CN114301271A - Power conversion system and control method - Google Patents

Abstract

A power conversion system and a control method are provided, which can reduce the volume and cost of a discharge resistor. The power conversion system includes: the DC/DC conversion module comprises a first DC/DC converter and a second DC/DC converter; the bleeder circuit comprises a discharge resistor R1 and a switching device Q4 which are connected in series; the controller is used for: when the power conversion system needs to discharge through the bleeder circuit, under the condition that the output ends of the first DC/DC converter and the second DC/DC converter are in a series state, controlling the on-off of a switch in a switch switching circuit to switch the output ends of the first DC/DC converter and the second DC/DC converter from a series state to a parallel state; and after the output ends of the first DC/DC converter and the second DC/DC converter are switched into a parallel connection state, controlling the bleeder circuit to be in a conducting state.

Description

Power conversion system and control method

technical field

The present application relates to the electrical field, and in particular, to a power conversion system and a control method.

Background technique

Many power conversion systems can output a variety of DC voltages to suit different application scenarios, that is, the DC output voltage has a wide output range. A typical wide voltage output range power conversion system includes charging systems such as passenger car charging stations and bus charging stations. Among them, the charging voltage range of passenger cars is about 100V to 500V, and the charging voltage range of bus charging stations is about 300V to 700V.

According to the requirements of energy industry standards, after the charging system stops power supply, the output voltage should be reduced to below 60VDC (DC voltage) within 1s (second). Therefore, in order to ensure that the discharge time of the charging system after the power supply is stopped meets the requirements of the industry standard, it is necessary to add a discharge circuit in the charging system to discharge the output capacitor. The discharge circuit includes a high-voltage switch device and a discharge resistor. Since the discharge resistor and switching device need to be selected according to the maximum output voltage, as the DC output range of the power conversion system becomes larger and larger, the volume and cost of the discharge resistor and the switching device also increase.

SUMMARY OF THE INVENTION

The present application provides a power conversion system and a control method, which can reduce the volume and cost of a discharge resistor.

In a first aspect, a power conversion system is provided, comprising: a controller, a DC/DC DC/DC conversion module, a switch switching circuit, and a bleeder circuit, the DC/DC conversion module is used for DC voltage conversion, and output the output voltage V _out of the power conversion system, the output voltage V _out is used to supply power to the load, the DC/DC conversion module includes a first DC/DC converter and a second DC/DC converter; the control The controller is used to control the output terminals of the first DC/DC converter and the second DC/DC converter to be in a series state or a parallel state by controlling the on-off of the switch in the switch switching circuit, so as to change the output voltage V _out ; the bleeder circuit is used to bleed the charge of the output port of the power conversion system after the power conversion system stops supplying power to the load, and the bleeder circuit is arranged in the power conversion system Between the positive output end and the negative output end of the system, the bleeder circuit includes a series-connected discharge resistor R1 and a switching device Q4; the controller is also used for: when the power conversion system needs to discharge through the bleeder circuit When the output terminal of the first DC/DC converter and the output terminal of the second DC/DC converter are in a series state, the on-off of the switch in the switch switching circuit is controlled, so that the first DC/DC converter is turned on and off. The output terminals of a DC/DC converter and the second DC/DC converter are switched from a series state to a parallel state; and the bleeder circuit is controlled to be in a conducting state.

By controlling the switch in the switch switching circuit in the power conversion system and the switching logic sequence of the switching device Q4 in the bleeder circuit, the DC/DC conversion module is discharged in parallel mode, and both ends of the discharge resistor R1 only need to be discharged during discharge. It can withstand the voltage of a single DC/DC converter, thus reducing the maximum transient power that the discharge resistor R1 bears. The selection of the discharge resistor R1 can effectively save the space and cost occupied by the discharge circuit.

With reference to the first aspect, in some implementation manners of the first aspect, the controller is further configured to: when the power conversion system needs to be discharged through the discharge circuit, perform the operation between the first DC/DC converter and the discharge circuit. When the output terminals of the second DC/DC converter are in a parallel state, the bleeder circuit is controlled to be in a conducting state.

When the power conversion system needs to discharge through the bleeder circuit, if it is determined that the output terminals of the first DC/DC converter and the second DC/DC converter are in a parallel state, there is no need to change the state of the switch switching circuit, and only the bleeder needs to be controlled. When the circuit 350 is in an on state, it can ensure that both ends of the discharge resistor R1 only bear the voltage of a single DC/DC converter during discharge.

With reference to the first aspect, in some implementations of the first aspect, the switch switching circuit includes: a switch S1 , which is arranged between the negative output terminal of the first DC/DC controller and the second DC/DC converter The switch S2 is set between the negative output terminal of the first DC/DC converter and the negative output terminal of the second DC/DC converter; the switch S3 is set between the first DC/DC converter between the positive output end of the second DC/DC converter and the positive output end of the second DC/DC converter; the controller is specifically configured to: control the switch S1 to be turned off; after the switch S1 is turned off, control the switch S2 and The switch S3 is turned on, so that the output ends of the first DC/DC converter and the second DC/DC converter are switched to a parallel state; after the switch S2 and the switch S3 are turned on, The switching device Q4 is controlled to be turned on, so that the bleeder circuit is turned on.

With reference to the first aspect, in some implementations of the first aspect, two ends of the switch S1 are also connected in parallel with a transistor Q1 for clamping, and the controller is specifically configured to: after the switch S1 is turned off, control the The transistor Q1 is turned off; after the transistor Q1 is turned off, the switch S2 and the switch S3 are controlled to be turned on.

Clamping devices are connected in parallel at both ends of the switches S1, S2 and S3, so that when the switches S1, S2 and S3 are turned off, the clamping devices keep the voltages across the switches S1, S2 and S3 below a certain threshold, thereby preventing the occurrence of arcing .

With reference to the first aspect, in some implementations of the first aspect, the power conversion system is a charging pile, and the load is an electric vehicle.

In a second aspect, a power conversion system is provided, including: a controller, a DC/DC DC/DC conversion module, a switch switching circuit, and a bleeder circuit, the DC/DC conversion module is used for DC voltage conversion, and output the output voltage V _out of the power conversion system, the output voltage V _out is used to supply power to the load, the DC/DC conversion module includes a first DC/DC converter and a second DC/DC converter; the control The controller is used to control the output terminals of the first DC/DC converter and the second DC/DC converter to be in a series state or a parallel state by controlling the on-off of the switch in the switch switching circuit, so as to change the output voltage V _out ; the bleeder circuit is used to bleed the electric charge of the output port of the power conversion system after the power conversion system stops supplying power to the load, and the bleeder circuit is arranged in the first Between the positive output terminal and the negative output terminal of the DC/DC converter, or, the bleeder circuit is arranged between the positive output terminal and the negative output terminal of the second DC/DC converter, and the bleeder circuit It includes a discharge resistor R1 and a switching device Q4 connected in series; the controller is also used for: when the power conversion system needs to discharge through the discharge circuit, the first DC/DC converter and the second When the output ends of the DC/DC converters are in a series state, the on-off of the switches in the switch switching circuit is controlled, so that the first DC/DC converter and the second DC/DC converter are connected to each other. The output terminal is switched from the series state to the parallel state; and after the output terminals of the first DC/DC converter and the second DC/DC converter are switched to the parallel state, the bleeder circuit is controlled to be in a conducting state .

By controlling the switch in the switch switching circuit in the power conversion system and the switching logic sequence of the switching device Q4 in the bleeder circuit, the DC/DC conversion module is discharged in parallel mode, and both ends of the discharge resistor R1 are only discharged during discharge. It needs to withstand the voltage of a single DC/DC converter, so the maximum transient power that the discharge resistor R1 bears is reduced, and the space and cost occupied by the discharge circuit can be effectively saved in the selection of the discharge resistor R1. In addition, since the bleeder circuit is arranged between the positive output terminal and the negative output terminal of a single DC/DC converter, the maximum voltage that both ends of the switching device Q4 in the bleeder circuit need to withstand is the output of a single DC/DC converter voltage, the switching device Q4 can be selected according to the specification of the output voltage of a single DC/DC converter, which reduces the space and cost occupied by the switching device Q4.

With reference to the second aspect, in some implementation manners of the second aspect, the controller is further configured to: when the power conversion system needs to be discharged through the discharge circuit, perform the operation between the first DC/DC converter and the first DC/DC converter When the output terminals of the second DC/DC converter are in a parallel state, the bleeder circuit is controlled to be in a conducting state.

When the power conversion system needs to discharge through the bleeder circuit, if it is determined that the output terminals of the first DC/DC converter and the second DC/DC converter are in a parallel state, there is no need to change the state of the switch switching circuit, and only the bleeder needs to be controlled. When the circuit 350 is in an on state, it can ensure that both ends of the discharge resistor R1 only bear the voltage of a single DC/DC converter during discharge.

With reference to the second aspect, in some implementations of the second aspect, the switch switching circuit includes: a switch S1 , which is arranged between the negative output terminal of the first DC/DC controller and the second DC/DC converter The switch S2 is set between the negative output terminal of the first DC/DC converter and the negative output terminal of the second DC/DC converter; the switch S3 is set between the first DC/DC converter between the positive output end of the second DC/DC converter and the positive output end of the second DC/DC converter; the controller is specifically configured to: control the switch S1 to be turned off; after the switch S1 is turned off, control the switch S2 and The switch S3 is turned on, so that the output ends of the first DC/DC converter and the second DC/DC converter are switched to a parallel state; after the switch S2 and the switch S3 are turned on, The switching device Q4 is controlled to be turned on, so that the bleeder circuit is turned on.

With reference to the second aspect, in some implementations of the second aspect, two ends of the switch S1 are also connected in parallel with a transistor Q1 for clamping, and the controller is specifically configured to: after the switch S1 is turned off, control the The transistor Q1 is turned off; after the transistor Q1 is turned off, the switch S2 and the switch S3 are controlled to be turned on.

Clamping devices are connected in parallel at both ends of the switches S1, S2 and S3, so that when the switches S1, S2 and S3 are turned off, the clamping devices keep the voltages across the switches S1, S2 and S3 below a certain threshold, thereby preventing the occurrence of arcing .

With reference to the second aspect, in some implementations of the second aspect, the power conversion system is a charging pile, and the load is an electric vehicle.

In a third aspect, a method for controlling a power conversion system is provided. The power conversion system includes: a controller, a DC/DC DC/DC conversion module, a switch switching circuit, and a bleeder circuit, and the DC/DC conversion module uses to perform DC voltage conversion and output the output voltage V _out of the power conversion system, the output voltage V _out is used to supply power to the load, and the DC/DC conversion module includes a first DC/DC converter and a second DC /DC converter; the controller is configured to control the output ends of the first DC/DC converter and the second DC/DC converter to be in a series state by controlling the on-off of the switch in the switch switching circuit or in a parallel state to change the output voltage V _out ; the bleeder circuit is used to bleed the charge of the output port of the power conversion system after the power conversion system stops supplying power to the load, the bleeder circuit The discharge circuit is arranged between the positive output terminal and the negative output terminal of the power conversion system, and the discharge circuit includes a discharge resistor R1 and a switching device Q4 connected in series; the method includes: the controller is in the power conversion When the system needs to discharge through the bleeder circuit, in the case that the output terminals of the first DC/DC converter and the second DC/DC converter are in a series state, control the switch in the switch switching circuit on and off, so that the output ends of the first DC/DC converter and the second DC/DC converter are switched from a series state to a parallel state; and the controller is in the first DC/DC converter. After the output end of the DC/DC converter and the second DC/DC converter are switched to a parallel state, the bleeder circuit is controlled to be in a conducting state.

By controlling the switch in the switch switching circuit in the power conversion system and the switching logic sequence of the switching device Q4 in the bleeder circuit, the DC/DC conversion module is discharged in parallel mode, and both ends of the discharge resistor R1 only need to be discharged during discharge. It can withstand the voltage of a single DC/DC converter, thus reducing the maximum transient power that the discharge resistor R1 bears. The selection of the discharge resistor R1 can effectively save the space and cost occupied by the discharge circuit.

With reference to the third aspect, in some implementation manners of the third aspect, the method further includes: when the power conversion system needs to be discharged through the discharge circuit, the controller performs the first DC/DC conversion when the power conversion system needs to be discharged through the discharge circuit. When the output end of the second DC/DC converter and the second DC/DC converter are in a parallel state, the bleeder circuit is controlled to be in a conducting state.

With reference to the third aspect, in some implementations of the third aspect, the switch switching circuit includes: a switch S1 , which is arranged between the negative output terminal of the first DC/DC controller and the second DC/DC converter The switch S2 is set between the negative output terminal of the first DC/DC converter and the negative output terminal of the second DC/DC converter; the switch S3 is set between the first DC/DC converter between the positive output end of the second DC/DC converter and the positive output end of the second DC/DC converter; the controller is in a series state between the output ends of the first DC/DC converter and the second DC/DC converter In this case, controlling the on-off of the switch in the switch switching circuit, so that the output terminals of the first DC/DC converter and the second DC/DC converter are switched from a series state to a parallel state, including: The controller controls the switch S1 to be turned off; after the switch S1 is turned off, the controller controls the switch S2 and the switch S3 to be turned on, so that the first DC/DC converter and the The output end of the second DC/DC converter is switched to the parallel state; after the controller switches the output ends of the first DC/DC converter and the second DC/DC converter to the parallel state, Controlling the bleeder circuit to be in an on state includes: after the switch S2 and the switch S3 are turned on, the controller controls the switching device Q4 to be turned on, so that the bleeder circuit is turned on state.

With reference to the third aspect, in some implementations of the third aspect, both ends of the switch S1 are further connected in parallel with a transistor Q1 for clamping, and the method further includes: the controller after the switch S1 is turned off , the transistor Q1 is controlled to be turned off; after the transistor Q1 is turned off, the controller controls the switch S2 and the switch S3 to be turned on.

With reference to the third aspect, in some implementations of the third aspect, the power conversion system is a charging pile, and the load is an electric vehicle.

In a fourth aspect, a method for controlling a power conversion system is provided, the power conversion system comprising: a controller, a DC/DC DC/DC conversion module, a switch switching circuit and a discharge circuit, the DC/DC conversion module using to perform DC voltage conversion and output the output voltage V _out of the power conversion system, the output voltage V _out is used to supply power to the load, and the DC/DC conversion module includes a first DC/DC converter and a second DC /DC converter; the controller is configured to control the output ends of the first DC/DC converter and the second DC/DC converter to be in a series state by controlling the on-off of the switch in the switch switching circuit or in parallel state to change the output voltage V _out ; the bleeder circuit is used to bleed the electric charge of the output port of the power conversion system after the power conversion system stops supplying power to the load, the bleeder circuit The discharge circuit is arranged between the positive output terminal and the negative output terminal of the first DC/DC converter, or the discharge circuit is arranged between the positive output terminal and the negative output terminal of the second DC/DC converter between, the discharge circuit includes a series-connected discharge resistor R1 and a switching device Q4;

By controlling the switch in the switch switching circuit in the power conversion system and the switching logic sequence of the switching device Q4 in the bleeder circuit, the DC/DC conversion module is discharged in parallel mode, and both ends of the discharge resistor R1 are only discharged during discharge. It needs to withstand the voltage of a single DC/DC converter, so the maximum transient power that the discharge resistor R1 bears is reduced, and the space and cost occupied by the discharge circuit can be effectively saved in the selection of the discharge resistor R1. In addition, since the bleeder circuit is arranged between the positive output terminal and the negative output terminal of a single DC/DC converter, the maximum voltage that both ends of the switching device Q4 in the bleeder circuit need to withstand is the output of a single DC/DC converter voltage, the switching device Q4 can be selected according to the specification of the output voltage of a single DC/DC converter, which reduces the space and cost occupied by the switching device Q4.

With reference to the fourth aspect, in some implementation manners of the fourth aspect, the method further includes: when the power conversion system needs to be discharged through the discharge circuit, the controller performs the first DC/DC conversion when the power conversion system needs to be discharged through the discharge circuit. When the output end of the second DC/DC converter and the second DC/DC converter are in a parallel state, the bleeder circuit is controlled to be in a conducting state.

With reference to the fourth aspect, in some implementations of the fourth aspect, the switch switching circuit includes: a switch S1 , which is arranged between the negative output end of the first DC/DC controller and the second DC/DC converter The switch S2 is set between the negative output terminal of the first DC/DC converter and the negative output terminal of the second DC/DC converter; the switch S3 is set between the first DC/DC converter between the positive output end of the second DC/DC converter and the positive output end of the second DC/DC converter; the controller is in a series state between the output ends of the first DC/DC converter and the second DC/DC converter In this case, controlling the on-off of the switch in the switch switching circuit, so that the output terminals of the first DC/DC converter and the second DC/DC converter are switched from a series state to a parallel state, including: The controller controls the switch S1 to be turned off; after the switch S1 is turned off, the controller controls the switch S2 and the switch S3 to be turned on, so that the first DC/DC converter and the The output end of the second DC/DC converter is switched to the parallel state; after the controller switches the output ends of the first DC/DC converter and the second DC/DC converter to the parallel state, Controlling the bleeder circuit to be in an on state includes: after the switch S2 and the switch S3 are turned on, the controller controls the switching device Q4 to be turned on, so that the bleeder circuit is turned on state.

With reference to the fourth aspect, in some implementations of the fourth aspect, both ends of the switch S1 are also connected in parallel with a transistor Q1 for clamping, and the method further includes: the controller after the switch S1 is turned off , the transistor Q1 is controlled to be turned off; after the transistor Q1 is turned off, the controller controls the switch S2 and the switch S3 to be turned on.

With reference to the fourth aspect, in some implementations of the fourth aspect, the power conversion system is a charging pile, and the load is an electric vehicle.

In a fifth aspect, a computer program product is provided, the computer program product includes a computer program that, when the computer program is executed, causes a computer to perform the third and fourth aspects and the third and fourth aspects above. method in any of the possible implementations.

In a sixth aspect, a computer-readable storage medium is provided, the computer-readable storage medium stores a computer program that, when executed on a computer, causes the computer to execute the third aspect and the fourth aspect and the third aspect and The method in any possible implementation manner of the fourth aspect.

Description of drawings

FIG. 1 is a schematic diagram of an application scenario of an embodiment of the present application.

FIG. 2 is a schematic diagram of an application scenario of another embodiment of the present application.

FIG. 3 is a schematic diagram of a power conversion system 200 according to an embodiment of the present application.

FIG. 4 is a current flow diagram for discharging the power conversion system 200 of FIG. 3 in series mode.

FIG. 5 is a schematic flowchart of a control method 300 of a power conversion system according to an embodiment of the present application.

FIG. 6 is a current flow diagram for discharging the power conversion system 200 in FIG. 3 in a parallel mode.

FIG. 7 is a schematic structural diagram of a power conversion system 400 according to another embodiment of the present application.

FIG. 8 is a schematic structural diagram of a power conversion system 400 according to another embodiment of the present application.

FIG. 9 is a schematic flowchart of a control method 600 of a power conversion system according to an embodiment of the present application.

FIG. 10 is a current flow diagram for discharging the power conversion system 400 in FIG. 7 in a parallel mode.

FIG. 11 is a current flow diagram for discharging the power conversion system 400 in FIG. 8 in a parallel mode.

Detailed ways

The technical solutions in the present application will be described below with reference to the accompanying drawings.

For ease of understanding, several terms involved in the embodiments of the present application are first introduced.

Metal-oxide-semiconductor field-effect transistor (MOSFET): It is a semiconductor device that works on the principle of field effect. terminals.

Insulated gate bipolar transistor (IGBT): It is a composite fully controlled voltage-driven power semiconductor device composed of a bipolar junction transistor (BJT) and a MOSFET, and has the high input impedance of the MOSFET and BJT's low on-voltage drop.

Silicon controlled rectifier (silicon controlled rectifier, SCR): is a high-power switching semiconductor device composed of three PN junctions, also known as thyristor. SCR has several types such as one-way, two-way, can be turned off and light control. It has the advantages of small size, light weight and convenient control. It is widely used in automatic control or high-power electric energy such as rectification, voltage regulation and contactless switch. the case of conversion.

Relay: It is an electrical control device, which is an electrical appliance that makes a predetermined step change of the controlled quantity in the electrical output circuit when the change of the input quantity meets the specified requirements. It has an interactive relationship between the control system and the controlled system, and is usually used in automated control circuits. The relay can be understood as an "automatic switch" that uses a small current to control the operation of a large current, so it plays the role of automatic adjustment, safety protection, and conversion circuit in the circuit, and can be widely used in remote control, telemetry, communication, automatic It is one of the most important control components in control, mechatronics and power electronic equipment.

FIG. 1 is a schematic diagram of an application scenario of an embodiment of the present application. As shown in FIG. 1 , the power conversion system 100 is used to realize the function of power conversion, and finally outputs the DC voltage V _out to supply power to the load. For example, the power conversion system 100 may convert alternating current into direct current, or may also output direct current after voltage conversion of direct current. The power conversion system 100 can have a wide DC output voltage range, so the output voltage can be adapted to different application scenarios. As an example, the power conversion system 100 may be a charging pile, a charging station, a mobile supplementary electric vehicle, or the like. The load can be electric vehicle, intelligent driving vehicle, power battery, energy storage battery, capacitive load, etc. Alternatively, the power conversion system 100 may also be a rectifier, a DC uninterruptible power supply (UPS), or the like.

FIG. 2 is a schematic diagram of an application scenario of another embodiment of the present application. As shown in FIG. 2 , the power conversion system 100 in FIG. 1 may be the charging pile 21 in FIG. 2 , and the load may be the electric vehicle 24 in FIG. 2 . The input end of the charging pile 21 can be connected to alternating current, and the output end can output various different direct current voltages, so as to adapt to different types of electric vehicles 24 . Wherein, the alternating current received by the input end may be three-phase alternating current or single-phase alternating current. As an example, if the load is a passenger car, the output DC voltage of the charging pile 21 ranges from about 100V to 500V. If the load is a bus, the output DC voltage of the charging pile 21 ranges from about 300V to 700V. It can be seen that the DC output voltage of the charging pile 21 varies within a wide range, and with the advancement of technology, the charging pile 21 tends to develop to a higher charging voltage.

FIG. 3 is a schematic diagram of a power conversion system 200 according to an embodiment of the present application. The power conversion system 200 may be applied in the scenario of FIG. 1 or FIG. 2 . As shown in FIG. 3 , the power conversion system 200 may include a controller 310 , a pre-stage module 320 , a DC/DC conversion module 330 , a switching circuit 340 and a bleeder circuit 350 .

The controller 310 may be used to control the on-off of switches in each circuit module in the power conversion system 200 . Specifically, the controller 310 may be configured to send control signals to each switch to control the on-off of each switch. Optionally, the controller 310 may also be used to perform other management functions, such as detecting electrical parameters in the power conversion system 200, performing processing computing functions, and the like.

In some examples, after receiving the input voltage V _in , the power conversion system 200 may perform power conversion through the pre-stage module 320 and output the DC bus voltage V _bus . After receiving the DC bus voltage V _bus , the DC/DC conversion module 330 performs DC voltage conversion, and outputs the output voltage V _out of the power conversion system 200 .

In some examples, the above-mentioned input voltage _Vin may be alternating current or direct current. The above-mentioned alternating current may be three-phase alternating current or single-phase alternating current.

In some examples, front-end module 320 may refer to a circuit that precedes DC/DC conversion module 330 in power conversion system 200 on the circuit chain. The embodiment of the present application does not limit the function of the pre-stage module 320 as long as it can process the input voltage V _in and output the DC bus voltage V _bus to the DC/DC. For example, the front-end module 320 may be used for rectification, that is, to convert alternating current to direct current. As an example, the preceding module 320 includes a power factor correction (PFC) unit.

In order to realize various DC output voltages, the DC/DC conversion module 330 may include two DC/DC converters, namely the first DC/DC converter 331 and the second DC/DC converter 332, by changing the above two DC/DC converters The series-parallel relationship of the output terminals of the /DC converter can output different DC voltages. For example, if the output voltage of a single DC/DC converter is V _dc , when two DC/DC converters are connected in series, the output voltage of the power conversion system 200 is V _out =2V _dc . When two DC/DC converters are connected in parallel, the output voltage of the power conversion system 200 is V _out =V _dc .

Optionally, the above two DC/DC converters can achieve electrical isolation. As an example, the above two DC/DC converters may include, but are not limited to, an inductance inductance capacitance resonant circuit (LLC resonant circuit) or other types of bridge topologies.

The switch switching circuit 340 includes a plurality of switches, and by controlling the on-off of the plurality of switches in the switch switching circuit 340, the output terminals of the first DC/DC converter 331 and the second DC/DC converter 332 are in series mode or in parallel model.

As an example, the above-mentioned switch switching circuit 340 may include switches S1 , S2 and S3 . The switch S1 is disposed between the negative output terminal of the first DC/DC converter 331 and the positive output terminal of the second DC/DC converter 332 . The switch S2 is disposed between the negative output terminal of the first DC/DC converter 331 and the negative output terminal of the second DC/DC converter 332 . The switch S3 is disposed between the positive output terminal of the first DC/DC converter 331 and the positive output terminal of the second DC/DC converter 332 . When the switch S1 is turned on and the switches S2 and S3 are turned off, the output terminals of the first DC/DC converter 331 and the second DC/DC converter 332 are in series mode. When the switch S1 is turned off and the switches S2 and S3 are turned on, the output terminals of the first DC/DC converter 331 and the second DC/DC converter 332 are in a parallel mode.

In some examples, the switches S1 , S2 and S3 described above may be relays, contactors, etc. type switches.

In some examples, due to the high voltage state, if the switches S1, S2 and S3 are opened momentarily, an arc will be generated in the air. In order to avoid the above situation, clamping devices can be connected in parallel at both ends of the switches S1, S2 and S3. When the switches S1, S2 and S3 are turned off, the clamping devices keep the voltages across the switches S1, S2 and S3 below a certain threshold , thereby preventing arcing. For example, in FIG. 3, a transistor Q1 can be connected in parallel across the switch S1 as a clamping device. Diodes D2 and D3 can also be connected in parallel at the two ends of the switches S2 and S3 respectively as clamping devices.

The above clamping device may include, but is not limited to, at least one of the following: MOSFET, IGBT, SCR, and diode. For example, the above-mentioned transistor Q1 may be any one of the following: MOSFET, IGBT, and SCR.

It should be understood that the switch switching circuit 340 also has other specific implementation forms, as long as it can realize the serial-parallel state conversion of the output terminals of the first DC/DC converter 331 and the second DC/DC converter 332 to be controlled.

The bleeder circuit 350 may be disposed at the output port of the power conversion system 200 . For example, in FIG. 3 , the bleeder circuit 350 is disposed between the positive output terminal and the negative output terminal of the power conversion system 200 .

Optionally, an output capacitor C _out is also set at the output port of the power conversion system 200 .

The above-mentioned discharge circuit 350 includes a discharge resistor R1 and a switching device Q4 connected in series. After the power conversion system 200 stops supplying power, the bleeder circuit 350 can be used to bleed the electric charge of the output port of the power conversion system 200 . In other words, the charges at both ends of the output capacitor C _out can be discharged through the discharge circuit 350 . Specifically, the controller 310 can control the switching device Q4 to be turned on, and the output capacitor C _out , the discharge resistor R1 and the switching device Q4 form a discharge loop to discharge the charges at both ends of the output capacitor C _out .

It should be understood that when the power conversion system 200 works normally, the switching device Q4 is in an off state, and the bleeder circuit 350 does not work.

Optionally, the above-mentioned switching device Q4 may include any one of the following devices: MOSFET, IGBT, SCR and relay.

FIG. 4 is a current flow diagram for discharging the power conversion system 200 of FIG. 3 in series mode. Wherein, when the output terminals of the first DC/DC converter 331 and the second DC/DC converter 332 are in series mode, the output voltage of the power conversion system 200 is V _out =2V _dc , and both ends of the bleeder circuit need to withstand The maximum voltage of 2V _dc , then the maximum transient power of the discharge resistor R1 is:

P _c =(2V _dc ) ² /R1

Wherein, P _c represents the maximum transient power of the discharge resistor R1 , and V _dc represents the output voltages of the first DC/DC converter 331 and the second DC/DC converter 332 .

In addition, it can be known from FIG. 4 that the maximum voltage that both ends of the switching device Q4 need to withstand is 2V _dc .

Therefore, the discharge resistor R1 needs to be selected according to the maximum transient power P _c =(2V _dc ) ² /R1, while the switching device Q4 needs to be selected according to the 2V _dc specification, which is costly and occupies a large space.

In order to solve the above problems, the embodiments of the present application provide a power conversion system (200, 400) and a corresponding control method (300, 600), which can reduce the voltage borne by the discharge resistor R1, and reduce the voltage of the discharge resistor R1 and power, which can effectively reduce the risk of device failure.

FIG. 5 is a schematic flowchart of a control method 300 of a power conversion system according to an embodiment of the present application. Wherein, the control method 300 may be executed based on the power conversion system 200 in FIG. 3 . Specifically, the control method 300 may be executed by the controller 310 in the power conversion system 200 . As shown in FIG. 5, the control method 300 includes:

S301. When the power conversion system 200 needs to be discharged through the bleeder circuit 350 and the output terminals of the first DC/DC converter 331 and the second DC/DC converter 332 are connected in series, the controller 310 controls the switch to switch. The switches in the circuit 340 are turned on and off, so that the output terminals of the first DC/DC converter 331 and the second DC/DC converter 332 are switched from the series state to the parallel state.

For example, in series mode, switch S1 is turned on and transistor Q1 is turned on. When discharging is required, the controller 310 first turns off the switch S1, and after determining that S1 is reliably turned off, for example, after a delay of 10-20 ms (milliseconds), turns off the transistor Q1. Then, the switches S2 and S3 are closed, so that the DC/DC conversion modules 330 are in a parallel state, and at this time V _out =V _dc .

S302: After the output ends of the first DC/DC converter 331 and the output ends of the second DC/DC converter 332 are switched to a parallel state, the controller 310 controls the bleeder circuit 350 to be in a conducting state.

Specifically, the controller 310 can control the switching device Q4 in the bleeder circuit 350 to be turned on, so that the output capacitor C _out and the bleeder circuit 350 form a path, so that the output capacitor C _out is discharged through the bleeder circuit 350 .

In addition, if the controller 310 determines that the output terminals of the first DC/DC converter 331 and the second DC/DC converter 332 are in a parallel state when the power conversion system 200 needs to discharge through the bleeder circuit 350, there is no need to change the switching The state of the circuit 340 only needs to control the discharge circuit 350 to be in a conducting state, at which time the output voltage V _out =V _dc .

FIG. 6 is a current flow diagram for discharging the power conversion system 200 in FIG. 3 in a parallel mode. As shown in Figure 6, after the switching device Q4 is turned on, the maximum transient power of the discharge resistor R1 is:

P _c =V _dc ² /R1

Wherein, P _c represents the maximum transient power of the discharge resistor R1 , and V _dc represents the output voltages of the first DC/DC converter 331 and the second DC/DC converter 332 .

Therefore, the discharge resistor R1 can be selected according to the maximum transient power P _c =V _dc ² /R1, and the resistance power of the discharge resistor R1 is reduced by 3/4, which can effectively save the space and cost occupied by the discharge circuit 350 .

It should be noted that since the bleeder circuit 350 is provided between the positive output terminal of the DC/DC converter 331 and the negative output terminal of the second DC/DC converter 332, there is no difference between the first DC/DC converter 331 and the second DC/DC converter 331. Before the /DC converter 332 is switched to the parallel mode, the voltage across the bleeder circuit 350 is still 2V _dc , so the maximum voltage across the switching device Q4 is still 2V _dc , and the switching device Q4 can be selected according to the 2V _dc specification.

In the embodiment of the present application, by controlling the switch in the switch switching circuit 340 in the power conversion system and the switching logic sequence of the switching device Q4 in the bleeder circuit 350, the DC/DC conversion module 330 discharges in the parallel mode, and discharges Both ends of the resistor R1 only need to bear the voltage of a single DC/DC converter during discharge, so the maximum transient power that the discharge resistor R1 bears is reduced, and the selection of the discharge resistor R1 can effectively save the bleeder circuit 350. space and cost.

7 and 8 are schematic structural diagrams of a power conversion system 400 according to still another embodiment of the present application. The difference between the power conversion system 400 and the power conversion system 200 is that the bleeder circuit 350 in the power conversion system 400 is connected in parallel at the output port of a single DC/DC converter. For example, the bleeder circuit 350 can be arranged between the positive output terminal and the negative output terminal of the first DC/DC converter 331 , or can also be arranged between the positive output terminal and the negative output terminal of the second DC/DC converter 332 . between. In FIG. 7 , it is taken as an example that the bleeder circuit 350 is disposed between the positive output terminal and the negative output terminal of the second DC/DC converter 332 . In FIG. 8 , it is taken as an example that the bleeder circuit 350 is disposed between the positive output terminal and the negative output terminal of the first DC/DC converter 331 .

It should be noted that the functions of other modules in FIG. 7 and FIG. 8 are the same as those in FIG. 3 , and details are not repeated here.

FIG. 9 is a schematic flowchart of a control method 600 of a power conversion system according to an embodiment of the present application. The control method 600 is performed based on the power conversion system 400 in FIG. 7 or FIG. 8 . Specifically, the control method 600 may be executed by the controller 310 in the power conversion system 400 . As shown in FIG. 9, the control method 600 includes:

S601. When the power conversion system 400 needs to be discharged through the discharge circuit 350, the controller 310 controls the switch to switch when the output terminals of the first DC/DC converter 331 and the second DC/DC converter 332 are connected in series The switches in the circuit 340 are turned on and off, so that the output terminals of the first DC/DC converter 331 and the second DC/DC converter 332 are switched from the series state to the parallel state.

For example, in the series mode, the controller 310 controls the switch S1 to be turned on, and the transistor Q1 to be turned on. When discharging is required, the controller 310 first turns off the switch S1, and after determining that S1 is reliably turned off, for example, after a delay of 10-20 ms (milliseconds), turns off the transistor Q1. Switches S2 and S3 are then closed, where V _out =V _dc .

S602. After the output ends of the first DC/DC converter 331 and the output ends of the second DC/DC converter 332 are switched to a parallel state, the controller 310 controls the bleeder circuit 350 to be in a conducting state.

As a specific example, the controller may control the switching device Q4 in the bleeder circuit 350 to be turned on, so that the output capacitor C _out and the bleeder circuit 350 form a path, so that the output capacitor C _out is discharged through the bleeder circuit 350 .

FIG. 10 is a current flow diagram for discharging the power conversion system 400 in FIG. 7 in a parallel mode. FIG. 11 is a current flow diagram for discharging the power conversion system 400 in FIG. 8 in a parallel mode. As shown in Figure 10 and Figure 11, after the switching device Q4 is turned on, the maximum transient power of the discharge resistor R1 is:

P _c =V _dc ² /R1

Wherein, P _c represents the maximum transient power of the discharge resistor R1 , and V _dc represents the output voltages of the first DC/DC converter 331 and the second DC/DC converter 332 .

Therefore, the discharge resistor R1 can be selected according to the maximum transient power P _c =V _dc ² /R1, and the resistance power of the discharge resistor R1 is reduced by 3/4, which can effectively save the space and cost occupied by the discharge circuit 350 .

In addition, since the bleeder circuit 350 is disposed between the positive output terminal and the negative output terminal of a single DC/DC converter (331, 332), the maximum transient voltage that both ends of the bleeder circuit 350 bear is V _dc , that is, the switch The maximum voltage that both ends of the device Q4 need to bear is only the output voltage V _dc of a single DC/DC converter. The switching device Q4 can be selected according to the V _dc specification, which reduces the space and cost occupied by the switching device Q4.

In the embodiment of the present application, by controlling the switch in the switch switching circuit 340 in the power conversion system and the switching logic sequence of the switching device Q4 in the bleeder circuit 350, the DC/DC conversion module 330 discharges in a parallel mode, Both ends of the discharge resistor R1 only need to bear the voltage of a single DC/DC converter when discharging, so the maximum transient power that the discharge resistor R1 bears is reduced, and the selection of the discharge resistor R1 can effectively save the bleeder circuit 350 occupancy space and cost. In addition, since the bleeder circuit 350 is arranged between the positive output terminal and the negative output terminal of a single DC/DC converter, the maximum voltage that the switching device Q4 in the bleeder circuit 350 needs to withstand is the same as that of the single DC/DC converter. The output voltage of the switching device Q4 can be selected according to the specification of the output voltage of a single DC/DC converter, which reduces the space and cost occupied by the switching device Q4.

Those of ordinary skill in the art can realize that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Skilled artisans may implement the described functionality using different methods for each particular application, but such implementations should not be considered beyond the scope of this application.

Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working process of the above-described systems, devices and units may refer to the corresponding processes in the foregoing method embodiments, which will not be repeated here.

In the several embodiments provided in this application, it should be understood that the disclosed system, apparatus and method may be implemented in other manners. For example, the apparatus embodiments described above are only illustrative. For example, the division of the units is only a logical function division. In actual implementation, there may be other division methods. For example, multiple units or components may be combined or Can be integrated into another system, or some features can be ignored, or not implemented. On the other hand, the shown or discussed mutual coupling or direct coupling or communication connection may be through some interfaces, indirect coupling or communication connection of devices or units, and may be in electrical, mechanical or other forms.

The units described as separate components may or may not be physically separated, and components displayed as units may or may not be physical units, that is, may be located in one place, or may be distributed to multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution in this embodiment.

In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically alone, or two or more units may be integrated into one unit.

The functions, if implemented in the form of software functional units and sold or used as independent products, may be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application can be embodied in the form of a software product in essence, or the part that contributes to the prior art or the part of the technical solution, and the computer software product is stored in a storage medium, including Several instructions are used to cause a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (Read-Only Memory, ROM), random access memory (Random Access Memory, RAM), magnetic disk or optical disk and other media that can store program codes .

The above are only specific embodiments of the present application, but the protection scope of the present application is not limited to this. should be covered within the scope of protection of this application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims (20)

1. A power conversion system, comprising: a controller, a DC/DC/DC conversion module, a switch switching circuit and a bleeder circuit,

the DC/DC conversion module is used for performing DC voltage conversion and outputting an output voltage V of the power conversion system_outSaid output voltage V_outThe DC/DC conversion module is used for supplying power to a load and comprises a first DC/DC converter and a second DC/DC converter;

the controller is used for controlling the output ends of the first DC/DC converter and the second DC/DC converter to be in a series state or a parallel state by controlling the on-off of a switch in the switch switching circuit so as to change the output voltage V_out；

The bleeder circuit is used for discharging the charge of an output port of the power conversion system after the power conversion system stops supplying power to the load, the bleeder circuit is arranged between a positive output end and a negative output end of the power conversion system, and the bleeder circuit comprises a discharge resistor R1 and a switching device Q4 which are connected in series;

the controller is further configured to:

when the power conversion system needs to discharge through the bleeder circuit, under the condition that the output ends of the first DC/DC converter and the second DC/DC converter are in a series state, controlling the on-off of a switch in the switch switching circuit to switch the output ends of the first DC/DC converter and the second DC/DC converter from a series state to a parallel state; and

and controlling the bleeder circuit to be in a conducting state.

2. The power conversion system of claim 1, wherein the controller is further to: when the power conversion system needs to discharge through the bleeder circuit, the bleeder circuit is controlled to be in a conducting state under the condition that the output ends of the first DC/DC converter and the second DC/DC converter are in a parallel connection state.

3. The power conversion system according to claim 1 or 2, wherein the switch switching circuit includes:

a switch S1 disposed between the negative output terminal of the first DC/DC controller and the positive output terminal of the second DC/DC converter;

a switch S2 disposed between the negative output terminal of the first DC/DC converter and the negative output terminal of the second DC/DC converter;

a switch S3 provided between the positive output terminal of the first DC/DC converter and the positive output terminal of the second DC/DC converter;

the controller is specifically configured to:

controlling the switch S1 to be opened;

after the switch S1 is turned off, controlling the switches S2 and S3 to be turned on so that the output terminals of the first DC/DC converter and the second DC/DC converter are switched into a parallel state;

after the switches S2 and S3 are turned on, the switching device Q4 is controlled to be turned on so that the bleeding circuit is in a conductive state.

4. The power conversion system of claim 3, wherein a transistor Q1 for clamping is further connected in parallel across the switch S1,

the controller is specifically configured to:

after the switch S1 is turned off, controlling the transistor Q1 to be turned off;

after the transistor Q1 is turned off, the switch S2 and the switch S3 are controlled to be turned on.

5. The power conversion system according to any one of claims 1 to 4, wherein the power conversion system is a charging pile and the load is an electric vehicle.

6. A power conversion system, comprising: a controller, a DC/DC/DC conversion module, a switch switching circuit and a bleeder circuit,

the DC/DC conversion module is used for performing DC voltage conversion and outputting an output voltage V of the power conversion system_outSaid output voltage V_outThe DC/DC conversion module is used for supplying power to a load and comprises a first DC/DC converter and a second DC/DC converter;

the controller is used for controlling the output ends of the first DC/DC converter and the second DC/DC converter to be in a series state or a parallel state by controlling the on-off of a switch in the switch switching circuit so as to change the output voltage V_out；

The bleeder circuit is used for discharging the charge of an output port of the power conversion system after the power conversion system stops supplying power to the load, and is arranged between the positive output end and the negative output end of the first DC/DC converter or between the positive output end and the negative output end of the second DC/DC converter, and the bleeder circuit comprises a discharge resistor R1 and a switching device Q4 which are connected in series;

the controller is further configured to:

when the power conversion system needs to discharge through the bleeder circuit, under the condition that the output ends of the first DC/DC converter and the second DC/DC converter are in a series state, controlling the on-off of a switch in the switch switching circuit to switch the output ends of the first DC/DC converter and the second DC/DC converter from a series state to a parallel state; and

controlling the bleeding circuit to be in a conductive state after the output terminals of the first DC/DC converter and the second DC/DC converter are switched to a parallel state.

7. The power conversion system of claim 6, wherein the controller is further configured to: when the power conversion system needs to discharge through the bleeder circuit, the bleeder circuit is controlled to be in a conducting state under the condition that the output ends of the first DC/DC converter and the second DC/DC converter are in a parallel connection state.

8. The power conversion system of claim 6 or 7, wherein the switch switching circuit comprises:

a switch S1 disposed between the negative output terminal of the first DC/DC controller and the positive output terminal of the second DC/DC converter;

a switch S2 disposed between the negative output terminal of the first DC/DC converter and the negative output terminal of the second DC/DC converter;

a switch S3 provided between the positive output terminal of the first DC/DC converter and the positive output terminal of the second DC/DC converter;

the controller is specifically configured to:

controlling the switch S1 to be opened;

after the switch S1 is turned off, controlling the switches S2 and S3 to be turned on so that the output terminals of the first DC/DC converter and the second DC/DC converter are switched into a parallel state;

after the switches S2 and S3 are turned on, the switching device Q4 is controlled to be turned on so that the bleeding circuit is in a conductive state.

9. The power conversion system of claim 8, wherein a transistor Q1 for clamping is further connected in parallel across the switch S1,

the controller is specifically configured to:

after the switch S1 is turned off, controlling the transistor Q1 to be turned off;

after the transistor Q1 is turned off, the switch S2 and the switch S3 are controlled to be turned on.

10. The power conversion system according to any one of claims 6 to 9, wherein the power conversion system is a charging pile and the load is an electric vehicle.

11. A method of controlling a power conversion system, the power conversion system comprising: a controller, a DC/DC/DC conversion module, a switch switching circuit and a bleeder circuit,

the DC/DC conversion module is used for performing DC voltage conversion and outputting an output voltage V of the power conversion system_outSaid output voltage V_outThe DC/DC conversion module is used for supplying power to a load and comprises a first DC/DC converter and a second DC/DC converter;

the controller is used for controlling the output ends of the first DC/DC converter and the second DC/DC converter to be in a series state or a parallel state by controlling the on-off of a switch in the switch switching circuit so as to change the output voltage V_out；

The bleeder circuit is used for discharging the charge of an output port of the power conversion system after the power conversion system stops supplying power to the load, the bleeder circuit is arranged between a positive output end and a negative output end of the power conversion system, and the bleeder circuit comprises a discharge resistor R1 and a switching device Q4 which are connected in series;

the method comprises the following steps:

when the power conversion system needs to be discharged through the bleeder circuit, the controller controls the on-off of a switch in the switch switching circuit under the condition that the output ends of the first DC/DC converter and the second DC/DC converter are in a series state, so that the output ends of the first DC/DC converter and the second DC/DC converter are switched from a series state to a parallel state; and

the controller controls the bleeding circuit to be in a conductive state after the output terminals of the first DC/DC converter and the second DC/DC converter are switched to a parallel state.

12. The method of claim 11, wherein the method further comprises:

the controller controls the bleeder circuit to be in a conducting state under the condition that the output ends of the first DC/DC converter and the second DC/DC converter are in a parallel connection state when the power conversion system needs to be discharged through the bleeder circuit.

13. The method of claim 11 or 12, wherein the switch switching circuit comprises:

a switch S1 disposed between the negative output terminal of the first DC/DC controller and the positive output terminal of the second DC/DC converter;

a switch S2 disposed between the negative output terminal of the first DC/DC converter and the negative output terminal of the second DC/DC converter;

a switch S3 provided between the positive output terminal of the first DC/DC converter and the positive output terminal of the second DC/DC converter;

the controller controls on/off of a switch in the switch switching circuit so that the output terminals of the first DC/DC converter and the second DC/DC converter are switched from a series state to a parallel state when the output terminals of the first DC/DC converter and the second DC/DC converter are in a series state, including:

the controller controls the switch S1 to open;

the controller controls the switch S2 and the switch S3 to be turned on after the switch S1 is turned off, so that the output terminals of the first DC/DC converter and the second DC/DC converter are switched into a parallel state;

the controller controls the bleeding circuit to be in a conducting state after the output terminals of the first DC/DC converter and the second DC/DC converter are switched to a parallel state, including:

the controller controls the switching device Q4 to be turned on after the switches S2 and S3 are turned on, so that the bleeding circuit is in a conductive state.

14. The method of claim 13, wherein the switch S1 further has a transistor Q1 connected in parallel across it for clamping, the method further comprising:

the controller controls the transistor Q1 to turn off after the switch S1 turns off;

the controller controls the switch S2 and the switch S3 to be turned on after the transistor Q1 is turned off.

15. The method of any one of claims 11 to 14, wherein the power conversion system is a charging pile and the load is an electric vehicle.

16. A method of controlling a power conversion system, the power conversion system comprising: a controller, a DC/DC/DC conversion module, a switch switching circuit and a bleeder circuit,

the DC/DC conversion module is used for performing DC voltage conversion and outputting an output voltage V of the power conversion system_outSaid output voltage V_outThe DC/DC conversion module is used for supplying power to a load and comprises a first DC/DC converter and a second DC/DC converter;

the controller is used for controlling the switchSwitching on/off of a switch in a switching circuit to control output ends of the first DC/DC converter and the second DC/DC converter to be in a series state or a parallel state so as to change the output voltage V_out；

The bleeder circuit is used for discharging the charge of an output port of the power conversion system after the power conversion system stops supplying power to the load, and is arranged between the positive output end and the negative output end of the first DC/DC converter or between the positive output end and the negative output end of the second DC/DC converter, and the bleeder circuit comprises a discharge resistor R1 and a switching device Q4 which are connected in series;

the method comprises the following steps:

when the power conversion system needs to be discharged through the bleeder circuit, the controller controls the on-off of a switch in the switch switching circuit under the condition that the output ends of the first DC/DC converter and the second DC/DC converter are in a series state, so that the output ends of the first DC/DC converter and the second DC/DC converter are switched from a series state to a parallel state; and

the controller controls the bleeding circuit to be in a conductive state after the output terminals of the first DC/DC converter and the second DC/DC converter are switched to a parallel state.

17. The method of claim 16, wherein the method further comprises:

the controller controls the bleeder circuit to be in a conducting state under the condition that the output ends of the first DC/DC converter and the second DC/DC converter are in a parallel state when the power conversion system needs to be discharged through the bleeder circuit.

18. The method of claim 16 or 17, wherein the switch switching circuit comprises:

a switch S1 disposed between the negative output terminal of the first DC/DC controller and the positive output terminal of the second DC/DC converter;

a switch S2 disposed between the negative output terminal of the first DC/DC converter and the negative output terminal of the second DC/DC converter;

a switch S3 provided between the positive output terminal of the first DC/DC converter and the positive output terminal of the second DC/DC converter;

the controller controls on/off of a switch in the switch switching circuit so that the output terminals of the first DC/DC converter and the second DC/DC converter are switched from a series state to a parallel state when the output terminals of the first DC/DC converter and the second DC/DC converter are in a series state, including:

the controller controls the switch S1 to open;

the controller controls the switch S2 and the switch S3 to be turned on after the switch S1 is turned off, so that the output terminals of the first DC/DC converter and the second DC/DC converter are switched into a parallel state;

the controller controls the bleeding circuit to be in a conducting state after the output terminals of the first DC/DC converter and the second DC/DC converter are switched to a parallel state, including:

the controller controls the switching device Q4 to be turned on after the switches S2 and S3 are turned on, so that the bleeding circuit is in a conductive state.

19. The method of claim 18, wherein the switch S1 further has a transistor Q1 connected in parallel across it for clamping, the method further comprising:

the controller controls the transistor Q1 to turn off after the switch S1 turns off;

the controller controls the switch S2 and the switch S3 to be turned on after the transistor Q1 is turned off.

20. The method of any one of claims 16 to 19, wherein the power conversion system is a charging pile and the load is an electric vehicle.

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