Proposal of SOC Unbalancing Solution Combined with Flux-weakening Control for Two-battery HEECS Chopper-based EV Powertrain

This paper proposes a State of Charge (SOC) balancing control combined with flux-weakening for two-battery high-efficiency energy conversion system (HEECS) chopper-based powertrain. The HEECS chopper has an advantage of very high DC-DC power conversion efficiency using two batteries. This HEECS chopper based EV power train can realize longer driving range by changing the DC bus voltage depending on the EV speed [1]. However, SOCs of batteries can be imbalance because the driving pattern is not predictable. This paper proposes an effective method for balancing SOCs by modifying HEECS chopper's control according to the driving speed. Simulation results show the proposed method extends driving range by 2.8% compared with the conventional SOC balancing method. The SOC difference is very small when the one of SOCs become zero.