Influence of Battery/Ultracapacitor Energy-Storage Sizing on Battery Lifetime in a Fuel Cell Hybrid Electric Vehicle

TLDR

Fuel cell hybrid electric vehicles combine high‑energy batteries with high‑power ultracapacitors, yet sizing the battery solely on energy can cause deep discharges that shorten its lifetime. This study examines how battery and ultracapacitor ratings affect system performance and battery longevity. Two energy‑management strategies that allocate load among the fuel cell, battery, and ultracapacitors, plus a charging strategy responsive to vehicle conditions, are proposed. The analysis shows that sizing energy‑storage devices by both power and energy while accounting for battery lifetime reduces system volume and mass and improves overall durability, providing design recommendations for FCHEVs.

Abstract

Combining high-energy-density batteries and high-power-density ultracapacitors in fuel cell hybrid electric vehicles (FCHEVs) results in a high-performance, highly efficient, low-size, and light system. Often, the battery is rated with respect to its energy requirement to reduce its volume and mass. This does not prevent deep discharges of the battery, which are critical to the lifetime of the battery. In this paper, the ratings of the battery and ultracapacitors are investigated. Comparisons of the system volume, the system mass, and the lifetime of the battery due to the rating of the energy storage devices are presented. It is concluded that not only should the energy storage devices of a FCHEV be sized by their power and energy requirements, but the battery lifetime should also be considered. Two energy-management strategies, which sufficiently divide the load power between the fuel cell stack, the battery, and the ultracapacitors, are proposed. A charging strategy, which charges the energy-storage devices due to the conditions of the FCHEV, is also proposed. The analysis provides recommendations on the design of the battery and the ultracapacitor energy-storage systems for FCHEVs.