Relay detection circuit

Abstract

The utility model relates to the technical field of new energy automobile fault detection, and specifically relates to a relay detection circuit. The pre-charging relay and the pre-charging resistor are connected in series, then are connected in parallel with the main positive relay and are connected to the positive electrode of the power battery, the main negative relay is connected to the negative electrode of the power battery, and the quick-charging relay is connected to the rear end of the main positive relay after being connected in parallel with the load; the first voltage measuring device is bridged at two ends of the power battery; the second voltage measuring device is connected to the outer end of the main positive relay; the third voltage measuring device is connected to the outer end of the main negative relay; the fourth voltage measuring device is used for measuring the outer end voltage of the fast charging relay; the fourth voltage measuring device is connected to the outer end of the fast charging relay; and the battery management system is used for acquiring voltage data and judging whether a fault exists or not. According to the technical scheme, the problems of complex relay adhesion detection circuit, high detection input cost and tedious detection logic can be solved.

Description

TECHNICAL FIELD

[0001] The utility model relates to new energy automobile fault detection technical field, concretely relates to a relay detection circuit. BACKGROUND

[0002] With the vigorous development of new energy automobile industry, as the switching device of controlling current communication and cut-off, relay is widely used in the circuit system of new energy automobile. However, in the actual application process, due to improper control strategy, poor working environment or other external factors, relay often faces overload operation, and then causes relay sticking problem. Relay sticking, that is, relay cannot normally open due to the sticking between contact points in the closed state, this fault phenomenon not only can cause circuit anomaly and equipment damage, but also can cause serious safety accidents, and threatens the life and property safety of passengers.

[0003] In view of the importance of relay in automobile high-voltage electrical safety, its switching state and fault diagnosis become the research focus. At present, although the relay with feedback can provide state information to a certain extent, its reliability is poor, and false failure often occurs, which not only increases the maintenance cost, but also may cause new safety hazards due to misoperation.

[0004] In the field of high-voltage battery control, although enterprises have made significant progress in the research of power battery management system, there is still a lack of in-depth research on the control and fault detection of stateless feedback relay. Some researchers have made preliminary exploration, but most of them are still at the theoretical research stage, and no mature and reliable solution has been formed. Therefore, it is particularly urgent to develop a simple, efficient and low-cost relay sticking detection circuit to solve the problems of complex circuit, high detection investment cost and complicated detection logic in current relay sticking detection. UTILITY MODEL CONTENT

[0005] The utility model aims at: propose a simple, efficient, low-cost relay sticking detection circuit, which can solve the problems of complex relay sticking detection circuit, high detection investment cost and complicated detection logic.

[0006] To achieve the above-mentioned purpose, the relay detection circuit provided by the embodiment of the present disclosure comprises a pre-charging relay, a pre-charging resistor, a main positive relay, a main negative relay, a fast-charging relay, a first voltage measuring device, a second voltage measuring device, a third voltage measuring device and a fourth voltage measuring device.

[0007] The pre-charging relay and the pre-charging resistor are connected in series and connected in parallel with the main positive relay, and are connected to the positive electrode of the power battery. The main negative relay is connected to the negative electrode of the power battery.

[0008] The first voltage measuring device is connected across the power battery for measuring the voltage across the power battery.

[0009] The second voltage measuring device is connected to the outer end of the main positive relay for measuring the outer end voltage of the main positive relay under different working conditions.

[0010] The third voltage measuring device is connected to the outer end of the main negative relay for measuring the outer end voltage of the main negative relay, and the fourth voltage measuring device is used for measuring the outer end voltage of the fast charging relay.

[0011] The fourth voltage measuring device is connected to the outer end of the fast charging relay for measuring the outer end voltage of the fast charging relay.

[0012] The battery management system further comprises a controller for continuously acquiring voltage data collected by each voltage collecting device and determining whether a fault exists according to the voltage data.

[0013] The beneficial effects of the basic scheme: In terms of high-voltage electrical safety of the automobile, the switching state of the relay and fault diagnosis are crucial. The technical scheme can identify and report faults under specific working conditions when the relay itself fails, so that relevant personnel can take timely measures to avoid serious safety accidents caused by relay failure, greatly improving the safety of the automobile high-voltage electrical system.

[0014] By setting the first, second, third and fourth voltage measuring devices, the voltage across the power battery, the outer end voltage of the main positive relay, the outer end voltage of the main negative relay and the outer end voltage of the fast charging relay are measured respectively. The controller of the battery management system continuously acquires these voltage data, and can accurately determine whether a fault exists based on the voltage data. Compared with traditional feedback relays, the accuracy of fault detection is greatly improved, avoiding unnecessary maintenance and safety hazards caused by false fault reports.

[0015] The technical scheme can correctly respond to the request of closing and opening the relay of the whole vehicle. Whether it is the regular control of the relay state during normal operation of the vehicle or in special working conditions, it can quickly and accurately perform related operations, ensuring the stable operation of the automobile high-voltage electrical system.

[0016] As a preferred embodiment, the controller is further configured to receive instructions from the vehicle control unit and control the closing or opening of the relay according to the instructions.

[0017] As a preferred embodiment, the battery management system further comprises an alarm module for reporting fault information when a fault is determined.

[0018] As an implementable preferred solution, during the starting stage of the vehicle, the controller is configured to acquire the voltage across the power battery measured by the first voltage measuring device V1 and the voltage at the outer end of the main positive relay measured by the second voltage measuring device V2, and determine whether the main positive relay or the pre-charging relay is stuck by comparing the voltage difference between V1 and V2 with a sticking detection judgment threshold.

[0019] As an implementable preferred solution, when the battery management system receives the high-voltage raising instruction sent by the vehicle control unit, the controller is configured to acquire the voltage across the power battery measured by the first voltage measuring device V1 and the voltage at the outer end of the main positive relay measured by the second voltage measuring device V2, and determine whether the pre-charging fails and whether the pre-charging relay is unable to close by comparing the voltage difference between V1 and V2 with a pre-charging failure judgment threshold and a pre-charging closing judgment threshold.

[0020] As an implementable preferred solution, after the pre-charging relay is successfully closed, the controller is configured to acquire the voltage across the power battery measured by the first voltage measuring device V1 and the voltage at the outer end of the main negative relay measured by the third voltage measuring device V3, and determine whether the main negative relay is unable to close by comparing the voltage difference between V1 and V3 with a main negative relay closing judgment threshold. When the main negative relay is successfully closed and the pre-charging relay is disconnected, the controller is configured to determine whether the main positive relay is unable to close by comparing the voltage difference between V1 and V3 with the main negative relay closing judgment threshold.

[0021] As an implementable preferred solution, when the vehicle enters the charging process, the controller is configured to acquire the voltage at the outer end of the main negative relay measured by the third voltage measuring device V3 and the voltage at the outer end of the fast-charging relay measured by the fourth voltage measuring device V4, and determine whether the fast-charging relay is unable to close by comparing the voltage difference between V3 and V4 with a fast-charging relay closing detection threshold.

[0022] As an implementable preferred solution, the controller is provided with a longest detection time threshold of the fast-charging relay closing.

[0023] As an implementable preferred solution, when the battery management system is in a high-voltage state and receives the high-voltage lowering instruction sent by the vehicle control unit, the controller is configured to acquire the voltage data collected by the first voltage measuring device V1 and the third voltage measuring device V3, and determine whether the main positive relay is stuck by comparing the voltage difference between V3 and V4 with a main positive relay sticking judgment threshold.

[0024] As an implementable preferred solution, after the vehicle is in the discharging mode and successfully high-voltage, or in the charging mode, when the controller detects the termination charging instruction to exit the charging, the controller is used to obtain the voltage data collected by the third voltage detection device V3 and the fourth voltage detection device V4, and judge whether the fast charging relay exists the sticking fault by comparing the voltage difference of V3 and V4 with the sticking judgment threshold of the fast charging relay. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is a structural schematic diagram of a relay detection circuit. DETAILED DESCRIPTION

[0026] In order to make the technical scheme of the present application and its advantages clearer, the technical scheme of the present application will be further described in detail below with reference to the drawings. It can be understood that the specific embodiments described herein are only part of the embodiments of the present application, and are only used to explain the present application, but not to limit the present application. It should be noted that the technical features or combinations of technical features described in the following embodiments should not be considered in isolation, and they can be combined with each other to achieve better technical effects. The same reference numerals in the drawings of the following embodiments represent the same features or components, which can be applied to different embodiments.

[0027] In the description of the present application, it should be noted that, unless otherwise explicitly specified and limited, the terms "set", "connected" should be understood in a broad sense. For example, it can be fixedly connected, or detachably connected, or integrally connected; it can be mechanically connected (including various mechanical connection forms, such as shaft coupling or gear pair, etc.), or electrically connected; it can be directly connected, or indirectly connected through an intermediate medium; it can be the communication inside two elements. For ordinary skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0028] In addition, unless otherwise defined, the technical terms or scientific terms used in the description of the present application should be understood as the general meaning of the technical terms or scientific terms understood by the ordinary skilled in the art to which the present application belongs.

[0029] The present application will be further described in detail below with reference to the drawings:

[0030] Reference signs: power battery 1, pre-charging relay 2, pre-charging resistor 3, main positive relay 4, main negative relay 5, fast charging relay 6, first voltage measurement device V1, second voltage measurement device V2, third voltage measurement device V3, fourth voltage measurement device V4.

[0031] Reference Figure 1The application relates to a relay detection circuit based on the main circuit architecture of a new energy automobile power battery, which comprises a pre-charging relay 2, a pre-charging resistor 3, a main positive relay 4, a main negative relay 5, a fast-charging relay 6, a first voltage measuring device V1, a second voltage measuring device V2, a third voltage measuring device V3 and a fourth voltage measuring device V4.

[0032] The pre-charging relay 2 and the pre-charging resistor 3 are connected in series and then connected in parallel with the main positive relay 4, and are connected to the positive pole of the power battery 1; the main negative relay 5 is connected to the negative pole of the power battery 1; and the fast-charging relay 6 is connected to the rear end of the main positive relay 4 after being connected in parallel with a load (an electric appliance).

[0033] The first voltage measuring device V1 is connected across the power battery 1, and is used for measuring the voltage across the power battery 1 and obtaining the total voltage value of the battery.

[0034] The second voltage measuring device V2 is connected to the outer end (the end far from the load) of the main positive relay 4, and is used for measuring the outer end voltage of the main positive relay 4 under different working conditions.

[0035] The third voltage measuring device V3 is connected to the outer end (the end far from the load) of the main negative relay 5, and is used for measuring the outer end voltage of the main negative relay 5.

[0036] The fourth voltage measuring device V4 is connected to the outer end (the end far from the load) of the fast-charging relay 6, and is used for measuring the outer end voltage of the fast-charging relay 6.

[0037] The application further comprises a battery management system (BMS), wherein the BMS comprises a controller and an alarm module; the controller is used for receiving the instructions of a vehicle control unit (VCU) and controlling the closing or opening of the relay according to the instructions; the controller is further used for continuously obtaining the voltage data collected by each voltage collecting device during the processes of vehicle power-on, high-voltage application and charging and discharging, and judging whether faults exist according to the data; when faults are found, the faults are reported, and the reporting content comprises the fault codes corresponding to the faults.

[0038] At the starting stage of the new energy vehicle, the vehicle end first supplies power to the battery management system (BMS) controller, prompting it to enter the working state. At this time, the BMS detects whether the main positive and pre-charging relays 2 exist adhesion conditions. The BMS controller obtains the voltage between the power battery measured by the first voltage measuring device V1 and the voltage at the outer end of the main positive relay 4 measured by the second voltage measuring device V2, compares the voltage data collected by V1 and V2, judges the size relationship of |V1-V2| (voltage difference), and in one embodiment, considering the measurement error and the possible small voltage fluctuation in the circuit, the adhesion detection judgment threshold is set to 20V. If the sampling voltage |V1-V2|≤20V, it is judged that the relay is stuck, and the alarm module reports the main positive or pre-charging relay 2 sticking fault code, so as to avoid the serious consequences of circuit abnormalities, equipment damage and other serious consequences caused by relay sticking; otherwise, the relay is not stuck.

[0039] When the BMS receives the high voltage raising instruction issued by the VCU (Vehicle Control Unit), the pre-charging process is started, and the pre-charging process is closely monitored. In this process, the BMS controller obtains the voltage between the power battery measured by the first voltage measuring device V1 and the voltage at the outer end of the main positive relay 4 measured by the second voltage measuring device V2, and judges the size relationship of |V1-V2|. In one embodiment, the pre-charging failure judgment threshold is 10V, and if the sampling voltage difference |V1-V2|>10V, it indicates that the pre-charging process may have a timeout problem. The BMS will continuously monitor the voltage difference |V1-V2|. If |V1-V2|≤10V after three consecutive attempts, it means that the pre-charging process has experienced ups and downs, but eventually succeeds, and the vehicle can continue the subsequent high voltage raising operation. Otherwise, if |V1-V2| is still >10V after three consecutive attempts, the alarm module will report the information that the pre-charging at the time of reporting the fault does not allow high voltage raising again, and the vehicle is prohibited from continuing to execute the high voltage raising instruction, in order to prevent the vehicle electrical system from being damaged due to pre-charging failure.

[0040] When the BMS receives the high voltage raising instruction issued by the VCU, the BMS will detect whether the pre-charging relay 2 can normally close, the BMS controller obtains the voltage data collected by the first voltage detection device V1 and the second voltage detection device V2, and judges the size relationship of |V1-V2|. In one embodiment, the pre-charging closing judgment threshold is 20V, and if the BMS sampling voltage |V1-V2|>20V, it indicates that the pre-charging relay 2 may not be able to close normally. At this time, the alarm module will report the pre-charging relay 2 cannot close fault, reminding the vehicle maintenance personnel to check and maintain the pre-charging relay 2 and related circuit in time. Otherwise, if |V1-V2|≤20V, it indicates that the pre-charging relay 2 is successfully closed, and the pre-charging circuit is working normally. The BMS will continue to follow the vehicle starting process to promote the subsequent operation.

[0041] After the pre-charge relay 2 is successfully closed, the BMS will receive a command to close the main negative relay 5, and the BMS will immediately detect the closing state of the main negative relay 5. The BMS controller acquires the voltage between the power battery measured by the first voltage detection device VI and the voltage at the outer end of the main negative relay 5 measured by the third voltage detection device V3, compares the voltage data collected by VI and V3, and determines the size relationship of |VI-V3|. In an embodiment, the threshold for determining whether the main negative relay 5 is closed is 20V. If |VI-V3| > 20V, it indicates that the main negative relay 5 fails to close, which may be due to a fault in the main negative relay 5 itself, such as contact burnout, coil damage, etc., or a problem in its control circuit, resulting in failure to close normally. The alarm module will immediately report that the main negative relay 5 fails to close, and the vehicle control system will take appropriate safety measures based on this fault information, such as prohibiting the vehicle from starting or limiting the vehicle's operating range, to ensure the safety of the vehicle and personnel. Conversely, if |VI-V3| ≤ 20V, it indicates that the main negative relay 5 is successfully closed, and the negative loop of the vehicle electrical system is normally connected, and the BMS will continue subsequent operations, such as detecting the closing state of the main positive relay 4.

[0042] After the main negative relay 5 is successfully closed and the pre-charge relay 2 is disconnected, the BMS will detect the closing state of the main positive relay 4. The BMS controller again determines whether the main positive relay 4 can be normally closed based on the voltage data collected by the first voltage detection device VI and the third voltage detection device V3 by judging the size relationship of |VI-V3|.

[0043] In an embodiment, the threshold for detecting whether the main positive relay 4 is closed is 20V. If |VI-V3| > 20V, it indicates that the main positive relay 4 fails to close. After the main negative relay 5 is closed, if the main positive relay 4 can be normally closed, the voltage at the outer end of the main positive relay 4 should be similar to the positive voltage of the power battery, and the difference between the voltage at the outer end of the main positive relay 4 and the voltage between the power battery should be small. The alarm module will report that the main positive relay 4 fails to close, and the vehicle control system will take appropriate measures based on the fault condition, such as cutting off the high-voltage power supply to prevent abnormal circuit and safety accidents caused by the main positive relay 4 not being closed. Conversely, if |VI-V3| ≤ 20V, it indicates that the main positive relay 4 is successfully closed, and the high-voltage power supply loop of the vehicle is completely connected, and the vehicle can enter a normal operating or charging state.

[0044] When the vehicle enters the charging process, the BMS detects the closing state of the fast charging relay 6 after detecting the closing instruction of the fast charging relay 6. The BMS controller obtains the voltage at the outer end of the main negative relay 5 measured by the third voltage detection device V3 and the voltage at the outer end of the fast charging relay 6 measured by the fourth voltage detection device V4, and determines whether the fast charging relay 6 can be normally closed by judging the size relationship of the voltage difference |V3-V4|.

[0045] In an embodiment, the fast charging relay 6 closing detection threshold is 20V. If |V3-V4|>20V, it indicates that the fast charging relay 6 fails to close, which may be due to faults in the fast charging relay 6 itself, such as poor contact of the contacts, coil failure, etc., or due to abnormalities in the charging circuit, causing the fast charging relay 6 to fail to close normally. The alarm module will report that the fast charging relay 6 fails to close, and the vehicle charging system will stop the charging operation to prevent charging abnormalities and equipment damage caused by the failure of the fast charging relay 6 to close.

[0046] On the contrary, if |V3-V4|≤20V, it indicates that the fast charging relay 6 is successfully closed, and the vehicle can smoothly enter the DC charging state. The BMS will continue to monitor and control the charging process in real time.

[0047] In an embodiment, a longest detection time threshold for the closing of the fast charging relay 6 is set in the BMS controller. If |V3-V4|≤20V cannot be detected within the time, it is determined that the fast charging relay 6 fails to close and the fault is reported, further improving the accuracy of detection and the timeliness of the alarm.

[0048] When the BMS is in a high-voltage state and receives a high-voltage lowering instruction sent by the VCU, the BMS will detect the disconnection state of the main positive relay 4. The BMS judges the size relationship of |V1-V3| by obtaining the voltage data collected by the first voltage detection device V1 and the third voltage detection device V3.

[0049] In an embodiment, the main positive relay 4 sticking judgment threshold is 20V. If |V1-V3|≤20V, it indicates that the main positive relay 4 may fail to disconnect, i.e., the main positive relay 4 is stuck, indicating that the contacts of the main positive relay 4 may be stuck due to long-term use or other reasons, causing the main positive relay 4 to fail to disconnect normally. The BMS will timely report the sticking fault of the main positive relay 4, and the vehicle control system will take emergency measures, such as cutting off the high-voltage power supply, to ensure the safety of the vehicle and personnel. On the contrary, if |V1-V3|>20V, it indicates that the main positive relay 4 is successfully disconnected, and the vehicle high-voltage system performs the high-voltage lowering operation according to the normal process.

[0050] After the vehicle receives the high-voltage command from the VCU and successfully closes the pre-charge relay 2, the BMS will monitor the status of the main negative relay 5 before detecting the closing command of the main negative relay 5. The BMS determines the magnitude relationship of |V1-V3| by acquiring the voltage data collected by the first voltage acquisition device V1 and the third voltage acquisition device V3.

[0051] In one embodiment, the threshold for judging the sticking of the main negative relay 5 is 20V. If |V1-V3|≤20V, it indicates that the main negative relay 5 may be stuck, meaning the contacts of the main negative relay 5 may have stuck together, preventing it from disconnecting normally. The alarm module will report the main negative relay sticking fault, and the vehicle control system will take corresponding measures according to the fault situation, such as prohibiting high-voltage operation to prevent circuit abnormalities and safety accidents caused by the sticking of the main negative relay 5. Conversely, if |V1-V3|>20V, it indicates that the main negative relay 5 is in a normal open state, and the BMS will continue to wait for the main negative relay 5 to close and proceed with subsequent operations according to the normal procedure.

[0052] After the vehicle is in discharge mode and successfully connected to high voltage, the BMS continuously monitors the status of the fast charging relay 6. The BMS controller determines the relationship between |V3-V4| by acquiring voltage data collected by the third voltage detection device V3 and the fourth voltage detection device V4.

[0053] In one embodiment, the fast-charging relay 6 adhesion detection threshold is 20V. In discharge mode, if |V3-V4|>20V, it indicates that the fast-charging relay 6 may be stuck, meaning the contacts of the fast-charging relay 6 may have become stuck, preventing normal disconnection. In this case, the alarm module will record the fault flag but will not report the fault immediately. When the vehicle mode switches to charging mode, the BMS will immediately report the fast-charging relay 6 adhesion fault, reminding vehicle maintenance personnel to check and repair the fast-charging relay 6 in a timely manner. Conversely, if |V3-V4|≤20V, it indicates that the fast-charging relay 6 is in a normal disconnected state, and the vehicle can continue to discharge.

[0054] In charging mode, when a charging termination command is detected and charging is stopped, if |V3-V4|≤20V, it indicates that the fast charging relay 6 may have failed to disconnect, meaning that the fast charging relay 6 has become stuck. The contacts of the fast charging relay 6 may have become stuck due to long-term use or other reasons, preventing normal disconnection. The alarm module will report the fast charging relay 6 sticking fault, and the vehicle charging system will stop charging and take appropriate safety measures, such as cutting off the charging power supply, to prevent charging abnormalities and equipment damage caused by the sticking of the fast charging relay 6. Conversely, if |V3-V4|>20V, it indicates that the fast charging relay 6 has successfully disconnected, and the vehicle can smoothly exit the charging state.

[0055] The battery management system (BMS) also includes a storage module that is communicatively connected to the controller for storing historical records of relay sticking or other faults.

[0056] The above content is merely an embodiment of this utility model. Commonly known structures and characteristics are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, are aware of all existing technologies in that field, and have the ability to apply conventional experimental methods prior to that date. Those skilled in the art can improve and implement this solution based on the guidance provided in this application and their own capabilities. Typical known structures or methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of this utility model. These should also be considered within the scope of protection of this utility model, and will not affect the effectiveness of the implementation of this utility model or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A relay detection circuit, characterized in that: It includes a pre-charge relay, a pre-charge resistor, a main positive relay, a main negative relay, a fast-charge relay, a first voltage measuring device, a second voltage measuring device, a third voltage measuring device, and a fourth voltage measuring device; The pre-charge relay and the pre-charge resistor are connected in series and then in parallel with the main positive relay, and connected to the positive terminal of the power battery. The main negative relay is connected to the negative terminal of the power battery. The fast charging relay is connected in parallel with the load and then connected to the rear end of the main positive relay. The first voltage measuring device is connected across the two ends of the power battery to measure the voltage at both ends of the power battery. The second voltage measuring device is connected to the outer terminal of the main positive relay and is used to measure the voltage at the outer terminal of the main positive relay under different operating conditions. The third voltage measuring device is connected to the external terminal of the main negative relay and is used to measure the voltage at the external terminal of the main negative relay. The fourth voltage measuring device is used to measure the voltage at the external terminal of the fast charging relay. The fourth voltage measuring device is connected to the external terminal of the fast charging relay and is used to measure the voltage at the external terminal of the fast charging relay. It also includes a battery management system, which includes a controller for continuously acquiring voltage data collected by various voltage acquisition devices and determining whether a fault exists based on the voltage data.

2. The relay detection circuit according to claim 1, characterized in that: The controller is also used to receive instructions from the vehicle control unit and control the closing or opening of the relay according to the instructions.

3. A relay detection circuit according to claim 1 or 2, characterized in that: The battery management system also includes an alarm module, which is used to report fault information when a fault is detected.

4. A relay detection circuit according to claim 1, characterized in that: The controller is used to acquire the voltage across the power battery measured by the first voltage measuring device V1 and the voltage at the outer terminal of the main positive relay measured by the second voltage measuring device V2, and compare the voltage difference between V1 and V2 with the adhesion detection threshold.

5. A relay detection circuit according to claim 1, characterized in that: The controller is used to acquire the voltage across the power battery measured by the first voltage measuring device V1 and the voltage at the outer terminal of the main positive relay measured by the second voltage measuring device V2, and compare the voltage difference between V1 and V2 with the adhesion detection threshold.

6. A relay detection circuit according to claim 1, characterized in that: The controller is used to acquire the voltage across the power battery measured by the first voltage detection device V1 and the voltage at the outer end of the main negative relay measured by the third voltage detection device V3, and compare the voltage difference between V1 and V3 with the threshold for determining the closure of the main negative relay.

7. A relay detection circuit according to claim 1, characterized in that: The controller is used to acquire the voltage at the outer terminal of the main negative relay measured by the third voltage detection device V3 and the voltage at the outer terminal of the fast charging relay measured by the fourth voltage detection device V4, and compare the voltage difference between V3 and V4 with the fast charging relay closing detection threshold.

8. A relay detection circuit according to claim 1, characterized in that: The controller is set with a maximum detection time threshold for the fast charging relay to close.

9. A relay detection circuit according to claim 1, characterized in that: The controller is used to compare the voltage data collected by the first voltage detection device V1 and the third voltage detection device V3 with the voltage difference between V3 and V4 and the threshold value determined by the adhesion of the main positive relay.

10. A relay detection circuit according to claim 1, characterized in that: The controller is used to acquire voltage data collected by the third voltage detection device V3 and the fourth voltage detection device V4, and compare the voltage difference between V3 and V4 with the fast charging relay adhesion to determine the threshold.

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