Research On Energy Management Strategy Of Hybrid Energy Storage System Of Electric Vehicle

Regenerative braking is the significant way to improve the driving range of electric vehicle(EV).However,regenerative braking will cause the battery switched frequently between charging and discharging mode and large current discharging will reduce the cycle life of battery.The physical energy storage character of ultra-capacitor(UC)determined it can achieve large current charging and discharging and the cycle life of UC is far greater than the battery.The battery/UC energy storage system(ESS)is proposed benefited from the advantages of battery and UC.This paper aimed to improve the cycle life of battery and the driving range of EV.Based on the basic idea of "battery/UC",the energy storage system is optimized.Specifically,a small number of UCs are used as auxiliary power source to protect the battery.The regenerative braking energy is charged to the UC,which worked as auxiliary energy source for battery to supply power when the vehicle is starting or accelerating.Based on the driving cycles of EV,this paper proposed and studied the concept of the occurrence confidence interval of "probability event" and the proportion of "likelihoodenergy" of regenerative braking.Defining the critical speeds of regenerative braking for EV and the capacity of the UC was determined by vehicle model and two critical speed defining methods.Bi-directional DC/DC converter are analyzed under different working state corresponding to EV working mode.We expounded the working principle of bidirectional DC/DC converter,analyzed and established the corresponding control objectives in order to satisfy the demands of practical application of EV.Establishing the corresponding mode of dynamic system model and designing the controller of bidirectional DC/DC converter.The simulation and experiment results of optimized hybrid ESS and single ESS are analyzed and compared.Finally,we illustrate the optimization effect to the battery by the capacity loss model.