Research On Balance System Of New Electric Vehicle Battery Pack

Electric vehicles have gradually become a popular and development trend.Although gasoline and diesel vehicles have not been completely replaced,their development speed is extremely fast,and their share in the market is also increasing year by year.The core part of the electric vehicles is the power battery pack and the battery pack equalization system.The battery pack is the source of power output of electric vehicles,and the management system can monitor and protect the battery pack in all directions.The battery pack is connected by a large number of lithium-ion single batteries,which results in individual differences due to factors such as manufacturing process and working environment.After the batteries are grouped,this difference has a great impact on the power battery.It will seriously reduce the overall performance of the battery pack,and even cause battery damage and reduce battery life.The equalization technology in the management system is the main means to solve this inconsistency.Therefore,it is of great significance to study it.The equalization technology includes two parts: the equalization control strategy and the equalization topology circuit.The equalization control strategy is the decision maker of equalization control.By calculating and processing the battery information collected by the system,the optimal control signal is output to control the circuit,change the action state of the switch device.The equalization topology circuit is the executor of the whole equalization control,which is directly connected with the battery pack,and changes the magnitude and direction of the circuit current through the action of the switch device,so as to transfer the energy of the battery and achieve the goal of making the state of charge(SOC)of the single cell consistent.Based on the study of some classical circuits,the equalization circuit based on Buck-Boost is designed,the second-order RC battery model is established,and the extended Kalman filter algorithm is designed to estimate the SOC of the batteries.By analyzing the state of battery charge and discharge,a new stage-by-stage equalization control strategy is proposed,which uses different strategies to control the charge and discharge of the battery in the beginning and end stage and intermediate stage.The equalization method controls the different states of the battery,the control is more accurate,and the equalization effect is better.The battery model,battery SOC estimation algorithm,equalization circuit and equalization control strategy are simulated and analyzed by MATLAB/ SIMULINK.Taking the equalization control strategy and equalization circuit as the core,the related hardware and software are further designed,and the battery pack equalization system of electric vehicle is built.STM32F103 series chips are selected to construct the main control circuit to realize the functions of data processing and communication with the host computer.The acquisition circuit of voltage,current and temperature is also designed to collect the battery information and transmit the data to the main control module.At the same time,it includes other peripheral circuits and software parts designed to form the battery pack equalization system.The feasibility of the method is verified by experiments in the experimental platform built by the comprehensive test system of ITS5300 power battery pack and other instruments.compared with other methods,it is proved that the equalization effect of this method is better.It can not only effectively reduce the range of battery SOC,more than 5% less than the method of single equalization strategy,but also increase the amount of electricity that can be charged and discharged by the battery pack.Compared with the method using a single equalization strategy,in the charging stage,this method charges more 1967.36 mAh energy into the battery pack,and in the discharge stage,the battery pack discharges more 680 mAh power.And according to the latest national standard “Energy consumption rate limitation of Electric vehicles” in 2019,the lowest limit of energy utilization rate is 78.1%,and the designed phased equalization strategy control method has an energy utilization rate of more than 92% in the process of charging and discharge.The utilization rate meets the requirements of the national standard.