A low-noise control method for dual three-phase permanent magnet motor based on dual centralized SVPWM with variable delay

Abstract

The present invention discloses a low-noise control method for a dual three-phase permanent magnet motor based on a double-centered SVPWM variable-delay method, which mainly includes establishing a mathematical model and a decoupling matrix of a dual three-phase permanent magnet synchronous motor; based on the maximum four-vector SVPWM algorithm adopted by a traditional dual three-phase permanent magnet synchronous motor, sector judgment and voltage vector action time calculation are performed to generate a PWM switch sequence; further, the action sequence of the voltage vector is adjusted to achieve the repetition of the output voltage of the front and rear half carrier cycles, and a suitable zero voltage vector is selected to reduce the number of additional switches; a centering is performed once in the front and rear half carrier cycles respectively to generate a double-neutralized SVPWM strategy of a symmetrical PWM waveform; finally, the double-neutralized SVPWM and the variable-delay SVPWM are combined to make the switching period T s Randomly change the harmonics at the carrier frequency and its integer multiples to the specified frequency domain, suppressing the high-frequency vibration and noise generated by the dual three-phase permanent magnet synchronous motor during operation.

Description

Technical Field

[0001] The invention belongs to the field of multi-phase motor control and relates to a control method for realizing dual-centralized SVPWM low vibration based on variable delay for a dual three-phase permanent magnet synchronous motor under vector control. Background Art

[0002] When the inverter is used to drive the dual three-phase permanent magnet synchronous motor, the fixed switching frequency will cause the high-frequency harmonic current to be concentrated at its carrier frequency and its integer multiples. These concentrated high-frequency harmonic currents will bring high-frequency harmonic magnetomotive force, which will act on the stator teeth to generate radial electromagnetic force, thereby exciting high-frequency vibration and noise, and have an adverse effect on the operation of the motor. In some specific applications, such as underwater submarines, household appliances, transportation, etc., the high-frequency vibration and noise problems caused by the operation of the motor cannot be ignored. Domestic and foreign scholars have carried out a lot of research on this issue, mostly starting from the modulation strategy. The most studied method at present is mainly random PWM technology, which introduces random variables into the control variables related to PWM harmonics, so that the concentrated PWM harmonics are expanded in a certain frequency domain, thereby reducing the high-frequency vibration and noise caused by them. Random PWM technology includes random zero vector PWM, random carrier frequency PWM, random position PWM, etc. Among them, random carrier frequency PWM is the simplest to implement. By randomizing the carrier period, the harmonic amplitude at the switching frequency and its integer multiples can be reduced, and the suppression effect of high-frequency current harmonics is the best. However, the random range of the random carrier frequency SVPWM needs to be subject to certain restrictions. Too large a random range may cause harmonic energy to invade the low-frequency band, generate low-frequency radial electromagnetic force, and affect the control effect of the motor.

[0003] Most existing research methods can only suppress part of the PWM harmonics, and the total content of the harmonic current will not change, and high-frequency vibration still exists. The improved SVPWM technology starts with the PWM switching sequence. By adjusting the action sequence of the voltage vector in a switching cycle, the voltage output by the inverter is repeated once in a switching cycle, and finally the current harmonics at odd carrier frequencies can be eliminated, thereby eliminating the odd carrier frequency vibration and noise of the motor. However, the improved SVPWM technology cannot suppress the current harmonics at even carrier frequencies, and even carrier frequency vibration still exists.

[0004] By combining the improved SVPWM with the random carrier frequency SVPWM technology, the harmonic current at the odd multiple of the carrier frequency can be eliminated while the harmonic current at the even multiple of the carrier frequency can be effectively suppressed. Compared with the traditional random carrier frequency SVPWM technology, the improved SVPWM technology can extend the frequency domain of harmonic energy to a wider range without affecting the control performance of the motor. Summary of the invention

[0005] The present invention eliminates high-frequency harmonics at odd multiples of carrier frequency by adjusting the action order of the voltage vector in the second half of the cycle. And select appropriate zero vectors according to the PWM characteristics of different sectors to reduce the number of additional switches caused by the reconstruction of the switching sequence. In order to simplify the algorithm and facilitate implementation, the switching sequence is further centered in the first and second half of the carrier cycle to obtain a symmetrical switching PWM waveform and reduce the low-frequency even harmonics caused by asymmetric PWM. The double-centered SVPWM algorithm is adopted to eliminate the harmonics at odd multiples of the carrier frequency. Combined with the variable delay method, the carrier cycle is randomized, so that the high-frequency harmonics at the even multiples of the carrier frequency are significantly suppressed, thereby achieving comprehensive vibration suppression of the entire frequency band.

[0006] The low vibration control method of a dual three-phase permanent magnet synchronous motor is characterized by comprising the following steps:

[0007] Step 1: First, construct the mathematical model of the dual three-phase permanent magnet synchronous motor and obtain its decoupling coordinate transformation matrix.

[0008] Step 2: Based on the maximum four-vector SVPWM algorithm, sector judgment and basic voltage vector action time calculation are performed to obtain the switching sequence of the traditional SVPWM algorithm.

[0009] Step 3: Adjust the voltage vector action sequence of the traditional SVPWM so that the output voltages of the first and second half carrier cycles are the same, thus eliminating high-frequency harmonics at odd multiples of the carrier frequency.

[0010] Step 4: Select an appropriate zero voltage vector to reduce the number of additional switches caused by rearranging the voltage vector action sequence.

[0011] Step 5: Perform centering once in the first and second half carrier cycles respectively to obtain a symmetrical PWM waveform, which is simpler in algorithm implementation and reduces the low-frequency even harmonics caused by asymmetrical PWM.

[0012] Step 6: Use variable delay SVPWM to make the switching period T s Random changes disperse the harmonics at even carrier frequencies into the specified frequency domain, greatly reducing the amplitude of high-frequency harmonics.

[0013] The research object of the present invention is a dual three-phase permanent magnet synchronous motor. The dual three-phase permanent magnet synchronous motor is a complex system with strong coupling and nonlinearity. In order to realize the control of the dual three-phase permanent magnet synchronous motor, by deriving the relationship between commonly used coordinate systems, the sixth-order decoupling transformation matrix of the dual three-phase permanent magnet synchronous motor can be obtained, and the mathematical model of the decoupled dual three-phase permanent magnet synchronous motor can be obtained.

[0014]

[0015]

[0016] In the formula, θ e is the rotor position angle.

[0017] The mathematical model of the dual three-phase permanent magnet synchronous motor is constructed as follows:

[0018]

[0019] Among them, u d and u q are dq axis voltage, u x ,u y is the xy axis voltage; i d and i q is the dq axis current, i x ,i y are the x- and y-axis currents; R is the winding resistance; L d and L q are the dq axis inductance respectively; L z is the harmonic plane leakage inductance; f Represents the flux linkage of a permanent magnet.

[0020] The present invention is based on the maximum four-vector SVPWM algorithm, performs sector judgment, calculates the voltage vector action time, and obtains the original PWM switch sequence.

[0021] The dual three-phase permanent magnet synchronous motor is decoupled into αβ subspace and xy subspace through coordinate transformation. The αβ subspace is related to the electromechanical energy conversion of the motor, while the xy subspace is not related to the electromechanical energy conversion. The maximum four-vector SVPWM algorithm is adopted, and the four largest voltage vectors on the outermost edge are selected to synthesize the fundamental voltage vector and the harmonic voltage vector, and the PWM is centralized to realize closed-loop control of the harmonic space to reduce harmonics and losses. At the same time, the voltage vector with the largest amplitude can improve the voltage utilization.

[0022] The voltage vector action sequence of the traditional SVPWM is adjusted to make the output voltage of the first and second half carrier cycles the same, thereby eliminating high-frequency harmonics at odd multiples of the carrier frequency.

[0023] Taking the maximum four-vector SVPWM algorithm adopted in the present invention as an example, in order to synthesize the reference voltage vector, four effective voltage vectors and two zero vectors are selected in each switching cycle. In order to facilitate control, the traditional SVPWM algorithm often performs centralization processing on PWM. The effective voltage vector produced after centralization will change, but the reference voltage vector synthesized in one cycle will not change, that is, the use of PWM after centralization will not affect the control effect. After the PWM is centralized, an 11-segment PWM is formed. The switching sequence is further processed to swap the order of the voltage vector in the second half cycle, so that the voltage vectors acting in the two half cycles are completely consistent, thereby obtaining the switching sequence of the improved SVPWM algorithm. The output voltage of the improved inverter satisfies the expression:

[0024] u(t+0.5T s )=u(t)

[0025] Where, T s Indicates the carrier period. It can be seen that the minimum period of the voltage becomes 0.5T s By implementing the improved SVPWM algorithm, the harmonic current at odd switching frequencies can be eliminated and the vibration and noise at odd switching frequencies can be suppressed.

[0026] The present invention selects a suitable zero voltage vector to reduce the number of additional switches caused by the reconstruction of the voltage action sequence. After the voltage vector action sequence of the second half of the carrier cycle is readjusted, the symmetrical PWM sequence changes, and the switching action in some phases increases to 2 times. Therefore, a suitable zero voltage vector is selected by referring to the sector where the voltage vector is located to reduce the number of switches in one carrier cycle. The selected voltage vectors are as follows: In sectors I, II, V, VI, IX, and X, a zero vector V is selected. 77 , select zero vector V in sectors III, IV, VII, VIII, XI, XII 00 .

[0027] The PWM switching sequence is centered once in the first and second half of the carrier cycle to obtain a symmetrical PWM waveform and implement the dual-centered SVPWM algorithm. Compared with the asymmetric improved SVPWM, the dual-centered SVPWM is simpler in algorithm and implementation, while reducing the low-frequency even harmonics caused by asymmetric PWM, reducing the harm to the motor and reducing the low-frequency vibration it excites.

[0028] The present invention adopts variable delay SVPWM so that the switching period T s Random changes disperse the harmonics at the switching frequency and its integer multiples into the specified frequency domain, greatly reducing the harmonic amplitude. The principle of variable delay SVPWM is as follows:

[0029] The variable delay SVPWM randomly changes the switching frequency while keeping the sampling frequency unchanged, and ensures that the average value of the switching frequency is equal to the sampling frequency. This not only retains the advantage of the random switching frequency SVPWM in terms of obvious harmonic suppression effect, but also does not affect the control performance. The variable delay SVPWM calculates the delay time Δt of the next switching cycle in each sampling cycle, and the expression of the nth switching cycle is:

[0030] T s (n) = T samp +Δt n -Δt n-1

[0031] Δt=R vtd T samp

[0032] Where, T s (n) represents the generated n switching cycles, Δt n and Δt n-1 Indicates the delay time of the nth and n-1th switching cycles; T samp is the sampling period; R vtd is a random number uniformly distributed between [0,1].

[0033] Random zero vector-variable delay SVPWM can disperse the high-frequency harmonics at the switching frequency and its integer multiples into the specified frequency domain, significantly reducing the harmonic amplitude without affecting the control performance of the system, and has excellent harmonic suppression effect. The beneficial effects of the present invention are:

[0034] 1. The present invention improves the switching sequence of the traditional four-vector SVPWM algorithm, changes the action order of the effective voltage vector in the second half of the switching cycle, and eliminates high-frequency current harmonics at odd switching frequencies without affecting the control performance.

[0035] 2. The present invention selects a suitable zero vector to reduce the number of switching times based on adjusting the action sequence of the voltage vector; and performs centering once in the front and rear half carrier cycles respectively, thereby reducing the low-frequency even harmonics caused by the asymmetric PWM waveform and reducing the complexity of the algorithm and the difficulty of implementation.

[0036] 3. The present invention uses random switching frequency SVPWM with constant sampling frequency, combined with dual centralized SVPWM, to avoid the low-frequency resonance problem that may be caused by the traditional random switching frequency method, expand the random frequency change range, and significantly reduce the high-frequency vibration and noise problems caused by concentrated harmonic currents. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is the control block diagram of the low vibration control strategy for dual three-phase permanent magnet synchronous motors;

[0038] Figure 2 The voltage vector distribution diagram of the dual three-phase permanent magnet synchronous motor; (a) is the fundamental wave space; (b) is the harmonic space;

[0039] Figure 3 The switching sequence of the traditional SVPWM: (a) is the traditional seven-segment PWM switching sequence (b) is the 11-segment PWM switching sequence;

[0040] Figure 4 Schematic diagram of the switching sequence and corresponding phase voltage of the improved SVPWM algorithm; (a) is the 11-segment PWM switching sequence and phase voltage (b) is the PWM switching sequence and phase voltage of the improved SVPWM (c) is the PWM switching sequence and phase voltage of the improved SVPWM with reduced switching times;

[0041] Figure 5 PWM switching sequence and phase voltage for dual centralized SVPWM;

[0042] Figure 6 It is a schematic diagram of the dual centralized SVPWM algorithm based on variable delay;

[0043] Figure 7 The following are the Fourier analysis results of phase current under various methods: (a) is the Fourier analysis result of phase current of traditional 11-segment SVPWM; (b) is the Fourier analysis result of phase current of dual-centered SVPWM; (c) is the Fourier analysis result of phase current of variable-delay SVPWM; (d) is the Fourier analysis result of phase current of dual-centered SVPWM based on variable-delay; Figure 8 The vibration test results of each method are as follows: (a) is the vibration test result of the traditional 11-segment SVPWM, (b) is the vibration test result of the dual-centralized SVPWM, (c) is the vibration test result of the variable-delay SVPWM, and (d) is the vibration test result of the dual-centralized SVPWM based on the variable-delay.

[0044] Specific implementation method

[0045] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0046] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0047] like Figure 1As shown in the structural block diagram, the present invention is a low vibration control strategy for dual three-phase permanent magnet synchronous motors, mainly dual centralized SVPWM and variable delay SVPWM.

[0048] The present invention takes a dual three-phase permanent magnet synchronous motor as the control object, performs double centralization processing on its switching sequence, and further combines variable delay SVPWM to suppress high-frequency harmonics. The specific measures are as follows:

[0049] Step 1: The dual three-phase permanent magnet synchronous motor is a complex system with strong coupling and nonlinearity. In order to realize the control of the dual three-phase permanent magnet synchronous motor, by deriving the relationship between commonly used coordinate systems, the sixth-order decoupling transformation matrix of the dual three-phase permanent magnet synchronous motor can be obtained, and the mathematical model of the decoupled dual three-phase permanent magnet synchronous motor can be obtained.

[0050]

[0051] In the formula, θ e is the rotor position angle.

[0052] The mathematical model of permanent magnet synchronous motor is constructed as follows:

[0053]

[0054] Among them, u d and u q are dq axis voltage, u x ,u y is the xy axis voltage; i d and i q is the dq axis current, i x ,i y are the x- and y-axis currents; R is the winding resistance; L d and L q are the dq axis inductance respectively; L z is the harmonic plane leakage inductance; f Represents the flux linkage of a permanent magnet.

[0055] Step 2: Based on the maximum four-vector SVPWM algorithm, perform sector judgment, calculate the voltage vector action time, and obtain the original PWM switching sequence.

[0056] The dual three-phase permanent magnet synchronous motor is decoupled into the αβ subspace and the xy subspace through coordinate transformation, where the αβ subspace is related to the electromechanical energy conversion of the motor, and the xy subspace is irrelevant to the electromechanical energy conversion, and the maximum four-vector SVPWM algorithm is adopted. Figure 2 The voltage vector distribution diagram of the αβ subspace and the xy subspace is shown in Figure 2. Taking the first sector as an example, the voltage vector v is selected 55 、v 45 、v 44 、v64 The reference voltage vector is synthesized, the action time of the corresponding voltage vector is calculated, the switching sequence of the traditional SVPWM is obtained, and a centralization process is performed, such as Figure 3 As shown. The four largest voltage vectors at the outermost edge are selected to synthesize the fundamental voltage vector and the harmonic voltage vector, and the PWM is centralized to realize closed-loop control of the harmonic space to reduce harmonics and losses. At the same time, the voltage vector with the largest amplitude can improve the voltage utilization rate.

[0057] Step 3: Adjust the voltage vector action sequence of the traditional SVPWM so that the output voltages of the first and second half carrier cycles are the same, thus eliminating high-frequency harmonics at odd multiples of the carrier frequency.

[0058] Taking the maximum four-vector SVPWM algorithm used in this paper as an example, in order to synthesize the reference voltage vector, four effective voltage vectors and two zero vectors are selected in each switching cycle. In order to facilitate control, the traditional SVPWM algorithm often performs centralization on PWM. The effective voltage vector produced after centralization will change, but the reference voltage vector synthesized in one cycle will not change, that is, the use of PWM after centralization will not affect the control effect. After the PWM is centralized, an 11-segment PWM is formed, such as Figure 4 As shown in (a), the switching sequence is further processed by swapping the action order of the voltage vectors in the second half cycle so that the voltage vectors acting in the first and second half cycles are completely consistent, thereby obtaining the switching sequence of the improved SVPWM algorithm, as shown in Figure 4 (b) is shown. The output voltage of the improved inverter satisfies the expression:

[0059] u(t+0.5T s )=u(t)

[0060] Where, T s Indicates the carrier period. It can be seen that the minimum period of the voltage becomes 0.5T s .

[0061] By implementing the improved SVPWM algorithm, the harmonic current at odd switching frequencies can be eliminated and the vibration and noise at odd switching frequencies can be suppressed.

[0062] Step 4: Select an appropriate zero voltage vector to reduce the number of additional switches caused by the reconstruction of the voltage action sequence. Figure 4As shown in (b), compared with the traditional SVPWM, the number of switching times in one carrier cycle of the improved SVPWM increases from 6 to 9, which will bring additional switching losses. Therefore, a suitable zero voltage vector is selected by referring to the sector where the voltage vector is located to reduce the number of switching times in one carrier cycle. The selected voltage vectors are as follows: Zero vector V is selected in sectors I, II, V, VI, IX, and X 77 , select zero vector V in sectors III, IV, VII, VIII, XI, XII 00 The obtained PWM waveform is as follows Figure 4 As shown in (c), the number of switching times in one carrier cycle is reduced to 8 times.

[0063] Step 5: Figure 4 As shown in (c), after adjusting the voltage vector action sequence and selecting the zero vector, the PWM waveform is asymmetric, which not only introduces the problem of low-frequency even harmonics, but also increases the difficulty of implementation. Therefore, the PWM switching sequence is centered once in the first and second half of the carrier cycle to obtain a symmetrical PWM waveform and implement the dual-centered SVPWM algorithm. Its PWM switching sequence is as follows: Figure 5 As shown in the figure, it can be seen that the phase voltage is still the same in the first and second half carrier cycles. Therefore, the high-frequency harmonics and vibration acceleration at odd carrier frequencies can still be eliminated. Compared with the asymmetric improved SVPWM, the dual centralized SVPWM is simpler in algorithm and implementation, while reducing the low-frequency even harmonics caused by asymmetric PWM, reducing the harm to the motor and reducing the low-frequency vibration it excites.

[0064] Step 6: Use variable delay SVPWM to make the switching period T s Random changes disperse the harmonics at the switching frequency and its integer multiples into the specified frequency domain, greatly reducing the harmonic amplitude. The principle of variable delay SVPWM is as follows:

[0065] The variable delay SVPWM randomly changes the switching frequency while keeping the sampling frequency unchanged, and ensures that the average value of the switching frequency is equal to the sampling frequency. This not only retains the advantage of the random switching frequency SVPWM in terms of obvious harmonic suppression effect, but also does not affect the control performance. The variable delay SVPWM calculates the delay time Δt of the next switching cycle in each sampling cycle, and the expression of the nth switching cycle is:

[0066] T s (n) = T samp +Δt n -Δt n-1

[0067] Δt=R vtd T samp

[0068] Where, T s (n) represents the generated n switching cycles, Δt n and Δt n-1 Indicates the delay time of the nth and n-1th switching cycles; T samp is the sampling period; R vtd is a random number uniformly distributed between [0,1].

[0069] Figure 6 This is a schematic diagram of a dual centralized SVPWM algorithm based on variable delay. By adding a comparison value register, the logic of the switch action is changed in the half cycle before and after each PWM cycle, thereby realizing dual centralized SVPWM. At the same time, combined with variable delay, the delay time of the next cycle is calculated in the current cycle, so that the sampling value will not be lost and the normal function of the dual centralized SVPWM algorithm will not be affected.

[0070] Figure 7 The experimental results of the dual three-phase permanent magnet synchronous motor under normal operation using different control algorithms are given, and the phase current waveform, PWM waveform, phase voltage and Fourier analysis are given, and the carrier frequency is 10kHz. Figure 7 As shown in (a), when using traditional SVPWM, there are obvious harmonic peaks at the carrier frequency and its integer multiples. Figure 7 As shown in (b), when the dual-centered SVPWM algorithm is used, the high-frequency harmonics at odd carrier frequencies are almost completely eliminated. Figure 7 (c) and Figure 7 (d) are the experimental results of the variable delay SVPWM algorithm and the dual centralized SVPWM algorithm based on variable delay. It can be seen that compared with the variable delay, the combination of dual centralized SVPWM can better suppress high-frequency harmonics and has less impact on the low-frequency band.

[0071] Figure 8 The vibration test results of dual three-phase permanent magnet synchronous motors using different control algorithms are shown in Figure 2. Figure 8 As shown in (a), when using traditional SVPWM, there are obvious acceleration spikes at the carrier frequency and its integer multiples. Figure 8 As shown in (b), when the dual-centered SVPWM algorithm is used, the vibration at odd carrier frequencies is almost completely eliminated. Figure 8 (c) and Figure 8 (d) are the vibration test results of the variable delay SVPWM algorithm and the dual centralized SVPWM algorithm based on variable delay. It can be seen that compared with the variable delay, the combination of dual centralized SVPWM can better suppress high-frequency vibration and has less impact on the low-frequency band.

[0072] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0073] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A low-noise control method for dual three-phase permanent magnet motor based on dual centralized SVPWM with variable delay, characterized in that: It includes the following steps: Step 1: Using the vector space decoupling method, a mathematical model of the dual three-phase permanent magnet synchronous motor including the fundamental wave plane and the harmonic wave plane is constructed; Step 2: Based on the maximum four-vector SVPWM algorithm of the dual three-phase permanent magnet synchronous motor, sector judgment and basic voltage vector action time calculation are performed to obtain the switching sequence of the maximum four-vector SVPWM algorithm; Step 3: Adjust the voltage vector action sequence of the maximum four-vector SVPWM so that the output voltages of the first and second half carrier cycles are the same, thereby eliminating high-frequency harmonics at odd multiples of the carrier frequency. In the step 3, in order to synthesize the reference voltage vector, four effective voltage vectors and two zero vectors are selected in each switching cycle; the PWM is centered, and the effective voltage vector that is effective after the centering will change, but the reference voltage vector synthesized in one cycle will not change, that is, the use of the PWM after the centering will not affect the control effect; after the PWM is centered, an 11-segment PWM is formed, and the switching sequence is further processed to exchange the order of the voltage vector in the second half cycle, so that the voltage vectors acting in the two half cycles are completely consistent, thereby obtaining the switching sequence of the improved SVPWM algorithm; The output voltage of the improved inverter satisfies the expression: u(t+0.5T s )=u(t) Where, T s Indicates the carrier period. It can be seen that the minimum period of the voltage becomes 0.5T s ; By implementing the improved SVPWM algorithm, the harmonic current at odd switching frequencies can be eliminated, and the vibration and noise at odd switching frequencies can be suppressed; Step 4: Select an appropriate zero voltage vector to reduce the number of additional switches caused by rearranging the voltage vector action sequence; In step 4, a suitable zero voltage vector is selected to reduce the number of additional switches caused by the reconstruction of the voltage action sequence. The specific process is as follows: After the voltage vector action sequence of the second half of the carrier cycle is readjusted, the symmetrical PWM sequence changes, and the switching action of some phases increases to 2 times in one control cycle, which will produce greater switching losses; therefore, according to the sector where the reference voltage vector is located, the number of switches in each cycle can be reduced by selecting a suitable zero voltage vector; the principle of selecting the zero voltage vector is: select the zero vector V in sectors I, II, V, VI, IX, and X 77 , in sectors III, IV, VII, VIII, XI, XII, use zero vector V 00 ; Step 5: Perform centering processing on the PWM waveforms in the front and rear half carrier cycles respectively to obtain symmetrical PWM waveforms in the front and rear half wave cycles respectively; Step 6: Use variable delay SVPWM to make the switching period T s Random changes disperse the harmonics at even carrier frequencies into the specified frequency domain, thereby reducing the harmonic amplitude and suppressing vibration.

2. The method according to claim 1, characterized in that: In the step 1, the dual three-phase permanent magnet synchronous motor is a complex system with strong coupling and nonlinearity. In order to realize the control of the dual three-phase permanent magnet synchronous motor, the relationship between the coordinate systems is derived to obtain the sixth-order decoupling transformation matrix of the dual three-phase permanent magnet synchronous motor, and the mathematical model of the decoupled dual three-phase permanent magnet synchronous motor is obtained; In the formula, θ e is the rotor position angle, T αβ , T dq They are the transformation matrices corresponding to the original coordinate system to the stationary coordinate system and the stationary coordinate system to the rotating coordinate system; The mathematical model of the dual three-phase permanent magnet synchronous motor is constructed as follows: Among them, u d and u q are dq axis voltage, u x ,u y are x and y axis voltages respectively; i d and i q is the dq axis current, i x ,i y are the x- and y-axis currents; R is the winding resistance; L d and L q are the dq axis inductance respectively; L z is the harmonic plane leakage inductance; f represents the magnetic flux of the permanent magnet; ω is the electrical angular velocity.

3. The method according to claim 1, characterized in that: In the step 2, the dual three-phase permanent magnet synchronous motor is decoupled into the αβ subspace and the xy subspace through coordinate transformation, wherein the αβ subspace is related to the electromechanical energy conversion of the motor, and the xy subspace is not related to the electromechanical energy conversion. The maximum four-vector SVPWM algorithm is adopted, and the four largest voltage vectors at the outermost edge are selected to synthesize the fundamental voltage vector and the harmonic voltage vector, and the PWM is centralized to realize closed-loop control of the harmonic space, so as to reduce harmonics and reduce losses. At the same time, the voltage vector with the largest amplitude is selected to improve the voltage utilization rate.

4. The method according to claim 1, characterized in that: In step 5, the PWM switch sequence is centered once in the front and rear half carrier cycles respectively, so as to obtain a symmetrical PWM waveform and realize a dual-centered SVPWM algorithm; the dual-centered SVPWM is simpler in algorithm and implementation than the asymmetric improved SVPWM, and at the same time reduces the low-frequency even harmonics caused by the asymmetric PWM.

5. The method according to claim 1, characterized in that: In step 6, based on the dual centralized SVPWM, variable delay SVPWM is introduced so that the switching period T s Random changes disperse the harmonics at the switching frequency and its integer multiples into the specified frequency domain, greatly reducing the harmonic amplitude; variable delay SVPWM is as follows: The variable delay SVPWM randomly changes the switching frequency while keeping the sampling frequency unchanged, and ensures that the average value of the switching frequency is equal to the sampling frequency; this not only retains the advantage of the random switching frequency SVPWM in terms of obvious harmonic suppression effect, but also does not affect the control performance; the variable delay SVPWM calculates the delay time Δt of the next switching cycle in each sampling cycle, and the expression of the nth switching cycle is: T s (n)=T samp +Δt n -Δt n-1 Δt=R vtd T samp Where, T s (n) represents the generated n switching cycles, Δt n and Δt n-1 Indicates the delay time of the nth and n-1th switching cycles; T samp is the sampling period; R vtd is a random number uniformly distributed between [0,1].

6. The method according to claim 5, characterized in that: It also includes that the random zero vector-variable delay SVPWM can disperse the high-frequency harmonics at the switching frequency and its integer multiples into the specified frequency domain, significantly reducing the harmonic amplitude without affecting the control performance of the system.

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