WO2024065280A1 - 多电平变换电路、功率变换器和电力系统 - Google Patents

多电平变换电路、功率变换器和电力系统 Download PDF

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Publication number
WO2024065280A1
WO2024065280A1 PCT/CN2022/122148 CN2022122148W WO2024065280A1 WO 2024065280 A1 WO2024065280 A1 WO 2024065280A1 CN 2022122148 W CN2022122148 W CN 2022122148W WO 2024065280 A1 WO2024065280 A1 WO 2024065280A1
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Prior art keywords
level conversion
bridge arm
switch tube
level
capacitor
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PCT/CN2022/122148
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English (en)
French (fr)
Inventor
陆丰隆
石磊
唐云宇
陈东
辛凯
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华为数字能源技术有限公司
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Priority to PCT/CN2022/122148 priority Critical patent/WO2024065280A1/zh
Publication of WO2024065280A1 publication Critical patent/WO2024065280A1/zh

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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/487—Neutral point clamped inverters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration

Definitions

  • the present application relates to the field of power electronics technology, and in particular to a multi-level conversion circuit, a power converter and a power system.
  • the multi-level conversion circuit is one of the indispensable topological circuits in the field of power electronics technology. It can generate high voltages of multiple voltage levels based on a small number of switching tubes and other devices to meet the requirements of different levels of loads. It is widely used in power systems such as DC transmission, renewable energy generation, and energy storage.
  • the specifications of switching tubes and other devices are usually designed according to the requirements of supporting full capacity under typical working conditions.
  • the coexistence of transient large current and high bus voltage makes it impossible for the specifications of the devices in the three-level conversion circuit designed according to typical working conditions to maintain full current operation.
  • the overload current capacity of the three-level conversion circuit is insufficient and often requires derating. Therefore, how to solve the problem of insufficient overload current capacity of the three-level conversion circuit in the application scenario of transient support power grid has become one of the technical problems that need to be solved urgently.
  • the present application provides a multi-level conversion circuit, a power converter and a power system, which can improve the input/output level of the multi-level conversion circuit, reduce the switching voltage of each switch tube in the multi-level conversion circuit, improve the circuit stability of the multi-level conversion circuit, and have high applicability.
  • the present application provides a multi-level conversion circuit, which includes a first bridge arm, a first inductor, and a first level conversion unit and a second level conversion unit connected in series between a first DC connection terminal (optionally, the first DC connection terminal may be a connection terminal of a positive DC bus) and a second DC connection terminal (optionally, the second DC connection terminal may be a connection terminal of a negative DC bus), the first bridge arm is connected in parallel between the input/output terminal of the first level conversion unit and the input/output terminal of the second level conversion unit, and the midpoint of the bridge arm of the first bridge arm is connected to the first inductor.
  • any level conversion unit of the first level conversion unit and the second level conversion unit includes a first switch tube and a second switch tube connected in series, a first capacitor and a second capacitor connected in series, and a level boosting circuit, wherein the series connection end of the first switch tube and the second switch tube serves as the input/output end of any of the above-mentioned level conversion units, and the series connection end of the first capacitor and the second capacitor is connected to the series connection end of the first switch tube and the second switch tube through the level boosting circuit; the first capacitor and the first switch tube of the first level conversion unit are connected to the first DC connection end, the second capacitor and the second switch tube of the first level conversion unit are respectively connected to the first capacitor and the first switch tube of the second level conversion unit, and the second capacitor and the second switch tube of the second level conversion unit are connected to the second DC connection end.
  • the level boosting circuit of the first level conversion unit and the second level conversion unit is used to coordinate the first switch tube and the second switch tube to boost the input/output level of the multi-level conversion circuit to the target multi-level, which can support the boosting of the input/output level of the multi-level conversion circuit in the application scenario of the transient support power grid, reduce the switching voltage of each switch tube in the multi-level conversion circuit, reduce the current ripple of the inductor, and improve the circuit stability of the multi-level conversion circuit, with high applicability.
  • the level boosting circuit in the first level conversion unit and the second level conversion unit includes a third switch tube and a fourth switch tube connected in reverse series; the first switch tube and the fourth switch tube in the first level conversion unit and the second level conversion unit are complementarily turned on, and the second switch tube and the third switch tube are complementarily turned on, which are used to boost the input/output level of the above-mentioned multi-level conversion circuit to the target multi-level, and the circuit structure is simple and has strong applicability.
  • the first switch tube and the second switch tube in the first level conversion unit and the second level conversion unit are complementary turned on, and the third switch tube and the fourth switch tube are turned off, so as to realize the conventional multi-level input/output of the multi-level conversion circuit.
  • the conventional multi-level can be three-level
  • the target multi-level can be five-level, that is, the conventional multi-level is less than the target multi-level, or the number of levels of the conventional multi-level is less than the number of levels of the target multi-level.
  • the multi-level conversion circuit can be operated with a three-level input/output, and the multi-level conversion circuit can also be operated with a five-level input/output, which can improve the conversion flexibility of the input/output level of the multi-level conversion circuit, and the circuit structure is simple and the stability is strong.
  • the withstand voltage values of the third switch tube and the fourth switch tube in any level conversion unit are less than the withstand voltage values of the first switch tube and the second switch tube in any level conversion unit and each switch tube in the first bridge arm, which can support the changing requirements of the voltage and/or current supported by the transient power grid, and the device selection is convenient, the operation is simple, and the applicability is strong.
  • the multi-level conversion circuit further includes a plurality of balancing circuits connected in series between the first DC connection terminal and the second DC connection terminal, wherein one balancing circuit is connected in parallel to both ends of a capacitor in the first level conversion unit or the second level conversion unit.
  • Any balancing circuit among the above-mentioned plurality of balancing circuits is used to adjust the voltage across both ends of any capacitor to the target voltage when the voltage across both ends of any capacitor connected in parallel with any balancing circuit is greater than the target voltage.
  • the target voltage may be one-quarter of the bus voltage.
  • the terminal voltage of the bus capacitor can be balanced during transient target multi-level operation, thereby improving the circuit operation stability, and the circuit structure is simple and has strong applicability.
  • any of the above-mentioned balancing circuits includes a switching tube and a voltage-dividing resistor connected in series; here, the switching tube is used to turn on the connection between the voltage-dividing resistor and any capacitor when the voltage across any capacitor connected in parallel in any of the above-mentioned balancing circuits is greater than the target voltage, and the energy of any capacitor is consumed by the voltage-dividing resistor, so that the voltage across any capacitor can be adjusted to the target voltage, the circuit structure is simple, and the feasibility is high.
  • the above-mentioned multi-level conversion circuit also includes a second bridge arm, a third bridge arm, a second inductor and a third inductor, where the second bridge arm is connected in parallel between the first DC connection end and the third DC connection end, where the third DC connection end is the series connection end of the first level conversion unit and the second level conversion unit, and the midpoint of the second bridge arm is connected to the series connection end of the first capacitor and the second capacitor in the first level conversion unit through the second inductor, and the upper and lower bridge arms of the second bridge arm complementarily generate waves to achieve voltage balance between the first capacitor and the second capacitor in the first level conversion unit, which can ensure that when the multi-level conversion circuit operates in a five-level input/output mode, the terminal voltage of the first capacitor and the second capacitor is maintained at one-quarter of the bus voltage, and the terminal voltage balance of the capacitor can be achieved.
  • the third bridge arm is connected in parallel between the third DC connection end and the second DC connection end, and the midpoint of the third bridge arm is connected to the series connection end of the first capacitor and the second capacitor in the second level conversion unit through the third inductor.
  • the upper and lower bridge arms of the third bridge arm complement each other to achieve voltage balance between the first capacitor and the second capacitor in the second level conversion unit, thereby achieving balance of terminal voltages of each bus capacitor in the multi-level conversion circuit.
  • the circuit structure is simple, the stability is strong, and the applicability is high.
  • the present application provides a multi-level conversion circuit, wherein the multi-level conversion circuit includes a level conversion auxiliary unit, a first bridge arm, an inductor, and a second bridge arm and a third bridge arm connected in series between a first DC connection terminal and a second DC connection terminal.
  • the first bridge arm is connected in parallel between the midpoint of the bridge arm of the second bridge arm and the midpoint of the bridge arm of the third bridge arm, and the midpoint of the bridge arm of the first bridge arm is connected to the inductor through the level conversion auxiliary unit, and the level conversion auxiliary unit is used to increase the input/output level of the multi-level conversion circuit to the target multi-level.
  • the access of the level conversion auxiliary unit can be used to increase the input/output level of the multi-level conversion circuit to the target multi-level (such as five levels), and the input/output level of the multi-level conversion circuit can be increased in the application scenario of the transient support power grid, and the switching voltage of each switch tube in the multi-level conversion circuit is reduced, and the current ripple of the inductor is reduced.
  • the first DC connection terminal can be a connection terminal of a positive DC bus
  • the second DC connection terminal can be a connection terminal of a negative DC bus.
  • the specific details can be determined according to the actual application scenario and are not limited here.
  • the multi-level conversion unit can achieve an increase in the input/output level from three levels to five levels, which can solve the problem of insufficient overload current capacity of the three-level conversion circuit.
  • the circuit structure is simple, the stability is strong, and the applicability is high.
  • the level conversion auxiliary unit includes an auxiliary bridge arm, a first switch tube, a second switch tube and a flying capacitor.
  • the upper bridge arm of the auxiliary bridge arm is connected in series with the upper bridge arm of the first bridge arm in the first series connection point
  • the lower bridge arm of the auxiliary bridge arm is connected in series with the lower bridge arm of the first bridge arm in the second series connection point
  • the flying capacitor is connected in series between the first series connection point and the second series connection point
  • the bridge arm midpoint of the auxiliary bridge arm is connected to the inductor
  • the first switch tube is connected in parallel to the two ends of the upper bridge arm of the auxiliary bridge arm
  • the second switch tube is connected in parallel to the two ends of the lower bridge arm of the auxiliary bridge arm.
  • the level conversion auxiliary unit may also include an auxiliary switch, and the auxiliary switch and the flying capacitor are connected in series.
  • the first switch tube and the second switch tube are used to conduct the connection between the upper bridge arm and the lower bridge arm of the auxiliary bridge arm and the upper bridge arm and the lower bridge arm of the first bridge arm, and the upper and lower bridge arms of each bridge arm in the first bridge arm, the second bridge arm, the third bridge arm and the auxiliary bridge arm are complementary and turned on, which can be used to increase the input/output level of the multi-level conversion circuit to the target multi-level.
  • the level conversion auxiliary unit has fewer circuit components and simple device types, which can improve the feasibility of level enhancement of a multi-level conversion circuit based on the level conversion auxiliary unit, and has simple operation and strong applicability.
  • the first switch tube and the second switch tube are disconnected when the electrical parameter of any bridge arm or the inductor is greater than the target parameter threshold, and are used to conduct the connection between the upper bridge arm and the lower bridge arm of the auxiliary bridge arm and the upper bridge arm and the lower bridge arm of the first bridge arm.
  • the auxiliary switch tube is turned on when the electrical parameter of any bridge arm or the inductor is greater than the target parameter threshold, and is used to access the flying capacitor; the upper and lower bridge arms of each bridge arm in the first bridge arm, the second bridge arm, the third bridge arm and the auxiliary bridge arm are complementary, which can be used to increase the input/output level of the multi-level conversion circuit to the target multi-level, and the input/output level of the multi-level conversion circuit can be increased from three levels to five levels, and the circuit structure is simple and the stability is strong.
  • the electrical parameters include but are not limited to current, voltage, power, current change rate, voltage change rate or power change rate, etc., which can be determined according to the actual application scenario and are not limited here.
  • the level conversion auxiliary unit can be connected by turning on or off the first switch tube, the second switch tube and the auxiliary switch tube, which is simple to operate and has strong applicability.
  • the first switch tube and the second switch tube are turned on when the electrical parameter of any of the bridge arms or the inductor is less than or equal to the target parameter threshold, and are used to bypass the upper bridge arm and the lower bridge arm of the auxiliary bridge arm;
  • the auxiliary switch tube is turned off when the electrical parameter of any of the bridge arms or the inductor is less than or equal to the target parameter threshold, and is used to disconnect the flying capacitor;
  • the upper and lower bridge arms of each of the first bridge arm, the second bridge arm and the third bridge arm are complementary turned on, which can be used to realize the conventional multi-level input/output of the multi-level conversion circuit, where the conventional multi-level can be three-level, and the target multi-level can be five-level, that is, the conventional multi-level is less than the target multi-level.
  • the separation of the level conversion auxiliary unit and the three-level input/output circuit can be realized by turning on or off the first switch tube, the second switch tube and the auxiliary switch tube, which can improve the switching flexibility of the input/output level conversion of the multi-level conversion circuit, and the operation is simple and the applicability is strong.
  • the withstand voltage value of the switch tube of the above-mentioned auxiliary bridge arm and the withstand voltage value of the above-mentioned flying capacitor are smaller than the withstand voltage value of each switch tube in the above-mentioned first bridge arm, the above-mentioned second bridge arm and the above-mentioned third bridge arm.
  • the present application provides a power converter, which includes a controller and the multi-level conversion circuit provided by the first aspect.
  • the controller is used to control the first switch tube, the second switch tube and the level boosting circuit in the first level conversion unit and the second level conversion unit to increase the input/output level of the multi-level conversion circuit to a target multi-level when the electrical parameters of the switch tubes of the first bridge arm in the multi-level conversion circuit, the first switch tube and the second switch tube in any of the level conversion units, or the first inductor are greater than the parameter threshold.
  • the level boosting circuit includes a third switch tube and a fourth switch tube connected in reverse series; the controller is used to control the first switch tube and the fourth switch tube in the first level conversion unit and the second level conversion unit to be complementary turned on, and the second switch tube and the third switch tube to be complementary turned on when the electrical parameters of the switch tubes of the first bridge arm in the multi-level conversion circuit, the first switch tube and the second switch tube in any of the level conversion units, or the first inductor are greater than the parameter threshold, so as to boost the input/output level of the multi-level conversion circuit to the target multi-level.
  • the input/output level of the multi-level conversion circuit in the power converter can be improved, and the circuit structure is simple and the applicability is strong.
  • the controller is also used to control the first and second switch tubes in the first level conversion unit and the second level conversion unit to be complementary turned on, and the third and fourth switch tubes to be disconnected when the electrical parameters of the switch tubes of the first bridge arm, the first and second switch tubes in any of the level conversion units, or the first inductor are less than or equal to the parameter threshold, so as to realize the conventional multi-level input/output of the multi-level conversion circuit, and the conventional multi-level is less than the target multi-level.
  • the multi-level conversion circuit can be operated with three-level input/output, which can improve the conversion flexibility of the input/output level of the power converter, and the circuit structure is simple and the stability is strong.
  • the above-mentioned controller is also used to control the switching tube connected in parallel with any capacitor in the above-mentioned multi-level conversion circuit to be turned on when the voltage across both ends of any capacitor connected in parallel with any balanced circuit in the above-mentioned multi-level conversion circuit is greater than the target voltage, so as to consume the energy of any capacitor through the voltage-dividing resistor of any balanced circuit, so as to adjust the voltage across both ends of any capacitor to the target voltage, which can improve the circuit working stability of the power converter, and the circuit structure is simple and the applicability is strong.
  • the above-mentioned controller is also used to control the upper and lower bridge arms of the above-mentioned second bridge arm to complementally generate waves when the terminal voltages of the first capacitor and the second capacitor in the above-mentioned first level conversion unit are different, so as to achieve the terminal voltage balance of the first capacitor and the second capacitor in the above-mentioned first level conversion unit;
  • the above-mentioned controller is also used to control the upper and lower bridge arms of the above-mentioned third bridge arm to complementarily generate waves when the terminal voltages of the first capacitor and the second capacitor in the above-mentioned second level conversion unit are different, so as to achieve the terminal voltage balance of the first capacitor and the second capacitor in the above-mentioned second level conversion unit, which can improve the circuit working stability of the power converter, and the circuit structure is simple and the applicability is strong.
  • the present application provides a power converter, which includes a controller and a multi-level conversion circuit provided in the second aspect; the controller is used to control the first switch tube and the second switch tube in the level conversion auxiliary unit in the multi-level conversion circuit to be disconnected and the auxiliary switch tube to be turned on when the electrical parameters of any bridge arm or the inductor in the multi-level conversion circuit are greater than the parameter threshold, and control the upper and lower bridge arms of each bridge arm in the first bridge arm, the second bridge arm, the third bridge arm and the auxiliary bridge arm to be complementary, so as to increase the input/output level of the multi-level conversion circuit to the target multi-level.
  • the circuit structure of the power converter is simple and the applicability is strong.
  • the controller is also used to control the first and second switch tubes in the level conversion auxiliary unit to be turned on and the auxiliary switch tube to be turned off when the electrical parameters of any of the bridge arms or the inductor are less than or equal to the parameter threshold, and to control the upper and lower bridge arms of each of the first bridge arm, the second bridge arm, and the third bridge arm to be complementary turned on, so as to realize the conventional multi-level input/output of the multi-level conversion circuit, where the conventional multi-level can be three levels, and the target multi-level can be five levels, that is, the conventional multi-level is less than the target multi-level, which can improve the conversion flexibility of the input/output level of the power converter, is simple to operate, and has strong applicability.
  • the present application provides an electric power system, which includes a DC power supply and a power converter provided in the third aspect or the fourth aspect; the DC power supply is connected to an AC power supply or an AC load through the power converter, and is used to provide a DC input for the power converter, or based on the DC output energy storage provided by the power converter.
  • the flexible conversion of the input/output level based on the multi-level conversion circuit can enhance the circuit stability of the power system, improve the transient power grid support capability of the power system, and has strong applicability.
  • FIG1 is a schematic diagram of an application scenario of a power system provided in an embodiment of the present application.
  • FIG2 is a schematic diagram of the structure of a power system provided in an embodiment of the present application.
  • FIG3 is a schematic diagram of a structure of a multi-level conversion circuit provided in an embodiment of the present application.
  • FIG4 is a schematic diagram of a driving signal of a multi-level conversion circuit provided in an embodiment of the present application.
  • FIG5 is another schematic diagram of the structure of a multi-level conversion circuit provided in an embodiment of the present application.
  • FIG. 6 is another driving signal schematic diagram of the multi-level conversion circuit provided in an embodiment of the present application.
  • FIG7 is another schematic diagram of the structure of a multi-level conversion circuit provided in an embodiment of the present application.
  • FIG8 is another schematic diagram of the structure of a multi-level conversion circuit provided in an embodiment of the present application.
  • FIG9 is another schematic diagram of the structure of a multi-level conversion circuit provided in an embodiment of the present application.
  • FIG10 is another schematic diagram of the structure of a multi-level conversion circuit provided in an embodiment of the present application.
  • 11 is another driving signal schematic diagram of the multi-level conversion circuit provided in an embodiment of the present application.
  • FIG. 12 is a schematic diagram of the structure of a power converter provided in an embodiment of the present application.
  • the multi-level conversion circuit is widely used in power systems such as DC transmission, new energy power generation and energy storage. It is usually used to supply power to AC loads in the power system based on the DC input provided by the DC power supply or to charge the DC power supply in the power system based on the AC input provided by the AC power supply.
  • the power system provided in the embodiment of the present application can be applied to new energy stations, and the power system includes but is not limited to the centralized access power system of new energy stations (including wind farms and/or photovoltaic stations), the centralized access power system of energy storage power stations, the centralized access power system of light storage power stations or wind storage power stations, etc.
  • each power supply system can be connected in parallel through the grid connection point, and the above-mentioned each power supply system can also be connected in parallel through the grid-connected transformer.
  • the above-mentioned multiple power supply systems are connected to the grid (i.e., connected in parallel), they supply power to loads such as power grids and power electronic equipment.
  • the power system can also be any one of the multiple power supply systems connected to the AC grid, and any one of the power supply systems can support the grid for a short time and have transient grid support capabilities.
  • the power system may be a centralized access power system in which multiple power supply systems are connected to the grid, or it may be one of multiple power supply systems connected to the grid.
  • the specific details can be determined according to the actual application scenario, and are not limited here.
  • the power system will be used as an example below.
  • a DC power supply and a power converter may be included.
  • the DC power supply is connected to an AC power supply or an AC load through a power converter to provide a DC input for the power converter, or based on the DC output energy storage provided by the power converter.
  • the power system includes but is not limited to a photovoltaic power system, a wind power system or an energy storage power system.
  • the DC power supply includes but is not limited to at least one or a combination of multiple items of photovoltaic power supply components, wind power generation components, and energy storage batteries
  • the power converter includes but is not limited to a photovoltaic inverter, an energy storage converter or a wind power converter.
  • the photovoltaic power system will be used as an example below.
  • FIG 1 is a schematic diagram of an application scenario of the power system provided in an embodiment of the present application.
  • the photovoltaic power system includes at least a photovoltaic power supply component (such as a photovoltaic array) and a power converter (such as a photovoltaic inverter), and the photovoltaic array is connected to the grid connection point (not shown in the figure) and/or connected to the grid connection point through a photovoltaic inverter (not shown in the figure), and the grid is powered by the grid-connected transformer (for example, powering batteries, communication base stations or household appliances in the grid).
  • a photovoltaic power supply component such as a photovoltaic array
  • a power converter such as a photovoltaic inverter
  • the photovoltaic power supply component can be connected to the photovoltaic inverter through an energy storage battery, and the photovoltaic inverter is used to invert and convert the direct current provided by the energy storage battery to obtain alternating current for powering the AC grid or an AC power supply (such as an uninterruptible power supply), or the alternating current provided by the AC power supply is rectified by the photovoltaic inverter to obtain direct current for charging the energy storage battery.
  • the photovoltaic inverter can invert the direct current output by the photovoltaic power supply component (and/or energy storage battery), and output the alternating current obtained after the inversion conversion to the grid-connected transformer (and/or power grid) and/or the AC power supply.
  • the photovoltaic inverter can also rectify the alternating current provided by the AC power supply, and store the rectified direct current in the energy storage battery.
  • the photovoltaic power supply component can be composed of one or more photovoltaic strings in parallel, and a photovoltaic string can be obtained by connecting one or more photovoltaic components in series. The specific details can be determined according to the actual application scenario and are not limited here.
  • the energy storage power system includes at least an energy storage battery and an energy storage inverter
  • the output end of the energy storage battery can be connected to one end of the energy storage inverter
  • the other end of the energy storage inverter is connected to the grid connection point and/or connected to the low-voltage side of the grid-connected transformer through the grid connection point, or connected to an AC power source.
  • the energy storage inverter can invert the direct current provided by the energy storage battery, and output the alternating current obtained after the inversion conversion to the grid-connected transformer and/or the power grid.
  • the grid-connected transformer can perform voltage conversion on the alternating current provided by the photovoltaic inverter and/or the alternating current provided by the energy storage inverter to power electrical equipment such as batteries, communication base stations or household appliances in the AC power grid.
  • the energy storage inverter can also rectify the alternating current provided by the AC power source, and store the rectified direct current in the energy storage battery.
  • the wind power system includes at least a wind power generation component (such as a wind turbine or a wind turbine generator set) and a wind power converter.
  • the wind power converter can perform voltage conversion on the AC power provided by the wind power generation component (it can be to rectify the AC power provided by the wind power generation component to obtain DC power, and then invert the rectified DC power to obtain the AC power after voltage conversion), and output the AC power obtained after voltage conversion to the grid connection point and/or the grid-connected transformer.
  • the grid-connected transformer can perform voltage conversion on the AC power provided by the photovoltaic inverter, the AC power provided by the wind power converter, and/or the AC power provided by the energy storage converter to power power users such as batteries, communication base stations or household appliances in the AC power grid.
  • power converters in the form of, but not limited to, photovoltaic inverters, energy storage converters or wind power converters may include multi-level conversion circuits.
  • the flexible conversion of input/output levels based on the multi-level conversion circuit can enhance the circuit stability of the power system and improve the transient power grid support capability of the power system.
  • the circuit structure is simple and has strong applicability.
  • FIG. 2 is a schematic diagram of the structure of the power system provided by an embodiment of the present application.
  • the direct current power supply DC can provide a direct current input for the multi-level conversion circuit, and the multi-level conversion circuit can be based on the direct current provided by the direct current power supply.
  • the direct current is converted into alternating current by inversion, and the alternating current power supply AC is supplied after filtering by the filter capacitor C.
  • the multi-level conversion circuit can also be based on the alternating current provided by the alternating current power supply.
  • the alternating current is rectified to obtain direct current, and the direct current power supply DC is charged based on the direct current.
  • FIG. 1 the power system shown in FIG.
  • the multi-level conversion circuit can be a multi-level converter of a power converter such as the above-mentioned photovoltaic inverter, energy storage converter or wind power converter, and the multi-level conversion circuit can be a typical three-level conversion circuit.
  • the specification selection of devices such as switch tubes is usually designed according to the demand for supporting full capacity under typical working conditions, and three-level input and/or output can be achieved.
  • FIG3 is a schematic diagram of a structure of a multi-level conversion circuit provided in an embodiment of the present application.
  • the multi-level conversion circuit shown in FIG3 includes bus capacitors C1, C2, C3 and C4 connected in series, wherein C1 is connected to a first DC connection terminal, and C4 is connected to a second DC connection terminal.
  • the first DC connection terminal may be a connection terminal of a positive DC bus
  • the second DC connection terminal may be a connection terminal of a negative DC bus
  • the series connection terminal of capacitors C2 and C3 may be a bus midpoint, which may be determined according to the actual application scenario and is not limited here.
  • the multi-level conversion circuit further includes switches Q1, Q2, Q3, Q4, Q5 and Q6, wherein the switch tubes Q1 and Q2 form a bridge arm (for the convenience of description, the bridge arm 1 can be used as an example for description), which are connected in series between the first DC connection end and the series connection end of C2 and C3, the switch tubes Q3 and Q4 form a bridge arm (for the convenience of description, the bridge arm 2 can be used as an example for description), which are connected in series between the series connection end of C2 and C3 and the second DC connection end, the switch tubes Q5 and Q6 form a bridge arm (for the convenience of description, the bridge arm 3 can be used as an example for description), which are connected in series between the bridge arm midpoint of the bridge arm 1 (i.e., the series connection point of the switch tube Q1 and the switch tube Q2) and the bridge arm midpoint of the bridge arm 2 (i.e., the series connection point of the switch tube Q3 and the switch tube Q4), and the bridge arm midpoint of the
  • Fig. 4 is a schematic diagram of a driving signal of a multi-level conversion circuit provided by an embodiment of the present application.
  • the switch tube Q1 and Q2 are complementary turned on
  • Q3 and Q4 are complementary turned on
  • Q5 and Q6 are complementary turned on.
  • the complementary conduction of Q1 and Q2 is high-frequency complementation
  • the complementary conduction of Q3 and Q4 is also high-frequency complementation
  • the complementary conduction of Q5 and Q6 is industrial frequency complementation, which is used to realize the three-level input and/or output of the multi-level conversion circuit, and the circuit structure is simple and has strong applicability.
  • the coexistence of transient large current and high bus voltage makes it impossible for the specifications of the devices in the three-level conversion circuit designed according to the typical working conditions in the multi-level conversion circuit shown in FIG3 to maintain full current operation, and the overload current capacity of the three-level conversion circuit is insufficient.
  • the embodiment of the present application provides a multi-level conversion circuit, which can introduce a small number of smaller-specification devices, and can combine the various devices in the three-level conversion circuit designed according to the typical working conditions to obtain a multi-level conversion circuit that can increase the number of bridge arm levels in a short time, and can reduce the switching voltage of each switch tube in the multi-level conversion circuit, thereby reducing the switching loss of the switch tube of the multi-level conversion circuit and improving the power conversion capacity of the bridge arm in the multi-level conversion circuit.
  • FIG5 is another structural schematic diagram of a multi-level conversion circuit provided in an embodiment of the present application.
  • the multi-level conversion circuit may include a first bridge arm composed of a series connection of a switch tube Q5 and a switch tube Q6, a first inductor L1, and a first level conversion unit and a second level conversion unit connected in series between a first DC connection terminal and a second DC connection terminal, and the series connection terminal of the first level conversion unit and the second level conversion unit may be used as a third DC connection terminal.
  • any level conversion unit in the first level conversion unit and the second level conversion unit includes a first switch tube and a second switch tube connected in series, a first capacitor and a second capacitor connected in series, and a level boosting circuit, the series connection terminal of the first switch tube and the second switch tube serves as the input/output terminal of any of the above-mentioned level conversion units, and the series connection terminal of the first capacitor and the second capacitor is connected to the series connection terminal of the first switch tube and the second switch tube through the third switch tube and the fourth switch tube.
  • the first capacitor and the first switch tube of the first level conversion unit are connected to the first DC connection end
  • the second capacitor and the second switch tube of the first level conversion unit are respectively connected to the first capacitor and the first switch tube of the second level conversion unit
  • the second capacitor and the second switch tube of the second level conversion unit are connected to the second DC connection end
  • the level boosting circuit cooperates with the first switch tube and the second switch tube to boost the input/output level of the multi-level conversion circuit to the target multi-level.
  • the level boosting circuit may include a third switch tube and a fourth switch tube connected in reverse series, the first switch tube and the fourth switch tube in the first level conversion unit and the second level conversion unit are complementary turned on, and the second switch tube and the third switch tube are complementary turned on, so as to boost the input/output level of the multi-level conversion circuit to the target multi-level.
  • the level boosting circuit may also be composed of circuit devices such as a switch tube, a diode or a resistor, and correspondingly, the first switch tube, the second switch tube in the level conversion unit and the switch tube in the level boosting circuit are supplemented with corresponding drive control methods to boost the input/output level of the multi-level conversion circuit.
  • the circuit structure of the level boosting circuit and the supplementary drive control method can be determined according to the actual application scenario, and are not limited here.
  • the level boosting circuit composed of the third switch tube and the fourth switch tube connected in series in reverse order is used as an example for illustration.
  • the first level conversion unit includes a first switch tube Q1 and a second switch tube Q2 connected in series, a first capacitor C1 and a second capacitor C2 connected in series, and a third switch tube Qx1 and a fourth switch tube Qx2 connected in series in reverse order, wherein the series connection end of the switch tube Q1 and the switch tube Q2 is connected to the inductor L1 through the switch tube Q5 as the input/output end of the first level conversion unit, and the series connection end of the capacitor C1 and the capacitor C2 is connected to the series connection end of the switch tube Q1 and the switch tube Q2 through the switch tube Qx1 and the switch tube Qx2.
  • the second level conversion unit includes a first switch tube Q3 and a second switch tube Q4 connected in series, a first capacitor C3 and a second capacitor C4 connected in series, and a third switch tube Qx3 and a fourth switch tube Qx4 connected in reverse series, wherein the series connection end of the switch tube Q3 and the switch tube Q4 is connected to the inductor L1 through the switch tube Q6 as the input/output end of the second level conversion unit, and the series connection end of the capacitor C3 and the capacitor C4 is connected to the series connection end of the switch tube Q3 and the switch tube Q4 through the switch tube Qx3 and the switch tube Qx4. See FIG6, which is another driving signal schematic diagram of the multi-level conversion circuit provided in an embodiment of the present application.
  • the switch tubes Qx1 to Qx4 can be connected to the multi-level conversion circuit, Q1 and Qx are complementary turned on, Q2 and Qx1 are complementary turned on, Q3 and Qx4 are complementary turned on, Q4 and Qx3 are complementary turned on, Q5 and Q6 are complementary turned on, and Q5 and Qx1 are complementary turned on.
  • the addition of switch tubes Qx1 ⁇ Qx4 and the combination of switch tubes Q1 ⁇ Q6 in the existing three-level conversion circuit can realize the conversion from three levels to five levels, which can support the improvement of the input/output level of the multi-level conversion circuit in the application scenario of transient support power grid, reduce the switching voltage of each switch tube in the multi-level conversion circuit, reduce the current ripple of the inductor, solve the problem of insufficient overload current capacity of the three-level conversion circuit, improve the circuit stability of the multi-level conversion circuit, and have high applicability.
  • the multilevel conversion circuit shown in FIG5 in the application scenario of a transient support power grid, when the current, terminal voltage, instantaneous power, average power over a period of time, or electrical parameters such as the terminal voltage change rate, current change rate, or power change rate of any switch tube among the switches Q1, Q2, Q3, Q4, Q5, and Q6 in the multilevel conversion circuit or the inductor L1 fall back to less than or equal to the parameter threshold, the first switch tube and the second switch tube in the first level conversion unit and the second level conversion unit are complementarily turned on, and the third switch tube and the fourth switch tube are disconnected, so as to realize the conventional multilevel input/output of the multilevel conversion circuit, where the conventional multilevel may be three-level, and the target multilevel may be five-level, that is, the conventional multilevel is less than the above-mentioned target multilevel.
  • the switch tubes Qx1 to Qx4 are disconnected, Q1 and Q2 are complementary turned on, Q3 and Q4 are complementary turned on, and Q5 and Q6 are complementary turned on, wherein Q5 and Q6 are complementary at power frequency, Q1 and Q2 are complementary at high frequency, and Q3 and Q4 are complementary at high frequency, so that the input/output level of the multi-level conversion circuit can be restored from five-level input/output to three-level input/output, and the input/output level of the multi-level conversion circuit is more flexible and has strong applicability.
  • the three-level input/output is the conventional multi-level input/output of the multi-level conversion circuit, and the five-level input/output is the demand of the transient support power grid. Therefore, in the multi-level conversion circuit shown in FIG5, the withstand voltage values of the third switch tube and the fourth switch tube in any level conversion unit of the first level conversion unit or the second level conversion unit are less than the withstand voltage values of the first switch tube and the second switch tube in any level conversion unit and each switch tube in the first bridge arm.
  • the withstand voltage of the switch tubes Qx1 to Qx4 is less than that of the switch tubes Q1, Q2, Q3, Q4, Q5 and Q6, which can support the voltage and/or current changes required by the transient power grid, and also make the device selection of the switch tubes Qx1 to Qx4 easier, more convenient, simple to operate and highly applicable.
  • the selection of the above-mentioned switch tubes Qx1 to Qx4 includes but is not limited to one or more combinations of relays, contactors, insulated gate bipolar transistors (IGBT), metal oxide semiconductor field effect transistors (MOSFET), thyristors and diodes, which can be determined according to the actual application scenario and are not limited here.
  • the multi-level conversion circuit can be operated with a three-level input/output, and the multi-level conversion circuit can also be operated with a five-level input/output, which can improve the conversion flexibility of the input/output level of the multi-level conversion circuit, and the circuit structure is simple and the stability is strong.
  • the multi-level conversion circuit shown in Figure 5 during the period of five-level operation based on the switching control of each switch tube, a quarter bus voltage imbalance may occur between the four bus capacitors connected in series.
  • the multi-level conversion circuit provided in the embodiment of the present application may also include multiple balancing circuits for achieving voltage balance of each bus capacitor.
  • FIG. 7 is another schematic diagram of the structure of the multi-level conversion circuit provided by an embodiment of the present application.
  • a plurality of balancing circuits may be further included that are connected in series between the first DC connection terminal and the second DC connection terminal, wherein one balancing circuit is connected in parallel to both ends of a capacitor in the first level conversion unit or the second level conversion unit.
  • any of the above-mentioned multiple balancing circuits may include a switch tube and a voltage-dividing resistor connected in series, where the switch tube is used to conduct the connection between the voltage-dividing resistor and any capacitor when the voltage across both ends of any capacitor connected in parallel with any of the above-mentioned balancing circuits is greater than the target voltage, and the energy of any capacitor is consumed by the voltage-dividing resistor, so that the voltage across both ends of any capacitor can be adjusted to the target voltage, and the circuit structure is simple and the feasibility is high.
  • the target voltage can be one-quarter of the bus voltage. As shown in FIG.
  • a balancing circuit can be connected in parallel to both ends of the bus capacitor C1 (for convenience of description, the balancing circuit 1 can be used as an example for explanation), and the balancing circuit 1 can be composed of a switch tube Qy1 and a voltage-dividing resistor R1.
  • a balancing circuit can be connected in parallel at both ends of the bus capacitor C2 (for convenience of description, the balancing circuit 2 can be used as an example for explanation), and the balancing circuit 2 can be composed of a switch tube Qy2 and a voltage-dividing resistor R3.
  • a balancing circuit can be connected in parallel at both ends of the bus capacitor C3 (for convenience of description, the balancing circuit 3 can be used as an example for explanation), and the balancing circuit 3 can be composed of a switch tube Qy3 and a voltage-dividing resistor R3.
  • a balancing circuit can be connected in parallel at both ends of the bus capacitor C4 (for convenience of description, the balancing circuit 4 can be used as an example for explanation), and the balancing circuit 4 can be composed of a switch tube Qy4 and a voltage-dividing resistor R4.
  • Balancing circuit 1, balancing circuit 2, balancing circuit 3 and balancing circuit 4 can be used to adjust the voltages at both ends of the bus capacitor C1, bus capacitor C2, bus capacitor C3 and bus capacitor C4 to one-quarter of the bus voltage (i.e., the voltage between the positive DC bus and the negative DC bus) when the voltages at both ends of the bus capacitor C1, bus capacitor C2, bus capacitor C3 and bus capacitor C4 are greater than one-quarter of the bus voltage (i.e., the voltage between the positive DC bus and the negative DC bus). That is to say, in the multi-level conversion circuit shown in FIG7, when the multi-level conversion circuit operates in a five-level input/output mode, the target voltage may be a quarter of the bus voltage.
  • the connection between the voltage-dividing resistor and the bus capacitor can be disconnected by the switch tube (Qy1, Qy2, Qy3 or Qy4) connected in parallel with the bus capacitor to maintain the terminal voltage of the bus capacitor at a quarter of the bus voltage.
  • the switch tubes Qx1 to Qx4 in the multi-level conversion circuit shown in FIG7 are disconnected, when the multi-level conversion circuit operates in a three-level input/output working mode, the connection between each voltage-dividing resistor and the bus capacitor can also be disconnected by the switch tubes Qy1, Qy2, Qy3 and Qy4 to support the conventional three-level input/output of the multi-level conversion circuit.
  • the balancing circuit by accessing the balancing circuit, the terminal voltage of the bus capacitor can be balanced when the transient target multi-level is operated, the circuit working stability is improved, the circuit structure is simple, and the applicability is strong.
  • the selection of the above-mentioned switching tubes Qy1, Qy2, Qy3 and Qy4 can also be one or more combinations including but not limited to relays, contactors, IGBTs, MOSFETs, thyristors and diodes, which can be determined according to the actual application scenario and is not limited here.
  • FIG 8 is another schematic diagram of the structure of the multi-level conversion circuit provided by an embodiment of the present application.
  • it can also include a second bridge arm (composed of switch tubes Qy1 and Qy2 connected in series), a third bridge arm (composed of switch tubes Qy3 and Qy4 connected in series), a second inductor Ly1 and a third inductor Ly2.
  • the second bridge arm is connected in parallel between the first DC connection end and the third DC connection end, and the midpoint of the second bridge arm (i.e., the series connection point of the switch tubes Qy1 and Qy2) is connected to the series connection end of the first capacitor (i.e., capacitor C1) and the second capacitor (i.e., capacitor C2) in the first level conversion unit through the inductor Ly1.
  • the upper and lower bridge arms of the second bridge arm complement each other and generate waves, which can be used to achieve voltage balance between the capacitors C1 and C2 in the first level conversion unit, and ensure that when the multi-level conversion circuit operates in a five-level input/output mode, the terminal voltage of the capacitors C1 and C2 of the first level conversion unit is maintained at one-quarter of the bus voltage, thereby achieving capacitor terminal voltage balance.
  • the third bridge arm is connected in parallel between the third DC connection terminal and the second DC connection terminal, and the bridge arm midpoint of the third bridge arm (i.e., the series connection point of the switch tubes Qy3 and Qy4) is connected to the series connection end of the first capacitor (i.e., capacitor C3) and the second capacitor (i.e., capacitor C4) in the second level conversion unit through the third inductor Ly2.
  • the upper and lower bridge arms of the third bridge arm i.e., the switch tubes Qy3 and Qy4) complement each other to achieve voltage balance of the capacitors C3 and C4 in the second level conversion unit, thereby achieving terminal voltage balance of each bus capacitor in the multi-level conversion circuit, and the circuit structure is simple, stable, and highly applicable.
  • the selection of the above-mentioned switch tubes Qy1, Qy2, Qy3, and Qy4 can also be one or more combinations including but not limited to relays, contactors, IGBTs, MOSFETs, thyristors, and diodes, which can be determined according to the actual application scenario and are not limited here.
  • the terminal voltage of the bus capacitor can be kept stable when the multi-level conversion circuit operates in a five-level input/output working mode, thereby improving the working stability of the multi-level conversion circuit, and the circuit structure is simple and has strong applicability.
  • an embodiment of the present application provides another multi-level conversion circuit.
  • a level conversion auxiliary unit By adding a level conversion auxiliary unit, various devices in a three-level conversion circuit designed according to typical operating conditions can be combined to obtain a multi-level conversion circuit with another circuit structure.
  • the multi-level conversion circuit can also increase the number of bridge arm levels in a short time, and can reduce the switching voltage of each switch tube in the multi-level conversion circuit, thereby reducing the switching loss of the switch tube of the multi-level conversion circuit and improving the power conversion capability of the bridge arm in the multi-level conversion circuit.
  • FIG. 9 is another schematic diagram of the structure of the multi-level conversion circuit provided by an embodiment of the present application.
  • the multi-level conversion circuit includes a level conversion auxiliary unit, a first bridge arm (composed of switch tubes Q5 and Q6), an inductor L1, and a second bridge arm (composed of switch tubes Q1 and Q2 in series) and a third bridge arm (composed of switch tubes Q3 and Q4 in series) connected in series between the first DC connection terminal and the second DC connection terminal.
  • the first bridge arm is connected in parallel between the bridge arm midpoint of the second bridge arm (the series connection point of the switch tubes Q1 and Q2) and the bridge arm midpoint of the third bridge arm (the series connection point of the switch tubes Q3 and Q4), and the bridge arm midpoint of the first bridge arm (the series connection point of the switch tubes Q5 and Q6) is connected to the inductor L1 through the level conversion auxiliary unit, and the level conversion auxiliary unit is used to increase the input/output level of the multi-level conversion circuit to the target multi-level, where the target multi-level can be five levels.
  • the level conversion auxiliary unit may include an auxiliary bridge arm, a first switch tube S1, a second switch tube S2, and a flying capacitor C.
  • the upper bridge arm (switch tube Qx1) of the auxiliary bridge arm is connected in series with the upper bridge arm (switch tube Q5) of the first bridge arm at a first series connection point
  • the lower bridge arm (switch tube Qx6) of the auxiliary bridge arm is connected in series with the lower bridge arm (switch tube Q6) of the first bridge arm at a second series connection point
  • the flying capacitor C and the auxiliary switch tube Sc are connected in series between the first series connection point and the second series connection point
  • the bridge arm midpoint of the auxiliary bridge arm (the series connection point of the switch tube Qx1 and the switch tube Qx6) is connected to the inductor L.
  • the first switch tube S1 is connected in parallel to both ends of the upper bridge arm (switch tube Qx1) of the auxiliary bridge arm, and the second switch tube S2 is connected in parallel to both ends of the lower bridge arm (switch tube Qx6) of the auxiliary bridge arm. As shown in FIG9 , in the multi-level conversion circuit, the first switch tube S1 can bypass the switch tube Qx1 when it is closed, and the switch tube Qx1 is connected when the first switch tube S1 is disconnected.
  • FIG10 is another structural schematic diagram of the multi-level conversion circuit provided by an embodiment of the present application
  • the level conversion auxiliary unit may also include an auxiliary switch tube Sc, the auxiliary switch tube Sc and the flying capacitor are connected in series, the auxiliary switch tube Sc can be connected to the flying capacitor when it is closed, and the flying capacitor is also disconnected when the auxiliary switch tube Sc is disconnected.
  • the level conversion auxiliary unit is connected to the main power circuit of the multi-level conversion circuit.
  • the connection of the level conversion auxiliary unit can be used to increase the input/output level of the multi-level conversion circuit to the target multi-level (such as five-level), and can increase the input/output level of the multi-level conversion circuit in the application scenario of the transient support power grid, reduce the switching voltage of each switch tube in the multi-level conversion circuit, reduce the current ripple of the inductor, and realize the improvement of the input/output level from three levels to five levels, which can solve the problem of insufficient overload current capacity of the three-level conversion circuit.
  • the circuit structure is simple, the stability is strong, and the applicability is high.
  • the circuit components of the level conversion auxiliary unit are few, the device type is simple, and the feasibility of realizing the level improvement of the multi-level conversion circuit based on the level conversion auxiliary unit can be improved, and the operation is simple and the applicability is strong.
  • transient overvoltage or overcurrent may occur at each switch tube of each bridge arm in the multi-level conversion circuit or the inductor of the multi-level conversion circuit. Whether the bridge arm of the multi-level conversion circuit has overvoltage or overcurrent can be detected by whether the current or voltage of the bridge arm in the multi-level conversion circuit exceeds a preset threshold value within a preset time. Similarly, whether the bridge arm of the multi-level conversion circuit has overvoltage or overcurrent can also be detected by whether the current or voltage of the inductor in the multi-level conversion circuit exceeds a preset threshold value within a preset time.
  • the level conversion auxiliary unit can be started to increase the level of the multi-level conversion circuit to five levels, etc., which can reduce the switching voltage of the switch tubes of each bridge arm in the main power circuit of the multi-level conversion circuit, reduce the inductor ripple, etc. Therefore, when the electrical parameter of any bridge arm (such as any one of the first bridge arm, the second bridge arm or the third bridge arm) or the inductor L1 is greater than the target parameter threshold, the switch tube S1 and the switch tube S2 disconnect the connection between the upper bridge arm and the lower bridge arm of the auxiliary bridge arm and the upper bridge arm and the lower bridge arm of the first bridge arm.
  • the auxiliary switch tube Sc is turned on to access the flying capacitor, and the upper and lower bridge arms of each bridge arm in the first bridge arm, the second bridge arm, the third bridge arm and the auxiliary bridge arm are complementary.
  • the input/output level of the above-mentioned multi-level conversion circuit can be increased to the target multi-level, so that the input/output level of the multi-level conversion circuit can be increased from three levels to five levels, and the circuit structure is simple and the stability is strong.
  • the electrical parameters of any of the above-mentioned bridge arms or inductors include but are not limited to current, voltage, power, current change rate, voltage change rate or power change rate, etc., which can be determined according to the actual application scenario and are not limited here.
  • FIG. 11 is another driving signal schematic diagram of the multi-level conversion circuit provided in an embodiment of the present application.
  • the electrical parameter of any bridge arm such as any one of the first bridge arm, the second bridge arm or the third bridge arm
  • the switch tube S1 and the switch tube S2 are disconnected and the auxiliary switch tube Sc is closed, and the level conversion auxiliary unit is connected to the main power circuit of the multi-level conversion circuit.
  • the driving signals of Q1 and Q3 are the same, Q1 and Q2 are complementary turned on, and Q3 and Q4 are complementary turned on to realize the industrial frequency wave generation of the multi-level conversion circuit, Q6 and Q5 are complementary turned on to realize the high frequency wave generation of the multi-level conversion circuit, and Qx1 and Qx6 are complementary turned on, which are also used to realize the high frequency wave generation of the multi-level conversion circuit, and the input/output level of the multi-level conversion circuit can be increased from three levels to five levels, and the circuit structure is simple and the stability is strong.
  • the withstand voltage value of the switch tube of the auxiliary bridge arm and the withstand voltage value of the flying capacitor are less than the withstand voltage value of each switch tube (i.e., switch tube Q1, Q2, Q3, Q4, Q5, and Q6) in the first bridge arm, the second bridge arm, and the third bridge arm, and the device selection is flexible and has high applicability.
  • the selection of switch tube S1, switch tube S2, switch tube Qx1, and Qx6 can also include but are not limited to one or more combinations of relays, contactors, IGBTs, MOSFETs, thyristors, and diodes, which can be determined according to the actual application scenario and are not limited here.
  • the switch tube S1 and the switch tube S2 can be turned on to bypass the upper bridge arm and the lower bridge arm of the auxiliary bridge arm, and at the same time, the auxiliary switch tube Sc is turned off to disconnect the flying capacitor and the main power circuit.
  • the upper and lower bridge arms of each bridge arm in the first bridge arm, the second bridge arm and the third bridge arm are complementary turned on, that is, the switch tubes Q1 and Q2 are complementary turned on, Q3 and Q4 are complementary turned on, and Q5 and Q6 are complementary turned on, and the conventional multi-level input/output of the above multi-level conversion circuit can be realized, where the conventional multi-level can be three-level, and the target multi-level can be five-level, that is, the above conventional multi-level is less than the above target multi-level.
  • the switch tube S1 and the second switch tube S1 are disconnected, and the conduction of the auxiliary switch tube Sc can realize the access of the level conversion auxiliary unit, which can be used to increase the input/output level of the multi-level conversion circuit to the target multi-level (such as five levels), and can increase the input/output level of the multi-level conversion circuit in the application scenario of transient support power grid, reduce the switching voltage of each switch tube in the multi-level conversion circuit, reduce the current ripple of the inductor, and realize the improvement of the input/output level from three levels to five levels, which can solve the problem of insufficient overload current capacity of the three-level conversion circuit, and the circuit structure is simple, stable, and highly applicable.
  • the level conversion auxiliary unit which can be used to increase the input/output level of the multi-level conversion circuit to the target multi-level (such as five levels), and can increase the input/output level of the multi-level conversion circuit in the application scenario of transient support power grid, reduce the switching voltage of each switch tube in the multi-level conversion circuit,
  • the separation of the level conversion auxiliary unit and the three-level input/output circuit (i.e., the main power circuit of the multi-level conversion circuit shown in Figure 9) can be realized by turning on or off the switch tube S1, the second switch tube S1, and the auxiliary switch tube Sc, so as to realize the three-level input/output of the multi-level conversion circuit, which can improve the switching flexibility of the input/output level conversion of the multi-level conversion circuit, simple operation, and strong applicability.
  • FIG. 12 is a schematic diagram of the structure of the power converter provided in an embodiment of the present application.
  • the power converter may be a photovoltaic inverter, an energy storage converter or a wind power converter, etc., which may be determined specifically according to the application scenario of the multi-level conversion circuit, and is not limited here.
  • the photovoltaic inverter will be used as an example of a power converter for explanation below.
  • the photovoltaic inverter may include a controller and a multi-level conversion circuit, and the multi-level conversion circuit may be any of the structures shown in FIG5 to FIG8, which may be determined specifically according to the actual application scenario, and is not limited here.
  • the multi-level conversion circuit may perform an inversion conversion based on the direct current provided by the first DC connection terminal and the second DC connection terminal, and output the alternating current obtained by the inversion conversion to the AC power grid (or AC load, AC power supply, not shown in FIG12).
  • the controller can control the first switch tube and the fourth switch tube in the first level conversion unit and the second level conversion unit to be complementary turned on, and the second switch tube and the third switch tube to be complementary turned on when the electrical parameters of the switch tubes of the first bridge arm in the multi-level conversion circuit (such as the switch tubes Q5 and Q6 in the multi-level conversion circuit shown in any structure in FIG5 to FIG8 ), the first switch tube and the second switch tube in any level conversion unit (such as Q1 and Q2, or Q3 and Q4 in the multi-level conversion circuit shown in any structure in FIG5 to FIG8 ), or the first inductor (such as the inductor L1 in the multi-level conversion circuit shown in any structure in FIG5 to FIG8 ) are greater than the parameter threshold, so as to increase the input/output level of the multi-level conversion circuit to the target multi-level.
  • the electrical parameters of the switch tubes of the first bridge arm in the multi-level conversion circuit such as the switch tubes Q5 and Q6 in the multi-level conversion circuit shown in any structure in FIG5 to
  • the controller can control the switch tubes Qx1 to Qx4 to access the multi-level conversion circuit when it is detected that the current, terminal voltage, instantaneous power, average power over a period of time, or electrical parameters such as the terminal voltage change rate, current change rate, or power change rate of any switch tube among the switch tubes Q1, Q2, Q3, Q4, Q5, and Q6 or the inductor L1 exceed a certain parameter threshold, and can also control Q1 and Qx to be complementary turned on, Q2 and Qx1 to be complementary turned on, Q3 and Qx4 to be complementary turned on, Q4 and Qx3 to be complementary turned on, and Q5 and Q6 to be complementary turned on to realize the five-level input/output of the multi-level conversion circuit.
  • Q5 and Q6 are complementary at industrial frequency
  • Q1 and Qx2 are complementary at high frequency
  • Q2 and Qx1 are complementary at high frequency
  • Q3 and Qx4 are complementary at high frequency
  • Q4 and Qx3 are complementary at high frequency
  • the switching voltage of the switch tubes Q1 ⁇ Q6 of the multi-level conversion circuit in the photovoltaic inverter is reduced by half, which can reduce the current ripple of the inductor L1, and can significantly reduce the loss of the main power circuit of the existing three-level conversion circuit, thereby reducing the power loss of the photovoltaic inverter, and the circuit structure is simple and feasible.
  • the level boosting circuit may also be composed of other circuit structures.
  • the level boosting circuit may be composed of a switch tube and a diode, or a switch tube and a resistor.
  • the controller may control the first switch tube, the second switch tube and the level boosting circuit in the first level conversion unit and the second level conversion unit to operate, so as to boost the input/output level of the multi-level conversion circuit to the target multi-level.
  • the circuit structure of the level boosting circuit in the level conversion unit is different, and the first switch tube, the second switch tube and the switch tube in the level boosting circuit in the level conversion unit are supplemented by corresponding drive control methods, which are also used to boost the input/output level of the multi-level conversion circuit.
  • the circuit structure of the level boosting circuit and the supplementary drive control method can be determined according to the actual application scenario, and are not limited here.
  • a power converter (such as a photovoltaic inverter) can realize an improvement in the input/output level of a multi-level conversion circuit in a photovoltaic inverter based on the complementary conduction of the first switch tube and the fourth switch tube in the first level conversion unit and the second level conversion unit in the multi-level conversion unit and the complementary conduction of the second switch tube and the third switch tube. This can reduce the switching voltage of each switch tube in the multi-level conversion circuit in the photovoltaic inverter, reduce the current ripple of the inductor, improve the circuit stability in the photovoltaic inverter, and have high applicability.
  • the controller of the photovoltaic inverter can also control the first and second switch tubes in the first bridge arm of the multi-level conversion circuit, the first and second switch tubes in any level conversion unit, or the first inductor to be complementary turned on and the third and fourth switch tubes to be disconnected when the electrical parameters of the switch tubes in the first bridge arm, the first and second switch tubes in any level conversion unit, or the first inductor are less than or equal to the parameter threshold, so as to realize the conventional multi-level input/output of the multi-level conversion circuit.
  • the controller when the controller detects that the electrical parameters such as the current, terminal voltage, instantaneous power, average power over a period of time, or terminal voltage change rate, current change rate, or power change rate of any switch tube among the switch tubes Q1, Q2, Q3, Q4, Q5, and Q6 in the multi-level conversion circuit or the inductor L1 fall back to less than or equal to the parameter threshold, the controller can control the first and second switch tubes in the first and second level conversion units to be complementary turned on and the third and fourth switch tubes to be disconnected, so as to realize the conventional multi-level input/output of the multi-level conversion circuit.
  • the controller can control the switch tubes Qx1 to Qx4 to be disconnected, Q1 and Q2 to be complementary turned on, Q3 and Q4 to be complementary turned on, and Q5 and Q6 to be complementary turned on, wherein Q5 and Q6 are complementary at power frequency, Q1 and Q2 are complementary at high frequency, and Q3 and Q4 are complementary at high frequency, so that the input/output level of the multi-level conversion circuit can be restored from five-level input/output to three-level input/output, and the input/output level conversion of the multi-level conversion circuit is more flexible and has strong applicability.
  • the multi-level conversion circuit can be operated with three-level input/output, which can improve the conversion flexibility of the input/output level of the photovoltaic inverter, and the circuit structure is simple and the stability is strong.
  • the multi-level conversion circuit in the photovoltaic inverter shown in FIG12, during the period when the multi-level conversion circuit realizes five-level operation based on the switching control of each switch tube, a quarter bus voltage imbalance may occur between the four bus capacitors in series.
  • the multi-level conversion circuit provided in the embodiment of the present application may also include multiple balancing circuits for realizing the voltage balance of each bus capacitor.
  • the controller in the photovoltaic inverter can also control the switch tube connected in parallel with any capacitor in the multi-level conversion circuit to conduct when the voltage across the terminals of any capacitor connected in parallel with any balancing circuit is greater than the target voltage, so as to consume the energy of any capacitor through the voltage divider resistor of any balancing circuit, so as to adjust the voltage across the terminals of any capacitor to the target voltage, which can improve the circuit working stability of the power converter, and the circuit structure is simple and the applicability is strong.
  • the controller when it is detected that the terminal voltage of any bus capacitor is greater than one-quarter of the bus voltage, the controller can control the switch tube (Qy1, Qy2, Qy3 or Qy4) connected in parallel with the bus capacitor to be turned on, so as to consume the energy of any of the above capacitors through the voltage-dividing resistor connected in series with the switch tube (Qy1, Qy2, Qy3 or Qy4), so as to adjust the voltage across the two ends of any of the above capacitors to the target voltage.
  • the switch tube Qy1, Qy2, Qy3 or Qy4
  • the controller when it is detected that the terminal voltage of any bus capacitor is stabilized at one-quarter of the bus voltage, the controller can control the switch tube (Qy1, Qy2, Qy3 or Qy4) connected in parallel with the bus capacitor to be disconnected, so as to disconnect the connection between the voltage-dividing resistor and the bus capacitor, so as to maintain the terminal voltage of the bus capacitor at one-quarter of the bus voltage.
  • the multi-level conversion circuit operates in a three-level input/output working mode
  • the controller can also control the switch tubes Qy1, Qy2, Qy3 and Qy4 to disconnect, so as to disconnect the connection between each voltage dividing resistor and the bus capacitor, so as to support the conventional three-level input/output of the multi-level conversion circuit.
  • the balancing circuit by connecting the balancing circuit, the terminal voltage of the bus capacitor can be balanced during the transient target multi-level operation, the circuit working stability is improved, the circuit structure is simple, and the applicability is strong.
  • the controller of the photovoltaic inverter can also control the upper and lower bridge arms of the second bridge arm to complement each other when the terminal voltages of the first capacitor and the second capacitor of the first level conversion unit in the multi-level conversion circuit are different, so as to achieve the terminal voltage balance of the first capacitor and the second capacitor in the first level conversion unit.
  • the controller can also control the upper and lower bridge arms of the third bridge arm to complement each other when the terminal voltages of the first capacitor and the second capacitor in the second level conversion unit are different, so as to achieve the terminal voltage balance of the first capacitor and the second capacitor in the above-mentioned second level conversion unit, which can improve the circuit working stability of the power converter, and the circuit structure is simple and has strong applicability.
  • the second bridge arm is connected in parallel between the first DC connection terminal and the third DC connection terminal, and the midpoint of the second bridge arm (i.e., the series connection point of the switch tubes Qy1 and Qy2) is connected to the series connection end of the first capacitor (i.e., capacitor C1) and the second capacitor (i.e., capacitor C2) in the first level conversion unit through the inductor Ly1.
  • the controller controls the upper and lower bridge arms (i.e., the switch tubes Qy1 and Qy2) of the second bridge arm to complement each other to achieve voltage balance between the capacitors C1 and C2 in the first level conversion unit, thereby ensuring that when the multi-level conversion circuit works in the five-level input/output mode, the terminal voltage of the capacitors C1 and C2 of the first level conversion unit is maintained at one-quarter of the bus voltage, thereby achieving capacitor terminal voltage balance.
  • the upper and lower bridge arms i.e., the switch tubes Qy1 and Qy2
  • the third bridge arm is connected in parallel between the third DC connection end and the second DC connection end, and the midpoint of the third bridge arm (i.e., the series connection point of the switch tubes Qy3 and Qy4) is connected to the series connection ends of the first capacitor (i.e., capacitor C3) and the second capacitor (i.e., capacitor C4) in the second level conversion unit through the third inductor Ly2.
  • the controller can achieve voltage balance between the capacitor C3 and the capacitor C4 in the second level conversion unit by controlling the upper and lower bridge arms (i.e., the switch tubes Qy3 and Qy4) of the third bridge arm to complement each other, thereby achieving terminal voltage balance of each bus capacitor in the multi-level conversion circuit.
  • the circuit structure is simple, the stability is strong, and the applicability is high.
  • the controller in the photovoltaic inverter can also control the first switch tube and the second switch tube in the level conversion auxiliary unit in the multi-level conversion circuit to be disconnected and the auxiliary switch tube to be turned on when the electrical parameter of any bridge arm or inductor in the multi-level conversion circuit is greater than the parameter threshold, and control the upper and lower bridge arms of each bridge arm in the first bridge arm, the second bridge arm, the third bridge arm and the auxiliary bridge arm to be complementary and turned on to increase the input/output level of the multi-level conversion circuit to the target multi-level, and the circuit structure of the power converter is simple and has strong applicability.
  • the controller when the controller detects that the electrical parameter of any bridge arm (such as any one of the first bridge arm, the second bridge arm or the third bridge arm) or the inductor L1 in the main power circuit of the multi-level conversion circuit is greater than the target parameter threshold, the switch tube S1 and the switch tube S2 can be controlled to be disconnected, and the auxiliary switch tube Sc can be controlled to be closed at the same time, so as to connect the level conversion auxiliary unit to the main power circuit of the multi-level conversion circuit.
  • any bridge arm such as any one of the first bridge arm, the second bridge arm or the third bridge arm
  • the auxiliary switch tube Sc can be controlled to be closed at the same time, so as to connect the level conversion auxiliary unit to the main power circuit of the multi-level conversion circuit.
  • the controller can also control Q1 and Q3 to be turned on or off based on the same driving signal, and can also control Q1 and Q2 to be complementary turned on, and Q3 and Q4 to be complementary turned on, so as to realize the industrial frequency wave generation of the multi-level conversion circuit, control Q6 and Q5 to be complementary turned on to realize the high-frequency wave generation of the multi-level conversion circuit, and control Qx1 and Qx6 to be complementary turned on, which are also used to realize the high-frequency wave generation of the multi-level conversion circuit, and can realize the input/output level of the multi-level conversion circuit from three levels to five levels, with a simple circuit structure and strong stability.
  • the controller can also control the first switch tube and the second switch tube in the above-mentioned level conversion auxiliary unit to be turned on and the above-mentioned auxiliary switch tube to be turned off when the electrical parameter of the above-mentioned any bridge arm or the above-mentioned inductor is less than or equal to the above-mentioned parameter threshold, and control the upper and lower bridge arms of each bridge arm in the above-mentioned first bridge arm, the above-mentioned second bridge arm, and the above-mentioned third bridge arm to be complementary.
  • the conventional multi-level can be three levels
  • the target multi-level can be five levels
  • the above-mentioned conventional multi-level is less than the above-mentioned target multi-level, which can improve the conversion flexibility of the input/output level of the photovoltaic inverter, simple operation, and strong applicability.
  • the controller when the controller detects that the electrical parameter of any bridge arm or inductor in the first bridge arm, the second bridge arm or the third bridge arm in the main power circuit of the multi-level conversion circuit is less than or equal to the above target parameter threshold, the controller can control the switch tube S1 and the switch tube S2 to be turned on to bypass the upper bridge arm and the lower bridge arm of the auxiliary bridge arm, and at the same time, control the auxiliary switch tube Sc to be turned off to disconnect the flying capacitor and the main power circuit.
  • the controller can control the upper and lower bridge arms of each bridge arm in the first bridge arm, the second bridge arm and the third bridge arm to be complementary, that is, the switch tubes Q1 and Q2 are complementary, Q3 and Q4 are complementary, and Q5 and Q6 are complementary, so as to realize the conventional multi-level input/output of the above multi-level conversion circuit, with a simple circuit structure and strong applicability.
  • control of the photovoltaic inverter can be controlled by controlling the switch tube S1 and the second switch tube S1 to be disconnected, and controlling the conduction of the auxiliary switch tube Sc to control the access of the level conversion auxiliary unit, which can improve the input/output level of the multi-level conversion circuit to the target multi-level (such as five-level), and can improve the input/output level of the multi-level conversion circuit in the application scenario of transient support power grid, reduce the switching voltage of each switch tube in the multi-level conversion circuit, reduce the current ripple of the inductor, and realize the improvement of the input/output level from three levels to five levels, which can solve the problem of insufficient overload current capacity of the three-level conversion circuit, and the circuit structure is simple, stable, and highly applicable.
  • the separation of the level conversion auxiliary unit and the three-level input/output circuit i.e., the main power circuit of the multi-level conversion circuit shown in Figure 9) can be realized to realize the three-level input/output of the multi-level conversion circuit, which can improve the switching flexibility of the input/output level conversion of the multi-level conversion circuit, enhance the circuit stability of the photovoltaic inverter, and is simple to operate and highly applicable.

Abstract

本申请实施例提供多电平变换电路，包括桥臂、电感、第一电平变换单元和第二电平变换单元，桥臂并联第一电平变换单元和第二电平变换单元、桥臂中点连接电感，电平变换单元中包括第一开关管、第二开关管、第一电容、第二电容以及电平提升电路，第一电容和第二电容的串联连接端通过电平提升电路连接第一开关管和第二开关管的串联连接端；第一电平变换单元的第一电容和第一开关管连接第一直流连接端，第一电平变换单元的第二电容和第二开关管分别连接第二电平变换单元的第一电容和第一开关管，第二电平变换单元的第二电容和第二开关管连接第二直流连接端，电平提升电路用于提升电路电平。采用本申请，可降低各个开关管的切换电压，减少电感电流波纹。

Description

多电平变换电路、功率变换器和电力系统 技术领域
本申请涉及电力电子技术领域，尤其涉及一种多电平变换电路、功率变换器和电力系统。
背景技术
多电平变换电路是电力电子技术领域中不可或缺的拓扑电路之一，可基于少量的开关管管等器件产生多个电压等级的高压电压以满足不同等级的负载需求，广泛应用于直流输电、新能源发电以及储能等电力系统中。在典型的三电平变换电路中，开关管等器件的规格选型通常是按照典型工况下支撑满容量的需求设计，然而，在瞬态支撑电网的应用场景中，暂态大电流和高母线电压并存使得按照典型工况设计的三电平变换电路中器件的规格选型无法维持满电流运行，三电平变换电路的过载电流能力不足，往往需要降额。因此，如何解决在瞬态支撑电网的应用场景中，三电平变换电路的过载电流能力不足的问题，成为当前亟待解决的技术问题之一。
发明内容
本申请提供了一种多电平变换电路、功率变换器和电力系统，可提升多电平变换电路的输入/输出电平，降低多电平变换电路中各个开关管的切换电压，提高多电平变换电路的电路稳定性，适用性高。
第一方面，本申请提供了一种多电平变换电路，该多电平变换电路中包括第一桥臂、第一电感以及串联在第一直流连接端(可选的，第一直流连接端可为正直流母线的连接端)和第二直流连接端(可选的，第二直流连接端可为负直流母线的连接端)之间的第一电平变换单元和第二电平变换单元，第一桥臂并联在第一电平变换单元的输入/输出端和第二电平变换单元的输入/输出端之间，第一桥臂的桥臂中点连接第一电感。在本申请中，第一电平变换单元和第二电平变换单元中任一电平变换单元中均包括串联的第一开关管和第二开关管，串联的第一电容和第二电容，以及电平提升电路，这里第一开关管和第二开关管的串联连接端作为上述任一电平变换单元的输入/输出端，第一电容和第二电容的串联连接端通过电平提升电路连接第一开关管和第二开关管的串联连接端；第一电平变换单元的第一电容和第一开关管连接第一直流连接端，第一电平变换单元的第二电容和第二开关管分别连接第二电平变换单元的第一电容和第一开关管，第二电平变换单元的第二电容和第二开关管连接第二直流连接端。在本申请中，第一电平变换单元和所述第二电平变换单元的电平提升电路用于协同第一开关管和第二开关管提升多电平变换电路的输入/输出电平至目标多电平，可支持在瞬态支撑电网的应用场景中提升多电平变换电路的输入/输出电平，降低多电平变换电路中各个开关管的切换电压，减少电感的电流波纹，可提高多电平变换电路的电路稳定性，适用性高。
结合第一方面，在第一种可能的实施方式中，第一电平变换单元和第二电平变换单元中电平提升电路中包括反向串联的第三开关管和第四开关管；第一电平变换单元和第二电平变换单元中第一开关管和第四开关管互补导通且第二开关管和第三开关管互补导通，用于提升上述多电平变换电路的输入/输出电平至目标多电平，电路结构简单，适用性强。
结合第一方面第一种可能的实施方式，在第二种可能的实施方式中，上述第一电平变换单元和上述第二电平变换单元中第一开关管和第二开关管互补导通、第三开关管和第四开关 管断开，用于实现多电平变换电路的常规多电平输入/输出，这里，常规多电平可以为三电平，目标多电平可为五电平，即常规多电平小于上述目标多电平，或者说常规多电平的电平数量小于目标多电平的电平数量。在本申请中，基于多电平变换电路中第一电平变换单元和第二电平变换单元中各个开关管的导通或者关断，可实现多电平变换电路以三电平的输入/输出运行，也可实现多电平变换电路以五电平的输入/输出运行，可提高多电平变换电路的输入/输出电平的变换灵活性，电路结构简单，稳定性强。
结合第一方面第一种可能的实施方式或者第一方面第二种可能的实施方式，在第三种可能的实施方式中，在第一电平变换单元或者第二电平变换单元中，任一电平变换单元中第三开关管和第四开关管的耐压值小于任一电平变换单元中第一开关管和第二开关管、第一桥臂中各个开关管的耐压值，可支持瞬态电网支撑的电压和/或电流的变化需求，器件选型便捷，操作简单，适用性强。
结合第一方面至第一方面第三种可能的实施方式中任一种，在第四种可能的实施方式中，上述多电平变换电路中还包括串联在第一直流连接端和第二直流连接端之间的多个平衡电路，其中一个平衡电路并联于第一电平变换单元或者第二电平变换单元中一个电容的两端。上述多个平衡电路中任一平衡电路用于在任一平衡电路并联的任一电容的两端电压大于目标电压时，调节任一电容的两端电压至目标电压，这里，多电平变换电路工作在五电平输入/输出的模式时，目标电压可为四分之一母线电压。在本申请中，通过平衡电路的接入，可保证暂态目标多电平运行时母线电容的端电压的均衡，提高电路工作稳定性，电路结构简单，适用性强。
结合第一方面第四种可能的实施方式，在第五种可能的实施方式中，上述任一平衡电路中包括串联的开关管和分压电阻；这里，开关管用于在上述任一平衡电路并联的任一电容的两端电压大于目标电压时，导通分压电阻和任一电容的连接，通过分压电阻消耗任一电容的能量，可以调节任一电容的两端电压至目标电压，电路结构简单，可行性高。
结合第一方面至第一方面第三种可能的实施方式中任一种，在第六种可能的实施方式中，上述多电平变换电路中还包括第二桥臂、第三桥臂、第二电感和第三电感，这里，第二桥臂并联在第一直流连接端和第三直流连接端之间，这里，第三直流连接端为所述第一电平变换单元和第二电平变换单元的串联连接端，第二桥臂的桥臂中点通过第二电感连接第一电平变换单元中第一电容和第二电容的串联连接端，第二桥臂的上下桥臂互补发波可用于实现第一电平变换单元中第一电容和第二电容的电压均衡，可保证多电平变换电路工作在五电平输入/输出的模式时，第一电容和第二电容的端电压保持在四分之一母线电压，可实现电容的端电压均衡。同理，第三桥臂并联在第三直流连接端和第二直流连接端之间，第三桥臂的桥臂中点通过第三电感连接第二电平变换单元中第一电容和第二电容的串联连接端，第三桥臂的上下桥臂互补发波可实现第二电平变换单元中第一电容和第二电容的电压均衡，从而可实现多电平变换电路中各个母线电容的端电压的均衡，电路结构简单，稳定性强，适用性高。
第二方面，本申请提供了一种多电平变换电路，上述多电平变换电路中包括电平变换辅助单元、第一桥臂、电感和串联在第一直流连接端和第二直流连接端之间的第二桥臂和第三桥臂。第一桥臂并联在第二桥臂的桥臂中点和第三桥臂的桥臂中点之间，第一桥臂的桥臂中点通过电平变换辅助单元连接电感，电平变换辅助单元用于提升多电平变换电路的输入/输出电平至目标多电平。在本申请中，电平变换辅助单元的接入可用于提升多电平变换电路的输入/输出电平至目标多电平(比如五电平)，可在瞬态支撑电网的应用场景中提升多电平变换电路的输入/输出电平，降低多电平变换电路中各个开关管的切换电压，减少电感的电流波纹。 这里，第一直流连接端可为正直流母线的连接端，第二直流连接端可为负直流母线的连接端，具体可根据实际应用场景确定，在此不做限制，多电平变换单元可实现三电平到五电平的输入/输出电平的提升，可解决三电平变换电路的过载电流能力不足的问题，电路结构简单，稳定性强，适用性高。
结合第二方面，在第一种可能的实施方式中，上述电平变换辅助单元中包括辅助桥臂、第一开关管、第二开关管和飞跨电容。这里，辅助桥臂的上桥臂与上述第一桥臂的上桥臂串联于第一串联连接点，辅助桥臂的下桥臂与上述第一桥臂的下桥臂串联于第二串联连接点，飞跨电容串联在上述第一串联连接点和上述第二串联连接点之间，辅助桥臂的桥臂中点连接电感，第一开关管并联在辅助桥臂的上桥臂的两端，第二开关管并联在上述辅助桥臂的下桥臂的两端。可选的，电平变换辅助单元中还可包括辅助开关，辅助开关和飞跨电容串联。第一开关管和第二开关管用于导通辅助桥臂的上桥臂和下桥臂与第一桥臂的上桥臂和下桥臂的连接，第一桥臂、第二桥臂、第三桥臂和辅助桥臂中各个桥臂的上下桥臂互补导通，可用于提升所述多电平变换电路的输入/输出电平至目标多电平。在本申请中，电平变换辅助单元的电路器件少，器件类型简单，可提高基于电平变换辅助单元实现多电平变换电路的电平提升的可行性，操作简单，适用性强。
结合第二方面第一种可能的实施方式，在第二种可能的实施方式中，上述第一开关管和第二开关管在任一桥臂或者上述电感的电气参数大于目标参数阈值时断开，用于导通上述辅助桥臂的上桥臂和下桥臂与上述第一桥臂的上桥臂和下桥臂的连接。上述辅助开关管在上述任一桥臂或者上述电感的电气参数大于上述目标参数阈值时导通，用于接入上述飞跨电容；上述第一桥臂、上述第二桥臂、上述第三桥臂和上述辅助桥臂中各个桥臂的上下桥臂互补导通，可用于提升上述多电平变换电路的输入/输出电平至目标多电平，可实现多电平变换电路的输入/输出电平从三电平提升至五电平，电路结构简单，稳定性强。这里，上述电气参数包括但不限于电流、电压、功率、电流变化率、电压变化率或者功率变化率等，具体可根据实际应用场景确定，在此不做限制。在本申请中，通过第一开关管、第二开关管和辅助开关管的导通或者关断可实现电平变换辅助单元的接入，操作简单，适用性强。
结合第二方面第二种可能的实施方式，在第三种可能的实施方式中，上述第一开关管和第二开关管在上述任一桥臂或者上述电感的电气参数小于或者等于上述目标参数阈值时导通，用于旁路上述辅助桥臂的上桥臂和下桥臂；上述辅助开关管在上述任一桥臂或者上述电感的电气参数小于或者等于上述目标参数阈值时断开，用于断开上述飞跨电容；上述第一桥臂、上述第二桥臂和上述第三桥臂中各个桥臂的上下桥臂互补导通，可用于实现上述多电平变换电路的常规多电平输入/输出，这里，常规多电平可为三电平，目标多电平可为五电平，即上述常规多电平小于上述目标多电平。在本申请中，通过第一开关管、第二开关管和辅助开关管的导通或者关断可实现电平变换辅助单元和三电平输入/输出回路的分离，可提高多电平变换电路的输入/输出电平变换的切换灵活性，操作简单，适用性强。
结合第二方面至第二方面第三种可能的实施方式，在第四种可能的实施方式中，上述辅助桥臂的开关管的耐压值和上述飞跨电容的耐压值小于上述第一桥臂、上述第二桥臂和上述第三桥臂中各个开关管的耐压值。
第三方面，本申请提供了一种功率变换器，该功率变换器包括控制器和上述第一方面提供的多电平变换电路，上述控制器用于在上述多电平变换电路中第一桥臂的各开关管、上述任一电平变换单元中的第一开关管和第二开关管、或者上述第一电感的电气参数大于参数阈值时，控制第一电平变换单元和第二电平变换单元中第一开关管、第二开关管和电平提升电 路动作，以提升多电平变换电路的输入/输出电平至目标多电平，可以实现功率变换器中多电平变换电路的输入/输出电平的提升，可降低功率变换器中多电平变换电路中各个开关管的切换电压，减少电感的电流波纹，可提高功率变换器中的电路稳定性，适用性高。
结合第三方面，在第一种可能的实施方式中，电平提升电路中包括反向串联的第三开关管和第四开关管；所述控制器用于在上述多电平变换电路中第一桥臂的各开关管、上述任一电平变换单元中的第一开关管和第二开关管、或者上述第一电感的电气参数大于参数阈值时，控制第一电平变换单元和第二电平变换单元中第一开关管和第四开关管互补导通、第二开关管和第三开关管互补导通，以提升多电平变换电路的输入/输出电平至目标多电平。在本申请中，基于多电平变换单元中第一电平变换单元和第二电平变换单元中第一开关管和第四开关管互补导通且第二开关管和第三开关管互补导通，可以实现功率变换器中多电平变换电路的输入/输出电平的提升，电路结构简单，适用性强。
结合第三方面第一种可能的实施方式，在第二种可能的实施方式中，上述控制器还用于在上述第一桥臂的各开关管、上述任一电平变换单元中的第一开关管和第二开关管、或者上述第一电感的电气参数小于或者等于上述参数阈值时，控制上述第一电平变换单元和上述第二电平变换单元中第一开关管和第二开关管互补导通、第三开关管和第四开关管断开，以实现上述多电平变换电路的常规多电平输入/输出，上述常规多电平小于上述目标多电平。在本申请中，基于多电平变换电路中第一电平变换单元和第二电平变换单元中各个开关管的导通或者关断，可实现多电平变换电路以三电平的输入/输出运行，可提高功率变换器的输入/输出电平的变换灵活性，电路结构简单，稳定性强。
结合第三方面或者第三方面第二种可能的实施方式，在第三种可能的实施方式中，上述控制器还用于上述多电平变换电路中任一平衡电路并联的任一电容的两端电压大于目标电压时，控制上述任一电容并联的开关管导通，以通过上述任一平衡电路的分压电阻消耗上述任一电容的能量，以调节上述任一电容的两端电压至目标电压，可提高功率变换器的电路工作稳定性，电路结构简单，适用性强。
结合第三方面或者第三方面第二种可能的实施方式，在第四种可能的实施方式中，上述控制器还用于在上述第一电平变换单元中第一电容和第二电容的端电压不相同时，控制上述第二桥臂的上下桥臂互补发波，以实现上述第一电平变换单元中第一电容和第二电容的端电压均衡；上述控制器还用于在上述第二电平变换单元中第一电容和第二电容的端电压不相同时，控制上述第三桥臂的上下桥臂互补发波，以实现上述第二电平变换单元中第一电容和第二电容的端电压均衡，可提高功率变换器的电路工作稳定性，电路结构简单，适用性强。
第四方面，本申请提供了一种功率变换器，上述功率变换器包括控制器和第二方面提供的多电平变换电路；上述控制器用于在多电平变换电路中任一桥臂或者上述电感的电气参数大于参数阈值时，控制上述多电平变换电路中电平变换辅助单元中第一开关管和第二开关管断开、上述辅助开关管导通，并控制上述第一桥臂、上述第二桥臂、上述第三桥臂和上述辅助桥臂中各个桥臂的上下桥臂互补导通，以提升上述多电平变换电路的输入/输出电平至目标多电平，功率变换器的电路结构简单，适用性强。
结合第四方面，在第一种可能的实施方式中，上述控制器还用于在上述任一桥臂或者上述电感的电气参数小于或者等于上述参数阈值时，控制上述电平变换辅助单元中第一开关管和第二开关管导通、上述辅助开关管断开，并控制上述第一桥臂、上述第二桥臂、和上述第三桥臂中各个桥臂的上下桥臂互补导通，以实现上述多电平变换电路的常规多电平输入/输出，这里常规多电平可为三电平，目标多电平可为五电平，即上述常规多电平小于上述目标 多电平，可提高功率变换器的输入/输出电平的变换灵活性，操作简单，适用性强。
第五方面，本申请提供了一种电力系统，该电力系统包括直流电源和上述第三方面或者第四方面提供的功率变换器；上述直流电源通过上述功率变换器连接交流电源或者交流负载，用于为上述功率变换器提供直流输入、或者基于上述功率变换器提供的直流输出储能。在本申请中，基于多电平变换电路的输入/输出电平的灵活变换，可增强电力系统的电路稳定性，可提高电力系统的瞬态电网支撑能力，适用性强。
附图说明
图1是本申请实施例提供的电力系统的应用场景示意图；
图2是本申请实施例提供的电力系统的结构示意图；
图3是本申请实施例提供的多电平变换电路的一结构示意图；
图4是本申请实施例提供的多电平变换电路的一驱动信号示意图；
图5是本申请实施例提供的多电平变换电路的另一结构示意图；
图6是本申请实施例提供的多电平变换电路的另一驱动信号示意图；
图7是本申请实施例提供的多电平变换电路的另一结构示意图；
图8是本申请实施例提供的多电平变换电路的另一结构示意图；
图9是本申请实施例提供的多电平变换电路的另一结构示意图；
图10是本申请实施例提供的多电平变换电路的另一结构示意图；
图11是本申请实施例提供的多电平变换电路的另一驱动信号示意图；
图12是本申请实施例提供的功率变换器的结构示意图。
具体实施方式
多电平变换电路作为电力电子技术领域中不可或缺的拓扑电路之一，广泛应用于直流输电、新能源发电以及储能等电力系统中，通常用于基于直流电源提供的直流电输入为电力系统中的交流负载供电或者基于交流电源提供的交流电输入为电力系统中的直流电源充电等。本申请实施例提供的电力系统可适用于新能源场站，电力系统包括但不限于新能源场站(包括风电场和/或光伏场站)的集中接入电力系统，储能电站的集中接入电力系统，光储电站或风储电站的集中接入电力系统等，电力系统中各个供电系统可通过并网点并联接入，上述各个供电系统也可通过并网变压器并联接入，上述多个供电系统并网接入(即并联)后为电网、电力电子设备等负载供电。可以理解，在本申请实施例中，电力系统也可为上述并网接入交流电网的多个供电系统中的任意一个，任意一个供电系统均可短时支撑电网，具备瞬态电网支撑能力。换句话说，在本申请实施例中，电力系统可以是多个供电系统并网接入的集中接入电力系统，也可以是并网接入的多个供电系统中的一个，具体可根据实际应用场景确定，在此不做限制，为方便描述，下面将以电力系统进行示例说明。在本申请实施例提供的电力系统中可包括直流电源和功率变换器，直流电源通过功率变换器连接交流电源或者交流负载，用于为功率变换器提供直流输入、或者基于功率变换器提供的直流输出储能。这里，电力系统包括但不限于光伏电力系统、风电电力系统或者储能电力系统，对应的，直流电源包括但不限于光伏供电组件、风力发电组件、储能电池中至少一项或者多项组合，功率变换器包括但不限于光伏逆变器、储能变流器或者风电变流器。为方便描述，下面将以光伏电力系统为例进行示例说明。
参见图1，图1是本申请实施例提供的电力系统的应用场景示意图。如图1所示，光伏电力系统中至少包括光伏供电组件(如光伏阵列)和功率变换器(如光伏逆变器)，光伏阵列通过光伏逆变器连接电网并网点(图中未示出)和/或通过并网点连接并网变压器(图中未示出)，通过并网变压器为电网供电(比如为电网中的蓄电池、通信基站或者家用设备等供电)。可选的，如图1所示，光伏供电组件可通过储能电池连接光伏逆变器，通过光伏逆变器基于储能电池提供的直流电进行逆变转换得到为交流电网或者交流电源(比如不间断电源)供电的交流电，或者通过光伏逆变器基于交流电源提供的交流电进行整流得到为储能电池充电的直流电。换句话说，光伏逆变器可以对光伏供电组件(和/或储能电池)输出的直流电进行逆变转换，并将逆变转换后得到的交流电输出到并网变压器(和/或电网)和/或交流电源，光伏逆变器也可以对交流电源提供的交流电进行整流，并将整流得到的直流电存储至储能电池。如图1所示，光伏供电组件可以由一个或者多个光伏组串并联组成，一个光伏组串可以由一个或者多个光伏组件串联得到，具体可根据实际应用场景确定，在此不做限制。
在一些可行的实施方式中，在储能电力系统中至少包括储能电池和储能变流器，储能电池的输出端可以连接储能变流器的一端，储能变流器的另一端连接并网点和/或通过并网点连接并网变压器的低压侧，或者连接交流电源。在光伏电力系统和储能电力系统并联的集中接入电力系统中，储能变流器可以对储能电池提供的直流电进行逆变转换，并将逆变转换后得到的交流电输出到并网变压器和/或电网。并网变压器可以对光伏逆变器提供的交流电和/或储能变流器提供的交流电进行电压变换后为交流电网中的蓄电池、通信基站或者家用设备等用电设备供电。储能变流器还可以对交流电源提供的交流电进行整流，并将整流得到的直流电存储至储能电池。
在一些可行的实施方式中，在风电电力系统中则至少包括风电发电组件(如风力发电机或者风力发电机组)和风电变流器，风电变流器可以对风力发电组件提供的交流电进行电压变换(可以是对风力发电组件提供的交流电进行整流后得到直流电，再将整流得到的直流电进行逆变转换得到电压变换后的交流电)，并将电压变换后得到的交流电输出到并网点和/或并网变压器。在光伏电力系统、风电电力系统和/或储能电力系统并联的集中接入电力系统中，并网变压器可以对光伏逆变器提供的交流电、风电变流器提供的交流电、和/或储能变流器提供的交流电进行电压变换后为交流电网中的蓄电池、通信基站或者家用设备等用电设备供电。
在本申请实施例中，在电力系统中，包括但不限于光伏逆变器、储能变流器或者风电变流器等表现形式的功率变换器中均可包括多电平变换电路，基于多电平变换电路的输入/输出电平的灵活变换，可增强电力系统的电路稳定性，提高电力系统的瞬态电网支撑能力，电路结构简单，适用性强。
参见图2，图2是本申请实施例提供的电力系统的结构示意图。如图2所示，在电力系统中，直流电源DC可为多电平变换电路提供直流电输入，多电平变换电路可基于直流电源提供的直流电进行逆变转换得到交流电，通过滤波电容C滤波之后为交流电源AC供电。可选的，多电平变换电路还可以基于交流电源提供的交流电进行整流得到直流电，基于该直流电为直流电源DC充电。在图2所示的电力系统中，多电平变换电路可以为上述光伏逆变器、储能变流器或者风电变流器等功率变换器的多电平变换器，该多电平变换电路可为典型的三电平变换电路，在该三电平变换电路中，开关管等器件的规格选型通常是按照典型工况下支撑满容量的需求设计，可以实现三电平输入和/或输出。
参见图3，图3是本申请实施例提供的多电平变换电路的一结构示意图。在图3所示的多电平变换电路中包括串联的母线电容C1、C2、C3和C4，其中，C1连接第一直流连接端， C4连接第二直流连接端。这里，第一直流连接端可为正直流母线的连接端，第二直流连接端可为负直流母线的连接端，电容C2和C3的串联连接端可为母线中点，具体可根据实际应用场景确定，在此不做限制。如图3所示，多电平变换电路中还包括开关管Q1、Q2、Q3、Q4、Q5和Q6，其中，开关管Q1和开关管Q2组成一个桥臂(为方便描述，可以桥臂1为例进行说明)，串联于第一直流连接端以及C2和C3的串联连接端之间，开关管Q3和开关管Q4组成一个桥臂(为方便描述，可以桥臂2为例进行说明)，串联于C2和C3的串联连接端和第二直流连接端之间，开关管Q5和开关管Q6组成一个桥臂(为方便描述，可以桥臂3为例进行说明)，串联于桥臂1的桥臂中点(即开关管Q1和开关管Q2的串联连接点)和桥臂2的桥臂中点(即开关管Q3和开关管Q4的串联连接点)之间，桥臂3的桥臂中点(即开关管Q5和开关管Q6的串联连接点)通过电感L1连接交流负载(包括交流电网)或者交流电源。参见图4，图4是本申请实施例提供的多电平变换电路的一驱动信号示意图。在图3所示的多电平变换电路中，在开关管Q1、开关管Q2、开关管Q3、开关管Q4、开关管Q5和开关管Q6的驱动控制中，Q1和Q2互补导通，Q3和Q4互补导通，Q5和Q6互补导通，这里，Q1和Q2互补导通为高频互补，Q3和Q4互补导通也为高频互补，Q5和Q6互补导通为工频互补，用于实现多电平变换电路的三电平的输入和/或输出，电路结构简单，适用性强。
在一些可行的实施方式中，在瞬态支撑电网的应用场景中，暂态大电流和高母线电压并存使得如图3所示的多电平变换电路中，按照典型工况设计的三电平变换电路中器件的规格选型无法维持满电流运行，三电平变换电路的过载电流能力不足。因此，针对瞬态电网支撑场景下三电平变换电路的过载电流能力不足的问题，本申请实施例提供了一种多电平变换电路，可以通过引入少量的较小规格的器件，可以组合按照典型工况设计的三电平变换电路中各个器件得到一个可以短时提升桥臂电平数的多电平变换电路，可以降低多电平变换电路中各个开关管的切换电压，从而可降低多电平变换电路的开关管切换损耗，提升多电平变换电路中桥臂的功率变换能力。
参见图5，图5是本申请实施例提供的多电平变换电路的另一结构示意图。如图5所示，多电平变换电路中可包括由开关管Q5和开关管Q6的串联组成的第一桥臂、第一电感L1以及串联在第一直流连接端和第二直流连接端之间的第一电平变换单元和第二电平变换单元，第一电平变换单元和第二电平变换单元的串联连接端可作为第三直流连接端。如图5所示，第一桥臂并联在第一电平变换单元的输入/输出端和第二电平变换单元的输入/输出端之间，第一桥臂的桥臂中点连接第一电感L1。在本申请实施例中，第一电平变换单元和第二电平变换单元中任一电平变换单元中均包括串联的第一开关管和第二开关管，串联的第一电容和第二电容，以及电平提升电路，第一开关管和第二开关管的串联连接端作为上述任一电平变换单元的输入/输出端，第一电容和第二电容的串联连接端通过第三开关管和第四开关管连接第一开关管和第二开关管的串联连接端。这里，第一电平变换单元的第一电容和第一开关管连接第一直流连接端，第一电平变换单元的第二电容和第二开关管分别连接第二电平变换单元的第一电容和第一开关管，第二电平变换单元的第二电容和第二开关管连接第二直流连接端，电平提升电路协同第一开关管和所述第二开关管用以提升所述多电平变换电路的输入/输出电平至目标多电平。可选的，电平提升电路中可包括反向串联的第三开关管和第四开关管，第一电平变换单元和第二电平变换单元中第一开关管和第四开关管互补导通且第二开关管和第三开关管互补导通，用以提升所述多电平变换电路的输入/输出电平至目标多电平。可选的，电平提升电路还可以由开关管、二极管或者电阻等电路器件组成，对应的，电平变换单元中第一开关管、第二开关管和电平提升电路中的开关管辅以相应的驱动控制方式，用以提升多 电平变换电路的输入/输出电平。具体的，电平提升电路的电路结构，以及辅以的驱动控制方式可根据实际应用场景确定，在此不做限制。为方便描述，下面将以反向串联的第三开关管和第四开关管组成的电平提升电路为例进行示例说明。如图5所示，在第一电平变换单元中包括串联的第一开关管Q1和第二开关管Q2，串联的第一电容C1和第二电容C2，以及反向串联的第三开关管Qx1和第四开关管Qx2，这里开关管Q1和开关管Q2的串联连接端作为第一电平变换单元的输入/输出端通过开关管Q5连接电感L1，电容C1和电容C2的串联连接端通过开关管Qx1和开关管Qx2连接开关管Q1和开关管Q2的串联连接端。在第二电平变换单元中包括串联的第一开关管Q3和第二开关管Q4，串联的第一电容C3和第二电容C4，以及反向串联的第三开关管Qx3和第四开关管Qx4，这里开关管Q3和开关管Q4的串联连接端作为第二电平变换单元的输入/输出端通过开关管Q6连接电感L1，电容C3和电容C4的串联连接端通过开关管Qx3和开关管Qx4连接开关管Q3和开关管Q4的串联连接端。参见图6，图6是本申请实施例提供的多电平变换电路的另一驱动信号示意图。如图6所示，在图5所示的多电平变换电路中，在开关管Q1、Q2、Q3、Q4、Q5和Q6中任一开关管或者电感L1的电流、端电压、瞬时功率、一段时间内的平均功率，或者端电压变化率、电流变化率或者功率的变化率等电气参数超过某一个参数阈值期间，开关管Qx1～Qx4可以接入多电平变换电路，Q1和Qx互补导通、Q2和Qx1互补导通、Q3和Qx4互补导通、Q4和Qx3互补导通、Q5和Q6互补导通，其中Q5和Q6工频互补、Q1和Qx2高频互补、Q2和Qx1高频互补、Q3和Qx4高频互补、Q4和Qx3高频互补，可提升多电平变换电路的输入/输出电平至目标多电平(比如五电平输入/输出电平，实现了多电平变换电路的五电平输入和/或输出的同时可降低多电平变换电路的电路工作“伏秒”。此时，开关管Q1～Q6的切换电压降低一半，可减少电感L1的电流纹波，可显著降低既有三电平变换电路的主回路损耗，电路结构简单，可行性强。
在本申请实施例中，在图5所示的多电平变换电路中，开关管Qx1～Qx4的加入，组合既有三电平变换电路中开关管Q1～Q6可实现三电平到五电平的变换，可支持在瞬态支撑电网的应用场景中提升多电平变换电路的输入/输出电平，降低多电平变换电路中各个开关管的切换电压，减少电感的电流波纹，可解决三电平变换电路的过载电流能力不足的问题，提高多电平变换电路的电路稳定性，适用性高。
在一些可行的实施方式中，在图5所示的多电平变换电路中，在瞬态支撑电网的应用场景中，当多电平变换电路中开关管Q1、Q2、Q3、Q4、Q5和Q6中任一开关管或者电感L1的电流、端电压、瞬时功率、一段时间内的平均功率，或者端电压变化率、电流变化率或者功率的变化率等电气参数回落到小于或者等于参数阈值时，第一电平变换单元和第二电平变换单元中第一开关管和第二开关管互补导通、第三开关管和第四开关管断开，用于实现多电平变换电路的常规多电平输入/输出，这里，常规多电平可以为三电平，目标多电平可为五电平，即常规多电平小于上述目标多电平。此时，在图5所示的多电平变换电路中，开关管Qx1～Qx4断开，Q1和Q2互补导通、Q3和Q4互补导通、Q5和Q6互补导通，其中Q5和Q6工频互补、Q1和Q2高频互补、Q3和Q4高频互补，可实现多电平变换电路的输入/输出电平从五电平输入/输出恢复至三电平输入/输出，多电平变换电路的输入/输出电平的变换更灵活，适用性强。此外，在图5所示的多电平变换电路中，三电平输入/输出为多电平变换电路的常规多电平输入/输出，五电平输入/输出为瞬态支撑电网的需求，因此，在图5所示的多电平变换电路中，第一电平变换单元或者第二电平变换单元的任一电平变换单元中第三开关管和第四开关管的耐压值小于任一电平变换单元中第一开关管和第二开关管、第一桥臂中各个开关管的耐压值。如图5所示，开关管Qx1～Qx4的耐压值小于开关管Q1、Q2、Q3、Q4、Q5和Q6的耐压值，可 支持瞬态电网支撑的电压和/或电流的变化需求，同时也使得开关管Qx1～Qx4的器件选型更加容易，器件选型更便捷，操作简单，适用性强。可选的，上述开关管Qx1～Qx4的选型包括但不限于继电器、接触器、绝缘栅双极型晶体管(insulated gate bipolar transistor，IGBT)、金属氧化物半导体场效应晶体管(metallic oxide semiconductor field effect transistor，MOSFET)、晶闸管以及二极管中的一项或者多项组合，具体可根据实际应用场景确定，在此不做限制。
在本申请实施例中，基于多电平变换电路中第一电平变换单元和第二电平变换单元中各个开关管的导通或者关断，可实现多电平变换电路以三电平的输入/输出运行，也可实现多电平变换电路以五电平的输入/输出运行，可提高多电平变换电路的输入/输出电平的变换灵活性，电路结构简单，稳定性强。
在一些可行的实施方式中，在图5所示的多电平变换电路中，基于各个开关管的切换控制实现五电平运行的期间，串联的四个母线电容之间可能出现四分之一母线电压不均衡，为实现多电平变换电路以五电平运行时各个母线电容之间四分之一的母线电压的均衡，本申请实施例提供的多电平变换电路中还可包括多个平衡电路，用于实现各个母线电容的电压均衡。
参见图7，图7是本申请实施例提供的多电平变换电路的另一结构示意图。如图7所示，在图5所示的多电平变换电路的基础上还可以包括串联在第一直流连接端和第二直流连接端之间的多个平衡电路，其中一个平衡电路并联于第一电平变换单元或者第二电平变换单元中一个电容的两端。可选的，上述多个平衡电路中任一平衡电路中可包括串联的开关管和分压电阻，这里，开关管用于在上述任一平衡电路并联的任一电容的两端电压大于目标电压时，导通分压电阻和任一电容的连接，通过分压电阻消耗任一电容的能量，可以调节任一电容的两端电压至目标电压，电路结构简单，可行性高。这里，目标电压可为四分之一的母线电压。如图7所示，母线电容C1的两端可并联一个平衡电路(为方便描述可以平衡电路1为例进行说明)，该平衡电路1可由开关管Qy1和分压电阻R1组成。母线电容C2的两端可并联一个平衡电路(为方便描述可以平衡电路2为例进行说明)，该平衡电路2可由开关管Qy2和分压电阻R3组成。母线电容C3的两端可并联一个平衡电路(为方便描述可以平衡电路3为例进行说明)，该平衡电路3可由开关管Qy3和分压电阻R3组成。母线电容C4的两端可并联一个平衡电路(为方便描述可以平衡电路4为例进行说明)，该平衡电路4可由开关管Qy4和分压电阻R4组成。平衡电路1、平衡电路2、平衡电路3和平衡电路4可分别用于在母线电容C1、母线电容C2、母线电容C3和母线电容C4的两端电压大于四分之一的母线电压(即正直流母线和负直流母线之间的电压)时，调节母线电容C1、母线电容C2、母线电容C3和母线电容C4的两端电压至四分之一的母线电压。也就是说，在图7所示的多电平变换电路中，当多电平变换电路工作在五电平输入/输出的模式时，目标电压可为四分之一母线电压。可以理解，在图7所示的多电平变换电路中，当任一母线电容的端电压稳定在四分之一母线电压时，可以通过该母线电容并联的开关管(Qy1、Qy2、Qy3或者Qy4)断开分压电阻和母线电容的连接，以维持母线电容的端电压在四分之一的母线电压。同样的，当图7所示的多电平变换电路中开关管Qx1～Qx4断开时，多电平变换电路运行在三电平输入/输出的工作模式时，也可通过开关管Qy1、Qy2、Qy3和Qy4断开各个分压电阻和母线电容的连接，以支撑多电平变换电路的常规三电平的输入/输出。在本申请中，通过平衡电路的接入，可保证暂态目标多电平运行时母线电容的端电压的均衡，提高电路工作稳定性，电路结构简单，适用性强。可选的，在图7所示的电路结构中，上述开关管Qy1、Qy2、Qy3和Qy4的选型也可为包括但不限于继电器、接触器、IGBT、MOSFET、晶闸管以及二极管中的一项或者多项组合，具体可根据实际 应用场景确定，在此不做限制。
参见图8，图8是本申请实施例提供的多电平变换电路的另一结构示意图。为实现多电平变换电路以五电平运行时各个母线电容之间四分之一的母线电压的均衡，如图8所示，在图5所示的多电平变换电路的基础上还可以包括第二桥臂(由开关管Qy1和Qy2串联组成)、第三桥臂(由开关管Qy3和Qy4串联组成)、第二电感Ly1和第三电感Ly2。这里，第二桥臂并联在第一直流连接端和第三直流连接端之间，第二桥臂的桥臂中点(即开关管Qy1和Qy2的串联连接点)通过电感Ly1连接第一电平变换单元中第一电容(即电容C1)和第二电容(即电容C2)的串联连接端，第二桥臂的上下桥臂(即开关管Qy1和Qy2)互补发波，可用于实现第一电平变换单元中电容C1和电容C2的电压均衡，可保证多电平变换电路工作在五电平输入/输出的模式时，第一电平变换单元的电容C1和电容C2的端电压保持在四分之一母线电压，可实现电容的端电压均衡。同理，第三桥臂并联在第三直流连接端和第二直流连接端之间，第三桥臂的桥臂中点(即开关管Qy3和Qy4的串联连接点)通过第三电感Ly2连接第二电平变换单元中第一电容(即电容C3)和第二电容(即电容C4)的串联连接端，第三桥臂的上下桥臂(即开关管Qy3和Qy4)互补发波可实现第二电平变换单元中电容C3和电容C4的电压均衡，从而可实现多电平变换电路中各个母线电容的端电压的均衡，电路结构简单，稳定性强，适用性高。可选的，在图8所示的电路结构中，上述开关管Qy1、Qy2、Qy3和Qy4的选型也可为包括但不限于继电器、接触器、IGBT、MOSFET、晶闸管以及二极管中的一项或者多项组合，具体可根据实际应用场景确定，在此不做限制。
在本申请实施例中，通过母线电容的端电压的均衡控制，可保证多电平变换电路运行在五电平输入/输出的工作模式下，母线电容的端电压的稳定，从而可提高多电平变换电路的工作稳定性，电路结构简单，适用性强。
在一些可行的实施方式中，针对瞬态电网支撑场景下三电平变换电路的过载电流能力不足的问题，本申请实施例提供了另一种多电平变换电路，可以通过电平变换辅助单元的加入，组合按照典型工况设计的三电平变换电路中各个器件得到另一种电路结构的多电平变换电路，同样可以短时提升桥臂电平数的多电平变换电路，可以降低多电平变换电路中各个开关管的切换电压，从而可降低多电平变换电路的开关管切换损耗，提升多电平变换电路中桥臂的功率变换能力。
参见图9，图9是本申请实施例提供的多电平变换电路的另一结构示意图。如图9所示，多电平变换电路中包括电平变换辅助单元、第一桥臂(由开关管Q5和Q6组成)、电感L1和串联在第一直流连接端和第二直流连接端之间的第二桥臂(由开关管Q1和Q2串联组成)和第三桥臂(由开关管Q3和Q4串联组成)。第一桥臂并联在第二桥臂的桥臂中点(开关管Q1和Q2的串联连接点)和第三桥臂的桥臂中点(开关管Q3和Q4的串联连接点)之间，第一桥臂的桥臂中点(开关管Q5和Q6的串联连接点)通过电平变换辅助单元连接电感L1，电平变换辅助单元用于提升多电平变换电路的输入/输出电平至目标多电平，这里，目标多电平可为五电平。
在一些可行的实施方式中，如图9所示，上述电平变换辅助单元中可包括辅助桥臂、第一开关管S1、第二开关管S2和飞跨电容C。这里，辅助桥臂的上桥臂(开关管Qx1)与上述第一桥臂的上桥臂(开关管Q5)串联于第一串联连接点，辅助桥臂的下桥臂(开关管Qx6)与上述第一桥臂的下桥臂(开关管Q6)串联于第二串联连接点，飞跨电容C和辅助开关管Sc串联在上述第一串联连接点和上述第二串联连接点之间，辅助桥臂的桥臂中点(开关管Qx1和开关管Qx6的串联连接点)连接电感L。第一开关管S1并联在辅助桥臂的上桥臂(开关管 Qx1)的两端，第二开关管S2并联在上述辅助桥臂的下桥臂(开关管Qx6)的两端。如图9所示，在该多电平变换电路中，第一开关管S1闭合时可旁路开关管Qx1，第一开关管S1断开时开关管Qx1接入。可选的，如图10，图10是本申请实施例提供的多电平变换电路的另一结构示意图，电平变换辅助单元中还可包括辅助开关管Sc，辅助开关管Sc和飞跨电容串联，辅助开关管Sc闭合时可接入飞跨电容，辅助开关管Sc断开时飞跨电容也随着断开连接。当开关管S1和开关管S2断开且辅助开关管Sc闭合时，电平变换辅助单元接入多电平变换电路的主功率回路，电平变换辅助单元的接入可用于提升多电平变换电路的输入/输出电平至目标多电平(比如五电平)，可在瞬态支撑电网的应用场景中提升多电平变换电路的输入/输出电平，降低多电平变换电路中各个开关管的切换电压，减少电感的电流波纹，可实现三电平到五电平的输入/输出电平的提升，可解决三电平变换电路的过载电流能力不足的问题，电路结构简单，稳定性强，适用性高。在图9或者图10所示的电路结构中，电平变换辅助单元的电路器件少，器件类型简单，可提高基于电平变换辅助单元实现多电平变换电路的电平提升的可行性，操作简单，适用性强。
在一些可行的实施方式中，在瞬态支撑电网的应用场景中，多电平变换电路中各个桥臂的开关管或者多电平变换电路的电感各处均可能出现暂态过压或者过流，通过多电平变换电路中桥臂电流或者电压在某一个预设时间内是否超过某一个预设阈值，则可检测到多电平变换电路的桥臂是否出现过压或者过流。同样的，通过多电平变换电路中电感的电流或者电压在某一个预设时间内是否超过某一个预设阈值，也可检测到多电平变换电路的桥臂是否出现过压或者过流。在多电平变换电路的桥臂或者电感出现过压或者过流时，则可启动电平变换辅助单元，用于提升多电平变换电路的电平至五电平等，可降低多电平变换电路的主功率回路中各桥臂的开关管切换电压、减小电感纹波等。因此，当任一桥臂(比如第一桥臂、第二桥臂或第三桥臂中的任意一个)或者电感L1的电气参数大于目标参数阈值时，开关管S1和开关管S2断开可以导通辅助桥臂的上桥臂和下桥臂与第一桥臂的上桥臂和下桥臂的连接。同时事，辅助开关管Sc导通以接入飞跨电容，第一桥臂、第二桥臂、第三桥臂和辅助桥臂中各个桥臂的上下桥臂互补导通，可提升上述多电平变换电路的输入/输出电平至目标多电平，从而可实现多电平变换电路的输入/输出电平从三电平提升至五电平，电路结构简单，稳定性强。这里，上述任一桥臂或者电感的电气参数包括但不限于电流、电压、功率、电流变化率、电压变化率或者功率变化率等，具体可根据实际应用场景确定，在此不做限制。参见图11，图11是本申请实施例提供的多电平变换电路的另一驱动信号示意图。如图11所示，当多电平变换电路的主功率回路中任一桥臂(比如第一桥臂、第二桥臂或第三桥臂中的任意一个)或者电感L1的电气参数大于目标参数阈值时，开关管S1和开关管S2断开且辅助开关管Sc闭合，电平变换辅助单元接入多电平变换电路的主功率回路，此时Q1和Q3的驱动信号相同，Q1和Q2互补导通且Q3和Q4互补导通，以实现多电平变换电路的工频发波，Q6与Q5互补导通以实现多电平变换电路的高频发波，Qx1与Qx6互补导通，同样用于实现多电平变换电路的高频发波，可实现多电平变换电路的输入/输出电平从三电平提升至五电平，电路结构简单，稳定性强。这里，辅助桥臂的开关管的耐压值和飞跨电容的耐压值小于第一桥臂、第二桥臂和第三桥臂中各个开关管(即开关管Q1、Q2、Q3、Q4、Q5和Q6)的耐压值，器件选择灵活，适用性高。可选的，在图9或图10所示的电路结构中，开关管S1、开关管S2、开关管Qx1和Qx6的选型也可为包括但不限于继电器、接触器、IGBT、MOSFET、晶闸管以及二极管中的一项或者多项组合，具体可根据实际应用场景确定，在此不做限制。
在一些可行的实施方式中，在多电平变换电路的主功率回路中第一桥臂、第二桥臂或者 第三桥臂中任一桥臂或者电感的电气参数小于或者等于上述目标参数阈值时，表明当前多电平变换电路的主功率回路不存在过压或者过流的现象，此时开关管S1和开关管S2可导通，以旁路辅助桥臂的上桥臂和下桥臂，同时，辅助开关管Sc断开以断开飞跨电容和主功率回路的连接。当开关管S1和开关管S2导通且辅助开关管Sc断开时，第一桥臂、第二桥臂和第三桥臂中各个桥臂的上下桥臂互补导通，即开关管Q1和Q2互补导通、Q3和Q4互补导通，且Q5和Q6互补导通，可实现上述多电平变换电路的常规多电平输入/输出，这里，常规多电平可为三电平，目标多电平可为五电平，即上述常规多电平小于上述目标多电平。
在本申请实施例中，开关管S1和第二开关管S1断开，且辅助开关管Sc的导通可实现电平变换辅助单元的接入，可用于提升多电平变换电路的输入/输出电平至目标多电平(比如五电平)，可在瞬态支撑电网的应用场景中提升多电平变换电路的输入/输出电平，降低多电平变换电路中各个开关管的切换电压，减少电感的电流波纹，可实现三电平到五电平的输入/输出电平的提升，可解决三电平变换电路的过载电流能力不足的问题，电路结构简单，稳定性强，适用性高。同时，通过开关管S1、第二开关管S1和辅助开关管Sc的导通或者关断可实现电平变换辅助单元和三电平输入/输出回路(即图9所示的多电平变换电路的主功率回路)的分离，以实现多电平变换电路的三电平输入/输出，可提高多电平变换电路的输入/输出电平变换的切换灵活性，操作简单，适用性强。
参见图12，图12是本申请实施例提供的功率变换器的结构示意图。
在一些可行的实施方式中，上述功率变换器可为光伏逆变器、储能变流器或者风电变流器等，具体可根据上述多电平变换电路的应用场景确定，在此不做限制。为方便描述，下面将以光伏逆变器作为功率变换器的示例进行说明。如图12所示，光伏逆变器中可包括控制器和多电平变换电路，该多电平变换电路可为上述图5至图8所示的任一结构，具体可根据实际应用场景确定，在此不做限制。在图12所示的光伏逆变器中，多电平变换电路可基于第一直流连接端和第二直流连接端提供的直流电进行逆变转换，并将逆变转换得到的交流电输出至交流电网(或者交流负载、交流电源，图12中未示出)。在图12所示的光伏逆变器中，控制器可以在上述多电平变换电路中第一桥臂(如图5至图8中任一结构所示多电平变换电路中的开关管Q5和Q6)的各开关管、上述任一电平变换单元中的第一开关管和第二开关管(如图5至图8中任一结构所示多电平变换电路中的Q1和Q2，或Q3和Q4)、或者第一电感(如图5至图8中任一结构所示多电平变换电路中的电感L1)的电气参数大于参数阈值时，控制第一电平变换单元和第二电平变换单元中第一开关管和第四开关管互补导通、第二开关管和第三开关管互补导通，以提升多电平变换电路的输入/输出电平至目标多电平。如图6所示，在图5所示的多电平变换电路中，控制器可在检测到开关管Q1、Q2、Q3、Q4、Q5和Q6中任一开关管或者电感L1的电流、端电压、瞬时功率、一段时间内的平均功率，或者端电压变化率、电流变化率或者功率的变化率等电气参数超过某一个参数阈值的期间，控制开关管Qx1～Qx4接入多电平变换电路，同时可控制Q1和Qx互补导通、Q2和Qx1互补导通、Q3和Qx4互补导通、Q4和Qx3互补导通、Q5和Q6互补导通以实现多电平变换电路的五电平输入/输出。其中，Q5和Q6工频互补、Q1和Qx2高频互补、Q2和Qx1高频互补、Q3和Qx4高频互补、Q4和Qx3高频互补，可提升多电平变换电路的输入/输出电平至目标多电平(比如五电平输入/输出电平，实现了多电平变换电路的五电平输入和/或输出的同时可降低多电平变换电路的电路工作“伏秒”。此时，光伏逆变器中多电平变换电路的开关管Q1～Q6的切换电压降低一半，可减少电感L1的电流纹波，可显著降低既有三电平变换电路的主功率回路的损耗，从而可降低光伏逆变器的功率损耗，电路结构简单，可行性强。可选的，在图5至图8中任一结构所 示多电平变换电路中，电平提升电路中也可以有其他电路结构组成，电平提升电路可由开关管和二极管组成、或者由开关管和电阻组成，对应的，控制器可在第一桥臂的各开关管、任一电平变换单元中的第一开关管和第二开关管、或者第一电感的电气参数大于参数阈值时，控制第一电平变换单元和第二电平变换单元中第一开关管、第二开关管和电平提升电路动作，以提升多电平变换电路的输入/输出电平至目标多电平。可以理解，电平变换单元中电平提升电路的电路结构不同，电平变换单元中第一开关管、第二开关管和电平提升电路中的开关管辅以相应的驱动控制方式，同样用以提升多电平变换电路的输入/输出电平。具体的，电平提升电路的电路结构，以及辅以的驱动控制方式可根据实际应用场景确定，在此不做限制。
在本申请实施例中，功率变换器(如光伏逆变器)可基于多电平变换单元中第一电平变换单元和第二电平变换单元中第一开关管和第四开关管互补导通且第二开关管和第三开关管互补导通，实现光伏逆变器中多电平变换电路的输入/输出电平的提升，可降低光伏逆变器中多电平变换电路中各个开关管的切换电压，减少电感的电流波纹，可提高光伏逆变器中的电路稳定性，适用性高。
在一些可行的实施方式中，光伏逆变器的控制器还可以在上述多电平变换电路中第一桥臂的各开关管、任一电平变换单元中的第一开关管和第二开关管、或者第一电感的电气参数小于或者等于上述参数阈值时，控制第一电平变换单元和第二电平变换单元中第一开关管和第二开关管互补导通、第三开关管和第四开关管断开，以实现上述多电平变换电路的常规多电平输入/输出。比如，在图5所示的多电平变换电路中，在瞬态支撑电网的应用场景中，当控制器检测到多电平变换电路中开关管Q1、Q2、Q3、Q4、Q5和Q6中任一开关管或者电感L1的电流、端电压、瞬时功率、一段时间内的平均功率，或者端电压变化率、电流变化率或者功率的变化率等电气参数回落到小于或者等于参数阈值时，可控制第一电平变换单元和第二电平变换单元中第一开关管和第二开关管互补导通、第三开关管和第四开关管断开，用于实现多电平变换电路的常规多电平输入/输出。此时，在图5所示的多电平变换电路中，控制器可控制开关管Qx1～Qx4断开、Q1和Q2互补导通、Q3和Q4互补导通、Q5和Q6互补导通，其中Q5和Q6工频互补、Q1和Q2高频互补、Q3和Q4高频互补，可以实现多电平变换电路的输入/输出电平从五电平输入/输出恢复至三电平输入/输出，多电平变换电路的输入/输出电平的变换更灵活，适用性强。在本申请实施例中，基于多电平变换电路中第一电平变换单元和第二电平变换单元中各个开关管的导通或者关断，可实现多电平变换电路以三电平的输入/输出运行，可提高光伏逆变器的输入/输出电平的变换灵活性，电路结构简单，稳定性强。
在一些可行的实施方式中，在图12所示的光伏逆变器中，多电平变换电路基于各个开关管的切换控制实现五电平运行的期间，串联的四个母线电容之间可能出现四分之一母线电压不均衡，为实现多电平变换电路以五电平运行时各个母线电容之间四分之一的母线电压的均衡，本申请实施例提供的多电平变换电路中还可包括多个平衡电路，用于实现各个母线电容的电压均衡。当光伏逆变器中包括的多电平变换电路使用图7所示的电路结构时，光伏逆变器中的控制器还可以在多电平变换电路中任一平衡电路并联的任一电容的两端电压大于目标电压时，控制上述任一电容并联的开关管导通，以通过上述任一平衡电路的分压电阻消耗上述任一电容的能量，以调节上述任一电容的两端电压至目标电压，可提高功率变换器的电路工作稳定性，电路结构简单，适用性强。在图7所示的多电平变换电路中，当检测到任一母线电容的端电压大于四分之一母线电压时，控制器可控制该母线电容并联的开关管(Qy1、Qy2、Qy3或者Qy4)导通，以通过开关管(Qy1、Qy2、Qy3或者Qy4)串联的分压电阻消耗上述任一电容的能量，以调节上述任一电容的两端电压至目标电压。在图7所示的多电平变换电路 中，当检测到任一母线电容的端电压稳定在四分之一母线电压时，控制器可控制该母线电容并联的开关管(Qy1、Qy2、Qy3或者Qy4)断开，以分断分压电阻和母线电容的连接，以维持母线电容的端电压在四分之一的母线电压。同样的，当图7所示的多电平变换电路中开关管Qx1～Qx4断开时，多电平变换电路运行在三电平输入/输出的工作模式时，控制器也可控制开关管Qy1、Qy2、Qy3和Qy4断开，以分断各个分压电阻和母线电容的连接，以支撑多电平变换电路的常规三电平的输入/输出。在本申请中，通过平衡电路的接入，可保证暂态目标多电平运行时母线电容的端电压的均衡，提高电路工作稳定性，电路结构简单，适用性强。
在一些可行的实施方式中，当光伏逆变器中包括的多电平变换电路使用图8所示的电路结构时，光伏逆变器的控制器还可以在多电平变换电路中第一电平变换单元的第一电容和第二电容的端电压不相同时，控制第二桥臂的上下桥臂互补发波，以实现第一电平变换单元中第一电容和第二电容的端电压均衡。控制器还可以在第二电平变换单元中第一电容和第二电容的端电压不相同时，控制第三桥臂的上下桥臂互补发波，以实现上述第二电平变换单元中第一电容和第二电容的端电压均衡，可提高功率变换器的电路工作稳定性，电路结构简单，适用性强。如图8所示，第二桥臂并联在第一直流连接端和第三直流连接端之间，第二桥臂的桥臂中点(即开关管Qy1和Qy2的串联连接点)通过电感Ly1连接第一电平变换单元中第一电容(即电容C1)和第二电容(即电容C2)的串联连接端，控制器通过控制第二桥臂的上下桥臂(即开关管Qy1和Qy2)互补发波，可实现第一电平变换单元中电容C1和电容C2的电压均衡，从而可保证多电平变换电路工作在五电平输入/输出的模式时，第一电平变换单元的电容C1和电容C2的端电压保持在四分之一母线电压，可实现电容的端电压均衡。同理，第三桥臂并联在第三直流连接端和第二直流连接端之间，第三桥臂的桥臂中点(即开关管Qy3和Qy4的串联连接点)通过第三电感Ly2连接第二电平变换单元中第一电容(即电容C3)和第二电容(即电容C4)的串联连接端，控制器通过控制第三桥臂的上下桥臂(即开关管Qy3和Qy4)互补发波可实现第二电平变换单元中电容C3和电容C4的电压均衡，从而可实现多电平变换电路中各个母线电容的端电压的均衡，电路结构简单，稳定性强，适用性高。
在一些可行的实施方式中，当光伏逆变器中包括的多电平变换电路使用图9或者图10所示的电路结构时，光伏逆变器中的控制器还可以在多电平变换电路中任一桥臂或者电感的电气参数大于参数阈值时，控制多电平变换电路中电平变换辅助单元中第一开关管和第二开关管断开、上述辅助开关管导通，并控制上述第一桥臂、上述第二桥臂、上述第三桥臂和上述辅助桥臂中各个桥臂的上下桥臂互补导通，以提升上述多电平变换电路的输入/输出电平至目标多电平，功率变换器的电路结构简单，适用性强。如图11所示，当控制器检测到多电平变换电路的主功率回路中任一桥臂(比如第一桥臂、第二桥臂或第三桥臂中的任意一个)或者电感L1的电气参数大于目标参数阈值时，可控制开关管S1和开关管S2断开、同时控制辅助开关管Sc闭合，以将电平变换辅助单元接入多电平变换电路的主功率回路。此时，控制器还可基于相同的驱动信号控制Q1和Q3导通或关断，同时可控制Q1和Q2互补导通、Q3和Q4互补导通，以实现多电平变换电路的工频发波，控制Q6与Q5互补导通以实现多电平变换电路的高频发波、控制Qx1与Qx6互补导通，同样用于实现多电平变换电路的高频发波，可实现多电平变换电路的输入/输出电平从三电平提升至五电平，电路结构简单，稳定性强。
在一些可行的实施方式中，当光伏逆变器中包括的多电平变换电路使用图9或者图10所示的电路结构时，控制器还可以在上述任一桥臂或者上述电感的电气参数小于或者等于上述参数阈值时，控制上述电平变换辅助单元中第一开关管和第二开关管导通、上述辅助开关管断开，并控制上述第一桥臂、上述第二桥臂、和上述第三桥臂中各个桥臂的上下桥臂互补导 通，以实现上述多电平变换电路的常规多电平输入/输出，这里常规多电平可为三电平，目标多电平可为五电平，即上述常规多电平小于上述目标多电平，可提高光伏逆变器的输入/输出电平的变换灵活性，操作简单，适用性强。如图9所示，控制器可在检测到多电平变换电路的主功率回路中第一桥臂、第二桥臂或者第三桥臂中任一桥臂或者电感的电气参数小于或者等于上述目标参数阈值时，可控制开关管S1和开关管S2导通，以旁路辅助桥臂的上桥臂和下桥臂，同时，控制辅助开关管Sc断开以断开飞跨电容和主功率回路的连接。当开关管S1和开关管S2导通且辅助开关管Sc断开时，控制器可控制第一桥臂、第二桥臂和第三桥臂中各个桥臂的上下桥臂互补导通，即开关管Q1和Q2互补导通、Q3和Q4互补导通，且Q5和Q6互补导通，可实现上述多电平变换电路的常规多电平输入/输出，电路结构简单，适用性强。
在本申请实施例中，光伏逆变器的控制可通过控制开关管S1和第二开关管S1断开，且控制辅助开关管Sc的导通来控制电平变换辅助单元的接入，可提升多电平变换电路的输入/输出电平至目标多电平(比如五电平)，可在瞬态支撑电网的应用场景中提升多电平变换电路的输入/输出电平，降低多电平变换电路中各个开关管的切换电压，减少电感的电流波纹，可实现三电平到五电平的输入/输出电平的提升，可解决三电平变换电路的过载电流能力不足的问题，电路结构简单，稳定性强，适用性高。同时，通过控制开关管S1、开关管S2和辅助开关管Sc的导通或者关断可实现电平变换辅助单元和三电平输入/输出回路(即图9所示的多电平变换电路的主功率回路)的分离，以实现多电平变换电路的三电平输入/输出，可提高多电平变换电路的输入/输出电平变换的切换灵活性，增强光伏逆变器的电路稳定性，操作简单，适用性强。

Claims (20)

  1. 一种多电平变换电路，其特征在于，所述多电平变换电路中包括第一桥臂、第一电感以及串联在第一直流连接端和第二直流连接端之间的第一电平变换单元和第二电平变换单元，所述第一桥臂并联在所述第一电平变换单元的输入/输出端和所述第二电平变换单元的输入/输出端之间，所述第一桥臂的桥臂中点连接所述第一电感；
    所述第一电平变换单元和所述第二电平变换单元中任一电平变换单元中包括串联的第一开关管和第二开关管，串联的第一电容和第二电容，以及电平提升电路，所述第一开关管和所述第二开关管的串联连接端作为所述任一电平变换单元的输入/输出端，所述第一电容和所述第二电容的串联连接端通过所述电平提升电路连接所述第一开关管和所述第二开关管的串联连接端；所述第一电平变换单元的第一电容和第一开关管连接所述第一直流连接端，所述第一电平变换单元的第二电容和第二开关管分别连接所述第二电平变换单元的第一电容和第一开关管，所述第二电平变换单元的第二电容和第二开关管连接所述第二直流连接端；
    所述第一电平变换单元和所述第二电平变换单元的所述电平提升电路，用于协同所述第一开关管和所述第二开关管提升所述多电平变换电路的输入/输出电平至目标多电平。
  2. 根据权利要求1所述的多电平变换电路，其特征在于，所述电平提升电路中包括反向串联的第三开关管和第四开关管；
    所述第一电平变换单元和所述第二电平变换单元中所述第一开关管和所述第四开关管互补导通且所述第二开关管和所述第三开关管互补导通，用于提升所述多电平变换电路的输入/输出电平至目标多电平。
  3. 根据权利要求2所述的多电平变换电路，其特征在于，所述第一电平变换单元和所述第二电平变换单元中第一开关管和第二开关管互补导通、第三开关管和第四开关管断开，用于实现所述多电平变换电路的常规多电平输入/输出，所述常规多电平小于所述目标多电平。
  4. 根据权利要求2或3所述的多电平变换电路，其特征在于，所述任一电平变换单元中第三开关管和第四开关管的耐压值小于所述任一电平变换单元中第一开关管和第二开关管、所述第一桥臂中各个开关管的耐压值。
  5. 根据权利要求1-4任一项所述的多电平变换电路，其特征在于，所述多电平变换电路中还包括串联在所述第一直流连接端和所述第二直流连接端之间的多个平衡电路，一个所述平衡电路并联于所述第一电平变换单元或者所述第二电平变换单元中一个电容的两端；
    所述多个平衡电路中任一平衡电路用于在所述任一平衡电路并联的任一电容的两端电压大于目标电压时，调节所述任一电容的两端电压至目标电压。
  6. 根据权利要求5所述的多电平变换电路，其特征在于，所述任一平衡电路中包括串联的开关管和分压电阻；
    所述开关管用于在所述任一平衡电路并联的任一电容的两端电压大于目标电压时，导通所述分压电阻和所述任一电容的连接，以通过所述分压电阻消耗所述任一电容的能量，以调节所述任一电容的两端电压至目标电压。
  7. 根据权利要求1-4任一项所述的多电平变换电路，其特征在于，所述多电平变换电路中还包括第二桥臂、第三桥臂、第二电感和第三电感；
    所述第二桥臂并联在所述第一直流连接端和第三直流连接端之间，所述第三直流连接端为所述第一电平变换单元和第二电平变换单元的串联连接端，所述第二桥臂的桥臂中点通过所述第二电感连接所述第一电平变换单元中第一电容和第二电容的串联连接端，所述第二桥臂的上下桥臂互补发波用于实现所述第一电平变换单元中第一电容和第二电容的电压均衡；
    所述第三桥臂并联在所述第三直流连接端和所述第二直流连接端之间，所述第三桥臂的桥臂中点通过所述第三电感连接所述第二电平变换单元中第一电容和第二电容的串联连接端，所述第三桥臂的上下桥臂互补发波用于实现所述第二电平变换单元中第一电容和第二电容的电压均衡。
  8. 一种多电平变换电路，其特征在于，所述多电平变换电路中包括电平变换辅助单元、第一桥臂、电感和串联在第一直流连接端和第二直流连接端之间的第二桥臂和第三桥臂，所述第一桥臂并联在所述第二桥臂的桥臂中点和所述第三桥臂的桥臂中点之间，所述第一桥臂的桥臂中点通过所述电平变换辅助单元连接所述电感；
    所述电平变换辅助单元用于提升所述多电平变换电路的输入/输出电平至目标多电平。
  9. 根据权利要求8所述的多电平变换电路，其特征在于，所述电平变换辅助单元中包括辅助桥臂、第一开关管、第二开关管和飞跨电容；
    所述辅助桥臂的上桥臂与所述第一桥臂的上桥臂串联于第一串联连接点，所述辅助桥臂的下桥臂与所述第一桥臂的下桥臂串联于第二串联连接点，所述飞跨电容串联在所述第一串联连接点和所述第二串联连接点之间，所述辅助桥臂的桥臂中点连接所述电感，所述第一开关管并联在所述辅助桥臂的上桥臂的两端，所述第二开关管并联在所述辅助桥臂的下桥臂的两端；
    所述第一开关管和第二开关管用于导通所述辅助桥臂的上桥臂和下桥臂与所述第一桥臂的上桥臂和下桥臂的连接，所述第一桥臂、所述第二桥臂、所述第三桥臂和所述辅助桥臂中各个桥臂的上下桥臂互补导通，用于提升所述多电平变换电路的输入/输出电平至目标多电平。
  10. 根据权利要求9所述的多电平变换电路，其特征在于，所述第一开关管和第二开关管在任一桥臂或者所述电感的电气参数大于目标参数阈值时断开，用于导通所述辅助桥臂的上桥臂和下桥臂与所述第一桥臂的上桥臂和下桥臂的连接。
  11. 根据权利要求9所述的多电平变换电路，其特征在于，所述第一开关管和第二开关管在所述任一桥臂或者所述电感的电气参数小于或者等于所述目标参数阈值时导通，用于旁路所述辅助桥臂的上桥臂和下桥臂；
    所述第一桥臂、所述第二桥臂和所述第三桥臂中各个桥臂的上下桥臂互补导通，用于实现所述多电平变换电路的常规多电平输入/输出，所述常规多电平小于所述目标多电平。
  12. 根据权利要求10或11所述的多电平变换电路，其特征在于，所述电平变换辅助单元 中还包括辅助开关管，所述辅助开关管和所述飞跨电容串联；
    所述辅助开关管在所述任一桥臂或者所述电感的电气参数大于所述目标参数阈值时导通，用于接入所述飞跨电容；
    所述辅助开关管在所述任一桥臂或者所述电感的电气参数小于或者等于所述目标参数阈值时断开，用于断开所述飞跨电容。
  13. 根据权利要求8-12任一项所述的多电平变换电路，其特征在于，所述辅助桥臂的开关管的耐压值和所述飞跨电容的耐压值小于所述第一桥臂、所述第二桥臂和所述第三桥臂中各个开关管的耐压值。
  14. 一种功率变换器，其特征在于，所述功率变换器包括控制器和如权利要求1-7任一项所述的多电平变换电路；
    所述控制器用于在所述第一桥臂的各开关管、所述任一电平变换单元中的第一开关管和第二开关管、或者所述第一电感的电气参数大于参数阈值时，控制所述第一电平变换单元和所述第二电平变换单元中所述第一开关管、所述第二开关管和所述电平提升电路动作，以提升所述多电平变换电路的输入/输出电平至目标多电平。
  15. 根据权利要求14所述的功率变换器，其特征在于，所述电平提升电路中包括反向串联的第三开关管和第四开关管；
    所述控制器用于在所述第一桥臂的各开关管、所述任一电平变换单元中的第一开关管和第二开关管、或者所述第一电感的电气参数大于参数阈值时，控制所述第一电平变换单元和所述第二电平变换单元中所述第一开关管和所述第二开关管互补导通、所述第三开关管和所述第四开关管断开，以提升所述多电平变换电路的输入/输出电平至目标多电平。
  16. 根据权利要求14所述的功率变换器，其特征在于，所述控制器还用于在所述第一桥臂的各开关管、所述任一电平变换单元中的第一开关管和第二开关管、或者所述第一电感的电气参数小于或者等于所述参数阈值时，控制所述第一电平变换单元和所述第二电平变换单元中所述第一开关管和所述第二开关管互补导通、所述第三开关管和所述第四开关管断开，以实现所述多电平变换电路的常规多电平输入/输出，所述常规多电平小于所述目标多电平。
  17. 根据权利要求15或16所述的功率变换器，其特征在于，所述控制器还用于所述多电平变换电路中任一平衡电路并联的任一电容的两端电压大于目标电压时，控制所述任一电容并联的开关管导通，以通过所述任一平衡电路的分压电阻消耗所述任一电容的能量，以调节所述任一电容的两端电压至目标电压。
  18. 根据权利要求15或16所述的功率变换器，其特征在于，所述控制器还用于在所述第一电平变换单元中第一电容和第二电容的端电压不相同时，控制所述第二桥臂的上下桥臂互补发波，以实现所述第一电平变换单元中第一电容和第二电容的端电压均衡；
    所述控制器还用于在所述第二电平变换单元中第一电容和第二电容的端电压不相同时，控制所述第三桥臂的上下桥臂互补发波，以实现所述第二电平变换单元中第一电容和第二电容的端电压均衡。
  19. 一种功率变换器，其特征在于，所述功率变换器包括控制器和如权利要求8-13任一项所述的多电平变换电路；
    所述控制器用于在任一桥臂或者所述电感的电气参数大于参数阈值时，控制所述电平变换辅助单元中第一开关管和第二开关管断开，并控制所述第一桥臂、所述第二桥臂、所述第三桥臂和所述辅助桥臂中各个桥臂的上下桥臂互补导通，以提升所述多电平变换电路的输入/输出电平至目标多电平。
  20. 根据权利要求19所述的功率变换器，其特征在于，所述控制器还用于在所述任一桥臂或者所述电感的电气参数小于或者等于所述参数阈值时，控制所述电平变换辅助单元中第一开关管和第二开关管导通，并控制所述第一桥臂、所述第二桥臂、和所述第三桥臂中各个桥臂的上下桥臂互补导通，以实现所述多电平变换电路的常规多电平输入/输出，所述常规多电平小于所述目标多电平。
PCT/CN2022/122148 2022-09-28 2022-09-28 多电平变换电路、功率变换器和电力系统 WO2024065280A1 (zh)

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WO2011024010A2 (en) * 2009-08-29 2011-03-03 Turbo Power Systems Limited Inverter
CN103475249A (zh) * 2013-09-11 2013-12-25 华为技术有限公司 一种多电平逆变器
CN106787922A (zh) * 2016-12-23 2017-05-31 华为技术有限公司 变流器
CN106887965A (zh) * 2017-04-26 2017-06-23 阳光电源股份有限公司 多电平逆变器的控制方法、控制装置以及逆变器
CN110829872A (zh) * 2019-11-26 2020-02-21 西南交通大学 一种永磁牵引系统用混合多电平逆变器及其控制方法

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2011024010A2 (en) * 2009-08-29 2011-03-03 Turbo Power Systems Limited Inverter
CN103475249A (zh) * 2013-09-11 2013-12-25 华为技术有限公司 一种多电平逆变器
CN106787922A (zh) * 2016-12-23 2017-05-31 华为技术有限公司 变流器
CN106887965A (zh) * 2017-04-26 2017-06-23 阳光电源股份有限公司 多电平逆变器的控制方法、控制装置以及逆变器
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