Bidirectional Converter Integrating Voltage Equalizer Based on Symmetrical Voltage Multiplier by Sharing a Magnetic Component for Series-Connected Cells

Abstract

Conventional energy storage systems include a bidirectional converter for charging and discharging the series-connected cells and a separate voltage equalizer. In this article, to simplify the system, the equalizer is integrated into the charging and discharging system. Only one magnetic component is required in the proposed integrated architecture, and more importantly, the equalizer no longer needs a separate converter as the driver. The voltage equalizer is composed of a symmetrical voltage multiplier (SVM) and a series-resonant circuit. The equalizer operates in a discontinuous conduction mode (DCM) and can provide a constant equalization current for the energy storage cells. A detailed operation analysis is performed for integrated architecture, and the steady-state characteristics are mathematically derived. The integrated architecture can automatically equalize the cell voltage when the energy storage is charged or discharged. A prototype for six series-connected cells was built and tested to verify the analytical results and demonstrate the properties of the proposed architecture.