Power electronics enabled energy management for energy storage with extended cycle life and improved fuel economy in a PHEV

Active combination of the ultracapacitor (UC) with an energy dense Lithium-ion (Li-ion) battery (BU) is seen as the promising approach in plug-in hybrid electric vehicle (PHEV) application. In this paper, the sizing of Li-ion battery and ultracapacitor, as well as the degree of hybridization (DH) between UC power and battery power are analyzed through a different perspective, i.e., to solve an optimization problem targeting maximized fuel economy. To implement this optimized power sharing in real time, a novel energy management strategy is proposed, which includes battery power reference generation, UC state-of-charge (SOC) regulation, and forecast control according to the driver command. Finally, simulation and experimental results are provided to verify the reduced battery current stress and improved fuel economy by the proposed method, in which flywheel + generator + controlled load is used to emulate the vehicle drivetrain in the laboratory.