Inverter device and control method thereof

Abstract

The present invention provides an inverter device and a control method thereof, wherein a soft start circuit is provided between a DC neutral point and an AC neutral port in the inverter device. In the control method of the inverter device, the soft start circuit is first controlled to switch the output preset impedance to the DC neutral point and the AC neutral port to suppress the impact of the common-mode impact current, and the first voltage and the second voltage of the negative DC bus to the ground are respectively obtained before and after the soft start circuit outputs the preset impedance, and the system impedance can be determined in combination with the preset impedance. When it is detected that the change rate of the terminal voltage of the soft start circuit or the voltage value is less than the preset value, the soft start circuit is controlled to directly conduct the DC neutral point and the AC neutral port, and the grid-connected switch circuit is controlled to conduct the grid-connected output AC power supply to the power grid, so that the common-mode impact current suppression and system impedance detection are realized synchronously, and there is no need to additionally set up a compensation circuit and an insulation impedance detection circuit, thereby simplifying the structure of the inverter device and reducing the circuit design cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of inverters, and in particular relates to an inverter device and a control method thereof. Background Art

[0002] In new energy grid-connected power generation systems, such as photovoltaic power generation and energy storage systems, the inverter device converts the direct current generated by the battery into alternating current with the same frequency and phase as the grid voltage, thereby realizing the energy feedback of renewable energy to the grid.

[0003] However, before the inverter is connected to the grid, due to the difference between the common-mode voltage on the DC side of the inverter (i.e. the voltage of the DC neutral point BUS_N relative to the ground PE) and the common-mode voltage on the grid side (i.e. the voltage of the grid side N relative to PE), a large impact current will be generated at the moment the inverter is connected to the grid, which may cause instantaneous interference to the sampling and control system of the inverter and cause failure of the inverter operation.

[0004] In the existing scheme, in order to suppress the common-mode impact current at the moment of grid connection before the inverter device is connected to the grid, it is usually necessary to introduce an additional compensation power supply and a corresponding common-mode voltage sampling circuit. In the process of detecting the common-mode voltage change, the compensation power supply is applied to compensate for the common-mode impact current. The control complexity is relatively increased and an additional compensation circuit needs to be added, and the structure and cost will also increase.

[0005] Furthermore, when the inverter is connected to the grid, it is necessary to determine the insulation impedance of the current system to judge the insulation impedance performance of the current circuit. In order to realize the insulation impedance detection, an impedance detection circuit needs to be additionally provided, which complicates the structure of the inverter device and increases the cost. Summary of the invention

[0006] The object of the present invention is to provide an inverter device, aiming to solve the problems of complex structure and high cost in traditional inverter devices when realizing common mode impulse current suppression and insulation detection.

[0007] A first aspect of an embodiment of the present invention provides a control method for an inverter device, wherein the inverter device includes a DC input terminal, a positive DC bus, a negative DC bus, a positive bus capacitor, a negative bus capacitor, an inverter circuit, a grid-connected switch circuit, an AC port, and a soft start circuit;

[0008] The positive DC bus and the negative DC bus are connected to the DC input terminal and the inverter circuit respectively, the positive bus capacitor and the negative bus capacitor are connected in series between the positive DC bus and the negative DC bus, the midpoints of the positive bus capacitor and the negative bus capacitor constitute a DC neutral point, the AC port includes an AC output port and an AC neutral port, the AC neutral port is grounded, the grid-connected switch circuit is connected in series between the output terminal of the inverter circuit and the AC output port, and the soft start circuit is connected between the DC neutral point and the AC neutral port;

[0009] The control method of the inverter device comprises:

[0010] Switching to the grid-connected mode based on the grid-connected instruction, and acquiring a first voltage of the negative DC bus to the ground;

[0011] Output a first switch signal to trigger the soft start circuit to switch to an impedance circuit with a preset impedance, and read a second voltage of the negative DC bus to ground, and determine the insulation impedance of the DC side of the inverter circuit to ground based on the first voltage, the second voltage and the preset impedance;

[0012] The terminal voltage of the soft start circuit is read, and when the rate of change or voltage value of the terminal voltage is less than a preset value, a second switch signal is output to trigger the soft start circuit to turn on, and directly connect the DC neutral point and the AC neutral port, and a grid-connected control signal is output to control the grid-connected switch circuit to turn on.

[0013] A second aspect of an embodiment of the present invention provides an inverter device, comprising:

[0014] DC input terminal;

[0015] A positive DC bus and a negative DC bus, wherein the positive DC bus and the negative DC bus are connected to the DC input terminal;

[0016] A positive bus capacitor and a negative bus capacitor, wherein the positive bus capacitor and the negative bus capacitor are connected in series between the positive DC bus and the negative DC bus, and the midpoints of the positive bus capacitor and the negative bus capacitor constitute a DC neutral point;

[0017] An AC port, the AC port comprising an AC output port and an AC neutral port, the AC neutral port being grounded;

[0018] An inverter circuit, wherein an input end of the inverter circuit is respectively connected to the positive DC bus, the negative DC bus and the DC neutral point, and an output end of the inverter circuit is used to output an AC power supply;

[0019] A grid-connected switch circuit, connected in series between the output end of the inverter circuit and the AC output port;

[0020] A soft start circuit connected between the DC neutral point and the AC neutral port;

[0021] The inverter device further includes a control circuit, and the control circuit is used to implement the control method of the inverter device as described above.

[0022] Optionally, the inverter device further includes:

[0023] A leakage protection switch, wherein the input end of the leakage protection switch is respectively connected to the output end of the grid-connected switch circuit and the output end of the soft start circuit, and the output end of the leakage protection switch is connected to the AC port. The leakage protection switch is used to monitor the leakage current between the grid-connected switch circuit, the soft start circuit and the AC port respectively, and is shut down when the leakage current is greater than a preset current.

[0024] Optionally, the leakage protection switch and the inverter circuit are arranged separately.

[0025] Optionally, the inverter device further includes:

[0026] A filter circuit is connected in series between the output end of the inverter circuit and the grid-connected switch circuit, and the filter circuit is used to filter the AC power output by the inverter circuit.

[0027] Optionally, the inverter circuit is a three-phase inverter circuit;

[0028] The grid-connected switch circuit includes three grid-connected switches, and the three grid-connected switches are respectively connected in series between the three-phase output end of the inverter circuit and the AC output port.

[0029] Optionally, the inverter circuit is a split-phase inverter circuit;

[0030] The grid-connected switch circuit includes two grid-connected switches, and the two grid-connected switches are respectively connected in series between the two-phase output ends of the inverter circuit and the AC output port.

[0031] Optionally, the inverter device further includes:

[0032] Multi-way grounding capacitors;

[0033] Each output terminal of the inverter circuit and the DC neutral point are grounded through a grounding capacitor respectively.

[0034] Optionally, the grounding capacitor is a parasitic capacitor.

[0035] Optionally, the soft start circuit includes a first resistive element, a first switch and a second switch;

[0036] The first resistive element is connected in parallel with the first switch, and the parallel circuit of the first resistive element and the first switch and the second switch are connected in series and are connected in series between the DC neutral point and the AC neutral port.

[0037] Optionally, the soft start circuit includes a second resistive element, a third resistive element, a third switch and a fourth switch;

[0038] The second resistive element is connected in parallel with the third switch, the third resistive element is connected in parallel with the fourth switch, the parallel circuit of the second resistive element and the third switch and the parallel circuit of the third resistive element and the fourth switch are connected in series and are connected in series between the DC neutral point and the AC neutral port.

[0039] Optionally, the soft start circuit includes a fourth resistive element, a fifth switch, a sixth switch and a seventh switch;

[0040] The fourth resistive element and the fifth switch are connected in series between the DC neutral point and the AC neutral port, and the sixth switch and the seventh switch are connected in series between the DC neutral point and the AC neutral port.

[0041] Optionally, each resistive element comprises a resistor.

[0042] Compared with the prior art, the embodiments of the present invention have the following beneficial effects: the control method of the inverter device is applicable to the inverter device, in which a soft start circuit is arranged between a DC neutral point and an AC neutral port. In the control method of the inverter device, the soft start circuit is first controlled to switch the output preset impedance to the DC neutral point and the AC neutral port, the preset impedance can suppress the impact of the common-mode impact current, and improve the safety of grid connection, and the first voltage and the second voltage of the negative DC bus to the ground are respectively obtained before and after the soft start circuit outputs the preset impedance, the system impedance can be determined based on the first voltage, the second voltage and the preset impedance, and when it is detected that the change rate of the terminal voltage of the soft start circuit or the voltage value is less than the preset value, the soft start circuit is controlled to directly conduct the DC neutral point and the AC neutral port, and the grid-connected switch circuit is controlled to conduct the grid-connected output AC power to the power grid, and by setting the soft start circuit, common-mode impact current suppression and system impedance detection are synchronously realized, without the need to additionally set up a compensation circuit and an insulation impedance detection circuit, the structure of the inverter device is simplified and the circuit design cost is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0044] Figure 1 is a circuit diagram of a conventional inverter device;

[0045] Figure 2 A first circuit diagram of an inverter device provided by an embodiment of the present invention;

[0046] Figure 3 A schematic flow chart of a control method for an inverter device provided by an embodiment of the present invention;

[0047] Figure 4 A schematic diagram of a first equivalent circuit of an inverter device provided in an embodiment of the present invention;

[0048] Figure 5 A second equivalent circuit diagram of the inverter device provided in an embodiment of the present invention;

[0049] Figure 6 A third equivalent circuit diagram of the inverter device provided in an embodiment of the present invention;

[0050] Figure 7 A second circuit diagram of an inverter device provided by an embodiment of the present invention;

[0051] Figure 8 A third circuit diagram of the inverter device provided by an embodiment of the present invention;

[0052] Fig. 9 A fourth circuit diagram of an inverter device provided by an embodiment of the present invention;

[0053] Fig.10 A fifth circuit diagram of the inverter device provided by an embodiment of the present invention;

[0054] Fig.11 A sixth circuit diagram of an inverter device provided by an embodiment of the present invention;

[0055] Fig.12 A seventh circuit diagram of the inverter device provided by an embodiment of the present invention;

[0056] Fig.13 An eighth circuit diagram of the inverter device provided in an embodiment of the present invention.

[0057] Among them, the reference numerals in the figures are:

[0058] 100, inverter device; 200, power grid; 10, inverter circuit; 20, grid-connected switch circuit; 30, soft start circuit; 40, leakage protection switch; 50, filter circuit;

[0059] C Y1 , positive bus capacitor; C Y2 , negative bus capacitance; K 11 , the first grid-connected switch; K 12 , the second grid-connected switch; K 21 , the third grid-connected switch; K 22 , the fourth grid-connected switch; K 31 , the fifth grid-connected switch; K 32 , the sixth grid-connected switch; K 41 , first switch; K 42 , the second switch; K 43 , the third switch; K 44 , the fourth switch; K 45 , the fifth switch; K 46 , the sixth switch; K 47 , the seventh switch; Z 41 , the first resistive element; Z 42 , the second resistive element; Z 43 , the third resistive element; Z 44 , fourth resistive element; C1, first capacitor; C2, second capacitor; C3, third capacitor; C4, first grounding capacitor; C5, second grounding capacitor; C6, third grounding capacitor; C7, fourth grounding capacitor; L1, first inductor; L2, second inductor; L3, third inductor;

[0060] BUS+, positive DC bus; BUS-, negative DC bus; BUS_N, DC neutral point; N, AC neutral port; L A , the first AC output port; L B , the second AC output port; Lc, the third AC output port. DETAILED DESCRIPTION

[0061] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0062] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0063] Before the inverter is connected to the grid, due to the difference between the common-mode voltage on the DC side of the inverter device 100 (i.e. the voltage of the DC neutral point BUS_N relative to the ground PE) and the common-mode voltage on the grid side (i.e. the voltage of the grid side's N relative to PE), a large impact current will be generated at the moment the inverter circuit 10 is connected to the grid, which may cause instantaneous interference to the sampling and control system of the inverter circuit 10, resulting in malfunction of the inverter circuit 10.

[0064] For example Figure 1 As shown, the bus capacitor midpoint BUS_N is connected to the AC neutral point N of the power grid 200, and the inverter circuit 10 provides a stable point N, which can meet the requirements of unbalanced load of each phase in the off-grid scenario implemented by the inverter device 100.

[0065] In the inverter device 100, the circuit path of the common-mode impact generated at the moment of grid connection is shown as the dotted line in the figure. It will pass through the AC output capacitor of the inverter circuit 10 to the ground in sequence, and then return to the AC output end of the inverter circuit 10 from the ground through the power grid 200, the leakage protection switch 40 and the grid-connected switch. The impedance in this current loop is very small, so the instantaneous common-mode impact current will be very large.

[0066] Furthermore, in conventional insulation detection solutions, an additional insulation detection circuit is usually provided, and structural reuse cannot be achieved, resulting in a complicated structure and high cost of the inverter device 100 .

[0067] In order to solve the above problems, the first aspect of an embodiment of the present invention proposes a control method for an inverter device 100. The inverter device 100 is suitable for a photovoltaic power generation system, an energy storage system, etc. The inverter device 100 converts the direct current VIN generated by the photovoltaic cell array or the energy storage battery into alternating current with the same frequency and phase as the voltage of the power grid 200, thereby realizing the energy feeding of renewable energy to the power grid 200.

[0068] Among them, Figure 2 As shown, the inverter device 100 includes a DC input terminal, a positive DC bus BUS+, a negative DC bus BUS-, a positive bus capacitor C Y1 , negative bus capacitor C Y2, inverter circuit 10, grid-connected switch circuit 20, AC port and soft start circuit 30. The DC input terminal can be a photovoltaic port or a DC port of an energy storage system. The positive DC bus BUS+ and the negative DC bus BUS- are connected to the DC input terminal and the inverter circuit 10 respectively. The DC power VIN inputted from the DC input terminal is transmitted to the positive DC bus BUS+ and the negative DC bus BUS-, and is converted from DC to AC through the inverter circuit 10, and the AC power is output to the back end.

[0069] Positive bus capacitor C Y1 and negative bus capacitor C Y2 Connected in series between the positive DC bus BUS+ and the negative DC bus BUS-, it is used to store and filter the DC power VIN. The positive bus capacitor C Y1 and negative bus capacitor C Y2 The midpoint of the DC power supply constitutes the DC neutral point BUS_N, providing a stable N point.

[0070] The AC port includes an AC output port and an AC neutral port N. The AC output port may be a first AC output port L. A , the second AC output port L B and the third AC output port L C , or includes a first AC output port L A , the second AC output port L B and the third AC output port L C The two AC output ports, the AC neutral port N is grounded to PE, the AC output port and the AC neutral port N are respectively connected to the power grid 200, wherein the AC output port is used to output AC power, the AC power supply can be a three-phase or split-phase AC power supply, and at the same time, the neutral point of the AC power supply is connected to the AC neutral port N and grounded to PE.

[0071] The grid-connected switch circuit 20 is connected in series between the output end of the inverter circuit 10 and the AC output port. The grid-connected switch circuit 20 is triggered to turn on based on the received grid-connected switch signal and transmits the AC power output by the inverter circuit 10 to the AC output port to achieve grid-connected operation. When the grid-connected switch signal is not received, the grid-connected switch circuit 20 remains in the off state and remains in the off-grid state.

[0072] The soft start circuit 30 is connected between the DC neutral point BUS_N and the AC neutral port N. The soft start circuit 30 triggers switching to output a preset impedance between the DC neutral point BUS_N and the AC neutral port N based on the received first switching signal. The preset impedance can suppress and reduce the sudden change of the common mode voltage, thereby reducing the common mode impact current. The soft start circuit 30 is triggered to turn on based on the received second switching signal, and directly connects the DC neutral point BUS_N and the AC neutral port N.

[0073] In order to suppress common mode impulse current and insulation impedance detection, such as Figure 3 As shown, in this embodiment, the control method of the inverter device 100 includes:

[0074] Step S10: switching to the grid-connected mode based on the grid-connected instruction, and obtaining a first voltage between the negative DC bus BUS- and the ground PE;

[0075] Step S20, outputting a first switch signal to trigger the soft start circuit 30 to switch to an impedance circuit with a preset impedance, and reading a second voltage of the negative DC bus BUS- to the ground PE, and determining the insulation impedance of the DC side of the inverter circuit 10 to the ground PE based on the first voltage, the second voltage and the preset impedance;

[0076] Step S30, read the terminal voltage of the soft start circuit 30, when the change rate of the terminal voltage or the voltage value is less than the preset value, output a second switch signal to trigger the soft start circuit 30 to turn on the DC neutral point BUS_N and the AC neutral port N, and output a grid-connected control signal to control the grid-connected switch circuit 20 to turn on.

[0077] In this embodiment, the system insulation impedance refers to the insulation impedance of the DC side of the inverter circuit 10 to the ground PE, and the insulation impedance of the DC side of the inverter circuit 10 to the ground PE includes the insulation impedance of the DC input terminal to the ground PE and the insulation impedance of the positive and negative DC bus BUS- to the ground PE.

[0078] The insulation impedance detection method and the common-mode impulse current suppression method share the same circuit and respectively adopt different strategic methods.

[0079] When the inverter device 100 receives the grid-connected instruction, it starts the grid-connected operation. At this time, the insulation impedance detection can be performed. First, the first voltage of the negative DC bus BUS- to the ground PE before the soft start circuit 30 is activated is obtained, which is assumed to be u1. Then, the first switching signal is output to the soft start circuit 30. The soft start circuit 30 is triggered to the first switching state and switches the output preset impedance to between the DC neutral point BUS_N and the AC neutral port N. The second voltage of the negative DC bus BUS- to the ground PE in the first switching state of the soft start circuit 30 is obtained, which is assumed to be u2.

[0080] by Figure 4 For example, according to Thevenin's theorem, the two ends of the linear network including an independent voltage source, an independent current source and a resistor on the DC side of the inverter circuit 10 can be equivalent to a two-port network of an independent voltage source and a series resistor, that is, Figure 4 u iso and R iso Among them, R iso The meaning of is all equivalent impedances of the DC side of the inverter circuit 10 to PE.

[0081] Assume that R1 is the total equivalent resistance of the negative DC bus BUS- to PE, R2 is the total equivalent resistance of the positive DC bus BUS+ to PE, R3 is the total equivalent resistance of the DC neutral point BUS_N to PE, and R4 is the total equivalent resistance of the DC neutral point BUS_N to PE of the soft start circuit 30 in the first switching state, wherein R4 is the total resistance of the line impedance between the preset impedance and the DC neutral point BUS_N to the ground PE.

[0082] Before the soft start circuit 30 switches to the first switch state, assuming that the current flowing through the negative DC bus BUS- to the PE branch is i1, the current flowing through the positive DC bus BUS+ to the PE branch is i2, and the current flowing through the DC neutral point BUS_N to the PE branch is i3, the positive direction of the current is defined as follows: Figure 4 As shown in the mark, at this time, the voltage u1 of the negative DC bus BUS- to PE can be expressed as:

[0083]

[0084] The Kirchhoff voltage equation for the circuit from the positive DC bus BUS+ to PE to the DC neutral point BUS_N is:

[0085]

[0086] The Kirchhoff voltage equation for the circuit from the negative DC bus BUS- to PE to the DC neutral point BUS_N is:

[0087]

[0088] The Kirchhoff voltage equation for the negative DC bus BUS- and the equivalent insulation impedance loop is:

[0089]

[0090] Combining (1)(2)(3)(4) we get the following relationship:

[0091]

[0092] Similarly, when the soft start circuit 30 switches to the first switch state and outputs the preset impedance R4, it can be obtained:

[0093]

[0094] Combining (5) and (6), the calculation formula for insulation resistance is:

[0095]

[0096] In practical applications, the equivalent impedance of the positive DC bus BUS+ to PE and the equivalent impedance of the negative DC bus BUS- to PE are approximately equal, that is:

[0097]

[0098] In order to suppress the common mode voltage difference between the inverter circuit 10 and the grid 200 when connected to the grid, the impedance R4 is usually preset to be relatively small, that is:

[0099]

[0100] Substituting (8) and (9) into (7) and simplifying, we obtain:

[0101]

[0102] Among them, the total equivalent resistance of the negative DC bus BUS- to PE and the resistance of the preset impedance are known. Therefore, by obtaining the first voltage and the second voltage and the preset impedance, the insulation impedance of the DC side of the current inverter circuit 10 to the ground PE can be determined. There is no need to set up an additional insulation impedance detection circuit, which simplifies the structure and design cost of the inverter device 100.

[0103] At the same time, when suppressing common-mode impact current, it can be analyzed from the steady-state and transient directions respectively.

[0104] In steady state, Figure 5 For example, assuming that the bus voltage of the inverter device 100 is controlled at u bus , the total equivalent impedance of the positive DC bus BUS+ relative to the DC neutral point BUS_N in the inverter device 100 is recorded as R5, the total equivalent impedance of the negative DC bus BUS- relative to the DC neutral point BUS_N is recorded as R6, the total equivalent impedance of the positive DC bus BUS+ relative to PE (i.e. GRID_N) is recorded as R7, and the total equivalent impedance of the negative DC bus BUS- relative to PE (i.e. GRID_N) is recorded as R8. Before the soft start circuit 30 switches to the first switching state, the equivalent impedance of the DC neutral point BUS_N relative to PE (i.e. GRID_N) is recorded as R9. When the soft start circuit 30 switches to the first switching state, the soft start circuit 30 outputs a preset impedance, and the preset impedance is connected in parallel with R9, so it can be considered that the equivalent impedance R9 of the DC neutral point BUS_N relative to PE (i.e. GRID_N) is significantly reduced after the parallel connection.

[0105] Therefore, under this model, the voltage across the soft start circuit 30 (ie, the common mode voltage difference between the DC neutral point BUS_N and the AC neutral port N) can be expressed as:

[0106]

[0107] It can be seen from formula (11) that before and after the soft start circuit 30 switches to the first switch state, since the equivalent impedance R9 of the DC neutral point BUS_N relative to PE (ie, GRID_N) is significantly reduced, the common mode voltage difference between the DC neutral point BUS_N and the AC neutral port N is also significantly reduced.

[0108] When analyzing the transient state, at the moment when the soft start circuit 30 switches to the first switch state, the common mode impact current loop in the loop can be equivalent to the following: Figure 6 As shown in the schematic diagram, it is assumed that the capacitance of all equivalent capacitors from the DC neutral point BUS_N to PE is C g , the equivalent inductance in the circuit is recorded as L g , the equivalent resistance is recorded as R g After the soft start circuit 30 switches to the first switch state, the capacitor C g The voltage u gm-n When the discharge starts, the common-mode impulse current i(t) generated can be expressed as the following second-order difference equation:

[0109]

[0110] In order to prevent the common-mode impulse current i(t) from oscillating, all equivalent inductances in the loop need to satisfy the following constraints:

[0111]

[0112] Therefore, under the premise that the current does not oscillate, the maximum peak current under critical damping conditions can be expressed as the peak common-mode impulse current:

[0113]

[0114] In order to suppress the common-mode impact current so that the AC relay will not trigger the leakage protection by mistake at the moment of closing, it is assumed that the threshold of the leakage current of the leakage protection is I th-lk , then the requirements are met:

[0115]

[0116] In summary, by serially or parallelly inserting a resistor element or an inductor element with a preset impedance between the DC neutral point BUS_N and the AC neutral port N, the magnitude of the common-mode impulse current can be effectively suppressed, thereby avoiding malfunction of the leakage protection.

[0117] During this process, the terminal voltage of the soft start circuit 30 changes from large to small, and the common-mode impact current gradually decreases. When the magnitude or change rate of the monitored terminal voltage is less than the preset value, it indicates that the current common-mode impact current is small, and the voltage between the DC neutral point BUS_N and the AC neutral port N is almost equal. At this time, the soft start circuit 30 is controlled to switch to the second switching state and turn on the DC neutral point BUS_N and the AC neutral port N, thereby completing the soft start between the AC and DC neutral points BUS_N, and effectively suppressing the common-mode impact current at the moment of grid connection.

[0118] Then, the grid-connected switch signal is output to the grid-connected switch circuit 20, the grid-connected switch circuit 20 is turned on, and the AC power is transmitted to the grid 200, and the inverter circuit 10 outputs an AC power with the same amplitude, frequency and phase as the grid 200 voltage, thereby completing the grid-connected work.

[0119] By adopting the soft start circuit 30 , there is no need to set up an additional compensation circuit, which simplifies the circuit structure and reduces the design cost.

[0120] Compared with the prior art, the embodiments of the present invention have the following beneficial effects: the control method of the inverter device 100 is applicable to the inverter device 100, in which a soft start circuit 30 is provided between the DC neutral point BUS_N and the AC neutral port N. In the control method of the inverter device 100, the soft start circuit 30 is first controlled to switch the output preset impedance to the DC neutral point BUS_N and the AC neutral port N, and the preset impedance can suppress the impact of the common mode impact current, improve the safety of the grid connection, and obtain the negative DC bus BUS-to-ground PE before and after the soft start circuit 30 outputs the preset impedance. The first voltage and the second voltage are based on which the system impedance can be determined. When it is detected that the rate of change of the terminal voltage of the soft start circuit 30 or the voltage value is less than the preset value, the soft start circuit 30 is controlled to directly conduct the DC neutral point BUS_N and the AC neutral port N, and the grid-connected switch circuit 20 is controlled to conduct the grid-connected output AC power to the power grid 200. By setting the soft start circuit 30, common-mode impact current suppression and system impedance detection are realized synchronously without additionally setting a compensation circuit and an insulation impedance detection circuit, thereby simplifying the structure of the inverter device 100 and reducing the circuit design cost.

[0121] Corresponding to the control method of the inverter device 100, the second aspect of the embodiment of the present invention provides an inverter device 100, including a DC input terminal, a positive DC bus BUS+, a negative DC bus BUS-, a positive bus capacitor C Y1 , negative bus capacitor C Y2, inverter circuit 10, grid-connected switch circuit 20, AC port and soft start circuit 30. The DC input terminal can be a photovoltaic port or a DC port of an energy storage system. The positive DC bus BUS+ and the negative DC bus BUS- are connected to the DC input terminal and the inverter circuit 10 respectively. The DC power VIN inputted from the DC input terminal is transmitted to the positive DC bus BUS+ and the negative DC bus BUS-, and is converted from DC to AC through the inverter circuit 10, and the AC power is output to the back end.

[0122] Positive bus capacitor C Y1 and negative bus capacitor C Y2 Connected in series between the positive DC bus BUS+ and the negative DC bus BUS-, it is used to store and filter the DC power VIN. The positive bus capacitor C Y1 and negative bus capacitor C Y2 The midpoint of the DC power supply constitutes the DC neutral point BUS_N, providing a stable N point.

[0123] The AC port includes an AC output port and an AC neutral port N. The AC output port may be a first AC output port L. A , the second AC output port L B and the third AC output port L C , or includes a first AC output port L A , the second AC output port L B and the third AC output port L C The two AC output ports, the AC neutral port N is grounded to PE, the AC output port and the AC neutral port N are respectively connected to the power grid 200, wherein the AC output port is used to output AC power, the AC power supply can be a three-phase or split-phase AC power supply, and at the same time, the neutral point of the AC power supply is connected to the AC neutral port N and grounded to PE.

[0124] The grid-connected switch circuit 20 is connected in series between the output end of the inverter circuit 10 and the AC output port. The grid-connected switch circuit 20 is triggered to turn on based on the received grid-connected switch signal and transmits the AC power output by the inverter circuit 10 to the AC output port to achieve grid-connected operation. When the grid-connected switch signal is not received, the grid-connected switch circuit 20 remains in the off state and remains in the off-grid state.

[0125] The soft start circuit 30 is connected between the DC neutral point BUS_N and the AC neutral port N. The soft start circuit 30 triggers switching to output a preset impedance between the DC neutral point BUS_N and the AC neutral port N based on the received first switching signal. The preset impedance can suppress and reduce the sudden change of the common mode voltage, thereby reducing the common mode impact current. The soft start circuit 30 is triggered to turn on based on the received second switching signal, and directly connects the DC neutral point BUS_N and the AC neutral port N.

[0126] At the same time, the inverter device 100 also includes a control circuit (not shown in the figure), which is used to implement the control method of the inverter device 100 as described above. The control circuit may include a corresponding voltage sampling circuit, a controller and a memory. The voltage sampling circuit is used to sample the voltage of the negative DC bus BUS- to the ground PE, and to sample the terminal voltage of the soft start circuit 30. The memory is used to store a computer program that can be run in the controller. When the processor executes the computer program, the steps of the control method of the inverter device 100 are implemented.

[0127] That is, after receiving the grid-connected instruction, the controller obtains the first voltage of the negative DC bus BUS- to the ground PE through the voltage sampling circuit, and then outputs the first switching signal to the soft start circuit 30, so that the soft start circuit 30 switches to the first switching state and switches the output preset impedance. At this time, the second voltage of the negative DC bus BUS- to the ground PE is obtained through the voltage sampling circuit, and the insulation impedance of the DC side of the inverter circuit 10 to the ground PE is determined based on the detected first voltage and second voltage and the preset impedance of the soft start circuit 30.

[0128] Among them, it can be known from the above formula that the insulation impedance of the DC side of the inverter circuit 10 to the ground PE is related to the bus voltage, the first voltage, the second voltage, the total equivalent resistance of the negative DC bus BUS- to PE and the preset impedance, wherein the bus voltage, the total equivalent resistance of the negative DC bus BUS- to PE and the preset impedance are known. Therefore, by detecting the first voltage and the second voltage and combining the calculation with the known value, the insulation impedance of the DC side of the current inverter circuit 10 to the ground PE can be determined, without the need to additionally set up an insulation impedance detection circuit, thereby simplifying the structure and design cost of the inverter device 100.

[0129] At the same time, when the soft start circuit 30 switches to the first switching state, the preset impedance is connected in parallel with the equivalent impedance of the DC neutral point BUS_N relative to PE. The impedance after parallel connection becomes smaller, and the common-mode voltage difference between the DC neutral point BUS_N and the AC neutral port N is also reduced accordingly, thereby effectively suppressing the magnitude of the common-mode impulse current, avoiding damage to components caused by the common-mode impulse current, and avoiding false protection of the leakage protection.

[0130] During this process, the terminal voltage of the soft start circuit 30 changes from large to small, and the common-mode impact current gradually decreases. When the magnitude or change rate of the monitored terminal voltage is less than the preset value, it indicates that the current common-mode impact current is small, and the voltage between the DC neutral point BUS_N and the AC neutral port N is almost equal. At this time, the controller controls the soft start circuit 30 to switch to the second switching state and turn on the DC neutral point BUS_N and the AC neutral port N, thereby completing the soft start between the AC and DC neutral points BUS_N, effectively suppressing the common-mode impact current at the moment of grid connection, and then, the controller outputs a grid-connected switch signal to the grid-connected switch circuit 20, the grid-connected switch circuit 20 is turned on, and the AC power is transmitted to the power grid 200, and the inverter circuit 10 outputs an AC ground power with the same amplitude, frequency and phase as the voltage of the power grid 200, thereby completing the grid connection work.

[0131] Furthermore, in order to achieve leakage protection, Figure 7 As shown, in an optional embodiment, the inverter device 100 further includes:

[0132] The leakage protection switch 40 has its input end connected to the output end of the grid-connected switch circuit 20 and the output end of the soft-start circuit 30 respectively, and its output end connected to the AC port. The leakage protection switch 40 is used to monitor the leakage current between the grid-connected switch circuit 20, the soft-start circuit 30 and the AC port, and shuts down when the leakage current is greater than a preset current.

[0133] The leakage protection switch 40 is used to implement leakage protection, and can implement leakage protection for the leakage current of the AC output port and the AC neutral port N respectively. By setting the soft start circuit 30, after being connected to the grid, the common mode impact current is suppressed and reduced, and the common mode impact current is less than the preset current. After being connected to the grid, the leakage protection switch 40 will not be shut down due to the common mode impact current, resulting in grid failure, thereby improving the reliability of leakage protection and grid connection.

[0134] Among them, the leakage protection switch 40 can be built into the inverter circuit 10 or independently set externally. In an optional embodiment, the leakage protection switch 40 is set separately from the inverter circuit 10. When it is independently set outside the inverter circuit 10, the leakage protection switch 40 can be set at the front end or the rear end of the grid-connected switch circuit 20, and realize leakage protection when the grid-connected switch circuit 20 is turned on and connected to the grid.

[0135] Furthermore, in order to reduce the interference of clutter on the power grid 200, as Figure 8 As shown, in an optional embodiment, the inverter device 100 further includes:

[0136] The filter circuit 50 is connected in series between the output end of the inverter circuit 10 and the grid-connected switch circuit 20. The filter circuit 50 is used to filter the AC power output by the inverter circuit 10, reduce output noise, and improve grid-connected reliability.

[0137] The filter circuit 50 may be an L-type filter circuit, an LC-type filter circuit, or an LCL-type filter circuit. Figure 8 As shown, an LC type filter circuit is used, and the LC type filter circuit includes a plurality of filter units, each of which is connected to one phase output terminal of the inverter circuit 10 and filters one phase of the AC power supply, and each of which includes an inductor and a capacitor. For example, the first filter unit includes a first inductor L1 and a first capacitor C1, the second filter unit includes a second inductor L2 and a second capacitor C2, and the third filter unit includes a third inductor L3 and a third capacitor C3. Each inductor is connected between the inverter circuit 10 and the grid-connected switch circuit 20, and each capacitor is respectively connected to the corresponding inductor and the DC neutral point BUS_N.

[0138] Among them, the inverter circuit 10 can adopt structures such as T-type three-level topology, diode clamped topology, flying capacitor topology and cascaded H-bridge topology. The inverter circuit 10 can output three-phase AC power supply or split-phase AC power supply, and the specific structure is not limited.

[0139] Corresponding to the structure of the inverter circuit 10, the grid-connected switch circuit 20 may adopt different types of switch structures. In an optional embodiment, for example Figure 8 As shown, the inverter circuit 10 is a three-phase inverter circuit 10, and the inverter circuit 10 outputs a three-phase AC power supply. The grid-connected switch circuit 20 includes three grid-connected switches, and the three grid-connected switches are respectively connected in series between the three-phase output end and the AC output port of the inverter circuit 10. Each phase of AC power is output to the leakage protection switch 40 or the power grid 200 at the rear end through a grid-connected switch. The grid-connected switch can be a single switch or a plurality of switches connected in series and parallel. For example, the first grid-connected switch includes a first grid-connected switch K connected in series. 11 and the second grid-connected switch K 12 The second grid-connected switch includes a third grid-connected switch K connected in series 21 And the fourth grid-connected switch K 22 The third grid-connected switch includes a fifth grid-connected switch K connected in series. 31 And the sixth grid-connected switch K 32 Each switch can adopt a switching device with controlled on-off, such as a relay, a circuit breaker, etc.

[0140] In another alternative embodiment, if Fig. 9As shown, the inverter circuit 10 is a split-phase inverter circuit, and the grid-connected switch circuit 20 includes two grid-connected switches, which are respectively connected in series between the two-phase output ends and the AC output port of the inverter circuit 10. The inverter circuit 10 outputs a two-phase AC power supply. The grid-connected switch circuit 20 includes two grid-connected switches, which are respectively connected in series between the two-phase output ends and the AC output port of the inverter circuit 10. Each phase of AC power is output to the rear-end leakage protection switch 40 or the power grid 200 through a grid-connected switch. The grid-connected switch can adopt a single switch or a plurality of switches connected in series and parallel. Each switch can adopt a switching device with controlled on and off, such as a relay, a circuit breaker, etc.

[0141] Furthermore, in order to provide a ground PE reference point so that the AC power output by the inverter circuit 10 has the same ground PE reference point, in an optional embodiment, as Figure 8 or Fig. 9 As shown, the inverter device 100 also includes multiple grounding capacitors, such as a first grounding capacitor C4, a second grounding capacitor C5, a third grounding capacitor C6 and a fourth grounding capacitor C7. Each output end of the inverter circuit 10 and the DC neutral point BUS_N are respectively connected to the ground PE through a grounding capacitor, and each grounding capacitor provides the same grounding PE reference point for each phase of the AC power supply.

[0142] The grounding capacitor may be arranged in a circuit or obtained by line parasitism. In an optional embodiment, the grounding capacitor may be a parasitic capacitor.

[0143] The soft start circuit 30 can adopt a variety of different structures. In an optional embodiment, for example Fig.10 or Fig.11 As shown, the soft start circuit 30 includes a first resistive element Z 41 , the first switch K 41 and the second switch K 42 ;

[0144] The first resistive element Z 41 With the first switch K 41 In parallel, the first resistive element Z 41 With the first switch K 41 The parallel circuit and the second switch K 42 Connected in series between the DC neutral point BUS_N and the AC neutral port N.

[0145] Based on the structure of the soft start circuit 30, after receiving the grid connection instruction, the control circuit first obtains the first voltage of the negative DC bus BUS- to the ground PE, and then controls the second switch K 42 The first switch K is turned on. 41 Keep off, the first resistive element Z 41It has a preset impedance and is connected in series between the DC neutral point BUS_N and the AC neutral port N. The control circuit synchronously obtains the second voltage of the negative DC bus BUS- to the ground PE, and determines the insulation impedance of the DC side of the inverter circuit 10 to the ground PE based on the first voltage, the second voltage and the preset impedance.

[0146] At the same time, the second switch K 42 When conducting, the first resistive element Z 41 When connected in parallel with the equivalent impedance of the DC neutral point BUS_N relative to PE, the impedance after parallel connection becomes smaller, and the common-mode voltage difference between the DC neutral point BUS_N and the AC neutral port N is also reduced accordingly, thereby effectively suppressing the size of the common-mode impulse current, avoiding damage to devices due to the common-mode impulse current, and avoiding false protection of the leakage protection.

[0147] During this process, the terminal voltage of the soft start circuit 30 changes from large to small, the common mode impact current gradually decreases, and the control circuit monitors the first resistive element Z 41 When the magnitude or change rate of the terminal voltage is less than a preset value, the voltage between the DC neutral point BUS_N and the AC neutral port N is approximately equal, and the control circuit controls the first switch K 41 It is turned on, connecting the DC neutral point BUS_N and the AC neutral port N, thereby completing the soft start between the AC and DC neutral points BUS_N, and effectively suppressing the common-mode impact current at the moment of grid connection.

[0148] In another alternative embodiment, if Fig.12 As shown, the soft start circuit 30 includes a second resistive element Z 42 , the third resistive element Z 43 , the third switch K 43 and the fourth switch K 44 ;

[0149] The second resistive element Z 42 With the third switch K 43 In parallel, the third resistive element Z 43 With the fourth switch K 44 In parallel, the second resistive element Z 42 With the third switch K 43 The parallel circuit and the third resistive element Z 43 With the fourth switch K 44 The parallel circuit is connected in series between the DC neutral point BUS_N and the AC neutral port N.

[0150] Assume that the second resistive element Z 42 The impedance is much larger than the third resistive element Z 43 Based on the structure of the soft start circuit 30, after receiving the grid connection instruction, the control circuit first obtains the first voltage of the negative DC bus BUS- to the ground PE, and then controls the fourth switch K44 The third switch K is turned on. 43 Keep off, the second resistive element Z 42 It has a preset impedance and is connected in series between the DC neutral point BUS_N and the AC neutral port N. The control circuit synchronously obtains the second voltage of the negative DC bus BUS- to the ground PE, and determines the insulation impedance of the DC side of the inverter circuit 10 to the ground PE based on the first voltage, the second voltage and the preset impedance.

[0151] At the same time, the fourth switch K 44 When conducting, the second resistive element Z 42 When connected in parallel with the equivalent impedance of the DC neutral point BUS_N relative to PE, the impedance after parallel connection becomes smaller, and the common-mode voltage difference between the DC neutral point BUS_N and the AC neutral port N is also reduced accordingly, thereby effectively suppressing the size of the common-mode impulse current, avoiding damage to devices due to the common-mode impulse current, and avoiding false protection of the leakage protection.

[0152] In this process, the terminal voltage of the soft start circuit 30 changes from large to small, and the common mode impact current gradually decreases. The control circuit monitors the terminal voltage of the soft start circuit 30, and when the magnitude or change rate of the terminal voltage is less than the first preset value, the control circuit controls the voltage between the DC neutral point BUS_N and the AC neutral port N to be approximately equal, and the control circuit controls the third switch K 43 Turn on and control the fourth switch K 44 Turn off, the preset impedance is transformed into the third resistive element Z 43 The control circuit continues to monitor the terminal voltage of the soft start circuit 30, and when the magnitude or change rate of the terminal voltage is less than the second preset value, controls the third switch K 43 and the fourth switch K 44 It is turned on, connecting the DC neutral point BUS_N and the AC neutral port N, thereby completing the two-stage soft start between the AC and DC neutral points BUS_N, further effectively suppressing the common-mode impact current at the moment of grid connection.

[0153] In another alternative embodiment, if Fig.13 As shown, the soft start circuit 30 includes a fourth resistive element Z 44 , the fifth switch K 45 , the sixth switch K 46 and the seventh switch K 47 ;

[0154] The fourth resistive element Z 44 and the fifth switch K 45 The sixth switch K is connected in series between the DC neutral point BUS_N and the AC neutral port N. 46 and the seventh switch K 47 Connected in series between the DC neutral point BUS_N and the AC neutral port N.

[0155] Based on the structure of the soft start circuit 30, after receiving the grid connection instruction, the control circuit first obtains the first voltage of the negative DC bus BUS- to the ground PE, and then controls the fifth switch K 45 The sixth switch K is turned on. 46 and the seventh switch K 47 Keep off, the fourth resistive element Z 44 It has a preset impedance and is connected in series between the DC neutral point BUS_N and the AC neutral port N. The control circuit synchronously obtains the second voltage of the negative DC bus BUS- to the ground PE, and determines the insulation impedance of the DC side of the inverter circuit 10 to the ground PE based on the first voltage, the second voltage and the preset impedance.

[0156] At the same time, the fifth switch K 45 When conducting, the fourth resistive element Z 44 When connected in parallel with the equivalent impedance of the DC neutral point BUS_N relative to PE, the impedance after parallel connection becomes smaller, and the common-mode voltage difference between the DC neutral point BUS_N and the AC neutral port N is also reduced accordingly, thereby effectively suppressing the size of the common-mode impulse current, avoiding damage to devices due to the common-mode impulse current, and avoiding false protection of the leakage protection.

[0157] During this process, the terminal voltage of the soft start circuit 30 changes from large to small, and the common mode impact current gradually decreases. The control circuit monitors the terminal voltage of the soft start circuit 30, and when the magnitude or change rate of the terminal voltage is less than a preset value, the voltage between the DC neutral point BUS_N and the AC neutral port N is close to equal, and the control circuit controls the sixth switch K 46 and the seventh switch K 47 It is turned on, connecting the DC neutral point BUS_N and the AC neutral port N, thereby completing the soft start between the AC and DC neutral points BUS_N, and effectively suppressing the common-mode impact current at the moment of grid connection.

[0158] Each resistive element may adopt a corresponding component. In an optional embodiment, each resistive element includes a resistor, wherein the number and connection method of each resistor can be set according to requirements.

[0159] Each switch may be a switch device with controlled on / off function, such as a relay, a circuit breaker, etc.

[0160] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A control method for an inverter device, characterized in that: The inverter device includes a DC input terminal, a positive DC bus, a negative DC bus, a positive bus capacitor, a negative bus capacitor, an inverter circuit, a grid-connected switch circuit, an AC port and a soft start circuit; The positive DC bus and the negative DC bus are connected to the DC input terminal and the inverter circuit respectively, the positive bus capacitor and the negative bus capacitor are connected in series between the positive DC bus and the negative DC bus, the midpoints of the positive bus capacitor and the negative bus capacitor constitute a DC neutral point, the AC port includes an AC output port and an AC neutral port, the AC neutral port is grounded, the grid-connected switch circuit is connected in series between the output terminal of the inverter circuit and the AC output port, and the soft start circuit is connected between the DC neutral point and the AC neutral port; The control method of the inverter device comprises: Switching to the grid-connected mode based on the grid-connected instruction, and acquiring a first voltage of the negative DC bus to the ground; Output a first switch signal to trigger the soft start circuit to switch to an impedance circuit with a preset impedance, and read a second voltage of the negative DC bus to ground, and determine the insulation impedance of the DC side of the inverter circuit to ground based on the first voltage, the second voltage and the preset impedance; The terminal voltage of the soft start circuit is read, and when the rate of change or voltage value of the terminal voltage is less than a preset value, a second switch signal is output to trigger the soft start circuit to turn on, and directly connect the DC neutral point and the AC neutral port, and a grid-connected control signal is output to control the grid-connected switch circuit to turn on.

2. An inverter device, characterized in that: include: DC input terminal; A positive DC bus and a negative DC bus, wherein the positive DC bus and the negative DC bus are connected to the DC input terminal; A positive bus capacitor and a negative bus capacitor, wherein the positive bus capacitor and the negative bus capacitor are connected in series between the positive DC bus and the negative DC bus, and the midpoints of the positive bus capacitor and the negative bus capacitor constitute a DC neutral point; An AC port, the AC port comprising an AC output port and an AC neutral port, the AC neutral port being grounded; An inverter circuit, wherein an input end of the inverter circuit is respectively connected to the positive DC bus, the negative DC bus and the DC neutral point, and an output end of the inverter circuit is used to output an AC power supply; A grid-connected switch circuit, connected in series between the output end of the inverter circuit and the AC output port; A soft start circuit connected between the DC neutral point and the AC neutral port; The inverter device further includes a control circuit, and the control circuit is used to implement the control method of the inverter device according to claim 1.

3. The inverter device according to claim 2, characterized in that: The inverter device also includes: A leakage protection switch, wherein the input end of the leakage protection switch is respectively connected to the output end of the grid-connected switch circuit and the output end of the soft start circuit, and the output end of the leakage protection switch is connected to the AC port. The leakage protection switch is used to monitor the leakage current between the grid-connected switch circuit, the soft start circuit and the AC port respectively, and is shut down when the leakage current is greater than a preset current.

4. The inverter device according to claim 3, characterized in that: The leakage protection switch and the inverter circuit are arranged separately.

5. The inverter device according to claim 3, characterized in that: The inverter device also includes: A filter circuit is connected in series between the output end of the inverter circuit and the grid-connected switch circuit, and the filter circuit is used to filter the AC power output by the inverter circuit.

6. The inverter device according to claim 5, characterized in that: The inverter circuit is a three-phase inverter circuit; The grid-connected switch circuit includes three grid-connected switches, and the three grid-connected switches are respectively connected in series between the three-phase output end of the inverter circuit and the AC output port.

7. The inverter device according to claim 5, characterized in that: The inverter circuit is a split-phase inverter circuit; The grid-connected switch circuit includes two grid-connected switches, and the two grid-connected switches are respectively connected in series between the two-phase output ends of the inverter circuit and the AC output port.

8. The inverter device according to claim 2, characterized in that: The inverter device also includes: Multi-way grounding capacitors; Each output terminal of the inverter circuit and the DC neutral point are grounded through a grounding capacitor respectively.

9. The inverter device according to claim 8, characterized in that: The grounding capacitor is a parasitic capacitor.

10. The inverter device according to claim 3, characterized in that: The soft start circuit includes a first resistive element, a first switch and a second switch; The first resistive element is connected in parallel with the first switch, and the parallel circuit of the first resistive element and the first switch and the second switch are connected in series and are connected in series between the DC neutral point and the AC neutral port.

11. The inverter device according to claim 3, characterized in that: The soft start circuit includes a second resistive element, a third resistive element, a third switch and a fourth switch; The second resistive element is connected in parallel with the third switch, the third resistive element is connected in parallel with the fourth switch, the parallel circuit of the second resistive element and the third switch and the parallel circuit of the third resistive element and the fourth switch are connected in series and are connected in series between the DC neutral point and the AC neutral port.

12. The inverter device according to claim 3, characterized in that: The soft start circuit includes a fourth resistive element, a fifth switch, a sixth switch and a seventh switch; The fourth resistive element and the fifth switch are connected in series between the DC neutral point and the AC neutral port, and the sixth switch and the seventh switch are connected in series between the DC neutral point and the AC neutral port.

13. The inverter device according to any one of claims 10 to 12, characterized in that: Each resistive element includes a resistor.

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