Research On Key Technologies Of Active Battery Balance System

As a power source for electric vehicles,the voltage and energy power that single-cell electrochemical batteries can provide is far from sufficient to meet the requirements.Generally,multi-cell batteries are used in series to form a high-voltage battery pack to meet the voltage and power requirements in electric vehicles.However,due to the complexity of the battery production process and the manufacturing process,the cells of the series battery group are difficult to achieve complete consistency,and the environmental difference in the use process further exacerbates the inconsistency among the battery unit battery performances,resulting the imbalance has worsened between the cell.Therefore,during the use of the battery pack,it is necessary to improve the inconsistency among the cells through equalization control.It can improve the energy utilization efficiency of the battery pack,increase the service life of the battery pack,and further improve the battery life of the electric vehicle.This article analyzes the causes and effects of inconsistency in the performance of battery packs.Based on the charge and discharge of the battery pack and the Hybrid Pulse Power Characteristic(HPPC)test,the manifestations of inconsistency in cell performance are studied.Comparing the advantages and disadvantages of the open circuit voltage,working voltage,and State of Charge(SOC)as the equalization variable,the working voltage is selected as the equalization variable of the battery pack equalization control.To realize the goal of high efficiency and fast balancing,this paper proposes an improved bidirectional DC-DC converter based on active clamp forward converter as the equalizer main circuit.The topology can be realized between the whole battery and any single cell.Energy flows in both directions.The working principle of the topology in the charge and discharge mode is analyzed,and the theoretical basis for implementing the soft switch of the main switch tube is proposed.Taking the four-cell series battery pack as an example,the main parameters of the bidirectional DC-DC converter are designed.On this basis,Saber software is used to verify theoretical analysis and design results.The control circuit of the equalization control system is designed,including a driving circuit,a sampling circuit,a switch array,and so on.To design the voltage detection circuit of multiple cells,this paper uses the LTC6803-4 chip through SPI communication and DSP exchange information,and improves the sampling accuracy of the battery voltage.Besides,the drive circuit of the switcharray is optimized to improve the switching speed.The balanced control strategy is designed for the entire battery pack to improve the equilibrium efficiency and reduce the equalization charge-discharge time.Finally,a four-cell battery pack is taken as the control object,and an experimental platform for the battery balance control system is set up.The experiments are carried out under the conditions of the equalization control system charge and discharge,and the constant current charge and discharge of the equalization main circuit is realized.The effects of the equalization control system are evaluated,and it is proved that the equalization control system can improve the inconsistency of the battery pack well.