Research On Battery Life And Application To Control Of Extended-Range Electric Vehicle

With the increasing number of the production and sales of automobiles,energy and environmental problems become increasingly serious,and new energy vehicles have become an important strategic direction for the development of China's automobile industry.As a breakthrough in the new energy vehicles,the development of Pure Electric Vehicle(PEV)is restricted to the factors of power battery's cost,energy density,life and so on.However at this stage,the Extended-Range Electric Vehicle(E-REV)has become an important development direction for the promotion of new energy vehicles,because it is a key transition to PEV.Power battery,the main energy source of E-REV,its life characteristic directly affects the cost and usage of vehicles.Therefore,a “Blended control strategy” is developed on the basis of research on battery life in this paper.The purpose is to reduce the decline in the battery's capacity and to extend its service life.The main contents are as follows:1.Take lithium iron phosphate battery as the research object.The research on life decline of lithium iron battery can be divided into three steps.Firstly,complete the theoretical analysis and summary about the influence factor of lithium iron battery life and degradation.Secondly,An accelerated life test of battery are experimented in order to acquire battery life declining data.Thirdly,The basic life model of lithium iron phosphate battery was determined,and the parameters in the basic life model were identified.Then by the relevant data about the short-term experiment of battery accelerated life,the characteristic parameters of the battery research object are fitted and the specific life model is verified.Finally we can get the life decline model of target battery.2.According to the power system's structure and performance requirement index of E-REV,this paper matches the parameters about the main components of power system.The main purpose is to determine the parameters of power battery pack and auxiliary power unit(APU).Then the target vehicle is determined and the research on power battery can be applied on it.3.Power battery pack and APU are two power supplies of E-REV.In order to improve the battery's service life,We have a strategy named “Blended control strategy” which need using APU to compensate the pack of power battery.And then,based on the control system of E-REV,we can establish a detailed control flow.At the same time,we also explore the feasibility that combine the vehicle's simulation platform that built in Cruise and the control algorithm written in the MATLAB/Simulink to verity the control strategy.4.According to the simulation results of different control strategy,power battery's life decline data are calculated by using the life model.Comparing the battery's life decline under the traditional EV+CS control strategy with the Blended control strategy,we can conclude that the decrease of battery's capacity can be reduced effectively and the service life can be extended under the Blended control strategy.Defining battery retirement at 80% remaining capacity,Blended control strategy can extend the life of battery for 1.56 years.Considering the influence of battery capacity reduction on the control strategy,an adaptive algorithm based on threshold dynamic adjustment is proposed to improve the Blended control strategy.After simulation,the improved control strategy can further extend the battery's 3.75% of the service life.5.The energy consumption of full vehicle was counted with the cost of the daly use as evaluation index.After different control strategy's contrast,Blended control strategy can reduce the cost of daily use on three years later.And this effect is more significant with the increase of service years.This is mainly due to the reduction of battery's capacity increases the pure electric drive ratio.