A switched-coupling-capacitor equalizer for series-connected battery strings

An automatic switched-coupling-capacitor equalizer (SCCE) is proposed, which can realize the any-cells-to-any-cells equalization for a battery string. Only two switches and one capacitor are needed for each battery cell. All MOSFETs are controlled by a pair of complementary PWM signals, and energy can be automatically and directly delivered from any higher voltage cells to any lower voltage ones without the need of monitoring circuits. The inherent advantages of the proposed system are the simple control, high efficiency, and easy modularization. A prototype for four lithium-ion battery cells is implemented, and a comparison between the proposed circuit and the conventional one is presented. Experimental results show the proposed circuit exhibits a substantially improved balancing performance, and the measured peak efficiency is about 92.7%.