A protection circuit and control method for preventing reverse connection of load for lithium battery power supply

Abstract

This invention provides a protection circuit and control method for preventing reverse connection of loads in lithium battery power supply, relating to the field of lithium battery power system technology. It includes a lithium battery pack, a battery management system (BMS), an insulation detection module (IMD), a vehicle control unit (VCU), and a motor control unit (MCU). The lithium battery pack is communicatively connected to the BMS. The positive terminal of the lithium battery pack is connected to the MCU via relays K1, K3, a pre-charge resistor R, and K4. The negative terminal of the lithium battery pack is connected to the IMD via relay K2 and to the MCU via relay K5. The BMS is connected to the IMD and the VCU. This invention features a dual polarity detection and comparison mechanism, providing system-level collaborative protection, comprehensive pre-charge protection, automated operation, reduced human error, and fault self-recovery capability.

Description

Technical Field

[0001] This invention relates to the field of lithium battery power system technology, and more specifically, to a protection circuit and control method for preventing reverse connection of loads in lithium battery power supply. Background Technology

[0002] With the rapid development of new energy lithium battery technology, lithium battery power technology is increasingly penetrating underground mining scenarios, namely the field of new energy in mining. More and more diesel-powered underground mining vehicles are moving towards pure electric technology using lithium battery power, which is also an important way to improve the safety and economy of mining operations. However, as non-road vehicles, underground mining vehicles have relatively crude system design technology, and assembly and debugging personnel generally lack professional training and have limited understanding of new energy technologies. In actual assembly and maintenance, it often happens that the polarity of the power load on the vehicle side, such as the MCU bus of the vehicle's motor controller, is reversed. Once the load polarity is reversed, it can cause damage to key components such as the vehicle's motor controller, or even lead to major safety accidents such as short circuits and fires, resulting in serious casualties and property losses. Currently, traditional reverse connection protection schemes mainly adopt the following methods: Diode reverse connection protection: A high-power diode is connected in series at the power input terminal, using the diode's unidirectional conductivity to prevent reverse current. This scheme is simple and reliable, but the diode will generate a large forward voltage drop and power loss during operation, and will generate serious heat in high-current applications, reducing system efficiency. MOSFET reverse connection protection: This method uses a MOSFET as a reverse protection switch, leveraging its low on-resistance to reduce losses. However, this solution requires additional control circuitry, and the MOSFET may fail under reverse voltage, so reliability needs improvement. Relay-controlled reverse connection protection: This method controls the relay's closure by detecting the power supply polarity to achieve reverse connection protection. This solution typically relies on manual judgment or simple voltage comparison in the detection stage, lacking system-level collaborative verification, and is prone to protection failure due to detection errors.

[0003] For special application scenarios such as underground mining, traditional lithium battery power supply reverse connection protection schemes lack a polarity coordination detection mechanism between the battery side and the load side, and cannot complete the comparison and confirmation of the polarity of both sides before closing the main circuit; they are highly dependent on the professional level of operators, and it is difficult to fundamentally solve the polarity reverse connection problem caused by assembly errors; they lack a complete CAN bus communication and fault alarm mechanism, and cannot realize remote monitoring and fault tracing. Summary of the Invention

[0004] This invention aims to solve the problems of existing lithium battery power supply reverse connection protection schemes lacking a polarity coordination detection mechanism between the battery side and the load side, making it impossible to complete the comparison and confirmation of the polarity of both sides before closing the main circuit; and having a high dependence on the professional level of operators, making it impossible to achieve remote monitoring and fault tracing.

[0005] To address the aforementioned issues, this invention provides a protection circuit for preventing reverse load connection in lithium battery power supply, comprising a lithium battery pack subsystem and a vehicle power load subsystem; the lithium battery pack subsystem includes a lithium battery pack and a battery management system (BMS), and the vehicle power load subsystem includes an insulation detection module (IMD), a vehicle control unit (VCU), and a motor control unit (MCU). The lithium battery pack is communicatively connected to the battery management system (BMS); the positive terminal of the lithium battery pack is connected to the high voltage acquisition point PACK+, one end of relay K1, and one end of relay K3; the other end of relay K1 is connected to the DC+ port. The other end of relay K3 is connected to one end of pre-charge resistor R, and the other end of pre-charge resistor R is connected to port DC+; port DC+ is connected to high-voltage acquisition point LINK+. The negative terminal of the lithium battery pack is connected to the high-voltage acquisition point PACK- and one end of the relay K2; the other end of the relay K2 is connected to the port DC-; the port DC- is connected to the high-voltage acquisition point LINK-. Port DC+ is connected to the motor controller MCU via relay K4; port DC+ is connected to the insulation detection module IMD via detection line LOAD+; the battery management system BMS is connected to the insulation detection module IMD and the vehicle controller VCU via CAN1 bus. The vehicle control unit (VCU) is connected to the motor control unit (MCU) via the CAN2 bus. Port DC is connected to the insulation detection module IMD via the detection line LOAD; Port DC is connected to the motor controller MCU via relay K5.

[0006] The present invention provides a protection circuit for reverse connection of load for lithium battery power supply, which, compared with the prior art, has the following beneficial effects, but is not limited to: The two subsystems of this invention communicate with each other via the CAN1 bus, realizing the collaborative detection and comparison of high voltage polarity between the battery side and the load side, and providing a hardware foundation for solving the load reverse connection problem from the system architecture level.

[0007] This invention features a dual polarity detection and comparison mechanism. The battery management system (BMS) of the lithium battery pack subsystem detects the polarity of the front end of relay K1, and the insulation detection module (IMD) of the vehicle power load subsystem detects the polarity of the outer end of bus relay K4. Information exchange and comparison are achieved through the CAN bus. The main circuit is only allowed to be closed when the polarities on both sides are consistent, thus fundamentally solving the problem of reverse load connection.

[0008] This invention provides system-level collaborative protection. It tightly couples the lithium battery pack subsystem and the vehicle power load subsystem through the CAN bus, realizing full-link polarity monitoring from the battery side to the load side, forming a complete system-level protection scheme, and avoiding blind spots that may exist at a single detection point.

[0009] This invention features comprehensive pre-charge protection. The pre-charge unit, consisting of relay K3 and pre-charge resistor R, is designed in the discharge unit to pre-charge the bus capacitor inside the motor controller before closing the main relay K1. This effectively suppresses inrush current, protects the relay and load devices, and extends the system life.

[0010] This invention realizes CAN bus communication and fault alarm. It makes full use of the high reliability and real-time performance of CAN bus to realize information interaction between battery management system (BMS), vehicle controller (VCU), and insulation detection module (IMD). When reverse connection of load is detected, it can issue an alarm and record fault information in a timely manner, which is convenient for remote monitoring and fault tracing. It is particularly suitable for scenarios with extremely high safety requirements, such as underground mining.

[0011] This invention achieves automated operation and reduces human error. By replacing manual judgment with an automated detection and control system, this invention fundamentally solves the problem of reverse polarity connection caused by insufficient professional training of assembly and debugging personnel, and significantly improves the safety of the system.

[0012] This invention has a fault self-recovery capability. It is designed with a fault self-recovery mechanism. After eliminating the load reverse connection fault, the system can automatically reset and re-execute the detection process, which simplifies the operation process and improves the ease of use.

[0013] Furthermore, relays K1, K2, K3, K4, and K5 are all high-voltage DC relays, and their rated voltage is not lower than the rated voltage of the lithium battery pack.

[0014] Furthermore, relays K1, K2, K3, K4, and K5 are all equipped with auxiliary contacts, which are respectively connected to the input terminals of the battery management system (BMS) or the vehicle control unit (VCU).

[0015] Furthermore, a voltage sampling circuit is connected in parallel between port DC+ and port DC-. The voltage sampling circuit includes a voltage divider resistor network and an isolation operational amplifier. The output of the voltage sampling circuit is connected to the ADC input of the battery management system (BMS).

[0016] Furthermore, the pre-charge resistor R is an NTC thermistor or a PTC thermistor.

[0017] Furthermore, a freewheeling diode is connected in parallel across the two ends of the relay K3. The cathode of the freewheeling diode is connected to the positive terminal of the coil of the relay K3, and the anode of the freewheeling diode is connected to the negative terminal of the coil of the relay K3.

[0018] A control method for preventing reverse connection of load in lithium battery power supply includes the following steps: Step S1: The system sets the front end of relay K1 of the lithium battery pack subsystem to the DC+ polarity of the lithium battery pack, and sets the bus relay K4 of the vehicle power load subsystem to the DC+ polarity of the load. Step S2: When the lithium battery pack subsystem is powered on at low voltage, the battery management system (BMS) enters a self-test. After the self-test shows no abnormalities, it actively shakes hands with the vehicle controller (VCU) of the vehicle power load subsystem via the CAN1 bus to exchange information and confirm the status. Step S3: The vehicle control unit (VCU) of the vehicle power load subsystem initiates a battery polarity detection request to the battery management system (BMS) via the CAN1 bus; Step S4: After receiving the high voltage polarity detection request reported by the VCU, the Battery Management System (BMS) first actively detects whether there is a short circuit or low insulation at the external terminals of relays K1 and K2 through the high voltage acquisition points LINK+ and LINK-. If there is no abnormality, relay K2 is actively closed, and then the pre-charge unit is started. After the pre-charge is successful, relay K1 is closed and pre-charge relay K3 is released. At the same time, the detected voltage value and the polarity information of relay K1 are sent to the vehicle controller (VCU) of the vehicle power load subsystem through the CAN1 bus. Step S5: After receiving the information from the Battery Management System (BMS) regarding the closure of relays K1 and K2 and their high-voltage polarity, the Vehicle Control Unit (VCU) of the Vehicle Power Load Subsystem (VCU) keeps relays K4 and K5 open. It then uses the CAN1 bus to control the Insulation Detection Module (IMD) to detect the high voltage at the external terminals of relays K4 and K5 and the polarity data of relay K4. The VCU compares the polarities of relays K1 and K4. If they are inconsistent, it determines that the load is reversed, refuses to close relays K4 and K5, and sends an error message to the BMS via the CAN1 bus, instructing the BMS to disconnect relays K1 and K2.

[0019] Furthermore, in step S4, starting the pre-charge unit specifically involves closing relay K3, allowing current to flow through pre-charge resistor R to port DC+, pre-charging the bus capacitor inside the motor controller MCU; when the bus capacitor voltage rises to a preset proportional threshold of the lithium battery pack voltage, the pre-charge is determined to be successful, relay K1 is closed, and then relay K3 is opened to complete the pre-charge process.

[0020] Furthermore, in step S5, comparing the polarities of relays K1 and K4 specifically involves the vehicle controller (VCU) acquiring the relay K1 polarity information reported by the battery management system (BMS), which indicates that the front-end connection point of relay K1 is DC+ polarity; the VCU also acquires the relay K4 external polarity detection result reported by the insulation detection module (IMD). If the detected polarity at the external end of relay K4 is DC+, the polarities are considered to be consistent; if the detected polarity at the external end of relay K4 is DC-, the polarities are considered to be inconsistent, indicating a reverse load connection.

[0021] Furthermore, in step S5, after reporting an error to the battery management system (BMS) via the CAN1 bus, the BMS performs the following protection actions: disconnecting relay K1 and battery management system K2 to cut off the external output of the lithium battery pack; recording the fault information to the local memory; and continuously sending load reverse connection alarm information via the CAN1 bus until the fault is cleared and the system is manually reset. Attached Figure Description

[0022] Figure 1 This is a circuit diagram of a protection circuit for preventing reverse connection of load for lithium battery power supply according to an embodiment of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings showing multiple embodiments according to this application. It should be understood that the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments described in this application without creative effort will fall within the scope of protection of this application.

[0024] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in the specification of this application is for the purpose of describing specific embodiments only and is not intended to limit this application; the terms "comprising," "including," "having," "containing," etc., in the specification, claims, and accompanying drawings of this application are open-ended terms. Therefore, "comprising," "including," or "having" refers to, for example, a method or apparatus having one or more steps or elements, but is not limited to having only these one or more elements. The terms "first," "second," etc., in the specification, claims, or accompanying drawings of this application are used to distinguish different objects, not to describe a specific order or hierarchy. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0025] In the description of this invention, it should be understood that the terms "upper", "lower", "left", "right", "front", "rear", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0026] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "attachment" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0027] It should be emphasized that when the term "comprising / including" is used in this specification, it is used to explicitly indicate the presence of the stated feature, integer, step, or component, but does not exclude the presence or addition of one or more other features, integers, steps, components, or groups of features, integers, steps, or components.

[0028] In this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, in this application, the character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0029] See Figure 1 An embodiment of the present invention provides a protection circuit for preventing reverse connection of load for lithium battery power supply, comprising a lithium battery pack subsystem and a vehicle power load subsystem; the lithium battery pack subsystem includes a lithium battery pack and a battery management system (BMS), and the vehicle power load subsystem includes an insulation detection module (IMD), a vehicle control unit (VCU), and a motor control unit (MCU). The lithium battery pack is communicatively connected to the battery management system (BMS); the positive terminal of the lithium battery pack is connected to the high voltage acquisition point PACK+, one end of relay K1, and one end of relay K3; the other end of relay K1 is connected to the DC+ port. The other end of relay K3 is connected to one end of pre-charge resistor R, and the other end of pre-charge resistor R is connected to port DC+; port DC+ is connected to high-voltage acquisition point LINK+. The negative terminal of the lithium battery pack is connected to the high-voltage acquisition point PACK- and one end of the relay K2; the other end of the relay K2 is connected to the port DC-; the port DC- is connected to the high-voltage acquisition point LINK-. Port DC+ is connected to the motor controller MCU via relay K4; port DC+ is connected to the insulation detection module IMD via detection line LOAD+; the battery management system BMS is connected to the insulation detection module IMD and the vehicle controller VCU via CAN1 bus. The vehicle control unit (VCU) is connected to the motor control unit (MCU) via the CAN2 bus. Port DC is connected to the insulation detection module IMD via the detection line LOAD; Port DC is connected to the motor controller MCU via relay K5.

[0030] The two subsystems of this invention exchange information via the CAN1 bus, enabling coordinated detection and comparison of the high-voltage polarity between the battery side and the load side, thus providing a hardware foundation for solving the load reverse connection problem from a system architecture perspective. Relays K1 and K2 in the discharge unit serve as main circuit switches, while the pre-charge unit uses relay K3 and a pre-charge resistor R to pre-charge the capacitor, preventing excessive inrush current at the moment of closure and protecting the relays and load devices.

[0031] The Battery Management System (BMS) collects real-time status and operating data of the lithium battery pack, and also collects the high voltage at the front end of relays K1 and K2 in the discharge unit, i.e., the voltage between the high voltage acquisition points PACK+ and PACK-. The vehicle power load subsystem includes an Insulation Detection Module (IMD), a Vehicle Control Unit (VCU), a Motor Control Unit (MCU), and bus relays K4 and K5 that connect the load. The IMD's detection lines LOAD+ and LOAD- monitor the high voltage of the vehicle power load's power interface according to a strategy, and allow calibration of the external voltage polarity of bus relay K4.

[0032] The Insulation Detection Module (IMD) has polarity detection and calibration functions, capable of identifying the high-voltage polarity of the external terminal of bus relay K4 and reporting the detection results via the CAN1 bus. The Vehicle Control Unit (VCU), as the control core of the vehicle's power load subsystem, is responsible for information exchange and status confirmation with the Battery Management System (BMS), and coordinating the closing control of the bus relays. Relays K1 and K2 in the discharge unit act as main circuit switches. The pre-charge unit uses relay K3 and pre-charge resistor R to pre-charge the capacitor, preventing excessive inrush current during closing and protecting the relays and load devices. The BMS collects real-time status and operating data of the lithium battery pack and also collects the high-voltage inputs from relays K1 and K2 in the discharge unit, specifically the voltage between the high-voltage acquisition points PACK+ and PACK-.

[0033] This invention features a dual polarity detection and comparison mechanism. The battery management system (BMS) of the lithium battery pack subsystem detects the polarity of the front end of relay K1, and the insulation detection module (IMD) of the vehicle power load subsystem detects the polarity of the outer end of bus relay K4. Information exchange and comparison are achieved through the CAN bus. The main circuit is only allowed to be closed when the polarities on both sides are consistent, thus fundamentally solving the problem of reverse load connection.

[0034] This invention provides system-level collaborative protection. It tightly couples the lithium battery pack subsystem and the vehicle power load subsystem through the CAN bus, realizing full-link polarity monitoring from the battery side to the load side, forming a complete system-level protection scheme, and avoiding blind spots that may exist at a single detection point.

[0035] This invention features comprehensive pre-charge protection. The pre-charge unit, consisting of relay K3 and pre-charge resistor R, is designed in the discharge unit to pre-charge the bus capacitor inside the motor controller before closing the main relay K1. This effectively suppresses inrush current, protects the relay and load devices, and extends the system life.

[0036] This invention realizes CAN bus communication and fault alarm. It makes full use of the high reliability and real-time performance of CAN bus to realize information interaction between battery management system (BMS), vehicle controller (VCU), and insulation detection module (IMD). When reverse connection of load is detected, it can issue an alarm and record fault information in a timely manner, which is convenient for remote monitoring and fault tracing. It is particularly suitable for scenarios with extremely high safety requirements, such as underground mining.

[0037] This invention achieves automated operation and reduces human error. By replacing manual judgment with an automated detection and control system, this invention fundamentally solves the problem of reverse polarity connection caused by insufficient professional training of assembly and debugging personnel, and significantly improves the safety of the system.

[0038] This invention has a fault self-recovery capability. It is designed with a fault self-recovery mechanism. After eliminating the load reverse connection fault, the system can automatically reset and re-execute the detection process, which simplifies the operation process and improves the ease of use.

[0039] Furthermore, relays K1, K2, K3, K4, and K5 are all high-voltage DC relays, and their rated voltage is not lower than the rated voltage of the lithium battery pack.

[0040] High-voltage DC relays have stronger arc-extinguishing capabilities: Since direct current does not have a natural zero-crossing point, once an arc is generated, it is difficult to extinguish itself. High-voltage DC relays employ special arc-extinguishing chamber designs, such as magnetic blowout arc extinguishing and sealed gas-filled arc extinguishing, which effectively lengthen and cool the arc, quickly extinguishing it when breaking high-voltage DC circuits and preventing the arc from continuing to burn and damaging the contacts or causing a fire. High-voltage DC relays use special contact materials such as silver alloys and tungsten alloys that are resistant to arc erosion, maintaining good conductivity and mechanical strength even after multiple breaks of high-voltage DC circuits. The internal housing of high-insulation ceramic or engineering plastic is designed with high-voltage creepage distance and electrical clearance requirements in mind, ensuring that breakdown or flashover will not occur under rated voltage.

[0041] Furthermore, relays K1, K2, K3, K4, and K5 are all equipped with auxiliary contacts, which are respectively connected to the input terminals of the battery management system (BMS) or the vehicle control unit (VCU).

[0042] Relays K1, K2, K3, K4, and K5 are used to provide feedback on the actual on / off status of the relays. The Battery Management System (BMS) or Vehicle Control Unit (VCU) monitors the status of the auxiliary contacts and compares it with the relay control commands. If an inconsistency is detected, the relay is determined to be faulty and an alarm is issued. At the same time, subsequent high-voltage on / off operations are prohibited.

[0043] Furthermore, a voltage sampling circuit is connected in parallel between port DC+ and port DC-. The voltage sampling circuit includes a voltage divider resistor network and an isolation operational amplifier. The output of the voltage sampling circuit is connected to the ADC input of the battery management system (BMS).

[0044] The voltage sampling circuit is used to monitor the voltage value of the DC bus in real time. When the battery management system (BMS) detects that the voltage polarity between port DC+ and port DC- is negative, it determines that the external load is reverse connected, immediately prevents the closing of relays K1 and K2, and sends a load reverse connection alarm message to the VCU through the CAN1 bus.

[0045] Furthermore, the pre-charge resistor R is an NTC thermistor or a PTC thermistor.

[0046] The resistance of the pre-charge resistor R increases with temperature to ensure the safety of the circuit operation.

[0047] Furthermore, a freewheeling diode is connected in parallel across the two ends of the relay K3. The cathode of the freewheeling diode is connected to the positive terminal of the coil of the relay K3, and the anode of the freewheeling diode is connected to the negative terminal of the coil of the relay K3.

[0048] The freewheeling diode D1 is used to absorb the reverse induced electromotive force generated by the coil when the relay K3 is disconnected, so as to prevent the induced voltage from damaging the drive circuit of the BMS.

[0049] A control method for preventing reverse connection of load in lithium battery power supply includes the following steps: Step S1: The system sets the front end of relay K1 of the lithium battery pack subsystem to the DC+ polarity of the lithium battery pack, and sets the bus relay K4 of the vehicle power load subsystem to the DC+ polarity of the load. Step S2: When the lithium battery pack subsystem is powered on at low voltage, the battery management system (BMS) enters a self-test. After the self-test shows no abnormalities, it actively shakes hands with the vehicle controller (VCU) of the vehicle power load subsystem via the CAN1 bus to exchange information and confirm the status. Step S3: The vehicle control unit (VCU) of the vehicle power load subsystem initiates a battery polarity detection request to the battery management system (BMS) via the CAN1 bus; Step S4: After receiving the high voltage polarity detection request reported by the VCU, the Battery Management System (BMS) first actively detects whether there is a short circuit or low insulation at the external terminals of relays K1 and K2 through the high voltage acquisition points LINK+ and LINK-. If there is no abnormality, relay K2 is actively closed, and then the pre-charge unit is started. After the pre-charge is successful, relay K1 is closed and pre-charge relay K3 is released. At the same time, the detected voltage value and the polarity information of relay K1 are sent to the vehicle controller (VCU) of the vehicle power load subsystem through the CAN1 bus. Step S5: After receiving the information from the Battery Management System (BMS) regarding the closure of relays K1 and K2 and their high-voltage polarity, the Vehicle Control Unit (VCU) of the Vehicle Power Load Subsystem (VCU) keeps relays K4 and K5 open. It then uses the CAN1 bus to control the Insulation Detection Module (IMD) to detect the high voltage at the external terminals of relays K4 and K5 and the polarity data of relay K4. The VCU compares the polarities of relays K1 and K4. If they are inconsistent, it determines that the load is reversed, refuses to close relays K4 and K5, and sends an error message to the BMS via the CAN1 bus, instructing the BMS to disconnect relays K1 and K2.

[0050] Step S1 explicitly designates K1 and K4 as DC+ polarity terminals, avoiding misjudgments caused by unclear polarity definitions and ensuring a clear and consistent polarity detection logic for the entire system. This provides a clear polarity identifier for system assembly and maintenance, allowing assembly personnel to perform correct wiring and reducing the probability of human error. Establishing a mapping relationship between physical relays and software-defined polarity terminals facilitates programmed judgment by the BMS and VCU.

[0051] Step S2: Before entering high-voltage operation, the BMS performs a self-check, including internal communication, sensors, and drive circuits, to ensure it is in good health and prevent high-voltage operation from being performed if the BMS is faulty. An active handshake confirms normal CAN1 bus communication, ensuring reliable transmission of subsequent polarity detection requests and information exchange, preventing control command loss due to communication interruption. The BMS and VCU synchronize their states through a handshake, confirming each other's readiness and laying the foundation for subsequent collaborative operation. If the self-check fails or the handshake fails, the system can terminate the process early and issue an alarm to avoid blindly entering high-voltage operation with an unclear system status, reducing safety risks.

[0052] Step S3, where the VCU initiates the testing process, demonstrates the proactive participation of the vehicle's power load subsystem, rather than passively waiting for information from the battery side, thus forming a two-way interactive collaborative working mechanism. Through a request-response interaction mode, each step of the testing process becomes traceable and recordable, facilitating fault diagnosis and system debugging. The timing for initiating polarity testing is clearly defined as after the VCU has completed its own initialization, ensuring that the load side is ready and avoiding testing when the load side is not ready.

[0053] Step S4 checks for short circuits or low insulation faults in the external circuit via LINK+ and LINK- before closing any high-voltage relays. This design is crucial—if the external circuit is short-circuited, directly closing the relay will result in a huge short-circuit current, potentially burning out the relay, damaging the battery pack, or even causing a fire. Pre-detection allows for timely termination of operation before a fault occurs, protecting the system. The motor controller contains a large-capacity bus capacitor. If K1 is closed directly, the initial capacitor voltage is 0, equivalent to a short circuit, generating an inrush current several times the rated current. The pre-charge unit limits the charging current through K3 and the pre-charge resistor R, causing the bus capacitor voltage to rise slowly. When the voltage reaches a preset threshold, K1 is closed. At this point, the voltage difference across K1 is very small, and there is virtually no inrush current at the moment of closure—this mechanism effectively protects the relay contacts, bus capacitor, and battery pack, extending system life.

[0054] In step S5, the system sets the polarity of K1 to DC+. The information reported by the BMS confirms this setting. The IMD detects the actual polarity of the external terminal of K4. If the load wiring is correct, the external terminal of K4 should be DC+; if the load is reversed, the external terminal of K4 should be DC-. The VCU obtains these two pieces of information through the CAN bus and compares them. If they match, it is safe; if they do not match, it is determined that the load is reversed. This comparison mechanism solves the problem of load reversal detection at the system architecture level, without relying on manual judgment.

[0055] Furthermore, in step S4, starting the pre-charge unit specifically involves closing relay K3, allowing current to flow through pre-charge resistor R to port DC+, pre-charging the bus capacitor inside the motor controller MCU; when the bus capacitor voltage rises to a preset proportional threshold of the lithium battery pack voltage, the pre-charge is determined to be successful, relay K1 is closed, and then relay K3 is opened to complete the pre-charge process.

[0056] The technical design of the pre-charge process in step S4 of this invention, through limiting the charging current, accurately judging the voltage threshold, and controlling the sequence of relays, avoids contact welding and erosion by closing K1 under extremely small voltage differences, thus increasing the electrical life of K1 from tens of cycles to tens of thousands or even hundreds of thousands of cycles. The smooth charging process avoids the impact of high dV / dt on the electrolytic capacitor, preventing failure modes such as capacitor bulging, breakdown, and explosion. It eliminates the impact of instantaneous high current on the battery terminals and internal structure, reducing the risk of battery thermal runaway and extending battery pack life. Through voltage threshold judgment, the BMS can monitor the pre-charge status in real time, promptly detect charging anomalies, and take protective measures. The complete pre-charge mechanism enables the system to adapt to motor controllers of different capacities and brands, improving the system's versatility and reliability.

[0057] Furthermore, in step S5, comparing the polarities of relays K1 and K4 specifically involves the vehicle controller (VCU) acquiring the relay K1 polarity information reported by the battery management system (BMS), which indicates that the front-end connection point of relay K1 is DC+ polarity; the VCU also acquires the relay K4 external polarity detection result reported by the insulation detection module (IMD). If the detected polarity at the external end of relay K4 is DC+, the polarities are considered to be consistent; if the detected polarity at the external end of relay K4 is DC-, the polarities are considered to be inconsistent, indicating a reverse load connection.

[0058] The polarity comparison process in step S5 of this invention involves the VCU precisely comparing the K1 polarity information reported by the BMS with the K4 external polarity detection result reported by the IMD. The polarity information from the battery side and the load side comes from two completely independent detection systems, creating detection source redundancy. An anomaly in either detection source will not lead to a misjudgment. The polarity comparison logic is simple and clear: DC+ matches DC+, and DC+ does not match DC-, making it easy to implement in software, test and verify, and analyze faults. The polarity comparison is completed before K4 and K5 are closed, and closure is only allowed if the polarities match, achieving proactive fault prevention rather than passive protection. Once a polarity inconsistency is detected, the VCU immediately refuses to close K4 / K5 and notifies the BMS to disconnect K1 / K2, isolating the fault within milliseconds. The polarity comparison results and fault information are recorded and reported via the CAN bus, facilitating subsequent fault analysis and system optimization. The entire comparison process is completed automatically by the system, requiring no manual inspection or confirmation, fundamentally solving the load reversal problem caused by insufficient professional skills of assembly and debugging personnel.

[0059] Furthermore, in step S5, after reporting an error to the battery management system (BMS) via the CAN1 bus, the BMS performs the following protection actions: disconnecting relay K1 and battery management system K2 to cut off the external output of the lithium battery pack; recording the fault information to the local memory; and continuously sending load reverse connection alarm information via the CAN1 bus until the fault is cleared and the system is manually reset.

[0060] The three protection actions performed by the BMS in step S5 of this invention—disconnecting K1 and K2, recording fault information, and continuously sending alarm information—constitute a complete, reliable, and intelligent fault response mechanism. The BMS immediately disconnects K1 and K2, completely severing the connection between the lithium battery pack and the outside world at the physical level, preventing reverse current flow and fault expansion. This is the most crucial and critical part of the protection actions. Recording fault information to local memory provides valuable first-hand data for subsequent fault analysis, responsibility identification, and system optimization, achieving closed-loop fault management. Continuously sending alarm information via the CAN bus ensures that all relevant nodes—VCU, IMD, instruments, and remote platforms—can be aware of the fault status in real time. Simultaneously, a manual reset mechanism forces operators to confirm that the fault has been resolved, preventing accidental system recovery without a clear fault solution. These three protection actions work together to form a complete protection chain from logical prevention to physical isolation, from state locking to manual reset. Failure of any single link will not cause the system to power on in a faulty state. The system can automatically identify, isolate, record, and alarm faults. At the same time, it guides operators to troubleshoot faults correctly through clear alarm prompts and manual reset procedures, which reduces the reliance on the professional skills of operators and ensures the standardization of fault handling.

[0061] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A protection circuit for reverse connection of load in lithium battery power supply, characterized in that, It includes a lithium battery pack subsystem and a vehicle power load subsystem; the lithium battery pack subsystem includes a lithium battery pack and a battery management system (BMS), and the vehicle power load subsystem includes an insulation detection module (IMD), a vehicle control unit (VCU), and a motor control unit (MCU). The lithium battery pack is communicatively connected to the battery management system (BMS); the positive terminal of the lithium battery pack is connected to the high voltage acquisition point PACK+, one end of relay K1, and one end of relay K3; the other end of relay K1 is connected to the DC+ port. The other end of relay K3 is connected to one end of pre-charge resistor R, and the other end of pre-charge resistor R is connected to port DC+; port DC+ is connected to high-voltage acquisition point LINK+. The negative terminal of the lithium battery pack is connected to the high-voltage acquisition point PACK- and one end of the relay K2; the other end of the relay K2 is connected to the port DC-; the port DC- is connected to the high-voltage acquisition point LINK-. Port DC+ is connected to the motor controller MCU via relay K4; port DC+ is connected to the insulation detection module IMD via detection line LOAD+; the battery management system BMS is connected to the insulation detection module IMD and the vehicle controller VCU via CAN1 bus. The vehicle control unit (VCU) is connected to the motor control unit (MCU) via the CAN2 bus. Port DC is connected to the insulation detection module IMD via the detection line LOAD; Port DC is connected to the motor controller MCU via relay K5.

2. The protection circuit against reverse connection under load for lithium batteries according to claim 1, characterized in that, The relays K1, K2, K3, K4, and K5 are all high-voltage DC relays, and their rated voltage is not lower than the rated voltage of the lithium battery pack.

3. The protection circuit against reverse connection under load for lithium batteries according to claim 2, characterized in that, The relays K1, K2, K3, K4, and K5 are all equipped with auxiliary contacts, which are respectively connected to the input terminals of the battery management system (BMS) or the vehicle control unit (VCU).

4. The protection circuit against reverse connection under load for lithium batteries according to claim 1, characterized in that, A voltage sampling circuit is connected in parallel between port DC+ and port DC-. The voltage sampling circuit includes a voltage divider resistor network and an isolation operational amplifier. The output of the voltage sampling circuit is connected to the ADC input of the battery management system (BMS).

5. The protection circuit against reverse connection under load for lithium batteries according to claim 1, characterized in that, The pre-charge resistor R is an NTC thermistor or a PTC thermistor.

6. The protection circuit against reverse connection under load for lithium batteries according to claim 2, characterized in that, A freewheeling diode is connected in parallel across the two ends of the relay K3. The cathode of the freewheeling diode is connected to the positive terminal of the coil of the relay K3, and the anode of the freewheeling diode is connected to the negative terminal of the coil of the relay K3.

7. The control method of the lithium battery power supply reverse connection protection circuit according to any one of claims 1-6, characterized in that, Includes the following steps: Step S1: The system sets the front end of relay K1 of the lithium battery pack subsystem to the DC+ polarity of the lithium battery pack, and sets the bus relay K4 of the vehicle power load subsystem to the DC+ polarity of the load. Step S2: When the lithium battery pack subsystem is powered on at low voltage, the battery management system (BMS) enters a self-test. After the self-test shows no abnormalities, it actively shakes hands with the vehicle controller (VCU) of the vehicle power load subsystem via the CAN1 bus to exchange information and confirm the status. Step S3: The vehicle control unit (VCU) of the vehicle power load subsystem initiates a battery polarity detection request to the battery management system (BMS) via the CAN1 bus; Step S4: After receiving the high voltage polarity detection request reported by the VCU, the Battery Management System (BMS) first actively detects whether there is a short circuit or low insulation at the external terminals of relays K1 and K2 through the high voltage acquisition points LINK+ and LINK-. If there is no abnormality, relay K2 is actively closed, and then the pre-charge unit is started. After the pre-charge is successful, relay K1 is closed and pre-charge relay K3 is released. At the same time, the detected voltage value and the polarity information of relay K1 are sent to the vehicle controller (VCU) of the vehicle power load subsystem through the CAN1 bus. Step S5: After receiving the information from the Battery Management System (BMS) that relays K1 and K2 are closed and their high voltage polarity, the Vehicle Control Unit (VCU) of the Vehicle Power Load Subsystem (VCU) keeps relays K4 and K5 open and controls the Insulation Detection Module (IMD) via the CAN1 bus to detect the high voltage at the external terminals of relays K4 and K5 and the polarity data of relay K4. The vehicle control unit (VCU) compares the polarities of relays K1 and K4. If they are not in agreement, it determines that the load is reversed, refuses to close relays K4 and K5, and reports an error to the battery management system (BMS) via the CAN1 bus, notifying the BMS to disconnect relays K1 and K2.

8. The control method of the load reverse connection protection circuit for lithium battery power supply according to claim 7, characterized in that, In step S4, starting the pre-charge unit specifically involves closing relay K3, allowing current to flow through pre-charge resistor R to port DC+, pre-charging the bus capacitor inside the motor controller MCU; when the bus capacitor voltage rises to a preset proportional threshold of the lithium battery pack voltage, the pre-charge is determined to be successful, relay K1 is closed, and then relay K3 is opened to complete the pre-charge process.

9. The control method for the reverse connection protection circuit for lithium battery power supply according to claim 8, characterized in that, In step S5, comparing whether the polarities of relay K1 and relay K4 are consistent specifically involves the vehicle controller (VCU) obtaining the relay K1 polarity information reported by the battery management system (BMS), which indicates that the front-end connection point of relay K1 is DC+ polarity. The vehicle control unit (VCU) obtains the polarity detection result of the external terminal of relay K4 reported by the insulation detection module (IMD). If the polarity detected at the external terminal of relay K4 is DC+, it is determined that the polarity is consistent; if the polarity detected at the external terminal of relay K4 is DC-, it is determined that the polarity is inconsistent and there is a reverse load connection.

10. The control method for the reverse connection protection circuit for lithium battery power supply according to claim 9, characterized in that, In step S5, after reporting an error to the battery management system (BMS) via the CAN1 bus, the BMS performs the following protection actions: disconnecting relay K1 and battery management system K2 to cut off the external output of the lithium battery pack; recording the fault information to the local memory; and continuously sending load reverse connection alarm information via the CAN1 bus until the fault is cleared and the system is manually reset.

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