Bidirectional chopper using cell voltage equalizing with flyback transformer

Recently, the technology on electric vehicle (EV) is more and more focused. In order to control the motor driving, power conversion circuits are applied, and as the energy storage, rechargeable battery and electric double layer capacitor (EDLC) are generally used. The energy storage is composed of series connected cells to get high output voltage, therefore cell voltage unbalance occurs by means of the unequal characteristic of each cell. To avoid the voltage unbalance, several voltage equalizing circuits have been proposed. In this paper, motor driving circuit using hybrid energy storage is proposed. This circuit has two sets of energy storages, and enables cell voltage equalization and energy transfer among energy storages. In proposed circuit, flyback transformer is connected to each energy storage cell. The circuit operation has been confirmed by reduced scale circuit experiment.