Diagnostic Circuit and Method for State of Health of Electric Vehicle Battery System

Abstract

The present invention provides a diagnostic circuit and method for the health state of an electric vehicle battery system. The diagnostic circuit includes: a battery pack, a motor controller, and a drive motor; the first end of the battery pack is connected to the center line of the drive motor through a pre-charge unit, a diagnostic circuit relay, and a fuse, and the first end of the battery pack is connected to the first end of the motor controller through a main positive relay. The second end of the battery pack is connected to the second end of the motor controller through a negative relay and a sensor module. Each of the three-phase stator windings of the drive motor is respectively connected to each set of inverter bridge power groups in the motor controller module; a control module, a discharge resistor, and a thin-film capacitor are connected to all the inverter bridge power groups to form a diagnostic circuit, which is used to control the on-off of each set of inverter bridge power groups and inject an alternating voltage into the battery system. The present invention can realize the online measurement of the health state of the battery pack without adding additional hardware devices, reducing the diagnostic cost.

Description

Technical Field

[0001] The present invention relates to the technical field of battery detection, and particularly to a diagnostic circuit and method for the state of health of an electric vehicle battery system. Background Art

[0002] As the main energy storage unit of electric vehicles, the state of health (SoH) of lithium-ion batteries is directly related to the performance, safety, and service life of electric vehicles.

[0003] The accurate diagnosis and prediction of the state of health of the battery system are crucial for ensuring the reliable operation of electric vehicles. Currently, common diagnostic methods for the state of health of electric vehicle battery systems include capacity fade analysis, internal resistance testing, and electrochemical impedance spectroscopy (EIS) measurement, etc. EIS is a very effective method that can provide detailed information about the internal electrochemical processes of the battery and conduct in-depth analysis of the battery degradation mechanism. This method is also the most commonly used diagnostic method at present.

[0004] However, traditional EIS measurements usually require expensive dedicated equipment and the battery needs to be removed from the vehicle, which not only increases the cost but also affects the normal use of the vehicle. Summary of the Invention

[0005] Embodiments of the present invention provide a diagnostic circuit and method for the state of health of an electric vehicle battery system to solve the problems that the current diagnostic methods are costly and affect the normal use of the vehicle.

[0006] In a first aspect, embodiments of the present invention provide a diagnostic circuit for the state of health of an electric vehicle battery system, including a battery pack, a motor controller, and a drive motor;

[0007] The first end of the battery pack is connected to the center line of the drive motor through a pre-charge unit, a diagnostic circuit relay, and a fuse, and the first end of the battery pack is connected to the first end of the motor controller through a main positive relay. The second end of the battery pack is connected to the second end of the motor controller through a negative relay and a sensor module. Each of the three-phase stator windings of the drive motor is respectively connected to each inverter bridge power group in the motor controller module;

[0008] The motor controller includes multiple groups of inverter bridge power units, a control module, a discharge resistor, and a thin-film capacitor. The control module, the discharge resistor, and the thin-film capacitor are connected to all the inverter bridge power units to form a diagnostic circuit, which is used to control the on / off of each group of inverter bridge power units and inject an alternating voltage into the battery system. When the diagnostic circuit enters the diagnostic mode, the inverter bridge power unit corresponding to the target stator winding forms a resonant circuit with the discharge resistor and the thin-film capacitor. Among them, the target stator winding is any one of the three-phase stator windings of the drive motor.

[0009] In a possible implementation, for the diagnostic circuit of the health state of the electric vehicle battery system, each group of inverter bridge power units includes at least a first power switch tube and a second power switch tube. The base of the first power switch tube and the base of the second power switch tube are both electrically connected to the control module. The collector of the first power switch tube is connected to the first end of the motor controller, the emitter of the second power switch tube is connected to the second end of the motor controller, the emitter of the first power switch tube is connected to the collector of the second power switch tube, and the target stator winding of the drive motor is connected to the connection between the emitter of the first power switch tube and the collector of the second power switch tube. The target stator winding is any one of the three groups of stator windings.

[0010] In a possible implementation, for the diagnostic circuit of the health state of the electric vehicle battery system, the pre-charge unit includes a pre-charge resistor and a pre-charge relay switch.

[0011] In a possible implementation, for the diagnostic circuit of the health state of the electric vehicle battery system, the discharge resistor and the thin-film capacitor are connected in parallel. The first end of the discharge resistor is connected to the first end of the motor controller, and the second end of the discharge resistor is connected to the second end of the motor controller.

[0012] In a possible implementation, for the diagnostic circuit of the health state of the electric vehicle battery system, the battery pack includes multiple battery module units, and the sensor module is used to detect the current and voltage of the battery pack.

[0013] In a possible implementation, for the diagnostic circuit of the health state of the electric vehicle battery system, each battery module unit is provided with a detection unit matching the battery module unit, and the detection unit is used to detect the voltage and / or current of the battery module unit.

[0014] In a second aspect, the embodiments of the present invention provide a method for diagnosing the health state of an electric vehicle battery system. Based on the diagnostic circuit for the health state of the electric vehicle battery system in any item of the first aspect, the diagnostic method includes:

[0015] When the low-voltage system of the electric vehicle is powered on and enters the battery fault diagnosis and evaluation mode and the battery system is detected to be normal, enter the diagnostic mode, control the diagnostic circuit relay to close and control the main positive relay to open;

[0016] Control the inverter bridge power group corresponding to the target stator winding to conduct and turn off at a preset frequency, perturb the battery pack, and detect the current and voltage of the battery pack under perturbation; wherein, the target stator winding is any one of the three-phase stator windings of the drive motor.

[0017] Based on the detected current and voltage, determine the detected impedance value of the battery pack at the preset frequency at the target moment.

[0018] Based on the detected impedance value, the temperature at the target moment, the SOC value of the battery pack at the target moment, and the preset impedance comparison table, determine the health state of the battery pack.

[0019] In a possible implementation manner, determining the health state of the battery pack based on the detected impedance value, the temperature at the target moment, the SOC value of the battery pack at the target moment, and the preset impedance comparison table includes:

[0020] Based on the detected impedance value, the temperature at the target moment, and the SOC value of the battery pack at the target moment, determine the comparison impedance corresponding to the detected impedance value in the preset impedance comparison table; wherein, the preset impedance comparison table is the impedance table corresponding to the preset frequency.

[0021] Based on the detected impedance value and the comparison impedance, determine the health state of the battery pack.

[0022] In a possible implementation manner, determining the detected impedance value of the battery pack at the preset frequency at the target moment based on the detected current and voltage includes:

[0023] When the difference between the detected voltage peak value and the voltage valley value is greater than or equal to the preset difference, then power on again and continue to monitor.

[0024] When the difference between the detected voltage peak value and the voltage valley value is less than the preset difference, then based on the average value of the multiple detected voltage peak values and current peak values, determine the output voltage peak value and the output current peak value.

[0025] Based on the output voltage peak value and the output current peak value, determine the detected impedance value of the battery pack at the preset frequency at the target moment.

[0026] In a possible implementation manner, after controlling the inverter bridge power group corresponding to the target stator winding to conduct and turn off at a preset frequency, perturbing the battery pack, and detecting the current and voltage of the battery pack under perturbation, it further includes:

[0027] Detect the voltage and current of the target battery module under perturbation; wherein, the target battery module is any one battery module.

[0028] Based on the detected current and voltage, determine the detected impedance value of the target battery module at the preset frequency at the target moment.

[0029] Based on the detected impedance values of all target battery modules and a preset total impedance threshold, determine whether there is a fault in the connection lines between the target battery modules.

[0030] An embodiment of the present invention provides a diagnostic circuit for the health state of an electric vehicle battery system. When entering the diagnostic mode, based on the inductance perturbation of the stator winding of the drive motor in the electric vehicle by the motor controller, a resonant circuit is formed, and based on the motor controller to control the on / off of each inverter bridge power group, the health state of the battery system can be determined, so that the online measurement of the battery EIS can be realized without adding additional detection equipment. In addition, through the inductance perturbation of the stator winding by the motor controller, the impedance of the battery pack is obtained, thereby realizing the online diagnosis of the health state of the battery pack and avoiding the problem of having to disassemble the battery pack. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0032] Figure 1 is a schematic diagram of a diagnostic circuit for the health state of an electric vehicle battery system provided by an embodiment of the present invention;

[0033] Figure 2 is a process block diagram of a diagnostic method for the health state of an electric vehicle battery system provided by an embodiment of the present invention;

[0034] Figure 3 is a schematic diagram of a diagnostic circuit when the W phase is used as the inductance element in the detection provided by an embodiment of the present invention;

[0035] Figure 4 is a flowchart of a diagnostic method for the health state of an electric vehicle battery system provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] In the following description, specific details such as specific system structures and technologies are proposed for the purpose of illustration rather than limitation, so as to thoroughly understand the embodiments of the present invention. However, those skilled in the art should clearly understand that the present invention can also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to avoid unnecessary details from interfering with the description of the present invention.

[0037] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will be described through specific embodiments with reference to the accompanying drawings.

[0038] As introduced in the background art, currently commonly used EIS measurements usually require expensive dedicated equipment and the battery needs to be removed from the vehicle for detection, which not only increases the detection cost but also affects the normal use of the vehicle.

[0039] How to conveniently and real-time measure the battery without affecting the normal operation of the electric vehicle has become a research hotspot currently.

[0040] To solve the problems of the prior art, the embodiments of the present invention provide a diagnostic circuit and method for the health state of an electric vehicle battery system. First, the diagnostic circuit for the health state of the electric vehicle battery system provided by the embodiments of the present invention will be introduced below.

[0041] See Figure 1 , which shows a schematic diagram of the diagnostic circuit for the health state of the electric vehicle battery system provided by the embodiments of the present invention, and is described in detail as follows:

[0042] The diagnostic circuit for the health state of the electric vehicle battery system, where the battery system includes a battery pack 110, a motor controller 120, and a drive motor 130.

[0043] Specifically, the first end of the battery pack 110 is connected to the center line of the drive motor 130 through a pre-charge unit, a diagnostic circuit relay S2, and a fuse F2, and the first end of the battery pack 110 is connected to the first end of the motor controller 120 through a main positive relay S3. The second end of the battery pack 110 is connected to the second end of the motor controller 120 through a negative relay S4 and a sensor module 1110. The three-phase stator windings of the drive motor 130 are respectively connected to the inverter bridge power groups in the motor controller module. The first end of the motor controller 120 is connected to the positive electrode of the battery pack 110, and the second end of the motor controller 120 is connected to the negative electrode of the battery pack 110.

[0044] The motor controller 120 includes multiple groups of inverter bridge power groups, a control module 1210, a discharge resistor, and a thin-film capacitor. The control module 1210, the discharge resistor, and the thin-film capacitor are connected to all the inverter bridge power groups to form a diagnostic circuit for controlling the on / off of each group of inverter bridge power groups and injecting an alternating voltage into the battery system. When the diagnostic circuit enters the diagnostic mode, the inverter bridge power group corresponding to the target stator winding forms a resonant circuit with the discharge resistor and the thin-film capacitor. Among them, the target stator winding is any one of the three-phase stator windings of the drive motor.

[0045] In this embodiment, the battery pack 110 includes multiple battery module units. Figure 1In it, M0 and Mx are battery module units, and a fuse F0 is also connected between the battery module units. The sensor module 1110 is used to detect the current and voltage of the battery pack 110. Based on the voltage and current of the battery pack 110 detected by the sensor module 1110, the impedance value of the battery pack can be calculated. Thus, the health state of the battery pack can be determined based on the determined impedance value of the battery pack and the reference impedance in the preset impedance comparison table. Among them, the sensor module 1110 is a high-precision sensor.

[0046] Each battery module unit is provided with a detection unit matching the battery module unit. The detection unit is used to detect the voltage of the battery module unit. Since each battery module unit is in a series mode, the current is the same. Based on the voltage and current of each battery module, the impedance value of each battery module can be determined. Based on the impedance value of each battery module and the set total impedance value, it can also be used to detect the connection performance of the circuits and electronic devices in the battery pack, and determine the connection reliability and stability of this battery pack system.

[0047] In some embodiments, in order to disturb the detection circuit and inject an alternating voltage into the battery system, it can be achieved by controlling the on / off of the inverter bridge power group.

[0048] In this embodiment, each group of inverter bridge power groups includes at least a first power switch tube and a second power switch tube. The base of the first power switch tube and the base of the second power switch tube are both electrically connected to the control module 1210. The collector of the first power switch tube is connected to the first end of the motor controller 120. The emitter of the second power switch tube is connected to the second end of the motor controller 120. The emitter of the first power switch tube is connected to the collector of the second power switch tube, and the target stator winding of the driving motor 130 is connected to the emitter of the first power switch tube and the collector of the second power switch tube. Among them, the target stator winding is any one of the three-phase stator windings.

[0049] Specifically, it may include three groups of inverter bridge power groups, as Figure 1 shown, Q1 and Q4 are a group of inverter bridge power groups, Q2 and Q5 are a group of inverter bridge power groups, and Q3 and Q6 are a group of inverter bridge power groups. The V-phase stator winding of the driving motor 130 is connected to the emitter of Q1 and the collector of Q4. The U-phase stator winding of the driving motor 130 is connected to the emitter of Q2 and the collector of Q5. The W-phase stator winding of the driving motor 130 is connected to the emitter of Q3 and the collector of Q6. By controlling the on and off of different groups of inverter bridge power groups to make the circuit resonate, the voltage disturbance of the entire detection circuit can be realized, and an alternating voltage can be injected into the battery pack.

[0050] In some embodiments, such as Figure 1As shown, the pre-charge unit includes a pre-charge resistor R1 and a pre-charge relay switch S1 connected in series with the resistor.

[0051] In this embodiment, the motor controller 120 further includes a discharge resistor R2 and a thin-film capacitor C1. When entering the diagnostic mode, the switch S5 will close, and the discharge resistor R2 and the thin-film capacitor C1 are in parallel. The first end of the discharge resistor R2 is connected to the first end of the motor controller 120, and the second end of the discharge resistor R2 is connected to the second end of the motor controller 120.

[0052] The diagnostic circuit for the health state of the electric vehicle battery system provided by the present invention can determine the health state of the battery system based on the inductance perturbation of the stator winding of the drive motor in the electric vehicle by the motor controller, so that the on-line measurement of the battery EIS can be realized without adding additional detection equipment. In addition, through the inductance perturbation of the stator winding by the motor controller, the impedance of the battery pack is obtained, thereby realizing the on-line diagnosis of the health state of the battery pack and avoiding the problem of having to disassemble the battery pack.

[0053] Based on the diagnostic circuit for the health state of the electric vehicle battery system provided in the above embodiment, correspondingly, the present invention also provides a specific implementation manner of the diagnostic method for the health state of the electric vehicle battery system applied to the diagnostic circuit for the health state of the electric vehicle battery system. Please refer to the following embodiments.

[0054] As Figure 2 shown, a schematic diagram of a diagnostic method for the health state of an electric vehicle battery system provided by an embodiment of the present invention is described in detail as follows:

[0055] S210. When the low-voltage system of the electric vehicle is powered on and enters the battery fault diagnosis and evaluation mode and the battery system is detected to be normal, enter the diagnostic mode, control the diagnostic circuit relay to close and control the main positive relay to open.

[0056] After the low-voltage system of the electric vehicle is powered on and enters the battery fault diagnosis and evaluation mode, the control unit needs to first perform a loop short-circuit detection on the electric vehicle. After determining that the loop short-circuit detection is normal, that is, the system is detected to be normal, the diagnostic circuit relay can be controlled to close. After the diagnostic circuit relay S2 is closed and the main positive relay S3 is open, in order to perform a charge and discharge test on the entire battery pack, the control module will control all the power transistors Q1-Q6 simultaneously.

[0057] S220. Control the inverter bridge power group corresponding to the target stator winding to conduct and turn off at a preset frequency, perturb the battery pack, and detect the current and voltage of the battery pack under the perturbation.

[0058] The drive motor has three-phase stator windings. During perturbation, it is only necessary to control the conduction and cut-off of the inverter bridge power unit corresponding to one phase of the stator winding each time. When the W phase is used as the inductance element in the detection, the corresponding current flow circuit is as Figure 3 shown.

[0059] During steady-state operation, the output voltage of the battery pack is set to V DC . At this time, the discharge resistor R2 can be regarded as a load, and the voltage across it is the same as the output voltage of the battery pack. When the control module 1210 controls the inverter bridge power unit Q1 and Q6 to continuously conduct and cut off, a perturbation signal V DC with a small duty cycle is added to the original output voltage V ac , and its corresponding frequency is f p . At this time, the corresponding voltage V dc-batt of the battery pack and the current I dc-batt can be expressed by the following formula:

[0060]

[0061] At this time, the detected voltage peak and current peak superimposed on the circuit after perturbation are V batt-peak and I batt-peak respectively, and the impedance value corresponding to the frequency f p is:

[0062]

[0063] If there is a phase change between the voltage of the battery pack and the current of the battery pack, or phase information is required, the phase at f p can be determined by the following formula.

[0064]

[0065] At this time, the control module controls the conduction and cut-off of Q3 and Q6 at the frequency of f p to perform charge and discharge perturbation tests on the entire battery pack, and the sensor module in the system detects the current and voltage of the entire battery pack.

[0066] S230. Based on the detected current and voltage, determine the detected impedance value of the battery pack at the preset frequency at the target moment.

[0067] In some embodiments, such as Figure 4As shown, due to external interference and other factors, the peak voltages or currents detected before and after may be inconsistent, affecting the accuracy of battery impedance detection. Therefore, when the voltage peak and voltage valley are detected, a subtraction operation is performed, and it is determined whether it is stable by judging the magnitude of the difference between the voltage peak and voltage valley detected before and after and the preset difference. For example, the difference between the peak and valley detected at n is X(n), and the difference between the peak and valley detected at n - 1 is X(n - 1). If X(n) - X(n - 1) < Th, it proves that the system is in a stable state, and the detection continues and the detected current peak and voltage peak are recorded. To improve the detection accuracy, it can be continuously tested M times, and the average value of the M differences is taken as the final output current peak and voltage peak. Th is the preset difference.

[0068] However, when the difference between the peak and valley of the two consecutive times is greater than the preset difference, it is necessary to power on again and wait for a certain time before continuing the monitoring.

[0069] At this time, after the voltage peak and current peak superimposed on the circuit after the disturbance are detected, the detected impedance value can be determined based on the voltage peak and current peak.

[0070] The voltage peak and current peak are V batt-peak and I batt-peak respectively, and the detected impedance value corresponding to the frequency f p is:

[0071]

[0072] If there is a phase change between the voltage of the battery pack and the current of the battery pack, or phase information is required, the phase at f p can be determined by the following formula.

[0073]

[0074] In addition, to improve the accuracy of the detected impedance value of the battery pack at the preset frequency at the target moment, the inverter bridge power groups corresponding to each phase of the stator winding can be turned on and off at the preset frequency respectively to disturb the battery pack, and the current and voltage of the battery pack under the disturbance are detected. Thus, three detected impedance values of the battery pack will be obtained, and the average value of these three detected impedance values is taken as the final detected impedance value of the battery pack. It should be noted that turning on and off the inverter bridge power groups corresponding to each phase of the stator winding at the preset frequency respectively needs to be carried out at the same temperature and with the same SOC value of the battery pack.

[0075] In addition, in order to further detect the performance of the connections of the circuits and electronic devices in the battery pack, first, the voltage and current of the target battery module under perturbation can be detected, and then, based on the detected current and voltage, the detected impedance value of the target battery module at the target moment can be determined. Finally, based on the detected impedance values of all target battery modules at the target moment and the preset total impedance threshold, it can be determined whether there is a fault in the connection line between the target battery modules.

[0076] S240. Determine the health status of the battery pack based on the detected impedance value, the temperature at the target moment, the SOC value of the battery pack at the target moment, and the preset impedance comparison table.

[0077] Among them, the temperature at the target moment and the SOC value of the battery pack at the target moment can be obtained through the battery management system.

[0078] In some embodiments, first, based on the detected impedance value, the temperature at the target moment, and the SOC value of the battery pack at the target moment, the comparison impedance corresponding to the detected impedance value can be determined in the preset impedance comparison table. It should be noted that the comparison impedance corresponding to the detected impedance value needs to be determined in the preset impedance comparison table at the preset frequency.

[0079] Then, based on the detected impedance value and the comparison impedance, the health status of the battery pack can be determined.

[0080] In this embodiment, when the detected impedance value is less than the comparison impedance, it is determined that the battery pack is in a healthy state.

[0081] Specifically, when the detected impedance value is greater than or equal to the first preset multiple of the comparison impedance and less than the second preset multiple of the comparison impedance, the health status of the battery pack is determined to be level one. Exemplarily, the first preset multiple can be 0, and the second preset multiple can be 10%.

[0082] When the detected impedance value is greater than or equal to the second preset multiple of the comparison impedance and less than the third preset multiple of the comparison impedance, the health status of the battery pack is determined to be level two. Exemplarily, the second preset multiple can be 10%, and the third preset multiple can be 30%.

[0083] When the detected impedance value is greater than or equal to the second preset multiple of the comparison impedance, it is determined that the health status of the battery pack is serious, indicating that the battery pack needs to be replaced at this time.

[0084] Exemplarily, the preset impedance comparison table at the preset frequency can be as shown in Table 1 below:

[0085] Table 1 Preset Impedance Comparison Table of the Battery Pack

[0086]

[0087] The first column in Table 1 is temperature, and the subsequent columns are the SOC values of the battery pack. Based on the temperature at the target moment and the SOC value of the battery pack at the target moment, the corresponding reference impedance of the detected impedance value at the preset frequency at the target moment can be determined in the preset impedance reference table of the battery pack.

[0088] Similarly, Table 2 is the preset impedance reference table of the battery module at the preset frequency:

[0089] Preset Impedance Reference Table of Battery Module

[0090]

[0091] The diagnostic method for the health state of the electric vehicle battery system provided by the present invention, by using the constructed diagnostic circuit for the health state of the electric vehicle battery system, when the low-voltage system of the whole electric vehicle is powered on and enters the battery fault diagnosis and evaluation mode and the battery system is detected to be normal, it can enter the diagnostic mode, control the diagnostic circuit relay to close and control the main positive relay to open. Then, control the inverter bridge power group corresponding to the target stator winding to conduct and turn off at a preset frequency, perturb the battery pack, and detect the current and voltage of the battery pack under the perturbation. After detecting the voltage and current of the battery pack, the detected impedance value of the battery pack at the preset frequency at the target moment can be determined based on the detected data. Finally, based on the detected impedance value, the temperature at the target moment, the SOC value of the battery pack at the target moment, and the preset impedance reference table, the health state of the battery pack is determined. The diagnostic method provided by the present invention can obtain the impedance value of the battery pack by controlling the inverter bridge power group corresponding to the target stator winding to conduct and turn off at a preset frequency and perturbing the battery pack, realizing the online real-time diagnosis of the battery health state, avoiding the use of additional hardware devices, and being able to detect without disassembling the battery pack, thereby realizing the efficient and accurate diagnosis of the battery pack. The present invention makes full use of the existing drive motor and control module of the electric vehicle, making the diagnostic system more concise and with lower cost.

[0092] It should be understood that the magnitudes of the sequence numbers of the steps in the above embodiments do not mean the order of execution. The order of execution of each process should be determined according to its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present invention.

Claims

1. A diagnostic circuit for the health status of an electric vehicle battery system, characterized in that: The battery system includes a battery pack, a motor controller, and a drive motor; The first end of the battery pack is connected to the center line of the drive motor through a pre-charging unit, a diagnostic circuit relay and a fuse, and the first end of the battery pack is connected to the first end of the motor controller through a main positive relay, and the second end of the battery pack is connected to the second end of the motor controller through a negative relay and a sensor module, and the three-phase stator windings of the drive motor are respectively connected to each group of inverter bridge power groups in the motor controller module; The motor controller includes multiple inverter bridge power groups, a control module, a bleeder resistor and a thin film capacitor. The control module, the bleeder resistor, the thin film capacitor and all the inverter bridge power groups are connected to form a diagnostic circuit for controlling the on and off of each inverter bridge power group and injecting AC voltage into the battery system. When the diagnostic circuit enters the diagnostic mode, the inverter bridge power group corresponding to the target stator winding forms a resonant circuit with the bleeder resistor and the thin film capacitor. The target stator winding is any one of the three-phase stator windings of the drive motor.

2. The electric vehicle battery system health status diagnosis circuit as claimed in claim 1, characterized in that: Each inverter bridge power group includes at least a first power switch tube and a second power switch tube, the base of the first power switch tube and the base of the second power switch tube are both electrically connected to the control module, the collector of the first power switch tube is connected to the first end of the motor controller, the emitter of the second power switch tube is connected to the second end of the motor controller, the emitter of the first power switch tube is connected to the collector of the second power switch tube, and the emitter of the first power switch tube in the inverter bridge power group corresponding to the stator winding of the drive motor and the stator winding is connected to the collector of the second power switch tube.

3. The electric vehicle battery system health status diagnosis circuit as claimed in claim 1 or 2, characterized in that: The pre-charging unit includes a pre-charging resistor and a pre-charging relay switch.

4. The electric vehicle battery system health status diagnosis circuit as claimed in claim 1, characterized in that: The discharge resistor and the film capacitor are connected in parallel, a first end of the discharge resistor is connected to a first end of the motor controller, and a second end of the discharge resistor is connected to a second end of the motor controller.

5. The electric vehicle battery system health status diagnosis circuit as claimed in claim 1, characterized in that: The battery pack includes a plurality of battery module units, and the sensor module is used to detect the current and voltage of the battery pack.

6. The electric vehicle battery system health status diagnosis circuit as claimed in claim 5, characterized in that: Each of the battery module units is provided with a detection unit matched with the battery module unit, and the detection unit is used to detect the voltage and / or current of the battery module unit.

7. A method for diagnosing the health status of an electric vehicle battery system, characterized in that: Based on the electric vehicle battery system health status diagnosis circuit according to any one of claims 1 to 6, the diagnosis method comprises: When the low-voltage system of the electric vehicle is powered on and enters the battery fault diagnosis and evaluation mode and the battery system is detected to be normal, it enters the diagnosis mode, controls the diagnosis circuit relay to close and controls the main positive relay to disconnect; Control the inverter bridge power group corresponding to the target stator winding to turn on and off at a preset frequency, disturb the battery pack, and detect the current and voltage of the battery pack under disturbance; wherein the target stator winding is any one phase of the three-phase stator winding of the drive motor; Determine, based on the detected current and voltage, a detection impedance value of the battery pack at a preset frequency at a target time; The health state of the battery pack is determined based on the detected impedance value, the temperature at the target time, the SOC value of the battery pack at the target time and a preset impedance comparison table.

8. The method for diagnosing the health status of an electric vehicle battery system as claimed in claim 7, characterized in that: The determining the health state of the battery pack based on the detected impedance value, the temperature at the target time, the SOC value of the battery pack at the target time and a preset impedance comparison table includes: Based on the detection impedance value, the temperature at the target time, and the battery pack SOC value at the target time, determining the comparison impedance corresponding to the detection impedance value in the preset impedance comparison table; wherein the preset impedance comparison table is an impedance table corresponding to the preset frequency; Based on the detection impedance value and the control impedance, a health state of the battery pack is determined.

9. The method for diagnosing the health status of an electric vehicle battery system as claimed in claim 7, characterized in that: The step of determining the detection impedance value of the battery pack at a preset frequency at a target time based on the detected current and voltage includes: When it is detected that the difference between the voltage peak value and the voltage valley value is greater than or equal to the preset difference value, the power is turned on again to continue monitoring; When it is detected that the difference between the voltage peak value and the voltage valley value is less than the preset difference value, the output voltage peak value and the output current peak value are determined based on the average of the voltage peak value and the current peak value detected multiple times; Based on the output voltage peak value and the output current peak value, a detection impedance value of the battery pack at a preset frequency at a target time is determined.

10. The method for diagnosing the health status of an electric vehicle battery system as claimed in claim 7, characterized in that: The inverter bridge power group corresponding to the control target stator winding is turned on and off at a preset frequency to disturb the battery pack, and the current and voltage of the battery pack under disturbance are detected, and further comprising: Detecting the voltage and current of a target battery module under disturbance; wherein the target battery module is any battery module; Determine the detection impedance value of the target battery module at a preset frequency at a target time based on the detected current and voltage; Based on the detected impedance values ​​of all the target battery modules and a preset total impedance threshold, it is determined whether there is a fault in the connection lines between the target battery modules.

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