Research On Modeling And Control Strategy Of Composite Power Supply System For Electric Bus

As an significant member of new energy vehicles,electric buses have gradually become the object of vigorous development of China’s green transportation.Due to the limitation of battery technology at the current stage,electric vehicles with a single energy storage device have some limitations which are continue voyage course and operational life span.As a new type of energy storage device,the super capacitor has the advantages of high power density,high charge and discharge speed,long cycle life,etc,and is combined with a power battery to form a composite power supply,which can effectively compensate for the defects of a single energy storage device.This paper will study the modeling and energy control strategies of the composite power system for electric buses.This paper analyzes the advantages and disadvantages of several common power batteries,selects a lithium iron phosphate battery with higher safety and longer cycle life as the research object of this paper,and the characteristics of the charge and discharge characteristics and internal resistance of lithium iron phosphate batteries.Detailed analysis of operating characteristics such as efficiency characteristics and cycle life.At the same time,the structural principles and operating characteristics of super capacitors and DC/DC converters are also analyzed.In order to improve the simulation accuracy of power battery model,this paper designs a battery SOC estimation algorithm based on BP neural network for the characteristics of frequent start and stop and load changes of electric buses.Firstly,the factors affecting the SOC of the power battery and several typical estimation algorithms are analyzed.Afterwards the structural principle of the BP neural network is analyzed.The SOC neural network estimation model of the lithium iron phosphate battery is established and trained,and the BP neural network can be effectively improved through simulation.Power battery SOC estimation accuracy.Furthermore,several kinds of topological structures of the composite power supply are analyzed,and a super capacitor series DC/DC converter with high efficiency and initiative is selected,and then the structure is connected in parallel with the power battery,and the specific operating conditions of the electric bus are combined.The principle and operation mode of composite power supply are analyzed.By comparing several equivalent models of power battery and super capacitor,a simulation model of power battery,super capacitor,DC/DC converter and power bus was established based on Matlab/Simulink,and a composite power system simulation was established based on this model.According to the actual operating conditions of the electric bus,combined with the control objectives of the composite power supply,this paper designs a logic threshold control strategy.Based on this,the fuzzy control strategy based on SOC optimization of power battery is designed,and the design schemes and control rules of the two control strategies are formulated in detail.The simulation model was established in Matlab/Simulink.Then,the composite power model,control strategy model,and vehicle parameters are set in the Advisor simulation software.The simulation analysis was performed on the driving conditions of typical Chinese cities that can reflect the actual operation of electric buses.Through the simulation results,we can see that the super capacitor in the composite power supply fully exerts the function of “dispelling the peak and filling the valley”.It can effectively avoid frequent high-current charge and discharge of the power battery and improve the braking energy recovery efficiency.Compared with the logic threshold control strategy,the optimized fuzzy control strategy can further reduce the peak current of the power battery and prolong its service life.