A switched-capacitor battery equalization method for improving balancing speed

Abstract

The switched-capacitor equalizer (SCE) has a broad application prospect because of its small size, easy control, and implementation. However, the conventional SCE by shifting energy between two adjacent cells usually has a lower balancing speed the number of imbalanced battery cells increases. Therefore, an automatic SCE is proposed to improve the balancing speed for a long battery string. The main advantage of the proposed method is taking the highest-voltage battery cell as the source for balancing. By controlling the MOSFETs alternately with one pair of complementary pulse width modulation signals, the energy can be directly delivered from the highest-voltage battery cell to other lower-voltage ones, to avoid the frequent energy inflow or outflow from the same battery cell. A prototype for four lithium battery cells is implemented, and the comparisons between the proposed SCE and other SCEs in simulation and experiment are presented. Results show that the proposed SCE topology exhibits an obvious improvement in balancing speed at different initial voltage mismatch distributions.