Li-ion battery charge balancing circuit for application in Electric vehicles

Abstract

Electric vehicles (EVs) are becoming popular and considered as future transportation with the apparent capability of zero fuel consumption and pollution. In case of the hybrid electric vehicles and energized battery vehicles are more efficiently used in private and public transportation systems. In the EVs system, an energy storage device is main concern due to charge and discharge issue. This device faces some problems which are electrochemical cell voltage imbalance, state of charge imbalance and state of discharge imbalance. These problems occur due to cell chemical digression, internal resistance and temperature effects which reduce the lifecycle and performance of the cell. Also storage devices are challenged a formidable to immediately deliver the unpredictable driving power required by the electric vehicle. Therefore, the effective voltage balancing technique is highly necessary to balance the voltage differences between cell to cell in the battery pack. Balancing circuits are taken for a long time, which create a voltage gap. To overcome this issue, a design of single resonant converter-based active charge balancing circuit is used to reduce the balancing time and voltage gap. This balancing circuit performs on charging, discharging and inoperative mode. A single series LC tank is connected with switching components and battery cells. The balancing speed has been improved by allowing energy transfer between any two cells in the battery string, and power consumption for balancing is reduced by operating all switches in the circuit at a zero-current switching condition. In general, high spark current is introduced in the inductor that can damage switching devices. Experimental results represented that the balancing circuit provides the balancing current to the cell, which reduces the voltage differences between any cells to cell. The results exposed two 4400mAh Li-ion batteries voltage balancing process. The initial voltage gap between two batteries is 246 mV and the voltage deviation was reduced of 0 mV whereas the voltage balancing process terminated. In addition, the total time duration of the tested voltage equalization process is 76 minutes. This circuit proves an effective and automated system to balance the battery charge that improves the safety and life cycle of the battery. Therefore, this balancing circuit is applicable to equalize the unbalanced voltage of the batteries in electric vehicles and energy storage systems.