Rule-filter-integrated Control of LFP/LTO Hybrid Energy Storage System for Vehicular Application

This paper proposes a semi-active hybrid energy storage system (HESS), which uses lithium titanate batteries (LTO) to prolong the life cycle of lithium iron phosphate batteries (LFP). A bidirectional DC/DC converter is adopted to decouple the LTO battery from the LFP battery and system load. To evaluate the life cycle of proposed LTO/LFP HESS, the dynamic model is established firstly, including the degradation model of LFP battery. Second, the operating modes of LTO/LFP HESS are explored, and a novel rule-filter-integrated power split strategy is proposed to reduce the peak or root mean square (RMS) values of LFP battery's current. Simulation results of taxi application show the proposed HESS improves the lifespan of LFP by 35.4% compared to the system with single LFP, resulting in 7.14% annual cost and 32.18% cycle-related cost reduction.