Research On Active Battery Management System Battery Equalization Technology Based On MMC

In recent years,many factors,such as energy crisis,environmental pollution and energy security problems,have put electric vehicles on the historical stage.Power lithium battery has become the preferred energy storage component for electric vehicles because of its superior performance,but its capacity limitation and high cost also restrict the development of electric vehicles.Superior battery management system can maximize the performance of power lithium battery and extend its life.This paper focuses on two key technologies of battery management system,SOC estimation and battery equalization.This paper begins with the battery model.The second-order RC equivalent circuit model was established by battery capacity test,parameter identification and curve fitting.Combining with the second-order RC equivalent circuit model,EKF algorithm is studied to estimate battery SOC.In order to verify the accuracy of EKF algorithm in estimating SOC of batteries,an off-line EKF estimation experiment was conducted under FUDS operating conditions.Aiming at the existing problems in the equalization topology of lithium batteries,combining cascade equalization topology with MMC DC-DC converter,an equalization topology based on MMC DC-DC is proposed.The basic principle of the equalization topology and the characteristics of carrier phase shift modulation are analyzed.In order to meet the control requirements of the system,according to the characteristics of the system,the battery module voltage is determined as the equalization variable.The average,range and standard deviation of voltage are used to analyze the equalization speed and effect.The mathematical model of MMC DC-DC converter is derived.In view of the coupling relationship between the voltage outer loop and the equalization inner loop in the model,a control strategy based on the average voltage of the battery module as the given value of the equalization inner loop is proposed,which can realize the decoupling of the double closed-loop.According to the decoupled mathematical model,the double closed-loop is designed independently.Voltage outer loop compensation is designed by frequency domain design method.Two control strategies,P regulator and adaptive P regulator,are used to realize the balancing control for the inner loop of the equalizer.The results show that the equalization speed is only determined by the voltage difference when the P regulator is used,and the equalization speed decreases as the battery voltage gradually converges during the equalization process.In order to solve this problem,an adaptive P regulator is proposed to adjust the parameters adaptively so as to keep the equilibrium speed constant.The above control strategies are validated by simulation and their balancing effects are compared.The BMS hardware experiment platform is built,and the specific hardware circuit is designed in detail,including controller,sampling circuit,driving circuit and so on.On the basis of hardware circuit,software architecture is built to refine the flow of each task.The computer software is designed to analyze and record data.The corresponding experimental scheme is formulated,and the EKF algorithm estimates SOC and balanced topology are tested using BMS experimental platform.According to the experimental results,the EKF algorithm and equilibrium control strategy are analyzed and evaluated.