Research On Energy Management Strategy Of Battery And Supercapacitor Hybrid Energy Storage Systme

In recent years,the shortage of fossil fuel reserves and global warming have been increasingly concerned.The improvement of the concept of environmental protection has made people strongly demand that petroleum consumption be reduced in transportation.With this opportunity,the replacement of traditional fuel vehicles with pure electric vehicle that has the advantages of energy saving,low noise,and low emissions is bound to become the future development trend.Pure electric vehicle can choose battery and supercapacitor hybrid energy storage system as a power support.In the hybrid energy storage system,energy management of the energy storage unit is performed to achieve energy distribution between the storage battery and the supercapacitor energy storage unit,so that the two energy storage units release or absorb energy according to their characteristics to meet the load power requirement,that prolong the cycle life of each energy storage unit and meet the energy and power needs of pure electric vehicles.Therefore,it is of great significance to study the energy management strategy of hybrid energy storage system.The common electric vehicles and commonly used energy storage units are introduced in this thesis,and through the comparative analysis of their characteristics,the battery and supercapacitor hybrid energy storage system are selected as an energy storage unit.The topology characteristics and application occasions of energy management converters are analyzed such as forward bidirectional DC/DC,dual-transistor forward bidirectional DC/DC,push-pull bidirectional DC/DC and bidirectional full-bridge isolated DC/DC.Two-way fullbridge isolated DC/DC converters serve as the main energy management circuit for battery and supercapacitor hybrid energy storage systems.Therefore,the working principle of the bidirectional full-bridge isolated DC/DC converter is mainly analyzed,and the mathematical model and power transfer function of the bidirectional full-bridge isolated DC/DC converter are derived.Based on the analysis of basic principle of battery and supercapacitor energy storage unit,the traditional phase shift control strategy of the bidirectional full-bridge isolated DC/DC converter is studied.Combining the load power requirements and transient characteristics of electric vehicles,in order to better achieve a reasonable distribution of power and energy between the battery and the supercapacitor energy storage unit,this thesis is based on an approximate instantaneous power model of a two-way bidirectional full-bridge isolated DC/DC converter.A two-channel model predictive direct power control strategy is studied.The strategy can flexibly distribute the output power according to the operating characteristics of the battery and the supercapacitor,and can achieve fast transient response to changes in the hybrid energy storage system in the event of a sudden load change.On this basis,the DC bus voltage constant pressure control strategy of the hybrid energy storage system is further studied.This thesis uses MATLAB/Simulink software to build a simulation model of battery and supercapacitor hybrid energy storage system.The simulation results show the feasibility of the research control strategy.Finally,based on the theory and simulation analysis,an experimental prototype is built.The experimental results proved the correctness of theoretical analysis and simulation results.