Protection method for under-voltage charging and discharging of battery pack unit

Abstract

The invention discloses a protection method for under-voltage charging and discharging of a battery pack unit. A lithium battery BMS module, the battery pack unit, a switching circuit, a charging and discharging end and a charging and discharging detection circuit are included. The lithium battery BMS module judges whether the battery pack unit is in a charging state or a discharging state in real time; when the battery pack unit is in a charging state, the lithium battery BMS module controls the charging and discharging detection circuit to be converted into a charging detection mode; when the charging and discharging detection circuit detects that the voltage input by the charging and discharging end is smaller than the set minimum charging voltage, the switching circuit is controlled to be switched off; when the battery pack unit is in a discharging state, the lithium battery BMS module controls the charging and discharging detection circuit to be converted into a discharging detection mode, and when the charging and discharging detection circuit detects that the voltage output by the battery pack unit is smaller than the set discharging minimum voltage, the switching circuit is controlled to be switched off. Under-voltage charging and discharging of the protection circuit are avoided, safety and stability of the battery during charging or discharging are guaranteed, and the service life of the battery is prolonged.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a method for protecting a battery pack unit from undervoltage charging and discharging. Background Art

[0002] Leasing and using lithium battery PACK has become the choice of more and more users. The leasing company is responsible for the update, maintenance and recycling of lithium battery PACK, which improves the utilization rate of energy and has positive significance for resource reuse and environmental protection. Lithium batteries are usually equipped with a BMS module to detect the power of the battery pack and the input and output current of the battery; the BMS module is usually equipped with an overvoltage protection circuit. When the charging voltage is too high, it will accelerate the speed of the chemical reaction inside the battery, causing damage to the internal structure of the battery, thereby reducing the service life of the battery; an overvoltage protection circuit is used to protect the problem of excessive charging voltage in the circuit. However, when the charging voltage is too low, the battery will also be in an undervoltage state. Undervoltage charging will cause the capacity and performance of the battery to decrease, and will also damage the internal structure of the battery and shorten the life of the battery; the existing battery pack charging does not effectively protect against low voltage, and the battery will be damaged if the time is too long; at the same time, when the battery output voltage is too low, it will not only fail to drive the motor, but also cause a waste of power. The battery output power has nowhere to be released, which may cause the hazard of high temperature fire. Summary of the invention

[0003] Purpose of the invention: In order to overcome the deficiencies in the prior art, the present invention provides a method for protecting a battery pack unit from undervoltage charging and discharging, which ensures the safety and stability of the battery during charging or discharging and extends the battery life by switching between a charging detection mode and a discharging detection mode in a charging and discharging detection circuit and cutting off or closing the switch circuit according to the detection voltage.

[0004] Technical solution: To achieve the above-mentioned purpose, a method for protecting a battery pack unit from undervoltage charging and discharging of the present invention comprises a lithium battery BMS module, a battery pack unit, a switch circuit, a charging and discharging terminal and a charging and discharging detection circuit; the real-time state of the battery pack unit is judged by the lithium battery BMS module to judge whether the battery pack unit is in a charging state or a discharging state;

[0005] When the battery pack unit is in charging state, the lithium battery BMS module controls the charge and discharge detection circuit to switch to the charge detection mode; the charge and discharge detection circuit detects the voltage input at the charge and discharge end, and when it detects that the voltage input at the charge and discharge end is less than the set minimum charging voltage, the switch circuit is controlled to disconnect;

[0006] When the battery pack unit is in the discharge state, the lithium battery BMS module controls the charge and discharge detection circuit to switch to the discharge detection mode. The charge and discharge detection circuit detects the voltage output by the battery pack unit. When it is detected that the voltage output by the battery pack unit is less than the set minimum discharge voltage, the switch circuit is controlled to disconnect.

[0007] Furthermore, the detection end of the lithium battery BMS module is connected to the signal output end of the battery pack unit, the positive end of the battery pack unit is electrically connected to the positive end of the charging and discharging end through the KM1 contactor switch in the switching circuit, and the negative end of the battery pack unit is electrically connected to the negative end of the charging and discharging end; the control output end of the lithium battery BMS module and the output end of the charge and discharge detection circuit are both electrically connected to the signal end of the switching circuit to control the opening and closing of the switching circuit.

[0008] Furthermore, one end of the detection end of the charge and discharge detection circuit is electrically connected to the negative end of the charge and discharge end, and the other end of the detection end of the charge and discharge detection circuit is electrically connected to the positive end of the battery pack unit or the positive end of the charge and discharge end through a state switching circuit; the other control output end of the lithium battery BMS module is transmitted and connected to the control end of the charge and discharge detection circuit to control the conversion of the charge detection mode and the discharge detection mode of the charge and discharge detection circuit.

[0009] Further, when the lithium battery BMS module controls the charge and discharge detection circuit to be in the charge detection mode, the lithium battery BMS module controls the other end of the detection end of the charge and discharge detection circuit to be connected to the positive end of the charge and discharge end through the state switching circuit, and the lithium battery BMS module controls the reference voltage VREF output by the bandgap reference circuit in the charge and discharge detection circuit to be the minimum voltage allowed for charging;

[0010] When the lithium battery BMS module controls the charge and discharge detection circuit to be in the discharge detection mode, the other end of the detection end of the charge and discharge detection circuit controlled by the lithium battery BMS module is connected to the positive end of the battery pack unit through the state switching circuit, and the reference voltage VREF output by the bandgap reference circuit in the charge and discharge detection circuit controlled by the lithium battery BMS module is the minimum voltage allowed for discharge.

[0011] Furthermore, the switching circuit also includes a KM contactor coil, an OR gate circuit and an M1 transistor switch; the source of the M1 transistor switch is electrically connected to the positive pole of the power output end of the low-power power supply unit, the drain of the M1 transistor switch is electrically connected to one end of the KM contactor coil, the other end of the KM contactor coil is electrically connected to the negative pole of the power output end of the low-power power supply unit, and the gate of the M1 transistor switch is electrically connected to the output end of the OR gate circuit.

[0012] Furthermore, the charge and discharge detection circuit also includes a DA1 differential amplifier and a Comp comparator; the output end of the DA1 differential amplifier is electrically connected to the positive input end of the Comp comparator; the negative input end of the Comp comparator is electrically connected to the output end of the bandgap reference circuit, the output end of the Comp comparator is electrically connected to one input end of the OR gate circuit, the control output end of the lithium battery BMS module is electrically connected to the other input end of the OR gate circuit; the other control output end of the lithium battery BMS module is transmission-connected to the control end of the bandgap reference circuit.

[0013] Furthermore, the state switching circuit includes an M2 transistor switch and an M3 transistor switch; the drain of the M2 transistor switch and the drain of the M3 transistor switch are electrically connected to the positive input terminal of the DA1 differential amplifier, and the negative input terminal of the DA1 differential amplifier is electrically connected to the negative terminal of the charge and discharge terminal; the source of the M2 transistor switch is electrically connected to the positive terminal of the battery pack unit, and the source of the M3 transistor switch is electrically connected to the positive terminal of the charge and discharge terminal.

[0014] Furthermore, the two signal output terminals of the lithium battery BMS module are electrically connected to the gate of the M2 transistor switch and the gate of the M3 transistor switch, respectively, to control the on and off of the M2 transistor switch and the M3 transistor switch, respectively.

[0015] Further, when the charge and discharge detection circuit is in the charge detection mode, the M2 transistor switch is turned off and the M3 transistor switch is turned on; when the charge and discharge detection circuit is in the discharge detection mode, the M2 transistor switch is turned on and the M3 transistor switch is turned off.

[0016] Beneficial effects: The undervoltage charging and discharging protection method of a battery pack unit of the present invention ensures the safety and stability of the battery during charging or discharging and extends the service life of the battery by switching the charging detection mode and the discharging detection mode in the charging and discharging detection circuit and cutting off or closing the switching circuit according to the detection voltage; through the circuit design of the comparator and the differential amplifier in the charging and discharging detection circuit, the protection circuit will not have undervoltage charging and discharging, so that the safety of the battery is effectively guaranteed, the internal structure and performance of the battery are stabilized, and the battery service life is extended. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A flow chart of a method for protecting a battery pack unit from undervoltage charging and discharging;

[0018] Figure 2 This is a protection circuit diagram for undervoltage charging and discharging of lithium batteries;

[0019] Figure 3 Schematic diagram of the state switching circuit. DETAILED DESCRIPTION

[0020] The present invention will be further described below in conjunction with the accompanying drawings.

[0021] like Figure 1 As shown, a protection method for undervoltage charging and discharging of a battery pack unit includes a lithium battery BMS module 1, a battery pack unit 2, a switch circuit 3, a charging and discharging terminal 4, and a charging and discharging detection circuit 5; the real-time state of the battery pack unit 2 is judged by the lithium battery BMS module 1 to judge whether the battery pack unit 2 is in a charging state or a discharging state;

[0022] When the battery pack unit 2 is in the charging state, the lithium battery BMS module 1 controls the charge and discharge detection circuit 5 to switch to the charge detection mode; the charge and discharge detection circuit 5 detects the voltage input to the charge and discharge terminal 4, and when it is detected that the voltage input to the charge and discharge terminal 4 is less than the set minimum charging voltage, the switch circuit 3 is controlled to be disconnected; at this time, the charge and discharge detection circuit 5 still detects the voltage input to the charge and discharge terminal 4, and when the voltage input to the charge and discharge terminal 4 is greater than the set minimum charging voltage, the switch circuit 3 is controlled to be closed.

[0023] When the battery pack unit 2 is in the discharge state, the lithium battery BMS module 1 controls the charge and discharge detection circuit 5 to switch to the discharge detection mode. The charge and discharge detection circuit 5 detects the voltage output by the battery pack unit 2. When it is detected that the voltage output by the battery pack unit 2 is less than the set minimum discharge voltage, the switch circuit 3 is controlled to be disconnected; at this time, the charge and discharge detection circuit 5 still detects the voltage output by the battery pack unit 2. When the voltage output by the battery pack unit 2 is greater than the set minimum discharge voltage, the switch circuit 3 is controlled to be closed. Of course, when the battery discharge has ended and charging begins, the lithium battery BMS module 1 controls the charge and discharge detection circuit 5 to switch to the charge detection mode.

[0024] like Figure 2 As shown, it also includes a low-power power supply unit 6; the power output end of the low-power power supply unit 6 is connected to the power end of the lithium battery BMS module 1, the power end of the charge and discharge detection circuit 5 and the power end of the switch circuit 3, so as to supply power to the lithium battery BMS module 1, the charge and discharge detection circuit 5 and the switch circuit 3; the detection end of the lithium battery BMS module 1 is connected to the signal output end of the battery pack unit 2, and the lithium battery BMS module 1 detects various status data of the battery pack unit 2; the positive end of the battery pack unit 2 is electrically connected to the positive end of the charge and discharge end 4 through the KM1 contactor switch 31 in the switch circuit 3, and the negative end of the battery pack unit 2 is electrically connected to the negative end of the charge and discharge end 4; the control output end of the lithium battery BMS module 1 and the output end of the charge and discharge detection circuit 5 are electrically connected to the signal end of the switch circuit 3 to control the opening and closing of the switch circuit 3.

[0025] like Figure 2As shown, it also includes a communication client unit 7 and a server end 8 connected to the communication client for communication. The communication client unit input end 7 is bidirectionally connected to the output end of the lithium battery BMS module 1 for transmission, so as to receive the lithium battery BMS data and send data to the lithium battery BMS. The communication client unit 7 and the server end 8 connected to the communication client for communication are bidirectionally wirelessly connected, and the communication client unit 7 receives and sends data to the server end through wireless transmission. In addition to the most basic lithium battery protection functions such as voltage, temperature, and current, the lithium battery BMS module 1 measures the total discharge amount and usage time of the lithium battery and other data, and exchanges data with the server end to determine whether the customer has the right to use the lithium battery PACK through the controller inside the battery PACK to power on and off. The charge and discharge end 4 is used to electrically connect to the load motor or charger, and is responsible for discharging and charging.

[0026] One end of the detection end of the charge and discharge detection circuit 5 is electrically connected to the negative end of the charge and discharge end 4, and the other end of the detection end of the charge and discharge detection circuit 5 is electrically connected to the positive end of the battery pack unit 2 or the positive end of the charge and discharge end 4 through the state switching circuit 9; the other control output end of the lithium battery BMS module 1 is transmitted and connected to the control end of the charge and discharge detection circuit 5 to control the conversion between the charge detection mode and the discharge detection mode of the charge and discharge detection circuit 5.

[0027] When the lithium battery BMS module 1 controls the charge and discharge detection circuit 5 to be in the charge detection mode, the lithium battery BMS module 1 controls the other end of the detection end of the charge and discharge detection circuit 5 to be connected to the positive end of the charge and discharge end 4 through the state switching circuit 9, and the lithium battery BMS module 1 controls the bandgap reference circuit 53 in the charge and discharge detection circuit 5 to output a reference voltage VREF that is the minimum voltage allowed for charging;

[0028] When the lithium battery BMS module 1 controls the charge and discharge detection circuit 5 to be in the discharge detection mode, the lithium battery BMS module 1 controls the other end of the detection end of the charge and discharge detection circuit 5 to be connected to the positive end of the battery pack unit 2 through the state switching circuit 9, and the lithium battery BMS module 1 controls the reference voltage VREF output by the bandgap reference circuit 53 in the charge and discharge detection circuit 5 to be the minimum voltage allowed for discharge.

[0029] The switch circuit 3 also includes a KM contactor coil 32, an OR gate circuit 34 and an M1 transistor switch 33; the source of the M1 transistor switch 33 is electrically connected to the positive pole of the power output end of the low-power power supply unit 6, the drain of the M1 transistor switch 33 is electrically connected to one end of the KM contactor coil 32, the other end of the KM contactor coil 32 is electrically connected to the negative pole of the power output end of the low-power power supply unit 6, and the gate of the M1 transistor switch 33 is electrically connected to the output end of the OR gate circuit 34.

[0030] The KM1 contactor switch 31 and the KM contactor coil 32 are two structures of the same contactor; the KM1 contactor switch 31 is a normally closed switch. When the KM contactor coil 32 is energized, the KM1 contactor switch 31 is opened; when the KM contactor coil 32 is de-energized, the KM1 contactor switch 31 is closed.

[0031] The charge and discharge detection circuit 5 also includes a DA1 differential amplifier 51 and a Comp comparator 52; the output end of the DA1 differential amplifier 51 is electrically connected to the positive input end of the Comp comparator 52, and the output end of the DA1 differential amplifier 51 is grounded through the R1 resistor; the negative input end of the Comp comparator 52 is electrically connected to the output end of the bandgap reference circuit 53, the output end of the Comp comparator 52 is electrically connected to one input end of the OR gate circuit 34, and the control output end of the lithium battery BMS module 1 is electrically connected to the other input end of the OR gate circuit 34; the other control output end of the lithium battery BMS module 1 is transmission-connected to the control end of the bandgap reference circuit 53. The DA1 differential amplifier 51, the Comp comparator 52 and the bandgap reference circuit 53 are all powered by a low-power power supply unit.

[0032] When the signal output end of the lithium battery BMS module 1 outputs a high level, and the output end of the Comp comparator 52 outputs a high level; the OR gate circuit 34 outputs a high level to the gate of the M1 transistor switch 33, the M1 transistor switch 33 is turned off, and the circuit where the KM contactor coil 32 is located is powered off and not powered; at this time, the KM1 contactor switch 31 is closed, and normal charging and discharging are possible. When the signal output end of the lithium battery BMS module outputs a low level, or the output end of the Comp comparator 52 outputs a low level, either one of them outputs a low level or both output a low level; the OR gate circuit 34 outputs a low level to the gate of the M1 transistor switch 33, the M1 transistor switch 33 is turned on, and the circuit where the KM contactor coil 32 is located is powered on; at this time, the KM1 contactor switch 31 is disconnected, and normal charging and discharging are not possible.

[0033] like Figure 3 As shown, the state switching circuit 9 includes an M2 transistor switch 91 and an M3 transistor switch 92; the drain of the M2 transistor switch 91 and the drain of the M3 transistor switch 92 are electrically connected to the positive input terminal of the DA1 differential amplifier 51, and the negative input terminal of the DA1 differential amplifier 51 is electrically connected to the negative terminal of the charge and discharge terminal 4; the source of the M2 transistor switch 91 is electrically connected to the positive terminal of the battery pack unit 2, and the source of the M3 transistor switch 92 is electrically connected to the positive terminal of the charge and discharge terminal 4.

[0034] The two signal output terminals of the lithium battery BMS module 1 are electrically connected to the gate of the M2 transistor switch 91 and the gate of the M3 transistor switch 92, respectively, to control the on and off of the M2 transistor switch 91 and the M3 transistor switch 92. When the charge and discharge detection circuit 5 is in the charge detection mode, the M2 transistor switch 91 is turned off and the M3 transistor switch 92 is turned on; the positive input terminal of the DA1 differential amplifier 51 is connected to the positive terminal of the charge and discharge terminal 4 through the M3 transistor switch 92; even if the switch circuit 3 is disconnected, the charge and discharge detection circuit can detect the input voltage of the charge and discharge terminal 4. When the charge and discharge detection circuit 5 is in the discharge detection mode, the M2 transistor switch 91 is turned on and the M3 transistor switch 92 is turned off; the positive input terminal of the DA1 differential amplifier 51 is connected to the positive terminal of the battery pack unit 2 through the M2 transistor switch 91; even if the switch circuit 3 is disconnected, the charge and discharge detection circuit can detect the output voltage of the battery pack unit 2. The voltage output by the battery pack unit 2 or the voltage input by the charge and discharge terminal 4 will not be detected due to the disconnection of the KM1 contactor switch 31.

[0035] When the switch circuit is disconnected, that is, the KM1 contactor switch 31 is disconnected, and at this time the battery pack unit is in a charging state; the charge and discharge detection circuit 5 detects the input voltage of the charge and discharge terminal 4 through the conduction of the M3 transistor open tube 92; it is determined whether the input voltage of the charge and discharge terminal 4 is greater than the set minimum voltage allowed for charging. If it is, the charge and discharge detection circuit 5 outputs a high level, and at this time the lithium battery BMS module 1 outputs a high level, and the KM1 contactor switch 31 is closed, and the charging operation is performed. If the input voltage of the charge and discharge terminal 4 is less than the set minimum voltage allowed for charging, the charge and discharge detection circuit 5 outputs a low level. At this time, even if the lithium battery BMS module 1 outputs a high level, the KM1 contactor switch 31 remains disconnected and does not perform a charging operation.

[0036] When the switch circuit is disconnected, that is, the KM1 contactor switch 31 is disconnected, and the battery pack unit is in a discharge state at this time; the charge and discharge detection circuit 5 detects the output voltage of the battery pack unit 2 through the conduction of the M2 transistor open tube 91, and determines whether the output voltage of the battery pack unit 2 is greater than the set minimum voltage allowed for discharge. If it is, the charge and discharge detection circuit 5 outputs a high level, and the lithium battery BMS module 1 outputs a high level, and the KM1 contactor switch 31 is closed to perform a discharge operation. If the output voltage of the battery pack unit 2 is less than the set minimum voltage allowed for charging, the charge and discharge detection circuit 5 outputs a low level. At this time, even if the lithium battery BMS module 1 outputs a high level, the KM1 contactor switch 31 remains disconnected and does not perform a discharge operation.

[0037] Example

[0038] When users rent batteries, unexpected situations are inevitable; when users do not return the batteries after renting them, but keep them for their own use, and cannot operate the batteries through signals; when the batteries are used up, users may take the batteries back to their homes or charge them elsewhere, instead of charging them in the battery cabinet of the rented batteries. The charging voltage is not fixed, and too low a charging voltage will damage the batteries and their internal structures; it is generally believed that low charging voltage will not damage the batteries, so there are not many protection circuits and methods for low charging voltages. In fact, too low a charging voltage will still damage the internal structure of the batteries and reduce the battery life. At the same time, when the battery is discharged, the output voltage will not be high before the power is almost used up, and there is no way to drive the motor to run, which will generate high temperatures on the transmission line of the motor, and high-temperature fires are inevitable.

[0039] Therefore, when charging the battery, the lithium battery BMS module 1 controls the charge and discharge detection circuit 5 to be in the charge detection mode, at which time the M3 transistor switch 92 is turned on, and the reference voltage VREF output by the bandgap reference circuit 53 of the lithium battery BMS module 1 is the minimum voltage allowed for charging; the DA1 differential amplifier 51 in the charge and discharge detection circuit 5 collects the input voltage of the charge and discharge terminal 4, and when the input voltage of the charge and discharge terminal 4 is greater than the reference voltage VREF; the output end of the Comp comparator 52 and the output end of the lithium battery BMS module 1 both output a high voltage, the KM contactor coil 32 is powered off and the KM1 contactor switch 31 is closed, and normal charging is performed; when the input voltage of the charge and discharge terminal 4 is less than the reference voltage VREF; the output end of the Comp comparator 52 outputs a low level, the output end of the lithium battery BMS module 1 outputs a high voltage, the KM contactor coil 32 is powered on and the KM1 contactor switch 31 is disconnected, and charging is no longer performed. Similarly, when the battery pack unit 2 is fully charged, even if the voltage input to the charge and discharge terminal 4 is greater than the reference voltage VREF, the output terminal of the Comp comparator 52 outputs a high voltage. At this time, the lithium battery BMS module 1 can output a low level according to the instructions transmitted by the communication client unit 7 and the server end 8 connected to the communication client, so that the KM contactor coil 32 is energized and the KM1 contactor switch 31 is disconnected, and charging is no longer performed.

[0040] Therefore, when discharging the battery, the lithium battery BMS module 1 controls the charge and discharge detection circuit 5 to be in the discharge detection mode. At this time, the M2 transistor switch 91 is turned on, and the reference voltage VREF output by the bandgap reference circuit 53 of the lithium battery BMS module 1 is the minimum voltage allowed for discharge; the DA1 differential amplifier 51 in the charge and discharge detection circuit 5 collects the output voltage of the battery pack unit 2; when the output voltage of the battery pack unit 2 is greater than the reference voltage VREF; the output end of the Comp comparator 52 and the output end of the lithium battery BMS module 1 both output a high voltage, the KM contactor coil 32 is powered off, and the KM1 contactor switch 31 is closed, and normal discharge is performed; when the output voltage of the battery pack unit 2 is less than the reference voltage VREF; Quasi-voltage VREF; the output end of the Comp comparator 52 outputs a low level, the output end of the lithium battery BMS module 1 outputs a high voltage, the KM contactor coil 32 is energized, the KM1 contactor switch 31 is disconnected, and no discharge occurs; similarly, when the lithium battery BMS module 1 needs to shut down the battery and stop discharging, even if the voltage output by the battery pack unit 2 is greater than the reference voltage VREF, the output end of the Comp comparator 52 outputs a high voltage. At this time, the lithium battery BMS module 1 can output a low level according to the instructions transmitted by the communication client unit 7 and the server end 8 connected to the communication client, so that the KM contactor coil 32 is energized, the KM1 contactor switch 31 is disconnected, and no discharge occurs.

[0041] The input or output voltage of the battery pack is detected by the set charge and discharge detection circuit 5. When the voltage is lower than the set minimum voltage, the switch circuit 3 can be automatically disconnected to protect the internal structure of the battery pack and the performance of the battery; when the internal and external communication modules of the rental battery cannot communicate, the lithium battery BMS module 1 cannot be controlled to disconnect the switch circuit through the instructions issued by the server. At this time, the charging and discharging voltage can only be detected by the charge and discharge detection circuit 5 to protect the safety and stability of the battery; it is also possible that a circuit failure occurs in the charging battery cabinet, and the charging voltage is too low to cause damage to the battery. Therefore, the internal structure of the battery is protected by detecting the charging voltage.

[0042] The above is only a description of the preferred embodiments of the present invention. Ordinary technicians in this technical field can make several modifications and optimizations based on the above disclosure without departing from the above basic principles. These improvements and optimizations should be regarded as the understood protection scope of the present invention.

Claims

1. A method for protecting a battery pack unit from undervoltage charging and discharging, characterized in that: The invention comprises a lithium battery BMS module (1), a battery pack unit (2), a switch circuit (3), a charge and discharge terminal (4) and a charge and discharge detection circuit (5); the real-time state of the battery pack unit (2) is judged by the lithium battery BMS module (1), and it is judged whether the battery pack unit (2) is in a charging state or a discharging state; When the battery pack unit (2) is in a charging state, the lithium battery BMS module (1) controls the charge and discharge detection circuit (5) to switch to a charge detection mode; the charge and discharge detection circuit (5) detects the voltage input to the charge and discharge end (4), and when it is detected that the voltage input to the charge and discharge end (4) is less than a set minimum charging voltage, the switch circuit (3) is controlled to be disconnected; When the battery pack unit (2) is in a discharging state, the lithium battery BMS module (1) controls the charge and discharge detection circuit (5) to switch to a discharge detection mode. The charge and discharge detection circuit (5) detects the voltage output by the battery pack unit (2). When it is detected that the voltage output by the battery pack unit (2) is less than a set minimum discharge voltage, the switch circuit (3) is controlled to be disconnected.

2. The undervoltage charge and discharge protection method of a battery pack unit according to claim 1, characterized in that: The detection end of the lithium battery BMS module (1) is connected to the signal output end of the battery pack unit (2) for transmission; the positive end of the battery pack unit (2) is electrically connected to the positive end of the charge and discharge end (4) through the KM1 contactor switch (31) in the switch circuit (3); the negative end of the battery pack unit (2) is electrically connected to the negative end of the charge and discharge end (4); the control output end of the lithium battery BMS module (1) and the output end of the charge and discharge detection circuit (5) are both electrically connected to the signal end of the switch circuit (3) to control the opening and closing of the switch circuit (3).

3. A method for protecting a battery pack unit from undervoltage charging and discharging according to claim 2, characterized in that: One end of the detection end of the charge and discharge detection circuit (5) is electrically connected to the negative end of the charge and discharge end (4), and the other end of the detection end of the charge and discharge detection circuit (5) is electrically connected to the positive end of the battery pack unit (2) or the positive end of the charge and discharge end (4) through a state switching circuit (9); the other control output end of the lithium battery BMS module (1) is connected to the control end of the charge and discharge detection circuit (5) to control the conversion of the charge detection mode and the discharge detection mode of the charge and discharge detection circuit (5).

4. The undervoltage charge and discharge protection method of a battery pack unit according to claim 3, characterized in that: When the lithium battery BMS module (1) controls the charge and discharge detection circuit (5) to be in the charge detection mode, the lithium battery BMS module (1) controls the other end of the detection end of the charge and discharge detection circuit (5) to be connected to the positive end of the charge and discharge end (4) through the state switching circuit (9), and the lithium battery BMS module (1) controls the bandgap reference circuit (53) in the charge and discharge detection circuit (5) to output a reference voltage VREF that is the minimum voltage allowed for charging; When the lithium battery BMS module (1) controls the charge and discharge detection circuit (5) to be in the discharge detection mode, the lithium battery BMS module (1) controls the other end of the detection end of the charge and discharge detection circuit (5) to be connected to the positive end of the battery pack unit (2) through the state switching circuit (9), and the lithium battery BMS module (1) controls the bandgap reference circuit (53) in the charge and discharge detection circuit (5) to output a reference voltage VREF that is the minimum voltage allowed for discharge.

5. The undervoltage charge and discharge protection method of a battery pack unit according to claim 2, characterized in that: The switch circuit (3) further comprises a KM contactor coil (32), an OR gate circuit (34) and an M1 transistor switch (33); the source of the M1 transistor switch (33) is electrically connected to the positive electrode of the power output end of the low power supply unit (6), the drain of the M1 transistor switch (33) is electrically connected to one end of the KM contactor coil (32), the other end of the KM contactor coil (32) is electrically connected to the negative electrode of the power output end of the low power supply unit (6), and the gate of the M1 transistor switch (33) is electrically connected to the output end of the OR gate circuit (34).

6. A method for protecting a battery pack unit from undervoltage charging and discharging according to claim 2, characterized in that: The charge and discharge detection circuit (5) further comprises a DA1 differential amplifier (51) and a Comp comparator (52); the output end of the DA1 differential amplifier (51) is electrically connected to the positive input end of the Comp comparator (52); the negative input end of the Comp comparator (52) is electrically connected to the output end of the bandgap reference circuit (53); the output end of the Comp comparator (52) is electrically connected to an input end of an OR gate circuit (34); the control output end of the lithium battery BMS module (1) is electrically connected to the other input end of the OR gate circuit (34); and the other control output end of the lithium battery BMS module (1) is transmission-connected to the control end of the bandgap reference circuit (53).

7. A method for protecting a battery pack unit from undervoltage charge and discharge according to claim 6, characterized in that: The state switching circuit (9) comprises an M2 transistor switch (91) and an M3 transistor switch (92); the drain of the M2 transistor switch (91) and the drain of the M3 transistor switch (92) are electrically connected to the positive input terminal of the DA1 differential amplifier (51), and the negative input terminal of the DA1 differential amplifier (51) is electrically connected to the negative terminal of the charge and discharge terminal (4); the source of the M2 transistor switch (91) is electrically connected to the positive terminal of the battery pack unit (2), and the source of the M3 transistor switch (92) is electrically connected to the positive terminal of the charge and discharge terminal (4).

8. A method for protecting a battery pack unit from undervoltage charge and discharge according to claim 7, characterized in that: The two signal output ends of the lithium battery BMS module (1) are electrically connected to the gate of the M2 transistor switch (91) and the gate of the M3 transistor switch (92), respectively, to control the on and off of the M2 transistor switch (91) and the M3 transistor switch (92).

9. A method for protecting a battery pack unit from undervoltage charging and discharging according to claim 8, characterized in that: When the charge and discharge detection circuit (5) is in a charge detection mode, the M2 transistor switch (91) is turned off and the M3 transistor switch (92) is turned on; when the charge and discharge detection circuit (5) is in a discharge detection mode, the M2 transistor switch (91) is turned on and the M3 transistor switch (92) is turned off.

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