Research On Balance Control Strategy Of Power Battery Pack

The power battery system is the core technology of new energy vehicles.The difference in the manufacturing process of the battery cell makes the chemical and electrical properties of the single cell battery have certain differences.During the charging and discharging cycle,the individual cells in the battery pack are inconsistent,thereby affecting the overall performance of the battery pack.In order to improve the consistency of the battery pack,it is necessary to balance the management of the power battery pack.At present,the power battery pack equalization technology is still immature,and it is necessary to continue to carry out related research.Therefore,this paper has made further research and design on the equalization control technology from the following aspects.Firstly,through reviewing a large number of literatures,the current research status of battery pack equalization technology at home and abroad is discussed.On the one hand,the existing balanced topological structure is introduced in detail,and their respective advantages and some existing shortcomings are pointed out.On the other hand,a brief overview of several equalization strategies currently in use is outlined.Secondly,combining the electrochemical reaction mechanism and physical charge and discharge experimental data,the basic characteristics of lithium ion batteries are described.Through the analysis of the production,work engineering and storage process of lithium-ion batteries,the sources of inconsistency of lithium batteries are summarized,and effective treatment measures are proposed.The experimental test method is used to summarize the manifestations of lithium battery inconsistency from the three aspects of open circuit voltage,working voltage and SOC.Next,the equalization main circuit is miniaturized and the unit is modularized on the basis of the traditional transformer-type equalization topology.For a battery pack of different scales,an appropriate number of equalization main circuit units are selected,and the equalization main circuits are cascaded.The unit performs line connection to realize a bidirectional active equalization topology with good scalability,achieving the goal that energy can be efficiently transferred between a specified single cell and a battery pack.At the same time,the advantages and disadvantages of commonly used equalization variables are compared and analyzed,and an equalization control strategy with open circuit voltage as the equilibrium variable is proposed.Then,the hardware of the equalization system is designed by modular method,including the main control module based on STM32,the single voltage monitoring module based on LTC6803,the temperature monitoring module based on DS18B20,The equalization switch controller based on LTC3300 and the equalization main circuit based on the fly-back transformer realize the hardware system of the equalization system based on the previous theoretical analysis and experimental tests.The software of the equalization system is designed by the idea of low coupling and high cohesion,including the driver of each hardware circuit and the system of equalization control algorithm to complete the software system of the equalization system.Finally,according to the design of this paper,the prototype of the equalization control system that can manage 12 single cells is completed,and the test platform is built under the existing conditions of the laboratory.The main functional units such as battery cell voltage monitoring,temperature monitoring and equalization module are built.Tests were carried out to test the system static balance,charge balance,and discharge balance.The test results verify the correctness and feasibility of the design.