A novel multimode hybrid energy storage system and its energy management strategy for electric vehicles

• A novel topology of multimode HESS is proposed for EVs.
• The rule-based control strategy and the power-balancing strategy are developed for the mode selection and the power distribution.
• The energy management strategy is proposed to reduce energy losses in the DC–DC converter.
• The proposed multimode HESS could extend the batteries life and improve the operation efficiency of the HESS.

This paper proposes a novel topology of multimode hybrid energy storage system (HESS) and its energy management strategy for electric vehicles (EVs). Compared to the conventional HESS, the proposed multimode HESS has more operating modes and thus it could in further enhance the efficiency of the system. The rule-based control strategy and the power-balancing strategy are developed for the energy management strategy to realize mode selection and power distribution. Generally, the DC–DC converter will operate at peak efficiency to convey the energy from the batteries to the UCs. Otherwise, the pure battery mode or the pure ultracapacitors (UCs) mode will be utilized without the DC–DC converter. To extend the battery life, the UCs have the highest priority to recycle the energy and the batteries are isolated from being recharged directly during regenerative braking. Simulations and experiments are established to validate the proposed multimode HESS and its energy management strategy. The results reveal that the energy losses in the DC–DC converter, the total energy consumption and the overall system efficiency of the proposed multimode HESS are improved compared to the conventional HESS.