Series-parallel switching circuit, control method, and inverter

Abstract

The application provides a series-parallel switching circuit, a control method and an inverter. The series-parallel switching circuit comprises a first DC output unit, a second DC output unit, a state switching circuit and a voltage control circuit, the state switching circuit comprises a plurality of AC relays; the state switching circuit is connected with the first DC output unit, the second DC output unit and the voltage control circuit respectively; the state switching circuit switches the connection state of the first DC output unit and the second DC output unit through the on-off of the AC relays, and the connection state comprises a series connection state and a parallel connection state; the voltage control circuit is used for adjusting the voltage across a target AC relay, so that the voltage difference across the target AC relay satisfies a conduction condition, and the target AC relay is determined based on a target connection state of the first DC output unit and the second DC output unit. The scheme of the application can solve the problem of arc sticking when the series-parallel switching circuit uses the AC relay.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power electronics, and in particular to a series-parallel switching circuit, a control method and an inverter. BACKGROUND

[0002] With the development of technology, the demand for direct current output power also increases accordingly. In order to adapt to a wider output range, a series-parallel switching circuit for direct current output has been widely used. For example, a switching device is arranged at the output side to realize switching between series connection and parallel connection of direct current output units, so as to meet the output demand of different voltages.

[0003] However, the switching device will be impacted by transient current at the moment of mode switching. In order to solve this problem, a direct current relay or an alternating current relay can be used as the switching device. However, the direct current relay has high cost and large size; if the alternating current relay is used, there may be a problem of arc sticking, thereby affecting the stability of the circuit. SUMMARY

[0004] The present application provides a series-parallel switching circuit, a control method and an inverter to solve the problem of arc sticking when an alternating current relay is used in the series-parallel switching circuit.

[0005] In a first aspect, the present application provides a series-parallel switching circuit, comprising: a first direct current output unit, a second direct current output unit, a state switching circuit and a voltage control circuit, wherein the state switching circuit comprises: a plurality of alternating current relays; the state switching circuit is connected with the first direct current output unit, the second direct current output unit and the voltage control circuit respectively; the state switching circuit is configured to switch the connection state of the first direct current output unit and the second direct current output unit by the on-off of the alternating current relays, and the connection state comprises: a series connection state and a parallel connection state; the voltage control circuit is configured to adjust the voltage across a target alternating current relay among the alternating current relays, so that the voltage difference across the target alternating current relay satisfies a conduction condition, and the target alternating current relay is determined based on a target connection state of the first direct current output unit and the second direct current output unit.

[0006] In conjunction with the first aspect, one possible implementation further includes: a first output capacitor and a second output capacitor; a first terminal of the first output capacitor is connected to the positive output terminal of the first DC output unit, and a second terminal of the first output capacitor is connected to the negative output terminal of the first DC output unit; a first terminal of the second output capacitor is connected to the positive output terminal of the second DC output unit, and a second terminal of the second output capacitor is connected to the negative output terminal of the second DC output unit; the first output capacitor is used to filter the voltage output by the first DC output unit; and the second output capacitor is used to filter the voltage output by the second DC output unit.

[0007] In conjunction with the first aspect, in one possible implementation, the state switching circuit includes: a first AC relay, a second AC relay, and a third AC relay; the voltage control circuit includes: resistors R1, R2, and R3, and a switching transistor Q1, wherein the resistance values ​​of resistors R1 and R2 meet a preset requirement; the first terminal of the first AC relay is connected to the second terminal of the first output capacitor, the first terminal of the second AC relay, and the first terminal of resistor R3; the second terminal of the first AC relay is connected to the first terminal of the second output capacitor, the first terminal of the third AC relay, the first terminal of resistor R1, and the first terminal of resistor R2; the first terminal of the first output capacitor is connected to the second terminal of resistor R1 and the second terminal of the third AC relay; the second terminal of the second AC relay is connected to the second terminal of the second output capacitor and the second terminal of resistor R3; and the second terminal of resistor R2 is connected to the second terminal of the second output capacitor through the switching transistor Q1.

[0008] In conjunction with the first aspect, in one possible implementation, the series-parallel switching circuit further includes: a filter capacitor; a first terminal of the filter capacitor is connected to the positive output terminal of the first DC output unit, and a second terminal of the filter capacitor is connected to the negative output terminal of the second DC output unit; the filter capacitor is used to filter the output voltage of the series-parallel switching circuit.

[0009] In conjunction with the first aspect, in one possible implementation, the positive output terminal of the first DC output unit is connected to the positive terminal of the common bus in the inverter, and the negative output terminal of the second DC output unit is connected to the negative terminal of the common bus.

[0010] Secondly, this application provides a control method that can be applied to a series-parallel switching circuit in the first aspect or any possible implementation of the first aspect. The control method includes: determining a target connection state of a first DC output unit and a second DC output unit, wherein the target connection state includes a series state or a parallel state; controlling the voltage across a target AC relay through a voltage control circuit, wherein the target AC relay is determined based on the target connection state; and closing the target AC relay when the voltage difference across the target AC relay meets the conduction requirement.

[0011] In conjunction with the second aspect, in one possible implementation, when the target connection state is a series connection, the target AC relay is a first AC relay; the step of controlling the voltage across the target AC relay via the voltage control circuit includes: controlling the switch Q1 to close, controlling the voltage at the second terminal of the first AC relay via resistors R1 and R2, and controlling the voltage at the first terminal of the first AC relay via resistor R3, so that the voltage difference across the first AC relay meets the conduction requirement.

[0012] In conjunction with the second aspect, in one possible implementation, the method further includes: disconnecting the switching transistor Q1 after the first AC relay is closed.

[0013] In conjunction with the second aspect, in one possible implementation, when the target connection state is in parallel, the target AC relays are a second AC relay and a third AC relay; the step of controlling the voltage across the target AC relays via a voltage control circuit includes: controlling switch Q1 to disconnect, controlling the voltage at the first terminal of the third AC relay via resistor R1, and controlling the voltage at the first terminal of the second AC relay via resistor R3, so that the voltage difference between the second AC relay and the third AC relay both meet the conduction requirement; the second terminal of the third AC relay is connected to the first terminal of the first output capacitor, and the second terminal of the second AC relay is connected to the second terminal of the second output capacitor.

[0014] In conjunction with the second aspect, in one possible implementation, the method further includes: disconnecting AC relays in the state switching circuit other than the target AC relay.

[0015] Thirdly, this application provides a control device comprising various functional modules for implementing the method in the second aspect or any implementation thereof, each functional module being implemented in hardware and / or software.

[0016] For example, the control device may include a processing module. The processing module is configured to determine the target connection state of the first DC output unit and the second DC output unit, the target connection state including a series connection or a parallel connection; the processing module is further configured to control the voltage across a target AC relay via a voltage control circuit, the target AC relay being determined based on the target connection state; the processing module is further configured to close the target AC relay when the voltage difference across the target AC relay meets the conduction requirement.

[0017] In conjunction with the third aspect, in one possible implementation, when the target connection state is a series state, the target AC relay is a first AC relay; the processing module controls the switch Q1 to close, controls the voltage at the second terminal of the first AC relay through resistors R1 and R2, and controls the voltage at the first terminal of the first AC relay through resistor R3, so that the voltage difference across the first AC relay meets the conduction requirement.

[0018] In conjunction with the third aspect, in one possible implementation, the processing module is further configured to disconnect the switching transistor Q1 after the first AC relay is closed.

[0019] In conjunction with the third aspect, in one possible implementation, when the target connection state is in parallel, the target AC relays are a second AC relay and a third AC relay; the processing module is further configured to control the switch Q1 to disconnect, control the voltage at the first terminal of the third AC relay through resistor R1, and control the voltage at the first terminal of the second AC relay through resistor R3, so that the voltage difference between the second AC relay and the third AC relay both meet the conduction requirements, the second terminal of the third AC relay is connected to the first terminal of the first output capacitor, and the second terminal of the second AC relay is connected to the second terminal of the second output capacitor.

[0020] In conjunction with the third aspect, in one possible implementation, the processing module is further configured to disconnect AC relays in the state switching circuit other than the target AC relay.

[0021] Fourthly, this application provides a control device including a processor coupled to a memory, which can be used to execute instructions in the memory to implement the method in the second aspect or any possible implementation thereof. Optionally, the device further includes a memory. Optionally, the device further includes a communication interface, to which the processor is coupled.

[0022] Fifthly, this application provides an inverter that includes a series-parallel switching circuit as in the first aspect or any possible implementation of the first aspect, or may include a control device as in the third aspect or any possible implementation of the third aspect, or include a control device as in the fourth aspect.

[0023] In a sixth aspect, this application provides a computer-readable medium storing program code for execution by a device, the program code including methods for performing as described in the second aspect or any possible implementation thereof.

[0024] In a seventh aspect, this application provides a computer program product containing instructions that, when run on a computer, cause the computer to perform the method as described in the second aspect or any possible implementation thereof.

[0025] This application provides a series-parallel switching circuit, a control method, and an inverter. The technical solution provided in this application uses an AC relay as the switching device, and a voltage control circuit is added to control the voltage across the AC relay. The AC relay is closed only when the voltage difference across it meets the conduction requirement, thereby solving the problem of arcing and sticking of the AC relay, thus reducing costs and improving the operational stability of the series-parallel switching circuit. Attached Figure Description

[0026] Figure 1 This is a schematic structural diagram of a series-parallel switching circuit in the prior art;

[0027] Figure 2 A schematic structural diagram of a series-parallel switching circuit provided in this application;

[0028] Figure 3 A schematic structural diagram of another series-parallel switching circuit provided in this application;

[0029] Figure 4 A schematic flowchart illustrating a control method provided in this application. Detailed Implementation

[0030] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] With the development of technology, the demand for DC output power has also increased accordingly. To adapt to a wider range of outputs, DC output series-parallel switching circuits have been widely used. For example, switching devices are set on the output side to switch between series and parallel modes of DC output units, thereby meeting different voltage output requirements.

[0032] Figure 1 This is a schematic structural diagram of a series-parallel switching circuit in the prior art. Figure 1 The series-parallel switching circuit shown includes: a first DC output unit, a second DC output unit, and a state switching circuit. The state switching circuit includes: switching device S1, switching device S2, and switching device S3. It can be seen that... Figure 1 The positive output voltage of the first DC output unit is A+, and the negative output voltage is A-. The positive output voltage of the second DC output unit is B+, and the negative output voltage is B-. The output voltages of the first and second DC output units meet the requirements for series-parallel connection. Both the first and second DC output units are in a powered-on state.

[0033] like Figure 1 As shown, in the series connection mode of the first and second DC output units, switching device S1 can be closed while switching devices S2 and S3 can be opened. However, due to the parasitic impedance in the two DC output units, the output potentials A- and B+ are not completely equal, resulting in a voltage difference across switching device S1. If switching device S1 is closed at this time, a large current surge will be generated at the moment of closure, which may damage switching device S1.

[0034] Correspondingly, in the parallel connection mode of the first and second DC output units, switching devices S2 and S3 can be closed, while switching device S1 can be opened. However, due to the parasitic impedance in the two DC output units, the output potentials A- and B-, and A+ and B+ are not completely equal, resulting in a voltage difference between switching devices S2 and S3. If switching devices S2 and S3 are closed at this time, a large current surge will be generated at the moment of closure, which may damage switching devices S2 and S3.

[0035] It can be seen that existing series-parallel switching circuits are subject to instantaneous current surges during mode switching. To address this issue, DC or AC relays can be used as the switching devices. However, DC relays are more expensive and larger; using AC relays may result in arcing and sticking, thus affecting circuit stability.

[0036] In view of this, this application provides a series-parallel switching circuit, a control method, and an inverter. The technical solution provided in this application uses an AC relay as the switching device, and a voltage control circuit is added to control the voltage across the AC relay. The AC relay is closed only when the voltage difference across it meets the conduction requirement, thereby solving the problem of arcing and sticking of the AC relay, thus reducing costs and improving the operational stability of the series-parallel switching circuit.

[0037] The following is combined with Figures 2 to 4 This application provides a detailed description of the technical solution provided.

[0038] Figure 2 A schematic structural diagram of a series-parallel switching circuit provided in this application. Figure 2 The series-parallel switching circuit 200 shown includes: a first DC output unit 210, a second DC output unit 220, a state switching circuit 230, and a voltage control circuit 240. The state switching circuit 230 includes: multiple AC relays.

[0039] like Figure 2 As shown, the state switching circuit 230 is connected to the first DC output unit 210, the second DC output unit 220 and the voltage control circuit 240 respectively.

[0040] The state switching circuit 230 is used to switch the connection state of the first DC output unit 210 and the second DC output unit 220 by switching the AC relay on and off. The connection states include: series state and parallel state.

[0041] The voltage control circuit 240 is used to adjust the voltage across the target AC relay in the AC relay so that the voltage difference across the target AC relay meets the conduction requirement. The target AC relay can be determined based on the target connection state of the first DC output unit 210 and the second DC output unit 220. The target connection state can be determined based on load requirements. It should be understood that the target connection state can be a series connection or a parallel connection.

[0042] Optionally, if the voltage difference across the target AC relay meets a preset threshold, then the voltage difference across the target AC relay can be considered to meet the conduction condition, or in other words, the target AC relay meets the conduction requirement. The preset threshold can be set according to actual needs, and this application does not impose specific limitations on it. For example, the preset threshold can be 0.

[0043] The technical solution provided in this application employs an AC relay and adds a voltage control circuit to control the voltage across the AC relay. This allows the AC relay to close only when the voltage difference across it meets the conduction requirement, thus solving the problem of arcing and sticking of the AC relay. The technical solution provided in this application can reduce implementation costs and improve the operational stability of series-parallel switching circuits.

[0044] Figure 3 A schematic structural diagram of another series-parallel switching circuit provided in this application. Figure 3 The series-parallel switching circuit 200 shown also includes a first output capacitor and a second output capacitor. The first output capacitor is C1 as shown in the figure, and the second output capacitor is C2 as shown in the figure.

[0045] like Figure 3 As shown, the first end of the first output capacitor is connected to the positive output terminal of the first DC output unit 210, and the second end of the first output capacitor is connected to the negative output terminal of the first DC output unit 210; the first end of the second output capacitor is connected to the positive output terminal of the second DC output unit 220, and the second end of the second output capacitor is connected to the negative output terminal of the second DC output unit 220.

[0046] The first output capacitor is used to filter the voltage output by the first DC output unit 210 to improve the stability of the output voltage.

[0047] Correspondingly, the second output capacitor is used to filter the voltage output by the second DC output unit 220 to improve the stability of the output voltage.

[0048] like Figure 3 As shown, the state switching circuit 230 includes a first AC relay, a second AC relay, and a third AC relay. The first AC relay is S1 as shown in the figure, the second AC relay is S2 as shown in the figure, and the third AC relay is S3 as shown in the figure. It should be understood that when the target connection state of the first DC output unit 210 and the second DC output unit 220 is a series connection, the target AC relay is the first AC relay; when the target connection state is a parallel connection, the target AC relays are the second and third AC relays.

[0049] The voltage control circuit 240 includes resistors R1, R2, and R3, and a switching transistor Q1. The resistance values ​​of resistors R1 and R2 meet preset requirements, such as the resistance value of R1 being much greater than the resistance value of R2.

[0050] like Figure 3As shown, the first terminal of the first AC relay is connected to the second terminal of the first output capacitor, the first terminal of the second AC relay, and the first terminal of resistor R3. The second terminal of the first AC relay is connected to the first terminal of the second output capacitor, the first terminal of the third AC relay, the first terminal of resistor R1, and the first terminal of resistor R2. The first terminal of the first output capacitor is connected to the second terminal of resistor R1 and the second terminal of the third AC relay. The second terminal of the second AC relay is connected to the second terminal of the second output capacitor and the second terminal of resistor R3. The second terminal of resistor R2 is connected to the second terminal of the second output capacitor through the switching transistor Q1.

[0051] Optionally, the series-parallel switching circuit 200 may also include a filter capacitor, such as C3 in the figure.

[0052] like Figure 3 As shown, the first end of the filter capacitor is connected to the positive output terminal of the first DC output unit 210, and the second end of the filter capacitor is connected to the negative output terminal of the second DC output unit 220.

[0053] Filter capacitors are used to filter the output voltage of series-parallel switching circuits, thereby supplying power to the load.

[0054] In one possible implementation, the series-parallel switching circuit provided in this application can be applied to an inverter. In this implementation, the positive output terminal of the first DC output unit 210 can be connected to the positive terminal of the common bus (BUS) in the inverter, and the negative output terminal of the second DC output unit 220 can be connected to the negative terminal of the common bus. That is, A+ in the figure can be represented as BUS+, and B- can be represented as BUS-.

[0055] Optionally, the inverter may also include a control unit, which may be connected to the AC relay in the state switching circuit and the switching transistor Q1 in the voltage control circuit. The control unit can switch the connection state between the first DC output unit 210 and the second DC output unit 220 by controlling the on / off state of the AC relay and the switching transistor Q1.

[0056] The following is combined with Figure 4 The control method for the series-parallel switching circuit provided in this application is described. For example... Figure 4 As shown, the control method may include S410 to S430.

[0057] As an example, the method can be implemented by a control unit in the inverter, which can be a hardware and / or software module, and this application does not impose any specific limitations on this.

[0058] S410, determine the target connection state of the first DC output unit and the second DC output unit. The target connection state includes: series connection or parallel connection.

[0059] In this application, the target connection state of the first DC output unit and the second DC output unit can be determined based on load requirements. The target connection state includes: series connection or parallel connection.

[0060] S420 controls the voltage across the target AC relay via a voltage control circuit. The target AC relay is determined based on the target connection status.

[0061] In this application, after determining the target connection state, the target AC relay can be further determined, and the voltage across the target AC relay can be controlled by a voltage control circuit so that the voltage difference across the target AC relay meets the conduction requirements.

[0062] Specifically, when the target connection is in a series connection, the target AC relay is the first AC relay; when the target connection is in a parallel connection, the target AC relays are the second AC relay and the third AC relay.

[0063] In this application, when the target connection state is a series state, the control unit can control the switch Q1 to close, control the voltage of the second terminal of the first AC relay through resistors R1 and R2, and control the voltage of the first terminal of the first AC relay through resistor R3, so that the voltage difference across the first AC relay meets the conduction requirement.

[0064] Specifically, after switch Q1 is closed, the voltage across the second output capacitor is equivalent to the voltage across resistor R2. Since the resistance of resistor R1 is much greater than that of resistor R2, the voltage across the second output capacitor is relatively small, meaning the voltage difference between it is small, specifically the difference between B+ and B-. B+ is the voltage at the second terminal of the first AC relay. Simultaneously, the first output capacitor is charged through resistor R3. When the first output capacitor is fully charged, it is essentially open-circuited, and the voltages across it are A+ and B-. At this point, the voltage difference across resistor R3 is close to zero, meaning A- and B- are close to each other. A- is the voltage at the first terminal of the first AC relay. Therefore, the voltage difference across the first AC relay is close to zero, and the first AC relay meets the conduction condition.

[0065] In this application, when the target connection is in a parallel state, the control unit can control the switch Q1 to open, control the voltage at the first terminal of the third AC relay through resistor R1, and control the voltage at the first terminal of the second AC relay through resistor R3, so that the voltage difference between the second and third AC relays meets the conduction requirement. The second terminal of the third AC relay is connected to the first terminal of the first output capacitor, and the second terminal of the second AC relay is connected to the second terminal of the second output capacitor.

[0066] Specifically, after switch Q1 is turned off, the second output capacitor is charged through resistor R1, and the first output capacitor is charged through resistor R3. When the second output capacitor is fully charged, it is essentially an open circuit, and the voltages across it are A+ and B-. At this time, the voltage difference across resistor R1 is close to 0, meaning B+ is close to A+. Therefore, the voltage difference across the third AC relay is also close to 0, meaning the third AC relay meets the conduction requirement. Similarly, when the first output capacitor is fully charged, it is essentially an open circuit, and the voltages across it are A+ and B-. At this time, the voltage difference across resistor R3 is close to 0, meaning A- is close to B-. Therefore, the voltage difference across the second AC relay is also close to 0, meaning the second AC relay meets the conduction condition.

[0067] S430: When the voltage difference across the target AC relay meets the conduction requirement, the target AC relay is closed.

[0068] In this application, when the voltage difference across the target AC relay is close to 0, it can be considered that the voltage difference across the target AC relay meets the conduction condition, or in other words, the target AC relay meets the conduction condition. Closing the target AC relay at this time allows for zero-voltage conduction of the target AC relay, thereby avoiding current surges.

[0069] Optionally, when the target AC relay is in the first AC relay state, after the first AC relay is closed, the switching transistor Q1 can be disconnected, so that the first DC output unit and the second DC output unit are connected in series to supply power to the outside.

[0070] It should be noted that before the series-parallel switching circuit is started, the AC relays can be considered to be in the open state. Therefore, the target connection state of the first DC output unit and the second DC output unit can be achieved by closing the target AC relay.

[0071] In some implementations, if the connection state of the first DC output unit and the second DC output unit needs to be switched, it is also necessary to disconnect the AC relays other than the target AC relay, or in other words, disconnect the AC relays that were closed in the previous connection state. For example, when switching from a parallel state to a series state, when closing the first AC relay, the second and third AC relays also need to be disconnected. Since the voltage of the capacitor cannot change abruptly, it will not impact the second and third AC relays. Similarly, when switching from a series state to a parallel state, when closing the second and third AC relays, the first AC relay also needs to be disconnected. Since the voltage of the capacitor cannot change abruptly, it will not impact the first AC relay.

[0072] In the technical solution provided in this application, the voltage across the target AC relay is controlled by controlling the voltage across the first output capacitor and the second output capacitor, so as to achieve zero-voltage conduction of the target AC relay. This solves the problem of arcing and sticking that occurs when using AC relays in DC output and improves operational stability.

[0073] This application also provides a control device comprising various functional modules for implementing the control method shown in the foregoing embodiments, each functional module being implemented in hardware and / or software.

[0074] This application also provides a control device, including a processor coupled to a memory, which can be used to execute instructions in the memory to implement the control method shown in the foregoing embodiments. Optionally, the device further includes a memory. Optionally, the device further includes a communication interface, to which the processor is coupled.

[0075] This application also provides an inverter that can implement the control method shown in the foregoing embodiments.

[0076] This application also provides a computer-readable medium storing program code for execution by a device, the program code including control methods shown in the foregoing embodiments.

[0077] This application provides a computer program product containing instructions that, when run on a computer, cause the computer to execute the control method shown in the foregoing embodiments.

[0078] The term "multiple" in this document refers to two or more. The term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. Furthermore, the character " / " in this document generally indicates an "or" relationship between the preceding and following related objects; in formulas, " / " indicates a "division" relationship. Additionally, it should be understood that in the description of this application, words such as "first" and "second" are used only for descriptive purposes and should not be construed as indicating or implying relative importance or order.

[0079] It is understood that, in the embodiments of this application, the order of the above-mentioned process numbers does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0080] It should be emphasized that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A series-parallel switching circuit, characterized in that, include: The system comprises a first DC output unit, a second DC output unit, a state switching circuit, and a voltage control circuit, wherein the state switching circuit includes multiple AC relays. The state switching circuit is connected to the first DC output unit, the second DC output unit, and the voltage control circuit, respectively. The state switching circuit is used to switch the connection state of the first DC output unit and the second DC output unit by switching the AC relay on and off. The connection state includes: series state and parallel state. The voltage control circuit is used to adjust the voltage across the target AC relay in the AC relay so that the voltage difference across the target AC relay meets the conduction condition. The target AC relay is determined based on the target connection state of the first DC output unit and the second DC output unit. The series-parallel switching circuit further includes: a first output capacitor and a second output capacitor; The first end of the first output capacitor is connected to the positive output terminal of the first DC output unit, and the second end of the first output capacitor is connected to the negative output terminal of the first DC output unit. The first end of the second output capacitor is connected to the positive output terminal of the second DC output unit, and the second end of the second output capacitor is connected to the negative output terminal of the second DC output unit. The first output capacitor is used to filter the voltage output by the first DC output unit; The second output capacitor is used to filter the voltage output by the second DC output unit; The series-parallel switching circuit also includes: a filter capacitor; The first end of the filter capacitor is connected to the positive output terminal of the first DC output unit, and the second end of the filter capacitor is connected to the negative output terminal of the second DC output unit. The filter capacitor is used to filter the output voltage of the series-parallel switching circuit. The state switching circuit includes: a first AC relay, a second AC relay, and a third AC relay; The voltage control circuit includes: resistors R1, R2, and R3, and a switching transistor Q1. The resistance values ​​of resistors R1 and R2 meet a preset requirement. The first terminal of the first AC relay is connected to the second terminal of the first output capacitor, the first terminal of the second AC relay, and the first terminal of the resistor R3. The second terminal of the first AC relay is connected to the first terminal of the second output capacitor, the first terminal of the third AC relay, the first terminal of the resistor R1, and the first terminal of the resistor R2. The first terminal of the first output capacitor is connected to the second terminal of the resistor R1 and the second terminal of the third AC relay. The second terminal of the second AC relay is connected to the second terminal of the second output capacitor and the second terminal of the resistor R3. The second terminal of the resistor R2 is connected to the second terminal of the second output capacitor through the switching transistor Q1.

2. The series-parallel switching circuit according to claim 1, characterized in that, The positive output terminal of the first DC output unit is connected to the positive terminal of the common bus in the inverter, and the negative output terminal of the second DC output unit is connected to the negative terminal of the common bus.

3. A control method, characterized in that, Applied to the series-parallel switching circuit as described in claim 1 or 2, the method includes: Determine the target connection state of the first DC output unit and the second DC output unit, wherein the target connection state includes: series connection or parallel connection. The voltage across the target AC relay is controlled by a voltage control circuit, and the target AC relay is determined based on the target connection state. When the voltage difference across the target AC relay meets the conduction requirement, the target AC relay is closed.

4. The control method according to claim 3, characterized in that, When the target connection state is in series, the target AC relay is the first AC relay; The control of the voltage across the target AC relay via the voltage control circuit includes: The control switch Q1 is closed, and the voltage at the second terminal of the first AC relay is controlled by resistors R1 and R2, and the voltage at the first terminal of the first AC relay is controlled by resistor R3, so that the voltage difference across the first AC relay meets the conduction requirement.

5. The control method according to claim 4, characterized in that, The method further includes: After the first AC relay is closed, the switch Q1 is disconnected.

6. The control method according to claim 3, characterized in that, When the target connection state is in parallel, the target AC relays are the second AC relay and the third AC relay; The control of the voltage across the target AC relay via the voltage control circuit includes: The control switch Q1 is turned off, the voltage at the first terminal of the third AC relay is controlled by resistor R1, and the voltage at the first terminal of the second AC relay is controlled by resistor R3, so that the voltage difference between the second AC relay and the third AC relay meets the conduction requirement. The second terminal of the third AC relay is connected to the first terminal of the first output capacitor, and the second terminal of the second AC relay is connected to the second terminal of the second output capacitor.

7. An inverter, characterized in that, It includes the series-parallel switching circuit as described in claim 1 or 2, or includes various functional modules for implementing the control method as described in any one of claims 3 to 6.

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