The Research Of Hybrid Energy Storage System Based On FLC

With the increasingly serious global energy issues and the environmental problems,people tend to be stricter about automobiles in terms of energy conservation andenvironmental protection. In order to solve the energy crisis and environmental degradation,governments, researchers and automobile enterprises all over the world are all increasing thedevelopment and investment efforts of the non-polluting electric vehicles to accelerate thecommercialization pace of electric vehicles.At present, the main reason that restricts the development of electric vihichles is that thedriving range is not satisfactory. Therefore, it is necessary to design a reasonable energyallocation and recovery strategy to maximize the use of limited loaded energy, thus increasingthe mileage. The hybrid energy storage system, which composed of high-power densityultracapacitors and high-energy density batteries, can improve the performance of the energystorage system of electric vehicles.The storage system can output high power instantaneously,absorb regenerative braking energy quickly by taking advantage of the long life cycle, fastcharge and discharge speed and high power density of ultracapacitors, then the driving rangewill be increased. Distributing the discharge current of ultracapacitors and batteriesreasonably could optimize batteries’ discharge curve thus extending the life of batteries. Thispaper mainly analyzes the advantages and disadvantages of different vehicle power storagedevices, selects ultracapacitors and lithium-ion batteries as energy storage devices to assemblethe hybrid energy storage system. Discusses the advantages and disadvantages of severalcommonly used hybrid energy storage system topologies, then use the topology’ lithium-ionbatteries connected with ultracapacitors in parallelthrough a bidirectional DC/DC converter’which is able to fully take advantage of ultracapacitors to build the system model on Matlab/Simulink simulation platform.In this paper, the load current, the SOC (State Of Charge, remaining capacity) ofultracapacitors, and the SOC of lithium-ion batteries are taken as input variables, thedutyfactor of power switches used in the bidirectional DC/DC converter devices is taken asthe controlled object to design a fuzzy logic controller. A list of fuzzy logic rules is developedbased on the distribution of the energy storage systems under different circumstances alongwith the controller. Then the system is studied and simulated respectively in two states: thenormal operation and regenerative braking of electric vehicles.The simulation results show that the energy can be reasonably distributed by thefuzzy-logic controller and the use of ultracapacitors greatly improves the power outputcapacity of electric vehicles while optimizing the discharge current of the battery. The systemcan also absorb the regenerative braking energy quickly. It turns out that the whole system isconducive to extend batteries’ life and increase the driving range of electric vehicles, withpreferably technical performance and economic practicality.