Research On Compound Energy Storage System Of Pure Electric Bus With Dual Energy Supply

In recent years,due to the increasing environmental problems and energy shortages caused by traditional fuel vehicles,pure electric vehicles have gradually entered the public view.Pure electric vehicles use electric energy as a source of power,and no exhaust is generated during driving,which is environmentally friendly and pollution-free.Compared with traditional fuel vehicles,it has huge advantages in energy saving and emission reduction.The state has also continuously issued relevant policies to vigorously support the development of pure electric vehicles.Due to the current bottleneck of power battery technology development,the energy density,power density,and high-current charge and discharge capacity of power batteries need to be improved,resulting in the driving range,power performance,ride comfort,and operating reliability of pure electric vehicles are still far from traditional fuel vehicles.Aiming at the inherent shortcomings of pure electric bus power batteries,this dissertation adds a super capacitor and a bidirectional DC-DC converter to form a composite energy storage system.The advantages of high power density of supercapacitors are used to compensate for the low power density of power batteries,thereby optimizing the power performance of pure electric buses and extending the driving range.In this dissertation,the type of power battery for pure electric bus is lithium iron phosphate battery.Charge and discharge experiments were performed on lithium iron phosphate batteries at different rates to analyze the charge and discharge characteristics,and charge and discharge experiments of super capacitors with different current values.By comparing the advantages and disadvantages of different topologies of bidirectional DC-DC converters,a bidirectional half-bridge topology is selected,however,considering the higher power level in practical applications,two bidirectional half-bridge topologies are eventually connected in parallel as a bidirectional DC-DC converter topology.After analyzing the working characteristics of the battery and super capacitor,and comparing the advantages and disadvantages of the four types of composite energy storage system topologies,the semi-active structure of the super capacitor series bidirectional DC-DC converter was finally selected.The parameters of the composite energy storage system were matched according to the design performance indicators of pure electric bus.This dissertation develops fuzzy control strategy and wavelet transform control strategy.A pure electric bus model is built in AVL＿CRUISE,and the control strategy is embedded in the model.Perform joint simulations on the road cycle conditions of city bus in China and road cycle conditions of city in Harbin.The simulation results show that the proposed control strategy can reduce the power taken by the power battery,realize a reasonable allocation of power battery and supercapacitor energy,save more energy,and in comparison,the wavelet transform control strategy is more effective.In order to verify the effectiveness of the control strategy of the composite energy storage system for pure electric bus,properly reduce the power system parameters of pure electric bus through similar principles to build an experimental bench.Using test bench to simulate the acceleration,climbing and braking feedback of pure electric bus.The curve obtained from the test is consistent with the result obtained from the joint simulation,which proves that the control strategy of the pure electric bus composite energy storage system can achieve reasonable power distribution.