Energy management with dual droop plus frequency dividing coordinated control strategy for electric vehicle applications

In this paper, a dual droop-frequency diving coordinated control strategy is proposed for electric vehicle (EV) applications, where the hybrid energy storage system (HESS) with supercapacitors and batteries is integrated to prolong the life time of storage elements. The dynamic power allocation between the supercapacitor and batteries are obtained through the voltage cascaded control, upon which the high and low frequency power fluctuation are absorbed by the supercapacitors and batteries respectively to fully exploit the advantages of the supercapacitors and batteries. Moreover, the power capacity is scaled up by connecting storage blocks in parallel. A dual droop control scheme for parallel-connected energy storage system and its operation principle is introduced on the aspect of current sharing characteristic and state-of-charging (SOC) management. After detailed analysis and formula derivation, the corresponding loop parameters are designed. Through this control method, the current sharing performance is ensured and each block makes the self-adaptive adjustment according to their SOC. Consequently, the load power can be shared effectively, which helps to avoid the over-charge/ over-discharge operation and contributes to the life cycle of the energy storage system. Each module is autonomous controlled without the necessity of communication, which is easy, economic and effective to realize. Finally, the simulation and experimental results are exhibited to verify the effectiveness of the proposed control scheme.