Space vector layering-based cascaded multilevel converter zero common-mode voltage SVM (Support Vector Machine) method

Abstract

A cascaded multilevel converter zero common-mode voltage SVM method based on space vector layering comprises the steps that firstly, the nearest level of three phase voltage reference signals is obtained, the difference values of a reference vector, the nearest vector and two vectors in the two coordinate axis directions of a two-dimensional coordinate system are calculated, and whether three simple plus and minus numbers formed by the difference values in the two directions are larger than zero or not is judged; and directly obtaining three zero common-mode voltage switch states of the synthetic reference vector and action time corresponding to the zero common-mode voltage switch states according to the three phase voltage reference signals and a specific numerical value of the sum of the nearest levels of the three phase voltage reference signals. And finally, judging whether the three zero common-mode voltage switching states are located in the inner layer in sequence according to the layering relationship, and determining a switching sequence with the minimum switching times. According to the method, the zero common-mode voltage switching states corresponding to the three basic vectors which are closest to the reference vector and have the zero common-mode voltage switching states, the corresponding action time and the optimal switching sequence of the three zero common-mode voltage switching states can be directly obtained, and the minimum switching frequency can be achieved.

Description

Technical Field

[0001] The invention relates to the technical field of cascade multi-level converter modulation, in particular to a cascade multi-level converter zero common mode voltage SVM method based on space vector layering. Background Art

[0002] Compared with traditional low-level converters, cascaded multilevel converters have the characteristics of low stress on switching devices, low cost, good reliability, and high output waveform quality. They are widely used in various high-power occasions, such as clean energy power generation occasions such as centralized photovoltaic power stations and offshore wind farms. The driving signal of the switch device of the cascaded multilevel converter is generated by the multilevel converter modulation technology, so the multilevel modulation technology determines the output power quality and efficiency of the converter. Compared with other multilevel modulation strategies, space vector modulation (Space Vector Modulation—SVM) can improve the utilization rate of DC voltage and optimize the converter performance by selecting appropriate redundant switch states. It is widely used in cascaded multilevel converters. Traditional SVM technology uses the nearest three basic vectors to synthesize the reference vector, and each basic vector corresponds to multiple switch states (called redundant switch state vectors). However, the number of redundant switch states increases significantly with the increase of the number of levels, resulting in large workload for selecting the optimal switch state and complex switching path selection. The amount of calculation increases exponentially, greatly increasing the difficulty of SVM implementation. The traditional SVM algorithm uses the three most recent basic vectors to synthesize the reference vector, which cannot completely eliminate the common-mode voltage, resulting in the system still having problems such as bearing current and electromagnetic interference caused by the common-mode voltage, which will significantly increase the probability of motor damage in high-power situations. Although the common-mode voltage can be completely eliminated by selecting the three most recent basic vectors with zero common-mode voltage switching states to synthesize the reference vector, the difficulty of finding the three most recent basic vectors with zero common-mode voltage switching states is further increased, and the optimal switching sequence is also difficult to determine, resulting in a significant increase in the number of switches. The above problems make it difficult to apply the zero common-mode voltage SVM method to cascaded multilevel converters. Summary of the invention

[0003] The purpose of the present invention is to provide a zero common mode voltage SVM method for a cascaded multilevel converter based on space vector stratification. First, the nearest levels of three phase voltage reference signals are obtained, and the reference vector, the nearest vector and the difference between the two vectors in the two coordinate axis directions of the two-dimensional coordinate system are calculated. By judging whether the three simple additions and subtractions composed of the two-directional differences are greater than zero, and the specific value of the sum of the nearest levels of the three phase voltage reference signals, the three zero common mode voltage switch states of the synthetic reference vector and the action time corresponding to the zero common mode voltage switch state are directly obtained. Finally, according to the hierarchical relationship, it is judged whether the three zero common mode voltage switch states are located in the inner layer in turn, and the switching order with the minimum number of switches is determined. The present invention is applicable to multilevel converters of any number of stages.

[0004] The technical solution for achieving the purpose of the present invention is:

[0005] The zero common mode voltage SVM method of cascaded multilevel converter based on space vector layering includes:

[0006] Step 1: respectively calculate the three-phase voltage reference signal a r ,b r ,c r Round off to get the nearest three-phase level a nl ,b nl ,c nl ; Step 2, obtain the reference vector V r (α r ,β r ) and the nearest vector V nl (α nl ,β nl );

[0007] Among them, α r and β r Represents the three-phase voltage reference signal a r ,b r ,c r The horizontal and vertical components in the 45° space vector coordinate system, α r =a r -c r , β r =-a r +b r ; α nl and β nl Indicates the three-phase nearest level a nl ,b nl ,c nl The horizontal and vertical components in the 45° space vector coordinate system, α nl =a nl -c nl , β nl =-a nl +bnl ;

[0008] Step 3: Calculate the reference vector V r (α r ,β r ) and the closest vector V nl (α nl ,β nl ) The difference in the α and β directions Δα=α r -α nl , Δβ=β r -β nl ;

[0009] Step 4: According to the three-phase nearest level a nl ,b nl ,c nl The sum of the three zero common-mode voltage switch states and their corresponding action times is determined:

[0010] If the three-phase nearest level a nl ,b nl ,c nl The sum is 1, and the three zero common-mode voltage switch states are S za (a nl -1,b nl ,c nl ), S zb (a nl ,b nl -1,c nl ) and S zc (a nl ,b nl ,c nl -1), the corresponding action time t za =[t s -t s *(Δα-αβ)] / 3, t zb =[t s -t s *(Δα+2Δβ)] / 3 and t zc =[t s +t s *(2Δα+Δβ)] / 3, where t s Represents the sampling frequency of the phase voltage reference signal;

[0011] If the three-phase nearest level a nl ,b nl ,c nl The sum is -1, so the three zero common mode voltage switch states are S za (a nl +1,b nl ,c nl ), S zb (anl ,b nl +1,c nl ) and S zc (a nl ,b nl ,c nl +1), the corresponding action time t za =[t s +t s *(Δα-Δβ)] / 3, t zb =[t s +t s *(Δα+2Δβ)] / 3 and t zc =[t s -t s *(2Δα+Δβ)] / 3;

[0012] If the three-phase nearest level a nl ,b nl ,c nl If the sum is 0, then after further judgment, three zero common mode voltage switch states and their action times are determined:

[0013] If Δα+2Δβ<0 and 2Δα+Δβ>0, the three zero common mode voltage switch states are S za (a nl ,b nl ,c nl ), S zb (a nl +1,b nl -1,c nl ) and S zc (a nl +1,b nl ,c nl -1), the corresponding action times are t za =t s -t s *(Δα-Δβ) / 3, t zb =-t s *(Δα+2Δβ) / 3 and t zc =t s *(2Δα+Δβ) / 3;

[0014] If Δα-Δβ>0 and Δα+2Δβ>0, the three zero common-mode voltage switch states are S za (a nl +1,b nl ,c nl -1) S zb (a nl ,b nl +1,c nl -1) and S zc (anl ,b nl ,c nl ), the corresponding action times are t za =t s *(Δα-Δβ) / 3, t zb =t s *(Δα+2Δβ) / 3 and t zc =t s -t s *(2αΔ+Δβ) / 3;

[0015] If Δα-Δβ<0 and 2αΔ+Δβ>0, the three zero common-mode voltage switch states are S za (a nl -1,b nl +1,c nl ), S zb (a nl ,b nl ,c nl ) and S zc (a nl ,b nl +1,c nl -1), the corresponding action times are t za =t s *(Δα-Δβ) / 3, t zb =t s -t s *(Δα+2Δβ) / 3 and t zc =t s *(2Δα+Δβ) / 3;

[0016] If Δα+2Δβ>0 and 2Δα+Δβ<0, the three zero common-mode voltage switch states are S za (a nl ,b nl ,c nl ), S zb (a nl -1,b nl +1,c nl ) and S zc (a nl -1,b nl ,c nl +1), the corresponding action times are t za =t s +t s *(Δα+Δβ) / 3, t zb =t s *(Δα+2Δβ) / 3 and t zc =-t s *(2Δα+Δβ) / 3;

[0017] If Δα-Δβ<0 and Δα+2Δβ<0, the three zero common-mode voltage switch states are S za (a nl -1,b nl ,c nl +1), S zb (a nl ,b nl -1,c nl +1) and S zc (a nl ,b nl ,c nl ), the corresponding action times are t za =-t s *(Δα-Δβ) / 3, t zb =-t s *(Δα+2Δβ) / 3 and t zc =t s +t s *(2Δα+Δβ) / 3;

[0018] If Δα-Δβ>0 and 2Δα+Δβ<0, the three zero common mode voltage switch states are S za (a nl +1,b nl -1,c nl ), S zb (a nl ,b nl ,c nl ) and S zc (a nl ,b nl -1,c nl +1), the corresponding action times are t za =t s *(Δα-Δβ) / 3, t zb =t s +t s *(Δα+2Δβ) / 3 and t zc =-t s *(2Δα+Δβ) / 3;

[0019] Step 5: According to the switch state S za , S zb , S zc The maximum value i of the absolute value of the three-phase output level is i, that is, i=max{|a za |,|b za |,|c za |,|a zb |,|b zb |,|c zb |,|a zc|,|b zc |,|c zc |}, the switch state S za , S zb , S zc The corresponding space vector layer: If the absolute values ​​of the three-phase output levels of the switch state S are all within [-i, i], then the space vector corresponding to the switch state S is in the i layer, S∈{S za ,S zb ,S zc}; where a za 、b za 、c za Indicates that the switch state is S za The three-phase output level when a zb 、b zb 、c zb Indicates that the switch state is S zb The three-phase output level when a zc 、b zc 、c zc Indicates that the switch state is S zc The three-phase output level when

[0020] Step 6, select the switch state S of the space vector in the i layer as the first switch of the space vector; then use the five-segment algorithm to synthesize the switching sequence of the three zero common mode voltage switch states and their corresponding action times to realize SVM;

[0021] The five-segment algorithm is used to synthesize the switching sequence of three zero common mode voltage switch states and their corresponding action times, specifically:

[0022] when|a za |<i、|b za |<i and |c za |<i, the five-segment algorithm is used, and the switching order of the three zero common-mode voltage switching states of the synthetic reference vector is S za →S zb →S zc →S zb →S za The corresponding action times are t za / 2→t zb / 2→t zc →t zb / 2→t za / 2;

[0023] when|a zb |<i、|b zb |<i and |c zb |<i, the five-segment algorithm is used, and the switching order of the three zero common-mode voltage switching states of the synthetic reference vector is S zb →Sza →S zc →S za →S zb The corresponding action times are t zb / 2→t za / 2→t zc →t za / 2→t zb / 2;

[0024] when|a zc |<i、|b zc |<i and |c zc |<i, the five-segment algorithm is used, and the switching order of the three zero common-mode voltage switching states of the synthetic reference vector is S zc →S za →S zb →S za →S zc The corresponding action times are t zc / 2→t za / 2→t zb →t za / 2→t zc / 2.

[0025] The beneficial effect of the present invention is that the zero common mode voltage switch state corresponding to the three basic vectors with the zero common mode voltage switch state closest to the reference vector, the corresponding action time of the zero common mode voltage switch state and the optimal switching order of the three zero common mode voltage switch states can be directly obtained, so as to achieve the minimum number of switching times. The algorithm can be implemented only through simple addition, subtraction and comparison, avoiding complex trigonometric functions and irrational number operations, and is easy to implement by computer. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the topology diagram of the three-phase cascaded multilevel converter.

[0027] Figure 2 It is the sector distribution map where the reference vector is located.

[0028] Figure 3 This is the distribution diagram of the seven-level zero common-mode voltage switch state.

[0029] Figure 4 It is a flow chart of the present invention.

[0030] Figure 5 Schematic diagram of the five-stage algorithm implementation of the embodiment. DETAILED DESCRIPTION

[0031] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] Take a three-phase converter consisting of n cascaded H-bridge units in each phase as an example. Figure 1 The sampling period is t s , the three phase voltage reference signals are a r ,b r ,c r .

[0033] Step 1: Three phase voltage reference signals a r ,b r ,c r Round to the nearest integer to get the three-phase nearest level a nl ,b nl ,c nl .

[0034]

[0035] round(*) means rounding the value * to the nearest integer.

[0036] Step 2: The expression of 45° space vector coordinate system is:

[0037]

[0038] Among them, α and β represent the horizontal axis component and the vertical axis component in the 45° space vector coordinate system respectively. r ,b r ,c r and a nl ,b nl ,c nl Substitute into formula (2) to obtain the reference vector V r (α r ,β r ) and the nearest vector V nl (α nl ,β nl ).

[0039] Step 3: Calculate the reference vector V r (α r ,β r ) and the nearest vector V nl (α nl ,β nl )The differences Δα and Δβ in the α and β directions.

[0040]

[0041] Step 4: Determine whether Δα-Δβ, Δα+2Δβ, 2Δα+Δβ is greater than zero and N=a nl +b nl +c nlFor which value among 1, -1, 0, the zero common mode voltage switch state S corresponding to the three vertex space vectors of the sector where the reference vector is located is obtained. za (a za ,b za ,c za ), S zb (a zb ,b zb ,c zb ), S zc (a zc ,b zc ,c zc ) and the action time t corresponding to the zero common mode voltage switching state za ,t zb ,t zc When N is 1 or -1, the zero common mode voltage switching state required for synthesizing the reference vector can be obtained directly by subtracting 1 or adding 1 level on each phase. When N is 0, it is necessary to determine the sector where the reference vector is located. The sector where the reference vector is located is as follows: Figure 2 As shown, after determining the sector, the zero common mode voltage switching state of the synthetic reference vector is obtained.

[0042] Case 1: When N=1, the three zero common-mode voltage switches are in the state of S za (a nl -1,b nl ,c nl ), S zb (a nl ,b nl -1,c nl ) and S zc (a nl ,b nl ,c nl -1), the corresponding action time t za =[t s -t s *(Δα-Δβ)] / 3, t zb =[t s -t s *(Δα+2Δβ)] / 3 and t zc =[t s +t s *(2Δα+Δβ)] / 3;

[0043] Case 2: When N = -1, the three zero common-mode voltage switches are in the state of S za (a nl +1,b nl ,c nl ), S zb (a nl ,b nl +1,c nl ) and Szc (a nl ,b nl ,c nl +1), the corresponding action time t za =[t s +t s *(Δα-Δβ)] / 3, t zb =[t s +t s *(Δα+2Δβ)] / 3 and t zc =[t s -t s *(2Δα+Δβ)] / 3;

[0044] Case 3: When N = 0, when Δα+2Δβ<0 and 2Δα+Δβ>0, the reference vector is located at the position indicated by V nl (α nl ,β nl )、V1(α nl +1,β nl -2) and V2(α nl +2,β nl -1) Sector I composed of three vertex vectors, the three zero common mode voltage switch states corresponding to the three vertex vectors are S za (a nl ,b nl ,c nl ), S zb (a nl +1,b nl -1,c nl ) and S zc (a nl +1,b nl ,c nl -1), the action time is t za =t s -t s *(Δα-Δβ) / 3, t zb =-t s *(Δα+2Δβ) / 3 and t zc =t s *(2Δα+Δβ) / 3;

[0045] Case 4: When N = 0, when Δα-Δβ>0 and Δα+2Δβ>0, the reference vector is located at the position indicated by V nl (α nl ,β nl )、V2(α nl +2,β nl -1) and V3(α nl +1,β nl+1) The three vertex vectors form sector II. The three zero common mode voltage switch states corresponding to the three vertex vectors are S za (a nl +1,b nl ,c nl -1) S zb (a nl ,b nl +1,c nl -1) and S zc (a nl ,b nl ,c nl ), the action time is t za =t s *(Δα-Δβ) / 3, t zb =t s *(Δα+2Δβ) / 3 and t zc =t s -t s *(2Δα+Δβ) / 3;

[0046] Case 5: When N = 0, when Δα-Δβ<0 and 2Δα+Δβ>0, the reference vector is located at the position indicated by V nl (α nl ,β nl )、V3(α nl +1,β nl +1) and V4(α nl -1,β nl +2) The three vertex vectors form sector III. The three zero common mode voltage switch states corresponding to the three vertex vectors are S za (a nl -1,b nl +1,c nl ), S zb (a nl ,b nl ,c nl ) and S zc (a nl ,b nl +1,c nl -1), the action time is t za =-t s *(Δα-Δβ) / 3, t zb =t s -t s *(Δα+2Δβ) / 3 and t zc =t s *(2Δα+Δβ) / 3;

[0047] Case 6: When N = 0, when Δα+2Δβ>0 and 2Δα+Δβ<0, the reference vector is located at the position indicated by V nl (αnl ,β nl )、V4(α nl -1,β nl +2) and V5(α nl -2,β nl +1) The three vertex vectors form the IV sector, and the three zero common mode voltage switch states corresponding to the three vertex vectors are S za (a nl ,b nl ,c nl ), S zb (a nl -1,b nl +1,c nl ) and S zc (a nl -1,b nl ,c nl +1), the action time is t za =t s +t s *(Δα-Δβ) / 3, t zb =t s *(Δα+2Δβ) / 3 and t zc =-t s *(2Δα+Δβ) / 3;

[0048] Case 7: When N = 0, when Δα-Δβ<0 and Δα+2Δβ<0, the reference vector is located at V nl (α nl ,β nl )、V5(α nl -2,β nl +1) and V6(α nl -1,β nl -1) The V sector is composed of three vertex vectors. The three zero common mode voltage switch states corresponding to the three vertex vectors are S za (a nl -1,b nl ,c nl +1), S zb (a nl ,b nl -1,c nl +1) and S zc (a nl ,b nl ,c nl ), the action time is t za =-t s *(Δα-Δβ) / 3, t zb =-t s *(Δα+2Δβ) / 3 and t zc =t s +ts *(2Δα+Δβ) / 3;

[0049] Case 8: When N = 0, when Δα-Δβ>0 and 2Δα+Δβ<0, the reference vector is located at V nl (α nl ,β nl )、V6(α nl -1,β nl -1) and V1(α nl +1,β nl -2) The VI sector is composed of three vertex vectors. The three zero common mode voltage switch states corresponding to the three vertex vectors are S za (a nl +1,b nl -1,c nl ), S zb (a nl ,b nl ,c nl ) and S zc (a nl ,b nl -1,c nl +1), the action time is t za =t s *(Δα-Δβ) / 3, t zb =t s +t s *(Δα+2Δβ) / 3 and t zc =-t s *(2Δα+Δβ) / 3.

[0050] Step 5: If Figure 3 From the zero common-mode voltage switch state distribution shown in the figure, it can be seen that when the three-phase levels in the switch state S(a,b,c) are all within [-i,i], where i=max{|a za |,|b za |,|c za |,|a zb |,|b zb |,|c zb |,|a zc |,|b zc |,|c zc |}, then the space vector corresponding to the switch state is in the i layer. When the absolute value of one or two phases of the three-phase level is equal to i or -i, then the space vector corresponding to the switch state is in the i layer. In order to achieve the minimum number of switches, the space vector located in the inner layer among the three vertex vectors should be used first to switch, which can ensure the minimum number of switching between sectors. According to the zero common mode voltage switch state S corresponding to the three vertex space vectors in the sector where the reference vector is located za (a za,b za ,c za ), S zb (a zb ,b zb ,c zb ), S zc (a zc ,b zc ,c zc ) three-phase level, there are three situations:

[0051] Case 1: When |a za |<i、|b za |<i and |c za |<i, the five-segment algorithm is used to implement the three zero common mode voltage switch states of the synthetic reference vector. The switching order is S za →S zb →S zc →S zb →S za The corresponding action times are t za / 2→t zb / 2→t zc →t zb / 2→t za / 2;

[0052] Case 2: When |a zb |<i、|b zb |<i and |c zb |<i, the five-segment algorithm is used to implement the three zero common mode voltage switch states of the synthetic reference vector. The switching order is S zb →S za →S zc →S za →S zb The corresponding action times are t zb / 2→t za / 2→t zc →t za / 2→t zb / 2;

[0053] Case 3: When |a zc |<i、|b zc |<i and |c zc |<i, the five-segment algorithm is used to implement the three zero common mode voltage switch states of the synthetic reference vector. The switching order is S zc →S za →S zb →S za →S zc The corresponding action times are t zc / 2→t za / 2→t zb→t za / 2→t zc / 2.

[0054] Step 6: In order to track the change of the reference vector, repeat steps 1 to 5 to achieve zero common mode voltage space vector modulation of the cascaded multilevel converter.

[0055] The specific process of the present invention is as follows Figure 4 shown.

[0056] Example:

[0057] Take a three-phase converter consisting of 6 cascaded H-bridge units in each phase as an example. s The converter can output 13 different levels per phase, namely {0, ±1, ±2, ±3, ±4, ±5, ±6}, so there are 13 three-phase levels. 3 = 2197 combinations, i.e. 2197 switch states.

[0058] Assume that the three-phase voltage reference signal is a r =4.25,b r =-5.21,c r =0.96, and substitute into formula (1) to obtain the three-phase nearest level a nl =4,b nl =-5,c nl =1.

[0059] A r ,b r ,c r and a nl ,b nl ,c nl Substitute into formula (2) to obtain the reference vector V r (3.29,-9.46) and the nearest vector V nl (3,-9).

[0060] V r (3.29, -9.46) and V nl Substituting (3, -9) into formula (3), we obtain Δα = 0.29 and Δβ = -0.46.

[0061] Determine whether Δα-Δβ, Δα+2Δβ, 2Δα+Δβ is greater than zero and N=a nl +b nl +c nl Which value is 1, -1, 0? Since Δα-Δβ>0, Δα+2Δβα+0 and 2Δα+Δβ>0 and N=0, it belongs to case 3. At this time, the three zero common mode voltage switch states are S za (4,-5,1),S zb(5,-6,1) and S zc (5,-5,0), the action time is t za =0.025ms, t zb = 0.063ms and t zc =0.012ms.

[0062] At this time, i=6, and |a za |<6,|b za |<6 and |c za |<6, it belongs to case 1, and the five-segment algorithm is used to implement it. The switching order of the three zero common-mode voltage switching states of the synthetic reference vector is S za →S zb →S zc →S zb →S za The corresponding action times are t za / 2→t zb / 2→t zc →t zb / 2→t za / 2, the implementation process is as follows Figure 5 As shown, it can be seen that the converter output common-mode voltage is always 0.

[0063] In order to track the changes of the reference vector, the above work is repeated.

Claims

1. A zero common mode voltage SVM method for cascaded multilevel converters based on space vector stratification, characterized in that: include: Step 1: respectively calculate the three-phase voltage reference signal a r ,b r ,c r Round off to get the nearest three-phase level a nl ,b nl ,c nl ; Step 2: Obtain the reference vector V r (α r ,β r ) and the nearest vector V nl (α nl ,β nl ); Among them, α r and β r Represents the three-phase voltage reference signal a r ,b r ,c r The horizontal and vertical components in the 45° space vector coordinate system, α r =a r -c r , β r =-a r +b r ; α nl and β nl Indicates the three-phase nearest level a nl ,b nl ,c nl The horizontal and vertical components in the 45° space vector coordinate system, α nl =a nl -c nl , β nl =-a nl +b nl ; Step 3: Calculate the reference vector V r (α r ,β r ) and the closest vector V nl (α nl ,β nl ) The difference in the α and β directions Δα=α r -α nl , Δβ=β r -β nl ; Step 4: According to the three-phase nearest level a nl ,b nl ,c nl The sum of the three zero common-mode voltage switch states and their corresponding action times is determined: If the three-phase nearest level a nl ,b nl ,c nl The sum is 1, and the three zero common-mode voltage switch states are S za (a nl -1,b nl ,c nl ), S zb (a nl ,b nl -1,c nl ) and S zc (a nl ,b nl ,c nl -1), the corresponding action time t za =[t s -t s *(Δα-Δβ)] / 3, t zb =[t s -t s *(Δα+2Δβ)] / 3 and t zc =[t s +t s *(2Δα+Δβ)] / 3, where t s Represents the sampling frequency of the phase voltage reference signal; If the three-phase nearest level a nl ,b nl ,c nl The sum is -1, so the three zero common mode voltage switch states are S za (a nl +1,b nl ,c nl ), S zb (a nl ,b nl +1,c nl ) and S zc (a nl ,b nl ,c nl +1), the corresponding action time t za =[t s +t s *(Δα-Δβ)] / 3, t zb =[t s Δα+t s *(Δα+2Δβ)] / 3 and t zc =[t s -t s *(2Δα+Δβ)] / 3; If the three-phase nearest level a nl ,b nl ,c nl If the sum is 0, then after further judgment, three zero common mode voltage switch states and their action times are determined: If Δα+2Δβ<0 and 2Δα+Δβ>>0, the three zero common-mode voltage switch states are S za (a nl ,b nl ,c nl ), S zb (a nl +1,b nl -1,c nl ) and S zc (a nl +1,b nl ,c nl -1), the corresponding action times are t za =t s -t s *(Δα-Δβ) / 3, t zb =-t s *(Δα+2Δβ) / 3 and t zc =t s *(2Δα+Δβ) / 3; If Δα-Δβ>0 and Δα+2αβ>0, the three zero common-mode voltage switch states are S za (a nl +1,b nl ,c nl -1) S zb (a nl ,b nl +1,c nl -1) and S zc (a nl ,b nl ,c nl ), the corresponding action times are t za =t s *(Δα-Δβ) / 3, t zb =t s *(Δα+2Δβ) / 3 and t zc =t s -t s *(2Δα+Δβ) / 3; If Δα-Δβ<0 and 2Δα+Δβ>0, the three zero common mode voltage switch states are S za (a nl -1,b nl +1,c nl ), S zb (a nl ,b nl ,c nl ) and S zc (a nl ,b nl +1,c nl -1), the corresponding action times are t za =-t s *(Δα-Δβ) / 3, t zb =t s -t s *(Δα+2Δβ) / 3 and t zc =t s *(2Δα+Δβ) / 3; If Δα+2Δβ>0 and 2Δα+Δβ<0, the three zero common-mode voltage switch states are S za (a nl ,b nl ,c nl ), S zb (a nl -1,b nl +1,c nl ) and S zc (a nl -1,b nl ,c nl +1), the corresponding action times are t za =t s +t s *(Δα-Δβ) / 3, t zb =t s *(Δα+2Δβ) / 3 and t zc =-t s *(2Δα+Δβ) / 3; If Δα-Δβ<0 and Δα+2Δβ<0, the three zero common-mode voltage switch states are S za (a nl -1,b nl ,c nl +1), S zb (a nl ,b nl -1,c nl +1) and S zc (a nl ,b nl ,c nl ), the corresponding action times are t za =-t s *(Δα-Δβ) / 3, t zb =-t s *(Δα+2Δβ) / 3 and t zc =t s +t s *(2Δα+Δβ) / 3; If Δα-Δβ>0 and 2Δα+Δβ<0, the three zero common mode voltage switch states are S za (a nl +1,b nl -1,c nl ), S zb (a nl ,b nl ,c nl ) and S zc (a nl ,b nl -1,c nl +1), the corresponding action times are t za =t s *(Δα-Δβ) / 3, t zb =t s +t s *(Δα+2Δβ) / 3 and t zc =-t s *(2Δα+Δβ) / 3; Step 5: According to the switch state S za , S zb , S zc The maximum value i of the absolute value of the three-phase output level is i, that is, i=max{a za |,|b za |,|c za |,|a zb |,|b zb |,|c zb |,|a zc |,|b zc |,|c zc |}, the switch state S za , S zb , S zc The corresponding space vector layer: If the absolute values ​​of the three-phase output levels of the switch state S are all within [-i, i], then the space vector corresponding to the switch state S is in the i layer, S∈{S za ,S zb ,S zc }; where a za 、b za 、c za Indicates that the switch state is S za The three-phase output level when a zb 、b zb 、c zb Indicates that the switch state is S zb The three-phase output level when a zc 、b zc 、c zc Indicates that the switch state is S zc The three-phase output level when Step 6, select the switch state S of the space vector in the i layer as the first switch of the space vector; then use the five-segment algorithm to synthesize the switching order of the three zero common mode voltage switch states and their corresponding action time to realize SVM; the five-segment algorithm is used to synthesize the switching order of the three zero common mode voltage switch states and their corresponding action time, specifically: when|a za |<i、|b za |<i and |c za |<i, the five-segment algorithm is used, and the switching order of the three zero common-mode voltage switching states of the synthetic reference vector is S za →S zb →S zc →S zb →S za The corresponding action times are t za / 2→t zb / 2→t zc →t zb / 2→t za / 2; when|a zb |<i、|b zb |<i and |c zb |<i, the five-segment algorithm is used, and the switching order of the three zero common-mode voltage switching states of the synthetic reference vector is S zb →S za →S zc →S za →S zb The corresponding action times are t zb / 2→t za / 2→t zc →t za / 2→t zb / 2; when|a zc |<i、|b zc |<i and |c zc |<i, the five-segment algorithm is used, and the switching order of the three zero common-mode voltage switching states of the synthetic reference vector is S zc →S za →S zb →S za →S zc The corresponding action times are t zc / 2→t za / 2→t zb →t za / 2→t zc / 2.

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