Battery Management System

These large high-power batteries require a battery man­agement system with refined monitoring and protection functions for the battery (Figure 4 [5]). In normal operation, only the monitoring functions are active; their principal tasks are:

• Voltage, current and temperature monitoring: These primary data are used to derive other values. These in­clude for example the internal electrical resistance, which gives information about the charge state and the general condition of the battery;

• Charge equalization: Since the characteristics of the battery cells are never precisely the same, and further­more, the temperature may vary at different points with­in the battery pack, charging and discharging can load the cells differently. Over time, the capacity of the cells would drift apart, and the capacity of the weakest cell would limit the whole battery. Therefore, discharging re­sistances in parallel or actively-controlled recharging cir­cuits provide for charge equalization among the cells.

• Monitoring the charge state: This plays a very impor­tant role in managing the battery and in the information display for the driver. While the battery management monitors the operation of the battery only within cer­tain charge-state limits, a superordinate con-sumption computer calculates the remaining cruising range from the charge state.

The protection functions become active in case the battery is loaded outside its specified range, or in case of accident.

Подпись:Подпись: +Подпись: Cathode Oxygen atom Metal atom The battery must then be reliably disconnected from the rest of the high-voltage circuitry within the vehicle.