The battery management system (BATTERYMANAGEMENTSYSTEM), commonly known as battery nanny or battery housekeeper, is an important link between the on-board power battery and the electric vehicle. Its main functions include: real-time monitoring of battery physical parameters; battery state estimation; online diagnosis and early warning; Precharge control; balance management and thermal management, etc. The battery management system (BMS) is mainly to improve the utilization of the battery, prevent the battery from being overcharged and over-discharged, extend the service life of the battery, and monitor the status of the battery.

The battery management system is not only closely connected with the battery, but also has various connections with the vehicle system. Among all the faults, the fault of the battery management system is relatively high compared to other systems, and it is also more difficult to deal with. This article summarizes some common methods when dealing with battery management system failures and case analysis of common failures of battery management system, for reference by related personnel of vehicle, battery, and management system manufacturers.

BMS failure analysis method

Observation

When a communication interruption or control abnormality occurs in the system, observe whether each module of the system has an alarm and whether there is an alarm icon on the display screen, and then check the phenomenon one by one.

Failure reproduction method

The failures of vehicles under different conditions are different. If conditions permit, try to reproduce the failures under the same conditions as much as possible to confirm the problem. Elimination method When similar interference phenomenon occurs in the system, each component in the system should be removed one by one to determine which part is affecting the system.

Substitution method

When a module has abnormalities in temperature, voltage, control, etc., change the position of the module with the same number of strings to diagnose the module or wiring harness problem.

Environmental Inspection Act

When the system fails, such as the system cannot be displayed, we should not rush to carry out in-depth consideration, because often we will ignore some details. First of all, we should look at the obvious things: if it is plugged in? Is the switch turned on? Are all the wires connected? Perhaps the root of the problem lies in it.

Program upgrade method

When an unknown fault occurs after the new program is burned, which leads to abnormal system control, the previous version of the program can be burned for comparison to analyze and deal with the fault.

Data analysis

When a control or related failure occurs in the BMS, the BMS stored data can be analyzed, and the message content in the CAN bus can be analyzed.

Analysis of common failure cases

1. The whole system does not work after the system is powered

possible reason

Abnormal power supply, short circuit or open circuit in the wiring harness, and no voltage output of DCDC.

Troubleshooting

Check whether the external power supply to the management system is normal, whether it can reach the minimum operating voltage required by the management system, and whether the external power supply is set to limit current, resulting in insufficient power supply to the management system; the external power supply can be adjusted to meet the requirements of the management system Electricity requirements; check whether the harness of the management system is short-circuited or open, modify the harness to make it work normally; if the external power supply and harness are normal, check whether the DCDC powering the entire system in the management system has a voltage output; if so If abnormal, the bad DCDC module can be replaced.

2. BMS cannot communicate with ECU

possible reason

The BMU (main control module) is not working, and the CAN signal line is disconnected

Troubleshooting

Check whether the 12V/24V power supply of the BMU is normal; check whether the CAN signal transmission line is withdrawn or the plug is not plugged in; monitor the CAN port data and whether the BMS or ECU data packet can be received.

3. The communication between BMS and ECU is unstable

possible reason

Poor external CAN bus matching, too long bus branch

Troubleshooting

Check whether the bus matching resistance is correct; whether the matching position is correct and whether the branch is too long.

4. The internal communication of the BMS is unstable

possible reason

The communication cable plug is loose, the CAN wiring is not standardized, and the BSU address is duplicated.

Troubleshooting

Check whether the wiring is loose; check whether the bus matching resistance is correct, whether the matching position is correct, and whether the branch is too long; check whether the BSU address is duplicated.

5. Insulation detection alarm

possible reason

Leakage of battery or drive, wrong connection of insulation module detection wire.

Troubleshooting

Use the BDU display module to check the insulation test data, check the battery bus voltage, whether the negative bus voltage to ground is normal; use the insulation shaker to measure the insulation resistance of the bus and the driver to the ground.

6. The main relay does not close after power on

possible reason

The load detection line is not connected, the precharge relay is open, and the precharge resistor is open.

Troubleshooting

Use the BDU display module to check the bus voltage data, check the battery bus voltage, whether the load bus voltage is normal; check whether the load bus voltage rises during the pre-charging process.

7. Acquisition module data is 0

possible reason

The collection line of the collection module is disconnected and the collection module is damaged.

Troubleshooting

Re-plug the module wiring, measure whether the battery voltage is normal at the collection line connector, and measure the resistance at the temperature sensor line plug.

8. Battery current data error

possible reason

The Hall signal cable plug is loose, the Hall sensor is damaged, and the acquisition module is damaged.

Troubleshooting

Re-plug the current Hall sensor signal line; check whether the power supply of the Hall sensor is normal and whether the signal output is normal; replace the acquisition module.

9. The battery temperature difference is too large

possible reason

The cooling fan plug is loose and the cooling fan is faulty.

Troubleshooting

Re-plug the fan plug cable; supply power to the fan separately and check whether the fan is normal.

10. The battery temperature is too high or too low

possible reason

The cooling fan plug is loose, the cooling fan is faulty, and the temperature probe is damaged.

Troubleshooting

Re-plug the fan plug wire; power the fan separately to check whether the fan is normal; check whether the actual temperature of the battery is too high or too low; measure the internal resistance of the temperature probe.

11. The system reports an error after the relay operates

possible reason

The relay auxiliary contacts are disconnected and the relay contacts are stuck

Troubleshooting

Re-plug the wiring harness; use a multimeter to measure whether the auxiliary contacts are on or off correctly.

12. Cannot use charger to charge

possible reason

Abnormal communication between charger and BMS

Troubleshooting

Replace a charger or BMS to confirm whether the BMS is faulty or the charger is faulty; check whether the matching resistance of the BMS charging port is normal.

13. No BMS data display on vehicle instrument

possible reason

The main control module wiring harness connection is abnormal

Troubleshooting

Check whether the wiring harness of the main control module is well connected, whether there is a normal low-voltage working voltage for the car, and whether the module is working properly

14. The detection data of some battery boxes is lost

possible reason

Some connectors of the vehicle may be in poor contact, or the BMS slave control module may not work normally

Troubleshooting

Check the contact of the connector, or replace the BMS module;.

15. SOC abnormal

Phenomenon: SOC changes greatly during the working process of the system, or repeatedly jumps between several values; during the charging and discharging process of the system, the SOC has a large deviation; the SOC always shows a fixed value.

possible reason

The current is not calibrated; the current sensor model does not match the host program; the battery has not been deeply charged and discharged for a long time; the data acquisition module acquisition jumps, causing the SOC to automatically calibrate;

Two conditions for SOC calibration: 1) to achieve overcharge protection; 2) average voltage to reach xxV or more. The customer battery has poor consistency, and the second condition cannot be met when overcharged. Check the remaining capacity and total capacity of the battery through the display; the current sensor is not connected correctly;

Troubleshooting:

Calibrate the current in the touch screen configuration page; modify the host program or replace the current sensor; perform a deep charge and discharge of the battery; replace the data acquisition module and manually calibrate the system SOC. It is recommended that customers do a deep charge and discharge once a week; modify the host program, Adjust xxV in the condition of "average voltage above xxV" according to the actual situation of the customer. Set the correct total battery capacity and remaining capacity; correctly connect the current sensor to make it work normally.