Energy Management Method for Hybrid Energy Storage Tram Based on Equivalent Loss Instantaneous Optimization

In order to improve the system efficiency and operational economy of hybrid energy storage (HES) tramway under cycle conditions, this paper presents an energy management method based on equivalent loss instantaneous optimization (ELIO) for lithium battery/supercapacitor hybrid energy storage system (HESS) with dual DC/DC topology. The online convex programming method is used to solve the problem, and the optimal dynamic mixing degree at each moment of the system is obtained. This proposed method properly allocates the power flow between lithium battery and supercapacitor to minimum the system equivalent loss in the unit control period. According to the equivalent loss theory, the ELIO problem is converted to the optimal output power solution of the HESS. Under various operating conditions, the multi-index performance is tested and analyzed by a HESS test platform, which consists of lithium battery, supercapacitor, bidirectional DC/DC converter and energy management system. The experimental results show that compared with the power following strategy, this proposed ELIO method can effectively improve more than system efficiency, operational economy and driving mileage, and improved the service life of HESS by smoothing battery operating pressure.