A pre-charge discharge plate assembly, DCDC converter and control method for a fuel cell

Abstract

The present invention discloses a pre-charge and discharge plate assembly, a DCDC converter and a control method for a fuel cell. The pre-charge and discharge plate assembly comprises a circuit board, a plurality of relays, a plurality of resistors, a plurality of hardware terminals and a plurality of low-voltage connectors. The plurality of relays, a plurality of resistors, a plurality of hardware terminals and a plurality of low-voltage connectors are welded on the circuit board to form two pre-charge circuits and one discharge circuit. All devices are centrally designed on a circuit board, and electrical connection between various devices is directly achieved through printed circuits on the circuit board, so that the pre-charge circuit and the discharge circuit are modularly designed, thereby making the overall structure of the pre-charge and discharge plate assembly more compact. When the various devices are connected, there is no need to use a connecting harness, so that the wiring of the pre-charge and discharge plate assembly becomes simple and highly integrated, which can effectively improve the space utilization of the pre-charge and discharge plate assembly and reduce the manufacturing cost.

Description

Technical field:

[0001] The invention relates to a pre-charge discharge plate assembly, a DCDC converter and a control method for a fuel cell. Background technology:

[0002] At present, the DCDC converter used in fuel cell power generation systems usually contains several pre-charge circuits and discharge circuits, such as Figure 1 As shown, these pre-charge circuits and discharge circuits are completed by separate relays 1A and resistors 2A connected by copper bars. Disadvantages of the current solution:

[0003] 1. The devices are scattered and cannot be integrated into a modular design;

[0004] 2. Since the devices are scattered and parts cannot be shared, the manufacturing cost is high;

[0005] 3. There are many connecting harnesses between devices, which affects integration and reduces space utilization;

[0006] 4. Too many wiring harnesses bring great instability to installation, maintenance and disassembly. Summary of the invention:

[0007] The object of the present invention is to provide a pre-charge and discharge plate assembly and a DCDC converter for a fuel cell, which can solve the technical problems in the prior art that the pre-charge circuit and the discharge circuit contained in the DCDC converter are completed by connecting separate relays and resistors, resulting in scattered devices, inability to modularize, inability to share components, resulting in high manufacturing costs, many connecting harnesses, affecting integration, and reduced space utilization.

[0008] The purpose of the present invention is achieved through the following technical solutions.

[0009] A DCDC converter, which is connected to the output end of a fuel cell power generation system, comprises a box and a pre-charge and discharge plate assembly for a fuel cell installed in the box, the pre-charge and discharge plate assembly for the fuel cell comprises a circuit board, a plurality of relays, a plurality of resistors, a plurality of hardware terminals and a plurality of low-voltage connectors, the plurality of relays, a plurality of resistors, a plurality of hardware terminals and a plurality of low-voltage connectors are welded on the circuit board to form two pre-charge circuits and one discharge circuit;

[0010] The plurality of relays include a relay J2 and a relay J1, the plurality of resistors include a resistor R1, the two pre-charging circuits include a first pre-charging circuit and a second pre-charging circuit, the first pre-charging circuit is formed in series with the relay J1 and the resistor R1, and the second pre-charging circuit is formed in series with the relay J2 and the resistor R1;

[0011] The box is also provided with a DC-DC boost conversion unit and a DC-DC main control board. The DC-DC boost conversion unit is controlled by the DC-DC main control board. The output end of the DC-DC boost conversion unit outputs a voltage U1 and is connected to the positive electrode of the capacitor C1. The positive electrode of the capacitor C1 is also connected to the voltage U2 through the relay J1 and the resistor R1.

[0012] The output end of the pre-charge discharge plate assembly is connected to a relay J4 and a capacitor C2, the relay J4 and the capacitor C2 are connected in series, the second pre-charge circuit is connected in parallel with the relay J4, the positive electrode of the capacitor C2 is connected to one end of the relay J2, the other end of the relay J2 is connected between the relay J1 and the resistor R1, and the positive electrode of the capacitor C2 is connected to the voltage U2 through the relay J2 and the resistor R1.

[0013] Preferably, the plurality of relays further include a relay J3, the plurality of resistors further include a resistor R2, the discharge circuit is formed by connecting the relay J3 and the resistor R2 in series, and the discharge circuit is connected in parallel across the capacitor C1.

[0014] Preferably, the internal circuits of the two pre-charging circuits and the one discharge circuit are electrically connected by printed circuits on a circuit board.

[0015] Preferably, the positive and negative signals of the relay are obtained through a low voltage connector.

[0016] Preferably, the relay J1 , the relay J2 and the relay J3 are electrically connected to an independent low-voltage connector respectively.

[0017] Preferably, the hardware terminal is used to be electrically connected to a high voltage circuit.

[0018] Preferably, the low-voltage connector is electrically connected to the positive and negative electrodes of the relay through the printed circuit on the circuit board, and the hardware terminals are electrically connected to the relay and the resistor respectively through the printed circuit on the circuit board.

[0019] Preferably, a reverse connection protection diode D1 is further welded on the circuit board, and a first pre-charging circuit in the pre-charging circuit is connected in parallel to both ends of the reverse connection protection diode D1.

[0020] Preferably, the box is also provided with a voltage detection circuit, which is used to input the voltage of the capacitor C1 and the capacitor C2 into the DC-DC main control board, and the DC-DC main control board controls the on and off of relays J1, relay J2, relay J3 and relay J4 according to the detection results.

[0021] A control method for a DCDC converter, characterized in that the DCDC converter described above is adopted, the control method includes a pre-charge control method, and the pre-charge control method includes the following steps:

[0022] Step 1: Power on, relay J0, relay J1 and relay J2 are energized, charging capacitor C1 and capacitor C2 respectively;

[0023] Step 2: The DC-DC main control board calculates the difference between the voltage U2 and the voltage U1 and the difference between the voltage U2 and the voltage U3, and compares the calculation results with the first preset voltage threshold, and controls the on and off of the relays J1, J2 and J4 according to the comparison results; the voltage across the capacitor C2 is U3;

[0024] Step 3: When voltage U2-voltage U1 < 5V, voltage U2-voltage U3 < 5V, the DC-DC main control board determines that the charging of capacitors C1 and C2 is complete, and the DC-DC main control board first controls relay J1 to disconnect and relay J4 to turn on, and then controls relay J2 to disconnect; otherwise, return to step 2.

[0025] Preferably, the control method further includes a discharge control method, and the discharge control method includes the following steps:

[0026] Step 4: Power off, relay J0 is disconnected, relay J3 is energized, relay J1 is energized, relay J4 remains energized, and relay J2 remains disconnected, so as to discharge the charges of capacitors C1 and C2, that is, the charge of capacitor C1 is discharged through relay J3 and resistor R2, and the charge of capacitor C2 is discharged through relay J4, resistor R1, relay J1, relay J3, and resistor R2;

[0027] Step 5: The DC-DC main control board detects the voltage U1 and voltage U3 across the capacitor C1 and the capacitor C2 respectively, and compares the voltage U1 and voltage U3 with the second preset voltage threshold, and controls the on and off of the relay J3, the relay J1 and the relay J4 according to the comparison result;

[0028] Step 6: When voltage U1 is less than 36V and voltage U3 is less than 36V, the DC-DC main control board determines that the charge discharge of capacitors C1 and C2 is completed, and the DC-DC main control board controls relays J1, J3 and J4 to be disconnected; otherwise, return to step 5.

[0029] Compared with the prior art, the present invention has the following effects:

[0030] 1) The pre-charging and discharging board assembly for a fuel cell provided by the present invention forms two pre-charging circuits and one discharging circuit by welding a plurality of relays, a plurality of resistors, a plurality of hardware terminals and a plurality of low-voltage connectors on a circuit board, and designs all devices on a circuit board in a centralized manner. The electrical connection between the devices is directly achieved through the printed circuits on the circuit board, and the pre-charging circuit and the discharging circuit are modularly designed, so that the overall structure of the pre-charging and discharging board assembly is more compact, and there is no need to use a connecting harness when connecting the devices, so that the wiring of the pre-charging and discharging board assembly becomes simple and highly integrated, which can effectively improve the space utilization of the pre-charging and discharging board assembly and reduce the manufacturing cost.

[0031] 2) Other advantages of the present invention are described in detail in the embodiment section. Description of the drawings:

[0032] Figure 1 It is a structural schematic diagram of a pre-charging circuit and a discharge circuit provided by the prior art;

[0033] Figure 2 is a structural schematic diagram of a pre-charge discharge plate assembly provided in Embodiment 1 of the present invention;

[0034] Figure 3 is a circuit diagram of a pre-charge discharge plate assembly provided in Embodiment 1 of the present invention;

[0035] Figure 4 is a structural schematic diagram of a DCDC converter provided in Embodiment 2 of the present invention;

[0036] Figure 5 is a circuit diagram of a DCDC converter provided in Embodiment 2 of the present invention;

[0037] Figure 6 This is a circuit diagram of the application of the pre-charge discharge plate assembly provided in the second embodiment of the present invention;

[0038] Figure 7 This is a circuit diagram of a DC-DC main control board control relay provided in Embodiment 2 of the present invention;

[0039] Figure 8 1 is a logic flow diagram of a pre-charging control method provided in Embodiment 3 of the present invention;

[0040] Fig. 9 It is a logical flow chart of the discharge control method provided for the third embodiment of the present invention. Specific implementation method:

[0041] The present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings.

[0042] Embodiment 1:

[0043] like Figure 2 As shown, the present embodiment provides a pre-charging and discharging board assembly for a fuel cell, which includes a circuit board 1, a plurality of relays 2, a plurality of resistors 3, a plurality of hardware terminals 4 and a plurality of low-voltage connectors 5, wherein the plurality of relays 2, a plurality of resistors 3, a plurality of hardware terminals 4 and a plurality of low-voltage connectors 5 are all welded on the circuit board 1 to form two pre-charging circuits 100 and one discharging circuit 200, so that all devices are centrally designed on a circuit board 1, and electrical connection between various devices is directly achieved through the printed circuits on the circuit board 1, so that the pre-charging circuit 100 and the discharging circuit 200 are modularly designed, thereby making the overall structure of the pre-charging and discharging board assembly more compact, and no connection harness is required when connecting various devices, so that the wiring of the pre-charging and discharging board assembly becomes simple and highly integrated, which can effectively improve the space utilization of the pre-charging and discharging board assembly and reduce the manufacturing cost.

[0044] like Figure 3 As shown, the plurality of relays 2 include relays J2 and relays J1, the plurality of resistors 3 include resistor R1, the two pre-charging circuits 100 include a first pre-charging circuit 101 and a second pre-charging circuit 102, the first pre-charging circuit 101 is formed by the relay J1 and the resistor R1 being connected in series, the second pre-charging circuit 102 is formed by the relay J2 and the resistor R1 being connected in series, the two pre-charging circuits share one resistor R1, and the use of resistors is reduced while ensuring the stability of the pre-charging circuit function, thereby simplifying the circuit structure of the two pre-charging circuits, making the circuit design simpler, and reducing the manufacturing cost.

[0045] like Figure 3 As shown, the plurality of relays 2 further include a relay J3, and the plurality of resistors 3 further include a resistor R2. The discharge circuit 200 is formed by connecting the relay J3 and the resistor R2 in series.

[0046] like Figure 3 As shown, an anti-reverse connection diode D1 is also welded on the circuit board 1, and the first pre-charging circuit 101 in the pre-charging circuit 100 is connected in parallel to the two ends of the anti-reverse connection diode D1. The pre-charging and discharging board assembly provided in this embodiment is connected between the high-voltage circuit and the output circuit. The anti-reverse connection diode D1 can prevent the reverse connection phenomenon when the pre-charging and discharging board assembly is connected between the high-voltage circuit and the output circuit. The design of the anti-reverse connection diode D1 can improve the safety of the use of the pre-charging and discharging board assembly.

[0047] The internal circuits of the two pre-charging circuits 100 and the one discharging circuit 200 are electrically connected by printed circuits on the circuit board 1. The electrical connection between the various devices is achieved through the printed circuits on the circuit board 1. There is no need to use a connecting harness when connecting the various devices, which makes the wiring of the pre-charging and discharging board assembly simple and highly integrated, can effectively improve the space utilization of the pre-charging and discharging board assembly, and can reduce the manufacturing cost.

[0048] The positive and negative signals of the relay 2 are obtained through the low-voltage connector 5, and the hardware terminal 4 is used to be electrically connected to the high-voltage circuit. The design of the low-voltage connector 5 and the hardware terminal 4 facilitates the connection of the pre-charge and discharge board assembly between the high-voltage circuit and the output circuit, making the application of the pre-charge and discharge board assembly simple; specifically, the low-voltage connector 5 is electrically connected to the positive and negative electrodes of the relay 2 through the printed circuit on the circuit board 1, and the hardware terminal 4 is electrically connected to the relay 2 and the resistor 3 respectively through the printed circuit on the circuit board 1; when connecting the various devices, there is no need to use a connecting harness, which makes the wiring of the pre-charge and discharge board assembly simple and highly integrated, which can effectively improve the space utilization of the pre-charge and discharge board assembly and reduce the manufacturing cost.

[0049] Relay J1, relay J2 and relay J3 are electrically connected to an independent low voltage connector 5 respectively, so as to facilitate the connection of the pre-charge discharge board assembly to the DCDC converter.

[0050] Embodiment 2:

[0051] like Figure 4 and Figure 5 As shown, this embodiment provides a DCDC converter, which is connected to the output end of the fuel cell power generation system. The DCDC converter includes a box body 6 and a pre-charged discharge plate assembly 7 for a fuel cell installed in the box body 6. The pre-charged discharge plate assembly 7 for the fuel cell adopts a pre-charged discharge plate assembly for a fuel cell as described in Example 1.

[0052] like Figure 5 and Figure 6 As shown, the box body 6 is also provided with a DC-DC boost conversion unit 8 and a DC-DC main control board 10. The DC-DC boost conversion unit 8 is controlled by the DC-DC main control board 10. The output end of the DC-DC boost conversion unit 8 is connected to a capacitor C1 and a pre-charge discharge plate assembly. The direct current output by the fuel cell system is boosted by the DC-DC boost conversion unit 8 to form a voltage U1 output. The output end of the DC-DC boost conversion unit 8 outputs the voltage U1 and is connected to the positive electrode of the capacitor C1. The positive electrode of the capacitor C1 is also connected to the voltage U2 through the relay J1 and the resistor R1; The output end of the pre-charge discharge plate assembly 7 is connected to a relay J4 and a capacitor C2, the relay J4 and the capacitor C2 are connected in series, the second pre-charge circuit 102 is connected in parallel with the relay J4, the positive electrode of the capacitor C2 is connected to one end of the relay J2, the other end of the relay J2 is connected between the relay J1 and the resistor R1, the positive electrode of the capacitor C2 is connected to the voltage U2 through the relay J2 and the resistor R1, the DC-DC boost conversion unit 8 includes an energy storage inductor L1, a diode D1 and a switch tube MOS1, and the discharge circuit 200 of the pre-charge discharge plate assembly 7 is connected in parallel to both ends of the capacitor C1.

[0053] like Figure 5 and Figure 6 As shown, the output end of the pre-charge discharge plate assembly is connected to a relay J4 and a capacitor C2, the relay J4 and the capacitor C2 are connected in series, the second pre-charge circuit 102 of the pre-charge discharge plate assembly is connected in parallel with the relay J4, the capacitor C2 outputs a voltage U3 to power the load, and the relay J0 is connected to the negative output line of the voltage U2.

[0054] like Figure 5 As shown, the box body 6 is also provided with an air compressor drive module 9A, a hydrogen return pump drive module 9B and a water pump drive module 9C, and the output end of the DC-DC boost conversion unit 8 is electrically connected to the input end of the air compressor drive module 9A, the input end of the hydrogen return pump drive module 9B and the input end of the water pump drive module 9C respectively through the anti-reverse connection diode D1 and the relay J4 of the pre-charge discharge board assembly 7.

[0055] like Figure 6 As shown, the discharge circuit 200 of the pre-charge discharge board assembly is used to complete the charge discharge of the capacitor C1 and the capacitor C2.

[0056] like Figure 6 As shown, the housing 6 is also provided with a voltage detection circuit, which is used to input the voltage of the capacitor C1 and the capacitor C2 to the DC-DC main control board 10, and the DC-DC main control board 10 controls the on and off of the relays J1, J2, J3 and J4 according to the detection results.

[0057] Figure 7 It is an application circuit for the DC-DC main control board 10 to control the on and off of the relay.

[0058] The box body 6 is provided with a high-voltage circuit output interface 30, an air compressor output interface 40, a hydrogen return pump output interface 50, a water pump output interface 60 and a high-voltage power distribution output interface 70. The DC-DC boost conversion unit 8 output interface 30 is electrically connected to the output end of the DC-DC boost conversion unit 8, the air compressor output interface 40 is electrically connected to the output end of the air compressor drive module, the hydrogen return pump output interface 50 is electrically connected to the output end of the hydrogen return pump drive module, the water pump output interface 60 is electrically connected to the output end of the water pump drive module, and the high-voltage power distribution output interface 70 is electrically connected to the output end of the high-voltage power distribution module PDU.

[0059] An insulation detector 20 is also provided in the box body 6 . The insulation detector 20 is electrically connected to the output end of the pre-charge discharge board assembly to detect whether there is leakage, and the insulation detector 20 transmits the detection signal to the DC-DC main control board 10 .

[0060] Embodiment three:

[0061] like Figure 8 As shown, this embodiment provides a control method for a DCDC converter, using a DCDC converter as described in Embodiment 2, the control method includes a pre-charge control method, and the pre-charge control method includes the following steps:

[0062] Step 1: Power on, relay J0, relay J1 and relay J2 are energized, charging capacitor C1 and capacitor C2 respectively;

[0063] Step 2: The DC-DC main control board 10 calculates the difference between the voltage U2 and the voltage U1 and the difference between the voltage U2 and the voltage U3, and compares the calculation results with the first preset voltage threshold, and controls the on and off of the relays J1, J2 and J4 according to the comparison results; the voltage across the capacitor C2 is U3;

[0064] Step 3: When voltage U2-voltage U1<5V, voltage U2-voltage U3<5V, the DC-DC main control board 10 determines that the charging of capacitors C1 and C2 is complete, and the DC-DC main control board 10 first controls relay J1 to disconnect and relay J4 to turn on, and then controls relay J2 to disconnect; otherwise, return to step 2.

[0065] like Fig. 9 As shown, the control method also includes a discharge control method, and the discharge control method includes the following steps:

[0066] Step 4: Power off, relay J0 is disconnected, relay J3 is energized, relay J1 is energized, relay J4 remains energized, and relay J2 remains disconnected, so as to discharge the charge of capacitors C1 and C2; when relay J3 is energized, resistor R2 discharges the charge of capacitor C1, relay J1 is energized, and resistors R1 and R2 discharge the charge of capacitor C2, that is, the charge of capacitor C1 is discharged through relay J3 and resistor R2, and the charge of capacitor C2 is discharged through relay J4, resistor R1, relay J1, relay J3, and resistor R2;

[0067] Step 5: The DC-DC main control board 10 detects the voltage U1 and the voltage U3 of the capacitor C1 and the capacitor C2 respectively, and compares the voltage U1 and the voltage U3 with the second preset voltage threshold, and controls the on and off of the relay J3, the relay J1 and the relay J4 according to the comparison result;

[0068] Step 6: When voltage U1 is less than 36V and voltage U3 is less than 36V, DC-DC main control board 10 determines that charge discharge of capacitors C1 and C2 is completed, and DC-DC main control board 10 controls relays J1, J3 and J4 to be disconnected; otherwise, return to step 5.

[0069] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited thereto. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention are all equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A DCDC converter, the DCDC converter being connected to an output end of a fuel cell power generation system, the DCDC converter comprising a box (6) and a pre-charge and discharge plate assembly (7) for a fuel cell installed in the box (6), the pre-charge and discharge plate assembly (7) for the fuel cell comprising a circuit board (1), a plurality of relays (2), a plurality of resistors (3), a plurality of hardware terminals (4) and a plurality of low-voltage connectors (5), the plurality of relays (2), a plurality of resistors (3), a plurality of hardware terminals (4) and a plurality of low-voltage connectors (5) being welded on the circuit board (1) to form two pre-charge circuits (100) and one discharge circuit (200); The plurality of relays (2) include a relay J2 and a relay J1, the plurality of resistors (3) include a resistor R1, the two pre-charging circuits (100) include a first pre-charging circuit (101) and a second pre-charging circuit (102), the first pre-charging circuit (101) is formed by the relay J1 and the resistor R1 being connected in series, and the second pre-charging circuit (102) is formed by the relay J2 and the resistor R1 being connected in series; The box (6) is also provided with a DC-DC boost conversion unit (8) and a DC-DC main control board (10). The DC-DC boost conversion unit (8) is controlled by the DC-DC main control board (10). The output end of the DC-DC boost conversion unit (8) is connected in parallel with a capacitor C1 to output a voltage U1. The positive electrode of the capacitor C1 is also connected to the first output end through a relay J1 and a resistor R1 in sequence to output a voltage U2. The output end of the pre-charge discharge plate assembly (7) is connected to a relay J4 and a capacitor C2, the relay J4 and the capacitor C2 are connected in series, the second pre-charge circuit (102) is connected in parallel with the relay J4, the positive electrode of the capacitor C2 is connected to one end of the relay J2, the other end of the relay J2 is connected between the relay J1 and the resistor R1, and the positive electrode of the capacitor C2 is connected to the first output end via the relay J2 and the resistor R1; The plurality of relays (2) further include a relay J3, the plurality of resistors (3) further include a resistor R2, the discharge circuit (200) is formed by the relay J3 and the resistor R2 being connected in series, and the discharge circuit (200) is connected in parallel to both ends of the capacitor C1; An anti-reverse connection diode D1 is also welded on the circuit board (1), and a first pre-charging circuit (101) in the pre-charging circuit (100) is connected in parallel to both ends of the anti-reverse connection diode D1.

2. A DCDC converter according to claim 1, characterized in that: The internal circuits of the two pre-charging circuits (100) and the one discharging circuit (200) are electrically connected by printed circuits on the circuit board (1).

3. A DCDC converter according to claim 2, characterized in that: The positive and negative signals of the relay (2) are obtained through a low-voltage connector (5).

4. A DCDC converter according to claim 3, characterized in that: The relay J1, the relay J2 and the relay J3 are electrically connected to an independent low voltage connector (5) respectively.

5. A DCDC converter according to claim 4, characterized in that: The hardware terminal (4) is used for electrical connection with a high voltage circuit.

6. A DCDC converter according to claim 5, characterized in that: The low-voltage connector (5) is electrically connected to the positive and negative electrodes of the relay (2) via the printed circuit on the circuit board (1), and the hardware terminal (4) is electrically connected to the relay (2) and the resistor (3) respectively via the printed circuit on the circuit board (1).

7. A DCDC converter according to claim 1, characterized in that: The box (6) is also provided with a voltage detection circuit, which is used to input the voltage of the capacitor C1 and the capacitor C2 into the DC-DC main control board (10), and the DC-DC main control board (10) controls the on and off of the relay J1, the relay J2, the relay J3 and the relay J4 according to the detection result.

8. A control method for a DCDC converter, characterized in that: According to a DCDC converter as claimed in claim 7, the control method includes a pre-charge control method, and the pre-charge control method includes the following steps: Step 1: Power on, relay J0, relay J1 and relay J2 are energized, charging capacitor C1 and capacitor C2 respectively; Step 2: The DC-DC main control board (10) calculates the difference between the voltage U2 and the voltage U1 and the difference between the voltage U2 and the voltage U3, respectively, and compares the calculation results with the first preset voltage threshold, respectively, and controls the on and off of the relay J1, the relay J2 and the relay J4 according to the comparison results; the voltage across the capacitor C2 is U3; Step 3: When voltage U2-voltage U1<5V, voltage U2-voltage U3<5V, the DC-DC main control board (10) determines that the charging of capacitors C1 and C2 is complete, and the DC-DC main control board (10) first controls relay J1 to be disconnected and relay J4 to be turned on, and then controls relay J2 to be disconnected; otherwise, return to step 2.

9. The control method of a DCDC converter according to claim 8, characterized in that: The control method also includes a discharge control method, which includes the following steps: Step 4: Power off, relay J0 is disconnected, relay J3 is energized, relay J1 is energized, relay J4 remains energized, and relay J2 remains disconnected, so as to discharge the charges of capacitors C1 and C2, that is, the charge of capacitor C1 is discharged through relay J3 and resistor R2, and the charge of capacitor C2 is discharged through relay J4, resistor R1, relay J1, relay J3, and resistor R2; Step 5: The DC-DC main control board (10) detects the voltage U1 and the voltage U3 across the capacitor C1 and the capacitor C2 respectively, and compares the voltage U1 and the voltage U3 with the second preset voltage threshold, and controls the on and off of the relay J3, the relay J1 and the relay J4 according to the comparison result; Step 6: When the voltage U1 is less than 36V and the voltage U3 is less than 36V, the DC-DC main control board (10) determines that the charge discharge of the capacitors C1 and C2 is completed, and the DC-DC main control board (10) controls the relays J1, J3 and J4 to be disconnected; otherwise, the process returns to step 5.

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