Nine-phase permanent magnet synchronous motor multi-space harmonic current suppression method based on virtual voltage vector

Abstract

The invention discloses a nine-phase permanent magnet synchronous motor multi-space harmonic current suppression method based on a virtual voltage vector, and belongs to the technical field of multi-phase motor control. The method mainly comprises the following steps of: 1, performing vector space decoupling on a nine-phase system, and selecting four groups of totally 72 basic voltage vectors as a basic control set; 2, according to a volt-second balance principle, corresponding virtual voltage vectors with mapping amplitudes of 0 in other spaces are constructed in the three harmonic spaces; and 3, analyzing phase current distribution characteristics under a harmonic open-loop control method, and formulating a duty ratio optimal distribution rule for preferentially suppressing third harmonics. And 4, judging sectors of the reference voltage vectors in the fundamental wave space and the three harmonic wave spaces, and outputting the sectors after reasonable optimization distribution of the duty ratio. By utilizing the constructed virtual voltage vector and duty ratio optimization distribution rule, the full-space closed-loop control can be realized when the modulation degree is low, and the third harmonic can be preferentially suppressed when the modulation degree is high, so that the current quality is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of multi-phase motor control, and in particular relates to a harmonic suppression method for a nine-phase permanent magnet synchronous motor. Background Art

[0002] The nine-phase permanent magnet synchronous motor has the characteristics of high power density, strong fault tolerance, and high control flexibility. It is suitable for shipboard propulsion, electric propulsion aircraft and other fields. In these high-reliability occasions, efficient control of the motor system is particularly required. At present, in the control methods used in the nine-phase system, the harmonic content of the phase current is extremely large, which seriously affects the control efficiency and causes great harm. Therefore, it is necessary to study control methods with excellent steady-state performance and low current harmonic content. The virtual vector method is a simple and direct effective control strategy to eliminate harmonic currents. It is widely used in multi-phase systems. However, this method has only been widely promoted in five-phase and six-phase systems, and its application in nine-phase systems is limited. Compared with other dual three-phase and five-phase motors, the nine-phase motor system has more harmonic space (third, fifth and seventh harmonic space), and the switching state is complicated (512), so it is necessary to reasonably combine and screen the voltage vectors in the nine-phase system. In the construction of a virtual voltage vector, a group of collinear or adjacent vectors are often selected to construct the virtual voltage vector. The virtual voltage vector method in the current nine-phase system can rarely achieve the goal of zero harmonic components, and it is difficult to perform closed-loop control of the harmonic space. The harmonic current is only simply open-loop controlled. In actual operation, the dead zone effect of the inverter and some nonlinear factors will cause harmonic currents to be generated. It will be difficult to control this part of the harmonic current by open-loop processing of the harmonic current. The Chinese invention patent "A model predictive control method for a nine-phase open-winding permanent magnet synchronous motor based on a virtual vector" (patent number CN202110627898.5) discloses a control method based on a virtual voltage vector. This method constructs a virtual voltage vector with zero harmonic components and uses it as a control set to improve current quality and reduce current harmonics. However, due to the open-loop control of the harmonic space, the harmonic content in the phase current is large, especially the third harmonic, which already accounts for a large proportion. Therefore, the nine-phase system requires a multi-space closed-loop harmonic current suppression strategy, and the virtual voltage vector is reasonably designed after screening and combining the voltage vector, and a virtual voltage vector that can also have zero mapping amplitude in other spaces is constructed in the harmonic space. These virtual voltage vectors are used as control sets to avoid complex control after multi-space closed-loop, making the control method simple and efficient. Summary of the invention

[0003] Purpose of the invention: In order to solve the problems existing in the prior art and to achieve multi-space closed-loop harmonic current suppression in a nine-phase permanent magnet synchronous motor system, the present invention discloses a multi-space closed-loop harmonic current suppression strategy based on dynamic optimization allocation of duty cycle for a nine-phase permanent magnet synchronous motor.

[0004] Technical solution: To achieve the above-mentioned invention object, the technical solution adopted by the present invention is as follows:

[0005] The present invention provides a multi-space closed-loop harmonic current suppression method based on virtual voltage vector for a nine-phase permanent magnet synchronous motor. The implementation steps include: Step 1) obtaining a fundamental space reference voltage u through a speed loop d 、u q In the harmonic space, the expected value of the harmonic current is zero and the harmonic current feedback is subtracted. The corresponding harmonic reference voltage u is obtained by adjusting the PI controller. d357 、u q357 Step 2) After coordinate transformation of each spatial reference voltage, the reference voltage u of the α-axis and β-axis in the stationary coordinate system is obtained. α 、u β and u α357 、u β357 , and then calculate to obtain the reference voltage vector of each space: u r * ,u r3 * ,u r5 * ,u r7 * Step 3) Determine the sector to which each space voltage vector belongs, select the corresponding virtual voltage vector, and calculate the action time of each virtual voltage vector to synthesize the corresponding reference voltage vector. Step 4) Redistribute the action time of each virtual voltage vector according to the established duty cycle optimization allocation rule and then output it.

[0006] Further, the specific process of the step) is:

[0007] Real-time detection of phase current i in the nine-phase natural coordinate system abcdefghi After the coordinate transformation from the nine-phase natural coordinate system to the two-phase rotating coordinate system, the current component i in the two-phase rotating coordinate system of the current control period is obtained. d 、i q 、i d357 、i q357 , the given speed is obtained after passing through the PI controller q The expected value of q * The error between the two can be obtained after passing through the PI controller. q , at the same time, i d Given i d * is 0, the given harmonic current is 0, and the respective errors can be obtained through the PI controller u d 、u d357 、u q357 ,

[0008] Further, the specific process of step 2) is: after the fundamental voltage and the harmonic voltage are transformed from the two-phase rotating coordinate system to the two-phase stationary coordinate system, u α 、u β and u α357 、u β357 After calculation, the reference voltage vector of each space can be obtained: r * ,u r3 * ,u r5 * ,u r7 * .

[0009] The reference voltage vector calculation method is:

[0010]

[0011] Among them, u α 、u β is the reference voltage of the α-axis and β-axis in the stationary coordinate system, and θ is the reference voltage vector u r * Angle

[0012] Further, the specific process of step 3) is as follows:

[0013] Step 3.1) Construct a virtual voltage vector set. First, classify the switch states of the nine-phase inverter in the form of (ab), where a is the number of states 1 and b is the number of states 0. Specifically, they are divided into (1-8), (2-7), (3-6), and (4-5). Based on the principle that the amplitude of the voltage vector of the adjacent combined conducting bridge arm is the largest, the 18 largest voltage vectors in each group can be selected from the four groups of vectors and named as {1-8}max, {2-7}max, {3-6}max, and {4-5}max subsets, respectively, and denoted by V S 、V M 、V ML and V L Indicates that it can be expressed in each space as:

[0014]

[0015] Where u1, u3, u5, and u7 represent the space voltage vectors, γ = 2π / 9, S (A～I) is the switching state of each phase bridge arm, thereby screening out 72 voltage vectors and obtaining their distribution characteristics in each space. In the fundamental wave space, according to the mapping amplitude and phase of each voltage vector in the three harmonic spaces, four collinear vectors are selected to eliminate the third, fifth and seventh harmonic voltages. The action time of each vector is calculated as:

[0016]

[0017] Among them U dc is the DC bus voltage, T S is the control period, t1, t2, t3, t4, respectively correspond to V S 、V M 、V ML and V L In the fundamental wave space, a total of 18 virtual voltage vectors are synthesized, starting from 0° and distributed at 20° intervals, named VV1. In the third harmonic space, three collinear vectors are selected to eliminate the mapping amplitude in the fundamental wave space and the fifth and seventh harmonic spaces. A group of virtual voltage vectors that are only mapped in the third harmonic space are constructed, named VV3. The action time of each vector is calculated as follows

[0018]

[0019] Among them, t5, t6, and t7 correspond to V S 、V M and V L In the fifth harmonic space, four collinear vectors are selected to eliminate the amplitude mapping in the fundamental space and the third and seventh harmonic spaces. A set of virtual voltage vectors that are only mapped in the fifth harmonic space is constructed and named VV5. The action time of each vector is calculated as follows

[0020]

[0021] Among them U dc is the DC bus voltage, T S is the control period, t9, t 10 ,t 11 ,t 12 Corresponding to V S 、V M 、V ML and V L In the fifth harmonic space, a total of 18 virtual vectors are synthesized, with the same distribution as VV1. In the seventh harmonic space, four collinear vectors are selected to eliminate the amplitude mapping in the fundamental space and the third and fifth harmonic spaces. A set of virtual voltage vectors that are only mapped in the seventh harmonic space is constructed, named VV7. The action time of each vector is calculated as follows

[0022]

[0023] Among them U dc is the DC bus voltage, T S is the control period, t13 ,t 14 ,t 15 ,t 16 Corresponding to V S 、V M 、V ML and V L During the action time, a total of 18 virtual voltage vectors are synthesized in the seventh harmonic space, with the same distribution as VV1.

[0024] Step 3.2) Sector division is performed in each space. The fundamental wave space, fifth harmonic space and seventh harmonic space start with sector 1 (0°~20°), and every 20° is a sector, for a total of 18 sectors; the third harmonic space starts with sector 1 (0°~60°), and every 60° is a sector, for a total of 6 sectors.

[0025] Step 3.3) After each space sector is determined, two virtual voltage vectors at the edge of the sector are selected for reference voltage vector synthesis. The action time of each space virtual voltage vector can be obtained by the following formula:

[0026]

[0027]

[0028] are the action time of two virtual voltage vectors used to synthesize the reference voltage vector in the fundamental wave space, third, fifth and seventh harmonic spaces respectively; where t 11 With t 12 ,t 31 With t 32 ,t 51 With t 52 ,t 71 With t 72 They are used to synthesize u r * ,u r3 * ,u r5 * ,u r7 * The action time of the two virtual voltage vectors, θ, θ3, θ5, θ7 are u r * ,u r3 * ,u r5 * ,u r7 * Angle

[0029] Further, the specific process of step 4) is:

[0030] Step 4.1) Formulate a duty cycle optimization allocation rule. First, determine the sum of the initial calculated action times of the two VV1s used to synthesize the fundamental space reference voltage vector. If the sum is equal to or greater than one, the duty cycles of the three harmonic spaces are reallocated to zero, and the action times of the two VV1s are adjusted according to t 11 With t 12 The optimal allocation method of fundamental wave space duty cycle is as follows:

[0031]

[0032] Among them, d 11 ,d 12 To synthesize u r * The duty cycle of the two virtual voltage vectors is 11 With t 12 If the sum is less than 1, there is no need to adjust t 11 With t 12 , and the process proceeds to the next step.

[0033] When allocating the duty cycle of the harmonic space, the third harmonic space is allocated first. First, determine t 31 With t 32 If the sum is greater than the remaining duty cycle, then according to t 31 With t 32 The proportion of the third harmonic space is redistributed, and the duty ratio of the fifth and seventh harmonic space is 0. The third harmonic space duty ratio optimization distribution method is as follows:

[0034]

[0035] Among them, d 31 ,d 32 To synthesize u r3 * The duty cycle of the two virtual voltage vectors is 31 With t 32 If the sum of is less than or equal to the remaining duty cycle, there is no need to adjust t 31 With t 32 , and the process proceeds to the next step.

[0036] When t 51 ,t 52 ,t 71 ,t 72 When the sum is greater than the remaining duty cycle, redistribution is performed based on the proportion of the preliminary calculation results of the action time of each virtual voltage vector. The optimal allocation method for the fifth and seventh harmonic space duty cycle is as follows:

[0037]

[0038] Among them, d 51 ,d 52 ,d 71 ,d 52 To synthesize u r5 * 、u r7 * If the sum of the duty cycles of the two virtual voltage vectors is less than or equal to the remaining duty cycle, no adjustment is required. If there is a remaining duty cycle after all allocations, fill the vector with zero. This process avoids overmodulation and ensures the priority suppression of the third harmonic. First, the fundamental wave space is met, and then the duty cycle is allocated to the harmonic space, giving priority to the third harmonic space allocation, and finally the fifth and seventh harmonic spaces are allocated.

[0039] Step 4.2) After the duty cycle allocation is completed, the corresponding switching pulse needs to be output. The present invention takes phase A analysis and centralizes the original pulse sequence. Each space outputs the corresponding pulse sequence, and the final output is the superposition of each pulse.

[0040] Beneficial effects of the present invention:

[0041] 1) Four groups of virtual voltage vectors are designed, among which VV1 can eliminate the third, fifth and seventh harmonic components, and VV3, VV5 and VV7 have no mapped voltage amplitude in other spaces. The combination of virtual voltage vectors in harmonic space can achieve current harmonic suppression.

[0042] 2) Multi-harmonic spatial closed-loop control is realized, making the control structure more stable and reducing current harmonics to a greater extent.

[0043] 3) The designed duty cycle optimization allocation rule achieves priority suppression of the third harmonic with a larger proportion, and this method is universal and can achieve priority suppression for any harmonic. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is the topology diagram of the nine-phase permanent magnet synchronous motor drive system;

[0045] Figure 2 It is a schematic diagram of the control principle involved in the present invention;

[0046] Figure 3 The four groups of original voltage vector diagrams after screening; (a) Group 1, (b) Group 2, (c) Group 3, (d) Group 4;

[0047] Figure 4The virtual voltage vector diagrams of each space; (a) is the distribution diagram of VV1 in the fundamental wave space, (b) is the distribution diagram of VV3 in the third harmonic space, (c) is the distribution diagram of VV5 in the fifth harmonic space, and (d) is the distribution diagram of VV7 in the seventh harmonic space;

[0048] Figure 5 Schematic diagrams of synthesis of various space reference voltage vectors; (a) is a schematic diagram of synthesis of fundamental wave space reference voltage vector, (b) is a schematic diagram of synthesis of third harmonic space reference voltage vector, (c) is a schematic diagram of synthesis of fifth harmonic space reference voltage vector, (d) is a schematic diagram of synthesis of seventh harmonic space reference voltage vector;

[0049] Figure 6 A schematic diagram of the duty cycle optimization allocation rule;

[0050] Figure 7 It is the schematic diagram of the switching pulse of phase A;

[0051] Figure 8 The experimental diagrams for validating the effectiveness of each virtual voltage vector; (a) traditional outer large vector, (b) VV1 verification experimental diagram; (c) VV3 verification experimental diagram; (d) VV5 verification experimental diagram; (e) VV7 verification experimental diagram;

[0052] Fig. 9 The static performance test diagram is shown in Figure 1. (a) Control method without duty cycle optimization allocation; (b) Control method with optimization allocation; DETAILED DESCRIPTION

[0053] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention:

[0054] Step 1) Obtain each space reference voltage vector in the two-phase stationary coordinate system and detect the phase current i in the nine-phase natural coordinate system in real time abcdefghi After the coordinate transformation from the nine-phase natural coordinate system to the two-phase rotating coordinate system, the current component i in the two-phase rotating coordinate system of the current control period is obtained. d 、i q 、i d357 、i q357 , the given speed is obtained after passing through the PI controller q The expected value of q * The error between the two can be obtained after passing through the PI controller. q , at the same time, i d Given i d *is 0, the given harmonic current is 0, and the respective errors can be obtained through the PI controller u d 、u d357 、u q357 ,

[0055] The coordinate transformation matrix from the nine-phase natural coordinate system to the two-phase rotating coordinate system is:

[0056]

[0057] where θ e is the motor electrical angle, γ=2π / 9.

[0058] Step 2) Transform the coordinates of each space reference voltage vector to obtain u α 、u β and u α357 、u β357 , and then calculate to obtain the reference voltage vector of each space: u r * ,u r3 * ,u r5 * ,u r7 * .

[0059] The coordinate transformation matrix from the two-phase rotating coordinate system to the two-phase stationary coordinate system is:

[0060]

[0061] The reference voltage vector calculation method is:

[0062]

[0063] Among them, u α 、u β is the reference voltage of the α-axis and β-axis in the stationary coordinate system, and θ is the reference voltage vector u r * Angle

[0064] Step 3) construct virtual voltage vectors in each space, and perform sector determination on the reference voltage vector to select the corresponding virtual voltage vector, and calculate the action time of each virtual voltage vector used to synthesize the reference voltage vector.

[0065] Step 3.1) Construct a virtual voltage vector set. First, classify the switch states of the nine-phase inverter in the form of (ab), where a is the number of states 1 and b is the number of states 0. Specifically, they are divided into (1-8), (2-7), (3-6), and (4-5). The 18 largest voltage vectors in each group can be selected from the four groups of vectors based on the principle that the amplitude of the voltage vector synthesized by the adjacent conducting bridge arms is the largest, as shown in Figure 3 As shown, they are named {1-8}max, {2-7}max, {3-6}max and {4-5}max subsets, respectively, with V S 、V M 、V ML and V L Indicates that it can be expressed in each space as:

[0066]

[0067] Where u1, u3, u5, and u7 represent the space voltage vectors, γ = 2π / 9, S (A～I) is the switching state of each phase bridge arm, thereby screening out 72 voltage vectors and obtaining their distribution characteristics in each space. In the fundamental wave space, according to the mapping amplitude and phase of each voltage vector in the three harmonic spaces, four collinear vectors are selected to eliminate the third, fifth and seventh harmonic voltages. The action time of each vector is calculated as:

[0068]

[0069] Among them U dc is the DC bus voltage, T S is the control period, t1, t2, t3, t4, respectively correspond to V S 、V M 、V ML and V L The action time of , a total of 18 virtual voltage vectors are synthesized in the fundamental wave space, starting from 0° and distributed at intervals of 20°, named VV1, such as Figure 4 In the third harmonic space, three collinear vectors are selected to eliminate the amplitude mapping in the fundamental space and the fifth and seventh harmonic spaces. A set of virtual voltage vectors that are mapped only in the third harmonic space is constructed and named VV3. The action time of each vector is calculated as follows:

[0070]

[0071] Among them, t5, t6, and t7 correspond to V S 、V M and V L The action time of , a total of 6 virtual voltage vectors are synthesized in the third harmonic space, starting from 0° and distributed at intervals of 60°, such as Figure 4 In the fifth harmonic space, four collinear vectors are selected to eliminate the amplitude mapping in the fundamental space and the third and seventh harmonic spaces. A set of virtual voltage vectors mapped only in the fifth harmonic space is constructed and named VV5. The action time of each vector is calculated as follows:

[0072]

[0073] Among them, t9, t 10 ,t 11 ,t 12 Corresponding to V S 、V M 、V ML and V L The action time of VV1 is 18 virtual vectors, which are distributed in the fifth harmonic space. Figure 4 In the seventh harmonic space, four collinear vectors are selected to eliminate the amplitude mapping in the fundamental space and the third and fifth harmonic spaces. A set of virtual voltage vectors mapped only in the fifth harmonic space is constructed and named VV5. The action time of each vector is calculated as follows:

[0074]

[0075] where t 13 ,t 14 ,t 15 ,t 16 Corresponding to V S 、V M 、V ML and V L The action time of VV1 is 18 virtual voltage vectors, which are distributed in the seventh harmonic space. Figure 4 (d) as shown.

[0076] Step 3.2) Sector division is performed in each space. The fundamental wave space, fifth harmonic space and seventh harmonic space start with sector 1 (0°<=θ<20°), and every 20° is a sector, for a total of 18 sectors; the third harmonic space starts with sector 1 (0°<=θ<60°), and every 60° is a sector, for a total of 6 sectors.

[0077] Step 3.3) After each space sector is determined, two virtual voltage vectors at the edge of the sector are selected for reference voltage vector synthesis. The synthesis diagram is shown in Figure 5 As shown, the action time of the fundamental wave space virtual voltage vector can be obtained by the following formula:

[0078]

[0079] Among them, t 11 With t 12 To synthesize u r * The action time of the two virtual voltage vectors, θ is u r * Angle

[0080] The action time of the third harmonic space virtual voltage vector can be obtained by the following formula:

[0081]

[0082] Among them, t 31 With t 32 To synthesize u r3 * The action time of the two virtual voltage vectors, θ3 is u r3 * Angle

[0083] The fifth harmonic space virtual voltage vector action time can be obtained by the following formula:

[0084]

[0085] where t 51 With t 52 To synthesize u r5 * The action time of the two virtual voltage vectors is u r5 * Angle

[0086] The seventh harmonic space virtual voltage vector action time can be obtained by the following formula:

[0087]

[0088] where t 71 With t 72 They are used to synthesize u r7 * The action time of the two virtual voltage vectors, θ7 is u r7 * Angle

[0089] Step 4) After obtaining the initial action time of each virtual voltage vector, it is necessary to allocate the duty cycle and output a pulse signal.

[0090] Step 4.1) Formulate a duty cycle optimization allocation rule, such as Figure 6 As shown, first, the sum of the initial calculated action times of the two VV1s used to synthesize the fundamental space reference voltage vector is determined. If the sum is equal to or greater than one, the duty cycles of the three harmonic spaces are redistributed to zero, and the action times of the two VV1s are adjusted according to t 11 With t 12 The optimal allocation method of fundamental wave space duty cycle is as follows:

[0091]

[0092] Among them, d 11 ,d 12 To synthesize u r* The duty cycle of the two virtual voltage vectors is 11 With t 12 If the sum is less than 1, there is no need to adjust t 11 With t 12 , and the process proceeds to the next step.

[0093] When allocating the duty cycle of the harmonic space, the third harmonic space is allocated first. First, determine t 31 With t 32 If the sum is greater than the remaining duty cycle, then according to t 31 With t 32 The proportion of the third harmonic space is redistributed, and the duty ratio of the fifth and seventh harmonic space is 0. The third harmonic space duty ratio optimization distribution method is as follows:

[0094]

[0095] Among them, d 31 ,d 32 To synthesize u r3 * The duty cycle of the two virtual voltage vectors is 31 With t 32 If the sum of is less than or equal to the remaining duty cycle, there is no need to adjust t 31 With t 32 , and the process proceeds to the next step.

[0096] When t 51 ,t 52 ,t 71 ,t 72 When the sum is greater than the remaining duty cycle, redistribution is performed based on the proportion of the preliminary calculation results of the action time of each virtual voltage vector. The optimal allocation method for the fifth and seventh harmonic space duty cycle is as follows:

[0097]

[0098] Among them, d 51 ,d 52 ,d 71 ,d 52 To synthesize u r5 * 、u r7 * If the sum of the duty cycles of the two virtual voltage vectors is less than or equal to the remaining duty cycle, no adjustment is required. If there is a remaining duty cycle after all allocations, fill the vector with zero. This process avoids overmodulation and ensures the priority suppression of the third harmonic. First, the fundamental wave space is met, and then the duty cycle is allocated to the harmonic space, giving priority to the third harmonic space allocation, and finally the fifth and seventh harmonic spaces are allocated.

[0099] Step 4.2) After the duty cycle allocation is completed, the corresponding switching pulse needs to be output. The present invention takes the A phase analysis when each spatial reference voltage vector is in sector 1. Since the present invention selects a large number of original voltage vectors, directly outputting the original pulse sequence corresponding to each vector will cause huge switching losses. Therefore, the present invention performs central processing on the original pulse sequence, such as Figure 7 As shown, each space outputs a corresponding pulse sequence, and the final output is the superposition of each pulse.

[0100] Figure 8 The validity verification diagram of each space virtual voltage vector constructed by the present invention includes the phase current waveform and the phase current THD analysis result diagram; the motor operating conditions are: the speed is 600r / min, the load is 5.75N·m, which can be obtained from Figure 8 The effectiveness of the constructed virtual voltage vectors can be seen in FIG.

[0101] Fig. 9 This is a static experiment comparison between the use of the duty cycle optimization allocation rule in the control method of the present invention and the use of the duty cycle optimization allocation rule designed in the present invention. The figure includes the phase current waveform and the phase current THD analysis result diagram. The speed is 750r / min and the load is 7.51N·m. Fig. 9 It can be seen from the figure that the effectiveness of the optimized duty cycle allocation rule formulated by the present invention is that on the basis of realizing multi-harmonic space closed-loop control, the third harmonic is preferentially suppressed, and the current harmonics are reduced to a greater extent.

Claims

1. A multi-space closed-loop harmonic current suppression method based on dynamic optimization allocation of duty cycle for a nine-phase permanent magnet synchronous motor, characterized in that: The following steps are involved: Step 1) Obtain the fundamental space reference voltage u through the speed loop d 、u q In the harmonic space, the expected value of the harmonic current is zero and the harmonic current feedback is subtracted. The corresponding harmonic reference voltage u is obtained by adjusting the PI controller. d357 、u q357 ; Step 2) Set u d 、u q 、u d357 、u q357 After coordinate transformation, the reference voltages of the α-axis and β-axis in the stationary coordinate system are obtained: u α 、u β And harmonic space reference voltage: u α357 、u β357 , and then calculate to obtain the reference voltage vector of each space: u r * ,u r3 * ,u r5 * ,u r7 * ; Step 3) determining the sector to which each space voltage vector belongs, selecting a corresponding virtual voltage vector, and calculating the action time of each virtual voltage vector to synthesize a corresponding reference voltage vector; Step 4) Redistribute the action time of each virtual voltage vector according to the established duty cycle optimization distribution rule and then output it.

2. The method according to claim 1, characterized in that The step 3 specifically comprises the following steps: Step 3.1) Construct a virtual voltage vector set In the fundamental wave space, according to the mapping amplitude and phase of each voltage vector in the three harmonic spaces, four collinear vectors are selected to eliminate the third, fifth and seventh harmonic voltages. The action time of each vector is calculated as: Among them U dc is the DC bus voltage, T S is the control period, t1, t2, t3, t4 correspond to the small vector V S , medium vector V M 、Zhongda Vector V ML and large vector V L During the action time, 18 virtual voltage vectors are synthesized in the fundamental wave space, starting from 0° and distributed at intervals of 20°, named VV1; In the third harmonic space, three collinear vectors are selected to eliminate the amplitude mapping in the fundamental space and the fifth and seventh harmonic spaces. A set of virtual voltage vectors mapped only in the third harmonic space is constructed and named VV3. The action time of each vector is calculated as follows: Among them, t5, t6, and t7 correspond to V S 、V M and V L In the third harmonic space, a total of 6 virtual voltage vectors are synthesized, starting from 0° and distributed at 60° intervals; in the fifth harmonic space, four collinear vectors are selected to eliminate the amplitude mapping in the fundamental space and the third and seventh harmonic spaces. A group of virtual voltage vectors mapped only in the fifth harmonic space is constructed, named VV5, and the action time of each vector is calculated as follows Among them, t9, t 10 ,t 11 ,t 12 Corresponding to V S 、V M 、V ML and V L The action time of 18 virtual vectors is synthesized in the seventh harmonic space, and the distribution is the same as VV1; in the seventh harmonic space, four collinear vectors are selected to eliminate the mapping amplitude in the fundamental space and the third and fifth harmonic spaces. A group of virtual voltage vectors that are only mapped in the seventh harmonic space is constructed, named VV7, and the action time of each vector is calculated as follows where t 13 ,t 14 ,t 15 ,t 16 Corresponding to V S 、V M 、V ML and V L During the action time, a total of 18 virtual voltage vectors are synthesized in the seventh harmonic space, with the same distribution as VV1; Step 3.2) Sector division is performed in each space. The fundamental wave space, fifth harmonic space and seventh harmonic space start with sector 1 (0°~20°), and every 20° is a sector, for a total of 18 sectors; the third harmonic space starts with sector 1 (0°~60°), and every 60° is a sector, for a total of 6 sectors; Step 3.3) After each space sector is determined, two virtual voltage vectors at the edge of the sector are selected for reference voltage vector synthesis. The action time of each space virtual voltage vector can be obtained by the following formula: are the action time of two virtual voltage vectors used to synthesize the reference voltage vector in the fundamental wave space, third, fifth and seventh harmonic space respectively; where t 11 With t 12 ,t 31 With t 32 ,t 51 With t 52 ,t 71 With t 72 They are used to synthesize u r * ,u r3 * ,u r5 * ,u r7 * The action time of the two virtual voltage vectors, θ, θ3, θ5, θ7 are u r * ,u r3 * ,u r5 * ,u r7 * angle.

3. The method according to claim 1, characterized in that The step 4 specifically comprises the following steps: Step 4.1) Formulate a duty cycle optimization allocation rule, first meet the fundamental wave space requirements, then allocate the duty cycle to the harmonic space, give priority to the third harmonic space allocation, and finally allocate the fifth and seventh harmonic spaces. If there is still a surplus of duty cycle, fill in the zero vector; Step 4.2) After the duty cycle allocation is completed, the corresponding switching pulse needs to be output. The present invention centralizes the original pulse sequence, and each space outputs the corresponding pulse sequence, and the final output is the superposition of each pulse.

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