Method and circuit for leakage current suppression of soft-switching grid-connected inverter

Abstract

The application discloses a leakage current suppression method and circuit of a soft-switching grid-connected inverter, and belongs to the technical field of power electronic converters. The method comprises the following steps: constructing a space voltage vector according to three-phase voltages, establishing a three-level vector space in a complex plane, and dividing sectors; defining a boundary condition, dividing each sub-sector into six small sectors according to the boundary condition; determining a small sector in which a 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 in which the reference voltage vector is located; obtaining a boundary switching frequency in a non-clamping two-phase according to the basic vector action sequence, selecting a minimum value of the boundary switching frequency in the non-clamping two-phase as a unified switching frequency; and modulating three-phase modulation waves, the unified switching frequency and a direct-current voltage sampling value to output a pulse width control signal of each power switch tube. The application realizes a low common-mode voltage change rate and a wide-range soft switching of the power switch tube, and can effectively suppress leakage current.

Description

TECHNICAL FIELD

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

[0002] As a commonly used grid-connected inverter, three-phase three-level inverters have become an important component of photovoltaic power generation systems due to their low switching stress and low output current. Most existing three-phase three-level inverters operate at low frequency with hard switching, which has problems such as large size of passive devices 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 making it possible to further improve the power density and efficiency of inverters. However, simply increasing the switching frequency will face the problem of switching process oscillation and sharp increase in switching loss, so soft switching technology is used to actively soften the switching process of the switching tube, i.e. to achieve zero-voltage switching (ZVS), which will help to realize the deep integration of wide-bandgap devices and grid-connected inverters.

[0003] Conventional methods can achieve soft switching of main switching devices by adding auxiliary circuits, but the auxiliary circuits increase the complexity of the control and driving circuits and generate additional costs and losses. On the other hand, when the grid-connected inverter is connected to a photovoltaic panel or an energy storage system on the DC side, there will be a parasitic capacitance from the DC side to ground, and a loop is formed with the AC side grounding point. The leakage current generated by this loop will cause electromagnetic interference, increase harmonic current, and endanger personal safety, so it needs to be strictly suppressed.

[0004] In recent years, some studies have proposed soft switching techniques for auxiliary network-free inverters. For example, the prior art document "J. Chen, J. Deng, L. Ming, et al. "A Variable Switching Frequency Control for ZVS Three-Phase Three-Level T-Type Inverter Using Hybrid Discontinuous PWM," IEEE Transactions on Power Electronics, 38(11)" proposes a full-range soft switching method for three-phase three-level grid-connected inverters by combining discontinuous pulse width modulation (DPWM) and variable frequency control strategies. 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, resulting in a large leakage current in the entire system. Currently, 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 for three-phase three-level soft switching grid-connected inverters, which can achieve soft switching of the grid-connected inverter while solving the reliability and safety problems caused by leakage current. SUMMARY

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

[0006] To achieve the above-mentioned purposes, the technical scheme of the present application is as follows:

[0007] A leakage current suppression method for a soft switching grid-connected inverter, comprising,

[0008] Constructing a space voltage vector according to a three-phase voltage, establishing a three-level vector space in a complex plane, and dividing the three-level vector space into six large sectors, each large sector being divided into two sub-sectors, including a first sub-sector and a second sub-sector;

[0009] Defining a boundary condition, and dividing each sub-sector into six small sectors according to the boundary condition;

[0010] Determining the small sector in which the reference voltage vector is located according to the boundary condition and the reference vector;

[0011] Selecting three space voltage vectors that do not act on one phase switch state according to the small sector in which the reference voltage vector is located, and determining a five-segment basic vector action sequence;

[0012] The non-clamped two-phase boundary switching frequency is obtained according to the basic vector action sequence, and the minimum value of the non-clamped two-phase boundary switching frequency is selected as the unified switching frequency;

[0013] The three-phase modulation wave, the unified switching frequency and the DC voltage sampling value are modulated to output a pulse width control signal of each power switch tube.

[0014] Optionally, the boundary conditions are defined as follows:

[0015]

[0016] Among them, L 1 represents a first boundary condition, L 2 represents a second boundary condition, L 3 represents a third boundary condition, L 4 represents a fourth boundary condition, L 5 represents a fifth boundary condition, L 6 represents a sixth boundary condition, L 7 represents a seventh boundary condition, L 8 represents an eighth boundary condition. u α represents a control component of an alpha axis in an alpha-beta coordinate system; u β represents a control component of a beta axis in the alpha-beta coordinate system.

[0017] Optionally, the reference vector includes: the control component of the alpha axis in the alpha-beta coordinate system and the control component of the beta axis in the alpha-beta coordinate system.

[0018] Optionally, according to the small sector in which the reference voltage vector is located, three space voltage vectors that do not act on the switching state of one phase are selected, 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.

[0019] The definition of the vector selection factor and the selection of the basic vector action sequence according to the vector selection factor include:

[0020] When the reference voltage vector is located in the third small sector of the Ith large sector, when the boundary switching frequency of the basic vector action sequence of the A-phase clamping is less than the boundary switching frequency of the basic vector action sequence of the C-phase clamping, the vector selection factor is 0, otherwise the vector selection factor is 1; when the vector selection factor is 1, the basic vector action sequence of the A-phase clamping is selected, and when the vector selection factor is 0, the basic vector action sequence of the C-phase clamping is selected.

[0021] When the reference voltage vector is located in the 5th sub-sector of the Ith sector, the vector selection factor is 0 when the boundary switching frequency of the basic vector action sequence of the A-phase clamping is less than that of the C-phase clamping, otherwise the vector selection factor is 1; the basic vector action sequence of the A-phase clamping is selected when the vector selection factor is 1, and the basic vector action sequence of the C-phase clamping is selected when the vector selection factor is 0;

[0022] When the reference voltage vector is located in the rest of the sectors, the reference voltage vector is mapped and converted to the Ith sector for calculation, and then mapped and converted back to the original sector to obtain the corresponding basic vector action sequence.

[0023] Optionally, when the reference voltage vector is located in the first sub-sector of the Ith sector, the boundary switching frequency of the non-clamped two-phase in the 1st sub-sector is calculated as follows:

[0024]

[0025] When the reference voltage vector is located in the first sub-sector of the Ith sector, the boundary switching frequency of the non-clamped two-phase in the 2nd sub-sector is calculated as follows:

[0026]

[0027] When the reference voltage vector is located in the first sub-sector of the Ith sector, the boundary switching frequency of the non-clamped two-phase in the 4th sub-sector is calculated as follows:

[0028]

[0029] When the reference voltage vector is located in the first sub-sector of the Ith sector, the boundary switching frequency of the non-clamped two-phase in the 6th sub-sector is calculated as follows:

[0030]

[0031] Wherein, f sa The boundary switching frequency of the A-phase bridge arm is represented by fA, f sb The boundary switching frequency of the B-phase bridge arm is represented by fB, f sc The boundary switching frequency of the C-phase bridge arm is represented by fC; m a The A-phase modulation wave is represented by mA, m b The B-phase modulation wave is represented by mB, m c The C-phase modulation wave is represented by mC; I bias The reverse reset current is represented by iR, which is a constant value;u dc The DC voltage sampling value is represented by uDC; iga represents a phase A grid current sample value, i gb represents a phase B grid current sample value, i gc represents a phase C grid current sample value; u ga represents a phase A AC voltage sample value, u gb represents a phase B AC voltage sample value, u gc represents a phase C AC voltage sample value;

[0032] When the reference voltage vector is located in the 3rd small sector of the first sub-sector of the Ith large sector, the boundary switching frequency calculation of the non-clamp two-phase in the basic vector action sequence of the A-phase clamp is expressed as follows:

[0033] ;

[0034] The boundary switching frequency calculation of the basic vector action sequence of the C-phase clamp is the same as that of the 2nd small sector;

[0035] When the reference voltage vector is located in the 5th small sector of the first sub-sector of the Ith large sector, the boundary switching frequency calculation of the non-clamp two-phase in the basic vector action sequence of the A-phase clamp is the same as that of the 3rd small sector; the boundary switching frequency calculation of the non-clamp two-phase in the basic vector action sequence of the C-phase clamp is the same as that of the 6th small sector;

[0036] When the reference voltage vector is located in the second sub-sector of the Ith large sector and the remaining large sectors, the reference voltage vector is mapped and converted to the first sub-sector of the Ith large sector for calculation, and then mapped and converted back to the original large sector to obtain the corresponding basic vector action sequence.

[0037] Optionally, a three-phase modulation wave is generated in combination with the small sector in which the reference voltage vector is located and a vector selection factor.

[0038] Optionally, when the reference voltage vector is located in the 1st small sector of any sub-sector of any large sector, the three-phase modulation wave is expressed as follows:

[0039] ;

[0040] When the reference voltage vector is located in the 2nd small sector of any sub-sector of any large sector, the three-phase modulation wave is expressed as follows:

[0041] ;

[0042] When the reference voltage vector is located in the third smallest sector of any subsector of any large sector and the vector selection factor is 0, the three-phase modulation wave is the same as the second smallest sector; when the reference voltage vector is located in the third smallest sector of any subsector of any large sector and the vector selection factor is 1, the three-phase modulation wave is as follows:

[0043] ;

[0044] When the reference voltage vector is located in the fourth smallest sector of any subsector of any large sector, the three-phase modulation wave is the same as the third smallest sector of any subsector of any large sector and the vector selection factor is 1;

[0045] When the reference voltage vector is located in the fifth smallest sector of any subsector of any large sector and the vector selection factor is 0, the three-phase modulation wave is the same as the second smallest sector; when the reference voltage vector is located in the fifth smallest sector of any subsector of any large sector and the vector selection factor is 1, the three-phase modulation wave is the same as the fourth smallest sector;

[0046] When the reference voltage vector is located in the sixth smallest sector of any subsector of any large sector, the three-phase modulation wave is the same as the second smallest sector of any subsector of any large sector.

[0047] A leakage current suppression circuit of 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 connected in parallel with a DC power supply; the AC filter module comprises 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 comprises an A-phase AC grid, a B-phase AC grid and a C-phase AC grid;

[0048] The leakage current suppression circuit of the soft-switching grid-connected inverter is used to perform the leakage current suppression method of the soft-switching grid-connected inverter as described in any one of the above embodiments, and 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.

[0049] Optionally, the sampling and driving unit comprises a bus voltage sampling module, a MOSFET driving module, a grid current sampling module and a grid voltage sampling module; wherein the input end of the bus voltage sampling module is connected with the first DC filter capacitor and the second DC filter capacitor, the output end of the MOSFET driving module is connected with 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 with 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 grid voltage sampling module are respectively connected with 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.

[0050] Optionally, the digital signal control unit comprises a first coordinate transformation module, a second coordinate transformation module, a phase-locked loop, 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 with the first input end of the first subtractor, and the second output end of the first coordinate transformation module is connected with 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, and the first output end and the second output end of the second coordinate transformation module are respectively connected with the first input end and the second input end of the phase-locked loop; the output end of the phase-locked loop is respectively connected with 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 with the input end of the reactive current PI regulator, and the output end of the second subtractor is connected with 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 with 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 with 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 with 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 end of the synchronous discontinuous pulse width controller and the first output end of the boundary switching frequency calculation module are respectively connected with the first input end and the second input end of the modulator, the second output end of the synchronous discontinuous pulse width controller is connected with the second input end of the boundary switching frequency calculation module; the third input end of the modulator is connected with the output end of the bus voltage sampling module, and the output end of the modulator is connected with the input end of the MOSFET driving module.

[0051] The soft-switching grid-connected inverter leakage current suppression method and circuit provided by the application can realize low common-mode voltage change rate by reasonably designing the switching sequence, thereby effectively suppressing the leakage current, realizing zero-voltage turn-on of the power switch tube of the soft-switching grid-connected inverter, without additional hardware cost and being easy to implement; meanwhile, the application can realize wide-range soft switching of the power switch tube and high switching frequency, thereby effectively reducing the size and weight of passive devices and further improving the power density of the grid-connected inverter. The control circuit and leakage current suppression method described in the application are suitable for renewable energy power generation occasions, and have broad application prospects in the field of photovoltaic power generation.

[0052] In order to make the above features and advantages of the application more obvious and easy to understand, the following embodiments are described in detail below, and the accompanying drawings are described as follows. BRIEF DESCRIPTION OF DRAWINGS

[0053] Figure 1 The schematic diagram of the leakage current suppression circuit of the soft-switching grid-connected inverter provided by the application.

[0054] Figure 2 The flowchart of the leakage current suppression method of the soft-switching grid-connected inverter.

[0055] Figure 3 The large sector division schematic diagram of the three-level vector space of the soft-switching grid-connected inverter of the application.

[0056] Figure 4 The (a) diagram in FIG. 1 is a small sector division schematic diagram of the sub-sector A of the first large sector of the three-level vector space.

[0057] Figure 4 The (b) diagram in FIG. 1 is a small sector division schematic diagram of the sub-sector B of the first large sector of the three-level vector space.

[0058] Figure 5 The (a) diagram in FIG. 1 is a three-phase boundary switching frequency curve diagram of the soft-switching grid-connected inverter leakage current suppression method and circuit embodiment provided by the application.

[0059] Figure 5 The (b) diagram in FIG. 1 is a unified switching frequency curve diagram of the soft-switching grid-connected inverter leakage current suppression method and circuit embodiment provided by the application.

[0060] Figure 6 The (a) diagram in FIG. 1 is a grid-connected current steady-state waveform diagram of the soft-switching grid-connected inverter leakage current suppression method and circuit embodiment provided by the application.

[0061] Figure 6 The (b) diagram in FIG. 1 is an inductance current steady-state waveform diagram of the soft-switching grid-connected inverter leakage current suppression method and circuit embodiment provided by the application.

[0062] Figure 6 Figure (c) in the figure is a common-mode voltage steady-state waveform diagram of a leakage current suppression method and circuit embodiment of the soft-switching grid-connected inverter provided in this application.

[0063] Figure 6 Figure (d) in the figure is a steady-state waveform of leakage current in an embodiment of the leakage current suppression method and circuit of the soft-switching grid-connected inverter provided in this application. Detailed Implementation

[0064] To make the objectives and technical solutions of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the described embodiments of this application without creative effort are within the scope of protection of this application.

[0065] In one embodiment of this application, a leakage current suppression method for a soft-switching grid-connected inverter is provided, which is applied to the leakage current suppression circuit of the soft-switching grid-connected inverter. Please refer to [link to relevant documentation]. Figure 1 , Figure 1 A schematic diagram of the leakage current suppression circuit for 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 power grid, which includes: Phase A AC power grid. u ga Phase B AC power grid u gb and C-phase AC power grid u gc .

[0066] 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 First DC bus filter capacitor C dc1 The first terminal is the first terminal of the DC bus filter capacitor module 11, and the second DC bus filter capacitor... C dc2 The second terminal is the second terminal of the DC bus filter capacitor module 11. The first DC bus filter capacitor... Cdc1 a second DC bus filter capacitor C dc2 a series-parallel DC power supply U dc a first DC filter capacitor C dc1 a first end of the first DC filter capacitor U dc a positive electrode of the first DC filter capacitor C dc1 a second end of the first DC filter capacitor C dc2 a first end of the second DC filter capacitor C dc2 a second end of the second DC filter capacitor U dc a negative electrode of the second DC filter capacitor

[0067] As an example, the power conversion module 12 includes an A-phase bridge arm first power switch S a1 an A-phase bridge arm second power switch S a2 an A-phase bridge arm third power switch S a3 an A-phase bridge arm fourth power switch S a4 a B-phase bridge arm first power switch S b1 a B-phase bridge arm second power switch S b2 a B-phase bridge arm third power switch S b3 a B-phase bridge arm fourth power switch S b4 a C-phase bridge arm first power switch S c1 a C-phase bridge arm second power switch S c2 a C-phase bridge arm third power switch S c3 and a C-phase bridge arm fourth power switch S c4 .

[0068] As an example, in the A-phase bridge arm, a drain of the A-phase bridge arm first power switch S a1 is connected to a first end of the first DC bus filter capacitor C dc1 a source of the A-phase bridge arm first power switch S a1 is connected to a drain of the A-phase bridge arm third power switch Sa3 The drain of the A-phase bridge arm and the fourth power switch transistor S a4 The drain connection of the third power switch in phase A bridge arm. S a3 The source of the second power switch in phase A bridge arm S a2 The source connection, the fourth power switch of phase A bridge arm S a4 The source and the second DC bus filter capacitor C dc The second end is connected; the first power switch of phase A bridge arm. S a1 The source stage and the third power switch of phase A bridge arm S a3 The drain of the A-phase bridge arm and the fourth power switch transistor S a4 The drain connection point is the output point A of phase A bridge arm; the first power switch of phase A bridge arm... S a1 The drain of the first DC bus filter capacitor C dc1 The connection point of the first end is point P; the fourth power switch of phase A 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.

[0069] As an example, in phase B bridge arm, the first power switch of phase B bridge arm... S b1 The drain of the first DC bus filter capacitor C dc1 The first terminal connection is the first power switch of phase B bridge arm. S b1 The source stage and the third power switch of the B-phase bridge arm S b3 The drain of the B-phase bridge arm and the fourth power switch transistor S b4 The drain connection of the third power switch in phase B bridge arm. S b3 The source of the second power switch in the B-phase bridge arm S b2 The source connection, the fourth power switch of phase B bridge arm S b4 The source and the second DC bus filter capacitor C dc The second end is connected; the first power switch of phase B bridge arm. S b1the drain of the third power switch tube of the B-phase bridge arm and the fourth power switch tube of the B-phase bridge arm S b3 the drain of the third power switch tube of the B-phase bridge arm and the fourth power switch tube of the B-phase bridge arm S b4 the connection point of the drain of the third power switch tube of the B-phase bridge arm and the fourth power switch tube of the B-phase bridge arm is the output point B of the B-phase bridge arm.

[0070] As an example, in the C-phase bridge arm, the source level of the first power switch tube of the C-phase bridge arm S c1 the first end of the first DC bus filter capacitor C dc1 the first end of the first DC bus filter capacitor S c1 the source level of the third power switch tube of the C-phase bridge arm and the first power switch tube of the C-phase bridge arm S b3 the drain of the third power switch tube of the C-phase bridge arm and the fourth power switch tube of the C-phase bridge arm S c4 the drain of the third power switch tube of the C-phase bridge arm and the fourth power switch tube of the C-phase bridge arm S c3 the source level of the second power switch tube of the C-phase bridge arm and the fourth power switch tube of the C-phase bridge arm S c2 the source level of the second power switch tube of the C-phase bridge arm and the fourth power switch tube of the C-phase bridge arm S c4 the second end of the second DC bus filter capacitor C dc the second end of the second DC bus filter capacitor S a2 the drain of the second power switch tube of the A-phase bridge arm, the drain of the second power switch tube of the B-phase bridge arm, and the drain of the second power switch tube of the C-phase bridge arm S b2 the drain of the second power switch tube of the A-phase bridge arm, the drain of the second power switch tube of the B-phase bridge arm, and the drain of the second power switch tube of the C-phase bridge arm S c2 the drain of the second power switch tube of the A-phase bridge arm, the drain of the second power switch tube of the B-phase bridge arm, and the drain of the second power switch tube of the C-phase bridge arm C dc1 the series connection point of the first DC bus filter capacitor and the second DC bus filter capacitor C dc the series connection point of the first DC bus filter capacitor and the second DC bus filter capacitor S c1 the source level of the third power switch tube of the C-phase bridge arm and the first power switch tube of the C-phase bridge arm S b3 the drain of the third power switch tube of the C-phase bridge arm and the fourth power switch tube of the C-phase bridge arm S c4 the connection point of the drain of the third power switch tube of the C-phase bridge arm and the fourth power switch tube of the C-phase bridge arm is the output point C of the C-phase bridge arm. C dc1 the series connection point of the first DC bus filter capacitor and the second DC bus filter capacitor C dc the series connection point of the first DC bus filter capacitor and the second DC bus filter capacitor is point O.

[0071] As an example, the AC filter module 13 includes an A-phase inverter side filter inductorL 1a B-phase inverter-side filter inductance L 1b C-phase inverter-side filter inductance L 1c A-phase AC filter capacitance C fa B-phase AC filter capacitance C fb C-phase AC filter capacitance C fc A-phase grid-side filter inductance L 2a B-phase grid-side filter inductance L 2b and C-phase grid-side filter inductance L 2c A-phase inverter-side filter inductance L 1a has a first end connected to an output point A of an A-phase bridge arm, and a second end of the A-phase inverter-side filter inductance L 1a is connected to a first end of an A-phase AC filter capacitance C fa and a first end of an A-phase grid-side filter inductance L 2a respectively, and a second end of the A-phase grid-side filter inductance L 2a is connected to a first end of an A-phase AC grid u ga ; a first end of a B-phase inverter-side filter inductance L 1b is connected to an output point B of a B-phase bridge arm, and a second end of the B-phase inverter-side filter inductance L 1b is connected to a first end of a B-phase AC filter capacitance C fb and a first end of a B-phase grid-side filter inductance L 2b respectively, and a second end of the B-phase grid-side filter inductance L 2b is connected to a first end of a B-phase AC grid u gb ; a first end of a C-phase inverter-side filter inductance L 1c is connected to an output point C of a C-phase bridge arm, and a second end of the C-phase inverter-side filter inductance L 1c is connected to a first end of a C-phase AC filter capacitance C fc and a first end of a C-phase grid-side filter inductance L 2ca first end of the A-phase AC filter capacitor L 2c a second end of the C-phase AC filter capacitor u gc a first end of the A-phase AC filter capacitor C fa a second end of the B-phase AC filter capacitor C fb a second end of the C-phase AC filter capacitor C fc a second end of the C-phase AC filter capacitor

[0072] a first end of the A-phase AC filter capacitor u ga a second end of the B-phase AC filter capacitor u gb a second end of the C-phase AC filter capacitor u gc a second end of the C-phase AC filter capacitor

[0073] Further, the leakage current suppression circuit of the soft-switching grid-connected inverter comprises a sampling and driving unit 2 and a digital signal control unit 3.

[0074] As an example, the sampling and driving unit 2 comprises 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 an input end of the bus voltage sampling module 21 is connected with a first DC filter capacitor C dc1 and a second DC filter capacitor C dc2 An output end of the MOSFET driving module 22 is connected with the power conversion module 12, a first input end, a second input end and a third input end of the grid current sampling module 23 are respectively connected with a first end of an A-phase grid-side filter inductor L 2a , a first end of a B-phase grid-side filter inductor L 2b and a first end of a C-phase grid-side filter inductor L 2c A first end of the grid voltage sampling module 24 is connected with a first end of the A-phase AC grid u ga , a first end of the B-phase AC grid u gb and a first end of the C-phase AC grid u gc A first end of the grid voltage sampling module 24 is connected with a first end of the A-phase AC grid

[0075] As an example, the digital signal control unit 3 comprises a first coordinate transformation module 31, a second coordinate transformation module 32, a phase-locked loop 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 (DPWM) controller 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, the first output end of the first coordinate transformation module 31 is connected to the first input end of the first subtractor 34, and the second output end of the first coordinate transformation module 31 is connected to the first input end of the second subtractor 35; the output end of the grid voltage sampling module 24 is connected to the first input end of the second coordinate transformation module 32, the first output end and the second output end of the second coordinate transformation module 32 are respectively connected to the first input end and the second input end of the phase-locked loop 33; the output end of the phase-locked loop 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; 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 input end of the synchronous discontinuous pulse width (DPWM) controller 310 and the first input end of the boundary switching frequency calculation module 311; the first output end of the synchronous discontinuous pulse width controller 310 and the output end of the boundary switching frequency calculation module 311 are respectively connected to the first input end and the second input end of the modulator 312, the second output end of the synchronous discontinuous pulse width controller 310 is connected to the second input end of the boundary switching frequency calculation module 311; the third input end of the modulator 312 is connected to the output end of the bus voltage sampling module 21, and the output end of the modulator 312 is connected to the input end of the MOSFET drive module 22.

[0076] As an example, the bus voltage sampling module 21 samples the voltage of the first direct-current filtering capacitor C dc1 and the voltage of the second direct-current filtering capacitor C dc2 and outputs a direct-current voltage sampling value u dc , and the grid current sampling module 23 samples the A-phase grid-side filtering inductance L 2athe B-phase grid-side filter inductance L 2b the C-phase grid-side filter inductance L 2c the current of the B-phase grid-side filter inductance and output three-phase grid current sampling values i ga 、 i gb and i gc the grid voltage sampling module 24 samples the voltage of the alternating current grid and outputs three-phase alternating current voltage sampling values u ga 、 u gb and u gc . The MOSFET drive module 22 receives the PWM signal output by the digital signal control unit 3 and outputs drive signals u gs1 ~ u gs12 , respectively output to the A-phase bridge arm first power switch tube S a1 , the A-phase bridge arm second power switch tube S a2 , the A-phase bridge arm third power switch tube S a3 , the A-phase bridge arm fourth power switch tube S a4 , the B-phase bridge arm first power switch tube S b1 , the B-phase bridge arm second power switch tube S b2 , the B-phase bridge arm third power switch tube S b3 , the B-phase bridge arm fourth power switch tube S b4 , the C-phase bridge arm first power switch tube S c1 , the C-phase bridge arm second power switch tube S c2 , the C-phase bridge arm third power switch tube S c3 and the C-phase bridge arm fourth power switch tube S c4 .

[0077] Further, the output end of the first coordinate transformation module 31 outputs the three-phase grid current d-axis component in the dq coordinate system i d and the q-axis component i q , and the output end of the grid voltage sampling module 24 outputs three-phase alternating current voltage sampling values uga 、 u gb and u gc to the 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 output the d-axis component and the q-axis component of the three-phase grid voltage respectively u gd and u gq to the first input end and the second input end of the phase-locked loop 33; the q-axis current reference value 0 and the q-axis component of the grid current i q are input into the reactive current PI regulator 36 through the first subtractor 34; the d-axis current reference value i d_ref and the d-axis component of the grid current i d are input into the active current PI regulator 37 through the second subtractor 35; 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 outputs the control components in the αβ coordinate system and u α and u β ; the control components in the αβ coordinate system and u α and u β are input into the sector calculation module 39; the boundary switching frequency calculation module 311 simultaneously receives the DC voltage sampling value u dc , the three-phase grid current sampling value i ga 、 i gb and i gc , and the three-phase AC voltage sampling value u ga 、 u gb and u gc , and outputs the unified switching frequency f s ; the three-phase modulation wave output by the synchronous discontinuous pulse width controller 310 m a 、 m b and m c is combined with the unified switching frequency fs and DC voltage sampling value u dc The inputs are fed into modulator 312, and modulator 312 outputs the first power switch of phase A bridge arm. S a1 Phase A bridge arm second power switch S a2 Phase A bridge arm third power switch S a3 Phase A bridge arm fourth power switch S a4 Phase B bridge arm first power switch tube S b1 Phase B bridge arm second power switch S b2 Phase B bridge arm third power switch S b3 Phase B bridge arm fourth power switch S b4 C-phase bridge arm first power switch S c1 C-phase bridge arm second power switch S c2 C-phase bridge arm third power switch S c3 and the fourth power switch of the C-phase bridge arm S c4 The PWM control signal is input to the MOSFET driver module 22.

[0078] This application provides a method for suppressing leakage current in a soft-switching grid-connected inverter. Please refer to [link to relevant documentation]. Figure 2 , Figure 2 The flowchart shows a method for suppressing leakage current in a soft-switching grid-connected inverter, which includes steps S1 to S6.

[0079] Step S1: Construct a space voltage vector based on the three-phase voltage, establish a three-level vector space in the complex plane, divide the three-level vector space into 6 large sectors, and divide each large sector into two sub-sectors, including: the first sub-sector and the second sub-sector;

[0080] Step S2: Define boundary conditions and divide each sub-sector into 6 smaller sectors based on the boundary conditions;

[0081] Step S3: Based on the boundary conditions and reference vector ( u α , u β Determine the reference voltage vector V ref The small sector it is located in;

[0082] Step S4, according to the reference voltage vector V ref The small sector selection determines the five-segment basic vector action sequence of the three space voltage vectors in which one phase switch state does not act;

[0083] Step S5, according to the basic vector action sequence to obtain the boundary switching frequency in the non-clamped two-phase, and select the minimum value of the boundary switching frequency in the non-clamped two-phase as the unified switching frequency f s

[0084] Step S6, modulate the three-phase modulation wave m x (x=a, b, c), the unified switching frequency f s and the DC voltage sampling value u dc to output the pulse width control signal of each power switch tube.

[0085] In the above leakage current suppression method of the soft-switching grid-connected inverter, in step S1, please refer to the S1 step in Figure 2 According to the three-phase voltage, construct the space voltage vector, establish a three-level vector space in the complex plane, and divide the three-level vector space into six large sectors, each large sector is divided into two sub-sectors.

[0086] As an example, the sector calculation module 39 constructs a space voltage vector according to the three-phase DC bus voltage, obtains 27 space voltage vectors, and the coordinates of each space voltage vector are as follows:

[0087]

[0088] Among them, represents the A-phase voltage; represents the B-phase voltage; represents the C-phase voltage; and j represents the imaginary unit.

[0089] Specifically, the three-phase voltage is as follows:

[0090]

[0091] Among them, taking the A-phase bridge arm as an example, the switch state P indicates that the first power switch tube S a1 and the second power switch tube S a2 of the A-phase bridge arm are turned on, and the third power switch tube S a3 and the fourth power switch tubeof the A-phase bridge arm are turned off.S a4 off; switch state is N indicates the A-phase bridge arm third power switch tube S a2 and the A-phase bridge arm fourth power switch tube S a3 on, the A-phase bridge arm first power switch tube S a1 and the A-phase bridge arm second power switch tube S a4 off; switch state is N indicates the A-phase bridge arm third power switch tube S a3 and the A-phase bridge arm fourth power switch tube S a4 on, the A-phase bridge arm first power switch tube S a1 and the A-phase bridge arm second power switch tube S a2 off.

[0092] 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 here.

[0093] As an example, please refer to Figure 3 , Figure 3 is a large sector division diagram of the three-level vector space of the soft-switching grid-connected inverter of the application. The space voltage vector divides the three-level vector space of the soft-switching grid-connected inverter into six large sectors, which specifically include: large sector I~large sector VI, each large sector is divided into two sub-sectors, which specifically include: sub-sector A and sub-sector B.

[0094] In the above-mentioned leakage current suppression method of the soft-switching grid-connected inverter, please refer to Figure 2 S2 step in the S2 step, define the boundary condition, and divide each sub-sector into six small sectors according to the boundary condition.

[0095] As an example, define eight boundary conditions, which specifically include: boundary condition L 1~boundary condition L 8, which are as follows:

[0096] .

[0097] As an example, please refer to Figure 4 , Figure 4 the small sector division diagram of the sub-sector A of the first large sector of the three-level vector space in (a) of Figure 4 the small sector division diagram of the sub-sector B of the first large sector of the three-level vector space in (b) of

[0098] In the above-mentioned leakage current suppression method for soft-switching grid-connected inverters, in step S3, please refer to... Figure 2 In step S3, based on the boundary conditions and reference vector ( u α , u β Determine the reference voltage vector V ref The small sector it is located in.

[0099] As an example, the sector calculation module 39 controls the α-axis component according to the αβ coordinate system. u α and the β-axis control components in the αβ coordinate system u β Calculate the reference voltage vector V ref , means as follows:

[0100] .

[0101] As an example, the reference voltage vector is obtained. V ref Then, compare the reference vector ( u α , u β ) and boundary conditions L 1~Boundary Conditions L 8. Determine the reference voltage vector V ref The small sector it is located in.

[0102] In the above-mentioned leakage current suppression method for soft-switching grid-connected inverters, in step S4, please refer to... Figure 2 In step S4, based on the reference voltage vector V ref The three spatial voltage vectors in the small sector are selected such that one phase switch is inactive, and the five-segment basic vector action sequence is determined.

[0103] As an example, based on the reference voltage vector V ref The sub-sector of the location determines the basic vector action sequence. Taking sub-sector A of the I-th largest sector in 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 minor sector, the basic vector action sequence is OON-ONN-PNN-ONN-OON. If the reference voltage vector... V reflocated in the 4th sub-sector, the basic vector action sequence is PON-PNN-PNO-PNN-PON, if the reference voltage vector V ref located in the 6th sub-sector, the basic vector action sequence is OON-PON-PNN-PON-OON.

[0104] In particular, if the reference voltage vector V ref located in the 3rd sub-sector, there are two basic vector action sequences to choose from, which are PON-POO-PNO-POO-PON and OON-ONN-PNN-ONN-OON respectively; define a vector selection factor k , the vector selection factor k According to the boundary switching frequency of the two basic vector action sequences of the 3rd sub-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 that of the basic vector action sequence OON-ONN-PNN-ONN-OON of the C-phase clamp, the vector selection factor k= 0, otherwise the vector selection factor k = 1. When the vector selection factor k = 1, the basic vector action sequence PON-POO-PNO-POO-PON of the A-phase clamp is selected, and when the vector selection factor k = 0, the basic vector action sequence OON-ONN-PNN-ONN-OON of the C-phase clamp is selected.

[0105] if the reference voltage vector V ref located in the 5th sub-sector, there are also two basic vector action sequences to choose from, which are PON-POO-PNO-POO-PON and OON-PON-PNN-PON-OON respectively, and the vector selection factor k According to the boundary switching frequency of the two basic vector action sequences of the 3rd sub-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 that of the basic vector action sequence OON-PON-PNN-PON-OON of the C-phase clamp, the vector selection factor k= 0, otherwise the vector selection factor k = 1. When the vector selection factor k = 1, the basic vector action sequence PON-POO-PNO-POO-PON of the A-phase clamp is selected, and when the vector selection factor k = 0, the basic vector action sequence OON-PON-PNN-PON-OON of the C-phase clamp is selected.

[0106] Specifically, the basic vector action sequence of the sub-sector B of the first sector and the determination principle of the vector selection factor k are the same as those of the sub-sector A of the first sector, which will not be repeated here.

[0107] Specifically, due to the similarity of each sector, the remaining sectors can be mapped to the first sector. In order to simplify the calculation, only the basic vector action sequence and the boundary switching frequency of the first sector need to be calculated. When the reference voltage vector V ref is located in the second sector to the sixth sector, the reference voltage vector V ref is converted to the first sector, and then mapped back to the remaining sectors. The only change is the order of the three phases, and 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 determination principle of the basic vector action sequence and the vector selection factor k of the second sector to the sixth sector is the same as that of the first sector, which will not be repeated here.

[0108] In the above soft-switching grid-connected inverter leakage current suppression method, in step S5, please refer to S5 step in Figure 2 , according to the basic vector action sequence, the boundary switching frequency in the non-clamped two-phase is obtained, and the minimum value of the boundary switching frequency in the non-clamped two-phase is selected as the unified switching frequency f s .

[0109] As an example, according to the above basic vector action sequence, it can be known that in each switching period, one phase power switch tube is clamped and does not act. The boundary switching frequency calculation module 311 calculates the boundary switching frequency required for the remaining non-clamped phase to realize zero voltage switching (ZVS) according to the small sector where the reference voltage vector V ref is located and the corresponding basic vector action sequence, and selects the minimum value of the boundary switching frequency in the non-clamped two-phase as the unified switching frequency f s of the current switching period, that is, the zero voltage switching of the power switch device can be realized.

[0110] Further, taking the sub-sector A of the first sector of the three-level vector space as an example, the boundary switching frequency of the first small sector is calculated as follows:

[0111]

[0112] The boundary switching frequency of the second small sector is calculated as follows:

[0113]

[0114] The boundary switching frequency of the 4th sub-sector is calculated as follows:

[0115]

[0116] The boundary switching frequency of the 6th sub-sector is calculated as follows:

[0117]

[0118] In particular, if the reference voltage vector V ref is located in the 3rd sub-sector, the boundary switching frequency of the basic vector action sequence OON-ONN-PNN-ONN-OON for C-phase clamping is calculated, denoted as f sn3 is the minimum value of the calculated non-clamping two-phase boundary switching frequency of the basic vector action sequence OON-ONN-PNN-ONN-OON, i.e. f sa The calculation method of f sb is the same as that of the 2nd sub-sector; meanwhile, the boundary switching frequency of the basic vector action sequence PON-POO-PNO-POO-PON for A-phase clamping is calculated, denoted as f sp3 is the minimum value of the calculated non-clamping two-phase boundary switching frequency of the basic vector action sequence PON-POO-PNO-POO-PON, i.e. f sb The calculation formula of f sc is as follows:

[0119]

[0120] When f sp3 f sn3 , the vector selection factor k =0, otherwise the vector selection factor k =1.

[0121] If the reference voltage vector V ref is located in the 5th sub-sector, the boundary switching frequency of the basic vector action sequence OON-PON-PNN-PON-OON for C-phase clamping is calculated, denoted as f sn5 is the minimum value of the calculated non-clamping two-phase boundary switching frequency of the basic vector action sequence OON-PON-PNN-PON-OON, i.e. f sa and​​​​f sb The calculation method of the first sub-sector is the same as that of the sixth sub-sector; the boundary switching frequency of the basic vector action sequence PON-POO-PNO-POO-PON of the A-phase clamped is calculated, and is recorded as f sp5 The calculation method of the first sub-sector is the same as that of the sixth sub-sector; the boundary switching frequency of the basic vector action sequence PON-POO-PNO-POO-PON of the A-phase clamped is calculated, and is recorded as , f sb The calculation method of the first sub-sector is the same as that of the sixth sub-sector; the boundary switching frequency of the basic vector action sequence PON-POO-PNO-POO-PON of the A-phase clamped is calculated, and is recorded as f sc The calculation method of the first sub-sector is the same as that of the sixth sub-sector; the boundary switching frequency of the basic vector action sequence PON-POO-PNO-POO-PON of the A-phase clamped is calculated, and is recorded as

[0122] When f sp5 < f sn5 , the vector selection factor is set as k = 0, otherwise, the vector selection factor is set as k = 1.

[0123] In the above boundary switching frequency calculation formula, f sa represents the boundary switching frequency of the A-phase bridge arm, f sb represents the boundary switching frequency of the B-phase bridge arm, f sc represents the boundary switching frequency of the C-phase bridge arm, m x ( x =a, b, c) represents the modulation wave of the three phases; I bias represents the reverse reset current, which is a constant value.

[0124] Specifically, the determination principle of 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, which will not be repeated here.

[0125] Specifically, the determination principle of the boundary switching frequency calculation formula of the first large sector to the sixth large sector is consistent with that of the first large sector, which will not be repeated here.

[0126] Further, the three-phase modulation wave V ref is generated in combination with the reference voltage vector k and the vector selection factor m x (x=a, b, c).

[0127] Specifically, if the reference voltage vector V refThe first small sector of any sub-sector in any large sector, the three-phase modulation wave calculation formula is as follows:

[0128] ;

[0129] If the reference voltage vector V ref The second small sector of any sub-sector in any large sector, the three-phase modulation wave calculation formula is as follows:

[0130] ;

[0131] If the reference voltage vector V ref The third small sector of any sub-sector in any large sector and the vector selection factor k =0, the three-phase modulation wave calculation formula is the same as the second small sector; if the reference voltage vector V ref The third small sector and the vector selection factor k =1, the three-phase modulation wave calculation formula is as follows:

[0132] ;

[0133] If the reference voltage vector V ref The fourth small sector of any sub-sector in any large sector, the three-phase modulation wave calculation formula is the same as the third small sector and the vector selection factor k =1;

[0134] If the reference voltage vector V ref The fifth small sector of any sub-sector in any large sector and the vector selection factor k =0, the three-phase modulation wave calculation formula is the same as the second small sector; if the reference voltage vector V ref The fifth small sector and the vector selection factor k =1, the three-phase modulation wave calculation formula is the same as the fourth small sector;

[0135] If the reference voltage vector V ref The sixth small sector of any sub-sector in any large sector, the three-phase modulation wave calculation formula is the same as the second small sector.

[0136] Further, after obtaining the non-clamped two-phase boundary switching frequency according to the basic vector action sequence, the minimum value of the non-clamped two-phase boundary switching frequency is selected as the unified switching frequency of the current switching period f s .

[0137] In the above-mentioned leakage current suppression method for soft-switching grid-connected inverters, in step S6, please refer to... Figure 2 Step S6 in the process modulates the three-phase modulated wave. m x (x=a,b,c), unified switching frequency f s and DC voltage sampling value u dc Pulse width modulation is performed to output the pulse width control signal for each power switch.

[0138] The following specific example verifies the leakage current suppression method and circuit of the soft-switching grid-connected inverter of this application. The soft-switching grid-connected inverter is connected to a 110V / 50Hz three-phase AC grid, with a DC-side input voltage of 320V, a rated power of 3.3kW, an inverter-side filter inductance of 8uH, a DC-side parasitic capacitance of 300nF, and a reverse reset current. I bias It is 2A. Figure 5 Figure (a) in the figure is a three-phase boundary switching frequency curve of an embodiment of the leakage current suppression method and circuit of the soft-switching grid-connected inverter provided in this application. Figure 5 Figure (b) in the figure is a unified switching frequency curve of the leakage current suppression method and circuit embodiment of the soft-switching grid-connected inverter provided in this application. Figure 5 The three-phase boundary switching frequency curves calculated by the boundary switching frequency calculation module 311 and the finally selected unified switching frequency curve are obtained within one power frequency cycle. f s It can be seen that the minimum switching frequency selected at any given time is greater than 100kHz and will not drop to 0. Therefore, the inverter uses this as a basis to unify the switching frequency curve. f s It can achieve a full range of soft switching during runtime. Figure 6 Figure (a) shows the steady-state waveform of the grid-connected current in an embodiment of the leakage current suppression method and circuit of the soft-switching grid-connected inverter provided in this application. Figure 6 Figure (b) shows the steady-state waveform of the inductor current in an embodiment of the leakage current suppression method and circuit of the soft-switching grid-connected inverter provided in this application. Figure 6 Figure (c) shows the common-mode voltage steady-state waveform of an embodiment of the leakage current suppression method and circuit of the soft-switching grid-connected inverter provided in this application. Figure 6 Figure (d) in the figure shows the steady-state waveform of the leakage current in an embodiment of the leakage current suppression method and circuit of the soft-switching grid-connected inverter provided in this application. Figure 6 It can be seen that the inductor current remains in the critical conduction mode in the non-clamped region, creating conditions for soft switching. Furthermore, the common-mode voltage variation also remains within a certain range. Udc / 6, has a lower common-mode voltage rate of change, so the final leakage current is also kept at a low level, verifying the effectiveness and feasibility of the application.

[0139] The soft-switching grid-connected inverter leakage current suppression method and circuit provided by the application can effectively suppress the leakage current by reasonably designing the switching sequence, realize zero-voltage turn-on of the power switch tube of the soft-switching grid-connected inverter, and does not require additional hardware costs and is easy to implement. At the same time, the application can realize wide-range soft switching of the power switch tube and a relatively high switching frequency, thereby effectively reducing the size and weight of the passive device and further improving the power density of the grid-connected inverter. The control circuit and leakage current suppression method described in the application are suitable for renewable energy power generation occasions, and particularly have broad application prospects in the field of photovoltaic power generation.

[0140] Although the application has been disclosed as above with examples, it is not intended to limit the application, and anyone with ordinary knowledge in the art can make some changes and modifications without departing from the spirit and scope of the application. Therefore, the protection scope of the application shall be subject to the appended patent claim.

Claims

1. A method for suppressing leakage current in a soft-switching grid-connected inverter, characterized in that, include, Based on the three-phase voltage, a space voltage vector is constructed, and a three-level vector space is established in the complex plane. The three-level vector space is divided into 6 large sectors, and each large sector is divided into two sub-sectors, including: the first sub-sector and the second sub-sector. Define boundary conditions, and divide each sub-sector into 6 smaller sectors based on the boundary conditions; The sector in which the reference voltage vector is located is determined based on the boundary conditions and the reference vector; Based on the small sector where the reference voltage vector is located, select three spatial voltage vectors that prevent one phase switch from operating, and determine the five-segment basic vector action sequence. The boundary switching frequency of the unclamped two-phase circuit is obtained based on the basic vector action sequence. The minimum value of the boundary switching frequency of the unclamped two-phase circuit is selected as the unified switching frequency to achieve soft switching of all power switching transistors. The three-phase modulation wave, the unified switching frequency, and the DC voltage sampling value are modulated to output the pulse width control signal for each power switch. If the reference voltage vector is located in the 3rd and 5th sub-sectors of any large sector, the five-segment basic vector action sequence is determined based on the boundary switching frequency of the basic vector action sequence of phase A clamping and the boundary switching frequency of the basic vector action sequence of phase C clamping.

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

3. The leakage current suppression method for a soft-switching grid-connected inverter as described in claim 2, characterized in that, The reference vector includes the control components of the α-axis and the β-axis in the αβ coordinate system.

4. The leakage current suppression method for a soft-switching grid-connected inverter as described in claim 3, characterized in that, Based on the small sector where the reference voltage vector is located, select three spatial voltage vectors that prevent one phase switch from operating, and determine the five-segment basic vector action sequence, including: if the reference voltage vector is located in the 3rd and 5th small sectors of any large sector, define the vector selection factor, and select the basic vector action sequence based on the vector selection factor. Define a vector selection factor, and select the basic vector action sequence based on the vector selection factor, including: When the reference voltage vector is located in the third minor sector of the first major sector, if the boundary switching frequency of the basic vector action sequence for clamping phase A is less than the boundary switching frequency of the basic vector action sequence for clamping phase C, 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 for clamping phase A is selected; when the vector selection factor is 0, the basic vector action sequence for clamping phase C is selected. When the reference voltage vector is located in the 5th sub-sector of the I-th major sector, if the boundary switching frequency of the basic vector action sequence for phase A clamping is less than that for phase C clamping, 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 for phase A clamping is selected; when the vector selection factor is 0, the basic vector action sequence for phase C clamping is selected. When the reference voltage vector is located in other large sectors, the reference voltage vector is mapped and converted to the I-th 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 leakage current suppression method for a soft-switching grid-connected inverter as described in claim 4, characterized in that, When the reference voltage vector is located in the first sub-sector of the I-th large sector, the mid-boundary switching frequency of the non-clamped two-phase system in the first small sector is calculated as follows: ； When the reference voltage vector is located in the first sub-sector of the I-th large sector, the mid-boundary switching frequency of the non-clamped two-phase system in the second small sector is calculated as follows: ； When the reference voltage vector is located in the first sub-sector of the I-th large sector, the mid-boundary switching frequency of the non-clamped two-phase system in the 4th small sector is calculated as follows: ； When the reference voltage vector is located in the first sub-sector of the I-th large sector, the mid-boundary switching frequency of the non-clamped two-phase system in the 6th small sector is calculated as follows: ； in, f sa This indicates the boundary switching frequency of phase A bridge arm. f sb This indicates the boundary switching frequency of phase B bridge arm. f sc Indicates the boundary switching frequency of the C-phase bridge arm; m a Indicates the A-phase modulated wave. m b Indicates phase B modulated wave, m c Indicates a C-phase modulated wave; I bias This represents the reverse reset current, which is a constant; u dc This represents the sampled DC voltage value; i ga This represents the sampled value of the grid-connected current of phase A. i gb This represents the sampled value of the B-phase grid-connected current. i gc This represents the sampled value of the C-phase grid-connected current; u ga This represents the sampled value of the AC voltage in phase A. u gb This represents the sampled value of the B-phase AC voltage. u gc This represents the sampled value of the C-phase AC voltage; When the reference voltage vector is located in the third sub-sector of the first sub-sector of the I-th major sector, the calculation of the non-clamped two-phase mid-boundary switching frequency of the basic vector action sequence of phase A clamping is expressed 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 5th sub-sector of the first sub-sector of the I major sector, the calculation of the mid-boundary switching frequency of the unclamped two-phase phases in the basic vector action sequence of phase A clamping is the same as that of phase A clamping in the 3rd sub-sector; the calculation of the mid-boundary switching frequency of the unclamped two-phase phases in the basic vector action sequence of phase C clamping is the same as that of the 6th sub-sector. When the reference voltage vector is located in the second sub-sector and other large sectors of the I large sector, the reference voltage vector is mapped and converted to the first sub-sector of the I large sector for calculation, and then mapped and converted back to the original large sector to obtain the corresponding basic vector action sequence.

6. The leakage current suppression method for a soft-switching grid-connected inverter as described in claim 5, characterized in that, A three-phase modulated wave is generated by combining the small sector where the reference voltage vector is located and the vector selection factor.

7. The leakage current suppression method for a soft-switching grid-connected inverter as described in claim 6, characterized in that, When the reference voltage vector is located in the first sector of any sub-sector of any large sector, the three-phase modulated wave is represented as follows: ； When the reference voltage vector is located in the second smallest sector of any sub-sector of any large sector, the three-phase modulation wave is represented as follows: ； When the reference voltage vector is located in the third sub-sector of any sub-sector of any large sector and the vector selection factor is 0, the three-phase modulated wave is the same as that in the second sub-sector; when the reference voltage vector is located in the third sub-sector of any sub-sector of any large sector and the vector selection factor is 1, the three-phase modulated wave is represented as follows: ； When the reference voltage vector is located in the 4th sub-sector of any sub-sector of any large sector, the three-phase modulated wave is the same as the reference voltage vector located in the 3rd sub-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 sub-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 that of the 2nd sub-sector; when the reference voltage vector is located in the 5th sub-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 that of the 4th sub-sector. When the reference voltage vector is located in the 6th sub-sector of any sub-sector of any large sector, the three-phase modulated wave is the same as that of the 2nd sub-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 leakage current suppression method for a soft-switching grid-connected inverter as described in 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 connected in parallel to a 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 power grid, which includes: an A-phase AC power grid, a B-phase AC power grid, and a C-phase AC power grid. The leakage current suppression circuit of the soft-switching grid-connected inverter includes a sampling and driving unit and a digital signal control unit, which are connected in sequence.

9. The leakage current suppression circuit of the soft-switching grid-connected inverter as described in 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 grid voltage sampling module. The input terminal of the bus voltage sampling module is connected to the first DC filter capacitor and the second DC filter capacitor. The output terminal of the MOSFET driving module is connected to the power conversion module. The first, second, and third input terminals of the grid current sampling module are respectively connected to the first terminals of the A-phase grid-side filter inductors, the B-phase grid-side filter inductors, and the C-phase grid-side filter inductors. The first, second, and third input terminals of the grid voltage sampling module are respectively connected to the first terminals of the A-phase AC grid, the B-phase AC grid, and the C-phase AC grid.

10. The leakage current suppression circuit of the soft-switching grid-connected inverter as described in claim 9, characterized in that, The digital signal control unit includes a first coordinate transformation module, a second coordinate transformation module, a phase-locked loop (PLL), 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. The output of the grid current sampling module is connected to the first input of the first coordinate transformation module; the first output of the first coordinate transformation module is connected to the first input of the first subtractor; and the second output of the first coordinate transformation module is connected to the first input of the second subtractor. The output of the grid voltage sampling module is connected to the first input of the second coordinate transformation module; the first and second outputs of the second coordinate transformation module are respectively connected to the first and second inputs of the PLL. The output of the PLL is respectively connected to the second input of the first coordinate transformation module, the second input of the second coordinate transformation module, and the first input of the third coordinate transformation module. The circuit is as follows: the output of the first subtractor is connected to the input of the reactive current PI regulator; the output of the second subtractor is connected to the input of the active current PI regulator; the outputs of the reactive current PI regulator and the active current PI regulator are respectively connected to the second and third inputs of the third coordinate transformation module; the first and second outputs of the third coordinate transformation module are respectively connected to the first and second inputs of the sector calculation module; the output of the sector calculation module is respectively connected to the input of the synchronous discontinuous pulse width controller and the first input of the boundary switching frequency calculation module; the first outputs of the synchronous discontinuous pulse width controller and the boundary switching frequency calculation module are respectively connected to the first and second inputs of the modulator; the second output of the synchronous discontinuous pulse width controller is connected to the second input of the boundary switching frequency calculation module; the third input of the modulator is connected to the output of the bus voltage sampling module; and the output of the modulator is connected to the input of the MOSFET drive module.

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