| In view of the increasingly severe situation of resources shortage and environmental pollution at present,electric vehicles have been rapidly developed due to their high efficiency,energy saving and environmental protection.Hybrid energy storage systems are widely used as power sources for electric vehicles as they synthesize the advantages of batteries and ultracapacitors.This paper mainly researches on the control methods of high efficiency bi-directional DC-DC and the control strategies of energy management in hybrid energy storage system,and specifically analyzes from following aspects:Firstly,this paper comprehensively analyzes the working principles and characteristics of each parts in hybrid energy storage system,and chooses the topological structure of ultracapacitor series bi-directional DC-DC as the studied hybrid energy storage system structure on the premise of system efficiency,stability and cost.According to different driving conditions of electric vehicles,power distribution methods of hybrid energy storage system are described in detail,then four different power supply modes of hybrid energy storage system are fully analyzed.Secondly,the dual-active-bridge(DAB)DC-DC converter which has the advantages of easy to realize soft-switching and high power density is select as research topology,severally elaborates the working states of converter under traditional single-phase-shifted(SPS)control and dual-phase-shifted(DPS)control,then the power characteristics of converter and soft switching ranges of switches are analyzed under two different control methods,the simulation models of converter under two different control methods are respectively built to verify the theoretical analysis by simulation.Thirdly,in order to further improve the power transmission efficiency of converter,this paper focuses on the research of DAB converter under dual-phase-shifting efficiency optimization control.The generating mechanism and main influence factors of each parts losses in converter when works steadily under DPS control are analyzed,and the mathematical model of dual-phase-shifting efficiency optimization control are deduced,it is concluded that the inner phase shift ratio of converter total losses reaching a minimum is obtained when transmission power is given,subsequently uses closed-loop control method to regulate outer phase shift ratio,thus the current stress and total loss in the working process of converter are reduced.Compared with traditional SPS control and DPS control,the dual-phase-shifting efficiency optimization control which is used in this paper can effectively improve the power transmission efficiency of converter by comparing and analyzing the simulation results.Finally,fuzzy control strategy is selected to manage the energy in hybrid energy storage system so as to reasonably allocate the energy between batteries and ultracapacitors.Then the hybrid energy storage system simulation model is built,on the basis of this model,electric vehicles simulation model powered by hybrid energy storage system is built with the secondary development of ADVISOR,and battery current waveforms respectively in single power supply and hybrid energy storage system are compared under typical driving cycle of urban roads in China.The use of dual-phase-shifting efficiency optimization control can not only save the energy of electric vehicles,but also increase its mileage by comparing and analyzing the SOC of battery after a complete cyclic working condition simulation. |
PDF Full Text Request