Abstract: The design of active parallel hybrid energy storage system (HESS) for light electric vehicles (LEVs) was presented by the use of high power density ultracapacitor and high energy density LiFePO4 battery. The battery efficiency was analyzed based on the experiment, and the theoretical efficiency of the bidirectional DC-DC power converter was derived. The combination of ultra-capacitor and LiFePO4 battery was discussed. The result demonstrates that the HESS with the bidirectional DC-DC power converter can improve the efficiency. The experimental result shows that the average efficiency of DC-DC is 90.5% in the HESS bench test, which is close to the theoretical efficiency 91.6%.

Key words: ultra-capacitor, LiFePO4 battery, hybrid energy storage system (HESS), light electric vehicles (LEVs), bidirectional DC-DC