An inverter structure and control method compatible with single-phase two-wire and single-phase three-wire systems

Abstract

The present invention discloses an inverter structure and control method compatible with single-phase two-wire and single-phase three-wire systems, characterized in that the inverter structure includes a DC bus capacitor C1 and a DC bus capacitor C2, switch tubes Q1-Q8, an auxiliary switch S1, an output filter inductor L1 and an output filter inductor L2, an output filter capacitor C3 and an output filter capacitor C4; the inverter conversion structure also includes three power output lines, which are respectively defined as a U-phase power line, an N-phase power line, and a V-phase power line. The inverter of the present invention does not need to be connected to a transformer with an intermediate tap, and can be compatible with single-phase two-wire and single-phase three-wire power supply systems, thereby reducing the size and cost of the inverter and improving efficiency.

Description

Technical Field

[0001] The invention relates to an inverter structure and a control method compatible with single-phase two-wire and single-phase three-wire systems, belonging to the technical field of power electronic conversion. Background Art

[0002] An inverter is an inverter device that converts direct current into alternating current. With the continuous development of the photovoltaic industry, in terms of household use, inverters have gradually developed from only having grid-connected functions to having both grid-connected and off-grid functions. The grid-connected function of the inverter means that the inverter converts DC energy into AC energy, and the AC energy can be used to meet the needs of local loads first, and the excess energy is sent to the grid. The DC energy can come from photovoltaic panels or batteries. The off-grid function of the inverter means that when the grid fails, the inverter performs off-grid output to supply local loads that are not connected to the grid. The DC energy can come from photovoltaic panels or batteries.

[0003] As for the household power supply system, the power grid architecture of different countries and regions is different. Currently, there are mainly single-phase two-wire system and single-phase three-wire system. The single-phase two-wire system has one live wire and one neutral wire. The voltage level of the live wire to the neutral wire is 220V, 230V, etc., and representative regions include Europe, China and other regions. The single-phase three-wire system has two live wires (referred to as live wire 1 and live wire 2 in this article) and one neutral wire. The voltage of the live wire to the neutral wire is 101V or 120V, and the voltage level between the two live wires is 202V or 240V. As for the application of the single-phase three-wire household power supply system, generally low-power household appliances can be connected between the live wire and the neutral wire, with the advantages of low voltage level and high safety. High-power household appliances can be connected between the two live wires, with the advantages of increased voltage level, reduced input current of appliances, and strong load capacity. Representative regions of single-phase three-wire household power supply systems are Japan and North America, where the voltage level in Japan is 101V / 202V and the voltage level in North America is 120V / 240V.

[0004] From the current technical point of view, if the inverter wants to be compatible with these two household power supply systems, the mainstream solution is to configure a transformer with a middle tap at the inverter output end, that is, the inverter only outputs one voltage. When it needs to be connected to a single-phase three-wire power supply network, a transformer with a middle tap is used to separate the two-phase voltage; or two sets of inverter circuits are used, one for single-phase two-wire power supply and the other for single-phase three-wire power supply. Both solutions will increase the size and weight of the inverter, which is not conducive to reducing system costs. Summary of the invention

[0005] The technical problem to be solved by the present invention is: how to reduce the volume and weight of the inverter and lower the system cost.

[0006] In order to solve the above technical problems, the technical solution of the present invention is to provide an inverter structure compatible with single-phase two-wire and single-phase three-wire systems, characterized in that the inverter structure includes two DC bus capacitors C1 and C2, eight switch tubes Q1 to Q8, an auxiliary switch S1, two output filter inductors L1 and L2 and two output filter capacitors C3 and C4; the inverter conversion structure also includes three power output lines, which are defined as U-phase power line, N-phase power line, and V-phase power line, and the three power output lines are connected in parallel with three nodes J1, J2, and J3 respectively; the U-phase power line is connected in series with an output filter inductor L 1. DC bus capacitor C1 and switch tube Q1; auxiliary switch S1 is connected in series on the N-phase power line; output filter inductor L2, switch tube Q8 and DC bus capacitor C2 are connected in series on the V-phase power line; switch tubes Q2 and Q3 are connected in parallel on the U-phase power line and the N-phase power line at the J2 node, and output filter capacitor C3 is connected in parallel at the node J3; switch tubes Q6 and Q7 are connected in parallel on the N-phase power line and the V-phase power line at the node J2, and output filter capacitor C4 is connected in parallel at the node J3; switch tubes Q5 and Q4 are connected in parallel on the U-phase power line and the V-phase power line between nodes J1 and J2.

[0007] Preferably, one end of the filter inductor L1 is connected to one end of the output filter capacitor C3, and the other end of the filter inductor L1 is connected to the emitter of the switch tube Q2, the emitter of the switch tube Q1, and the collector of the switch tube Q4; one end of the filter inductor L2 is connected to one end of the output filter capacitor C4, and the other end of the filter inductor L2 is connected to the emitter of the switch tube Q7, the emitter of the switch tube Q5, and the collector of the switch tube Q8; the collector of the switch tube Q3 is connected to the collector of the switch tube Q2, and the switch tube Q3 is connected to the collector of the switch tube Q3. The emitter of the switch tube Q7 is connected to the node J2; the collector of the switch tube Q7 is connected to the collector of the switch tube Q6, and the emitter of the switch tube Q6 is connected to the node J2; the collector of the switch tube Q5 and the collector of the switch tube Q1 are connected to the positive terminal of C1, and the emitter of Q8 and the emitter of Q4 are connected to the negative terminal of C2; the negative electrode of the bus capacitor C1 is connected to the positive electrode of the bus capacitor C2, and the connection node is J1; one end of the auxiliary switch S1 is connected to the node J1, and the other end is connected to the node J2.

[0008] Preferably, when the inverter conversion structure output is connected to a single-phase two-wire household power supply system, the auxiliary switch S1 is disconnected, and the U-phase and V-phase power lines form a bridge inverter circuit for power output. When the power grid is abnormal, off-grid output can also be performed; when the inverter conversion structure output is connected to a single-phase three-wire household power supply system, the auxiliary switch S1 is closed, the U-phase power line and the N-phase power line form an inverter unit one, and the V-phase power line and the N-phase power line form an inverter unit two. The control unit controls the inverter unit one and the inverter unit two to output power respectively. When the power grid is abnormal, off-grid output can also be performed. The inverter using this conversion structure does not need to be connected to a transformer with an intermediate tap, and can be compatible with single-phase two-wire and single-phase three-wire household power supply systems, thereby reducing the size and cost of the inverter and improving efficiency.

[0009] Preferably, the auxiliary switch S1 is arranged between nodes J1 and J2. When the inverter conversion structure is connected to a single-phase two-wire system, S1 is disconnected, so that the high voltage at the bus midpoint J1 is electrically isolated from the switch tube Q3 and the switch tube Q6, so that the switch tube Q3 and the switch tube Q6 have higher reliability and safety.

[0010] Preferably, the DC busbars C1 and C2 can be aluminum electrolytic capacitors, thin film capacitors, or a mixture of the two; the switch tubes Q1 to Q8 can be gate-turn-off semiconductor switch tubes; the auxiliary switch S1 can be a relay or a gate-turn-off semiconductor switch tube with an integrated body diode; the filter inductor L1 / L2 is a power reactor; and the filter capacitors C3 and C4 are generally thin film capacitors.

[0011] A control method for an inverter structure compatible with single-phase two-wire and single-phase three-wire systems, characterized in that it comprises the following steps:

[0012] Step 1: Connect the U-phase power line, N-phase power line and V-phase power line to the live wire and neutral wire of the power supply system;

[0013] Step 2: Configure the on / off of the auxiliary switch S1;

[0014] Step 3: Configure the control unit to control the switching timing of the switch tubes Q1 to Q8;

[0015] Step 4: Configure the output voltage, current and phase of the U-phase power line and the V-phase power line.

[0016] Preferably, in the step one, when the converter is connected to a single-phase two-wire power supply system, the U-phase power line and the V-phase power line are configured to be connected to the live wire and the neutral wire of the power grid; when the converter is connected to a single-phase three-wire power supply system, the U-phase power line and the V-phase power line are configured to be connected to the live wire, and the N-phase power line is configured to be connected to the neutral wire of the power grid.

[0017] Preferably, the on and off of the auxiliary switch S1 in step 2 is implemented according to the configuration of step 1. The inverter determines whether the inverter is connected to a single-phase two-wire or single-phase three-wire household power supply system by detecting the U, N, and V phase power line voltages. When the inverter is connected to a single-phase two-wire system, the auxiliary switch S1 is disconnected; when the inverter is connected to a single-phase three-wire system, the auxiliary switch S1 is closed.

[0018] Preferably, the switching timing of the switch tubes Q1 to Q8 in the step three is determined according to the configuration of the step one and the step two. When the converter is connected to the single-phase two-wire system, that is, the auxiliary switch S1 is disconnected, at this time, the switch tubes Q1 and Q8, the switch tubes Q5 and Q4 are used as high-frequency switch modulation, the switch tubes Q2, Q3, Q6 and Q7 are used as freewheeling tubes, and the output filter inductor L1, the output filter inductor L2, the output filter capacitor C3 and the output filter capacitor C4 are used as the output filter to perform the inverter conversion work; when the converter is connected to the single-phase two-wire system, that is, the auxiliary switch S1 is disconnected, and the switch tubes Q1 and Q8, the switch tubes Q5 and Q4 are used as high-frequency switch modulation, and the switch tubes Q2, Q3, Q6 and Q7 are used as freewheeling tubes, and the output filter inductor L1, the output filter inductor L2, the output filter capacitor C3 and the output filter capacitor C4 are used as the output filter to perform the inverter conversion work; When the single-phase three-wire system is input, the auxiliary switch S1 is closed. At this time, the switch tubes Q1 and Q4 are used as high-frequency switch modulations, the switch tubes Q2 and Q3 are used as freewheeling tubes, and the output filter inductor L1 and the output filter capacitor C3 are used as output filters to form a single-phase inverter unit one; the switch tubes Q5 and Q8 are used as high-frequency switch modulations, the switch tubes Q6 and Q7 are used as freewheeling tubes, and the output filter inductor L2 and the output filter capacitor C4 are used as output filters to form a single-phase inverter unit two. The control unit controls the power output of the inverter unit one and the inverter unit two respectively.

[0019] Preferably, when the inverter conversion structure output is connected to a single-phase two-wire power supply system, when the UV power line voltage is in the positive half cycle of the power grid, the control unit controls the switch tube Q1 and the switch tube Q8 to be in a high-frequency switching state, the switch tube Q4 and the switch tube Q5 to be in a normally closed state, the switch tube Q2 and the switch tube Q6 to be in a normally open state, and the switch tube Q3 and the switch tube Q7 to be in a high-frequency switching state, wherein the switch tube Q1, the switch tube Q8 and the switch tube Q3, Q7 switch states are complementary; when the UV voltage is in the negative half cycle of the power grid, the control unit controls the switch tube Q4 and the switch tube Q5 to be in a high-frequency switching state, and the switch tube Q1 and the switch tube Q8 to be in a normally closed state. The switch tubes Q3 and Q7 are in the normally open state, the switch tubes Q2 and Q6 are in the high-frequency switching state, wherein the switch tubes Q4, Q5 and Q2, Q6 are in complementary switching state; when the inverter conversion structure output is connected to a single-phase three-wire system, when the UV power line voltage is in the positive half cycle of the power grid, for the inverter unit 1, the switch tube Q1 is modulated at high frequency, the switch tube Q4 is normally closed, the switch tube Q2 is normally open, and the switch tube Q3 is modulated complementarily with the switch tube Q1; for the inverter unit 2, the switch tube Q8 is modulated at high frequency, the switch tube Q5 is normally closed, the switch tube Q6 is normally open, and the switch tube Q7 is modulated complementarily with the switch tube Q8.

[0020] The inverter of the present invention does not need to be connected to a transformer with an intermediate tap, and is compatible with single-phase two-wire and single-phase three-wire household power supply systems, thereby reducing the size and cost of the inverter and improving efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural schematic diagram of the present invention;

[0022] Figures 2 to 25 is a power flow diagram of an embodiment of the present invention;

[0023] Fig.26 This is a flow chart of the control method of the present invention. DETAILED DESCRIPTION

[0024] In order to make the present invention more clearly understood, preferred embodiments are described in detail below with reference to the accompanying drawings.

[0025] like Figure 1 As shown in the figure, the present invention is an inverter conversion structure that is compatible with single-phase two-wire and single-phase three-wire power supply systems. The inverter conversion structure includes: DC bus capacitors C1 and C2, switch tubes Q1-Q8, auxiliary switch S1, output filter inductors L1 and L2, and output filter capacitors C3 and C4.

[0026] The DC busbars C1 and C2 can be aluminum electrolytic capacitors, film capacitors, or a mixture of the two. The switch tubes Q1 to Q8 can be gate-turned semiconductor switch tubes, such as IGBTs, and the following description takes IGBTs as an example. The auxiliary switch S1 can be a relay or a gate-turned semiconductor switch tube with an integrated body diode. The filter inductor L1 / L2 is a power reactor. The filter capacitors C3 and C4 are generally film capacitors.

[0027] The inverter conversion structure described herein also includes three power output lines, which are defined as U-phase power line, N-phase power line, and V-phase power line. One end of each of the three power lines is connected between bus capacitors C1 and C2, i.e., at the bus midpoint, node J1. Switch tubes Q1 to Q4 and filter inductor L1 are connected to the U-phase power line, auxiliary switch S1 is connected to the N-phase power line, and switch tubes Q5 to Q8 and filter inductor L2 are connected to the V-phase power line.

[0028] The output filter capacitor C3 is connected between the U-phase and N-phase power line ports, and the output filter capacitor C4 is connected between the N-phase and V-phase power line ports. The intersection of C3, C4 and the N-line power line is the node J3. One end of L1 is connected to one end of C3, and the other end of L1 is connected to the emitter of Q2, the emitter of Q1, and the collector of Q4. One end of L2 is connected to one end of C4, and the other end of L2 is connected to the emitter of Q7, the emitter of Q5, and the collector of Q8. The collector of Q3 is connected to the collector of Q2, and the emitter of Q3 is connected to the node J2. The collector of Q7 is connected to the collector of Q6, and the emitter of Q6 is connected to the node J2. The collector of Q5 and the collector of Q1 are connected to the positive terminal of C1 together, and the emitter of Q8 and the emitter of Q4 are connected to the negative terminal of C2 together. The negative terminal of C1 is connected to the positive terminal of C2, and the connection node is J1. One end of the auxiliary switch S1 is connected to the node J1, and the other end is connected to the node J2.

[0029] When the inverter conversion structure output is connected to a single-phase two-wire household power supply system, the auxiliary switch S1 is disconnected, and the U-phase and V-phase power lines form a bridge inverter circuit for power output. When the power grid is abnormal, off-grid output can also be performed. When the inverter conversion structure output is connected to a single-phase three-wire household power supply system, the auxiliary switch S1 is closed, the U-phase power line and the N-phase power line form an inverter unit 1, and the V-phase power line and the N-phase power line form an inverter unit 2. The control unit controls the inverter unit 1 and the inverter unit 2 to output power. When the power grid is abnormal, off-grid output can also be performed. The inverter using this conversion structure does not need to be connected to a transformer with an intermediate tap, and can be compatible with single-phase two-wire and single-phase three-wire household power supply systems, thereby reducing the size and cost of the inverter and improving efficiency.

[0030] The advantages of placing the auxiliary switch S1 between nodes J1 and J2 are: when the inverter conversion structure is connected to a single-phase two-wire system, S1 is disconnected, so that the high voltage at the bus midpoint J1 is electrically isolated from Q3 and Q6, making Q3 and Q6 more reliable and safe.

[0031] Accordingly, the present invention also provides an output control method for the inverter conversion structure, and the specific implementation steps are as follows:

[0032] Step 1: Connect the U-phase power line, N-phase power line and W-phase power line to the live line 1, neutral line and live line 2 of the home power supply system

[0033] Step 2: Configure the on / off of auxiliary switch S1

[0034] Step 3: Configure the control unit to control the switching timing of the switch tubes Q1 to Q8

[0035] Step 4: Configure the output voltage, current and phase of the U-phase power line and the W-phase power line.

[0036] In step 1, when the converter is connected to a single-phase two-wire household power supply system, the U-phase power line and the W-phase power line are connected to the live wire and the neutral wire of the power grid. When the converter is connected to a single-phase three-wire household power supply system, the U-phase power line and the W-phase power line are connected to the live wire 1 and the live wire 2, and the N-phase power line is connected to the neutral wire of the power grid.

[0037] The on-off of S1 in step 2 is implemented according to the configuration of step 1. The inverter detects the voltage of the U, N, and W phase power lines to determine whether the inverter is connected to a single-phase two-wire or single-phase three-wire household power supply system. When the inverter is connected to a single-phase two-wire system, S1 is disconnected. When the inverter is connected to a single-phase three-wire system, S1 is closed.

[0038] The switching timing of the switch tubes Q1 to Q8 in step three is determined according to the configuration of step one and step two. When the converter is connected to a single-phase two-wire system, that is, S1 is disconnected, at this time, Q1 and Q8, Q5 and Q4 are used as high-frequency switch modulation, Q2, Q3, Q6, Q7 are used as freewheeling tubes, and L1, L2, C3, C4 are used as LC output filters. The inverter conversion topology performs the inverter conversion work. When the converter is connected to a single-phase three-wire system, that is, S1 is closed, at this time, Q1 and Q4 are used as high-frequency switch modulation, Q2 and Q3 are used as freewheeling tubes, and L1 and C3 are used as LC output filters. The single-phase inverter unit 1 is composed of Q5 and Q8 as high-frequency switch modulation, Q6 and Q7 as freewheeling tubes, and L2 and C4 as LC output filters. The control unit controls the power output of the inverter unit 1 and the inverter unit 2 respectively.

[0039] When the output is connected to a single-phase two-wire system, S1 is disconnected, so that nodes J1 and J2 are not electrically connected, and the control unit performs unipolar modulation on the U-phase power line and the V-phase power line to form an inverter topology.

[0040] When the voltage between UV and V is in the positive half cycle of the power grid, the control unit controls Q1 and Q8 to be in the high-frequency switching state, Q4 and Q5 to be in the normally closed state, Q2 and Q6 to be in the normally open state, and Q3 and Q7 to be in the high-frequency switching state, where the switching states of Q1, Q8 and Q3, Q7 are complementary, and a dead time Δt is left. Considering the generation of reactive power, the inverter topology has four power flow states at this time, which are called H1, H2, H3 and H4 states.

[0041] When Q1 and Q8 are turned on, Q4 and Q5 are turned off, Q2 and Q6 are turned on, and Q3 and Q7 are turned off, there are two power flow states: H1 and H2. The power flow direction of H1 is shown in the attached figure. Figure 2 , that is, C1→Q1→L1→U→V→L2→Q8→C2→C1. The power flow of H2 is shown in the attached Figure 3, that is, L1→Q1→C1→C2→Q8→L2→V→U→L1. The switch tube status is shown in the following table:

[0042] Switching tube Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 state open open close close close open close open

[0043] When Q1, Q8, Q5, and Q4 are turned off and Q2, Q3, Q6, and Q7 are turned on, there are two power flow states: H3 and H4. The power flow direction of H3 is shown in the attached figure. Figure 4 , that is, L2→Q7→Q6→Q3→Q2→L1→U→V→L2. The power flow of H4 is shown in the attached Figure 5 , that is, U→L1→Q2→Q3→Q6→Q7→L2→V→U.

[0044] The switch status is shown in the following table:

[0045] Switching tube Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 state close open open close close open open close

[0046] When the voltage between UV and V is in the negative half cycle of the power grid, the control unit controls Q4 and Q5 to be in the high-frequency switching state, Q1 and Q8 to be in the normally closed state, Q3 and Q7 to be in the normally open state, and Q2 and Q6 to be in the high-frequency switching state, where the switching states of Q4, Q5 and Q2, Q6 are complementary, and a dead time Δt is left. Considering the generation of reactive power, the inverter topology has four power flow states at this time, which are called H5, H6, H7 and H8 states.

[0047] When Q5 and Q4 are turned on, Q1 and Q8 are turned off, Q3 and Q7 are turned on, and Q2 and Q6 are turned off, there are two power flow states: H5 and H6. The power flow direction of H5 is shown in the attached figure. Figure 6 , i.e. C1→Q5→L2→V→U→L1→Q4→C2→C1, the power flow direction of H6 is shown in the attached Figure 7 , that is, L2→Q5→C1→C2→Q4→L1→U→V→L2. The switch tube status is shown in the table below:

[0048] Switching tube Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 state close close open open open close open close

[0049] When Q1, Q8, Q5, and Q4 are turned off and Q2, Q3, Q6, and Q7 are turned on, there are two power flow states: H7 and H8. Figure 8 , that is, L1→Q2→Q3→Q6→Q7→L2→V→U→L1. The power flow of H8 is shown in the attached Fig. 9 , that is, V→L2→Q7→Q6→Q3→Q2→L1→U→V.

[0050] The switch status is shown in the following table:

[0051] Switching tube Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 state close open open close close open open close

[0052] The modulation method of the switch tube can achieve 100% idle power output and reactive power output control. When the active power is fully output, the power flow direction has four power flow states: H1, H4, H5, and H7. When the active power and reactive power are output at the same time, the power flow direction has the above eight power flow states: H1 to H8.

[0053] When the output is connected to a single-phase three-wire system, S1 is closed, and the control unit separately controls the inverter unit 1 composed of the U-phase power line and the N-phase power line, and the inverter unit 2 composed of the V-phase power line and the N-phase power line, using unipolar modulation.

[0054] When the voltage between UV and V is in the positive half cycle of the power grid, for inverter unit 1, Q1 is modulated at high frequency, Q4 is always closed, Q2 is always open, Q3 and Q1 are modulated complementary, and a dead time Δt is left. For inverter unit 2, Q8 is modulated at high frequency, Q5 is always closed, Q6 is always open, Q7 and Q8 are modulated complementary, and a dead time Δt is left. Considering the generation of reactive power, inverter unit 1 and inverter unit 2 each have 4 different power flow states. The 4 power flow states of inverter unit 1 are called T1 state, T2 state, T3 state, and T4 state. The 4 power flow states of inverter unit 2 are called W1 state, W2 state, W3 state, and W4 state.

[0055] For inverter unit 1, when Q1 is turned on, Q4 is turned off, Q2 is turned on, and Q3 is turned off, there are two power flow states, T1 and T2. The power flow direction of T1 is shown in the attached figure. Fig.10 The solid thick arrow shows the flow direction, that is, C1→Q1→L1→U→N→S2→C1. The power flow direction of T2 is shown in the attached Fig.11 The flow direction is shown by the dashed bold arrow, that is, L1→Q1→C1→S2→N→U→L1. The switch status is shown in the table below:

[0056] Switching tube Q1 Q2 Q3 Q4 state open open close close

[0057] For inverter unit 1, when Q1 and Q4 are turned off and Q2 and Q3 are turned on, there are two power flow states: T3 and T4. Fig.12 The power flow direction of T4 is shown in the solid thick arrow, that is, L1→U→N→Q3→Q2→L1. Fig.13 The flow direction is shown by the dashed thick arrow, that is, U→L1→Q2→Q3→N→U. The switch status is shown in the table below:

[0058] Switching tube Q1 Q2 Q3 Q4 state close open open close

[0059] For inverter unit 2, when Q8 is turned on, Q5 is turned off, Q6 is turned on, and Q7 is turned off, there are two power flow states: W1 and W2. The power flow direction of W1 is shown in the attached figure. Fig.14 The solid thick arrow shows the flow direction, that is, C2→S2→N→V→L2→Q8→C2. The power flow direction of W2 is shown in the attached Fig.15 As shown by the dotted thick line, it is L2→V→N→S2→C2→Q8→L2. The switch tube status is shown in the following table:

[0060] Switching tube Q5 Q6 Q7 Q8 state close open close open

[0061] For the inverter unit 2, when Q5 and Q8 are turned off and Q6 and Q7 are turned on, there are two power flow states: W3 and W4. The power flow direction of W3 is shown in the attached figure. Fig.16 The power flow direction of W4 is shown in the solid thick arrow, that is, from L2→Q7→Q6→N→V→L2. Fig.17 As shown by the dotted thick line, it is N→Q6→Q7→L2→V→N. The switch tube status is shown in the following table:

[0062] Switching tube Q5 Q6 Q7 Q8 state close open open close

[0063] When the voltage between UV and V is in the negative half cycle of the power grid, for inverter unit 1, Q1 is always closed, Q4 is modulated at high frequency, Q3 is always on, Q2 and Q1 are modulated complementary, and a dead time Δt is left. For inverter unit 2, Q5 is modulated at high frequency, Q8 is always closed, Q7 is always on, Q6 and Q8 are modulated complementary, and a dead time Δt is left. Considering the generation of reactive power, inverter unit 1 and inverter unit 2 each have 4 different power flow states. The 4 power flow states of inverter unit 1 are called T5 state, T6 state, T7 state, and T8 state. The 4 power flow states of inverter unit 2 are called W5 state, W6 state, W7 state, and W8 state.

[0064] For inverter unit 1, when Q1 is off, Q4 is on, Q3 is on, and Q2 is off, there are two power flow states: T5 and T6. The power flow direction of T5 is shown in the attached figure. Fig.18 The solid thick arrow shows the flow direction, that is, C2→S2→N→U→L1→Q4→C2. The power flow direction of T6 is shown in the attached Fig.19 The flow direction is shown by the dashed bold arrow, that is, L1→U→N→S2→C2→Q4→L1. The switch status is shown in the table below:

[0065] Switching tube Q1 Q2 Q3 Q4 state close close open open

[0066] For inverter unit 1, when Q1 and Q4 are turned off and Q2 and Q3 are turned on, there are two power flow states: T7 and T8. The power flow direction of T7 is shown in the attached figure. Fig. 20 The power flow direction of T8 is shown in the solid thick arrow, that is, from L1→Q2→Q3→N→U→L1. Fig.21The flow direction is shown by the dashed thick arrow, that is, N→Q3→Q2→L1→U→N. The switch status is shown in the table below:

[0067] Switching tube Q1 Q2 Q3 Q4 state close open open close

[0068] For the inverter unit 2, when Q5 is on, Q8 is off, Q7 is on, and Q6 is off, there are two power flow states: W5 and W6. The power flow direction of W5 is shown in the attached figure. Fig. 22 The solid thick arrow shows the power flow direction, that is, C1→Q5→L2→V→N→S2→C1. See the attached Fig.23 The flow direction is shown by the dashed bold arrow, that is, L2→Q5→C1→S2→N→V→L2. The switch status is shown in the table below:

[0069] Switching tube Q5 Q6 Q7 Q8 state open close open close

[0070] For the inverter unit 2, when Q5 and Q8 are turned off and Q6 and Q7 are turned on, there are two power flow states: W7 and W8. The power flow direction of W7 is shown in the attached figure. Fig.24 The solid thick arrow shows the flow direction, that is, C1→Q5→L2→V→N→S2→C1. The power flow direction of W8 is shown in the attached Fig.25 The flow direction is shown by the dashed bold arrows, which is V→L2→Q5→C1→S2→N→V. The switch status is shown in the table below:

[0071] Switching tube Q5 Q6 Q7 Q8 state close open open close

[0072] The modulation method of the switch tube can achieve 100% idle power output and reactive power output control. When the active power is fully output, for inverter unit 1, there are four power flow directions of T1, T3, T5, and T7; for inverter unit 2, there are four power flow directions of W1, W3, W5, and W7. When active power and reactive power are output at the same time, for inverter unit 1, there are eight power flow directions of T1 to T8; for inverter unit 2, there are eight power flow directions of W1 to W8.

[0073] Accordingly, the present invention also provides a control method based on the inverter conversion structure of the present invention including the above-mentioned working states. The control method flow chart is shown in the attached Fig.26 The control method includes: step 1 of configuring the connection between the U-phase power line, the N-phase power line and the W-phase power line and the live line 1, the neutral line and the live line 2 of the household power supply system; step 2 of configuring the on-off of the auxiliary switch S1; step 3 of configuring the control unit to control the switching timing of the switch tubes Q1 to Q8; and step 4 of configuring the output voltage, current and phase of the U-phase power line and the W-phase power line.

[0074] The present invention has been described in detail above, and the description of the embodiments is only used to help understand the method and core idea of ​​the present invention, and its purpose is to enable people familiar with the technology in this field to understand the content of the present invention and implement it accordingly, and it cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. An inverter structure compatible with single-phase two-wire and single-phase three-wire systems, characterized in that: The invention comprises an inverter conversion structure, which comprises two DC bus capacitors C1 and C2, eight switch tubes Q1 to Q8, an auxiliary switch S1, two output filter inductors L1 and L2 and two output filter capacitors C3 and C4; the inverter conversion structure also comprises three power output lines, which are respectively defined as a U-phase power line, an N-phase power line and a V-phase power line, and the three power output lines are connected in parallel with three nodes J1, J2 and J3 respectively; the U-phase power line is connected in series with an output filter inductor L1, a DC bus capacitor C1 and a switch tube Q1; the N-phase power line is connected in series with an output filter inductor L1, a DC bus capacitor C1 and a switch tube Q1; the N-phase power line is connected in series with an output filter inductor L1, a DC bus capacitor C1 and a switch tube Q1; the N-phase power line is connected in series with an output filter inductor L1, a DC bus capacitor C1 and a switch tube Q2; the N-phase power line is connected in series with an output filter inductor L1, a DC bus capacitor C1 and a switch tube Q3; the N-phase power line is connected in series with an output filter inductor L1, a DC bus capacitor C1 and a switch tube Q2 ... The power line is connected in series with an auxiliary switch S1; the V-phase power line is connected in series with an output filter inductor L2, a switch tube Q8 and a DC bus capacitor C2; the U-phase power line and the N-phase power line are connected in parallel with switch tubes Q2 and Q3 at the J2 node, and an output filter capacitor C3 is connected in parallel at the node J3; the N-phase power line and the V-phase power line are connected in parallel with switch tubes Q6 and Q7 at the node J2, and an output filter capacitor C4 is connected in parallel at the node J3; the U-phase power line and the V-phase power line are connected in parallel with switch tubes Q5 and Q4 between nodes J1 and J2; The output filter capacitor C3 is connected between the U-phase power line and the N-phase power line port, the output filter capacitor C4 is connected between the N-phase power line and the V-phase power line port, one end of the filter inductor L1 is connected to one end of the output filter capacitor C3, and the other end of the filter inductor L1 is connected to the emitter of the switch tube Q2, the emitter of the switch tube Q1, and the collector of the switch tube Q4; one end of the filter inductor L2 is connected to one end of the output filter capacitor C4, and the other end of the filter inductor L2 is connected to the emitter of the switch tube Q7, the emitter of the switch tube Q5, and the collector of the switch tube Q8; the collector of the switch tube Q3 is connected to the collector of the switch tube Q2, and the emitter of the switch tube Q3 is connected to the node J2; the collector of the switch tube Q7 is connected to the switch The collector of the switch tube Q6 and the emitter of the switch tube Q6 are connected to the node J2; the collector of the switch tube Q5 and the collector of the switch tube Q1 are connected together to the positive terminal of the DC bus capacitor C1, and the emitter of Q8 and the emitter of Q4 are connected together to the negative terminal of the DC bus capacitor C2; the negative electrode of the DC bus capacitor C1 is connected to the positive terminal of the DC bus capacitor C2, and the connection node is J1; one end of the auxiliary switch S1 is connected to the node J1, and the other end is connected to the node J2, the output filter capacitor C3 is connected between the U-phase power line and the N-phase power line port, the output filter capacitor C4 is connected between the N-phase power line and the V-phase power line port, and the intersection of the output filter capacitor C3 and the output filter capacitor C4 with the N-line power line is the node J3.

2. An inverter structure compatible with single-phase two-wire and single-phase three-wire systems as claimed in claim 1, characterized in that: The N-phase power line passes through the connection node J2 of the switch tube Q3 and the switch tube Q6. One end of the auxiliary switch S1 is connected to the midpoint of the DC bus capacitor, namely the node J1, and the other end is connected to the node J2.

3. The inverter structure compatible with single-phase two-wire and single-phase three-wire systems as claimed in claim 1, characterized in that: When the inverter conversion structure output is connected to a single-phase two-wire power supply system, the auxiliary switch S1 is disconnected, and the U-phase and V-phase power lines form a bridge inverter circuit for power output; when the inverter conversion structure output is connected to a single-phase three-wire power supply system, the auxiliary switch S1 is closed.

4. The inverter structure compatible with single-phase two-wire and single-phase three-wire systems as claimed in claim 1, characterized in that: When the auxiliary switch S1 is closed, the U-phase power line and the N-phase power line form an inverter unit 1, and the V-phase power line and the N-phase power line form an inverter unit 2. The control unit controls the inverter unit 1 and the inverter unit 2 to output power.

5. A control method for an inverter structure compatible with single-phase two-wire and single-phase three-wire systems based on any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1: Connect the U-phase power line, N-phase power line and V-phase power line to the live wire and neutral wire of the power supply system; Step 2: Configure the on / off of the auxiliary switch S1; Step 3: Configure the control unit to control the switching timing of the switch tubes Q1 to Q8; Step 4: Configure the output voltage, current and phase of the U-phase power line and the V-phase power line.

6. A control method for an inverter structure compatible with single-phase two-wire and single-phase three-wire systems as claimed in claim 5, characterized in that: In the step 1, when the converter is connected to a single-phase two-wire power supply system, the U-phase power line and the V-phase power line are connected to the live line and the neutral line of the power grid; when the converter is connected to a single-phase three-wire power supply system, the U-phase power line and the V-phase power line are connected to the live line, and the N-phase power line is connected to the neutral line of the power grid.

7. A control method for an inverter structure compatible with single-phase two-wire and single-phase three-wire systems as claimed in claim 5, characterized in that: In the step 2, when the inverter is connected to a single-phase two-wire system, the auxiliary switch S1 is disconnected; when the inverter is connected to a single-phase three-wire system, the auxiliary switch S1 is closed.

8. The control method of the inverter structure compatible with single-phase two-wire and single-phase three-wire systems as claimed in claim 5, characterized in that: In the step 3, when the converter is connected to a single-phase two-wire system, the auxiliary switch S1 is disconnected, and the switch tubes Q1, Q8, Q5, and Q4 are used as high-frequency switch modulation, the switch tubes Q2, Q3, Q6, and Q7 are used as freewheeling tubes, and the output filter inductor L1, L2, C3, and C4 are used as output filter components for inverter conversion. When the converter is connected to a single-phase three-wire system, the auxiliary switch S1 is closed. At this time, the switch tube Q1 and the switch tube Q4 are used as high-frequency switch modulation, the switch tube Q2 and the switch tube Q3 are used as freewheeling tubes, and the output filter inductor L1 and the output filter capacitor C3 are used as output filtering to form a single-phase inverter unit one; the switch tube Q5 and the switch tube Q8 are used as high-frequency switch modulation, the switch tube Q6 and the switch tube Q7 are used as freewheeling tubes, and the output filter inductor L2 and the output filter capacitor C4 are used as output filtering to form a single-phase inverter unit two, and the control unit controls the power output of the inverter unit one and the inverter unit two respectively.

9. A control method for an inverter structure compatible with single-phase two-wire and single-phase three-wire systems as claimed in claim 5, characterized in that: When the inverter conversion structure output is connected to a single-phase two-wire power supply system, when the UV voltage is in the positive half cycle of the grid, the control unit controls the switch tubes Q1 and Q8 to be in a high-frequency switching state, the switch tubes Q4 and Q5 to be in a normally closed state, the switch tubes Q2 and Q6 to be in a normally open state, the switch tubes Q3 and Q7 to be in a high-frequency switching state, wherein the switch tubes Q1 and Q8 and the switch tubes Q3 and Q7 are complementary in switching state; when the UV voltage is in the negative half cycle of the grid, the control unit controls the switch tubes Q4 and Q5 to be in a high-frequency switching state, and the switch tubes Q1 and Q8 to be in a normally closed state. , switch tubes Q3 and Q7 are in a normally open state, switch tubes Q2 and Q6 are in a high-frequency switching state, wherein the switch states of switch tubes Q4, Q5 and Q2, Q6 are complementary; when the inverter conversion structure output is connected to a single-phase three-wire system, when the UV voltage is in the positive half cycle of the power grid, for inverter unit one, switch tube Q1 is modulated at high frequency, switch tube Q4 is normally closed, switch tube Q2 is normally open, and switch tube Q3 is modulated complementarily with switch tube Q1; for inverter unit two, switch tube Q8 is modulated at high frequency, switch tube Q5 is normally closed, switch tube Q6 is normally open, and switch tube Q7 is modulated complementarily with switch tube Q8.

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