Power Management Strategy for an Electric Vehicle Driven by Hybrid Energy Storage System

The selection, sizing, and management of energy storage system for an electric vehicle (EV) are critical while considering later's large-scale deployment. The complementary nature of battery and ultracapacitor (UC) makes the combination a suitable hybrid energy storage system (HESS) for EV since the peak to average power demand ratio is very high especially for an urban drive commonly characterized by frequent acceleration and deceleration. A suitably sized UC combined with the battery pack provides necessary high power density as well as high energy density. The HESS makes the EV more effective with improved dynamic response, higher kilometers per charge, and longer battery life. This paper presents a fuzzy logic control based power management strategy to employ UC to relieve the battery of peak discharge currents as well as rapid charging currents. The power conditioning unit limits the battery current as well as its rate of change by maintaining the UC state of charge in the desired limits. The paper presents some of the key simulation and experimental results for a prototype EV system tested for various modes of operations.