Research On Energy Control System Of Electric Bus With Compound Power Supply

In recent years,although China's economy has entered the stage of medium-high economic growth,the demand for energy continues to rise,and the external dependence of crude oil is about to enter 70%.At the same time,the burning of a large number of fossil fuels has led to the rise of global temperature,smog,acid rain and other environmental problems.Therefore,reducing the use of fossil fuels has become a top priority.Electric vehicles can achieve zero emission by using electric energy as power source.Compared with traditional vehicles,it can greatly reduce the impact on the environment and meet the requirements of energy saving and emission reduction.Therefore,all countries in the world focus on the development of electric vehicles.However,due to the influence of the existing battery technology,the driving mileage,power performance,comfort and safety of electric vehicles are not comparable to those of traditional vehicles,and the battery is also limited by its service life,specific power and other aspects,so the development of electric vehicles has suffered tremendous challenges.In view of the defects of batteries,a composite energy storage system is composed of batteries,supercapacitors and bidirectional DC/DC converters.The advantages of supercapacitor,such as fast charge and discharge speed and high specific power,are used to compensate for the shortcomings of battery,so as to improve the power performance of electric bus and extend its driving range.In this dissertation,the working characteristics,advantages and disadvantages of various batteries are analyzed,and the charging and discharging experiments and temperature characteristics experiments of selected lithium iron phosphate batteries are carried out.The working principle of supercapacitors is analyzed in detail,and the constant current charging and discharging experiments and constant power discharging experiments at different rates are carried out;the various topologies of bi-directional DC/DC converters are analyzed,and finally the bi-directional half-bridge DC/DC converter is selected.For the four connection modes of composite energy storage system,the most economical and efficient structure of is selected that lithium battery is passive and supercapacitor is active,and its working mode was formulated in detail,and the parameters of each part were matched.According to the working mode of the composite energy storage system,the power allocation strategy based on logic threshold and the power allocation strategy based on fuzzy control are formulated.In AVL CRUISE,the simulation model of electric bus with composite energy storage system is built,and the control strategies are simulated under typical urban road conditions in China and urban road conditions in Harbin respectively.The simulation results prove the rationality of the power allocation control strategy,and the effect of the fuzzy control strategy is better.To verify the feasibility of the fuzzy control strategy for the hybrid energy storage system of electric bus,a electric bus driving system test bench was built,and related experiments were carried out.The experimental results are in agreement with the simulation results,which prove that the power allocation strategy based on the fuzzy control is reasonable and effective.