A DC bus pre-charging and discharging control method and circuit

Abstract

The present invention relates to a DC bus pre-charge and discharge control method and circuit, the circuit includes a system input module for providing a DC voltage; a switching power supply module, the input end of which is connected to the system input module, and the first output end is connected to the DC bus pre-charge and discharge module; the DC bus pre-charge and discharge module includes a switch element, an isolation element and a pre-charge and discharge resistor, which are used to charge and discharge the DC bus; a DC bus module, connected to the DC bus pre-charge and discharge module, is used to store DC electric energy; the output end of the detection control module is connected to the DC bus pre-charge and discharge module. By sharing the pre-charge resistor and the discharge resistor, the circuit design is simplified; by turning on and off the switch element, the automatic switching of the pre-charge and discharge state is realized, without the need for additional control logic, and the complexity of the system is reduced; the isolation element is used to isolate the auxiliary source control signal from the DC bus, thereby improving the anti-interference ability and reliability of the system.

Description

Technical Field

[0001] The present invention relates to the technical field of direct current bus charging and discharging, and in particular to a direct current bus pre-charging and discharging control method and circuit. Background Art

[0002] The DC bus is an important link between the power supply and the load. When the existing DC bus system is started, the initial voltage of the bus capacitor is zero. Directly connecting the power supply will cause a large current shock, which may damage the components in the circuit or cause voltage fluctuations, affecting the stability and reliability of the system. In addition, when the system is shut down, if the electric energy stored in the DC bus is not released in time, it may cause safety hazards to maintenance personnel. Traditional solutions usually use independent pre-charge circuits and discharge circuits, which require additional components, increase the complexity and hardware cost of the system, and lack effective control methods, resulting in poor system response speed and low efficiency. Summary of the invention

[0003] In order to solve the above problems, the present invention provides a DC bus pre-charging control method, comprising the following steps: Step S101, the system input terminal is powered on, the switch power module works normally, provides power to the isolation element and the detection control module, and the isolation element is turned on; Step S102, the detection control module drives the control element to pre-charge the DC bus, and the energy storage element is charged through the pre-charging and discharging elements to form a pre-charging loop; Step S103, the detection control module detects the DC bus voltage Ψ, and within the specified pre-charge time t max Inside, determine whether the judgment conditions are met: , where φ is the precharge cut-off voltage, ; Step S104, if the discrimination condition is met, the detection control module adjusts the state of the control element, disconnects the pre-charging circuit, and the system works normally; if the discrimination condition is not met, the system sends a fault signal, and the detection control module disconnects all control elements.

[0004] Based on the above scheme, the isolation element is an isolation optocoupler. When the DC bus is pre-charged, the secondary collector and emitter of the isolation optocoupler are turned on, the detection control module controls the first contactor to disconnect, and the pre-charging relay and the second contactor to close.

[0005] On the basis of the above scheme, when the system works normally, the secondary collector and emitter of the isolation optocoupler are turned on, the detection control module controls the pre-charge relay to be disconnected, and the first contactor and the second contactor are closed.

[0006] The present invention also provides a DC bus discharge control method, comprising the following steps: Step S201, the system input end is powered off, the switch power supply module stops working, the isolation element is disconnected, and the control element is disconnected; Step S202, the residual voltage of the energy storage element is divided by a voltage divider and applied to the control port of the switch element. When the voltage reaches the turn-on threshold of the switch element, the switch element is turned on to form a discharge loop; In step S203, the energy storage element is rapidly discharged through the pre-charging and discharging elements. When the voltage is lower than the turn-on threshold of the switch element, the switch element is turned off and the discharge process ends.

[0007] On the basis of the above solution, the switch element is a MOS tube. When the system is in a discharge state, the MOS tube reaches a gate turn-on voltage, and the source and drain are turned on.

[0008] The present invention also provides a DC bus pre-charging and discharging circuit, the circuit comprising: System input module, used to provide DC voltage; A switching power supply module, wherein the input end thereof is connected to the system input module, and the first output end thereof is connected to the DC bus pre-charging and discharging module; A DC bus pre-charging and discharging module is used to charge and discharge the DC bus; A DC bus module, connected to the DC bus pre-charging and discharging module, for storing DC power; A detection control module, wherein a first input end is connected to the second output end of the switch power module, a second input end is connected to the DC bus module, and an output end is connected to the DC bus pre-charging and discharging module; The DC bus pre-charge and discharge module includes a switching element, an isolation element and a pre-charge and discharge resistor. The pre-charge and discharge state is achieved by turning on and off the switching element. The isolation element strongly isolates the control signal from the DC bus. The pre-charge and discharge resistor acts as a pre-charge resistor in the pre-charge state and as a discharge resistor in the discharge state.

[0009] On the basis of the above scheme, the isolation element is an isolation optocoupler, the switching element is a MOS tube, the anode of the primary input end of the isolation optocoupler is connected to the positive output end of the switching power supply module, the cathode is grounded, the collector of the secondary output end is connected to the gate port of the MOS tube, the cathode of the voltage regulator diode and the first port of the high-resistance voltage divider resistor, the emitter of the secondary output end is connected to the negative pole of the DC bus, and the isolation optocoupler forms electrical isolation between the low-voltage control signal and the strong current of the DC bus.

[0010] On the basis of the above scheme, the gate port of the MOS tube is controlled by the secondary collector of the isolation optocoupler, the source port is connected to the second port of the pre-charge relay and the first port of the pre-charge and discharge resistor, and the drain port is connected to the negative pole of the system bus; the second port of the high-resistance voltage divider resistor is connected to the second port of the pre-charge and discharge resistor, and the anode of the voltage regulator diode is connected to the negative pole of the system bus.

[0011] On the basis of the above solution, the DC bus module includes a DC bus capacitor, the positive electrode of the DC bus capacitor is connected to the positive electrode of the system bus, and the negative electrode is connected to the negative electrode of the system bus.

[0012] On the basis of the above scheme, the DC bus pre-charging and discharging module also includes a first contactor and a second contactor, the first port of the first contactor is connected to the positive pole of the system input module, and the second port is connected to the positive pole of the system bus; the second port of the second contactor is connected to the negative pole of the system bus, the first port is connected to the negative pole of the system input module, the first port of the pre-charging relay is connected to the positive pole of the system input module, and the output end of the detection control module is connected to the control end of the first contactor, the second contactor and the pre-charging relay.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: through pre-charging and discharging control, the safety and stability of the system are improved, and the operating efficiency is improved; by sharing the pre-charging resistor and the discharging resistor, the number of components is reduced and the circuit design is simplified; by turning on and off the switching elements, the pre-charging and discharging states are automatically switched, without the need for additional control logic, thereby reducing the complexity of the system; the auxiliary source control signal is electrically isolated from the DC bus by an isolation element to prevent control signal interference caused by power fluctuations, while avoiding potential electric shock hazards, thereby improving the system's anti-interference ability, reliability and safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A flow chart of the pre-charging control method provided in this application; Figure 2 A flow chart of the discharge control method provided in this application; Figure 3 The overall block diagram of the pre-charge and discharge circuit structure provided in this application; Figure 4 The circuit diagram provided for this application; Figure 5 This is a circuit equivalent schematic diagram when the circuit of this application is in a pre-charge state; Figure 6 This is the circuit equivalent schematic diagram when the circuit of this application is in a discharge state; DETAILED DESCRIPTION The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0015] The purpose of the present application is to provide a DC bus pre-charging and discharging control method and circuit, in which the pre-charging resistor and the discharging resistor are shared, and the DC bus pre-charging state and the discharging state are switched by turning on and off the MOS tube, so that the DC bus pre-charging circuit is combined with the DC bus discharging circuit to reduce hardware cost and volume.

[0016] The present invention will be further described below in conjunction with the accompanying drawings: like Figure 1 As shown, a DC bus pre-charging control method includes: The system is powered on, the input terminals DC+ and DC- are powered, the switch power module outputs normally, and the power supply is provided to the isolation element and the detection control module, and the isolation element is turned on. Preferably, the isolation element is an isolation optocoupler U1, the isolation optocoupler is turned on, the secondary collector and emitter are turned on, the detection control module controls the first contactor to be disconnected, and the pre-charge relay and the second contactor are closed; The detection control module drives the control element to form a DC bus pre-charging circuit. Specifically, the control element includes a first contactor K1, a pre-charging relay K2 and a second contactor K3. K1 is disconnected, and K2 and K3 are closed to pre-charge the DC bus. During the pre-charging process, the detection control module monitors the DC bus voltage Ψ. If Ψ meets the judgment condition, the pre-charging process ends. The judgment condition is: , , where the maximum precharge duration is t max , φ is the preset threshold of the pre-charge voltage, and t is the pre-charge time. If the judgment conditions are not met, the pre-charge fails, a fault alarm is given, and the control element is disconnected.

[0017] After the pre-charging process is completed, the pre-charging relay K2 is disconnected, and the first contactor K1 is closed. The system works normally, which improves the efficiency of powering the load. Using the pre-charging resistor R1 for pre-charging can prevent the impact caused by large current and effectively reduce the risk of damaging the device.

[0018] like Figure 2 As shown, a DC bus discharge control method includes: The system input end is powered off, the switch power supply module stops working, the isolation element is disconnected, and the detection control module drive control element is disconnected; The energy storage element is connected in parallel to the DC bus, and its storage voltage is equal to the DC bus voltage. The voltage of the energy storage element is divided by the voltage divider element and applied to the control port of the switch element. When the voltage reaches the turn-on threshold of the switch element, the switch element is turned on to form a discharge circuit. The energy storage element is rapidly discharged through the pre-charging and discharging elements. When the voltage is lower than the turn-on threshold of the switch element, the switch element is turned off and the discharge process ends.

[0019] Preferably, the voltage divider element is a high-resistance voltage divider resistor R2 and a voltage regulator diode D1. The storage voltage is applied to the gate port of the MOS tube Q1 after voltage division by R2 and D1. The minimum gate opening current of Q1 is I GSS , the voltage divider of the Zener diode D1 is V D1 It needs to be greater than the turn-on voltage V of Q1 GS .

[0020] According to this embodiment, the energy storage element is an energy storage capacitor C1, and the maximum discharge time of its storage voltage Ψ is T max ,when , satisfying the conditions , where T is the discharge time. At this time, the MOS tube Q1 is in the on state, and the stored voltage is discharged quickly through R1; when the voltage divider V D1 Less than Q1’s turn-on voltage V GS When , Q1 is turned off and the discharge process ends.

[0021] The DC bus pre-charging control method and discharge control method provided by the present invention control the on and off of the switch element through the isolation element, so as to realize automatic switching of the charging and discharging states during the system startup and shutdown process. When the system is started, the control detection module drives the opening and closing of the switch element, and the bus is pre-charged through the pre-charging and discharging elements to prevent large current shocks; when the system is powered off, the residual energy on the bus is quickly released through the pre-charging and discharging elements, so as to ensure the safety, reliability and efficiency of the system during operation.

[0022] According to another embodiment provided by the present application, Figure 3As shown, it includes a system input module 1, a switching power module 2, a DC bus pre-charge and discharge module 3, a DC bus module 4 and a detection control module 5. The system input module is responsible for providing the DC voltage; the input end of the switching power module is connected to the system input module, and the switching power module provides the conversion power through the system input module, the first output end of the switching power module is connected to the DC bus pre-charge and discharge module, and the second output end is connected to the detection control module; the DC bus pre-charge and discharge module is connected to the DC bus module, pre-charges the DC bus when the system starts, and quickly releases the residual energy on the DC bus when the system stops; the DC bus module includes a DC bus capacitor C1, one end of which is connected to the system bus BUS+ and the other end is connected to the system bus BUS-, which is used to store DC power; the first input end of the detection control module is connected to the second output end of the switching power module, the second input end is connected to the DC bus module, and the output end is connected to the DC bus pre-charge and discharge module, which is used to monitor the state of the system and control the operation of the DC bus pre-charge and discharge module.

[0023] The DC bus pre-charging and discharging module 3 includes an isolation element and a switch element. The circuit realizes the pre-charging and discharging states by turning on and off the switch element. The isolation element strongly isolates the control signal from the DC bus.

[0024] Preferably, the isolation element is an isolation optocoupler, and the switch element is a MOS tube (Metal-Oxide-Semiconductor Field-Effect Transistor, metal oxide semiconductor field effect transistor), such as Figure 4 As shown, the DC bus pre-charge and discharge module 3 includes an isolation optocoupler U1, a MOS tube Q1, a voltage regulator diode D1, a pre-charge and discharge resistor R1, and a high-resistance voltage divider resistor R2; the DC bus pre-charge and discharge module also includes a control element, specifically, the control element includes a first contactor K1, a pre-charge relay K2 and a second contactor K3.

[0025] Furthermore, a first port of the pre-charge and discharge resistor R1 is connected to the pre-charge relay K2 and the source port of the MOS tube Q1, and a second port is connected to the second port of the first contactor K1, the second port of the high-resistance voltage divider resistor R2 and the system bus BUS+; when the circuit is in a pre-charge state, R1 acts as a pre-charge resistor, and when the circuit is in a discharge state, R1 acts as a discharge resistor, thereby reducing the number of components.

[0026] The anode of the primary input end of the isolation optocoupler U1 is connected to the positive output end of the switching power supply module 2, the cathode is grounded, the collector of the secondary output end is connected to the gate port of the MOS tube Q1, the cathode of the voltage-stabilizing diode D1 and the first port of the high-resistance voltage-dividing resistor R2, and the emitter of the secondary output end is connected to the system bus BUS- and the second port of the second contactor K3. The isolation optocoupler U1 strongly isolates the auxiliary source control signal from the DC bus to prevent control signal interference caused by power fluctuations.

[0027] The gate port of the MOS tube Q1 is controlled by the secondary collector of the isolation optocoupler U1, the source port is connected to the first port of the pre-charge and discharge resistor R1 through the pre-charge relay K2, and the drain port is connected to the second port of the second contactor K3. The MOS tube Q1 switches between the pre-charge and discharge states by turning on and off, reducing redundant components and simplifying circuit logic.

[0028] The first port of the first contactor K1 is connected to the DC+ of the system input module 1, the second port is connected to the second port of the pre-charge and discharge resistor R1, and the control end is connected to the output end of the detection control module 5; the first port of the pre-charge relay K2 is connected to the DC+ of the system input module 1, the second port is connected to the source port of the MOS tube Q1, and the control end is connected to the output end of the detection control module 5; the first port of the second contactor K3 is connected to the DC- of the system input module 1, the second port is connected to the drain port of the MOS tube Q1, and the control end is connected to the output end of the detection control module 5.

[0029] The first port of the high-resistance voltage-dividing resistor R2 is connected to the secondary collector of the isolation optocoupler U1, and the second port is connected to the second port of the pre-charge and discharge resistor R1. The high-resistance voltage-dividing resistor R2 is used for voltage division to ensure that the gate voltage of the MOS tube is within a safe range; the cathode of the voltage-stabilizing diode D1 is connected to the secondary collector of the isolation optocoupler U1, and the anode is connected to the system bus BUS-. The voltage-stabilizing diode is used to protect the gate of the MOS tube to prevent overvoltage damage.

[0030] When the circuit is powered on, that is, the system input module is powered, the switching power supply module starts to work and provides auxiliary power output to the system. At this time, the DC bus is in the pre-charge state, such as Figure 5 As shown, in this state, the secondary collector and emitter of the isolation optocoupler U1 are turned on, and the gate voltage of the MOS tube Q1 is pulled down to make it non-conductive; the detection control module controls the first contactor K1 to be disconnected, and the pre-charge relay K2 and the second contactor K3 to be closed, and the pre-charge and discharge resistor R1 is used as a pre-charge resistor, and the bus is pre-charged through the pre-charge resistor, thereby avoiding the risk of component damage caused by large current impact.

[0031] When the DC bus capacitor C1 is pre-charged, the system enters the normal working state. At this time, the switching power supply module continues to work normally, and the secondary collector and emitter of the isolation optocoupler U1 are still turned on, keeping the gate voltage of the MOS tube Q1 pulled down to ensure that the MOS tube Q1 is not turned on. At the same time, the detection control module will control the first contactor K1 and the second contactor K3 to close, and the pre-charge relay K2 is disconnected, so that the system can operate stably.

[0032] If the system input module loses power, the DC bus module will enter the discharge state, such as Figure 6 As shown. The switching power supply module can no longer work, and the detection control module will also be powered off, causing the first contactor K1, the pre-charge relay K2, and the second contactor K3 to be all disconnected. At this time, the secondary collector and emitter of the isolation optocoupler U1 are no longer turned on. The voltage stored in the DC bus capacitor C1 can reach or exceed the gate turn-on voltage of the MOS tube Q1 after being divided by the high-resistance voltage divider resistor R2 and the voltage regulator diode D1, thereby turning on the source and drain of the MOS tube Q1. Therefore, the voltage on the DC bus capacitor C1 is quickly released through the pre-charge and discharge resistor R1. When the bus voltage drops below the safe level, that is, lower than the gate turn-on voltage of the MOS tube Q1, the MOS tube Q1 will automatically shut down to complete the discharge process.

[0033] According to the present application, an isolation optocoupler is used to isolate the auxiliary source control signal from the DC bus for strong electrical isolation, thereby improving system safety. In addition, the on and off of the MOS tube can be controlled by the isolation optocoupler to achieve automatic switching of the pre-charge and discharge states during system startup and shutdown. When the system starts, the pre-charge relay and contactor are controlled to open and close, and the bus is pre-charged through the pre-charge and discharge resistors to prevent large current shocks. When the system is powered off, the residual energy on the bus is quickly released through the pre-charge and discharge resistors to ensure safe, reliable and efficient operation of the system.

[0034] According to another embodiment of the present application, the switching element can select IGBT, and a dedicated IGBT driver chip is used to provide the driving voltage required by the IGBT. Since the IGBT is more sensitive to overvoltage and overcurrent, a protection circuit is added. Specifically, a current limiting resistor is added between the gate and source of the IGBT to limit the gate current; an absorption circuit is added between the collector and emitter of the IGBT to protect the IGBT from voltage spikes. The absorption circuit may include a series resistor and capacitor; a Zener diode is added between the gate and source of the IGBT to prevent the gate voltage from exceeding the safety range and avoid the IGBT from being broken down; a fast fuse is connected in series with the emitter of the IGBT to protect the IGBT from overcurrent damage. In addition, in order to adapt to higher driving voltage requirements, a dedicated IGBT driver chip can be used, which can provide stable driving voltage and current to ensure the reliable operation of the IGBT.

[0035] In one embodiment, a JFET (junction field effect transistor) is used to replace the MOS tube, and the secondary output terminal of the isolation optocoupler U1 is directly connected to the gate of the JFET, while ensuring that there is a pull-down resistor to stabilize the gate potential; a Zener diode is added across the gate and the source to prevent the gate voltage from exceeding a safe range and avoid damage to the JFET.

[0036] According to another embodiment, a transformer with a rated voltage and current matching the original isolation optocoupler is selected as an isolation element. The primary winding is connected to the output end of the detection control module to ensure that the signal can be transmitted through the transformer. The secondary winding is connected to the drive circuit of the switching element. A voltage regulator is added to provide a stable drive voltage. An overvoltage protection circuit is added at the output end of the secondary winding to ensure that the drive voltage is within a safe range.

[0037] The basic principles and main features of the present invention are shown and described above. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments. Therefore, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is limited by the appended claims rather than the above description. Therefore, it is intended to include all changes within the meaning and scope of the equivalent elements of the claims in the present invention.

[0038] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A DC bus pre-charging control method, characterized in that: The following steps are involved: Step S101, the system input terminal is powered on, the switch power module works normally, provides power to the isolation element and the detection control module, and the isolation element is turned on; Step S102, the detection control module drives the control element to pre-charge the DC bus, and the energy storage element is charged through the pre-charging and discharging elements to form a pre-charging loop; Step S103, the detection control module detects the DC bus voltage Ψ, and within the specified pre-charge time t max Inside, determine whether the judgment conditions are met: , where φ is the precharge cut-off voltage, ; Step S104, if the discrimination condition is met, the detection control module adjusts the state of the control element, disconnects the pre-charging circuit, and the system works normally; if the discrimination condition is not met, the system sends a fault signal, and the detection control module disconnects all control elements.

2. A DC bus pre-charging control method according to claim 1, characterized in that: The isolation element is an isolation optocoupler. When the DC bus is pre-charged, the secondary collector and emitter of the isolation optocoupler are turned on, the detection control module controls the first contactor to be disconnected, and the pre-charging relay and the second contactor to be closed.

3. A DC bus pre-charging control method according to claim 2, characterized in that: When the system works normally, the secondary collector and emitter of the isolation optocoupler are turned on, the detection control module controls the pre-charge relay to be disconnected, and the first contactor and the second contactor are closed.

4. A DC bus discharge control method, characterized in that: The following steps are involved: Step S201, the system input end is powered off, the switch power supply module stops working, the isolation element is disconnected, and the control element is disconnected; Step S202, the residual voltage of the energy storage element is divided by a voltage divider and applied to the control port of the switch element. When the voltage reaches the turn-on threshold of the switch element, the switch element is turned on to form a discharge loop; In step S203, the energy storage element is rapidly discharged through the pre-charging and discharging elements. When the voltage is lower than the turn-on threshold of the switch element, the switch element is turned off and the discharge process ends.

5. A DC bus discharge control method according to claim 4, characterized in that: The switch element is a MOS tube. When the system is in a discharge state, the gate turn-on voltage of the MOS tube reaches a value, and the source and the drain are turned on.

6. A DC bus pre-charging and discharging circuit, characterized in that: The circuit comprises A system input module (1) for providing a DC voltage; A switching power supply module (2), the input end of which is connected to the system input module (1), and the first output end of which is connected to the DC bus pre-charging and discharging module (3); A DC bus pre-charging and discharging module (3), used for charging and discharging the DC bus; A DC bus module (4), connected to the DC bus pre-charging and discharging module (3), and used for storing DC electric energy; A detection control module (5), wherein a first input end is connected to the second output end of the switch power supply module (2), a second input end is connected to the DC bus module (4), and an output end is connected to the DC bus pre-charging and discharging module (3); The DC bus pre-charging and discharging module (3) comprises a switch element, an isolation element and a pre-charging and discharging resistor. The pre-charging and discharging state is achieved by turning on and off the switch element. The isolation element strongly isolates the control signal from the DC bus. The pre-charging and discharging resistor acts as a pre-charging resistor in the pre-charging state and as a discharging resistor in the discharging state.

7. A DC bus pre-charging and discharging circuit according to claim 6, characterized in that: The isolation element is an isolation optocoupler, the switch element is a MOS tube, the anode of the primary input end of the isolation optocoupler is connected to the positive output end of the switching power supply module (2), the cathode is grounded, the collector of the secondary output end is connected to the gate port of the MOS tube, the cathode of the voltage-stabilizing diode and the first port of the high-resistance voltage-dividing resistor, the emitter of the secondary output end is connected to the negative pole of the DC bus, and the isolation optocoupler forms electrical isolation between the low-voltage control signal and the strong current of the DC bus.

8. A DC bus pre-charging and discharging circuit according to claim 6, characterized in that: The gate port of the MOS tube is controlled by the secondary collector of the isolation optocoupler, the source port is connected to the second port of the pre-charge relay and the first port of the pre-charge and discharge resistor, and the drain port is connected to the negative pole of the system bus; the second port of the high-resistance voltage divider resistor is connected to the second port of the pre-charge and discharge resistor, and the anode of the voltage regulator diode is connected to the negative pole of the system bus.

9. A DC bus pre-charging and discharging circuit according to claim 6, characterized in that: The DC bus module (4) comprises a DC bus capacitor, wherein the positive electrode of the DC bus capacitor is connected to the positive electrode of the system bus, and the negative electrode of the DC bus capacitor is connected to the negative electrode of the system bus.

10. A DC bus pre-charging and discharging circuit according to claim 6, characterized in that: The DC bus pre-charging and discharging module (3) further comprises a first contactor and a second contactor, wherein the first port of the first contactor is connected to the positive pole of the system input module, and the second port is connected to the positive pole of the system bus; the second port of the second contactor is connected to the negative pole of the system bus, and the first port is connected to the negative pole of the system input module; the first port of the pre-charging relay is connected to the positive pole of the system input module; and the output end of the detection control module (5) is connected to the control end of the first contactor, the second contactor and the pre-charging relay.

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