Sizing of hybrid energy storage system and propulsion unit for electric vehicle

Design and management of electric power source for Electric Vehicle (EV) is one of the key challenges in the pathway of large scale EV deployment. Commercially launched EVs are designed with power source primarily based on batteries and fuel cells or its hybrid. This paper presents sizing of the hybrid energy storage system (HESS) and the propulsion unit (PU) for a small electric car based on the Indian driving cycle. An HESS with LiFePO4 battery having high energy density and ultracapacitor (UC) having high power density is chosen. The power sharing is done so that the battery is relieved of the peaky discharge currents and the rapid charge currents due to regenerative braking. Battery is sized to meet the energy required per charge while UC to meet the peaky power requirement. Induction motor (IM) is selected as PU and its sizing is done based on the dynamic response and the maximum speed requirement of the car. Proper sizing of the HESS and PU with effective regenerative braking helps to improve the range and the dynamic response of the vehicle. It also enhances the battery cycle life.