Energy management strategies of battery-ultracapacitor hybrid storage systems for electric vehicles: Review, challenges, and future trends

The hybrid energy storage system is a promising candidate for electrically driven vehicles that enables superior capabilities compared to the single energy storage source. The energy management strategy (EMS) of hybrid energy storage systems in electric vehicles plays a key role in efficient utilization of each storage system. This paper investigates the challenges, merits, costs, and applications of the hybrid energy storage systems in electrical transportations. In recent studies of the hybrid storage system, the battery-ultracapacitor storage systems are significantly addressed. Therefore, the state-of-the-art energy management strategies of battery-ultracapacitor are categorized and their associated researches are surveyed. After EMS categorization and a detailed description of each strategy, a comparison is carried out in terms of robustness, causality, real-time feasibility, complexity, accuracy, solution type, necessity of mathematical model and other indexes. This comparison gives an overview and advantages of each strategy. Then, EMS implementation through hardware-in-loop and energy storage system industrial applications is delineated. Finally, the perspective and future trends are drawn based on current track and challenges of the EMS.