Leakage current suppression method and circuit for soft switching grid-connected inverter

Abstract

The invention discloses a leakage current suppression method and circuit for a soft switching grid-connected inverter, and belongs to the technical field of power electronic converters, and the method comprises the steps: building a space voltage vector according to a three-phase voltage, building a three-level vector space in a complex plane, and dividing sectors; defining boundary conditions, and dividing each sub-sector into six small sectors according to the boundary conditions; determining a small sector where the reference voltage vector is located according to the boundary condition and the reference vector; determining a five-segment basic vector action sequence according to the small sector where the reference voltage vector is located; according to the basic vector action sequence, boundary switching frequencies in the non-clamping two phases are obtained, and the minimum value of the boundary switching frequencies in the non-clamping two phases is selected as a unified switching frequency; and modulating the three-phase modulation wave, the unified switching frequency and the DC voltage sampling value, and outputting a pulse width control signal of each power switch tube. According to the invention, a low common-mode voltage change rate and wide-range soft switching of the power switch tube are realized, and leakage current can be effectively suppressed.

Description

Technical Field

[0001] The present application relates to the technical field of power electronic converters, and in particular to a leakage current suppression method and circuit for a soft-switching grid-connected inverter. Background Art

[0002] As a commonly used grid-connected inverter, three-phase, three-level inverters are a key component of photovoltaic power generation systems due to their low switching stress and low output current. Existing three-phase, three-level inverters mostly operate with low-frequency hard switching, resulting in bulky passive components and low efficiency. The application of wide-bandgap devices, such as silicon carbide (SiC) and gallium nitride (GaN), can significantly increase the switching frequency to kilohertz (kHz) or even megahertz (MHz), thereby further improving the inverter's power density and efficiency. However, simply increasing the switching frequency can lead to switching oscillations and a sharp increase in switching losses. Therefore, soft switching technology, which actively softens the turn-on process of the switching transistors—that is, achieving zero voltage turn-on (ZVS)—holds promise for the deep integration of wide-bandgap devices with grid-connected inverters.

[0003] Conventional methods can achieve soft switching of the main switching device by adding auxiliary circuits, but these circuits increase the complexity of the control and drive circuits, incurring additional costs and losses. Furthermore, when the DC side of a grid-connected inverter is connected to a photovoltaic panel or energy storage system, parasitic capacitance between the DC side and the ground forms a loop with the AC side ground point. The resulting leakage current can generate electromagnetic interference, increase harmonic currents, and pose a safety hazard, and therefore must be strictly suppressed.

[0004] In recent years, some studies have proposed soft switching technology methods without auxiliary networks. For example, the existing technical literature "J.Chen, J. Deng, L. Ming, et al. "A Variable Switching Frequency Control forZVS Three-Phase Three-Level T-Type Inverter Using Hybrid Discontinuous PWM," IEEE Transactions on Power Electronics, 38(11)" proposed a full-range soft switching method suitable for three-phase three-level grid-connected inverters by combining discontinuous pulse width modulation (DPWM) and variable frequency control strategy. The proposed method can be fully digitally implemented with high efficiency and power density. However, the common-mode voltage variation amplitude and frequency of this method are large, which generates a large leakage current in the entire system. At present, there is no effective and economical solution to the leakage current suppression problem of three-phase three-level soft switching grid-connected inverters. Therefore, it is necessary to study a leakage current suppression method suitable for three-phase three-level soft switching grid-connected inverters, which can solve the reliability and safety problems caused by leakage current while realizing soft switching of grid-connected inverters. Summary of the Invention

[0005] The present application aims to provide a leakage current suppression method and circuit for a soft-switching grid-connected inverter, which can simultaneously realize soft switching of the inverter power switch tube and leakage current suppression of the grid-connected system on a low-cost microcontroller unit (MCU) without using any hardware auxiliary circuits.

[0006] To achieve the above objectives, the technical solution of this application is: A method for suppressing leakage current of a soft-switching grid-connected inverter, comprising: Constructing a spatial voltage vector according to the three-phase voltage, establishing a three-level vector space in the complex plane, dividing the three-level vector space into six large sectors, and each large sector is divided into two sub-sectors, including: a first sub-sector and a second sub-sector; Define boundary conditions and divide each sub-sector into 6 small sectors according to the boundary conditions; Determine the small sector where the reference voltage vector is located according to the boundary conditions and the reference vector; According to the small sector where the reference voltage vector is located, three space voltage vectors are selected to make one phase switch state inactive, and a five-segment basic vector action sequence is determined; The mid-boundary switching frequencies of the unclamped two-phases are obtained according to the basic vector action sequence, and the minimum mid-boundary switching frequencies of the unclamped two-phases are selected as the unified switching frequency; The three-phase modulation wave, the unified switching frequency and the DC voltage sampling value are modulated to output the pulse width control signal of each power switch tube.

[0007] Optionally, define boundary conditions as follows: in, L 1 represents the first boundary condition, L 2 represents the second boundary condition, L 3 represents the third boundary condition, L 4 represents the fourth boundary condition, L 5 represents the fifth boundary condition, L 6 represents the sixth boundary condition, L 7 represents the seventh boundary condition, L 8 represents the eighth boundary condition; u α represents the control component of the α-axis in the αβ coordinate system; u β Represents the control component of the β axis in the αβ coordinate system.

[0008] Optionally, the reference vector includes: a control component of the α-axis in the αβ coordinate system and a control component of the β-axis in the αβ coordinate system.

[0009] Optionally, three space voltage vectors that cause one phase switch state to be inactive are selected according to the small sector where the reference voltage vector is located, and a five-segment basic vector action sequence is determined, including: if the reference voltage vector is located in the third small sector and the fifth small sector of any large sector, a vector selection factor is defined, and the basic vector action sequence is selected according to the vector selection factor; Define the vector selection factor and select the basic vector action sequence according to the vector selection factor, including: When the reference voltage vector is located in the third small sector of the first large sector, and when the boundary switching frequency of the basic vector action sequence of the A-phase clamp is less than the boundary switching frequency of the basic vector action sequence of the C-phase clamp, the vector selection factor is set to 0; otherwise, the vector selection factor is set to 1; when the vector selection factor is 1, the basic vector action sequence of the A-phase clamp is selected, and when the vector selection factor is 0, the basic vector action sequence of the C-phase clamp is selected; When the reference voltage vector is located in the fifth small sector of the first large sector, and when the boundary switching frequency of the basic vector action sequence of the A-phase clamp is less than that of the basic vector action sequence of the C-phase clamp, the vector selection factor is set to 0; otherwise, the vector selection factor is set to 1; when the vector selection factor is 1, the basic vector action sequence of the A-phase clamp is selected, and when the vector selection factor is 0, the basic vector action sequence of the C-phase clamp is selected; When the reference voltage vector is located in the remaining large sectors, the reference voltage vector is mapped and converted to the first large sector for calculation, and then mapped and converted back to the original large sector to obtain the corresponding basic vector action sequence.

[0010] Optionally, when the reference voltage vector is located in the first sub-sector of the first large sector, the boundary switching frequency of the unclamped two-phase in the first small sector is calculated as follows: When the reference voltage vector is located in the first sub-sector of the first large sector, the boundary switching frequency of the unclamped two-phase in the second small sector is calculated as follows: When the reference voltage vector is located in the first sub-sector of the first large sector, the boundary switching frequency of the unclamped two-phase in the fourth small sector is calculated as follows: When the reference voltage vector is located in the first sub-sector of the first large sector, the boundary switching frequency of the unclamped two-phase in the sixth small sector is calculated as follows: in, f sa Indicates the boundary switching frequency of the A-phase bridge arm, f sb Indicates the boundary switching frequency of the B-phase bridge arm, f sc Indicates the boundary switching frequency of the C-phase bridge arm; m a Represents the A-phase modulation wave, m b Represents the B-phase modulation wave, m c Represents C-phase modulation wave; I bias Represents the reverse reset current, which is a constant value; u dc Indicates the DC voltage sampling value; i ga Indicates the sampling value of the A phase grid current. i gb Indicates the sampling value of the B phase grid current. i gc Indicates the sampling value of the C phase grid current; u ga Indicates the A-phase AC voltage sampling value, u gb Indicates the B-phase AC voltage sampling value, u gc Indicates the C-phase AC voltage sampling value; When the reference voltage vector is located in the third small sector of the first sub-sector of the first large sector, the boundary switching frequency of the unclamped two phases of the basic vector action sequence of the A-phase clamp is calculated as follows: ; The calculation of the boundary switching frequency of the basic vector action sequence of the C-phase clamp is the same as that of the second small sector; When the reference voltage vector is located in the fifth small sector of the first sub-sector of the first large sector, the calculation of the boundary switching frequency of the unclamped two-phases in the basic vector action sequence of the A-phase clamp is the same as that of the basic vector action sequence of the A-phase clamp selected in the third small sector; the calculation of the boundary switching frequency of the unclamped two-phases in the basic vector action sequence of the C-phase clamp is the same as that of the sixth small sector. When the reference voltage vector is located in the second sub-sector of the first large sector and the remaining large sectors, the reference voltage vector is mapped and converted to the first sub-sector of the first large sector for calculation, and then mapped back to the original large sector to obtain the corresponding basic vector action sequence.

[0011] Optionally, a three-phase modulation wave is generated in combination with the small sector where the reference voltage vector is located and the vector selection factor.

[0012] Optionally, when the reference voltage vector is located in the first small sector of any sub-sector of any large sector, the three-phase modulation wave is expressed as follows: ; When the reference voltage vector is located in the second small sector of any sub-sector of any large sector, the three-phase modulation wave is expressed as follows: ; When the reference voltage vector is located in the third small sector of any sub-sector of any large sector and the vector selection factor is 0, the three-phase modulation wave is the same as the second small sector. When the reference voltage vector is located in the third small sector of any sub-sector of any large sector and the vector selection factor is 1, the three-phase modulation wave is expressed as follows: ; When the reference voltage vector is located in the 4th small sector of any sub-sector of any large sector, the three-phase modulation wave is the same as when the reference voltage vector is located in the 3rd small sector of any sub-sector of any large sector and the vector selection factor is 1; When the reference voltage vector is located in the 5th small sector of any sub-sector of any large sector and the vector selection factor is 0, the three-phase modulation wave is the same as the 2nd small sector; when the reference voltage vector is located in the 5th small sector of any sub-sector of any large sector and the vector selection factor is 1, the three-phase modulation wave is the same as the 4th small sector; When the reference voltage vector is located in the 6th small sector of any sub-sector of any large sector, the three-phase modulation wave is the same as when the reference voltage vector is located in the 2nd small sector of any sub-sector of any large sector.

[0013] A leakage current suppression circuit for a soft-switching grid-connected inverter, the soft-switching grid-connected inverter comprising a DC bus filter capacitor module, a power conversion module and an AC filter module; the DC bus filter capacitor module, the power conversion module and the AC filter module are connected in sequence; the DC bus filter capacitor module comprises a first DC bus filter capacitor and a second DC bus filter capacitor ， The first DC bus filter capacitor and the second DC bus filter capacitor are connected in series and then in parallel with the DC power supply; the AC filter module includes an A-phase inverter side filter inductor, a B-phase inverter side filter inductor, a C-phase inverter side filter inductor, an A-phase AC filter capacitor, a B-phase AC filter capacitor, a C-phase AC filter capacitor, an A-phase grid-side filter inductor, a B-phase grid-side filter inductor, and a C-phase grid-side filter inductor; the soft-switching grid-connected inverter is connected to a three-phase AC grid, and the three-phase AC grid includes: an A-phase AC grid, a B-phase AC grid, and a C-phase AC grid; The leakage current suppression circuit of the soft-switching grid-connected inverter is used to execute a leakage current suppression method for a soft-switching grid-connected inverter as described in any one of the above. The leakage current suppression circuit of the soft-switching grid-connected inverter includes a sampling and driving unit and a digital signal control unit. The soft-switching grid-connected inverter, the sampling and driving unit, and the digital signal control unit are connected in sequence.

[0014] Optionally, the sampling and driving unit includes a bus voltage sampling module, a MOSFET driving module, a grid current sampling module and a power grid voltage sampling module; wherein, the input end of the bus voltage sampling module is connected to the first DC filter capacitor and the second DC filter capacitor, the output end of the MOSFET driving module is connected to the power conversion module, the first input end, the second input end and the third input end of the grid current sampling module are respectively connected to the first end of the A-phase grid-side filter inductor, the first end of the B-phase grid-side filter inductor and the first end of the C-phase grid-side filter inductor, and the first input end, the second input end and the third input end of the power grid voltage sampling module are respectively connected to the first end of the A-phase AC grid, the first end of the B-phase AC grid and the first end of the C-phase AC grid.

[0015] Optionally, the digital signal control unit includes a first coordinate transformation module, a second coordinate transformation module, a phase lock, a first subtractor, a second subtractor, a reactive current PI regulator, an active current PI regulator, a third coordinate transformation module, a sector calculation module, a synchronous discontinuous pulse width controller, a boundary switching frequency calculation module and a modulator; wherein, the output end of the grid current sampling module is connected to the first input end of the first coordinate transformation module, the first output end of the first coordinate transformation module is connected to the first input end of the first subtractor, and the second output end of the first coordinate transformation module is connected to the first input end of the second subtractor; the output end of the grid voltage sampling module is connected to the first input end of the second coordinate transformation module, the first output end and the second output end of the second coordinate transformation module are respectively connected to the first input end and the second input end of the phase lock; the output end of the phase lock is respectively connected to the second input end of the first coordinate transformation module, the second input end of the second coordinate transformation module and the first input end of the third coordinate transformation module The output end of the first subtractor is connected to the input end of the reactive current PI regulator, the output end of the second subtractor is connected to the input end of the active current PI regulator, the output end of the reactive current PI regulator and the output end of the active current PI regulator are respectively connected to the second input end and the third input end of the third coordinate transformation module; the first output end and the second output end of the third coordinate transformation module are respectively connected to the first input end and the second input end of the sector calculation module; the output end of the sector calculation module is respectively connected to the input end of the synchronous discontinuous pulse width controller and the first input end of the boundary switching frequency calculation module; the first output ends of the synchronous discontinuous pulse width controller and the boundary switching frequency calculation module are respectively connected to the first input end and the second input end of the modulator, and the second output end of the synchronous discontinuous pulse width controller is connected to the second input end of the boundary switching frequency calculation module; the third input end of the modulator is connected to the output end of the bus voltage sampling module, and the output end of the modulator is connected to the input end of the MOSFET driving module.

[0016] The leakage current suppression method and circuit for a soft-switching grid-connected inverter provided in this application achieve a low common-mode voltage change rate through a rationally designed switching sequence, thereby effectively suppressing leakage current and achieving zero-voltage turn-on of the power switch tubes of the soft-switching grid-connected inverter. This method and circuit require no additional hardware cost and are easy to implement. Furthermore, the present application enables wide-range soft switching of the power switch tubes at a high switching frequency, thereby effectively reducing the volume and weight of passive components and further improving the power density of the grid-connected inverter. The control circuit and leakage current suppression method described in this application are suitable for renewable energy power generation applications, and particularly have broad application prospects in the field of photovoltaic power generation.

[0017] In order to make the above features and advantages of the application more obvious and easy to understand, the following embodiments are given and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the leakage current suppression circuit of the soft-switching grid-connected inverter provided in this application.

[0019] Figure 2 Flowchart of the leakage current suppression method for soft-switching grid-connected inverter.

[0020] Figure 3 Schematic diagram of large sector division of the three-level vector space of the soft-switching grid-connected inverter of this application.

[0021] Figure 4 Figure (a) is a schematic diagram of the small sector division of sub-sector A of the Ith large sector in the three-level vector space.

[0022] Figure 4 Figure (b) is a schematic diagram of the small sector division of sub-sector B of the Ith large sector in the three-level vector space.

[0023] Figure 5 Figure (a) is a three-phase boundary switching frequency curve diagram of the leakage current suppression method and circuit embodiment of the soft-switching grid-connected inverter provided by the present application.

[0024] Figure 5 Figure (b) is a unified switching frequency curve diagram of the leakage current suppression method and circuit embodiment of the soft-switching grid-connected inverter provided by the present application.

[0025] Figure 6 Figure (a) is a steady-state waveform diagram of the grid-connected current using the leakage current suppression method and circuit embodiment of the soft-switching grid-connected inverter provided by the present application.

[0026] Figure 6 Figure (b) is a steady-state waveform diagram of the inductor current using the leakage current suppression method and circuit embodiment of the soft-switching grid-connected inverter provided by the present application.

[0027] Figure 6 Figure (c) is a common-mode voltage steady-state waveform diagram of the leakage current suppression method and circuit embodiment of the soft-switching grid-connected inverter provided by the present application.

[0028] Figure 6 Figure (d) is a steady-state waveform diagram of leakage current using the leakage current suppression method and circuit embodiment of the soft-switching grid-connected inverter provided by the present application. DETAILED DESCRIPTION

[0029] To make the purpose and technical solutions of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be clearly and completely described below in conjunction with the drawings of the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the described embodiments of the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0030] In one embodiment of the present application, the present application provides a method for suppressing leakage current of a soft-switching grid-connected inverter, which is applied to a leakage current suppression circuit of a soft-switching grid-connected inverter. Figure 1 , Figure 1 This is a schematic diagram of the leakage current suppression circuit of the soft-switching grid-connected inverter provided in this application. Figure 1 As shown, the soft-switching grid-connected inverter 1 includes a DC bus filter capacitor module 11, a power conversion module 12, and an AC filter module 13; the DC bus filter capacitor module 11, the power conversion module 12, and the AC filter module 13 are connected in sequence. The soft-switching grid-connected inverter 1 is connected to a three-phase AC grid, which includes: Phase A AC grid u ga , B-phase AC power grid u gb and C-phase AC grid u gc .

[0031] As an example, the DC bus filter capacitor module 11 includes a first DC bus filter capacitor C dc1 And the second DC bus filter capacitor C dc2 ; The first DC bus filter capacitor C dc1 The first end of the DC bus filter capacitor module 11 is the first end of the second DC bus filter capacitor C dc2 The second end of is the second end of the DC bus filter capacitor module 11. The first DC bus filter capacitor C dc1 and the second DC bus filter capacitor C dc2 Series then parallel DC power supply U dc , the first DC filter capacitor C dc1 The first end is connected to the DC power supply U dc The positive pole of the first DC filter capacitor C dc1 The second end of the second DC filter capacitor is connected Cdc2 The first end of the second DC filter capacitor C dc2 The second end is connected to the DC power supply U dc The negative electrode; As an example, the power conversion module 12 includes a first power switch tube of the A-phase bridge arm S a1 , the second power switch tube of phase A bridge arm S a2 , the third power switch tube of phase A bridge arm S a3 , the fourth power switch tube of phase A bridge arm S a4 , the first power switch tube of the B phase bridge arm S b1 , the second power switch tube of the B phase bridge arm S b2 , the third power switch tube of the B phase bridge arm S b3 , the fourth power switch tube of the B phase bridge arm S b4 , C phase bridge arm first power switch tube S c1 , the second power switch tube of the C phase bridge arm S c2 , the third power switch tube of the C phase bridge arm S c3 And the fourth power switch tube of the C phase bridge arm S c4 .

[0032] As an example, in the A-phase bridge arm, the first power switch tube of the A-phase bridge arm S a1 The drain and the first DC bus filter capacitor C dc1 The first end of the A phase bridge arm is connected to the first power switch tube S a1 The source of the A-phase bridge arm and the third power switch tube S a3 The drain and the fourth power switch tube of the A phase bridge arm S a4 The drain connection of the A phase bridge arm third power switch tube S a3 The source of the A-phase bridge arm and the second power switch tube S a2 The source of the A-phase bridge arm is connected to the fourth power switch tube S a4 The source and the second DC bus filter capacitor C dcThe second end of the A phase bridge arm is connected to the first power switch tube S a1 The source level and the third power switch tube of the A phase bridge arm S a3 The drain and the fourth power switch tube of the A phase bridge arm S a4 The connection point of the drain of the A-phase bridge arm is the output point A; the first power switch tube of the A-phase bridge arm S a1 The drain and the first DC bus filter capacitor C dc1 The connection point of the first end is point P; the fourth power switch tube of the A phase bridge arm S a4 The source and the second DC bus filter capacitor C dc The connection point of the second end is point N.

[0033] As an example, in the B-phase bridge arm, the first power switch tube of the B-phase bridge arm S b1 The drain and the first DC bus filter capacitor C dc1 The first end of the B-phase bridge arm is connected to the first power switch tube S b1 The source level and the third power switch tube of the B phase bridge arm S b3 The drain of the B-phase bridge arm and the fourth power switch tube S b4 The drain of the B-phase bridge arm is connected to the third power switch tube S b3 The source of the second power switch tube of the B phase bridge arm S b2 The source of the B-phase bridge arm is connected to the fourth power switch tube S b4 The source and the second DC bus filter capacitor C dc The second end of the B phase bridge arm is connected to the first power switch tube S b1 The source level and the third power switch tube of the B phase bridge arm S b3 The drain of the B-phase bridge arm and the fourth power switch tube S b4 The connection point of the drain is the output point B of the B phase bridge arm.

[0034] As an example, in the C-phase bridge arm, the first power switch tube of the C-phase bridge arm S c1 The drain and the first DC bus filter capacitor C dc1The first end of the C phase bridge arm is connected to the first power switch tube S c1 The source stage and the third power switch tube of the C phase bridge arm S b3 The drain and the fourth power switch tube of the C phase bridge arm S c4 The drain connection of the C phase bridge arm third power switch tube S c3 The source of the C-phase bridge arm and the second power switch tube S c2 The source of the C-phase bridge arm is connected to the fourth power switch tube S c4 The source and the second DC bus filter capacitor C dc The second end of the A phase bridge arm is connected to the second power switch tube S a2 The drain of the B-phase bridge arm and the second power switch tube S b2 The drain and the second power switch tube of the C phase bridge arm S c2 The drain is connected to the first DC bus filter capacitor C dc1 And the second DC bus filter capacitor C dc The series midpoint connection; the first power switch tube of the C phase bridge arm S c1 The source stage and the third power switch tube of the C phase bridge arm S b3 The drain and the fourth power switch tube of the C phase bridge arm S c4 The connection point of the drain is the output point C of the C-phase bridge arm; the first DC bus filter capacitor C dc1 And the second DC bus filter capacitor C dc The midpoint of the series connection is point O.

[0035] As an example, the AC filter module 13 includes a filter inductor on the inverter side of phase A. L 1a , B-phase inverter side filter inductor L 1b , C-phase inverter side filter inductor L 1c , A phase AC filter capacitor C fa , B phase AC filter capacitor C fb , C-phase AC filter capacitor C fc , A phase grid side filter inductorL 2a , B phase grid side filter inductor L 2b And the C phase grid side filter inductor L 2c . A-phase inverter side filter inductor L 1a The first end is connected to the output point A of the A-phase bridge arm, and the filter inductor on the A-phase inverter side L 1a The second end of the A phase AC filter capacitor C fa The first end and the A phase grid side filter inductor L 2a The first end of the A phase grid side filter inductor is connected L 2a The second end is connected to the A-phase AC grid u ga The first end of the B-phase inverter side filter inductor is connected; L 1b The first end is connected to the output point B of the B-phase bridge arm, and the filter inductor on the B-phase inverter side L 1b The second end of the B phase AC filter capacitor C fb The first end and the B phase grid side filter inductor L 2b The first end of the B phase grid side filter inductor is connected L 2b The second end is connected to the B-phase AC grid u gb The first end of the C-phase inverter side filter inductor is connected; L 1c The first end is connected to the output point C of the C-phase bridge arm, and the filter inductor on the C-phase inverter side L 1c The second end of each phase is connected to the C phase AC filter capacitor C fc The first end and the C phase grid side filter inductor L 2c The first end of the C phase grid side filter inductor is connected L 2c The second end is connected to the C-phase AC grid u gc The first end of the A phase AC filter capacitor is connected C fa The second end of the B-phase AC filter capacitor C fb The second end and C phase AC filter capacitor C fc The second end of the

[0036] Phase A AC grid u ga The second end, B phase AC grid u gb The second end and the C-phase AC grid u gc The second end of is connected to point n.

[0037] Furthermore, the leakage current suppression circuit of the soft-switching grid-connected inverter includes a sampling and driving unit 2 and a digital signal control unit 3 .

[0038] As an example, the sampling and driving unit 2 includes a bus voltage sampling module 21, a MOSFET driving module 22, a grid current sampling module 23 and a grid voltage sampling module 24; wherein the input end of the bus voltage sampling module 21 is connected to the first DC filter capacitor C dc1 And the second DC filter capacitor C dc2 The output end of the MOSFET driver module 22 is connected to the power conversion module 12, and the first input end, the second input end and the third input end of the grid current sampling module 23 are respectively connected to the A phase grid side filter inductor L 2a The first end of the B phase grid side filter inductor L 2b The first end and the C phase grid side filter inductor L 2c The first input terminal, the second input terminal and the third input terminal of the grid voltage sampling module 24 are respectively connected to the A phase AC grid u ga The first end, B phase AC grid u gb The first end and C phase AC grid u gc The first end of the connection.

[0039] As an example, the digital signal control unit 3 includes a first coordinate transformation module 31, a second coordinate transformation module 32, a phase lock 33, a first subtractor 34, a second subtractor 35, a reactive current PI regulator 36, an active current PI regulator 37, a third coordinate transformation module 38, a sector calculation module 39, a synchronous discontinuous pulse width control (DPWM) device 310, a boundary switching frequency calculation module 311 and a modulator 312; wherein the output end of the grid current sampling module 23 is connected to the first input end of the first coordinate transformation module 31, and the first coordinate transformation module The first output end of the grid voltage sampling module 24 is connected to the first input end of the second coordinate transformation module 32, and the first output end and the second output end of the second coordinate transformation module 32 are connected to the first input end and the second input end of the phase lock 33 respectively; the output end of the phase lock 33 is connected to the second input end of the first coordinate transformation module 31, the second input end of the second coordinate transformation module 32 and the first input end of the third coordinate transformation module 38 respectively. The output end of the first subtractor 34 is connected to the input end of the reactive current PI regulator 36, the output end of the second subtractor 35 is connected to the input end of the active current PI regulator 37, the output end of the reactive current PI regulator 36 and the output end of the active current PI regulator 37 are respectively connected to the second input end and the third input end of the third coordinate transformation module 38; the first output end and the second output end of the third coordinate transformation module 38 are respectively connected to the first input end and the second input end of the sector calculation module 39; the output end of the sector calculation module 39 is respectively connected to the synchronous discontinuous pulse width (DPW) The input terminal of the synchronous discontinuous pulse width controller 310 is connected to the first input terminal of the boundary switching frequency calculation module 311; the first output terminal of the synchronous discontinuous pulse width controller 310 and the output terminal of the boundary switching frequency calculation module 311 are respectively connected to the first input terminal and the second input terminal of the modulator 312, and the second output terminal of the synchronous discontinuous pulse width controller 310 is connected to the second input terminal of the boundary switching frequency calculation module 311; the third input terminal of the modulator 312 is connected to the output terminal of the bus voltage sampling module 21, and the output terminal of the modulator 312 is connected to the input terminal of the MOSFET driving module 22.

[0040] As an example, the bus voltage sampling module 21 samples the first DC filter capacitor C dc1 The voltage of the second DC filter capacitor C dc2 The voltage and output DC voltage sampling value u dc , the grid current sampling module 23 samples the grid-side filter inductance of phase A L 2a, B phase grid side filter inductor L 2b And the C phase grid side filter inductor L 2c The current and output three-phase grid current sampling value i ga 、 i gb and i gc The grid voltage sampling module 24 samples the voltage of the AC grid and outputs the three-phase AC voltage sampling value. u ga 、 u gb and u gc The MOSFET driving module 22 receives the PWM signal output by the digital signal control unit 3 and outputs a driving signal u gs1 ~ u gs12 , respectively output to the first power switch tube of the A phase bridge arm S a1 , the second power switch tube of phase A bridge arm S a2 , the third power switch tube of phase A bridge arm S a3 , the fourth power switch tube of phase A bridge arm S a4 , the first power switch tube of the B phase bridge arm S b1 , the second power switch tube of the B phase bridge arm S b2 , the third power switch tube of the B phase bridge arm S b3 , the fourth power switch tube of the B phase bridge arm S b4 , C phase bridge arm first power switch tube S c1 , the second power switch tube of the C phase bridge arm S c2 , the third power switch tube of the C phase bridge arm S c3 And the fourth power switch tube of the C phase bridge arm S c4 .

[0041] Furthermore, the output terminal of the first coordinate transformation module 31 outputs the d-axis component of the three-phase grid-connected current in the dq coordinate system. i d and q-axis component i q The output terminal of the grid voltage sampling module 24 outputs the three-phase AC voltage sampling value uga 、 u gb and u gc The first output terminal and the second output terminal of the second coordinate transformation module 32 respectively output the d-axis component of the three-phase grid voltage. u gd and q-axis component u gq To the first input terminal and the second input terminal of the phase lock 33; the q-axis current reference value 0 and the q-axis component of the grid current i q After being subtracted by the first subtractor 34, the d-axis current reference value is input into the reactive current PI regulator 36. i d_ref The d-axis component of the grid current i d After the difference is made by the second subtractor 35, the active current PI regulator 37 is input; the third coordinate transformation module 38 receives the q-axis control component output by the reactive PI regulator 36 u q and the d-axis control component output by the active PI regulator 37 u d , and output the control components and u α and u β ; The control components and u α and u β Input sector calculation module 39; boundary switching frequency calculation module 311 simultaneously receives DC voltage sampling value u dc , three-phase grid current sampling value i ga 、 i gb and i gc And three-phase AC voltage sampling value u ga 、 u gb and u gc , and output a uniform switching frequency f s Synchronous discontinuous pulse width controller 310 outputs a three-phase modulated wave m a 、 m b and m c With uniform switching frequency fs And DC voltage sampling value u dc The modulator 312 outputs the first power switch of the A-phase bridge arm. S a1 , the second power switch tube of phase A bridge arm S a2 , the third power switch tube of phase A bridge arm S a3 , the fourth power switch tube of phase A bridge arm S a4 , the first power switch tube of the B phase bridge arm S b1 , the second power switch tube of the B phase bridge arm S b2 , the third power switch tube of the B phase bridge arm S b3 , the fourth power switch tube of the B phase bridge arm S b4 , C phase bridge arm first power switch tube S c1 , the second power switch tube of the C phase bridge arm S c2 , the third power switch tube of the C phase bridge arm S c3 And the fourth power switch tube of the C phase bridge arm S c4 The PWM control signal is input into the MOSFET driving module 22.

[0042] This application provides a method for suppressing leakage current of a soft-switching grid-connected inverter. Figure 2 , Figure 2 The flowchart of the leakage current suppression method of the soft-switching grid-connected inverter is shown. The leakage current suppression method of the soft-switching grid-connected inverter includes steps S1 to S6.

[0043] Step S1: constructing a spatial voltage vector based on the three-phase voltage, establishing a three-level vector space in the complex plane, dividing the three-level vector space into six large sectors, and dividing each large sector into two sub-sectors, including: a first sub-sector and a second sub-sector; Step S2: define boundary conditions and divide each sub-sector into 6 small sectors according to the boundary conditions; Step S3: According to the boundary conditions and reference vector ( u α , u β ) Determine the reference voltage vector V ref The small sector in which it is located; Step S4, according to the reference voltage vector Vref In the small sector, three space voltage vectors that make one phase switch inactive are selected to determine the five-segment basic vector action sequence; Step S5: Obtain the non-clamped two-phase mid-boundary switching frequency according to the basic vector action sequence, and select the minimum value of the non-clamped two-phase mid-boundary switching frequency as the unified switching frequency. f s ; Step S6: The three-phase modulated wave m x (x=a,b,c), uniform switching frequency f s And DC voltage sampling value u dc Modulate and output the pulse width control signal of each power switch tube.

[0044] In the above-mentioned method for suppressing leakage current of the soft-switching grid-connected inverter, in step S1, please refer to Figure 2 In step S1, a space voltage vector is constructed according to the three-phase voltage, a three-level vector space is established in the complex plane, and the three-level vector space is divided into 6 large sectors, each of which is divided into two sub-sectors.

[0045] As an example, the sector calculation module 39 constructs a space voltage vector according to the three-phase DC bus voltage to obtain 27 space voltage vectors. The coordinates of each space voltage vector are It is expressed as follows: in, Indicates the voltage of phase A; Indicates the B phase voltage; represents the C-phase voltage; j represents the imaginary unit.

[0046] Specifically, the three-phase voltage It is expressed as follows: Among them, taking the A phase bridge arm as an example, the switch state is P, which means the first power switch tube of the A phase bridge arm S a1 and the second power switch tube of the A phase bridge arm S a2 The third power switch tube of the A phase bridge arm is turned on. S a3 and the fourth power switch tube of the A phase bridge arm S a4 Off; the switch state is O, indicating that the second power switch tube of the A phase bridge arm S a2 and the third power switch tube of the A phase bridge arm S a3The first power switch tube of the A phase bridge arm is turned on. S a1 and the fourth power switch tube of the A phase bridge arm S a4 Off; the switch state is N, indicating that the third power switch tube of the A phase bridge arm S a3 and the fourth power switch tube of the A phase bridge arm S a4 The first power switch tube of the A phase bridge arm is turned on. S a1 and the second power switch tube of the A phase bridge arm S a2 Shut down.

[0047] Specifically, the switching states of the B-phase bridge arm and the C-phase bridge arm are consistent with those of the A-phase bridge arm, which will not be described in detail here.

[0048] As an example, see Figure 3 , Figure 3 Schematic diagram of the large-sector division of the three-level vector space of the soft-switching grid-connected inverter in this application. The spatial voltage vector divides the three-level vector space of the soft-switching grid-connected inverter into six large sectors, specifically including: Large Sector I through Large Sector VI. Each large sector is divided into two sub-sectors, specifically including: Sub-sector A and Sub-sector B.

[0049] In the above-mentioned method for suppressing leakage current of the soft-switching grid-connected inverter, in step S2, please refer to Figure 2 In step S2, boundary conditions are defined and each sub-sector is divided into 6 small sectors according to the boundary conditions.

[0050] As an example, eight boundary conditions are defined, including: L 1~Boundary conditions L 8, which means the following: .

[0051] As an example, see Figure 4 , Figure 4 Figure (a) is a schematic diagram of the small sector division of sub-sector A of the first large sector of the three-level vector space. Figure 4 Figure (b) is a schematic diagram of the small sector division of sub-sector B of the Ith large sector in the three-level vector space.

[0052] In the above-mentioned method for suppressing leakage current of the soft-switching grid-connected inverter, in step S3, please refer to Figure 2 In the S3 step, according to the boundary conditions and reference vector ( u α , u β ) Determine the reference voltage vector Vref The small sector where it is located.

[0053] As an example, the sector calculation module 39 controls the α-axis component in the αβ coordinate system according to u α and the β-axis control component in the αβ coordinate system u β Calculate the reference voltage vector V ref , which is expressed as follows: .

[0054] As an example, the reference voltage vector is obtained V ref After that, compare the reference vector ( u α , u β ) and boundary conditions L 1~Boundary conditions L 8Determine the reference voltage vector V ref The small sector where it is located.

[0055] In the above-mentioned method for suppressing leakage current of the soft-switching grid-connected inverter, in step S4, please refer to Figure 2 In step S4, according to the reference voltage vector V ref In the small sector, three space voltage vectors that make one phase switch inactive are selected to determine the five-segment basic vector action sequence.

[0056] As an example, according to the reference voltage vector V ref The small sector in which the basic vector is located determines the action sequence of the basic vector. Taking the sub-sector A of the first large sector of the three-level vector space as an example, if the reference voltage vector V ref Located in the first small sector, the basic vector action sequence is PON-POO-OOO-POO-PON. If the reference voltage vector V ref Located in the second small sector, the basic vector action sequence is OON-ONN-PNN-ONN-OON. If the reference voltage vector V ref Located in the 4th small sector, the basic vector action sequence is PON-PNN-PNO-PNN-PON. If the reference voltage vector V ref Located in the 6th small sector, the basic vector action sequence is OON-PON-PNN-PON-OON.

[0057] In particular, if the reference voltage vector Vref In the third small sector, there are two basic vector action sequences to choose from, namely PON-POO-PNO-POO-PON and OON-ONN-PNN-ONN-OON; define the vector selection factor k , vector selection factor k According to the boundary switching frequency of the two basic vector action sequences of the third small sector, when the boundary switching frequency of the basic vector action sequence PON-POO-PNO-POO-PON of the A phase clamp is less than the boundary switching frequency of the basic vector action sequence OON-ONN-PNN-ONN-OON of the C phase clamp, the vector selection factor is set to k= 0, otherwise let the vector selection factor k = 1. When the vector selection factor k =1, the basic vector action sequence PON-POO-PNO-POO-PON of phase A clamp is selected. When the vector selection factor k =0, the basic vector action sequence of C-phase clamping is selected: OON-ONN-PNN-ONN-OON.

[0058] If the reference voltage vector V ref Located in the 5th small sector, there are also two basic vector action sequences to choose from, namely PON-POO-PNO-POO-PON and OON-PON-PNN-PON-OON. The vector selection factor k According to the boundary switching frequency of the two basic vector action sequences of the third small sector, when the boundary switching frequency of the basic vector action sequence PON-POO-PNO-POO-PON of the A phase clamp is less than the basic vector action sequence OON-PON-PNN-PON-OON of the C phase clamp, the vector selection factor is set to k= 0, otherwise let the vector selection factor k = 1. When the vector selection factor k =1, the basic vector action sequence PON-POO-PNO-POO-PON of phase A clamp is selected. When the vector selection factor k =0, the basic vector action sequence of C-phase clamping is selected: OON-PON-PNN-PON-OON.

[0059] Specifically, the basic vector action sequence and vector selection factor of sub-sector B of the first large sector are k The determination principle is the same as that of sub-sector A of the first largest sector, and will not be repeated here.

[0060] Specifically, due to the similarity of each sector, the remaining large sectors can be mapped to the first large sector. In order to simplify the calculation, it is only necessary to calculate the basic vector action sequence and boundary switching frequency of the first large sector. When the reference voltage vectorV ref When it is in the IIth to VIth largest sectors, the reference voltage vector V ref The only thing that changes when switching to the first large sector and then mapping back to the remaining large sectors is the order of the three phases. The basic principle is the same as the mapping principle of the basic vector action sequence. This mapping is no different from other conventional space vector modulation methods. Therefore, the basic vector action sequence and vector selection factor of the second large sector to the sixth large sector are k The determination principle is the same as that of the first largest sector and will not be repeated here.

[0061] In the above-mentioned method for suppressing leakage current of the soft-switching grid-connected inverter, in step S5, please refer to Figure 2 In step S5, the non-clamped two-phase mid-boundary switching frequency is obtained according to the basic vector action sequence, and the minimum value of the non-clamped two-phase mid-boundary switching frequency is selected as the unified switching frequency f s .

[0062] As an example, it can be seen from the above basic vector action sequence that in each switching cycle, one phase power switch tube is clamped and does not act. Then the boundary switching frequency calculation module 311 calculates the frequency of the power switch according to the reference voltage vector. V ref The small sector and the corresponding basic vector action sequence are used to calculate the boundary switching frequency required for the remaining non-clamped phases to achieve zero voltage switching (ZVS). The minimum value of the boundary switching frequency in the non-clamped two phases is selected as the unified switching frequency of the current switching cycle. f s , that is, zero voltage switching of power switching devices can be achieved.

[0063] Furthermore, taking sub-sector A of the first largest sector in the three-level vector space as an example, the boundary switching frequency of the first small sector is calculated as follows: The boundary switching frequency of the second small sector is calculated as follows: The boundary switching frequency of the 4th small sector is calculated as follows: The boundary switching frequency of the 6th small sector is calculated as follows: In particular, if the reference voltage vector V ref Located in the third small sector, calculate the boundary switching frequency of the basic vector action sequence OON-ONN-PNN-ONN-OON of the C phase clamp, record fsn3 is the minimum value of the unclamped two-phase boundary switching frequency of the calculated basic vector action sequence OON-ONN-PNN-ONN-OON, that is, , f sa and f sb The calculation method is the same as that of the second small sector; at the same time, calculate the boundary switching frequency of the basic vector action sequence PON-POO-PNO-POO-PON of the A phase clamp, record f sp3 is the minimum value of the unclamped two-phase boundary switching frequency of the calculated basic vector action sequence PON-POO-PNO-POO-PON, that is, , f sb and f sc The calculation formula is as follows: when f sp3 < f sn3 When , let the vector selection factor k =0, otherwise let the vector selection factor k =1.

[0064] If the reference voltage vector V ref Located in the 5th small sector, calculate the boundary switching frequency of the basic vector action sequence OON-PON-PNN-PON-OON of the C phase clamp, and record f sn5 is the minimum value of the non-clamped two-phase boundary switching frequency of the calculated basic vector action sequence OON-PON-PNN-PON-OON, that is, , f sa and f sb The calculation method is the same as that of the 6th small sector; at the same time, calculate the boundary switching frequency of the basic vector action sequence PON-POO-PNO-POO-PON of the A phase clamp, and record f sp5 is the minimum value of the unclamped two-phase boundary switching frequency of the calculated basic vector action sequence PON-POO-PNO-POO-PON, that is, , f sb and f sc The calculation method is the same as when the PON-POO-PNO-POO-PON vector is selected for the third small sector; when fsp5 < f sn5 When , let the vector selection factor k =0, otherwise let the vector selection factor k =1.

[0065] In the above boundary switching frequency calculation formula, f sa Indicates the boundary switching frequency of the A-phase bridge arm, f sb Indicates the boundary switching frequency of the B-phase bridge arm, f sc Indicates the boundary switching frequency of the C-phase bridge arm, m x ( x =a, b, c) represents the three-phase modulation wave; I bias Represents the reverse reset current, which is a constant value.

[0066] Specifically, the calculation principle for determining the boundary switching frequency calculation formula of the sub-sector B of the first large sector is consistent with that of the sub-sector A of the first large sector, and will not be repeated here.

[0067] Specifically, the calculation principle for determining the boundary switching frequency calculation formula of the IIth to VIth large sectors is the same as that of the Ith large sector and will not be repeated here.

[0068] Furthermore, combined with the reference voltage vector V ref and vector selection factor k Generate three-phase modulation wave m x (x=a,b,c).

[0069] Specifically, if the reference voltage vector V ref The three-phase modulation wave calculation formula for the first small sector of any sub-sector in any large sector is as follows: ; If the reference voltage vector V ref The three-phase modulation wave calculation formula for the second small sector of any sub-sector in any large sector is as follows: ; If the reference voltage vector V ref The third small sector of any sub-sector of any large sector and the vector selection factor k =0, the calculation formula of the three-phase modulation wave is the same as that of the second small sector; if the reference voltage vector V refLocated in the third sector and the vector selection factor k =1, the three-phase modulation wave calculation formula is as follows: ; If the reference voltage vector V ref The calculation formula of the three-phase modulation wave for the 4th small sector of any sub-sector of any large sector is the same as that for the 3rd small sector and the vector selection factor k =1 same; If the reference voltage vector V ref The fifth small sector of any sub-sector of any large sector and the vector selection factor k =0, the calculation formula of the three-phase modulation wave is the same as that of the second small sector; if the reference voltage vector V ref Located in the 5th sector and the vector selection factor k =1, the calculation formula of the three-phase modulation wave is the same as that of the 4th small sector; If the reference voltage vector V ref For the sixth small sector of any sub-sector of any large sector, the three-phase modulation wave calculation formula is the same as that of the second small sector.

[0070] Furthermore, after obtaining the non-clamped two-phase mid-boundary switching frequency according to the basic vector action sequence, the minimum value of the non-clamped two-phase mid-boundary switching frequency is selected as the unified switching frequency of the current switching cycle. f s .

[0071] In the above-mentioned method for suppressing leakage current of the soft-switching grid-connected inverter, in step S6, please refer to Figure 2 In step S6, the three-phase modulated wave m x (x=a,b,c), uniform switching frequency f s And DC voltage sampling value u dc Perform pulse width modulation and output the pulse width control signal of each power switch tube.

[0072] The following is a specific example to verify the leakage current suppression method and circuit of the soft-switching grid-connected inverter of the present application. The soft-switching grid-connected inverter is connected to a 110V / 50Hz three-phase AC grid, the DC side input voltage is 320V, the rated power is 3.3kW, the inverter side filter inductor is 8uH, the DC side parasitic capacitance is 300nF, and the reverse reset current is 0. I bias is 2A. Figure 5Figure (a) is a three-phase boundary switching frequency curve diagram of the leakage current suppression method and circuit embodiment of the soft-switching grid-connected inverter provided by the present application. Figure 5 Figure (b) is a unified switching frequency curve diagram of the leakage current suppression method and circuit embodiment of the soft switching grid-connected inverter provided by this application. Figure 5 Obtain the three-phase boundary switching frequency curve calculated by the boundary switching frequency calculation module 311 and the unified switching frequency curve finally selected within one power frequency cycle. f s It can be seen that the minimum switching frequency selected at any time is greater than 100kHz and will not drop to 0, so the inverter uses this to unify the switching frequency curve. f s Full range of soft switching is possible during operation. Figure 6 Figure (a) is a steady-state waveform diagram of the grid-connected current using the leakage current suppression method and circuit embodiment of the soft-switching grid-connected inverter provided by this application. Figure 6 Figure (b) is a steady-state waveform diagram of the inductor current using the leakage current suppression method and circuit embodiment of the soft-switching grid-connected inverter provided by the present application. Figure 6 Figure (c) is a common-mode voltage steady-state waveform diagram of the leakage current suppression method and circuit embodiment of the soft-switching grid-connected inverter provided by the present application. Figure 6 Figure (d) is a leakage current steady-state waveform diagram of the leakage current suppression method and circuit embodiment of the soft-switching grid-connected inverter provided by this application. Figure 6 It can be seen that the inductor current always remains in the critical conduction mode in the non-clamping region, creating conditions for soft switching. And the common mode voltage change also always remains U dc / 6, which has a lower common-mode voltage change rate, so it can be seen that the final leakage current is also maintained at a low level, verifying the effectiveness and feasibility of this application.

[0073] The leakage current suppression method and circuit for a soft-switching grid-connected inverter provided in this application achieve a low common-mode voltage change rate through a rationally designed switching sequence, thereby effectively suppressing leakage current and achieving zero-voltage turn-on of the power switch tubes of the soft-switching grid-connected inverter. This method and circuit require no additional hardware cost and are easy to implement. Furthermore, the present application enables wide-range soft switching of the power switch tubes at a high switching frequency, thereby effectively reducing the volume and weight of passive components and further improving the power density of the grid-connected inverter. The control circuit and leakage current suppression method described in this application are suitable for renewable energy power generation applications, and particularly have broad application prospects in the field of photovoltaic power generation.

[0074] Although the present application has been disclosed above with reference to the embodiments, they are not intended to limit the present application. Anyone with ordinary knowledge in the technical field may make slight changes and modifications without departing from the spirit and scope of the present application. Therefore, the scope of protection of the present application shall be determined by the scope of the appended patent application.

Claims

1. A method for suppressing leakage current of a soft-switching grid-connected inverter, characterized in that: include, Constructing a spatial voltage vector according to the three-phase voltage, establishing a three-level vector space in the complex plane, dividing the three-level vector space into six large sectors, and each large sector is divided into two sub-sectors, including: a first sub-sector and a second sub-sector; Define boundary conditions and divide each sub-sector into 6 small sectors according to the boundary conditions; Determine the small sector where the reference voltage vector is located according to the boundary conditions and the reference vector; According to the small sector where the reference voltage vector is located, three space voltage vectors are selected to make one phase switch state inactive, and a five-segment basic vector action sequence is determined; The mid-boundary switching frequencies of the unclamped two-phases are obtained according to the basic vector action sequence, and the minimum mid-boundary switching frequencies of the unclamped two-phases are selected as the unified switching frequency; The three-phase modulation wave, the unified switching frequency and the DC voltage sampling value are modulated to output the pulse width control signal of each power switch tube.

2. The method for suppressing leakage current of a soft-switching grid-connected inverter according to claim 1, wherein: The boundary conditions are defined as follows: in, L 1 represents the first boundary condition, L 2 represents the second boundary condition, L 3 represents the third boundary condition, L 4 represents the fourth boundary condition, L 5 represents the fifth boundary condition, L 6 represents the sixth boundary condition, L 7 represents the seventh boundary condition, L 8 represents the eighth boundary condition; u α represents the control component of the α-axis in the αβ coordinate system; u β Represents the control component of the β axis in the αβ coordinate system.

3. The method for suppressing leakage current of a soft-switching grid-connected inverter according to claim 2, wherein: The reference vector includes: a control component of the α axis in the αβ coordinate system and a control component of the β axis in the αβ coordinate system.

4. The method for suppressing leakage current of a soft-switching grid-connected inverter according to claim 3, wherein: Selecting three spatial voltage vectors that cause one phase switch state to be inactive based on the small sector where the reference voltage vector is located, and determining a five-segment basic vector action sequence, including: if the reference voltage vector is located in the third and fifth small sectors of any large sector, defining a vector selection factor, and selecting a basic vector action sequence based on the vector selection factor; Define the vector selection factor and select the basic vector action sequence according to the vector selection factor, including: When the reference voltage vector is located in the third small sector of the first large sector, and when the boundary switching frequency of the basic vector action sequence of the A-phase clamp is less than the boundary switching frequency of the basic vector action sequence of the C-phase clamp, the vector selection factor is set to 0; otherwise, the vector selection factor is set to 1; when the vector selection factor is 1, the basic vector action sequence of the A-phase clamp is selected, and when the vector selection factor is 0, the basic vector action sequence of the C-phase clamp is selected; When the reference voltage vector is located in the fifth small sector of the first large sector, and when the boundary switching frequency of the basic vector action sequence of the A-phase clamp is less than that of the basic vector action sequence of the C-phase clamp, the vector selection factor is set to 0; otherwise, the vector selection factor is set to 1; when the vector selection factor is 1, the basic vector action sequence of the A-phase clamp is selected, and when the vector selection factor is 0, the basic vector action sequence of the C-phase clamp is selected; When the reference voltage vector is located in the remaining large sectors, the reference voltage vector is mapped and converted to the first large sector for calculation, and then mapped and converted back to the original large sector to obtain the corresponding basic vector action sequence.

5. The method for suppressing leakage current of a soft-switching grid-connected inverter according to claim 4, wherein: When the reference voltage vector is located in the first sub-sector of the first large sector, the boundary switching frequency of the unclamped two-phase in the first small sector is calculated as follows: When the reference voltage vector is located in the first sub-sector of the first large sector, the boundary switching frequency of the unclamped two-phase in the second small sector is calculated as follows: When the reference voltage vector is located in the first sub-sector of the first large sector, the boundary switching frequency of the unclamped two-phase in the fourth small sector is calculated as follows: When the reference voltage vector is located in the first sub-sector of the first large sector, the boundary switching frequency of the unclamped two-phase in the sixth small sector is calculated as follows: in, f sa Indicates the boundary switching frequency of the A-phase bridge arm, f sb Indicates the boundary switching frequency of the B-phase bridge arm, f sc Indicates the boundary switching frequency of the C-phase bridge arm; m a Represents the A-phase modulation wave, m b Represents the B-phase modulation wave, m c Represents C-phase modulation wave; I bias Represents the reverse reset current, which is a constant value; u dc Indicates the DC voltage sampling value; i ga Indicates the sampling value of the A phase grid current. i gb Indicates the sampling value of the B phase grid current. i gc Indicates the sampling value of the C phase grid current; u ga Indicates the A-phase AC voltage sampling value, u gb Indicates the B-phase AC voltage sampling value, u gc Indicates the C-phase AC voltage sampling value; When the reference voltage vector is located in the third small sector of the first sub-sector of the first large sector, the boundary switching frequency of the unclamped two phases of the basic vector action sequence of the A-phase clamp is calculated as follows: ； The calculation of the boundary switching frequency of the basic vector action sequence of the C-phase clamp is the same as that of the second small sector; When the reference voltage vector is located in the fifth small sector of the first sub-sector of the first large sector, the calculation of the boundary switching frequency of the unclamped two-phases in the basic vector action sequence of the A-phase clamp is the same as that of the basic vector action sequence of the A-phase clamp selected in the third small sector; the calculation of the boundary switching frequency of the unclamped two-phases in the basic vector action sequence of the C-phase clamp is the same as that of the sixth small sector. When the reference voltage vector is located in the second sub-sector of the first large sector and the remaining large sectors, the reference voltage vector is mapped and converted to the first sub-sector of the first large sector for calculation, and then mapped back to the original large sector to obtain the corresponding basic vector action sequence.

6. The method for suppressing leakage current of a soft-switching grid-connected inverter according to claim 5, wherein: A three-phase modulation wave is generated by combining the small sector where the reference voltage vector is located and the vector selection factor.

7. The method for suppressing leakage current of a soft-switching grid-connected inverter according to claim 6, wherein: When the reference voltage vector is located in the first small sector of any sub-sector of any large sector, the three-phase modulation wave is expressed as follows: ； When the reference voltage vector is located in the second small sector of any sub-sector of any large sector, the three-phase modulation wave is expressed as follows: ； When the reference voltage vector is located in the third small sector of any sub-sector of any large sector and the vector selection factor is 0, the three-phase modulation wave is the same as the second small sector. When the reference voltage vector is located in the third small sector of any sub-sector of any large sector and the vector selection factor is 1, the three-phase modulation wave is expressed as follows: ； When the reference voltage vector is located in the 4th small sector of any sub-sector of any large sector, the three-phase modulation wave is the same as when the reference voltage vector is located in the 3rd small sector of any sub-sector of any large sector and the vector selection factor is 1; When the reference voltage vector is located in the 5th small sector of any sub-sector of any large sector and the vector selection factor is 0, the three-phase modulation wave is the same as the 2nd small sector; when the reference voltage vector is located in the 5th small sector of any sub-sector of any large sector and the vector selection factor is 1, the three-phase modulation wave is the same as the 4th small sector; When the reference voltage vector is located in the 6th small sector of any sub-sector of any large sector, the three-phase modulation wave is the same as when the reference voltage vector is located in the 2nd small sector of any sub-sector of any large sector.

8. A leakage current suppression circuit for a soft-switching grid-connected inverter, characterized in that: A method for suppressing leakage current of a soft-switching grid-connected inverter according to any one of claims 1 to 7, wherein the soft-switching grid-connected inverter comprises a DC bus filter capacitor module, a power conversion module, and an AC filter module; the DC bus filter capacitor module, the power conversion module, and the AC filter module are connected in sequence; the DC bus filter capacitor module comprises a first DC bus filter capacitor and a second DC bus filter capacitor. ， The first DC bus filter capacitor and the second DC bus filter capacitor are connected in series and then in parallel with the DC power supply; the AC filter module includes an A-phase inverter side filter inductor, a B-phase inverter side filter inductor, a C-phase inverter side filter inductor, an A-phase AC filter capacitor, a B-phase AC filter capacitor, a C-phase AC filter capacitor, an A-phase grid-side filter inductor, a B-phase grid-side filter inductor, and a C-phase grid-side filter inductor; the soft-switching grid-connected inverter is connected to a three-phase AC grid, and the three-phase AC grid includes: an A-phase AC grid, a B-phase AC grid, and a C-phase AC grid; The leakage current suppression circuit of the soft-switching grid-connected inverter comprises a sampling and driving unit and a digital signal control unit, and the soft-switching grid-connected inverter, the sampling and driving unit and the digital signal control unit are connected in sequence.

9. The leakage current suppression circuit of the soft-switching grid-connected inverter according to claim 8, characterized in that: The sampling and driving unit includes a bus voltage sampling module, a MOSFET driving module, a grid current sampling module and a power grid voltage sampling module; wherein, the input end of the bus voltage sampling module is connected to the first DC filter capacitor and the second DC filter capacitor, the output end of the MOSFET driving module is connected to the power conversion module, the first input end, the second input end and the third input end of the grid current sampling module are respectively connected to the first end of the A-phase grid-side filter inductor, the first end of the B-phase grid-side filter inductor and the first end of the C-phase grid-side filter inductor, and the first input end, the second input end and the third input end of the power grid voltage sampling module are respectively connected to the first end of the A-phase AC grid, the first end of the B-phase AC grid and the first end of the C-phase AC grid.

10. The leakage current suppression circuit of the soft-switching grid-connected inverter according to claim 9, characterized in that: The digital signal control unit includes a first coordinate transformation module, a second coordinate transformation module, a phase lock, a first subtractor, a second subtractor, a reactive current PI regulator, an active current PI regulator, a third coordinate transformation module, a sector calculation module, a synchronous discontinuous pulse width controller, a boundary switch frequency calculation module and a modulator; wherein the output end of the grid current sampling module is connected to the first input end of the first coordinate transformation module, the first output end of the first coordinate transformation module is connected to the first input end of the first subtractor, and the second output end of the first coordinate transformation module is connected to the first input end of the second subtractor; the output end of the grid voltage sampling module is connected to the first input end of the second coordinate transformation module, the first output end and the second output end of the second coordinate transformation module are respectively connected to the first input end and the second input end of the phase lock; the output end of the phase lock is respectively connected to the second input end of the first coordinate transformation module, the second input end of the second coordinate transformation module and the first input end of the third coordinate transformation module The output end of the first subtractor is connected to the input end of the reactive current PI regulator, the output end of the second subtractor is connected to the input end of the active current PI regulator, the output end of the reactive current PI regulator and the output end of the active current PI regulator are respectively connected to the second input end and the third input end of the third coordinate transformation module; the first output end and the second output end of the third coordinate transformation module are respectively connected to the first input end and the second input end of the sector calculation module; the output end of the sector calculation module is respectively connected to the input end of the synchronous discontinuous pulse width controller and the first input end of the boundary switching frequency calculation module; the first output ends of the synchronous discontinuous pulse width controller and the boundary switching frequency calculation module are respectively connected to the first input end and the second input end of the modulator, and the second output end of the synchronous discontinuous pulse width controller is connected to the second input end of the boundary switching frequency calculation module; the third input end of the modulator is connected to the output end of the bus voltage sampling module, and the output end of the modulator is connected to the input end of the MOSFET driver module.

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