq rotating coordinate system using the coordinate transformation method can effectively simplify the time-varying parameters, making the high-frequency mathematical model analysis more accurate. The transformation matrix expression is as follows: ; in: Representative parameter (i.e., capable of representing voltage) It can also represent electric current. ), The electrical angle of the dq coordinate system relative to the abc coordinate system (the spatial electrical angle position of the rotor of the permanent magnet synchronous motor, i.e., the rotor position angle, which can directly reflect the spatial position of the magnetic flux direction (d-axis direction) of the rotor permanent magnet in the stationary coordinate system) is used to establish the dq rotating coordinate system.

[0023] When a high-frequency signal is injected into a permanent magnet synchronous motor, the rotor permanent magnets and stator windings undergo relative motion, thereby generating a back electromotive force (EMF) (the conductor moves in a magnetic field, cutting magnetic field lines, thus generating an induced EMF). Combining this with the stator winding parameters and the fact that the back EMF frequency is the motor's fundamental frequency, the basic stator voltage equation can be established: ; in: This is the dq-axis voltage. For stator winding resistance, For dq axis current; For the dq axis flux linkage, It is a differential operator, representing a function of time. Finding the derivative (also known as "differentiation with respect to time" or "time differential") The electric angular velocity of the permanent magnet synchronous motor; At this time, the dq axis current in the stator winding It will generate magnetic flux linkages in the d-axis and q-axis directions respectively, and can establish magnetic flux linkages along the dq-axis and dq-axis. The flux linkage equation between them is: ; in: These are the d-axis and q-axis inductances (for salient-pole permanent magnet synchronous motors). ), For rotor permanent magnet flux linkage.

[0024] Furthermore, since the injected high-frequency signal frequency is much higher than the fundamental frequency, the back electromotive force, under the "dominance" of the high-frequency voltage, has an approximately negligible impact on the voltage balance. At this time, the rotor position changes little within the high-frequency signal period (i.e., relatively stationary relative to the dq rotating coordinate system). Substituting the flux linkage equation into the basic stator voltage equation and differentiating it with respect to time, we obtain stator voltage equation A: This allows for the establishment of a high-frequency mathematical model.

[0025] To reduce the cost of permanent magnet synchronous motor control systems and improve their reliability and flexibility, sensorless control is required. This is achieved by injecting high-frequency voltage. ,in: This refers to the amplitude of the high-frequency voltage. The angular frequency of the high-frequency voltage, the q-axis high-frequency voltage Then, substituting the high-frequency voltage into the simplified stator voltage equation A further simplifies the stator voltage equation A. The expression for the further simplified stator voltage equation B is: ; in: The d-axis high-frequency current component; At this point, the high-frequency voltage will excite a high-frequency current that includes positional characteristics. This facilitates subsequent adjustments based on high-frequency current. Calculate the real-time position of the rotor.

[0026] Due to the inductance of the d-axis and q-axis At this time, the permanent magnet synchronous motor will generate different high-frequency currents. The response is that the rotor position can reflect the spatial position of the d-axis and q-axis relative to the stator windings. In this case, integrating the stator voltage equation B, we find that the d-axis high-frequency current equals the DC component of the d-axis high-frequency current plus the AC component of the d-axis current, expressed as: ; in: This represents the DC component of the d-axis current. This represents the AC component of the d-axis current, and the q-axis high-frequency current initially has no high-frequency current component. .

[0027] and high frequency angular frequency The discrete Fourier transform method is used to convert high-frequency current signals from the time domain to the frequency domain. For continuous time-domain signals of high-frequency currents... The calculation formula for the Discrete Fourier Transform is as follows: ; in: For continuous time domain signals The first one obtained after discretization The values ​​of discrete sampling points, This represents the total number of sampling points for the discrete signal. It is the frequency point index in the frequency domain, and its value is... And each Corresponding to a specific frequency component, It is the frequency domain signal obtained after the discrete Fourier transform, representing the signal at the 1st... Complex values ​​at each frequency point contain the amplitude and phase information of that frequency component. These are the basis functions of the discrete Fourier transform, where The imaginary unit ( At this point, by multiplying each sampling point with the corresponding basis function and summing the results, the high-frequency current signal is transformed from the time domain to the frequency domain, thus obtaining the spectrum of the high-frequency current signal. .

[0028] Receive and sense the angular frequency of high-frequency voltage signals Number of pole pairs of permanent magnet synchronous motor According to The resulting salient pole effect occurs when a high-frequency voltage signal (angular frequency of ω) is injected into the permanent magnet synchronous motor. When a high-frequency voltage is applied, it generates a high-frequency current in the motor windings. The response to the high-frequency voltage differs along different axes, resulting in a modulation component in the high-frequency current that is related to the rotor position. At this point, the characteristic frequency related to the rotor position will be at... In the vicinity of the rotor, the modulation effect of the electromagnetic torque is most strongly correlated with the rotor position. Therefore, analyzing the high-frequency current signal can directly obtain the rotor position. Since the characteristic frequency components related to the rotor position are modulated by the motor's salient pole effect and the rotor position, analyzing the spectrum... In the middle, the characteristic frequency of high-frequency voltage is at The maximum amplitude value in the vicinity determines the characteristic frequency distribution range.

[0029] Receive the angular frequency of the injected high-frequency voltage signal Generate a sine wave signal Sum and cosine signals and high-frequency current respectively with sinusoidal signals Sum and cosine signals Multiplying these values ​​yields the low-frequency and high-frequency signal amplitudes related to the rotor position (primarily those with characteristic frequencies within a certain range). The formula for calculating the maximum amplitude signal in the vicinity is: and ; By using a bandpass filter to suppress high-frequency signals and retain low-frequency signals (containing rotor position information), the characteristic frequency components related to rotor position are separated and the characteristic frequency is adjusted synchronously.

[0030] The amplitude of the two low-frequency signals after synchronous modulation (the low-frequency signal after being filtered by the bandpass filter is defined as the low-frequency signal) is received. and low frequency signals And the number of pole pairs of permanent magnet synchronous motors A sinusoidal signal with the same frequency and phase as the injected high-frequency signal. Sum and cosine signals Multiply and output the intermediate signal; The intermediate signal is calculated using the four-quadrant arctangent function, and the rotor position angle is output. The rotor position angle is obtained. (Electrical angle of rotor position), and the rotor position angle Divide by the extreme logarithm The mechanical rotor position angle is obtained. This provides crucial position feedback information for sensorless control of permanent magnet synchronous motors.

[0031] Since the generation of torque pulsation is closely related to the rotor position, the electromagnetic relationship inside the permanent magnet synchronous motor (such as magnetic flux distribution, winding induced electromotive force, etc.) is different when the rotor is in different positions, which will affect the torque output. Therefore, the rotor position angle is received. Calculate the electric angular velocity electric angular velocity equal to rotor position angle The derivative with respect to time is expressed as: ; Connected permanent magnet magnetic chain Number of pole pairs of permanent magnet synchronous motors dq axis inductance and and dq axis current and The number of pole pairs of the permanent magnet synchronous motor is increased by two-thirds. Multiplied by (permanent magnet flux) Multiply by the q-axis current and add the d-axis inductance. Subtract q-axis inductance The difference multiplied by the d-axis current Multiplied by q-axis current The product of these two components yields the electromagnetic torque in the dq rotating coordinate system. The calculation expression is: .

[0032] Then, the rotational inertia of the permanent magnet synchronous motor is sensed. And calculate the derivative of the electric angular velocity with respect to time, thereby obtaining the acceleration of the electric angular velocity. At this time, the load torque Equal to electromagnetic torque Subtract moment of inertia and electric angular velocity acceleration The product of the two, minus the electric angular velocity. and viscous friction coefficient The product of , is expressed as: ; in: The motor parameters (viscous friction coefficient) are used to obtain the load torque. .

[0033] Received load torque and electric angular velocity And motor parameters (moment of inertia) viscous friction coefficient ), to electromagnetic torque Subtract load torque Subtract the motor's viscous friction coefficient Multiply by electric angular velocity The equations of motion for the motor are obtained as follows: ; Then the load torque and electric angular velocity The state variables are combined into a state vector and an input vector, and the combination expressions are as follows: , ; in: For state vectors, The input vector; Then based on the state vector and input vector Construct the state-space equations: ; At this time, the state vector and input vector Consistent with the dynamic characteristics of permanent magnet synchronous motors, it is possible to directly establish the actual state-space model equations: ; in: For the output vector (electric angular velocity) (can be directly used as an output vector); The system matrix (based on the physical quantities transformed in the dq rotating coordinate system, the system matrix in the dq coordinate system is transformed to the abc coordinate system, thus obtaining) (System matrix).

[0034] Copy the actual state-space model and name it the observation model. The input vector at this point... Consistent with the actual state-space model, the observation model equations are as follows: ; in: Represents the observed state vector (as opposed to the actual state vector) (valuation).

[0035] Multiply the observed state vector by the system matrix The system output matrix The predicted output value is obtained (defined as follows). ), and then output vector Subtract the predicted output value of the observation model The output error is obtained. The expression is: ; To avoid this Or, the observation model may have errors, noise, or other influences. The value will gradually deviate The value of makes the observation model unable to accurately track the actual state space model, resulting in reduced speed control accuracy and slower torque response of the permanent magnet synchronous motor. Therefore, a gain matrix is ​​introduced. Output error Multiply by the gain matrix The feedback value is obtained and then fed back into the observation model equation. and combined with output error Establish an error feedback observation model to output the error. The state change of the corrected observation model, and the error feedback observation model equation are as follows: ; in: For output error Feedback items; Gain matrix based on With error feedback observation model equations The observed state vector is obtained. The dynamic equation: ; Due to the gain matrix Determined by eigenvalues ​​(extremes), if all extreme values ​​are negative, it indicates that the observed state vector... The faster the convergence to zero, the higher the output error. The smaller.

[0036] If at this time and Deviation will cause The error feedback observation model can dynamically correct the observation model equations, making... Fast convergence to Thus, to Make corrections to match the actual state vector. Thus, accurately tracking the load torque. Changes in load torque should be avoided. When a sudden change occurs, causing a large fluctuation in the speed of the permanent magnet synchronous motor or stalling, it can help the control system to stably control the speed of the permanent magnet synchronous motor.

[0037] Due to the cogging effect of permanent magnet synchronous motors, the air gap magnetic permeability is uneven, and the linearity factor of the inverter causes distortion in the output current, resulting in torque ripple. At this point, increasing the supply frequency by injecting a high-frequency voltage signal reduces the torque ripple while simultaneously increasing the high-frequency current. The medium will contain a large amount of 5th and 7th harmonic currents. In the dq rotating coordinate system, since the frequencies of the 5th and 7th harmonic currents are multiples of the fundamental frequency (the 5th harmonic frequency is 5 times the fundamental frequency, and the 7th harmonic frequency is 7 times the fundamental frequency), the 5th and 7th harmonic currents will... and The angular frequency rotation causes large torque pulsation, affecting the smooth operation and performance of the permanent magnet synchronous motor; Therefore, sensing the three-phase current of the permanent magnet synchronous motor The three-phase current Converted to two-phase static current Transform the expression: ; And because the angular frequencies corresponding to the 5th and 7th harmonic currents are respectively... and At this time, the two-phase static current Transform them into the dq rotating coordinate system using the Park transformation method. Switch to Below The expression is: ; in: For the rotation angle, and ( (for time) Rotation angle Substitution In the expression, Switch to Below The expression is: ; Rotation angle Substitution In the expression, Switch to Below The expression is: ; This allows the 5th and 7th harmonic currents to be converted into DC components.

[0038] When the 5th and 7th harmonic currents are converted to their respective dq rotating coordinate systems ( , At this time, the 5th and 7th harmonic currents exhibit DC components. This falls into the low-frequency range, while other AC components, such as noise and subharmonics, are suppressed by a low-frequency filter, thereby extracting the corresponding DC components from the 5th and 7th harmonics. , , , ).

[0039] Since the 5th and 7th harmonic currents each exhibit DC components in the dq rotating coordinate system, and the rate of change of the DC components with time is 0 ( , At this point, the equation for the base voltage of the harmonic current in the dq rotating coordinate system is: ; Therefore, the 5th harmonic is In coordinate system, , Substituting into the basic stator voltage equation, we obtain Voltage in coordinate system ( ): ; in: They are respectively The DC component of the fifth harmonic current in the coordinate system They are respectively Magnetic flux linkage in coordinate system; 7th harmonic in In coordinate system, , Substituting into the basic stator voltage equation, we obtain Voltage in coordinate system ( ): ; in: They are respectively DC component of the 7th harmonic current in the coordinate system They are respectively Magnetic flux linkage in coordinate system; To suppress harmonics, the harmonic current needs to be equal to zero, which requires injecting a compensation voltage. ), so that the total voltage satisfies Then, it is combined with the basic voltage equation to construct the compensation voltage equation, and the calculation formula is as follows: ; in: These are the equivalent resistances along the d and q axes, respectively. Receives DC components of the 5th and 7th harmonics , , , Magnetic flux linkages of the 5th and 7th harmonics , And the rotational angular frequencies of the 5th and 7th harmonics. , ( Let be the fundamental angular frequency. Substitute this into the compensation voltage equation to calculate the voltage compensation values ​​for suppressing the 5th and 7th harmonic currents. The voltage compensation values ​​corresponding to the 5th and 7th harmonic currents are calculated using the following formulas: , ; in: , These are the d-axis voltage compensation values ​​for the 5th and 7th harmonics, respectively. The equivalent d-axis resistances for the 5th and 7th harmonics are respectively. The fundamental angular frequency, These are the 5th harmonic q-axis flux linkage and the 5th harmonic d-axis flux linkage, respectively. These are the 7th harmonic q-axis flux linkage and the 7th harmonic d-axis flux linkage, respectively. This allows for the suppression of the 5th and 7th harmonic currents.

[0040] Since the control commands of a permanent magnet synchronous motor are implemented based on the dq rotating coordinate system, an inverse coordinate transformation is required to... and The voltage compensation values ​​calculated in the coordinate system are transformed into the dq rotating coordinate system. The voltage compensation values ​​for the 5th and 7th harmonics are then: , ; in: The 5th harmonic corresponds to The voltage compensation value in the coordinate system is transformed to the dq rotating coordinate system using the transformation matrix. ; corresponding to the 7th harmonic The voltage compensation amount in the coordinate system is transformed into the transformation matrix of the dq rotating coordinate system; In the dq rotating coordinate system, the fundamental voltage command is: The 5th and 7th harmonic voltage compensation values ​​after dq rotation and coordinate reversal are respectively , At this time, the voltage commands used to control the d-axis and q-axis of the permanent magnet synchronous motor are: ; This allows the harmonic voltage compensation value to overlap with the fundamental voltage command, enabling the voltage compensation value and the fundamental voltage to control the permanent magnet synchronous motor simultaneously. At this time, the compensation voltage value will have the opposite effect to the 5th and 7th harmonic currents, thereby suppressing the torque pulsation and other effects caused by the 5th and 7th harmonics in real time, and improving the stability and efficiency of the permanent magnet synchronous motor operation. As shown in the waveform diagram Figure 2 As shown, before torque ripple suppression, the current waveform has a large harmonic content at the peak, resulting in obvious waveform distortion; after suppression, the sinusoidality of the current waveform is significantly improved.

[0041] like Figure 3As shown, data analysis of the A-phase current using Fast Fourier Transform showed that, with torque ripple suppression, the 5th and 7th harmonic components in the permanent magnet synchronous motor decreased from 5.216% and 2.08% to 0.6024% and 0.6322%, respectively. The total harmonic distortion (THD) decreased from 9.29% to 3.66%.

[0042] Such as simulated waveforms Figure 4 It can be seen that when the rotational speed changes abruptly, The dynamic response is good, and its speed and The phase current has small fluctuations and can quickly recover to stability, and the changes are not caused by the torque ripple suppression process. Such as simulated waveforms Figure 5 It can be seen that, At that time, load disturbance is caused by Increase to Speed ​​fluctuation Left and right, in The internal speed returned to its set value, further demonstrating that the motor's speed and output torque have a good dynamic response.

[0043] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for suppressing torque ripple in a permanent magnet synchronous motor based on high-frequency square wave injection, characterized in that: Includes the following steps: The physical quantities of the permanent magnet synchronous motor are sensed, and the physical quantities of the permanent magnet synchronous motor in the three-phase stationary coordinate system are transformed to the dq rotating coordinate system to establish the dq rotating coordinate system. The basic stator voltage equation is constructed based on the back electromotive force of the permanent magnet synchronous motor and the stator winding parameters. Based on the magnetic flux generated by the dq axis current in the stator winding in the d-axis and q-axis directions respectively, the dq axis magnetic flux equation is constructed. The stator voltage equation and the magnetic flux equation are solved simultaneously to output the stator voltage equation A. Inject a high-frequency voltage into the d-axis of the permanent magnet synchronous motor, substitute the high-frequency voltage into the stator voltage equation A, output the stator voltage equation B, solve the stator voltage equation B by integration, obtain the d-axis high-frequency current, receive the d-axis high-frequency current, and calculate the rotor position angle. Receive rotor position angle to calculate electric angular velocity, receive permanent magnet synchronous motor parameters to calculate electromagnetic torque and load torque, output motor motion equation and state space model equation, construct observation model equation to calculate observation state vector, introduce gain matrix into observation model equation, and output error feedback observation model. The system senses the 5th and 7th harmonic currents, converts them into their corresponding DC components through the dq rotating coordinate system, obtains the harmonic voltage, suppresses the AC component using a low-pass filter, extracts the DC component, outputs the compensation voltage formula based on the stator voltage equation, calculates the voltage compensation value, overlaps the harmonic voltage with the voltage compensation value, and outputs the dq axis voltage command of the permanent magnet synchronous motor.

2. The method for suppressing torque ripple in a permanent magnet synchronous motor based on high-frequency square wave injection according to claim 1, characterized in that: The physical quantities in the three-phase stationary coordinate system are transformed by the transformation matrix. Based on the back electromotive force of the permanent magnet synchronous motor and the dq rotating coordinate system, the basic stator voltage equation is established. The flux linkage equation is established by combining the basic stator voltage equation and substituting the flux linkage equation into the basic stator voltage equation to output the stator voltage equation A.

3. The method for suppressing torque ripple in a permanent magnet synchronous motor based on high-frequency square wave injection according to claim 2, characterized in that: Solving the stator voltage equation B by integration yields the d-axis high-frequency current, which is the high-frequency current signal. The discrete Fourier transform method is used to convert the high-frequency current signal from the time domain to the frequency domain to obtain the spectrum of the high-frequency current signal, which includes the high-frequency voltage characteristic frequency. Receive the angular frequency of the high-frequency voltage signal and the number of pole pairs of the permanent magnet synchronous motor. Based on the salient pole effect of the permanent magnet synchronous motor, analyze the maximum amplitude of the characteristic frequency of the high-frequency voltage in the spectrum and determine the characteristic frequency distribution range. The high-frequency voltage signal angular frequency is received again to generate sine and cosine signals. The high-frequency current is multiplied by the sine and cosine signals respectively to obtain the amplitude of the low-frequency and high-frequency signals. The characteristic frequency components related to the rotor position are separated by a bandpass filter. The amplitudes of the two low-frequency signals after synchronous adjustment and the number of pole pairs of the permanent magnet synchronous motor are multiplied with the sinusoidal and cosine signals of the same frequency and phase in the injected high-frequency signal to obtain the intermediate signal. The rotor position angle in the intermediate signal is calculated using the four-quadrant arctangent function, and the rotor position angle is converted into the mechanical rotor position angle to obtain the real-time rotor position.

4. The method for suppressing torque ripple in a permanent magnet synchronous motor based on high-frequency square wave injection according to claim 3, characterized in that: The electric angular velocity is calculated by taking the derivative of the rotor position angle with respect to time, and the electromagnetic torque is calculated by receiving the permanent magnet flux linkage, the number of pole pairs of the permanent magnet synchronous motor, the dq-axis inductance, and the dq-axis current. The moment of inertia and viscous friction coefficient of the permanent magnet synchronous motor are sensed, and the derivative of the electric angular velocity with respect to time is calculated to obtain the acceleration of the electric angular velocity and calculate the load torque. Receive the load torque and electric angular velocity, as well as the motor parameters, subtract the load torque from the electromagnetic torque, then subtract the motor viscous friction coefficient, multiply by the electric angular velocity, and output the motor motion equation; The load torque and electric angular velocity are combined from state variables into state vector and input vector, and state space equations are constructed based on the state vector and input vector. The state vector and input vector are consistent with the dynamic characteristics of the permanent magnet synchronous motor, and the actual state space model equations are established.

5. The method for suppressing torque ripple in a permanent magnet synchronous motor based on high-frequency square wave injection according to claim 4, characterized in that: Copy the actual state-space model, receive the system output matrix, and since the input vector is consistent with the actual state-space model, construct the observation model equation to obtain the observation state vector; Multiply the observed state vector by the system output matrix in the system matrix to obtain the predicted output value, and then subtract the predicted output value of the observation model from the output vector to obtain the output error; By introducing a gain matrix, the output error is multiplied by the gain matrix to obtain the feedback value. The feedback value is then fed back into the observation model equation, and combined with the output error, an error feedback observation model is established. Based on the sign of the poles of the gain matrix, we can determine how quickly the observed state vector converges to 0. The faster the convergence, the smaller the output error; conversely, the slower the convergence, the larger the output error.

6. The method for suppressing torque ripple in a permanent magnet synchronous motor based on high-frequency square wave injection according to claim 5, characterized in that: The specific steps for suppressing 5th and 7th harmonic current distortion are as follows: By using the dq rotating coordinate system, the three-phase current of the permanent magnet synchronous motor is converted into two-phase static current. Then, the two-phase static current is converted into the dq rotating coordinate system by the Park transformation method to obtain the DC components of the 5th and 7th harmonic currents. The AC components in the 5th and 7th harmonic currents are suppressed by low-pass filter, the DC components are extracted, the basic voltage equation of the harmonic current in the dq rotating coordinate system is constructed, the compensation voltage is injected, and the compensation voltage equation is constructed by combining it with the basic voltage equation. The DC components of the 5th and 7th harmonics, the magnetic flux of the 5th and 7th harmonics, and the rotational angular frequencies of the 5th and 7th harmonics are received and substituted into the compensation voltage equation to obtain the voltage compensation values ​​corresponding to the 5th and 7th harmonic currents, respectively.

7. The method for suppressing torque ripple in a permanent magnet synchronous motor based on high-frequency square wave injection according to claim 6, characterized in that: The voltage compensation value is converted to the dq rotating coordinate system, the 5th and 7th harmonic voltage compensation values ​​in the dq rotating coordinate system are calculated, and control commands for the d-axis and q-axis of the permanent magnet synchronous motor are generated.

8. The method for suppressing torque ripple in a permanent magnet synchronous motor based on high-frequency square wave injection according to claim 7, characterized in that: The high-frequency current is equal to the DC component of the d-axis high-frequency current plus the AC component of the d-axis current, and the q-axis high-frequency current is 0 when there is no high-frequency current component initially. The bandpass filter suppresses high-frequency signals in the high-frequency current and retains low-frequency signals, including rotor position. The rotor position angle is obtained by dividing the rotor position angle by the number of pole pairs.

9. The method for suppressing torque ripple in a permanent magnet synchronous motor based on high-frequency square wave injection according to claim 8, characterized in that: The first value is defined as three times the number of pole pairs of a permanent magnet synchronous motor. The product of the permanent magnet flux linkage multiplied by the q-axis current, plus the difference between the d-axis inductance and the q-axis inductance, and multiplied by the difference by the d-axis current and the q-axis current, is defined as the second value. Multiplying the first value by the second value yields the electromagnetic torque in the dq rotating coordinate system; The load torque is obtained by subtracting the product of the moment of inertia and the electric angular velocity acceleration from the electromagnetic torque, and then subtracting the product of the electric angular velocity and the coefficient of viscous friction.

10. A method for suppressing torque ripple in a permanent magnet synchronous motor based on high-frequency square wave injection according to claim 9, characterized in that: The total voltage satisfies the condition that the sum of the fundamental voltage on the d-axis and the compensation voltage on the d-axis is 0, and the sum of the fundamental voltage on the q-axis and the compensation voltage on the q-axis is also 0.

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