A charging and discharging switching circuit for electric vehicles

Abstract

This application relates to the field of circuit design, and in particular to a charging and discharging switching circuit for electric vehicles, including a relay, a drive unit, and a switch; the relay is connected to the power supply voltage, the drive unit, the switch, and signal lines; the drive unit includes a transistor; it is connected to a power strip or adapter via signal lines; the relay includes a first state and a second state controlled by the switch, in which the first common terminal is connected to the first normally open contact, and the second common terminal is connected to the second normally open contact. By adopting the above technical solution, a single double-pole double-throw relay replaces the traditional two independent charging and discharging circuits, allowing charging and discharging to be combined into one gun, simplifying the hardware structure; at the same time, the drive unit, through resistor current limiting and transistor switch control, can accurately drive the relay to switch states, providing a reliable hardware foundation for the conversion of charging and discharging energy flow, and solving the problems of unidirectional charging and discharging, hardware redundancy, and high cost in existing technologies.

Description

Technical Field

[0001] This application relates to the field of circuit design, and in particular to a charging and discharging switching circuit for electric vehicles. Background Technology

[0002] Currently, electric vehicle charging and discharging technologies mainly focus on unidirectional charging or discharging modes, lacking an efficient bidirectional energy flow management system. Existing energy management systems often rely on complex hardware structures and control algorithms, resulting in high system costs, low efficiency, and susceptibility to energy loss and equipment wear during frequent switching of charging and discharging modes. In recent years, with the development of smart grids and distributed energy resources, the demand for electric vehicles as mobile energy storage units has gradually increased, necessitating an efficient and reliable charging and discharging switching system to meet this need. Summary of the Invention

[0003] In order to solve the problem that existing electric vehicle charging and discharging switching systems are not efficient and reliable enough, this application provides an electric vehicle charging and discharging switching circuit.

[0004] This application provides a charging and discharging switching circuit for an electric vehicle, including: a relay UK1, a drive unit, and a switch S1; The first fixed terminal of relay UK1 is connected to the first power supply voltage, the second fixed terminal of relay UK1 is connected to the drive unit, the first common terminal of relay UK1 is connected to the first terminal of switch S1, the second common terminal of relay UK1 is connected to the second terminal of signal line A, the first normally closed contact and the second normally closed contact of relay UK1 are connected to the first terminal of resistor R4B, the first normally open contact of relay UK1 is connected to the first terminal of resistor R4D, and the second normally open contact of relay UK1 is connected to the second terminal of resistor RG1. The driving unit includes a resistor RF1 and a transistor QK3. The first end of the resistor RF1 is connected to the driving signal, the base of the transistor QK3 is connected to the second end of the resistor RF1, and the collector of the transistor QK3 is connected to the second fixed end. The relay UK1 includes a first state and a second state controlled by the switch S1. In the first state, the first common terminal is connected to the first normally open contact, and the second common terminal is connected to the second normally open contact. In the second state, the first common terminal is connected to the first normally closed contact, and the second common terminal is connected to the second normally closed contact.

[0005] By adopting the above technical solution, a single double-pole double-throw relay can replace the traditional two independent charging and discharging circuits, simplifying the hardware structure. At the same time, the drive unit can accurately drive the relay to switch states through resistor current limiting and transistor switching control, providing a reliable hardware foundation for the conversion of charging and discharging energy flow, and solving the problems of unidirectional charging and discharging, hardware redundancy, and high cost in the existing technology.

[0006] In one specific implementation, the second terminal of the resistor R4D is grounded, the switch S1 is connected in parallel with the resistor R4A, the first terminal of the switch S1 is connected to the first terminal of the resistor R4A, and the second terminal of the switch S1 is connected to the second terminal of the resistor R4A.

[0007] By adopting the above technical solution, in charging mode, the connection of resistor R4A to ground can be switched by opening or closing switch S1. No additional sensors are required; the resistance of the CC point can be adjusted simply by switching the switch on and off, providing a precise resistance signal for the vehicle to identify the charging connection status and simplifying the status detection logic.

[0008] In one specific implementation, the second end of resistor R4B is connected to the first end of resistor R4C, the second end of resistor R4C is connected to the second end of switch S1, and the common connection point of switch S1, resistor R4A, and resistor R4C is connected to the signal point CC of the charging and discharging gun.

[0009] By adopting the above technical solution, a dedicated resistor network is formed in the discharge mode, which solves the problem of inaccurate identification of discharge status in bidirectional energy management and ensures that the discharge signal matches the protocol of the vehicle or power grid.

[0010] In one specific implementation, the trigger state of switch S1 changes the resistance value of the signal point CC to ground circuit, and switch S1 is a normally closed switch S1.

[0011] By adopting the above technical solution, it is clear that switch S1 is a normally closed switch and the trigger state changes the resistance of point CC. On the one hand, the normally closed characteristic makes switch S1 closed by default, ensuring that point CC is in the connected state when the system is not operated, reducing the risk of loose connection caused by mechanical failure of the switch and improving safety. On the other hand, it is only necessary to disconnect switch S1 to switch to the semi-connected state, without the need for additional electrical control components, simplifying the switching operation of charging and discharging connection state and reducing control complexity.

[0012] In one specific implementation, the electric vehicle charging / discharging switching circuit further includes an isolation unit, which comprises an optocoupler U2A, capacitors CG1 and CG2, resistors RG3 and RG4. The positive terminal of the input side of the optocoupler U2A is connected to the second terminal of resistor RG1 and the first terminal of capacitor CG1. The negative terminal of the input side of the optocoupler U2A shares a common ground with the second terminal of capacitor CG2. The collector of the output side of the optocoupler U2A is connected to the first terminals of resistors RG3 and RG4. The emitter of the output side of the optocoupler U2A shares a common ground with the second terminal of capacitor CG2.

[0013] By adopting the above technical solution, electrical isolation between the high-voltage charging and discharging circuit and the low-voltage MCU control terminal is achieved, preventing high-voltage interference from the mains power or vehicle end from being transmitted to the MCU, preventing chip damage, solving the problem of status recognition errors caused by high and low voltage signal interference, and improving signal transmission reliability.

[0014] In one specific implementation, the second end of the resistor RG4 and the first end of the capacitor CG2 are connected to the signal point GL on the output side of the optocoupler U2A, and the signal point GL is used to connect to the MCU.

[0015] By adopting the above technical solution, the load capacity can be intelligently determined based on the grounding status of the adapter, thus solving the overcurrent burnout accident that may be caused by mixing plugs and realizing load adaptive protection.

[0016] In one specific implementation, the electric vehicle charging and discharging switching circuit further includes a cable tray signal line B and a converter signal line C. The cable tray signal line B includes a resistor R4E, with its first end grounded and its second end connected to the first end of the signal line A. The first end of the converter signal line C is grounded, and its second end is connected to the first end of the signal line A.

[0017] By adopting the above technical solution, the device type can be passively identified by the difference in grounding resistance of external devices, eliminating the need for dedicated communication chips.

[0018] In one specific implementation, the driving unit further includes a diode DK3, the first end of which is connected to the collector of the transistor QK3 and the second fixed end, and the second end of which is connected to the first power supply voltage and the first fixed end.

[0019] By adopting the above technical solution, the reverse electromotive force when the relay coil is de-energized is absorbed, preventing the transistor QK3 from breaking down and improving the lifespan of the drive circuit.

[0020] In one specific implementation, the first terminal of resistor RG1 is connected to the second power supply voltage, and the first terminal of resistor RG3 is connected to the second power supply voltage.

[0021] By adopting the above technical solution, an independent voltage domain is provided for the input and output sides of the optocoupler, solving the problem of common ground noise interference with GL signals and improving the accuracy of plug type identification.

[0022] In one specific implementation, the switch S1 is located inside the charging and discharging gun; In the first state, and with switch S1 open, it corresponds to a charging half-connection state; in the first state, and with switch S1 closed, it corresponds to a charging connection state. In the second state, and with switch S1 open, it corresponds to a discharge half-connection state; in the second state, and with switch S1 closed, it corresponds to a discharge connection state.

[0023] By adopting the above technical solution, integrating switch S1 into the charging and discharging gun, and designing four connection states corresponding to the on / off state of relay and switch S1, the charging and discharging operation is concentrated in the integrated gun, improving user convenience and avoiding misidentification of state and protocol conflicts in bidirectional energy management.

[0024] In summary, this application includes at least one of the following beneficial effects: 1. This application achieves hardware reuse for both charging and discharging modes by switching the energy flow direction with a single relay, thus solving the problems of hardware redundancy, high cost, and large size caused by the need for independent charging and discharging circuits in traditional systems.

[0025] 2. This application solves the problems of high control complexity and response delay caused by the need for additional sensors in traditional solutions by dynamically changing the resistance value of the signal point detection loop through the on / off switching of a switch, and triggering the switching between half-connected and connected states through the switch operation.

[0026] 3. This application establishes a charging and discharging mode differentiated resistor network, enabling the same signal point to output resistance values ​​that conform to national standards in different modes, thereby solving the risks of misidentification of status and communication protocol conflicts in bidirectional energy management. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of an electric vehicle charging and discharging switching circuit according to an embodiment of this application; Figure 2 This is another structural schematic diagram of an electric vehicle charging and discharging switching circuit in the embodiments of this application. Detailed Implementation

[0028] The following is in conjunction with the appendix Figure 1 and attached Figure 2This application will be described in further detail.

[0029] This application discloses an electric vehicle charging and discharging switching circuit, such as... Figure 1 and Figure 2 As shown, the circuit includes a relay UK1, a drive unit, and a switch S1; The first fixed terminal of relay UK1 is connected to the first power supply voltage, the second fixed terminal of relay UK1 is connected to the drive unit, the first common terminal of relay UK1 is connected to the first terminal of switch S1, the second common terminal of relay UK1 is connected to the second terminal of signal line A, the first normally closed contact and the second normally closed contact of relay UK1 are connected to the first terminal of resistor R4B, the first normally open contact of relay UK1 is connected to the first terminal of resistor R4D, and the second normally open contact of relay UK1 is connected to the second terminal of resistor RG1. The driving unit includes a resistor RF1 and a transistor QK3. The first end of the resistor RF1 is connected to the driving signal K1, the base of the transistor QK3 is connected to the second end of the resistor RF1, and the collector of the transistor QK3 is connected to the second fixed end. The relay UK1 includes a first state and a second state controlled by switch S1. In the first state, the first common terminal is connected to the first normally open contact, and the second common terminal is connected to the second normally open contact. In the second state, the first common terminal is connected to the first normally closed contact, and the second common terminal is connected to the second normally closed contact.

[0030] The first state corresponds to the charging mode of the circuit, and the second state corresponds to the discharging mode. Specifically, when the drive signal K1 is high, the coil of relay UK1 is energized, connecting the first common terminal to the first normally open contact and the second common terminal to the second normally open contact. Relay UK1 is in the first state, and the circuit enters the charging mode. When the drive signal K1 is low, the coil of relay UK1 is not energized, connecting the first common terminal to the first normally closed contact and the second common terminal to the second normally closed contact. Relay UK1 is in the second state, and the circuit enters the discharging mode.

[0031] refer to Figure 2 The first fixed terminal of relay UK1 can be connected to pin 1, the first normally closed contact can be connected to pin 2, the first common terminal can be connected to pin 3, the first normally open contact can be connected to pin 4, the second normally open contact can be connected to pin 5, the second common terminal can be connected to pin 6, the second normally closed contact can be connected to pin 7, and the second common terminal can be connected to pin 8.

[0032] Specifically, relay UK1 can be a double-pole double-throw relay; resistor R4B can have a resistance of 3.3k ohms; resistor R4D can have a resistance of 680 ohms; resistor RG1 can have a resistance of 1k ohms; resistor RF1 can have a resistance of 2k ohms; transistor QK3 can be an S9013; when the circuit is in charging mode, it can draw power from the mains via a three-prong plug, with the first supply voltage being VCC12V, and the charging gun charges the electric vehicle; when the circuit is in discharging mode, it draws power from the vehicle via the charging gun, and the extension cord discharges to the outside, powering the device.

[0033] Based on the above embodiment, as another optional embodiment, the second end of resistor R4D is grounded, switch S1 is connected in parallel with resistor R4A, the first end of switch S1 is connected to the first end of resistor R4A, and the second end of switch S1 is connected to the second end of resistor R4A.

[0034] Specifically, the resistance of resistor R4A can be 2.7k ohms. In charging mode, resistor R4A is connected in parallel with switch S1, and the series resistor R4D is grounded. When the charging gun is plugged into the vehicle, the user presses switch S1, resistor R4A is short-circuited, the resistance of signal point CC to ground is 680 ohms, the vehicle recognizes it as fully connected and starts charging; when the user releases switch S1, resistor R4A is connected to the circuit, the resistance of signal point CC is 2.7k ohms + 680 ohms = 3.38k ohms, and the vehicle enters a semi-connected standby state.

[0035] In some embodiments, resistor R4A can be an adjustable resistor, such as a 3296 type, to adapt to future revisions of national standards.

[0036] Based on the above embodiment, as another optional embodiment, the second end of resistor R4B is connected to the first end of resistor R4C, the second end of resistor R4C is connected to the second end of switch S1, and the common connection point of switch S1, resistor R4A, and resistor R4C is connected to the signal point CC of the charging and discharging gun.

[0037] Specifically, the resistance of resistor R4C can be 75 ohms. The charging gun signal line has parasitic inductance, which may cause oscillation when switch S1 is switched. When resistor R4C is 75 ohms, the critical damping coefficient is 1, which can completely suppress the oscillation.

[0038] Based on the above embodiments, as another optional embodiment, the trigger state of switch S1 changes the resistance value of the signal point CC to ground circuit, and switch S1 is a normally closed switch.

[0039] Specifically, the default closing characteristic of the normally closed switch ensures that the signal point CC always maintains a fully connected resistance value (680Ω for charging / 2kΩ for discharging) in scenarios such as power failure, mechanical failure, and software crash, ensuring that the vehicle BMS can safely cut off energy transmission at any time and solve the safety hazards of power failure.

[0040] Based on the above embodiments, as another optional embodiment, the circuit may further include an isolation unit, which includes an optocoupler U2A, capacitors CG1 and CG2, resistors RG3 and RG4; the positive terminal of the input side of the optocoupler U2A is connected to the second terminal of resistor RG1 and the first terminal of capacitor CG1, the negative terminal of the input side of the optocoupler U2A is grounded with the second terminal of capacitor CG2, the collector of the output side of the optocoupler U2A is connected to the first terminal of resistor RG3 and the first terminal of resistor RG4, and the emitter of the output side of the optocoupler U2A is grounded with the second terminal of capacitor CG2.

[0041] Specifically, the optocoupler U2A can be an EL817; capacitors CG1 and CG2 can be 104 with a capacitance of 0.1 microfarads; resistor RG3 can have a resistance of 1k ohms; and resistor RG4 can have a resistance of 10k ohms. Capacitor CG1 filters high-frequency interference from signal line A; resistor RG1 current-limiting protects the LED of optocoupler U2A, limiting the input current to less than or equal to the safe current of optocoupler U2A; capacitor CG2 suppresses ringing of the GL signal and absorbs pulse width glitches; and resistor RG4 ensures that the signal point GL is at a high level of 3.3V when optocoupler U2A is off.

[0042] Based on the above embodiment, as another optional embodiment, the second end of resistor RG4 and the first end of capacitor CG2 are connected to the signal point GL on the output side of optocoupler U2A, and the signal point GL is used to connect to MCU.

[0043] Specifically, on the high-voltage side, the second normally open contact of relay UK1, resistor RG1, and capacitor CG1 are connected together at signal point GL-IN, forming a three-in-one signal preprocessing node. The impedance of signal point GL-IN to ground is capacitive, which can effectively attenuate relay switching noise. Resistor RG1 limits the input current of optocoupler U2A to ≤1.2mA (lower than the minimum trigger current of EL817 2mA), avoiding weak conduction. On the low-voltage side, resistor RG4 and capacitor CG2 are connected together at signal point GL, forming the MCU interface.

[0044] Based on the above embodiments, as another optional embodiment, the circuit may further include a cable tray signal line B and a converter signal line C. The cable tray signal line B includes a resistor R4E, the first end of which is grounded, and the second end of which is used to connect to the first end of the signal line A. The first end of the converter signal line C is grounded, and the second end of the converter signal line C is used to connect to the first end of the signal line A.

[0045] Specifically, the resistance of resistor R4E can be 2k ohms; the converter signal line C can be a 10A to 16A converter.

[0046] Based on the above embodiments, as another optional embodiment, the driving unit may further include a diode DK3, with the first end of the diode DK3 connected to the collector and the second fixed end of the transistor QK3, and the second end of the diode DK3 connected to the first power supply voltage and the first fixed end.

[0047] Specifically, diode DK3 can be an SM4007PL(A7). Since the coil of relay UK1 is an inductive load, when transistor QK3 changes from conducting to cutoff (e.g., during discharge mode switching), the coil will generate a back electromotive force (EMF), with voltage spikes reaching over -100V. Because the collector-emitter breakdown voltage of transistor QK3 is typically less than 60V, this back EMF could potentially damage transistor QK3 and interfere with the MCU control signal. Adding a freewheeling diode DK3 between the collector of transistor QK3 and the first supply voltage VCC can improve the reliability of the drive unit. When the drive signal K1 transitions from high to low, the back EMF generated by the coil of relay UK1 forms a discharge circuit through diode DK3, clamping the collector voltage of transistor QK3 at -0.7V and preventing transistor QK3 from being damaged.

[0048] Based on the above embodiments, as another optional embodiment, the first end of resistor RG1 is connected to the second power supply voltage, and the first end of resistor RG3 is connected to the second power supply voltage.

[0049] Specifically, the second supply voltage can be VCC3.3V, used to match the MCU. To eliminate power supply ground interference, the input-side current-limiting resistor RG1 and the output-side pull-up resistor RG3 of the optocoupler U2A can be independently connected to the second supply voltage VCC3.3V. The input-side VCC3.3V of the optocoupler U2A drives the internal LED of the optocoupler U2A through resistor RG1, preventing mains noise from coupling through the power supply; the output-side VCC3.3V of the optocoupler U2A pulls up the signal point GL through resistor RG3, ensuring that the high level accurately matches the MCU's 3.3V logic level.

[0050] Based on the above embodiments, as another optional embodiment, the switch S1 is located inside the charging and discharging gun. In the first state, and with switch S1 open, it corresponds to a charging half-connection state; in the first state, and with switch S1 closed, it corresponds to a charging connection state. In the second state, with switch S1 open, it corresponds to a discharge half-connection state; in the second state, with switch S1 closed, it corresponds to a discharge connection state.

[0051] Specifically, when the circuit is in charging mode and switch S1 is open, the signal point CC of the charging and discharging gun is connected to ground by resistors R4A and R4D in series, and the resistance of the signal point CC to ground is 3.38k ohms. At this time, the circuit is in a charging half-connection state.

[0052] When the circuit is in charging mode and switch S1 is closed, the signal point CC of the charging / discharging gun has a ground circuit resistance of resistor R4D, with a resistance of 680 ohms. At this time, the circuit is in a charging connection state. When signal line A is connected to signal line C of the 10A to 16A converter, signal line C is grounded (zero level), signal point GL-IN is low, optocoupler U2A is not working, and signal GL is high (3.3V). When signal line A is not connected to signal line C of the 10A to 16A converter, signal point GL-IN is high, optocoupler U2A is working, and signal point GL is low. The MCU identifies whether the three-prong plug is in a 10A or 16A state based on the level of signal point GL. Specifically, the resistance of signal point CC to ground is 3.38K ohms in the half-connected charging state and 680 ohms in the connected charging state, conforming to GB / T 18487.1 requirements.

[0053] When the circuit is in discharge mode and switch S1 is open, signal line A is connected to signal line B of the extension cord. The signal point CC of the charging and discharging gun is connected to ground by a parallel connection of resistor R4B, resistor R4C and resistor R4A, plus the resistor R4E of signal line B of the extension cord. At this time, the circuit is in a half-connected state of discharge, and the resistance of the signal point CC to ground is 3.5k ohms.

[0054] When the circuit is in discharge mode and switch S1 is closed, signal line A is connected to signal line B of the extension cord. The signal point CC of the charging / discharging gun has a resistance of R4E to ground. At this time, the circuit is in the discharge connection state with a resistance of 2k ohms. Specifically, the resistance of the signal point CC to ground is 3.5k ohms in the discharge half-connection state and 2k ohms in the charging connection state, which meets the requirements of GB / T 18487.4.

[0055] The working principle of this application embodiment is as follows: by outputting high / low level drive signals, the connection state of the relay circuit can be changed, the charging and discharging state of the circuit can be changed, and by pressing / disconnecting the built-in linkage switch of the charging gun, the resistance value of the gun head signal to ground circuit can be changed, thereby achieving reliable and efficient charging and discharging switching.

[0056] The above are preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made to the structure, shape and principle of this application should be included within the scope of protection of this application.

Claims

1. An electric vehicle charge-discharge switching circuit, characterized by comprising: include: Relay UK1, drive unit, switch S1; The first fixed terminal of relay UK1 is connected to the first power supply voltage, the second fixed terminal of relay UK1 is connected to the drive unit, the first common terminal of relay UK1 is connected to the first terminal of switch S1, the second common terminal of relay UK1 is connected to the second terminal of signal line A, the first normally closed contact and the second normally closed contact of relay UK1 are connected to the first terminal of resistor R4B, the first normally open contact of relay UK1 is connected to the first terminal of resistor R4D, and the second normally open contact of relay UK1 is connected to the second terminal of resistor RG1. The driving unit includes a resistor RF1 and a transistor QK3. The first end of the resistor RF1 is connected to the driving signal K1, the base of the transistor QK3 is connected to the second end of the resistor RF1, and the collector of the transistor QK3 is connected to the second fixed end. The relay UK1 includes a first state and a second state controlled by the switch S1. In the first state, the first common terminal is connected to the first normally open contact, and the second common terminal is connected to the second normally open contact. In the second state, the first common terminal is connected to the first normally closed contact, and the second common terminal is connected to the second normally closed contact.

2. The electric vehicle charging and discharging switching circuit according to claim 1, characterized in that, The second terminal of the resistor R4D is grounded, the switch S1 is connected in parallel with the resistor R4A, the first terminal of the switch S1 is connected to the first terminal of the resistor R4A, and the second terminal of the switch S1 is connected to the second terminal of the resistor R4A.

3. The electric vehicle charging and discharging switching circuit according to claim 1, characterized in that, The second end of resistor R4B is connected to the first end of resistor R4C, the second end of resistor R4C is connected to the second end of switch S1, and the common connection point of switch S1, resistor R4A, and resistor R4C is connected to the signal point CC of the charging and discharging gun.

4. The electric vehicle charging and discharging switching circuit according to claim 3, characterized in that, The trigger state of switch S1 changes the resistance value of the signal point CC to ground circuit. Switch S1 is a normally closed switch.

5. The electric vehicle charging and discharging switching circuit according to claim 1, characterized in that, It also includes an isolation unit, which includes an optocoupler U2A, a capacitor CG1, a capacitor CG2, a resistor RG3, and a resistor RG4; the positive terminal of the input side of the optocoupler U2A is connected to the second terminal of the resistor RG1 and the first terminal of the capacitor CG1, the negative terminal of the input side of the optocoupler U2A shares a common ground with the second terminal of the capacitor CG2, the collector of the output side of the optocoupler U2A is connected to the first terminal of the resistor RG3 and the first terminal of the resistor RG4, and the emitter of the output side of the optocoupler U2A shares a common ground with the second terminal of the capacitor CG2.

6. The electric vehicle charging and discharging switching circuit according to claim 5, characterized in that, The second end of the resistor RG4 and the first end of the capacitor CG2 are connected to the signal point GL on the output side of the optocoupler U2A. The signal point GL is used to connect to the MCU.

7. The electric vehicle charging and discharging switching circuit according to claim 1, characterized in that, It also includes a cable tray signal line B and a converter signal line C. The cable tray signal line B includes a resistor R4E. The first end of the resistor R4E is grounded, and the second end of the resistor R4E is used to connect to the first end of the signal line A. The first end of the converter signal line C is grounded, and the second end of the converter signal line C is used to connect to the first end of the signal line A.

8. The electric vehicle charging and discharging switching circuit according to claim 1, characterized in that, The driving unit also includes a diode DK3, the first end of which is connected to the collector of the transistor QK3 and the second fixed end, and the second end of which is connected to the first power supply voltage and the first fixed end.

9. The electric vehicle charging and discharging switching circuit according to claim 1, characterized in that, The first end of resistor RG1 is connected to the second power supply voltage, and the first end of resistor RG3 is also connected to the second power supply voltage.

10. The electric vehicle charging and discharging switching circuit according to claim 3, characterized in that, The switch S1 is located inside the charging and discharging gun. In the first state, and with switch S1 open, it corresponds to a charging half-connection state; in the first state, and with switch S1 closed, it corresponds to a charging connection state. In the second state, and with switch S1 open, it corresponds to a discharge half-connection state; In the second state, and with switch S1 closed, it corresponds to a discharge connection state.

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