Study On Key Technology And Design Method Of Hybrid Energy Storage System For Electric Vehicle

The greenhouse gas emissions and non-renewability of fossil energy are two major problems which restrict the development of traditional automobiles.Electric vehicles(EVs)have made rapid development in recent years in many countries of the world as an effective way to solve these problems.One of the key technologies of EVs is energy storage system,and it is also the biggest bottleneck for the development of EVs.In the energy storage system of electric vehicle,the design requirements usually can’t be met because of the restriction of power density and life of battery pack.The hybrid energy storage system(HESS)composed of supercapacitors and batteries can make full use of the advantages of batteries and supercapacitors.HESS can take system energy,power,life,efficiency and other needs into account which makes the electric vehicle energy storage system achieve more balanced performance.In this paper,the basic theory and design method of lithium-ion battery and super-capacitor HESS are studied according to the existing problems.Bellowed problems are solved: prediction of the battery life under the driving cycle,the design method of integrated power converter,the parameter matching and optimization of battery and ultracapacitor,the design of the energy management strategy.The following research work has been completed.(1)Characteristic study and modeling of lithium-ion batteries,supercapacitors,power converters and other key components.The life reduction characteristics of lithium batteries under driving cycle were studied in this paper,and prediction model for the battery life under automobile driving conditions is proposed.At the same time,the circuit model of lithium-ion battery and supercapacitor is established through the experimental data,and the models of the key components such as permanent magnet synchronous motor and its controller are deduced.In order to reduce the volume,weight and cost of the converter,an integrated converter for HESS is proposed in this paper.It has the functions of bidirectional DC/DC,single phase inverter and battery charger.(2)Study of the parameter matching and optimal design method of HESS.Based on the study of the key components of the HESS,the HESS with different configurations are analyzed and compared to obtain the best topology for the target vehicle.A HESS evaluation method which takes battery life,system hardware cost,power consumption,system loss,driving mileage and other factors into account is proposed.based on the target vehicle,a dynamic programming method to optimize the energy distribution is proposed by taking the cost per kilometer as the optimization objective.The effects of different battery and supercapacitor parameters on the performance of HESS are analyzed,thus obtaining the optimum parameters of lithium-ion battery and supercapacitor.(3)The study of energy management strategy of HESS.For the optimized HESS,an energy management strategy based on adaptive neural fuzzy rules is proposed.In contrast,an energy management strategy based on fixed rules and fuzzy rules is formulated.The simulation results show that the proposed adaptive neural fuzzy rules based on driving cycle prediction have the best effect on prolonging the life of lithium-ion batteries.(4)The development of prototype and experimental verification of HESS.Based on the proposed HESS design theory,a prototype of HESS,including lithium-ion battery pack,supercapacitor pack,integrated power converter and main controller is developed,and a test bench is established.The performance of the HESS prototype under different driving cycles and different energy management strategies is tested,which verifies the correctness of the HESS design theory.The test results show that HESS system can prolong the life of lithiumion batteries and reduce the use cost of energy storage system effectively.