System Description

SYSTEM

System Description


SYSTEM DIAGRAM







INPUT/OUTPUT SIGNAL ITEM

Input Signal Item





Output Signal Item






DESCRIPTION

The Li-ion battery controller (LBC) monitors the status of the inside of the Li-ion battery at all times and sends information, such as the charging status of Li-ion battery and possible power, to VCM (vehicle control module)
via EV system CAN communication.
The Li-ion battery controller performs control as per the following.
- Monitors the battery state and transfers chargeable/dischargeable power to VCM to prevent an error, such as overvoltage, over discharge or excessive temperature rise in the battery.
- Detects an error (overvoltage, over discharge, overcurrent, or excessive temperature rise) immediately at the time of error occurrence and requests VCM to disconnect the system main relay to interrupt the discharge/charge line.
- Maintains the optimum battery state constantly with a cell capacity adjustment function to prevent a reduction in charging/discharging capacity caused by cell capacity variations.
- Detects the connector fit state with the function to detect the fit of the high voltage harness connector and transfers the detected state to VCM so that the vehicle does not start with an unsteady state.
- Detects the insulation resistance state with the function to detect the insulation resistance between high and low voltage and transfers the detected state to VCM so that the vehicle does not start with an unusual state.
- Estimates a battery charge state and low battery state, based on the data obtained with the battery state detection function, and reflects on the battery capacity meter.

BATTERY PROTECTION

The Li-ion battery has a voltage range capable of charge/discharge. If charged/discharged exceeding the range, excessive low capacity or malfunction may be caused. To prevent this, the Li-ion battery controller detects voltage of each cell and requests the control of charging/discharging energy to VCM so that the cell voltage stays within the voltage range.






HOW TO ADJUST CELL CAPACITY

During cell capacity adjustment, the capacity of each cell is estimated based on the no-load voltage when the system starts, and the capacities are adjusted so that they are all at the target level. The voltage of each cell is detected inside the Li-ion battery controller. The bypass switches are then turned ON to discharge the cells that have excess capacity. In this way, capacity adjustment by the Li-ion battery controller allows the capacity of all cells to be fully utilized.






INSULATION RESISTANCE LOSS DETECTION FUNCTION

The insulation resistance detection circuit mounted inside the Li-ion battery controller measures the insulation resistance of each high voltage part and sends the measurement results to VCM via EV system CAN communication.
VCM judges abnormal insulation resistance in each high voltage part, based on the received insulation resistance value.