A New Battery/UltraCapacitor Hybrid Energy Storage System for Electric, Hybrid, and Plug-In Hybrid Electric Vehicles

TLDR

The authors propose a battery/ultracapacitor hybrid energy storage system for electric, hybrid, and plug‑in hybrid electric vehicles. The system employs a small dc/dc converter that pumps energy to keep the ultracapacitor voltage above the battery voltage during city driving, so the battery supplies power only when the ultracapacitor voltage falls below the battery voltage and is not charged directly from regenerative braking. This design yields a relatively constant battery load profile, reduces frequent charging of the battery, thereby extending its life, and simulation and experimental results confirm its effectiveness.

Abstract

In this paper, a new battery/ultracapacitor hybrid energy storage system (HESS) is proposed for electric drive vehicles including electric, hybrid electric, and plug-in hybrid electric vehicles. Compared to the conventional HESS design, which uses a larger dc/dc converter to interface between the ultracapacitor and the battery/dc link to satisfy the real-time peak power demands, the proposed design uses a much smaller dc/dc converter working as a controlled energy pump to maintain the voltage of the ultracapacitor at a value higher than the battery voltage for the most city driving conditions. The battery will only provide power directly when the ultracapacitor voltage drops below the battery voltage. Therefore, a relatively constant load profile is created for the battery. In addition, the battery is not used to directly harvest energy from the regenerative braking; thus, the battery is isolated from frequent charges, which will increase the life of the battery. Simulation and experimental results are presented to verify the proposed system.