A method for suppressing harmonic current of a permanent magnet synchronous motor

Abstract

The application discloses a kind of permanent magnet synchronous motor harmonic current's suppression method, comprising the following steps: step A, the voltage, current of three-phase permanent magnet synchronous motor is Fourier decomposition in three-phase stationary coordinate system;Step B, the phase current of motor is transformed into d-q coordinate system, then accurate harmonic current is obtained by adaptive low-pass filter, and total harmonic current is calculated;Step C, the control error of total harmonic current is adjusted to zero by PI controller, and then the output current of PI controller is obtained, then harmonic compensation voltage is obtained by harmonic suppression module;Step D, the harmonic compensation voltage obtained above is introduced into current loop to obtain d-axis voltage and q-axis voltage under d-q rotating coordinate system;Step E, the two-phase input phase voltage of the motor is modulated by SPWM, passes through voltage inverter, and is output to motor.The application can suppress motor torque ripple, improve the stability of motor system.

Description

Technical Field

[0001] This invention relates to a control method for permanent magnet synchronous motors, specifically to a method for suppressing harmonic currents in permanent magnet synchronous motors. Background Technology

[0002] Permanent magnet synchronous motors are widely used in electric vehicle drive systems and wind and thermal power generation systems due to their relatively simple structure, small size, light weight, and high output power efficiency. With the rapid rise and popularization of new energy vehicles, the NVH (noise, vibration, and harshness) issues caused by drive motors are receiving increasing attention. Unlike traditional fuel vehicles, the main factors affecting the NVH performance of new energy vehicles include: the order noise of the drive motor, the switching frequency noise of the motor, and the gear noise of the reducer. Furthermore, the nonlinear characteristics of the inverter circuit in the motor's frequency converter and the distortion of the air gap waveform in the magnetic field result in a large number of harmonic components in the three-phase current of the motor. This increases various losses such as copper loss, reducing motor operating efficiency; it also increases the steady-state torque pulsation of the motor, leading to vibration and noise, all of which seriously affect the motor's control performance and accuracy. This noise is transmitted into the passenger compartment through the structure and air, thus affecting the subjective experience of the driver and passengers.

[0003] Currently, the main methods used to suppress motor harmonic currents are:

[0004] 1. Dead-time-free switching control mode: Because the bridge inverter circuit requires a dead time in the switching states of the upper and lower bridge arms, the dead time will cause additional harmonics. Therefore, optimizing the switching states of the switching devices reduces the additional harmonics caused by the dead time. Although this control mode reduces the overall dead time, the dead time still exists and will still introduce current harmonics. Due to the higher real-time requirements of dead-time-free switching, it is also difficult to accurately compensate for the dead-time switching time in practice.

[0005] 2. Error Voltage Compensation Method: The error voltage compensation method uses a voltage signal with equal amplitude but opposite direction to cancel the inverter error voltage (the difference between the ideal voltage and the actual voltage) caused by the effects of dead time and tube voltage drop. This method not only increases hardware and software costs and algorithm complexity, but also fails to suppress harmonic components introduced by the non-sinusoidal distribution of the air gap in the magnetic field.

[0006] 3. Repetitive Control Method: The repetitive control method can achieve high-precision control of the stator current. The repetitive controller not only compensates for the deviation signal of the current cycle to the input of the controlled object, but also further compensates for the deviation signal of the previous cycle, thus keeping the deviation within a completely suppressed range. Repetitive control has a good suppression effect on harmonic components during steady-state motor operation. However, when the load changes, the motor enters a dynamic adjustment process, and the changes in speed, torque, and current are rapid and random, which leads to a deterioration in the performance of the repetitive controller. Furthermore, because repetitive control uses a variable sampling frequency, it is difficult to apply in practice.

[0007] 4. Adaptive Linear Neural Network Method: This method establishes steady-state voltage equations for the main harmonic components in the harmonic current. Building upon the harmonic injection method, it adds adaptive parameter identification to the model parameters. Identified parameters such as inductance, resistance, and flux linkage values ​​are imported into the neural network. By continuously adjusting the weights, the harmonics are reduced to zero. The harmonic voltage components are the weight coefficients in the adaptive neural network, thus obtaining the voltage compensation value. However, due to the large number of adaptive parameters and the complexity of the network, the adaptive neural network takes a long time to train and execute during dynamic motor operation, resulting in poor extraction and suppression of harmonic currents and voltages. Summary of the Invention

[0008] This invention provides a method for suppressing harmonic current in a permanent magnet synchronous motor. This invention can suppress motor torque pulsation and improve the stability of the motor system.

[0009] The technical solutions to the above technical problems are as follows:

[0010] A method for suppressing harmonic currents in a permanent magnet synchronous motor includes the following steps:

[0011] Step A: Perform Fourier decomposition of the voltage and current of the three-phase permanent magnet synchronous motor in the three-phase stationary coordinate system;

[0012] Step B: Transform the phase current of the motor into the dq coordinate system, then obtain the accurate harmonic current through an adaptive low-pass filter, and calculate the total harmonic current.

[0013] Step C: Adjust the control error of the total harmonic current to zero using the PI controller to obtain the output current of the PI controller, and then obtain the harmonic compensation voltage through the harmonic suppression module.

[0014] Step D: Introduce the harmonic compensation voltage obtained above into the current loop to obtain the d-axis voltage and q-axis voltage in the dq rotating coordinate system. Then, calculate the control voltage based on this dq voltage and obtain the two-phase input phase voltage of the motor in the static coordinate system through coordinate transformation.

[0015] Step E: The two-phase input phase voltage of the motor is modulated by SPWM, passed through a voltage inverter, and output to the motor to provide power, speed, and torque.

[0016] This invention combines Fourier decomposition and adaptive low-pass filter methods to accurately extract harmonic currents. Compared to selectively extracting only the 5th and 7th harmonics for suppression, the obtained harmonic currents are more faithful, with less signal feature loss, resulting in superior motor performance and a more universal algorithm. First, the three-phase currents are decomposed using Fourier transform to obtain all harmonic current components of the phase currents. Then, different low-pass filter algorithms (Butterworth, Chebyshev I, Chebyshev II, elliptic, etc.) are adaptively selected based on the cutoff frequency range and order of the motor controlled by the phase currents to obtain filters with fast response and high detection accuracy. The total harmonic current is extracted using the adaptive low-pass filter, and then a PI controller is used to minimize the current control error to zero, thereby obtaining the voltage compensation amount U for the current harmonics. sumu_c U sumv_c U sumw_c Then, the compensation voltage U along the dq axis is obtained through coordinate transformation. sum_dc U sum_qc The motor is then subjected to PI control in a rotating coordinate system after Clark / Park transformation. Fourier decomposition and an adaptive low-pass filter are used to extract the total harmonic current, ensuring the accuracy and coverage of the harmonic compensation voltage injection. This improves the dynamic response characteristics of the current, thereby enhancing the timeliness and accuracy of motor speed control.

[0017] Compared with existing technologies, the advantages of this invention are as follows:

[0018] 1. This invention combines Fourier decomposition and adaptive low-pass filter methods to extract total harmonic current, which can achieve accurate extraction of harmonic current;

[0019] 2. It eliminates the need to suppress harmonic currents of different orders separately, thus reducing the complexity of the system.

[0020] 3. Under the premise of ensuring the accuracy of harmonic compensation voltage injection, this invention improves the dynamic response characteristics of the current by using an adaptive low-pass filter method, thereby enhancing the speed and accuracy of the entire system control.

[0021] 4. The current signal feature extraction method used in this invention has less loss of current signal features and the calculated harmonic compensation voltage is more accurate. Therefore, the motor performance will be better. At the same time, the adaptive low-pass filter algorithm is also more universal. Attached Figure Description

[0022] Figure 1 Block diagram of the principle for extracting harmonic components of three-phase voltage / current of permanent magnet synchronous motor.

[0023] Figure 2 Block diagram of total harmonic suppression module for harmonic voltage.

[0024] Figure 3 Block diagram of the control system principle for harmonic current suppression method. Detailed Implementation

[0025] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0026] like Figures 1 to 3 The present invention provides a method for suppressing harmonic current in a permanent magnet synchronous motor, comprising the following steps:

[0027] Step A: Perform Fourier decomposition of the voltage and current of the three-phase permanent magnet synchronous motor in the three-phase stationary coordinate system;

[0028] Step B: Transform the phase current of the motor into the dq coordinate system, then obtain the accurate harmonic current through an adaptive low-pass filter, and calculate the total harmonic current.

[0029] Step C: Adjust the control error of the total harmonic current to zero using the PI controller to obtain the output current of the PI controller, and then obtain the harmonic compensation voltage through the harmonic suppression module.

[0030] Step D: Introduce the harmonic compensation voltage obtained above into the current loop to obtain the d-axis voltage and q-axis voltage in the dq rotating coordinate system. Then, calculate the control voltage based on this dq voltage and obtain the two-phase input phase voltage of the motor in the static coordinate system through coordinate transformation.

[0031] Step E: The two-phase input phase voltage of the motor is modulated by SPWM, passed through a voltage inverter, and output to the motor to provide power, speed, and torque.

[0032] As described above, the method for suppressing harmonic currents in a permanent magnet synchronous motor further includes, in step A:

[0033] Step A1: The expression for Fourier decomposition of the current with respect to the three-phase voltage and current is as follows:

[0034]

[0035]

[0036] Where n takes values ​​of 1, 2, 3, ..., T is the fundamental period of the input signal l, t is time, and U(t) is the amplitude of the current at time t. sum-i Let I be the current of the i-th phase, and I(t) be the amplitude of the current at time t. sum-i Let f be the current of the i-th phase, f be the fundamental frequency of the input signal, and a0 be the DC component.

[0037] The method for suppressing harmonic currents in permanent magnet synchronous motors as described above. Figure 2 This is a method for extracting harmonic currents, wherein, further, implementation step B specifically includes:

[0038] Step B1: Transform the phase current of the motor to the dq coordinate system; establish the correspondence between each harmonic current and its corresponding dq coordinate axis; for example, the coordinate transformation relationship for the 5th and 7th orders is as follows:

[0039]

[0040]

[0041] in, and θ is the coordinate transformation matrix of order 5 and order 7, and θ is the initial phase.

[0042] Step B2: According to the design of the harmonic current extraction algorithm, the current needs to be transformed into coordinates to obtain the harmonic current simulation model in the dq axis coordinate system.

[0043] The current equation in the dq coordinate system is:

[0044]

[0045] Among them, i d and i q Let i be the current in the dq rotating coordinate system. d1 i q1 Let i be the amplitude of the fundamental current in the dq coordinate system, i3, i5, i7 are the 3rd, 5th, and 7th current harmonic components, and ... are the initial phases.

[0046] Step B3: Find the optimal cutoff frequency; obtain accurate harmonic current through an adaptive low-pass filter; firstly, estimate the cutoff frequency using Butterworth, Chebyshev I, Chebyshev II, and elliptic filters respectively, and find the optimal cutoff frequency. The optimal solution for the cutoff frequency should meet the requirements of fast dynamic response and higher detection accuracy; the specific implementation method is as follows:

[0047] in, These are the combined weights for dynamic response time, curve smoothness, etc., represented by Butterworth, Chebyshev I, Chebyshev II, and elliptic filters, respectively; for the weights of any two decision variables, if they satisfy... Then it can be considered Weak dominance That is, choose The representative filter is the optimal one; among them, Let be any two decision variables.

[0048] Step B4: Find the optimal order; The current graph obtained by selecting the optimal order, cutoff frequency parameters, etc. should meet the characteristics of high detection accuracy, no obvious waveform jitter, and fast response time.

[0049] Step B5: Calculate the total harmonic current I sum-u I sum-v ,I sum-w The three-phase current is decomposed to obtain:

[0050]

[0051] In the formula, I sum-u I sum-v ,I sum-w θ1, θ3, θ5, and θ7 are the total harmonic currents of the three phases U, V, and W, respectively; θ1, θ3, θ5, and θ7 are the initial phases of the fundamental, 3rd, 5th, and 7th harmonics, respectively; I1, I3, I5, and I7 are the current amplitudes of the fundamental, 3rd, 5th, and 7th harmonics, respectively; and ω is the angular frequency.

[0052] Step B6: Extract the harmonics of the DC current component by using a low-pass filter to filter out the AC current component, and transform it to the dq rotating coordinate system:

[0053]

[0054] In the formula: n takes values ​​1, 2, 3, 4, 5, ..., i d *、i q * represents the amplitude of the fundamental current after being filtered by a low-pass filter in the dq coordinate system; t represents time; ω represents the angular frequency.

[0055] As described above, the method for suppressing harmonic currents in a permanent magnet synchronous motor further includes step C as follows: Figure 3 Specifically, it includes:

[0056] Step C1: Dynamically adjust the control error of the total harmonic current to zero using a PI controller;

[0057] Step C2: Obtain the output current of the PI controller;

[0058] Step C3: Obtain the harmonic compensation voltage U by using a harmonic suppression module composed of a steady-state voltage equation and a PI controller. u_c U v_c U w_c ;where U u_c U v_c U w_c These are the compensation voltages for the three phases U, V, and W, respectively.

[0059] As described above, the method for suppressing harmonic currents in a permanent magnet synchronous motor further includes, in step D:

[0060] Step D1: The harmonic compensation voltage U obtained above... u_c U v_c U w_c Introducing a current loop yields the d-axis voltage and the total harmonic voltage u along the q-axis in the dq rotating coordinate system. * sum-d u * sum-q :

[0061]

[0062] in, The total harmonic voltages along the d and q axes are respectively; ω is the angular frequency; L d Let L be the inductance along the d-axis. q R is the inductance along the q-axis. s For stator resistance, ψ f5 , ψ f11 , ψ f13 ... represent the 5th, 7th, and 13th flux linkages; θ1, θ3, θ5, and θ7 are the initial phases of the fundamental, 3rd, 5th, and 7th frequencies, respectively;

[0063] Step D2: Then calculate the control voltage in this dq axis coordinate system;

[0064] Step D3: Extract the total harmonic current I sum-u I sum-v I sum-w Transform to the dq coordinate system to obtain the total harmonic current i along the d-axis and q-axis. d and i q The total harmonic currents along the d-axis and q-axis are obtained:

[0065]

[0066] Among them, the total harmonic current i along the d-axis and q-axis d and i q , These are the total harmonic currents along the d and q axes, respectively; i d1 i q1 Let be the first-order current in the d-axis and q-axis coordinates;

[0067] Step D4: Finally, the compensation amount is transformed by Clark to the two-phase stationary α-β coordinate system, and then compensated to the input voltage with the fundamental frequency as the reference, to obtain the three-phase modulation reference voltage u that can suppress current harmonics. sum_αc u sum_βc ; where u sum_αc u sum_βc This represents the voltage compensation amount on the α and β axes.

[0068] Step D5: Calculation of total harmonic voltage compensation; using coordinate transformation principle, voltage equation and control target I. d-inj =0, I q-inj =0, where I d-inj I d-inj By injecting current values ​​into the d-axis and q-axis and controlling the target, the voltage compensation difference between the ideal and actual values ​​is calculated.

[0069] As described above, the method for suppressing harmonic currents in a permanent magnet synchronous motor further includes, in particular, step E:

[0070] Step E1: In MATLAB / Simulink, establish a harmonic extraction module, a harmonic voltage calculation module, and a harmonic voltage compensation module. Finally, after modulation and superposition, obtain the two-phase input phase voltages of the motor. Calculate the total compensation amount u of the d-axis and q-axis harmonic voltages based on the phase voltages. d-c u q-c :

[0071]

[0072] Where Rs is the stator resistance, u d-c u d-c L represents the voltage compensation amount under the dq rotating coordinate axis. d and L q Inductance and i are respectively the inductances along the dq rotating coordinate axis. dn i qn Let ω be the current at the nth order, where n takes values ​​of 1, 2, 3, 4, 5, ..., and ω is the angular frequency.

[0073] Step E2: The obtained new reference signal is modulated by the SVPWM module to generate the drive signal of the total reference voltage PMSM required for complete suppression of current harmonics in the dq rotating coordinate system;

[0074] Step E3: By injecting the drive signal into the control inverter and transmitting it to the three-phase windings of the motor, the current harmonics in the windings are suppressed.

[0075] The above control methods can achieve optimal control of the harmonic components of the motor phase current.

[0076] In summary, this invention first builds an electrical control system model of a permanent magnet synchronous motor in MATLAB Simulink to extract harmonic currents of all harmonic orders; then, it establishes a traditional control simulation system in Simulink, uses an adaptive filter to extract the input three-phase current, and performs a transformation in the dq coordinate system to obtain the total harmonic current i. d and i q Next, the total compensation voltage is calculated in the Simulink control simulation system. This invention, by using adaptive filters and methods for extracting total harmonic current, can adaptively select different filters to optimize the sinusoidal nature of the current waveform based on different motor types, cutoff frequencies, and harmonic orders. This effectively controls the torque pulsation generated by the DC component of the permanent magnet flux linkage and the harmonic components of the stator current in a permanent magnet synchronous motor from the source. This method offers fast, accurate, and simple control of vibration and noise.

[0077] It should be explained here that the above methods are only the best implementation methods of the present invention, and some illustrations and theoretical principles are only used for feature description and explanation; therefore, any modifications, substitutions, simplifications, etc. made without deviating from or departing from the spirit and theory of the present invention are included within the protection scope of the present invention.

Claims

1. A method for suppressing harmonic currents in a permanent magnet synchronous motor, characterized in that, Includes the following steps: Step A: Perform Fourier decomposition of the voltage and current of the three-phase permanent magnet synchronous motor in a three-phase stationary coordinate system; specifically including: Step A1: Extract the three-phase voltage and current from the drive power supply; Step A2: Perform Fourier decomposition on the three-phase voltage and current extracted from the drive power supply. The expression is as follows: ； ； Where n takes values ​​of 1, 2, 3, ..., T is the fundamental period of the input signal l, t is time, and U(t) is the amplitude of the current at time t. sum-i Let I be the voltage of the i-th phase, and I(t) be the amplitude of the current at time t. sum-i Let f be the current of the i-th phase, f be the fundamental frequency of the input signal, a0 be the DC component, and a n b n These are the Fourier coefficients; Step B: Transform the phase current of the motor into the dq coordinate system, then obtain the accurate harmonic current through an adaptive low-pass filter, and calculate the total harmonic current; including: Step B1: Transform the phase current of the motor to the dq coordinate system and establish the correspondence between each harmonic current and the corresponding harmonic dq coordinate axis. Step B2: Based on the design of the harmonic current extraction algorithm, the current is transformed to obtain the harmonic current simulation model in the dq axis coordinate system; Step B3: Find the optimal cutoff frequency. Obtain the accurate harmonic current through an adaptive low-pass filter. First, use Butterworth type, Chebyshev I, Chebyshev II, elliptic, etc. to estimate the cutoff frequency and find the optimal cutoff frequency. Step B4: Find the optimal order; Step B5: Calculate the total harmonic current I of the three phases U, V, and W. sum-u I sum-v , I sum-w The three-phase current is decomposed to obtain: ； In the formula, I sum-u I sum-v , I sum-w θ1, θ3, θ5, and θ7 are the initial phases of the fundamental, 3rd, 5th, and 7th harmonics, respectively; I1, I3, I5, and I7 are the current amplitudes of the fundamental, 3rd, 5th, and 7th harmonics, respectively; and ω is the angular frequency. Step B also includes: Step B6, using a low-pass filter to filter out the AC current component to extract the DC current component harmonics, and transforming it to the dq rotating coordinate system: ； In the above formula: n takes values ​​1, 2, 3, 4, 5..., i d *、i q * represents the amplitude of the fundamental current after being filtered by a low-pass filter in the dq coordinate system; t is time; ω is the angular frequency. Step C: Adjust the control error of the total harmonic current to zero using the PI controller to obtain the output current of the PI controller, and then obtain the harmonic compensation voltage through the harmonic suppression module. Step D: Introduce the harmonic compensation voltage obtained above into the current loop to obtain the d-axis voltage and q-axis voltage in the dq rotating coordinate system. Then, calculate the control voltage based on this dq voltage and obtain the two-phase input phase voltage of the motor in the static coordinate system through coordinate transformation. Step E: The two-phase input phase voltage of the motor is modulated by SPWM, passed through a voltage inverter, and output to the motor to provide power, speed, and torque.

2. The method for suppressing harmonic current in a permanent magnet synchronous motor according to claim 1, characterized in that, Step C includes: Step C1, dynamically adjusting the control error of the total harmonic current to zero using a PI controller; Step C2: Obtain the output current of the PI controller; Step C3: The three-phase harmonic compensation voltages U, V, and W are obtained by calculating the harmonics using the steady-state voltage equation and combining it with a PI controller. u_c U v_c U w_c .

3. The method for suppressing harmonic current in a permanent magnet synchronous motor according to claim 1, characterized in that, Step D includes: Step D1, obtaining the three-phase harmonic compensation voltages U, V, and W. u_c U v_c U w_c Introducing a current loop yields the d-axis voltage and the total harmonic voltage u along the q-axis in the dq rotating coordinate system. * sum-d u * sum-q ; Step D2: Then, calculate the control voltage based on this dq voltage; Step D3: Extract the total harmonic current I sum-u I sum-v , I sum-w Transform to the dq coordinate system to obtain the total harmonic current i along the d-axis and q-axis. d and i q , Step D4: Transform the compensation amount to a two-phase stationary α-β coordinate system using Clark transformation, and then compensate it to the input voltage referenced to the fundamental frequency to obtain a three-phase modulation reference voltage u that can suppress current harmonics. sum_αc u sum_βc , where u sum_αc u sum_βc This represents the voltage compensation amount on the α and β axes.

4. The method for suppressing harmonic current in a permanent magnet synchronous motor according to claim 3, characterized in that, In step D1, the d-axis voltage and the total harmonic voltage u of the q-axis are... * sum-d u * sum-q The calculation is as follows: ； Among them, u * sum-d u * sum-q These are the total harmonic voltages along the d and q axes, respectively; Based on the rotational frequency; L d Let L be the inductance along the d-axis. q R is the inductance along the q-axis. s For stator resistance, , , ...... θ1, θ3, θ5, and θ7 are the 5th, 7th, and 13th flux linkages, respectively; θ1, θ3, θ5, and θ7 are the initial phases of the fundamental, 3rd, 5th, and 7th frequencies, respectively.

5. The method for suppressing harmonic current in a permanent magnet synchronous motor according to claim 1, characterized in that, Step E includes: Step E1, establishing a harmonic extraction module, a harmonic voltage calculation module, and a harmonic voltage compensation module in MATLAB / Simulink, and finally obtaining the two-phase input phase voltage of the motor through modulation and superposition; Step E2: The obtained new reference signal is modulated by the SVPWM module to generate the drive signal of the total reference voltage PMSM required for complete suppression of current harmonics in the dq rotating coordinate system; Step E3: By injecting the drive signal into the control inverter and transmitting it to the three-phase windings of the motor, the current harmonics in the windings are suppressed.

6. The method for suppressing harmonic current in a permanent magnet synchronous motor according to claim 5, characterized in that, Calculate the total harmonic voltage compensation based on the obtained two-phase voltages: ； Where Rs is the stator resistance, u d-c u d-c L represents the voltage compensation amount under the dq rotating coordinate axis. d and L q Inductance and i are respectively the inductances along the dq rotating coordinate axis. dn i qn These are the currents at the nth order.

Images