Design of series resonant switched‐capacitor equaliser for series‐connected battery strings

Abstract

The traditional pure switched-capacitor equaliser brings the large inrush current and low energy density. This study proposes a series of resonant switched-capacitor (ReSC) voltage equaliser, which realises energy transferred directly from source cells to target cells by the series ReSC converter. The ReSC converter eliminates the inrush current and improves the capacitors' energy density to increase the balancing speed. Meanwhile, all the switches are controlled by a pair of complementary PWM signals at a fixed operational frequency without voltage monitors. Both simulation and experiment are used to verify the system feasibility and theoretical analysis of the proposed circuit. In the same experimental condition, the proposed series resonant circuit reduces the inrush current. It improves the energy density of capacitors three times compared with the pure series switched-capacitor equaliser.