Power battery management system (BMS) plays an important role in ensuring the safety and service life of battery packs in electric vehicles and maximizing the efficiency of battery systems. Usually, the single voltage, total voltage, total current and temperature are monitored and sampled in real time, and the real-time parameters are fed back to the vehicle controller.
If the power battery management system fails, it will lose the monitoring of the battery and cannot estimate the state of charge of the battery, which will easily lead to the increase of battery overcharge, overdischarge, overload, overheating and inconsistency, affecting the performance of the battery, service life and even driving safety.
The following lists common fault types of electric vehicle power battery management system, and makes a simple analysis of the possible causes, and provides common analysis ideas and treatment methods for reference:
Common types and troubleshooting methods of power battery management system faults
Common faults of power battery management system (BMS) include: CAN system communication fault, BMS does not work properly, abnormal voltage collection, abnormal temperature collection, insulation fault, internal and external total voltage measurement fault, pre-charging fault, failure to charge, abnormal current display fault, high voltage interlock fault, and so on.
- CAN communication is faulty
If the CAN cable or power cable falls off or the pin is removed from the terminal, the communication may fail. In guarantee the BMS under normal state of power supply, multimeter to dc voltage blocking, red table pen to touch the internal CANH, black table touch touch internal CANL, measuring line output voltage, namely the communication line between internal CANH and CANL voltage, normal voltage value is about 1, 5 v, if abnormal voltage value, can be judged to be BMS hardware failure, Need to change.
- BMS is not working properly
When this phenomenon occurs, we can focus on the following aspects:
(1) Power supply voltage of BMS: First measure the connector of the vehicle to see whether the power supply voltage of the vehicle to BMS has stable output.
(2) Unreliable connection of CAN line or low-voltage power line: Unreliable connection of CAN line or power output line may lead to communication failure. Check the communication cables and power cables from the main board to the slave board or high pressure board. Replace or reconnect the disconnected wiring harness if it is found.
(3) Lost pin or damaged connector: Lost pin of low-voltage communication aviation plug will cause no power supply from the board or data from the board cannot be transmitted to the main board. Check the plug and connector, and replace the lost pin or damaged one.
(4) Control board: replace the board for monitoring. If the fault is removed after replacement, it is determined that there is a problem with the main board.
- Abnormal voltage collection
When abnormal voltage acquisition occurs, the following situations should be considered:
(1) Battery undervoltage: Compare the monitored voltage with the actual voltage measured by the multimeter, and replace the battery after confirmation.
(2) Loose bolt or poor contact between the acquisition wire and the terminal: Loose bolt or poor contact between the acquisition wire and the terminal may lead to inaccurate voltage collection of the single unit. In this case, gently shake the acquisition terminal, and after confirming the poor contact, tighten or replace the acquisition wire.
(3) The fuse of the collection line is damaged: measure the fuse resistance value. If it is above LS2, it needs to be replaced.
(4) Slave board detection problem: Confirm that the collected voltage is inconsistent with the actual voltage. If the collected voltage of other slave boards is consistent with the battery voltage, it is necessary to replace the slave board, collect on-site data, and read historical fault data for analysis.
- The temperature collection is abnormal
When abnormal temperature collection occurs, the following situations should be considered:
(1) Temperature sensor failure: If a single temperature data is missing, check the middle butt plug. If there is no abnormal connection, it can be determined that the sensor is damaged and can be replaced.
(2) The wiring harness of the temperature sensor is not connected reliably: check the wiring harness of the temperature sensor at the middle butt plug or control port, and replace the wiring harness if it is loose or falls off.
(3) Hardware fault of BMS: If the monitoring finds that BMS cannot collect the temperature of the whole port, and the wiring harness from the control harness to the adapter to the temperature sensor probe is normal, it can be judged as the hardware problem of BMS, and the corresponding slave board should be replaced.
(4) Whether to reload the power supply after replacing the slave board: Reload the power supply after replacing the faulty slave board; otherwise, the monitored value will display abnormally.
- Insulation failure
In the power battery management system, the short connection between the inner core of the working wiring harness and the shell, the damage of the high-voltage cable and the short connection of the car body will lead to insulation faults. At the same time, the damage of the voltage collection cable and the short connection of the battery case will also lead to insulation faults. In this case, diagnosis and maintenance are analyzed respectively according to the following methods:
(1) High voltage load leakage: successively disconnect DC/DC, PCU, charger, air conditioner, etc., until the fault is removed, and then replace the faulty parts.
(2) High voltage cable or connector damage: use megohm meter to measure, check and confirm the replacement.
(3) Water in the battery box or battery leakage: Handle the inside of the battery box or replace the battery.
(4) Voltage collection line damage: Check the collection line after determining the leakage inside the battery box, and replace it if any damage is found.
(5) High pressure plate detection false alarm: replace the high pressure plate, and if the fault is removed after replacement, it is determined as the high pressure plate detection fault.
- Internal total voltage detection failure
The causes of the total voltage detection fault can be divided into: the connection between the collection line and the terminal is loose or falls off, resulting in the total voltage detection fault; Loose nut leads to ignition and total pressure collection failure; The high voltage connector is loose, causing ignition and total pressure detection failures. When the maintenance switch is pressed down, the total pressure collection fails. In the actual testing process, maintenance treatment can be carried out according to the following methods:
(1) The terminals at both ends of the total voltage collection line are not reliably connected: Use a multimeter to measure the total voltage of the detection point and the total monitored voltage, and then check the detection line. If the connection is found to be unreliable, tighten or replace it.
(2) Abnormal connection of the high voltage circuit: Use a multimeter to measure the total pressure of the detection point and the total pressure of the monitoring point, and make a comparison. Then check the maintenance switch, bolt, connector, insurance, etc., from the detection point in turn. If any abnormality is found, replace it.
(3) High-pressure plate fault detection: compare the actual total pressure with the monitored total pressure. After replacing the high-pressure plate, if the total pressure returns to normal, it can be identified as the high-pressure plate fault and replaced.
- Pre-charging failure
The causes of the precharging fault can be classified as follows: the external total pressure collecting terminal is loose and falls off, which leads to the precharging fault; There is no 12V voltage in the control line of the main board, so the precharging relay is not closed; The precharge fails because the precharge resistance is damaged. Combined with the real car, it can be inspected according to the following situations.
(1) External high-voltage component failure: When BMS reports a pre-charging fault, after disconnecting the total positive and total negative, if the pre-charging is successful, the fault is caused by the external high-voltage component, and the high-voltage junction box and PCU are checked in sections.
(2) The main board fails to close the precharging relay: check whether the precharging relay has 12V voltage. If not, replace the main board. If the precharging succeeds after replacement, the main board is faulty.
(3) Damage of main insurance or precharge resistance: measure the precharge insurance conduction and resistance value, if abnormal, replace.
(4) The external total pressure of the high pressure plate detection fault: after the high pressure plate is replaced, the precharge is successful, then the high pressure plate fault can be determined and replaced.
- It can’t be charged
The phenomenon of failure to charge CAN be roughly summarized as the following two situations: one is that the CAN cable terminals at both ends of the connector return pins or fall off, which leads to the failure of communication between the motherboard and the charger, resulting in failure of charging; Second, the damage of the charging insurance will lead to the formation of the charging loop, charging can not be completed. In the actual vehicle detection, if the charge cannot be charged, the following aspects can be used to repair and deal with the fault:
(1) Abnormal communication between the charger and the main board: Use the instrument to read the working data of the vehicle CAN system. If there is no working data of the charger or BMS, check the CAN communication harness immediately. If there is poor contact of the connector or line interruption, repair immediately.
(2) The charger or motherboard fails to start normally: replace the charger or motherboard, and then reload the voltage. If the charger or motherboard can be charged after replacement, it can be determined that the charger or motherboard is faulty.
(3) If BMS detects a fault, charging is not allowed: determine the fault type by monitoring, and then solve the fault until charging is successful.
(4) The charging fuse is damaged, and the charging loop cannot be formed: use a multimeter to detect the conduction of the charging fuse. If it cannot be conducted, replace it immediately.
- Abnormal current display
In the power battery management system, the terminal of the control wire harness falls off, the bolt is loose, and the surface of the terminal or bolt is oxidized. When abnormal current display occurs, the installation of the current collection line should be checked completely and in detail.
(1) The current collection line is not correctly connected: in this case, the positive and negative current will be reversed, and you can replace it;
(2) The connection of the current collection line is not reliable: firstly, it is determined that there is a stable current in the high-voltage loop. When the monitoring current fluctuates greatly, check the current collection line at both ends of the shunt and tighten the bolt immediately if it is found to be loose.
(3) Detect the oxidation of the terminal surface: first determine the high voltage loop has a stable current, and when the monitoring current is far lower than the actual current, detect whether there is an oxide layer on the surface of the terminal or bolt, and then the surface is processed.
(4) Abnormal current detection of HPA plate: After the maintenance switch is turned off, if the monitoring current value is above 0 and 2A, the current detection of HPA plate is abnormal, and the HPA plate should be replaced.
- High pressure interlock failure
When turning ON the ON block, measure whether there is a high voltage input, check whether the four terminals are securely connected, and measure whether there is 12V voltage at the driver end (the thin line is the voltage drive line). According to the specific situation, it can be divided into the following three categories:
(1) DC/DC fault: Measure the DC/DC high voltage input navigation plug, and if there is short-term high voltage when the ON gear is opened, it is determined as DC/DC fault, and it will be replaced.
(2) DC/DC relay terminals are not securely inserted: check the high and low voltage terminals of the relay. They are not reliably re-inserted securely.
(3) The DC/DC relay is not closed due to the fault of the main board or conversion board: measure the voltage driving end of the DC/DC relay, open the ON block for a short time and there is no 12V voltage, if the main board or conversion board is replaced.
I. Voltage fault
- High battery voltage: After the battery is fully charged and static, the voltage of single battery string or several battery strings is obviously high, and other monomers are normal.
Fault causes: ① Acquisition error; ②LMU balance function is poor or invalid; The cell capacity is low, the voltage rises faster when charging.
Treatment methods: ① The displayed voltage value of the monomer is higher than that of the other monomers, and the actual voltage value of the monomer is measured for comparison. If the actual value is lower than the displayed value and the voltage of the other monomers is the same, the actual value is used as the standard to calibrate the voltage of the LMU monomer. If the measured value is consistent with the displayed value, manually balance the discharge of a single battery. ② Check whether the voltage sampling line is broken or virtual; ③ Replace the LMU.
- Low battery voltage: after full static, the voltage of single or several cells of the battery is obviously low, and the other cells are normal.
Fault causes: ① Acquisition error; ②LMU balance function is poor or invalid; ③ the self-discharge rate of the cell is large; ④ The cell capacity is low, and the voltage drops faster when discharging.
Treatment methods: ① The displayed voltage value of the monomer is lower than that of the other monomers, and the actual voltage value of the monomer is measured for comparison. If the actual value is higher than the displayed value and the voltage of the other monomers is the same, the actual value is used as the standard to calibrate the voltage of the LMU monomer. If the measured value is consistent with the displayed value, charge the battery manually. ② Check whether the voltage sampling line is broken or virtual; ③ Replace the LMU. ④ Replace the faulty battery pack.
3, differential pressure: dynamic differential pressure/static differential pressure. When charging, the single voltage quickly reaches the full cutoff voltage jump gun; When stepping on the accelerator, the voltage of the single unit drops faster than that of the other series. When the brake is applied, the voltage of the single unit rises faster than that of the other series.
Fault causes: (1) The battery bronze nut is loose; (2) there is dirt on the connecting surface; ③ the self-discharge rate of the cell is large; (4) core welding connection bronze opening welding (resulting in the string monomer capacity is low); ⑤ Individual monomer cell leakage.
Treatment method: ① tighten the nut; ② Remove foreign bodies on the connecting surface; (3) Charge/discharge balance for single string battery; ④ Replace the faulty battery pack.
4, voltage jump: when the vehicle is running or charging, the single voltage jump.
Cause of failure: ① the connection point of voltage collection line is loose; (2) the fault LUM.
Treatment method: ① fastening the connection point; ② Replace the LMU.
Two, temperature fault
- Thermal management failure;
① Heating fault (heating plate); When the temperature is lower than a certain value, the heating will not be turned on when charging.
Fault causes: ① the heating relay or BMU is faulty; ② The heating plate or relay power supply circuit is abnormal.
Treatment method: ① Repair or replace the heating relay or BMU; ② Check and repair the power supply circuit.
② Heat dissipation fault (fan); When the temperature is higher than a certain value, the fan does not work.
Fault causes: (1) The fan relay or BMU is faulty. ② The power supply circuit of the fan or relay is abnormal.
Solution: ① Repair or replace the faulty fan relay or BMU. ② Check and repair the power supply circuit.
- High temperature: one or several temperature points in the battery system are on the high side, and the alarm threshold is reached during operation or charging.
Fault cause: ① temperature sensor fault; (2) LMU fault; ③ Abnormal local heating of electrical connection; (4) The fan is not turned on, resulting in poor heat dissipation. ⑤ Close to the motor and other heat sources; ⑥ Overcharging.
Treatment method: ① Compare the resistance value of the temperature sensor with the displayed value. If the actual value is lower than the displayed value and is the same as other temperature values, the actual value is used as the standard to calibrate the LMU temperature value; Tighten the electric connection point, clear connection point foreign body; (3) Ensure that the fan is on; ④ increase the insulation material and heat source isolation; ⑤ suspend operation for heat dissipation; ⑥ Stop charging immediately; ⑦ Replace the LMU.
- Low temperature: one or several temperature points in the battery system are low, and the alarm threshold is reached during operation or charging.
Fault cause: ① temperature sensor fault; (2) LMU fault; ③ The local heating plate is abnormal.
Treatment method: ① Compare the resistance value of the temperature sensor with the displayed value. If the actual value is higher than the displayed value and is the same as other temperature values, the actual value is used as the standard to calibrate the LMU temperature value; ② Check and repair the heating plate; ③ Replace the LMU.
4, temperature difference; Refer to the high and low temperature troubleshooting method. Cell heating difference.
Three, charging failure
- Dc charging failure; GB/T 27930-2015 Charging cannot start, charging jump gun, after the end of charging the SOC no longer bit.
Cause of failure:
① Battery faults (abnormal voltage, temperature, and insulation)
② BMU fault (The charging module or CAN is abnormal)
③ The main negative and charging relay are abnormal
④ Abnormal resistance of CC1 to earth and voltage of CC2 to earth
⑤ PE is abnormal
Treatment method:
① Rectify the battery fault
② Repair or replace the faulty component
③ Intercept the charging packet and analyze the fault cause.
- Ac charging failure;
Cause of failure:
① Battery faults (abnormal voltage, temperature, and insulation)
②BMU fault (The charging module or CAN is abnormal)
③ The main negative and charging relay are abnormal
④CC to ground resistance and CP to ground voltage are abnormal
(5) PE exception
Treatment method:
① Rectify the battery fault
② Repair or replace the faulty component
③ Intercept the charging packet and analyze the fault cause.
Four, insulation failure
Cause of failure: water in battery box or plug-in, leakage of battery core, high humidity, false insulation alarm, insulation of other high voltage parts of the vehicle (controller, compressor, etc.) but.
Treatment method: (1) the positive pole to the ground, if there is voltage or insulation resistance value is less than the specified value, then the negative circuit leakage; Negative to ground, if there is a voltage or insulation resistance value less than the specified value, the positive circuit is sentenced to leakage. The leakage point can be calculated according to the leakage voltage divided by the single string voltage value, and then analyzed and processed according to different situations.
Five, communication failure
LUM communication is faulty, BMU communication is faulty. The vehicle has 1 or more LMU information, or the vehicle has no BMS information.
The fault causes are as follows: (1) The LMU/BMU is faulty. ② The power supply circuit or communication line of the LMU/BMU is in poor contact or faulty. ③ Signal interference.
Solutions: ① Replace the LMU/BMU; ② Check and repair the power supply circuit/communication line; Check the shielding line, find and eliminate the source of interference.
- The SOC is abnormal
- Not accurate;
Charged power ÷ nominal capacity = Charged SOC If the “charged SOC” + “remaining SOC” is different from the actual displayed value or the actual electric quantity estimated according to the correspondence between SOC and OCV is not corresponding to SOC, we consider SOC is not accurate.
- No change;
Fault causes: ① abnormal communication (missing data); ② Abnormal current (Hall and its input and output circuit); (3) BMU fault; ④ Other battery alarms.
Processing methods: ① ensure data integrity; ② Repair/replace the failed parts; (3) Eliminate all battery alarms.
- Rapid decline;
Fault causes: ① Abnormal communication cycle ② abnormal current (hall forward current is large, feedback current is small); ③ The single voltage is low and decreases fast; (4) BMU fault; (5) at low temperature.
Solutions: ① Update the BMU program; ② Repair/replace the failed parts;
- Slow decline;
The fault causes are as follows: (1) The communication period is abnormal; (2) The current is abnormal (the Hall effect forward current is small and the feedback current is large); (3) The BMU is faulty.
Solutions: ① Update the BMU program; ② Repair or replace the faulty component.
5, beating; Verify that the program version number is correct
Seven, the current is abnormal
Cause of failure: ① Hall and its input and output circuit; (2) Hall retrofitting; ③ If the BMS demand voltage or current is 0 during DC charging, the charger will output according to the minimum output capacity.
Solutions: ① Update the BMU program; ② Repair or replace the faulty component.
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