阅读说明：本技术 一种共地型双输出开关电容型多电平逆变器 (Common-ground type double-output switch capacitance type multi-level inverter ) 是由 姚佳 许志远 林通 郑晓枫 张俊芳 于 2021-09-03 设计创作，主要内容包括：本发明公开了一种共地双输出开关电容型多电平逆变器,包括电源输入端、开关电容模块A、开关电容模块B、H桥单元以及两个交流输出端V-(o1)、V-(o2),其中H桥结构包括开关管S-(1)、S-(2)、S-(3)、S-(4),分别为第一桥臂的上桥臂开关管、第一桥臂的下桥臂开关管、第二桥臂的上桥臂开关管、第二桥臂的下桥臂开关管；开关电容模块A、B的输出端负极连接共地点,并且和交流输出负载z1、z2的共地点相连,形成共地端；开关电容模块A的输出端正极连接于开关管S-(1)、S-(3)的阴极；开关电容模块B的输出端正极连接于开关管S-(2)、S-(4)的阳极。本发明具有输入输出电压共地、输入电流连续、高增益的优点,系统共有两个输出端口,平均每个输出端口所采用器件数量比同类拓扑少,且输出波形的总谐波畸变率较低。(The invention discloses a common-ground dual-output switch capacitor type multi-level inverter which comprises a power input end, a switch capacitor module A, a switch capacitor module B, H bridge unit and two alternating current output ends V o1 、V o2 Wherein the H-bridge structure comprises a switch tube S 1 、S 2 、S 3 、S 4 The bridge arm switching tubes are respectively an upper bridge arm switching tube of a first bridge arm, a lower bridge arm switching tube of the first bridge arm, an upper bridge arm switching tube of a second bridge arm and a lower bridge arm switching tube of the second bridge arm; the negative electrode of the output end of the switched capacitor module A, B is connected with a common ground point and is connected with the common ground point of the alternating current output loads z1 and z2 to form a common ground end; the positive electrode of the output end of the switched capacitor module A is connected with the switchPipe S 1 、S 3 A cathode of (a); the positive electrode of the output end of the switched capacitor module B is connected with the switching tube S 2 、S 4 Of (2) an anode. The invention has the advantages of common input and output voltage, continuous input current and high gain, the system has two output ports, the number of devices adopted by each output port is smaller than that of similar topology, and the total harmonic distortion of output waveforms is lower.)

1. The common-ground dual-output switched capacitor type multi-level inverter is characterized by comprising a power input end, a switched capacitor module A, a switched capacitor module B, H bridge unit and two alternating current output ends V_o1、V_o2The H-bridge structure comprises a switch tube S₁Switch tube S₂Switch tube S₃Switch tube S₄The upper bridge arm switching tube of the first bridge arm is S₁The lower bridge arm switching tube of the first bridge arm is S₂The upper bridge arm switching tube of the second bridge arm is S₃The lower bridge arm switching tube of the second bridge arm is S₄(ii) a The midpoint of the first bridge arm is an alternating current output end V_o1The midpoint of the second bridge arm is an alternating current output end V_o2Wherein:

the power input end is connected with the anode of an input power Vin, and the cathode of the input power Vin is connected with a common place;

the input ends of the switched capacitor module A and the switched capacitor module B are connected with the power supply input end, the negative ends of the output ends of the switched capacitor module A and the switched capacitor module B are connected with a common ground point, and are connected with the common ground point of an alternating current output load z1 and a load z2 to form a common ground end; the positive electrode of the output end of the switched capacitor module A is connected with the switching tube S₁Cathode and switching tube S₃A cathode of (a); the positive electrode of the output end of the switched capacitor module B is connected to the switching tube S₂Anode and switching tube S₄The anode of (1);

the switch tube S₁Is connected to the switching tube S₃The cathode of the switch capacitor module A, the output positive end of the switch capacitor module A and the switch tube S₁Is connected to the switching tube S₂The non-common terminal of the ac output load z 1; the switch tube S₂Is connected to the switching tube S₄The anode of the switch capacitor module B and the output positive end of the switch capacitor module B; the switch tube S₃Is connected to the switching tube S₄The non-common terminal of the ac output load z 2;

the two alternating current output ends V_o1、V_o2The other ends of the load z1 and the load z2, the alternating current load z1 and the alternating current load z2 are connected to the common ground respectively.

2. A common-ground dual-output switched capacitor type multilevel inverter according to claim 1, wherein the switching tube S₁Switch tube S₂Switch tube S₃And a switching tube S₄A MOSFET or an IGBT is used.

3. The common ground dual output switched capacitor multi-level inverter of claim 1, wherein the switched capacitor module a and the switched capacitor module B use the same type of switched capacitor topology or different types of switched capacitor topologies.

4. The common-ground dual-output switched-capacitor multi-level inverter of claim 1, wherein the switched-capacitor module A and the switched-capacitor module B employ a series-parallel, cascaded, stepped, or Fibonacci switched-capacitor topology.

5. The common ground dual-output switched capacitor multi-level inverter of claim 1, wherein the switching devices of the switched capacitor modules A and B are MOSFETs or IGBTs.

6. The common-ground dual-output switched capacitor type multilevel inverter according to claim 1, wherein the inverter H-bridge unit has the following operation modes:

working mode 1: controlling a switching device S₁、S₄Conducting and controlling the switch tube S₂、S₃Turning off;

and (3) working mode 2: controlling a switching device S₁、S₃Conducting and controlling the switch tube S₂、S₄Turning off;

working mode 3: controlling a switching device S₂、S₃Conducting and controlling the switch tube S₁、S₄Turning off;

the working mode 4 is as follows: controlling a switching device S₂、S₄Conducting and controlling the switch tube S₁、S₃And (6) turning off.

7. The common-ground dual-output switched capacitor multi-level inverter according to claim 1, wherein the switched capacitor module A and the switched capacitor module B respectively generate stepped sine half waves of direct current, and the alternating current output terminals V_o1、V_o2The positive half-wave of (A) is generated by a switched capacitor module B, and an alternating current output end V_o1、V_o2Is generated by the switched capacitor module a.

8. The common-ground dual-output switched-capacitor multi-level inverter of claim 7, wherein the output voltage V of the switched-capacitor module A_AAnd the output voltage V of the switched capacitor module B_BThe same, the output voltage frequency f of the switched capacitor module A_AAnd the output voltage frequency f of the switched capacitor module B_BThe same; the AC output end V_o1、V_o2Are the same and are 180 degrees out of phase.

9. A control method of a common-ground dual-output switching capacitance type multi-level inverter, characterized in that the multi-level inverter control is realized based on the common-ground dual-output switching capacitance type multi-level inverter of any one of claims 1 to 8.

10. A method for controlling a common-ground dual-output switched capacitor multi-level inverter as claimed in claim 9, wherein the multi-level inverter control can be implemented but not limited to using LS-SPWM, SHE, NLC.

Technical Field

The invention belongs to the field of multi-level inverters and new energy distributed grid-connected power generation, and particularly relates to a common-ground double-output switch capacitor type multi-level inverter and a modulation method thereof.

Background

The current photovoltaic inverter has the following problems: 1. leakage current exists when connected to the grid; 2. there is no boosting effect. The existence of leakage current causes a potential safety hazard, and the reason for this is that the input and output are not grounded in common, and for this problem, a common-ground type inverter has been proposed. The absence of a boost characteristic results in a large output voltage THD and therefore requires a large filter resulting in low efficiency. The boost effect of the switch capacitor type inverter is good, the adjustment is easy, and the switch capacitor type inverter is commonly used in a multi-level topological structure. Therefore, the invention provides a common-ground dual-output switch capacitor type multi-level inverter and a modulation method thereof.

Disclosure of Invention

The invention aims to provide a common-ground dual-output switched capacitor type multi-level inverter and a modulation method thereof.

The technical scheme for realizing the purpose of the invention is as follows: a common-ground dual-output switch capacitor type multi-level inverter comprises a power input end, a switch capacitor module A, a switch capacitor module B, H bridge unit and two alternating current output ends V_o1、V_o2The H-bridge structure comprises a switch tube S₁Switch tube S₂Switch tube S₃Switch tube S₄The upper bridge arm switching tube of the first bridge arm is S₁The lower bridge arm switching tube of the first bridge arm is S₂The upper bridge arm switching tube of the second bridge arm is S₃The lower bridge arm switching tube of the second bridge arm is S₄(ii) a The midpoint of the first bridge arm is an alternating current output end V_o1The midpoint of the second bridge arm is an alternating current output end V_o2Wherein:

the power input end is connected with the anode of an input power Vin, and the cathode of the input power Vin is connected with a common place;

the input ends of the switched capacitor module A and the switched capacitor module B are connected with the power supply input end, the negative ends of the output ends of the switched capacitor module A and the switched capacitor module B are connected with a common ground point, and are connected with the common ground point of an alternating current output load z1 and a load z2 to form a common ground end; the positive electrode of the output end of the switched capacitor module A is connected with the switching tube S₁Cathode and switching tube S₃A cathode of (a); the positive electrode of the output end of the switched capacitor module B is connected to the switching tube S₂Anode and switching tube S₄The anode of (1);

the switch tube S₁Is connected to the switching tube S₃The cathode of the switch capacitor module A, the output positive end of the switch capacitor module A and the switch tube S₁Is connected to the switching tube S₂The non-common terminal of the ac output load z 1; the switch tube S₂Is connected to the switching tube S₄The anode of the switch capacitor module B and the output positive end of the switch capacitor module B; the switch tube S₃Is connected to the switching tube S₄The non-common terminal of the ac output load z 2;

the two alternating current output ends V_o1、V_o2The other ends of the load z1 and the load z2, the alternating current load z1 and the alternating current load z2 are connected to the common ground respectively.

Further, the switch tube S₁Switch tube S₂Switch tube S₃And a switching tube S₄A MOSFET or an IGBT is used.

Further, the switched capacitor module a and the switched capacitor module B use the same type of switched capacitor topology or different types of switched capacitor topologies.

Further, the switched capacitor module a and the switched capacitor module B adopt a series-parallel type, a cascade type, a step type or a fibonacci type switched capacitor topology.

Further, the switching devices used by the switched capacitor module a and the switched capacitor module B are MOSFETs or IGBTs.

Further, the operation mode of the inverter H-bridge unit is as follows:

working mode 1: controlling a switching device S₁、S₄Conducting and controlling the switch tube S₂、S₃Turning off;

and (3) working mode 2: controlling a switching device S₁、S₃Conducting and controlling the switch tube S₂、S₄Turning off;

working mode 3: controlling a switching device S₂、S₃Conducting and controlling the switch tube S₁、S₄Turning off;

the working mode 4 is as follows: controlling a switching device S₂、S₄Conducting and controlling the switch tube S₁、S₃And (6) turning off.

Further, the switched capacitor module a and the switched capacitor module B respectively generate a stepped sine half-wave of direct current, and the alternating current output end V_o1、V_o2The positive half-wave of (A) is generated by a switched capacitor module B, and an alternating current output end V_o1、V_o2Is generated by the switched capacitor module a.

Further, the output voltage V of the switched capacitor module A_AAnd the output voltage V of the switched capacitor module B_BThe same, the output voltage frequency f of the switched capacitor module A_AAnd the output voltage frequency f of the switched capacitor module B_BThe same; the AC output end V_o1、V_o2Are the same and are 180 degrees out of phase.

A control method of a common-ground dual-output switch capacitor type multi-level inverter is based on the common-ground dual-output switch capacitor type multi-level inverter, and multi-level inverter control is achieved.

Further, the multi-level inverter control is realized by using LS-SPWM, SHE or NLC.

Compared with the prior art, the invention has the remarkable advantages that: 1) the input and the load are grounded, so that the system leakage current can be inhibited; 2) a permanent non-zero input current; 3) compared with the common ground SC inverter of the same type, the common ground SC inverter has higher boosting multiple under the condition of the same number of devices; 4) two independently controllable output ac voltage sources (same amplitude, opposite phase) are provided, and the two loads need not be symmetrical and do not affect each other.

Drawings

Fig. 1 is a circuit diagram of an inverter in an embodiment of the invention;

FIG. 2 is a circuit diagram of an inverter using a series-parallel topology in an embodiment of the present invention;

fig. 3 is a schematic diagram of an operating current path of an inverter operating mode 1 according to an embodiment of the present invention;

fig. 4 is a schematic diagram of an operating current path of an inverter operating mode 2 according to an embodiment of the present invention;

fig. 5 is a schematic diagram of an operating current path of the inverter operating mode 3 according to the embodiment of the present invention;

fig. 6 is a schematic diagram of an operating current path of the inverter operating mode 4 according to the embodiment of the present invention;

fig. 7 is a schematic diagram of an operating current path of the inverter operating mode 5 in the embodiment of the invention;

fig. 8 is a schematic diagram of an operating current path of the inverter operating mode 6 according to the embodiment of the present invention;

fig. 9 is a schematic diagram of an operating current path of the inverter operating mode 7 according to the embodiment of the present invention;

fig. 10 is a schematic diagram of an operating current path of the inverter operating mode 8 according to the embodiment of the present invention;

fig. 11 is a schematic diagram of an operating current path of the inverter operating mode 9 according to the embodiment of the present invention;

FIG. 12 is a waveform diagram between input and output ground in an embodiment of the present invention;

fig. 13 is a graph of the output voltage waveform of the inverter in the embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

As shown in FIG. 1, a common-ground dual-output switched capacitor type multi-level inverterThe device comprises a power input end, a switched capacitor module A, a switched capacitor module B, H bridge unit and two AC output ends V_o1、V_o2。

The H-bridge unit comprises a switch tube S₁、S₂、S₃、S₄The switching device can be, but is not limited to, a controllable switching device such as a MOSFET, an IGBT, etc., and is defined as follows: one side of the current flowing into the device is an anode and one side of the current flowing out of the device is a cathode.

The upper bridge arm switching tube of the first bridge arm is S₁The lower bridge arm switching tube of the first bridge arm is S₂The upper bridge arm switching tube of the second bridge arm is S₃The lower bridge arm switching tube of the second bridge arm is S₄. The midpoint of the first bridge arm is an alternating current output V_o1The midpoint of the second bridge arm is an alternating current output V_o2Is not common to ground. The switch tube S₁Is connected to the switching tube S₃The cathode of the switch capacitor module A, the output positive end of the switch capacitor module A and the switch tube S₁Is connected to the switching tube S₂The non-common ground of the ac output load z1, the switching tube S₂Is connected to the switching tube S₄The anode of the switch capacitor module B, and the output positive end of the switch capacitor module B, and the switch tube S₃Is connected to the switching tube S₄And the non-common terminal of the ac output load z 2.

The switched capacitor module a and the switched capacitor module B may use the same type of switched capacitor topology, or may use different types of switched capacitor topologies, and the structure may be, but is not limited to, a series-parallel type, a cascade type, a Ladder type (Ladder), a fibonacci type, or other switched capacitor topologies. The switching devices used in the switched capacitor module a and the switched capacitor module B may be, but are not limited to, MOSFETs or IGBTs.

The input end of the switched capacitor module A is connected with the power input end, and the power input end is connected with an input power supply V_inThe positive pole of the output end of the switch capacitor module A is connected with the switch tube S₁Cathode and switching tube S₃The cathode of the switched capacitor module a is connected to the common ground of the load z1 and the load z 2. Switched capacitor moduleThe input end of B is connected with the input end of a power supply, and the positive electrode of the output end of the switched capacitor module B is connected with the switching tube S₂Anode and switching tube S₄The cathode of the output terminal of the switched capacitor module B is connected to the common ground of the load z1 and the load z 2.

The two alternating current output ends V_o1、V_o2The other ends of the load z1 and the load z2, the AC load z1 and the AC load z2 are connected to the same ground respectively, and the input power supply V is connected_inThe negative electrode of (1).

The working principle and the modulation process of the common-ground dual-output switched capacitor type multi-level inverter are explained through the analysis of the H-bridge unit and the switched capacitor module.

In the common-ground dual-output switched capacitor type multi-level inverter, the H-bridge unit has four working modes:

working mode 1: controlling a switching device S₁、S₄Conducting and controlling the switch tube S₂、S₃Turning off;

and (3) working mode 2: controlling a switching device S₁、S₃Conducting and controlling the switch tube S₂、S₄Turning off;

working mode 3: controlling a switching device S₂、S₃Conducting and controlling the switch tube S₁、S₄Turning off;

the working mode 4 is as follows: controlling a switching device S₂、S₄Conducting and controlling the switch tube S₁、S₃And (6) turning off.

Through the four working modes, two groups of alternating current output can be realized.

In the common-ground double-output switched capacitor type multi-level inverter, the switched capacitor module A and the switched capacitor module B respectively generate a step-shaped sine half-wave of direct current, wherein a waveform generated by the switched capacitor module A is used as an alternating current output end V_o1、V_o2The negative half wave of (2), the waveform generated by the switched capacitor module B as the AC output end V_o1、V_o2The positive half wave of (a). Output voltage V of switched capacitor module A_AAnd the output voltage V of the switched capacitor module B_BThe same, the output voltage frequency f of the switched capacitor module A_AAnd the output voltage frequency f of the switched capacitor module B_BThe same is true. Output voltage V_o1And V_o2Have the same effective value and have a phase difference of 180 degrees, and the frequency f of the output voltage_OIs half of the output voltage frequency of the switched capacitor module A and the switched capacitor module B.

The modulation scheme used may be, but is not limited to: LS-SPWM, SHE, NLC and other multi-level inverter control modes.

In conclusion, the invention has the characteristics of multi-level output, high gain, common ground structure and multi-path output, eliminates the leakage current of output and input, and realizes lower voltage harmonic wave and better electric energy quality on the alternating current side. The invention can be used in DC-AC converters of electric vehicles, photovoltaic grid-connected power generation and distributed power generation systems for researching fire and heat in recent years.

Examples

To verify the validity of the inventive scheme, the following simulation experiment was performed.

In this embodiment, the input voltage is 40V, the two groups of loads are both 60 Ω, the output frequency is 60HZ, and the output power is 400W. Capacitor C_L1＝C_L2＝C_L3＝C_L44700 μ F, capacitance C_R1＝C_R2＝C_R34700 μ F. The switching devices used are MOSFETs.

As shown in fig. 2, the switched capacitor module a and the switched capacitor module B are connected in series-parallel, and the positive electrode of the dc input power Vin is connected to S_L12、S_L22、S_L32、S_L42And S_R13、S_R23、S_R33A source electrode of (a); DC input voltage source V_inIs connected to S_L13、S_L23、S_L33、S_L43Drain electrode of (1), S_R12、S_R22、S_R32Source and S of_L11A source electrode of (a); capacitor C_L1、C_L2、C_L3、C_L4Is connected to S_L12、S_L22、S_L32、S_L42Source and S of_L11、S_L21、S_L31、S_L41A drain electrode of (1); capacitor C_L1、C_L2、C_L3、C_L4Is connected to S_L11、S_L21、S_L31、S_L41Source and S of_L13、S_L23、S_L33、S_L43A source electrode of (a); capacitor C_R1、C_R2、C_R3Is connected to S_R11、S_R21、S_R31And S_R13、S_R23、S_R33A drain electrode of (1); capacitor C_R1、C_R2、C_R3Is connected to S_R11、S_R21、S_R31Source and S of_L12、S_L22、S_L32、S_L42Of the substrate.

The H-bridge unit comprises a switch tube S₁Switch tube S₂Switch tube S₃Switch tube S₄Said switch tube S₁Is connected to the switching tube S₃Source electrode of the switch capacitor module A, output positive terminal of the switch capacitor module A, and switch tube S₁Is connected to the switching tube S₂The source of the ac output load z1, the switching tube S₂Is connected to the switching tube S₄The drain electrode of the switching capacitor module B, the output positive end of the switching capacitor module B, and the switching tube S₃Is connected to the switching tube S₄The non-common terminal of the ac output load z 2;

the output end of the inverter comprises two alternating current output ends which are respectively connected with a load z1 and a load z2, the alternating current load z1 and the alternating current load z2 are connected with the common ground, the common ground end of the load z1 and the load z2 is connected with the negative ends of the switched capacitor module A and the switched capacitor module B, and the non-common ground end of the load z1 is connected with the switching tube S₁Drain electrode of (1), and switching tube S₂The non-common ground terminal of the load z2 is connected to the switch tube S₃Drain electrode of (1), and switching tube S₄Of the substrate.

Based on the series-parallel structure, the inverter can make two paths of loads obtain the following levels by the series-parallel conversion of the power supply and the capacitor under the condition of using a small number of devices:

V_o1:0、±V_in、±2V_in、±3V_in、±4V_in；

V_o2:0、±V_in、±2V_in、±3V_in、±4V_in；

fig. 3 to 11 are working current paths of nine working modes of the inverter, respectively, in which a charging circuit in the diagram is analyzed in the working modes, two different dotted lines respectively represent discharging circuits of the switched capacitor module a and the switched capacitor module B, a virtual device represents that the device does not work, and the working modes of the inverter are as follows:

working mode 1: controlling a switching device S_L11、S_L21、S_L31、S_L41、S_R11、S_R21、S_R31、S₁、S₄And conducting to control the other switching devices to be switched off. Capacitor C_L1、C_L2、C_L3、C_L4Discharging in series to load z1, source V_inAnd a capacitor C_R1、C_R2、C_R3Series discharge to load z2, the output of the inverter is: v_o1＝-4V_in，V_o2＝4V_inThe operating current path is shown in fig. 3.

And (3) working mode 2: controlling a switching device S_L12、S_L13、S_L21、S_L31、S_L41、S_R12、S_R13、S_R21、S_R31、S₁、S₄And conducting to control the other switching devices to be switched off. Power supply V_inIs a capacitor C_L1、C_R1Charging, capacitance C_L2、C_L3、C_L4Discharging in series to load z1, source V_inAnd a capacitor C_R2、C_R3Series discharge to load z2, the output of the inverter is: v_o1＝-3V_in，V_o2＝3V_inThe operating current path is shown in fig. 4.

Working mode 3: controlling a switching device S_L12、S_L13、S_L22、S_L23、S_L31、S_L41、S_R12、S_R13、S_R22、S_R23、S_R31、S₁、S₄Conducting and controlling other switchesThe element is turned off. Power supply V_inIs a capacitor C_L1、C_L2、C_R1、C_R2Charging, capacitance C_L3、C_L4Discharging in series to load z1, source V_inAnd a capacitor C_R3Series discharge to load z2, the output of the inverter is: v_o1＝-2V_in，V_o2＝2V_inThe operating current path is shown in fig. 5.

The working mode 4 is as follows: controlling a switching device S_L12、S_L13、S_L22、S_L23、S_L32、S_L33、S_L41、S_R12、S_R13、S_R22、S_R23、S_R32、S_R33、S₁、S₄And conducting to control the other switching devices to be switched off. Power supply V_inIs a capacitor C_L1、C_L2、C_L3、C_R1、C_R2、C_R3Charging, capacitance C_L4Discharging to load z1, power supply V_inDischarge to load z2, the output of the inverter is: v_o1＝-V_in，V_o2＝V_inThe operating current path is shown in fig. 6.

Working mode 5: controlling a switching device S_L12、S_L13、S_L22、S_L23、S_L32、S_L33、S_L42、S_L43、S_R12、S_R13、S_R22、S_R23、S_R32、S_R33、S₁、S₃And conducting to control the other switching devices to be switched off. Power supply V_inIs a capacitor C_L1、C_L2、C_L3、C_L4、C_R1、C_R2、C_R3The power is charged, and the output of the inverter is as follows: v_o1＝0，V_o2The operating current path is shown in fig. 7 at 0.

The working mode 6 is as follows: controlling a switching device S_L12、S_L13、S_L22、S_L23、S_L32、S_L33、S_L41、S_R12、S_R13、S_R22、S_R23、S_R32、S_R33、S₂、S₃And conducting to control the other switching devices to be switched off. Power supply V_inIs a capacitor C_L1、C_L2、C_L3、C_R1、C_R2、C_R3Charging, capacitance C_L4Discharging to load z2, power supply V_inDischarge to load z1, the output of the inverter is: v_o1＝V_in，V_o2＝-V_inThe operating current path is shown in fig. 8.

The working mode 7 is as follows: controlling a switching device S_L12、S_L13、S_L22、S_L23、S_L31、S_L41、S_R12、S_R13、S_R22、S_R23、S_R31、S₂、S₃And conducting to control the other switching devices to be switched off. Power supply V_inIs a capacitor C_L1、C_L2、C_R1、C_R2Charging, capacitance C_L3、C_L4Discharging in series to load z2, source V_inAnd a capacitor C_R3Series discharge to load z1, the output of the inverter is: v_o1＝2V_in，V_o2＝-2V_inThe operating current path is shown in fig. 9.

The working mode 8 is as follows: controlling a switching device S_L12、S_L13、S_L21、S_L31、S_L41、S_R12、S_R13、S_R21、S_R31、S₂、S₃And conducting to control the other switching devices to be switched off. Power supply V_inIs a capacitor C_L1、C_R1Charging, capacitance C_L2、C_L3、C_L4Discharging in series to load z2, source V_inAnd a capacitor C_R2、C_R3Series discharge to load z1, the output of the inverter is: v_o1＝3V_in，V_o2＝-3V_inThe operating current path is shown in fig. 10.

The working mode 9 is as follows: controlling a switching device S_L11、S_L21、S_L31、S_L41、S_R11、S_R21、S_R31、S₂、S₃Conducting to control the other switch devices to be turned off. Capacitor C_L1、C_L2、C_L3、C_L4Discharging in series to load z2, source V_inAnd a capacitor C_R1、C_R2、C_R3Series discharge to load z1, the output of the inverter is: v_o1＝4V_in，V_o2＝-4V_inThe operating current path is shown in fig. 11.

The following results were obtained using PSIM simulation. Fig. 12 is a waveform between an input voltage ground and an output voltage ground, the voltages shown as zero, verifying the common ground nature of the topology. Fig. 13 shows an output voltage waveform, two output phases are 180 degrees apart, and the root mean square values are the same, which accords with theoretical analysis.

The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.