Part 1 of this article explained the challenges associated with implementation of large Li-Ion battery packs for automotive applications and highlighted the advantages of active balancing vs. passive balancing methods.
In this part, popular active balancing methods are reviewed and details given of a unique active cell balancing battery management system.
Hybrid electric and EV battery packs contain up to several hundred cells and are divided into modules. The need for module balancing is as important as the need for cell balancing due to module parameters mismatch, unequal temperatures affecting performance and causing uneven ageing, or the need to replace bad modules with new ones for maintenance purposes.
One of the methods providing module balancing capability involves connecting the circuitry of each module to one cell of the adjacent module to provide a path for charge transfer. This method is inefficient because the charge has to be transferred to one cell and redistributed among all cells of the module. Transferring the charge to a far away module requires several steps and the efficiency drops further.
A key to superior battery management system (BMS) performance lies in the accuracy and speed of the cell voltage measurement.
The cell voltages are affected by the fast changing currents. It is critical to measure the entire pack cell voltages almost simultaneously to guarantee the precision of the state-of-charge (SOC) and state-of-health (SOH) estimation.
Read the full article here, which describes a National Semiconductor solution optimized for large battery packs without the performance limitations of BMS solutions burdened by the legacy of small battery pack applications. (Courtesy of Automotive Designline Europe)