A Bridge-Structured Switched-Capacitor Voltage Equalizer for Li-Ion Battery Strings

A bridge-structured switched-capacitor (SC) equalizer (BSSCE) is proposed to increase the balancing speed and to improve the efficiency at different cell voltage distributions. The proposed BSSCE can transfer energy simultaneously among cells with more optimal balancing paths by using minimum components, which allows the equalizer to achieve improved balancing speed, efficiency, size, and cost. Also, the topology minimizes the effective resistance at slow and fast switching limits, which allows the equalizer to draw high currents to enhance the balancing speed. A simulation model for four series-connected battery cells with different switching frequencies is set up to validate the feasibility of the proposed equalizer. Simulation results and effective resistance analysis show that the proposed BSSCE can achieve any cell-to-cell equalization automatically concerning different switching frequencies. The proposed equalizer can achieve high balancing speed and efficiency.