August 13th, 2020
These large high-power batteries require a battery management system with refined monitoring and protection functions for the battery (Figure 4 ). 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.
The battery must then be reliably disconnected from the rest of the high-voltage circuitry within the vehicle.