Bidirectional Dual-Input DC-DC Converter for Ultra-Capacitor/Battery HESS in Electric Vehicles

Due to the limited life cycle of the battery in Electric Vehicles (EVs), nowadays, HESS (Hybrid Energy storage systems) are in demand (As the number of charges/discharges increases, the life span of the battery will decrease). Therefore, a new ultra-capacitor (UC)/battery HESS is proposed. As the energy density of the battery is higher than that of UC and the power density of UC is higher than that of the battery, combining these properties will achieve better overall performance. Four modes (low power mode, medium power mode, high power mode, and regenerative braking mode) of the proposed converters are described. In these modes, UC has preferred frequent charge and discharge so that the battery is limited in use, which will improve the lifetime of the battery. The control scheme is presented to achieve higher efficiency by establishing maximum direct power flow between input and output, and soft switching techniques such as MOSFET switches are used. The advantages of higher efficiency lead to higher power density, low-temperature rise and converter of smaller size and weight. The proposed converter system is verified with simulation studies.