A Practical Approach of Active Cell Balancing in a Battery Management System

Battery is the heart of electric vehicle and a way of improving the battery life is to equalize the energy of its cells. This can be done by either dissipating excess energy in the form of heat (passive cell balancing) or charging the low voltage cells through high voltage cells (active cell balancing). This paper presents a practical approach of active cell balancing along with a brief comparative study of passive and active cell balancing techniques. To improve the inconsistency present in the series-parallel connected lithium ion (Li-Ion) cells, a cell balancing scheme based on switch-matrix and forward converter with active clamp driver topology is presented. This cell balancing scheme is based on transferring the energy from the over-charged cell to auxiliary battery and from auxiliary battery to less charged cell. The balancing takes place for one cell at a time and the balancing current can be continuously monitored. The energy transfer efficiency of 90% for charging and 72% for discharging is achieved. The proposed battery management system can be used for communicating the faults generated in the battery pack to the master controller and corrective actions can be taken to avoid the damage to the battery.