Research On Energy Control Strategy For Electric Vehicle Composite Energy Storage System

With the increasingly serious problems of energy and environment,promoting the pure electric vehicle industry vigorously is not only an effective solution to solve the energy crisis,but also a powerful measure to promote China’s green development.At present,most electric vehicles use batteries as the energy source.However,electric vehicles need acceleration and deceleration switching frequently due to the variability of urban road conditions.When the electric vehicle is accelerating,it will generate a large current inside the battery pack,and will contribute a large impact,which affects its cycle life seriously.Besides,the energy cannot be recovered effectively when the electric vehicle decelerates owing to the low recovery rate of the battery.In view of the above problems,a composite energy storage system with lithium-ion battery pack and super-capacitor pack as energy storage units is constructed by making full use of the advantages of high energy density and high power density of lithium-ion battery and super-capacitor.Because of the different types of energy sources in the system,energy control strategies is an important part of the composite energy storage system.The main research contents are as follows:Firstly,aiming at the problem that large current has a great influence on the cycle life of pure electric vehicle battery pack,a composite energy storage system with lithium-ion battery and super-capacitor battery as energy storage unit and DC/DC converter as intermediate connection device is constructed.The components were studied,including the charging and discharging characteristics of lithium-ion battery and super-capacitor battery,the capacity characteristics,and the efficiency characteristics of DC/DC converters.On this basis,by comparing the advantages and disadvantages of different models of lithium-ion batteries,super-capacitor batteries and DC/DC converters,select the component models that meet the requirements of this paper,and construct a suitable overall structure for the electric vehicle composite energy storage system at the same time.Secondly,the special software for vehicle simulation ADVISOR is redeveloped to add the ability to simulate the composite energy storage electric vehicle.The original super-capacitor group drive mode is added and a new working mode is established on the basis of the traditional driving mode of the original lithium-ion battery pack alone,lithium-ion battery pack and super-capacitor group driving,regenerative braking and pure charging.Thirdly,based on the secondary development of ADVIOR and improved working mode,considering the shortcomings of inaccurate state partitioning parameters when using the traditional logic threshold method to formulate the energy control strategy,it is proposed to use the fuzzy control method to develop energy control strategy for the electric vehicle of the composite energy storage system.And it is verified by using the ADVISOR.The above simulation results are compared with the simulation results of logic threshold control strategy developed under the improved and unimproved working modes to verify that both the improved working mode and the fuzzy control strategy can reduce the current flowing through the lithium battery pack and extend its cycle service life.Finally,Based on the hardware and software structure design of the composite energy storage system,an energy control experimental platform for low-power composite energy storage system is built.And the energy control strategy is formulated with the fuzzy control method to verify the feasibility and effectiveness of the composite energy storage system under the improved working mode.