WO2017049924A1 - Multi-level inverter and capacitor charging method for circuit employing same - Google Patents

Abstract

Provided are a multi-level inverter and a capacitor charging method for a circuit employing the same. An inverter unit and a flying capacitor unit pre-charge, via different conduction combinations, a flying capacitor according to a driving signal for capacitor pre-charging outputted by a controller, respectively. Appropriate current paths can be selected to pre-charge the flying capacitor according to different driving signals for pre-charging without incurring additional hardware costs, thereby solving a problem in which existing flying capacitors require additional hardware for pre-charging.

Description

Multi-level inverter and capacitor charging method thereof

This application claims priority to Chinese Patent Application No. 201510612968.4, entitled "Capacitor Charging Method for Multi-Level Inverter and Its Application Circuit", filed on September 23, 2015, The entire contents are incorporated herein by reference.

Technical field

The invention relates to the field of photovoltaic new energy technologies, in particular to a multi-level inverter and a capacitor charging method thereof.

Background technique

The multi-level inverter topology has the advantages of small output harmonics, fast dynamic response, good electromagnetic compatibility, light weight, small size and high efficiency of the photovoltaic inverter, so it is more and more valued by the photovoltaic industry. However, the necessary condition for this type of topology to work properly is that the voltage of the floating capacitor in the topology needs to reach a certain value and remain stable during operation, which requires the PV inverter of this type of topology to be able to achieve suspension before starting. Pre-charging of the capacitor.

However, in the prior art of multi-level solar photovoltaic power generation systems, additional hardware costs are required to enable pre-charging of the floating capacitors.

Summary of the invention

In view of this, the present invention provides a multi-level inverter and an application circuit thereof to solve the problem of requiring an additional hardware cost increase in the prior art to achieve pre-charging of a floating capacitor.

To achieve the stated object, the technical solution provided by the present application is as follows:

A capacitance charging method for a multi-level inverter is applied to a grid-connected power generation system, the grid-connected power generation system includes a DC power source, a controller, and a multi-level inverter; the multi-level inverter includes: An inverter unit and a suspension capacitor unit; the suspension capacitor unit includes: a suspension capacitor, a first switch tube, and a second switch tube; the first switch tube and the second switch tube are all connected in parallel with one diode; wherein:

a first input end of the inverter unit is connected as a first input end of the multilevel inverter to a positive end of the DC power source; and a second input end of the inverter unit is used as the multiple power a second input end of the flat inverter is connected to a negative end of the DC power supply;

One end of the floating capacitor is connected to the first end of the first switch tube, and the connection point is connected as a first input end of the floating capacitor unit to a first output end of the inverter unit;

The other end of the suspension capacitor is connected to the second end of the second switch tube, and the connection point serves as a a second input end of the floating capacitor unit is connected to the second output end of the inverter unit;

a second end of the first switch tube is connected to a first end of the second switch tube, and a connection point is used as an output end of the multilevel inverter;

The control end of the inverter unit and the control end of the floating capacitor unit are respectively connected to respective control ends of the multilevel inverter and connected to an output end of the controller;

The method for charging a capacitor of the multilevel inverter includes:

The controller outputs a capacitor pre-charge driving signal;

The inverter unit and the floating capacitor unit respectively precharge the floating capacitor according to the capacitor pre-charge driving signal;

The controller collects and determines whether the voltage on the floating capacitor reaches a preset value;

When the controller determines that the voltage on the floating capacitor reaches the preset value, changing a duty ratio of the capacitive precharge driving signal, and controlling a voltage on the floating capacitor and the preset value The difference is less than the preset difference.

Preferably, the step of precharging the floating capacitor according to the capacitor pre-charge driving signal by the inverter unit and the floating capacitor unit respectively includes:

The inverter unit and the floating capacitor unit respectively control the energy of the DC power source side to precharge the floating capacitor through a first current path according to the capacitor precharge driving signal; wherein the first current is The path is: a first input of the inverter unit - a first output of the inverter unit - the floating capacitor - an anti-parallel diode of the second switch.

Preferably, the step of precharging the floating capacitor according to the capacitor pre-charge driving signal by the inverter unit and the floating capacitor unit respectively includes:

The inverter unit and the floating capacitor unit respectively control the energy of the grid side to precharge the suspension capacitor according to the capacitor precharge driving signal; wherein the second current path is: An anti-parallel diode of the first switching transistor - the floating capacitor - a second output of the inverter unit - a second input of the inverter unit.

Preferably, the plurality of floating capacitor units are plural, and a plurality of the floating capacitor units are sequentially connected in parallel; wherein:

a first end of the first switch tube in the first suspension capacitor unit is connected to a first output end of the inverter unit; a second end of the second switch tube in the first suspension capacitor unit is The inverter The second output of the unit is connected;

The first end of the first switch tube of the remaining ones of the floating capacitor units is connected to the second end of the first switch tube of the previous one of the floating capacitor units, and the second end of the second switch tube is adjacent to the previous one The first end of the second switch tube in the floating capacitor unit is connected;

a second end of the first switch tube in the last suspension capacitor unit is connected to a first end of the second switch tube, and a connection point is used as an output end of the multilevel inverter;

In the capacitor charging method of the multi-level inverter, the step of precharging the floating capacitor according to the capacitor pre-charging driving signal by the inverter unit and the floating capacitor unit respectively includes: The variable unit and the plurality of floating capacitor units respectively precharge each floating capacitor according to the capacitor pre-charge driving signal;

The step of the controller collecting and determining whether the voltage on the floating capacitor reaches a preset value comprises: the controller collecting and determining whether the voltages on the respective floating capacitors reach a preset value.

Preferably, the step of precharging each floating capacitor according to the capacitor pre-charge driving signal by the inverter unit and the plurality of the floating capacitor units respectively includes:

The inverter unit and the floating capacitor unit respectively control the energy of the DC power source side to perform the suspension capacitors through the third current path, the fourth current path, and the fifth current path according to the capacitor pre-charge driving signal. Precharged

The flow path of the precharge current of the floating capacitor in the first suspension capacitor unit is the third current path: flowing in from the first input end of the inverter unit, flowing through the inverse The first output end of the variable unit, after passing through the suspension capacitor, sequentially flows through the anti-parallel diodes of the second switching tube of the remaining ones of the floating capacitor units;

a flow path of a precharge current of the floating capacitor in the intermediate suspension capacitor unit is the fourth current path: flowing in from a first input end of the inverter unit, and sequentially flowing through the inverter unit The first output end and the first switch tube in the floating capacitor unit, after passing through the suspension capacitor, sequentially flow through the anti-parallel diode of the second switch tube in the later floating capacitor unit;

The flow path of the precharge current of the floating capacitor in the last suspension capacitor unit is the fifth current path: flowing in from the first input end of the inverter unit, and sequentially flowing through the inverter unit The first output end and the first switch tube in the floating capacitor unit are discharged from the anti-parallel diode of the second switch tube after passing through the suspension capacitor.

Preferably, the step of precharging each floating capacitor according to the capacitor pre-charge driving signal by the inverter unit and the plurality of the floating capacitor units respectively includes:

The inverter unit and the floating capacitor unit respectively control the energy of the grid side to precharge each of the suspension capacitors through the seventh current path, the eighth current path and the ninth current path according to the capacitor precharge driving signal;

The flow path of the precharge current of the floating capacitor in the last suspension capacitor unit is the seventh current path: flowing in the antiparallel diode of the first switch tube, flowing through the suspension capacitor Passing through the second switch tube in the floating capacitor unit and the second output end of the inverter unit in sequence, and flowing out from the second input end of the inverter unit;

a flow path of the precharge current of the floating capacitor in the middle of the floating capacitor unit is the eighth current path: flowing in an anti-parallel diode of the first switch tube in the latter floating capacitor unit, the flow After the capacitor is suspended, the second switch in the suspension capacitor unit and the second output terminal of the inverter unit are sequentially flowed out, and the second input end of the inverter unit flows out;

The flow path of the precharge current of the floating capacitor in the last suspension capacitor unit is the ninth current path: flowing from the anti-parallel diode of the first switch tube in the latter floating capacitor unit, the flow After the capacitor is suspended, the second output end of the inverter unit flows out through the second output end of the inverter unit.

A capacitor charging method for an application circuit of a multilevel inverter is applied to a grid-connected power generation system, and the grid-connected power generation system includes a DC power source, a controller, a first multilevel inverter, and a second multilevel An inverter and a third multilevel inverter; the first multilevel inverter, the second multilevel inverter, and the third multilevel inverter are all as claimed The multilevel inverter of 1; wherein:

a first input end of the first multilevel inverter, the second multilevel inverter, and the third multilevel inverter is connected to a positive end of the DC power source;

Connecting a midpoint of the first multilevel inverter, the second multilevel inverter, and the third multilevel inverter;

The second input terminals of the first multilevel inverter, the second multilevel inverter and the third multilevel inverter are connected to a negative end of the DC power supply;

The output ends of the first multilevel inverter, the second multilevel inverter, and the third multilevel inverter respectively serve as application circuits of the multilevel inverter An AC output;

The method for charging a capacitor of an application circuit of the multilevel inverter includes:

The controller outputs a capacitor pre-charge driving signal;

The inverter unit and the floating capacitor unit in the first multilevel inverter, the second multilevel inverter, and the third multilevel inverter are respectively configured according to the capacitor Precharging the driving signal to pre-charge the respective floating capacitors;

The controller collects and determines whether the voltage on each of the suspension capacitors reaches a preset value;

When the controller determines that the voltages on the respective floating capacitors reach the preset value, changing a duty ratio of the capacitor pre-charge driving signal, controlling a voltage on each of the floating capacitors and the preset The difference between the values is less than the preset difference.

Preferably, the inverter unit and the floating capacitor unit in the first multilevel inverter, the second multilevel inverter, and the third multilevel inverter are respectively configured according to The capacitor pre-charging driving signal, the step of pre-charging the respective floating capacitors includes:

The inverter unit and the floating capacitor unit in the first multilevel inverter respectively control the energy of the DC power source side to pass through the tenth current path pair according to the capacitor precharge driving signal The floating capacitor in the level inverter is precharged; wherein the tenth current path is: a first input end of the inverter unit - a first output end of the inverter unit - the suspension a capacitor - an anti-parallel diode of the second switching transistor;

The inverter unit and the floating capacitor unit in the second multilevel inverter respectively control the energy of the DC power source side through the eleventh current path pair according to the capacitor precharge driving signal The floating capacitor in the multilevel inverter is precharged; wherein the eleventh current path is: an anti-parallel diode of the first switching transistor - the floating capacitor - the first of the inverter unit Two output terminals - a third input end of the inverter unit;

The inverter unit and the floating capacitor unit in the third multilevel inverter respectively control the energy of the DC power source side through the twelfth current path pair to the third according to the capacitor precharge driving signal The floating capacitor in the multilevel inverter is precharged; wherein the twelfth current path is: an anti-parallel diode of the first switching transistor - the floating capacitor - the first of the inverter unit Two outputs - a third input of the inverter unit.

Preferably, the inverter unit and the floating capacitor unit in the first multilevel inverter, the second multilevel inverter, and the third multilevel inverter are respectively configured according to Capacitor precharge drive The moving signals, the steps of precharging the respective floating capacitors include:

The inverter unit and the floating capacitor unit in the first multilevel inverter respectively control the energy of the DC power source side through the thirteenth current path pair according to the capacitor precharge driving signal The floating capacitor in the multilevel inverter is precharged; wherein the thirteenth current path is: a second input end of the inverter unit - a first output end of the inverter unit a suspension capacitor - an anti-parallel diode of the second switching transistor;

The inverter unit and the floating capacitor unit in the second multilevel inverter respectively control the energy of the DC power source side through the fourteenth current path pair according to the capacitor precharge driving signal The floating capacitor in the multilevel inverter is precharged; wherein the fourteenth current path is: an anti-parallel diode of the first switching transistor - the floating capacitor - the first of the inverter unit Two output terminals - a third input end of the inverter unit;

The inverter unit and the floating capacitor unit in the third multilevel inverter respectively control the energy of the DC power source side through the fifteenth current path pair to the third according to the capacitor precharge driving signal The floating capacitor in the multilevel inverter is precharged; wherein the fifteenth current path is: an anti-parallel diode of the first switching transistor - the floating capacitor - the first of the inverter unit Two outputs - a third input of the inverter unit.

Preferably, the inverter unit and the floating capacitor unit in the first multilevel inverter, the second multilevel inverter, and the third multilevel inverter are respectively configured according to The capacitor pre-charging driving signal, the step of pre-charging the respective floating capacitors includes:

The inverter unit and the floating capacitor unit in the first multilevel inverter respectively control the energy of the grid side through the sixteenth current path to the first multilevel according to the capacitor precharge driving signal The floating capacitor in the inverter is precharged; wherein the sixteenth current path is: an anti-parallel diode of the first switching transistor - the floating capacitor - a second output of the inverter unit a second input of the inverter unit;

The inverter unit and the floating capacitor unit in the second multilevel inverter respectively control the energy of the grid side through the seventeenth current path to the second multilevel according to the capacitor precharge driving signal The floating capacitor in the inverter is precharged; wherein the seventeenth current path is: a first input end of the inverter unit - a first output end of the inverter unit - the floating capacitor - an anti-parallel diode of the second switching transistor;

The inverter unit and the floating capacitor unit in the third multilevel inverter respectively control the energy of the grid side through the eighteenth current path to the third multilevel according to the capacitor precharge driving signal The floating capacitor in the inverter is precharged; wherein the eighteenth current path is: a first input end of the inverter unit - a first output end of the inverter unit - the floating capacitor - an anti-parallel diode of the second switching transistor.

The capacitor charging method of the multi-level inverter provided by the present invention, the inverter unit and the floating capacitor unit respectively pre-charge a driving signal according to a capacitor outputted by the controller, so that the inverter unit And the suspension capacitor unit pre-charges the suspension capacitor through different conduction combinations, and according to the pre-charge driving signal, an appropriate current path can be selected to pre-charge the suspension capacitor, and no additional hardware cost is required. The problem is solved by solving the problem that the prior art requires additional hardware for pre-charging.

DRAWINGS

1 is a schematic structural diagram of a multilevel inverter according to an embodiment of the present invention;

2 is a flowchart of a method for charging a capacitor of a multilevel inverter and an application circuit thereof according to another embodiment of the present invention;

3 is a flow path diagram of a first precharge current for precharging a suspension capacitor according to another embodiment of the present invention;

4 is a flow path diagram of a second precharge current for precharging a suspension capacitor according to another embodiment of the present invention;

FIG. 5 is a schematic structural diagram of a second multilevel inverter according to another embodiment of the present invention; FIG.

6 is a flow path diagram of a first charging current for precharging a floating capacitor of a second multilevel inverter according to another embodiment of the present invention;

7 is a flow path diagram of a second charging current for precharging a suspension capacitor of a second multilevel inverter according to another embodiment of the present invention;

FIG. 8 is a topological view of a multilevel inverter according to another embodiment of the present invention; FIG.

FIG. 9 is another topology diagram of a multilevel inverter according to another embodiment of the present invention; FIG.

10 is a schematic diagram of application of a three-phase three-wire multi-level inverter according to an embodiment of the present invention;

11 is a flow path diagram of a first precharge current for precharging a suspension capacitor of a three-phase three-wire multi-level inverter according to an embodiment of the present invention;

12 is a flow path diagram of a first pre-charging current for precharging another suspension capacitor of a three-phase three-wire multi-level inverter according to an embodiment of the present invention;

13 is a flow path diagram of a first precharge current for precharging a third type of suspension capacitor of a three-phase three-wire multi-level inverter according to an embodiment of the present invention.

detailed description

In order to further understand the present invention, the preferred embodiments of the present invention are described in the accompanying drawings.

The present invention provides a multi-level inverter and its application circuit to solve the problem of requiring an additional hardware cost increase in the prior art to achieve pre-charging of a floating capacitor.

Specifically, the capacitor charging method of the multilevel inverter is applied to a grid-connected power generation system, and the grid-connected power generation system includes: a DC power source, a controller, and a multi-level inverter; As shown in FIG. 1 , the transformer includes: an inverter unit and a suspension capacitor unit; the suspension capacitor unit includes: a suspension capacitor C3, a first switch tube Q1 and a second switch tube Q2; and a first switch tube Q1 and a second switch Tube Q2 is connected in parallel with a diode; where:

a first input end of the inverter unit is connected as a first input end of the multi-level inverter to a positive end of the DC power source PV; a second input end of the inverter unit is used as the multi-level a second input end of the inverter is connected to a negative end of the DC power supply PV;

One end of the floating capacitor C3 is connected to the first end of the first switch tube Q1, and the connection point is connected as a first input end of the floating capacitor unit to the first output end of the inverter unit;

The other end of the floating capacitor C3 is connected to the second end of the second switch tube Q2, and the connection point is connected to the second output end of the floating capacitor unit and connected to the second output end of the inverter unit;

The second end of the first switch tube Q1 is connected to the first end of the second switch tube Q2, and the connection point is used as an output end of the multi-level inverter;

The control end of the inverter unit and the control end of the floating capacitor unit are respectively connected to respective control ends of the multilevel inverter and connected to an output end of the controller;

The voltage between the positive and negative terminals of the DC power supply PV is Udc, the voltages on the first capacitor C1 and the second capacitor C2 are Udc/2, respectively, and the voltage on the floating capacitor C3 is Udc/4.

In a specific practical application, the first switch tube Q1 and the second switch tube Q2 are connected in parallel in parallel The tube may be an additional diode or a separate body diode, which is not specifically limited herein, and is within the scope of the present application depending on the application environment.

The capacitor charging method of the multilevel inverter, as shown in FIG. 2, includes:

S101. The controller outputs a capacitor pre-charge driving signal.

S102, the inverter unit and the floating capacitor unit respectively pre-charge the floating capacitor C3 according to the capacitor pre-charge driving signal;

S103. The controller collects and determines whether a voltage on the floating capacitor C3 reaches a preset value.

S104. When the controller determines that the voltage on the floating capacitor C3 reaches the preset value, changing a duty ratio of the capacitor precharge driving signal, and controlling a voltage between the floating capacitor C3 and the preset value. The difference is less than the preset difference.

When the controller determines that the voltage on the floating capacitor C3 reaches the preset value, pre-charging of the floating capacitor C3 before the multi-level inverter is connected to the grid has been completed, but the multi-level inverse The transformer can only be connected to the grid after all the conditions for grid-connected startup are met, and the voltage on the floating capacitor C3 needs to be maintained at the preset value before all grid-connected conditions are met. Therefore, it is necessary to change the duty ratio of the capacitor precharge driving signal, and control the difference between the voltage on the floating capacitor C3 and the preset value to be less than a preset difference. In a specific application, the preset value and the preset difference may be determined according to the application environment, and are not limited herein.

In the capacitor charging method of the multi-level inverter provided by the embodiment, the inverter unit and the floating capacitor unit are pre-charged by the different conduction combinations for the floating capacitor C3 according to steps S101 and S102, according to The difference in the pre-charge drive signal can select a suitable current path for pre-charging the floating capacitor C3, and does not require an increase in additional hardware cost, solving the problem of requiring additional hardware for pre-charging in the prior art.

Specifically, step S102 includes:

The inverter unit and the floating capacitor unit respectively control the energy of the DC power source side to pre-charge the floating capacitor C3 through the first current path according to the capacitor pre-charge driving signal;

Alternatively, the inverter unit and the floating capacitor unit respectively control the energy of the grid side to pre-charge the suspension capacitor C3 through the second current path according to the capacitor pre-charge driving signal.

The first current path is as shown by the dotted line in FIG. 3, and is: the first input of the inverter unit. Inverter - the first output of the inverter unit - the anti-parallel diode of the floating capacitor C3 - the second switching transistor Q2.

The second current path is as shown by the dashed line in FIG. 4, and is: an anti-parallel diode of the first switching transistor Q1 - a floating capacitor C3 - a second output of the inverter unit - a second input of the inverter unit end.

It should be noted that the multi-level inverters shown in FIG. 1 , FIG. 3 and FIG. 4 are single-phase multi-level inverters, and in specific practical applications, the multi-level inverters The output end is connected to the power grid through an inductor, and the multi-level inverter has a ground terminal grounded, so that the multi-level inverter can form a loop through the currents in the two pre-charging modes, and finally realize Pre-charging the suspension capacitor C3.

Preferably, the capacitive charging method of the multilevel inverter can also be applied to another multilevel inverter. As shown in FIG. 5, the floating capacitor unit is plural, and the plurality of the suspensions are The capacitor units are connected in parallel; wherein:

a first end of the first switching transistor Q1 in the first floating capacitor unit is connected to a first output end of the inverter unit; a second second switching transistor Q2 in the first floating capacitor unit The end is connected to the second output end of the inverter unit;

The first end of the first switch tube Q1 of the remaining floating capacitor unit is connected to the second end of the first switch tube Q1 of the previous one of the floating capacitor units, and the second end of the second switch tube Q2 is Connected to the first end of the second switching transistor Q2 in the previous one of the floating capacitor units;

a second end of the first switching transistor Q1 of the last floating capacitor unit is connected to a first end of the second switching transistor Q2, and a connection point is used as an output end of the multilevel inverter;

In the capacitor charging method of the multi-level inverter, the step S102 includes: the inverter unit and the plurality of the floating capacitor units respectively pre-charging the suspension capacitors according to the capacitor pre-charge driving signals;

Step S103 includes: the controller collecting and determining whether the voltages on the respective floating capacitors all reach a preset value.

Specifically, the step of precharging each floating capacitor according to the capacitor pre-charge driving signal by the inverter unit and the plurality of the floating capacitor units respectively includes:

The inverter unit and the floating capacitor unit are respectively controlled according to the capacitor pre-charge driving signal The energy of the DC power supply side is precharged to each of the floating capacitors through the third current path, the fourth current path, and the fifth current path, respectively;

Alternatively, the inverter unit and the floating capacitor unit respectively control the energy of the grid side to advance the respective suspension capacitors through the seventh current path, the eighth current path, and the ninth current path according to the capacitor pre-charge driving signal. Charging.

Correspondingly, as shown by the dotted line in FIG. 6, the flow path of the precharge current of the floating capacitor C3 in the first suspension capacitor unit is the third current path: by the first input of the inverter unit The terminal flows in, flows through the first output end of the inverter unit, passes through the suspension capacitor C3, and sequentially flows through the anti-parallel diodes of the second switch tube Q2 in the remaining suspension capacitor units;

a flow path of a precharge current of the floating capacitor C3 in the middle of the floating capacitor unit is the fourth current path: flowing in from the first input end of the inverter unit, and sequentially flowing through the inverter unit The first output terminal and the first switching transistor Q1 in the floating capacitor unit, after passing through the suspension capacitor C3, sequentially flow through the anti-parallel diode of the second switching transistor Q2 in the later floating capacitor unit;

The flow path of the precharge current of the floating capacitor C3 in the last suspension capacitor unit is the fifth current path: flowing in from the first input end of the inverter unit, and sequentially flowing through the inverter unit The first output terminal and the first switching transistor Q1 in the floating capacitor unit are discharged from the anti-parallel diode of the second switching transistor Q2 after passing through the floating capacitor C3.

Alternatively, as shown by the broken line in FIG. 7, the flow path of the precharge current of the floating capacitor C3 in the last floating capacitor unit is the sixth current path: flowing in anti-parallel diode of the first switching transistor Q1 After flowing through the suspension capacitor C3, the second switching transistor Q2 in the floating capacitor unit and the second output terminal of the inverter unit are sequentially flowed out, and the second input end of the inverter unit flows out;

The flow path of the precharge current of the floating capacitor C3 in the middle of the floating capacitor unit is the seventh current path: flowing from the anti-parallel diode of the first switch tube Q1 in the latter floating capacitor unit, the flow After the capacitor C3 is suspended, the second switching transistor Q2 in the floating capacitor unit and the second output terminal of the inverter unit are sequentially discharged from the second input end of the inverter unit;

The flow path of the precharge current of the floating capacitor C3 in the last suspension capacitor unit Is the eighth current path: flowing in the anti-parallel diode of the first switching transistor Q1 in the following floating capacitor unit, flowing through the suspension capacitor C3, passing through the second output end of the inverter unit, The second input end of the inverter unit flows out.

It should be noted that the multi-level inverters shown in FIG. 5 to FIG. 7 each include a plurality of floating capacitors C3, so each floating capacitor C3 needs to be required before the multi-level inverter is put into operation. Precharge. In a specific practical application, the output end of the multilevel inverter is connected to the power grid through an inductor, and the multilevel inverter has a ground terminal grounded, thereby allowing the multilevel inverter to pass The currents in the above two pre-charging modes can form a loop, and finally realize pre-charging of each floating capacitor C3.

In a specific practical application, the inverter unit may include: a first capacitor C1, a second capacitor C2, a third switch tube Q3, a fourth switch tube Q4, and a fifth switch tube Q5, as shown in FIG. Six switch tube Q6, seventh switch tube Q7 and eighth switch tube Q8; third switch tube Q3, fourth switch tube Q4, fifth switch tube Q5, sixth switch tube Q6, seventh switch tube Q7 and eighth switch Tube Q8 is connected in reverse with a diode;

The first end of the third switch tube Q3 is connected to one end of the first capacitor C1, and the connection point is the first input end of the inverter unit;

The second end of the third switch tube Q3 is connected to the second end of the fourth switch tube Q4, and the connection point is the first output end of the inverter unit;

The first end of the fourth switch tube Q4 is connected to the first end of the fifth switch tube Q5;

The second end of the fifth switch tube Q5 is connected to the first end of the sixth switch tube Q6, the other end of the first capacitor C1, and one end of the second capacitor C2, and the connection point is the ground end of the inverter unit;

The second end of the sixth switch tube Q6 is connected to the second end of the seventh switch tube Q7;

The first end of the seventh switch tube Q7 is connected to the first end of the eighth switch tube Q8, and the connection point is the second output end of the inverter unit;

The second end of the eighth switch tube Q8 is connected to the other end of the second capacitor C2, and the connection point is the second input end of the inverter unit.

Alternatively, the inverter unit may include: a first capacitor C1, a second capacitor C2, a fourth capacitor C4, a third switch tube Q3, a fourth switch tube Q4, and a fifth switch tube Q5, as shown in FIG. Six switch tube Q6, seventh switch tube Q7 and eighth switch tube Q8; third switch tube Q3, fourth switch tube Q4, fifth switch tube Q5, sixth switch tube Q6, seventh switch tube Q7 and eighth switch tube Q8 Reverse paralleling a diode; where:

The first end of the third switch tube Q3 is connected to one end of the first capacitor C1, and the connection point is the first input end of the inverter unit;

The second end of the third switch tube Q3 is connected to the second end of the fourth switch tube Q4, and the connection point is the first output end of the inverter unit;

The first end of the fourth switch tube Q4 is connected to the first end of the fifth switch tube Q5;

The second end of the fifth switch tube Q5 is connected to the other end of the first capacitor C1 and one end of the fourth capacitor C4;

The other end of the fourth capacitor C4 is connected to one end of the second capacitor C2 and the first end of the sixth switch tube Q6;

The second end of the sixth switch tube Q6 is connected to the second end of the seventh switch tube Q7;

The first end of the seventh switch tube Q7 is connected to the first end of the eighth switch tube Q8, and the connection point is the second output end of the inverter unit;

The second end of the eighth switch tube Q8 is connected to the other end of the second capacitor, and the connection point is the second input end of the inverter unit, that is, the ground end.

The voltage between the positive and negative terminals of the DC power supply PV is Udc. The voltages on the first capacitor C1 and the second capacitor C2 in FIG. 2 are Udc/2, respectively, and the voltage on the floating capacitor C3 is Udc/4. In FIG. 5, the first capacitor C1, the second capacitor C2, and the fourth capacitor C4 are both Udc/3.

Specifically, corresponding to the flow path of the pre-charging current of the floating capacitor C3 shown in FIG. 3 or FIG. 6, in the inverter unit, only the third switching tube Q3 needs to be controlled to be turned on, and the remaining switching tubes can be at Shutdown status. The third switching transistor Q3 selects a high frequency operation, and the current (shown by a broken line) sequentially passes through the anti-parallel diodes of the third switching transistor Q3, the floating capacitor C3, and the second switching transistor Q2 (the plurality of said floating lines are also required in FIG. 6). The capacitor unit, as indicated by the dashed line, pre-charges the floating capacitor C3 through the inductor L1 and the grid forming loop.

In a specific practical application, the voltage on the floating capacitor C3 is monitored by the controller in real time, and when the voltage on the floating capacitor C3 reaches a preset value, the third switching transistor Q3 is controlled to stop working.

It is worth noting that the controller can also control the capacitance of the third switching transistor Q3. The duty cycle of the charge drive signal, which in turn controls the precharge speed of the floating capacitor C3.

Corresponding to the flow path of the precharge current of the floating capacitor C3 shown in FIG. 4 or FIG. 7 , in the inverter unit, only the eighth switch tube Q8 needs to be controlled to be turned on, and the other switch tubes can be in the off state. . The current (as indicated by the dashed line) passes through the grid, the inductor L1, the anti-parallel diode of the first switching transistor Q1, and the floating capacitor C3 (the plurality of the floating capacitor units are also shown in FIG. 7 as indicated by the dotted line) and the eighth Switching tube Q8 forms a loop to pre-charge floating capacitor C3. In a specific application, when it is detected that the voltage on the floating capacitor C3 reaches a preset value, the eighth switch tube Q8 is controlled to stop working. And the pre-charging speed of the floating capacitor C3 can be controlled by controlling the duty ratio of the capacitor pre-charging driving signal of the eighth switching transistor Q8.

In a specific practical application, each of the multi-level inverters shown in FIG. 8 and FIG. 9 may be an IGBT (Insulated Gate Bipolar Transistor) tube or a MOS tube. IGCT (Intergrated Gate Commutated Thyristors) or IEGT (Injection Enhanced Gate Transistor) or reverse-resistance IGBT anti-parallel diodes; the specific selection can be based on its application environment However, it is not specifically limited herein, and is within the scope of protection of the present application. The diodes in the reverse parallel connection of the respective switching tubes may be additional diodes or respective body diodes, which are not specifically limited herein, and are within the protection scope of the present application depending on the application environment.

It should be noted that, in a specific practical application, the specific implementation form of the inverter unit is not necessarily limited to the topology shown in FIG. 8 or FIG. 9, and may be appropriately selected according to specific conditions, as long as it can pass The controller controls the respective switching tubes in the multi-level inverter to realize pre-charging of the floating capacitor C3, so that the voltage during the normal operation can reach a certain value and remains stable, Within the scope of the protection of the present application, it will not be repeated here.

Another embodiment of the present invention further provides a capacitor charging method for an application circuit of a multilevel inverter, which is applied to a grid-connected power generation system, as shown in FIG. 10, the grid-connected power generation system includes a DC power source PV, and a control , a first multilevel inverter 201, a second multilevel inverter 202, and a third multilevel inverter 203; the first multilevel inverter 201 shown in FIG. The level inverter 203 and the third multilevel inverter 203 are the three-phase three-wire multi-level inverter topology diagram provided by the embodiment, and the first multi-level inverter 201 and the second multi-level The inverter 202 and the third multilevel inverter 203 are both shown in FIG. Multilevel inverter; where:

The first input terminals of the first multilevel inverter 201, the second multilevel inverter 202, and the third multilevel inverter 203 are all connected to the positive terminal of the DC power supply PV;

The midpoints of the first multilevel inverter 201, the second multilevel inverter 202, and the third multilevel inverter 203 are connected;

The second input terminals of the first multilevel inverter 201, the second multilevel inverter 202 and the third multilevel inverter 203 are connected to the second capacitor C2 and the negative terminal of the DC power source PV;

The outputs of the first multilevel inverter 201, the second multilevel inverter 202, and the third multilevel inverter 203 serve as three AC outputs of the application circuit of the multilevel inverter, respectively. end.

Specifically, the first multilevel inverter 201 is modulated by a first sine wave, the second multilevel inverter 202 is modulated by a second sine wave, and the third multilevel inverter 203 is third sinusoidal. Wave modulation

The phases of the first sine wave, the second sine wave, and the third sine wave are sequentially different by 120 degrees.

The capacitor charging method of the application circuit of the multilevel inverter, as shown in FIG. 2, includes:

S101. The controller outputs a capacitor pre-charge driving signal.

S102, the inverter unit and the floating capacitor unit pre-charge respective floating capacitors C3 according to the capacitor pre-charge driving signals respectively;

S103. The controller collects and determines whether a voltage on each of the floating capacitors C3 reaches a preset value.

S104. When the controller determines that the voltage on the floating capacitor C3 reaches the preset value, changing a duty ratio of the capacitor pre-charge driving signal, and controlling a voltage on the floating capacitor and the preset value. The difference between them is less than the preset difference.

Specifically, step S102 includes:

The inverter unit and the floating capacitor unit in the first multilevel inverter respectively control the energy of the DC power source side to pass through the tenth current path pair according to the capacitor precharge driving signal The floating capacitor C3 in the level inverter is precharged;

The inverter unit and the floating capacitor unit in the second multilevel inverter respectively control the energy of the DC power source side through the eleventh current path pair according to the capacitor precharge driving signal The floating capacitor C3 in the multilevel inverter is precharged;

The inverter unit and the suspension capacitor unit in the third multilevel inverter are respectively The capacitor precharges the driving signal, and controls the energy of the DC power source side to precharge the floating capacitor C3 in the third multilevel inverter through the twelfth current path.

Wherein, as indicated by the broken line in FIG. 11, the flow path of the precharge current of the floating capacitor C3 in the first multilevel inverter 201 is the tenth current path: the first input of the inverter unit End - the first output of the inverter unit - the anti-parallel diode of the floating capacitor C3 - the second switching transistor Q2;

The flow path of the precharge current of the floating capacitor C3 in the second multilevel inverter 202 is the eleventh current path: the anti-parallel diode-suspended capacitor C3 of the first switching transistor Q1 - the inverter unit a second output terminal - a third input terminal of the inverter unit;

The flow path of the precharge current of the floating capacitor C3 in the third multilevel inverter 203 is the twelfth current path: the antiparallel diode of the first switching transistor Q1 - the floating capacitor C3 - the inverter unit a second output terminal - a third input terminal of the inverter unit.

Alternatively, step S102 includes:

The inverter unit and the floating capacitor unit in the first multilevel inverter respectively control the energy of the DC power source side through the thirteenth current path pair according to the capacitor precharge driving signal The floating capacitor in the multilevel inverter is precharged;

The inverter unit and the floating capacitor unit in the second multilevel inverter respectively control the energy of the DC power source side through the fourteenth current path pair according to the capacitor precharge driving signal The floating capacitor in the multilevel inverter is precharged;

The inverter unit and the floating capacitor unit in the third multilevel inverter respectively control the energy of the DC power source side through the fifteenth current path pair to the third according to the capacitor precharge driving signal The floating capacitor in the multilevel inverter is precharged.

As shown by the broken line in FIG. 12, the flow path of the precharge current of the floating capacitor C3 in the first multilevel inverter 201 is the thirteenth current path: the second input terminal of the inverter unit - an anti-parallel diode of the first output of the inverter unit - a floating capacitor C3 - a second switching transistor Q2;

The flow path of the precharge current of the floating capacitor C3 in the second multilevel inverter 202 is the fourteenth current path: the anti-parallel diode-suspended capacitor C3 of the first switching transistor Q1 - the inverter unit a second output terminal - a third input terminal of the inverter unit;

The flow path of the precharge current of the floating capacitor C3 in the third multilevel inverter 203 is the fifteenth current path: the anti-parallel diode-suspended capacitor C3-the inverter of the first switching transistor Q1 a second output of the unit - a third input of the inverter unit.

Alternatively, step S102 includes:

The inverter unit and the floating capacitor unit in the first multilevel inverter respectively control the energy of the grid side through the sixteenth current path to the first multilevel according to the capacitor precharge driving signal The floating capacitor in the inverter is precharged;

The inverter unit and the floating capacitor unit in the second multilevel inverter respectively control the energy of the grid side through the seventeenth current path to the second multilevel according to the capacitor precharge driving signal The floating capacitor in the inverter is precharged;

The inverter unit and the floating capacitor unit in the third multilevel inverter respectively control the energy of the grid side through the eighteenth current path to the third multilevel according to the capacitor precharge driving signal The suspension capacitor in the inverter is precharged.

As indicated by the broken line in FIG. 13, the flow path of the precharge current of the floating capacitor C3 in the first multilevel inverter 201 is the sixteenth current path: the antiparallel diode of the first switching transistor Q1 - a suspension capacitor C3 - a second output end of the inverter unit - a second input end of the inverter unit;

The flow path of the precharge current of the floating capacitor C3 in the second multilevel inverter 202 is the seventeenth current path: the first input end of the inverter unit - the first of the inverter unit Output - suspension capacitor C3 - anti-parallel diode of the second switching transistor Q2;

The flow path of the precharge current of the floating capacitor C3 in the third multilevel inverter 203 is the eighteenth current path: the first input end of the inverter unit - the first of the inverter unit Output - Suspension capacitor C3 - Anti-parallel diode of the second switching transistor Q2.

The connection point O of the capacitors C11 and C21, the connection point O of the capacitors C12 and C22, and the connection point O of the capacitors C13 and C23 in FIGS. 11 to 13 are connected.

It is worth noting that, in the three-phase three-wire multi-level inverter shown in FIG. 11 to FIG. 13 , in specific practical applications, the three AC output ends of the three-phase three-wire multi-level inverter are both The inductor is connected to the grid of the three-phase system, and the other end of the grid of the three-phase system is connected. Therefore, the capacitor charging method of the application circuit of the multi-level inverter is applied to the diagrams shown in FIG. 11 to FIG. In the grid-connected power generation system, the three-phase three-wire multi-level inverter can form a loop through the currents in the above three pre-charging modes, without the connection point of the first capacitor C1 and the second capacitor C2 being grounded, and finally Pre-charging of the individual floating capacitors C3 can be achieved. But in specific practical applications, each of the pre-charge modes described The inverter units of at least two multilevel inverters are required to be turned on to ensure that the current in the three-phase three-wire multi-level inverter can form a loop, so that three suspension capacitors C3 can realize Charging; specifically, the inverter unit of the first multilevel inverter 201 in FIGS. 11 to 13 needs to be turned on, and the second multilevel inverter 202 and the third multilevel inverter 203 are The inverter unit requires at least one turn-on.

In addition, in a specific practical application, the current flow path in each multi-level inverter is not necessarily limited, as long as the current in the three-phase three-wire multi-level inverter can form a loop, and further It is sufficient to pre-charge the three floating capacitors C3, which are all within the protection scope of the present application, and will not be further described herein.

Specifically, as shown in FIG. 11 to FIG. 13 , the inverter units in the first multilevel inverter 201, the second multilevel inverter 202, and the third multilevel inverter 203 each include: Capacitors C11 and C21 (or C12 and C22, or C13 and C23), third switching transistor Q3, fourth switching transistor Q4, fifth switching transistor Q5, sixth switching transistor Q6, seventh switching transistor Q7, and eighth switch The tube Q8; the third switch tube Q3, the fourth switch tube Q4, the fifth switch tube Q5, the sixth switch tube Q6, the seventh switch tube Q7 and the eighth switch tube Q8 are all connected in parallel with one diode;

The specific connection relationship and working principle are the same as those in the foregoing embodiment, and will not be further described herein.

In addition, specific implementation forms of the inverter unit in the first multilevel inverter 201, the second multilevel inverter 202, and the third multilevel inverter 203 are not necessarily limited to FIG. 11 to The topology shown in FIG. 13 can also be appropriately selected according to the specific situation, as long as the pre-charging of each of the floating capacitors C3 can be realized by controlling the respective switching tubes in the multi-level inverter. The voltage can reach a certain value and remain stable when it is put into normal operation, which is within the protection scope of the present application, and will not be further described herein.

And the multi-level inverter is also applicable to a two-phase multi-level inverter and a three-phase four-wire multi-level inverter. The specific connection methods and working principles are not described here.

The various embodiments in the present specification are described in a progressive manner, and each embodiment focuses on differences from other embodiments, and the same similar parts between the various embodiments may be referred to each other.

The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be practiced without departing from the spirit or scope of the invention. Implemented in other embodiments. Therefore, the present invention is not to be limited to the embodiments shown herein, but the scope of the invention is to be accorded

Claims (10)

1. A capacitor charging method for a multi-level inverter, characterized in that it is applied to a grid-connected power generation system, the grid-connected power generation system includes a DC power source, a controller, and a multi-level inverter; The transformer includes: an inverter unit and a suspension capacitor unit; the suspension capacitor unit includes: a suspension capacitor, a first switch tube, and a second switch tube; the first switch tube and the second switch tube are all connected in reverse parallel Diode; where:

   a first input end of the inverter unit is connected as a first input end of the multilevel inverter to a positive end of the DC power source; and a second input end of the inverter unit is used as the multiple power a second input end of the flat inverter is connected to a negative end of the DC power supply;

   One end of the floating capacitor is connected to the first end of the first switch tube, and the connection point is connected as a first input end of the floating capacitor unit to a first output end of the inverter unit;

   The other end of the floating capacitor is connected to the second end of the second switch tube, and the connection point is connected to the second output end of the floating capacitor unit and connected to the second output end of the inverter unit;

   a second end of the first switch tube is connected to a first end of the second switch tube, and a connection point is used as an output end of the multilevel inverter;

   The control end of the inverter unit and the control end of the floating capacitor unit are respectively connected to respective control ends of the multilevel inverter and connected to an output end of the controller;

   The method for charging a capacitor of the multilevel inverter includes:

   The controller outputs a capacitor pre-charge driving signal;

   The inverter unit and the floating capacitor unit respectively precharge the floating capacitor according to the capacitor pre-charge driving signal;

   The controller collects and determines whether the voltage on the floating capacitor reaches a preset value;

   When the controller determines that the voltage on the floating capacitor reaches the preset value, changing a duty ratio of the capacitive precharge driving signal, and controlling a voltage on the floating capacitor and the preset value The difference is less than the preset difference.
2. The method of charging a capacitor of a multi-level inverter according to claim 1, wherein the inverter unit and the floating capacitor unit respectively pre-stage the floating capacitor according to the capacitor pre-charge driving signal The charging steps include:

   The inverter unit and the floating capacitor unit respectively control the energy of the DC power source side to precharge the floating capacitor through a first current path according to the capacitor precharge driving signal; wherein the first current is The path is: a first input of the inverter unit - a first output of the inverter unit - the floating capacitor - an anti-parallel diode of the second switch.
3. The method of charging a capacitor of a multi-level inverter according to claim 1, wherein the inverter unit and the floating capacitor unit respectively pre-stage the floating capacitor according to the capacitor pre-charge driving signal The charging steps include:

   The inverter unit and the floating capacitor unit respectively control the energy of the grid side to precharge the suspension capacitor according to the capacitor precharge driving signal; wherein the second current path is: An anti-parallel diode of the first switching transistor - the floating capacitor - a second output of the inverter unit - a second input of the inverter unit.
4. The method of charging a capacitor of a multi-level inverter according to claim 1, wherein the plurality of floating capacitor units are plural, and the plurality of floating capacitor units are sequentially connected in parallel; wherein:

   a first end of the first switch tube in the first suspension capacitor unit is connected to a first output end of the inverter unit; a second end of the second switch tube in the first suspension capacitor unit is The second output end of the inverter unit is connected;

   The first end of the first switch tube of the remaining ones of the floating capacitor units is connected to the second end of the first switch tube of the previous one of the floating capacitor units, and the second end of the second switch tube is adjacent to the previous one The first end of the second switch tube in the floating capacitor unit is connected;

   a second end of the first switch tube in the last suspension capacitor unit is connected to a first end of the second switch tube, and a connection point is used as an output end of the multilevel inverter;

   In the capacitor charging method of the multi-level inverter, the step of precharging the floating capacitor according to the capacitor pre-charging driving signal by the inverter unit and the floating capacitor unit respectively includes: The variable unit and the plurality of floating capacitor units respectively precharge each floating capacitor according to the capacitor pre-charge driving signal;

   The step of the controller collecting and determining whether the voltage on the floating capacitor reaches a preset value comprises: the controller collecting and determining whether the voltages on the respective floating capacitors reach a preset value.
5. The method of charging a capacitor of a multilevel inverter according to claim 4, wherein the inverter unit and the plurality of floating capacitor units are respectively according to the capacitor precharge driving signal The steps of precharging each suspension capacitor include:

   The inverter unit and the floating capacitor unit respectively control the energy of the DC power source side to perform the suspension capacitors through the third current path, the fourth current path, and the fifth current path according to the capacitor pre-charge driving signal. Precharged

   The flow path of the precharge current of the floating capacitor in the first suspension capacitor unit is the third current path: flowing in from the first input end of the inverter unit, flowing through the inverse The first output end of the variable unit, after passing through the suspension capacitor, sequentially flows through the anti-parallel diodes of the second switching tube of the remaining ones of the floating capacitor units;

   a flow path of a precharge current of the floating capacitor in the intermediate suspension capacitor unit is the fourth current path: flowing in from a first input end of the inverter unit, and sequentially flowing through the inverter unit The first output end and the first switch tube in the floating capacitor unit, after passing through the suspension capacitor, sequentially flow through the anti-parallel diode of the second switch tube in the later floating capacitor unit;

   The flow path of the precharge current of the floating capacitor in the last suspension capacitor unit is the fifth current path: flowing in from the first input end of the inverter unit, and sequentially flowing through the inverter unit The first output end and the first switch tube in the floating capacitor unit are discharged from the anti-parallel diode of the second switch tube after passing through the suspension capacitor.
6. The method of charging a capacitor of a multi-level inverter according to claim 4, wherein the inverter unit and the plurality of floating capacitor units respectively perform charging capacitors according to the capacitor pre-charge driving signals The steps to precharge include:

   The inverter unit and the floating capacitor unit respectively control the energy of the grid side to precharge each of the suspension capacitors through the seventh current path, the eighth current path and the ninth current path according to the capacitor precharge driving signal;

   The flow path of the precharge current of the floating capacitor in the last suspension capacitor unit is the seventh current path: flowing in the antiparallel diode of the first switch tube, flowing through the suspension capacitor Passing through the second switch tube in the floating capacitor unit and the second output end of the inverter unit in sequence, and flowing out from the second input end of the inverter unit;

   a flow path of the precharge current of the floating capacitor in the middle of the floating capacitor unit is the eighth current path: flowing in an anti-parallel diode of the first switch tube in the latter floating capacitor unit, the flow After suspending the capacitor, it passes through the second opening in the previously described suspension capacitor unit. And a second output end of the inverter unit is discharged from the second input end of the inverter unit;

   The flow path of the precharge current of the floating capacitor in the last suspension capacitor unit is the ninth current path: flowing from the anti-parallel diode of the first switch tube in the latter floating capacitor unit, the flow After the capacitor is suspended, the second output end of the inverter unit flows out through the second output end of the inverter unit.
7. A capacitor charging method for an application circuit of a multilevel inverter is characterized in that it is applied to a grid-connected power generation system, and the grid-connected power generation system includes a DC power source, a controller, a first multilevel inverter, and a a second multilevel inverter and a third multilevel inverter; the first multilevel inverter, the second multilevel inverter, and the third multilevel inverter A multilevel inverter as claimed in claim 1; wherein:

   a first input end of the first multilevel inverter, the second multilevel inverter, and the third multilevel inverter is connected to a positive end of the DC power source;

   Connecting a midpoint of the first multilevel inverter, the second multilevel inverter, and the third multilevel inverter;

   The second input terminals of the first multilevel inverter, the second multilevel inverter and the third multilevel inverter are connected to a negative end of the DC power supply;

   The output ends of the first multilevel inverter, the second multilevel inverter, and the third multilevel inverter respectively serve as application circuits of the multilevel inverter An AC output;

   The method for charging a capacitor of an application circuit of the multilevel inverter includes:

   The controller outputs a capacitor pre-charge driving signal;

   The inverter unit and the floating capacitor unit in the first multilevel inverter, the second multilevel inverter, and the third multilevel inverter are respectively configured according to the capacitor Precharging the driving signal to pre-charge the respective floating capacitors;

   The controller collects and determines whether the voltage on each of the suspension capacitors reaches a preset value;

   When the controller determines that the voltages on the respective floating capacitors reach the preset value, changing a duty ratio of the capacitor pre-charge driving signal, controlling a voltage on each of the floating capacitors and the preset The difference between the values is less than the preset difference.
8. The method of charging a capacitor of an application circuit of a multilevel inverter according to claim 7, wherein said first multilevel inverter, said second multilevel inverter, and said first Three levels The step of precharging the respective floating capacitors by the inverter unit and the floating capacitor unit in the inverter according to the capacitor pre-charge driving signal respectively includes:

   The inverter unit and the floating capacitor unit in the first multilevel inverter respectively control the energy of the DC power source side to pass through the tenth current path pair according to the capacitor precharge driving signal The floating capacitor in the level inverter is precharged; wherein the tenth current path is: a first input end of the inverter unit - a first output end of the inverter unit - the suspension a capacitor - an anti-parallel diode of the second switching transistor;

   The inverter unit and the floating capacitor unit in the second multilevel inverter respectively control the energy of the DC power source side through the eleventh current path pair according to the capacitor precharge driving signal The floating capacitor in the multilevel inverter is precharged; wherein the eleventh current path is: an anti-parallel diode of the first switching transistor - the floating capacitor - the first of the inverter unit Two output terminals - a third input end of the inverter unit;

   The inverter unit and the floating capacitor unit in the third multilevel inverter respectively control the energy of the DC power source side through the twelfth current path pair to the third according to the capacitor precharge driving signal The floating capacitor in the multilevel inverter is precharged; wherein the twelfth current path is: an anti-parallel diode of the first switching transistor - the floating capacitor - the first of the inverter unit Two outputs - a third input of the inverter unit.
9. The method of charging a capacitor of an application circuit of a multilevel inverter according to claim 7, wherein said first multilevel inverter, said second multilevel inverter, and said first The step of precharging the respective floating capacitors by the inverter unit and the floating capacitor unit in the three-level inverter according to the capacitor pre-charge driving signal respectively includes:

   The inverter unit and the floating capacitor unit in the first multilevel inverter respectively control the energy of the DC power source side through the thirteenth current path pair according to the capacitor precharge driving signal The floating capacitor in the multilevel inverter is precharged; wherein the thirteenth current path is: a second input end of the inverter unit - a first output end of the inverter unit a suspension capacitor - an anti-parallel diode of the second switching transistor;

   The inverter unit and the floating capacitor unit in the second multilevel inverter respectively control the energy of the DC power source side through the fourteenth current path pair according to the capacitor precharge driving signal The floating capacitor in the multilevel inverter is precharged; wherein the fourteenth current path The diameter is: an anti-parallel diode of the first switch tube - the floating capacitor - a second output end of the inverter unit - a third input end of the inverter unit;

   The inverter unit and the floating capacitor unit in the third multilevel inverter respectively control the energy of the DC power source side through the fifteenth current path pair to the third according to the capacitor precharge driving signal The floating capacitor in the multilevel inverter is precharged; wherein the fifteenth current path is: an anti-parallel diode of the first switching transistor - the floating capacitor - the first of the inverter unit Two outputs - a third input of the inverter unit.
10. The method of charging a capacitor of an application circuit of a multilevel inverter according to claim 7, wherein said first multilevel inverter, said second multilevel inverter, and said first The step of precharging the respective floating capacitors by the inverter unit and the floating capacitor unit in the three-level inverter according to the capacitor pre-charge driving signal respectively includes:

    The inverter unit and the floating capacitor unit in the first multilevel inverter respectively control the energy of the grid side through the sixteenth current path to the first multilevel according to the capacitor precharge driving signal The floating capacitor in the inverter is precharged; wherein the sixteenth current path is: an anti-parallel diode of the first switching transistor - the floating capacitor - a second output of the inverter unit a second input of the inverter unit;

    The inverter unit and the floating capacitor unit in the second multilevel inverter respectively control the energy of the grid side through the seventeenth current path to the second multilevel according to the capacitor precharge driving signal The floating capacitor in the inverter is precharged; wherein the seventeenth current path is: a first input end of the inverter unit - a first output end of the inverter unit - the floating capacitor - an anti-parallel diode of the second switching transistor;

    The inverter unit and the floating capacitor unit in the third multilevel inverter respectively control the energy of the grid side through the eighteenth current path to the third multilevel according to the capacitor precharge driving signal The floating capacitor in the inverter is precharged; wherein the eighteenth current path is: a first input end of the inverter unit - a first output end of the inverter unit - the floating capacitor - an anti-parallel diode of the second switching transistor.

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