Design And Research Of Battery Management System Based On STM32 And Active Cell Balancing

With the continuous replacement of the traditional fossil energy by various renewable energies,energy storage technology has been greatly developed.Especially,the battery pack with lithium-ion cells has been widely used in electric vehicles and micro-grid.In order to improve the energy storage capacity and to output higher power and voltage,a large battery energy storage system is usually composed of numerous cells connected in series and parallel.In this case,a battery management system（BMS）is necessary to manage these cells,so as to ensure the safe and stable operation of the battery pack.After analyzing the current research status of BMS,this paper makes a constructive research and designs a new BMS.Firstly,STM32 is used as the main control unit and BQ76940 is used as the data acquisition unit in the new BMS.After the preliminary completion of a battery management system,the active cell balancing circuit is studied and the equalization system is implemented.Then,the EKF algorithm is used to realize the real-time online estimation of battery SOC.Finally,the fault diagnosis of battery internal resistance increase is studied.The main contents of this paper are as follows:（1）Design of BMS based on STM32 and BQ76940.Firstly,the battery data acquisition system is designed by using STM32 MCU and BQ76940 chip.Through the design method of software and hardware,a BMS is built to realize the management of 15 lithium batteries in series.Then the sampling of battery voltage,current and temperature is tested.The experimental results show that the sampling accuracy of the BMS data acquisition system is high.（2）Research on active cell balancing technology.Firstly,an improved switched-capacitor active equalization circuit is analyzed and applied to the BMS equalization system.Then,a double-layer active equalization circuit based on switched-capacitor and switched-inductor is proposed.After analyzing the equalization principle,the simulation and experiment results show that the circuit has the advantages of simple control,fast equalization speed,good equalization effect and so on.Thus,this circuit can be applied to battery management system.（3）Research on battery SOC estimation.Firstly,Thevenin equivalent circuit model of lithium battery is built.After introducing the basic principle of RLS algorithm,the model parameters R₀,R_P,C_Pand U_OCare identified by using the algorithm.Then,the basic principle of EKF algorithm is introduced and the SOC of battery is estimated by using the algorithm.Finally,the simulation and experiment are combined to verify that the algorithm can realize the real-time online estimation of battery SOC with high accuracy.（4）Research on fault diagnosis of increasing internal resistance of battery.A two-stage decision method is proposed to diagnose the fault of increasing internal resistance of battery.Firstly,the internal resistance of battery is identified by the method of parameter identification.Then,the comprehensive diagnosis is made according to the temperature and voltage drop of battery during discharge.Finally,the effectiveness of the algorithm is verified by simulation.In the second chapter to the fourth chapter,the data acquisition system,active equalization system,SOC estimation and fault diagnosis of battery management system are analyzed in detail.On the basis of theoretical analysis,the feasibility and effectiveness of each part of BMS are proved by simulation and experiment.