A Study on the performance of the improved Energy Storage System for mild Hybrid Vehicles

Hybrid electric vehicles (HEV) utilize electric power as well as a mechanical engine for propulsion; therefore the performance of HEVs can be directly influenced by the characteristics of the energy storage system (ESS). The ESS for HEVs generally requires high power performance, long cycle life and reliability, as well as cost effectiveness, so the hybrid energy storage system (HESS), which combines different kinds of storage devices, has been considered to fulfill both performance and cost requirements. To improve operating efficiency, cycle life, cold cranking and life-time of the HESS, an advanced dynamic control regime with which pertinent storage devices in the HESS can be selectively operated based on their status was presented. Verification tests were performed to confirm the degree of improvement in energy efficiency. In this paper, an advanced HESS with improved battery management system (BMS), which has the optimal switching control function based on the estimated state of charge (SOC), has been developed and verified.