Research On Energy Management Strategy Of Composite Energy Storage System For Electric Vehicle

In recent years,the problems of resources and environment become more and more prominent,which makes electric vehicle become a hot research topic.Considering that there is no single energy storage device on the market that can meet the requirements of high power density,high energy density and high durability of electric vehicles.In this paper,a battery which has high energy density and short cycle life is combined with an supercapacitor which has high power density and long cycle life to constitute a composite energy storage system(CESS)which can make full use of their advantages of both.How to distribution between two kinds of energy source is directly related to the electric car’s range and the lifetime of the battery due to there are two kingd of energy sources,so this article mainly aims at the offline energy management strategy(EMS)of CESS and real-time EMS for research.In order to make most of CESS,reduce the system loss to increase the mileage of electric vehicles,extend the cycle life of batteries,and reduce the capacity configuration of supercapacitors,this paper proposes a CESS multi-objective EMS based on load power separation.Firstly,the load power is divided into static power and dynamic power by load power separation method.Then,combined with the loss model of CESS,a multi-objective optimization function was established according to the optimization objective.Then,the non-dominated sorting genetic algorithm with elite strategy(NSGA-II)was used to optimize the dynamic power allocation.Finally,the influence of different load separation methods on the optimization results is compared and analyzed.Multi-objective EMS based on load power separation relies on global working condition data and cannot realize real-time control.Therefore,a real-time EMS considering multiple targets is proposed in this paper.Digital first-order low-pass filter is selected as the load power separation method.Firstly,according to the system loss formula,the load dynamic current distribution method which can minimize the system loss is deduced.Then,according to the State Of Charge(SOC)of the supercapacitor,the filter coefficient adjustment function is constructed to adjust the SOC in the normal charging and discharging range to maintain the ability of buffering instantaneous high power.Then,according to the current change rate of the battery,the load dynamic current distribution ratio adjustment function is constructed to reduce the current fluctuation of the battery and extend the life of the battery.Finally,the simulation was built in Matlab/Simulink and compared with the rule-based EMS.Considering the limited experimental equipment and safety factors,a lowpower experimental platform was built,and the ECE15 working condition,which was easy to realize,was selected to verify the real-time EMS proposed in this paper.The experimental results essentially in agreement with the simulation results,indicating the practicability of the proposed strategy.