A Star-Structured LC Resonant Switched Capacitor Equalizer for Lithium-ion Battery Strings

The enhancement of balancing speed as well as fully equalization is a great challenge in switched capacitor (SC) based cell voltage equalizers. In this study, a star-structured LC resonant SC equalizer is proposed to equalize the unbalance cell voltages completely within minimum time. An inductor is used in series with each capacitors of the proposed equalizer. The designing procedure confirms the zero-current-switching (ZCS) and zero-voltage-gap (ZVG). ZCS reduces the switching loss by removing the current spike during the switching periods. ZVG confirms the complete voltage equalization among the cells. The star structure reduces the balancing time by creating the direct any-cell-to-any-cell paths for exchanging the excess energy among the cells. The MOSFET is used as switches and only a pair of complementary PWM signal is used to operate the whole circuit. The proposed equalizer is validated in both simulation and experimentally. Results show that the proposed equalizer performs better compare to the conventional equalizers especially in balancing time and complete equalization.