A discontinuous modulation method for multi-objective coordination

Abstract

The present invention relates to a method for midpoint voltage control and switching loss reduction based on DPWM. In view of the possible contradiction between reducing switching loss and controlling midpoint voltage, a multi-objective coordination function and a discontinuous modulation MCO_DPWM with multi-objective coordination optimization are proposed. This method comprehensively considers midpoint voltage control and switching loss reduction. In order to reduce the additional switching action introduced when switching between sequence modes, the relationship between the carrier and the sequence mode is discussed. Compared with traditional DPWM, the MCO_DPWM proposed in the present invention can adapt to the control requirements of different occasions by changing the upper and lower limits of the midpoint voltage offset. MCO_DPWM can effectively control the midpoint voltage and reduce switching loss; MCO_DPWM is not only suitable for NPC TLI with stable operating load, but also for NPC TLI with frequently changing load.

Description

Technical Field

[0001] The present invention belongs to the technical field of inverter modulation, and in particular relates to a multi-objective coordinated discontinuous modulation method. Background Art

[0002] With the continued development of power electronics technology, power electronics devices have made rapid progress. Converters, as a core component, have also received in-depth research. Advances in the energy industry have led to an increasing demand for high-voltage, high-power converters in the current industrial sector. Three-level converters, due to their superior performance, are widely used. This has also presented new challenges. The increased number of power transistors complicates control algorithms, and is accompanied by issues such as midpoint voltage offset and switching losses. Maintaining midpoint voltage balance is a prerequisite for safe and reliable converter operation. Unbalanced and fluctuating midpoint voltages not only degrade the converter's output voltage and current, impacting converter efficiency, but in severe cases, can even cause excessive DC-side capacitor withstand voltage, leading to losses and shortening the converter system's service life. Converter switching losses are also a key indicator of converter efficiency. Low switching losses ensure optimal converter operation, while high switching losses significantly reduce converter efficiency and shorten its lifespan.

[0003] In order to ensure that the three-level inverter has good output characteristics, an excellent pulse width modulation strategy should meet the following two requirements:

[0004] (1) It has a certain ability to balance the midpoint voltage. The fluctuation of the midpoint voltage is one of the key issues of the three-level inverter.

[0005] (2) Smaller switching losses to improve system efficiency. Switching loss is also one of the important indicators for measuring the efficient operation of the inverter. The increase in switching loss will inevitably reduce the use of power devices.

[0006] Currently, there are two main algorithms commonly used for achieving neutral point potential balancing: carrier pulse width modulation (CBPWM) based on zero-sequence component injection and space vector modulation (SVPWM) based on redundant vector adjustment. The computational complexity of the control algorithm is significantly increased by the zero-sequence voltage calculation in CBPWM and the complexity of the vector synthesis rules in space vector modulation. The SVPWM method, which uses vector synthesis rules to schedule the action time of each vector, is also computationally intensive and difficult to implement.

[0007] Soft switching technology can effectively reduce switching losses in power transistors, but its application increases cost, complicates control, and imposes phase restrictions during modulation. The switching losses of converters are closely related to the specific modulation method, and improving the modulation method can reduce switching losses to a certain extent.

[0008] Therefore, it is necessary to provide a modulation method for a three-level inverter that can simultaneously reduce system switching losses and control neutral point voltage balance. Summary of the Invention

[0009] The purpose of the present invention is to provide a multi-objective coordinated discontinuous modulation method in order to solve the above problems.

[0010] The present invention achieves the above-mentioned purpose through the following technical solutions:

[0011] A multi-objective coordinated discontinuous modulation method is applied to a neutral-point clamped three-level inverter, and is characterized by comprising the following steps:

[0012] S1: Collect DC side data of the three-level inverter;

[0013] S2: establishing a midpoint potential evaluation function and a switching loss evaluation function based on the DC side data, and establishing a coordination evaluation function based on the midpoint potential evaluation function and the switching loss evaluation function;

[0014] S3: Substituting the coordination evaluation function into different clamping modes to calculate and obtain evaluation function values ​​under different clamping modes, and selecting the clamping mode with the smallest evaluation function value as the optimal clamping mode;

[0015] S4: After determining the optimal clamping mode, different carrier modes are adopted to achieve multi-objective coordinated discontinuous modulation of the midpoint clamped three-level inverter.

[0016] As a further optimization solution of the present invention, the DC side data of the three-level inverter is collected in S1, and the DC side data includes the capacitor voltage u on the DC side of the three-level inverter. C1 , lower capacitor voltage u C2 , DC side voltage u dc , the maximum current of the three-phase output phase i L , intermediate current i M , minimum current i S , the maximum three-phase output voltage u L , intermediate voltage u M , minimum voltage u S .

[0017] As a further optimization solution of the present invention, in S2, a midpoint potential evaluation function and a switching loss evaluation function are respectively established based on the DC side data. The specific steps of establishing a coordinated evaluation function based on the midpoint potential evaluation function and the switching loss evaluation function are as follows:

[0018] Step 201: Set the midpoint current i of the three phases introduced in one switching cycle. NPfor:

[0019]

[0020] Among them, d X,1 Indicates the duty cycle of the X phase 1 level, L indicates the maximum phase, M indicates the middle phase, and S indicates the minimum phase;

[0021] Set the direction of current outflow to positive direction, the positive midpoint current i NP Causes the midpoint voltage to decrease; negative midpoint current i NP This causes the midpoint voltage to increase, so the midpoint voltage change Δu NP With the midpoint current i NP The relationship is:

[0022]

[0023] Among them, T S is the switching cycle;

[0024] It is assumed that at the initial moment of a switching cycle, the midpoint voltage has an offset Δu NP,init =u C2 -u C1 ≠0, in order to maintain the midpoint voltage balance, the midpoint voltage change Δu of the switching cycle NP satisfy:

[0025] Δu NP +Δu NP,init =0

[0026] Combine the above formula to calculate the expected current value i NPref :

[0027]

[0028] At a certain operating point, the optional clamping modes are mode1, ..., modeN, and the corresponding midpoint currents are named i NP，mode1 ,...,i NP，modeN In order to make the midpoint voltage return to the equilibrium state as quickly as possible without causing a large overshoot, select i NP Closest to i NPref mode; set the midpoint potential evaluation function F in each mode NP :

[0029]

[0030] Where G = max{|i NPref -i NP,mode1 |, ..., |i NPref -i NP,modeN |}, FNP ∈[0, 1];

[0031] S202: Set the switching loss evaluation function SL to:

[0032]

[0033] Among them, j X is the switching times of phase X;

[0034] When the CBPWM modulation method is used, there is no clamping phase and each phase has two switching actions. The switching loss evaluation function is:

[0035] SL CBPWM =2*(|i A |+|i B |+|i C |)

[0036] Switching loss evaluation function SL under CBPWM modulation method CBPWM As a base value to evaluate the degree of reduction in switching loss of each mode, the normalized switching loss evaluation function F is obtained. LOSS :

[0037]

[0038] Among them F LOSS ∈[0, 1];

[0039] S203: Based on the midpoint potential evaluation function and the switching loss evaluation function, a coordination evaluation function F is established to simultaneously achieve midpoint voltage balance and reduce switching losses:

[0040] F=k1F NP +k2F LOSS

[0041] Among them, k1 and k2 are F NP 、F LOSS The weight of k1+k2=1; the value of k1 is a piecewise function as follows:

[0042]

[0043] As a further optimization scheme of the present invention, the coordination evaluation function is substituted into different clamping modes in S3 to calculate the evaluation function values ​​under different clamping modes. There are 9 clamping modes, namely L_PB.1, L_PB.2, L_PB.3, L_NP, M_NP, S_NP, S_NB.1, S_NB.2, and S_NB.3; among them, L_PB.2 and S_NB.2 will produce ±0.5u dcThe remaining 7 clamp modes are applicable.

[0044] As a further optimization solution of the present invention, after determining the optimal clamping mode in S4, inverting part of the carrier wave to obtain a PWM wave includes the following steps:

[0045] Step S401: Divide the six large sectors SⅠ, SⅡ, SⅢ, SⅣ, SⅤ, and SⅥ into four small sectors SY_1, SY_2, SY_3, and SY_4 according to the magnitude relationship between the modulation voltages, where Y = I, II, III, IV, V, and VI:

[0046] SY_1:u L -u S <0.5u dc

[0047]

[0048] SY_3:u L -u M >0.5u dc

[0049] SY_4:u M -u S >0.5u dc

[0050] Step S402: According to the above partitioning, different small sectors and clamping modes are set to select corresponding carrier combinations as follows:

[0051]

[0052]

[0053] Among them, m represents the modulation index, u L 、u M and u S The carrier modes representing the maximum phase, middle phase and minimum phase respectively are used to obtain the PWM wave.

[0054] The beneficial effects of the present invention are:

[0055] The present invention obtains three-phase current and three-phase voltage signals through real-time sampling and determines the relationship between their magnitudes. To address the possible contradiction between reducing switching losses and controlling NPV, a multi-objective coordination function and a discontinuous modulation strategy with multi-objective coordinated optimization are proposed, which comprehensively considers NPV control and switching loss reduction. To address the additional switching action introduced when switching between sequential modes, the relationship between the carrier and the sequential mode is discussed. Compared with traditional DPWM, the method proposed in the present invention can adapt to the control requirements of different occasions by changing the upper and lower limits of the NPV offset. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 is a flow chart of the present invention;

[0057] Figure 2 It is the topology diagram of NPC TLI;

[0058] Figure 3 It is the spatial vector diagram of NPC TLI;

[0059] Figure 4 For all SVPWM-based DPWM sequences in the SI sector;

[0060] Figure 5 There are 9 PWM sequences for DPWM;

[0061] Figure 6 is the CB_DPWM sequence mode distribution;

[0062] Figure 7 The impact of clamping mode on NPV under different conditions

[0063] Figure 8a is the PWM sequence of sectors SI_1, ..., SVI_1 under the traditional carrier;

[0064] Figure 8b is the PWM sequence of sectors SI_2, ..., SVI_2 under the traditional carrier;

[0065] Figure 8c is the PWM sequence of sectors SI_3, ..., SVI_3, SI_4, ..., SVI_4 under the traditional carrier;

[0066] Figure 9 These are the four PWM sequences for the maximum phase-clamped positive bus under traditional CBPWM;

[0067] Figure 10a The switching loss ratio of MNPVF_DPWM modulation strategy in one fundamental cycle and CBPWM is given.

[0068] Figure 10b The switching loss ratio of MSL_DPWM modulation strategy in one fundamental wave cycle and CBPWM is given.

[0069] Figure 10c The switching loss ratio of the MCO_DPWM modulation strategy within one fundamental cycle and the CBPWM switching loss is given. DETAILED DESCRIPTION

[0070] The present application is described in further detail below in conjunction with the accompanying drawings. It is necessary to point out that the following specific implementation methods are only used to further illustrate the present application and cannot be understood as limiting the scope of protection of the present application. Technicians in this field can make some non-essential improvements and adjustments to the present application based on the above application content.

[0071] Example 1

[0072] like Figure 1-10c As shown, a multi-objective coordinated discontinuous modulation method includes the following steps:

[0073] Step S1: Use voltage sensor to collect Figure 2 The capacitor voltages of C1 and C2 on the DC side of the three-level inverter are u C1 、u C2 , the DC side voltage is u dc , three-phase output phase current i A 、i B 、i C , three-phase output phase voltage u A 、u B 、u C , judge the three-phase output phase current and three-phase output phase voltage, and get the maximum current i L =max(i A ,i B ,i C ), minimum current i S =min(i A ,i B ,i C ), intermediate current i M =mid(i A ,i B ,i C ), maximum voltage u L =max(u A ,u B ,u C ), minimum voltage u S =min(u A ,u B ,u C ) and the intermediate voltage u M =mid(u A ,u B ,u C ).

[0074] Step S2: Calculate the coordination evaluation function under 7 different clamping modes. The specific implementation is:

[0075] In NPC TLI, the midpoint voltage must be balanced or its offset and fluctuation must be controlled within a certain range. When a phase outputs a level 1, current is drawn from or injected into the midpoint, causing the midpoint voltage to change. In one switching cycle, the midpoint current i NP for:

[0076]

[0077] Among them, d X,1 Indicates the duty cycle of the X phase 1 level, L indicates the maximum phase, M indicates the middle phase, and S indicates the minimum phase;

[0078] The direction of current outflow is defined as the positive direction, and the positive i NP Causes the midpoint voltage to decrease; negative i NP This causes the midpoint voltage to increase. Therefore, the midpoint voltage change Δu NP With the midpoint current i NP The relationship is:

[0079]

[0080] Among them, T S is the switching cycle.

[0081] As can be seen from the above formula, the NPC TLI output current is determined by the load and cannot be changed arbitrarily. However, the NPV can be adjusted by changing the duty cycle of the 1-level.

[0082] Switching loss is another important metric for NPC TLI operation. Within a switching cycle, switching loss is closely related to the number of switches and the current handled. Strictly calculating switching loss is difficult, so for convenience, we define the switching loss evaluation function SL as:

[0083]

[0084] Among them, j X is the number of switching cycles for phase X. Therefore, if one phase is not switched during a switching cycle, switching losses can be reduced. If the phase with the largest absolute current can be kept from switching, switching losses can be minimized.

[0085] In NPC TLI, clamping can be achieved by injecting a specific ZSV into the modulation voltage, u ZSV The expression is:

[0086]

[0087] In the above formula, X_2 represents the X-phase clamp 2 level, X_1 represents the X-phase clamp 1 level, and X_0 represents the X-phase clamp 0 level.ZSV The modulated voltage is then recorded as u′ X :

[0088] u′ X =u X +u ZSV

[0089] Theoretically, the three phases are injected into ZSV Any clamping can be implemented, but considering the feasibility of modulation, the following conditions must be met:

[0090] -0.5u dc ≤u′ X ≤0.5u dc

[0091] Therefore, the phase with the maximum voltage can be clamped to the positive bus or the midpoint, the phase with the middle voltage can only be clamped to the midpoint, and the phase with the minimum voltage can be clamped to the negative bus or the midpoint. When the phase with the maximum voltage is clamped to the positive bus or the phase with the minimum voltage is clamped to the negative bus, three types of sequence modes can be further subdivided according to the level output of the remaining two phases. Therefore, CB_DPWM has 5 types of sequence modes and 9 types of sub-sequence modes, such as Figure 5 As shown. L_PB.1 represents the first sequence mode of the maximum phase clamp positive bus, and so on, all sequence modes are named L_PB.1,..., S_NB.3. It is worth noting that L_PB.2 and S_NB.2 will produce ±0.5u dc The common mode voltage of the two sequences will not be discussed in the subsequent process.

[0092] The sequence mode is only related to the instantaneous value of the three-phase output voltage, that is, to m and ωt. Different sequence modes will result in different midpoint currents. For example, taking the operating point m=0.9, ωt=15° as an example, sequence modes L_PB.1 and S_NB.3 are applicable sequence modes. Zero sequence voltage u is injected into the three phases. ZSV =-u L +0.5u dc The sequence mode L_PB.1 can be realized by injecting u ZSV The three-phase modulation voltage after is:

[0093] u′ L =0.5u dc , u′ M =u M -u L +0.5u dc , u′ S =u S -u L +0.5u dc

[0094] The midpoint current introduced by sequence mode L_PB.1 is:

[0095]

[0096] Where p = u L i L +u M i M +u S i S , is the instantaneous power flowing from the inverter to the load. In sequential mode L_PB.1, the maximum voltage phase has no switching action, while the intermediate voltage phase and the minimum voltage phase each have two switching actions. Therefore, the L_PB.1 switching loss evaluation function is:

[0097] SL=2|i M |+2|i S |

[0098] Inject zero-sequence voltage u into the three phases ZSV =-u S -0.5u dc The sequence mode S_NB.3 can be realized by injecting u ZSV The three-phase modulation voltage after is:

[0099] u′ L =u L -u S -0.5u dc , u′ M =u M -u S -0.5u dc , u′ S =-0.5u dc

[0100] The midpoint current and switching loss evaluation function is:

[0101]

[0102] SL=2|i L |+2|i M |

[0103] From the above analysis, it can be seen that at the same operating point, different sequence modes will lead to different mid-point currents and different switching losses.

[0104] Assume that at the beginning of a switching cycle, the midpoint voltage has an offset Δu NP,init =u C2 -u C1 ≠0. To maintain the midpoint voltage balance, the NPV change Δu during this switching cycle NP satisfy:

[0105] Δu NP +Δu NP,init =0

[0106] Combine the above formula to calculate the expected current value i NPref :

[0107]

[0108] If at a certain operating point, the optional sequence mode is mode1, ..., modeN, and the corresponding midpoint current is named i NP，mode1 ,...,i NP，modeN , Figure 7 The NPV active control method under CB_DPWM is given. NP,init >0 as an example, in case 1, all sequence modes will reduce NPV, but none of them can restore NPV to equilibrium. Therefore, the mode that can reduce NPV the fastest is selected; in case 2, all sequence modes will reduce NPV, and a certain mode will cause a large overshoot, so the mode that can restore NPV to the closest equilibrium is selected; in case 3, all sequence modes will continue to increase NPV offset, but a certain mode will cause the smallest increase, so this mode is selected. NP,init The situation of <0 is similar. In summary, in order to make NPV return to equilibrium as quickly as possible without causing a large overshoot, choose i NP Closest to i NPref pattern.

[0109] In order to describe the degree of closeness, if mode1, ..., modeN are available at a certain operating point, the NPV control function of each mode is defined as:

[0110]

[0111] Where G = max{|i NPref -i NP,mode1 |, ..., |i NPref -i NP,modeN |}. Yizhi, F NP ∈[0,1].i NP and i NPref The closer, the NP The smaller the F NP By selecting the sequence mode according to the minimum principle, the NPV optimization control under CB_DPWM can be achieved.

[0112] Under CB_DPWM, not only the NPV control performance needs to be considered, but also the degree of reduction in switching loss needs to be considered in order to give full play to the advantages of CB_DPWM in reducing switching loss. CBPWM =2(|i A |+|i B |+|i C |) is used as the base value to evaluate the degree of reduction in switching loss of each mode. The normalized switching loss evaluation function F LOSS for:

[0113]

[0114] Easy to know F LOSS ∈[0, 1]. When using the CB_DPWM modulation method, in order to achieve the two goals of NPV balance and switching loss reduction at the same time, a unified evaluation function F is established:

[0115] F=k1F NP +k2F LOSS

[0116] Among them, k1 and k2 are F NP 、F LOSS The weight of k1+k2=1. The following is a brief discussion on the values ​​of k1 and k2.

[0117] When a large imbalance in NPV is detected, such as Δu NP,init When the set value is exceeded, the primary goal is to restore the NPV to a balanced state, so it is advisable to take k1=1 and k2=0 to achieve rapid control of the NPV. This method is called MNPVF_DPWM.

[0118] When the detected NPV offset is very small or even negligible, the primary goal is to reduce switching losses. Therefore, it is recommended to set k1 = 0 and k2 = 1 to minimize switching losses. This method is called MSL_DPWM.

[0119] Because k1+k2=1, when the value of k1 is determined, k2=1-k1. In general, a piecewise function can be constructed to determine the value of k1:

[0120]

[0121] Step S3: Calculate the coordination evaluation functions of the seven clamping modes and select the clamping mode corresponding to the minimum coordination evaluation function value for clamping.

[0122] Step S4: After the clamping mode is determined, in order to avoid unnecessary switching actions caused by clamping, different carrier modes need to be adopted to finally obtain a PWM wave. The specific implementation is as follows:

[0123] In classic CBPWM, all three-phase carriers use the same carrier mode. If this is directly applied to CB_DPWM, it will cause additional switching actions when switching between sequential modes, weakening the advantage of DPWM in reducing switching losses.

[0124] Taking the sequence mode L_PB.1 as an example, Figure 9 Four PWM sequences are shown. If this clamping method ends the three phases at 2 levels, 1 levels, and 0 levels, respectively, unnecessary switching is avoided, achieving smooth switching. By selecting an appropriate carrier, the PWM sequence can be made to start and end at the levels described above. Each clamping mode is shown in the table below.

[0125]

[0126]

[0127] Where m represents the modulation index. L 、u M and u S The carrier modes for the maximum phase, the middle phase, and the minimum phase are shown respectively. The combination of these carrier modes can eliminate unnecessary switching caused by clamping, thereby reducing switching losses.

[0128] Figure 10a Given P MNPVF_DPWM / P CBPWM The variation in the full modulation and power factor range is between 0.65 and 0.85.

[0129] Figure 10b Given P MSL_DPWM / P CBPWM The variation in the full modulation and power factor range is between 0.65 and 0.85.

[0130] Figure 10c Given P MCO_DPWM / P CBPWM The variation in the full modulation and power factor range is between 0.55 and 0.8.

[0131] The above-described embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. A multi-objective coordinated discontinuous modulation method, the method being applied to a neutral-point clamped three-level inverter, characterized in that: The following steps are involved: Step S1: Collect DC side data of the three-level inverter; the DC side data includes the capacitor voltage on the DC side of the three-level inverter u C1 , lower capacitor voltage u C2 , DC side voltage u dc , maximum current of three-phase output phase i L , intermediate current i M , minimum current i S , maximum voltage of three-phase output phase u L , intermediate voltage u M , minimum voltage u S ; Step S2: establishing a midpoint potential evaluation function and a switching loss evaluation function based on the DC side data, and establishing a coordination evaluation function based on the midpoint potential evaluation function and the switching loss evaluation function; specifically: Step S201: Set the midpoint current of the three phases introduced in one switching cycle i NP for: ； in, d X,1 Indicates the duty cycle of the X phase 1 level, L indicates the maximum phase, M indicates the middle phase, and S indicates the minimum phase; Set the direction of current outflow to positive direction, positive midpoint current i NP Causes the midpoint voltage to decrease and the negative midpoint current to i NP This causes the midpoint voltage to increase, so the midpoint voltage change Δ u NP With midpoint current i NP The relationship is: ; in, T S is the switching cycle; It is assumed that at the initial moment of a switching cycle, the midpoint voltage has an offset Δ u NP,init = u C2 - u C1 ≠0, in order to maintain the midpoint voltage balance, the midpoint voltage change of this switching cycle Δ u NP satisfy: ; Combine the above formula to calculate the expected current value i NPref for: ; At a certain operating point, the optional clamping modes are mode1, ..., modeN, and the corresponding midpoint currents are named i NP，mode1 ,..., i NP，modeN In order to make the midpoint voltage return to the equilibrium state as quickly as possible without causing a large overshoot, select i NP Closest i NPref mode, the midpoint potential evaluation function F under each mode is established NP Expressed as: ； in, ; Step S202: Establish a switching loss evaluation function SL, which is expressed as: ； in, j X is the switching times of phase X; When the CBPWM modulation method is used, there is no clamping phase, and each phase has two switching actions. The switching loss evaluation function is: ; Switching loss evaluation function under CBPWM modulation method SL CBPWM As a base value to evaluate the degree of reduction in switching loss of each mode, the normalized switching loss evaluation function F is obtained. LOSS : ; Among them F LOSS ∈[0, 1]; Step S203: Based on the midpoint potential evaluation function and the switching loss evaluation function, a coordination evaluation function F is established to simultaneously achieve midpoint voltage balance and reduce switching losses: ； in, k 1. k 2 are F NP 、F LOSS The weight of k 1+ k 2=1; where k The value of 1 is piecewise function as follows: ； Step S3: Substituting the coordination evaluation function into different clamping modes to calculate and obtain evaluation function values ​​under different clamping modes, and selecting the clamping mode with the smallest evaluation function value as the optimal clamping mode; Step S4: After determining the optimal clamping mode, in order to avoid unnecessary switching actions caused by clamping, different carrier modes are adopted to achieve multi-objective coordinated discontinuous modulation of the neutral point clamped three-level inverter.

2. The multi-objective coordinated discontinuous modulation method according to claim 1, characterized in that: In step S3, the coordination evaluation function is substituted into different clamping modes to calculate the evaluation function values ​​under different clamping modes. There are 9 clamping modes, namely L_PB.1, L_PB.2, L_PB.3, L_NP, M_NP, S_NP, S_NB.1, S_NB.2, and S_NB.

3. Among them, L_PB.2 and S_NB.2 will produce ±0.5 u dc The remaining 7 clamp modes are applicable.

3. The multi-objective coordinated discontinuous modulation method according to claim 1, characterized in that: After determining the optimal clamping mode in step S4, adopting a corresponding carrier mode to eliminate redundant switching actions caused by the clamping mode includes the following steps: Step S401: Divide the six large sectors SⅠ, SⅡ, SⅢ, SⅣ, SⅤ, and SⅥ into SY_1 and SY_2 respectively according to the magnitude relationship between the modulation voltages. ， Four small sectors SY_3 and SY_4, where Y=Ⅰ, Ⅱ, Ⅲ, Ⅳ, Ⅴ, Ⅵ: ； Step S402: According to the above partitioning, different small sectors and clamping modes are set to select corresponding carrier combinations as follows: ； Among them, m represents the modulation index, u L 、 u M and u S The carrier modes representing the maximum phase, middle phase and minimum phase respectively are used to obtain the PWM wave.

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