Research On Active Equalization Topology And Control Strategy Of Lithium Battery Based On Improved MMC

With the increasingly serious environmental problems and the continuous reduction of world energy reserves,the problems of pollution and oil shortages caused by the widespread use of traditional fuel vehicles have become increasingly serious.The development of electric vehicles is an important measure to solve environmental and energy problems.In order to meet the operating requirements of electric vehicles,a large number of power batteries are connected in series and parallel to increase the capacity and voltage level of the battery pack.The service life of the battery requires an excellent battery management system to monitor the power battery.This article takes lithium batteries as the research object,starting with the battery balancing module in the battery management system to study the balancing problem of the battery pack.In order to solve the balance problem of the lithium battery pack,the causes of the inconsistency of the power battery pack and the characterization of the inconsistency are analyzed.According to the manifestation of the inconsistency of the battery pack,the battery voltage and remaining capacity are selected as the balance index of the battery pack.In order to accurately obtain the remaining capacity of the battery pack,an 18650 Lithium battery is used as an example to identify the parameters of the secondorder RC model,and the Kalman filter algorithm is combined to estimate the remaining capacity of the battery pack,which lay the foundation for the follow-up with the remaining battery capacity as a balance indicatorThis paper analyzes the balance principle and control strategy of the existing MMC topology,and summarizes its advantages and disadvantages.Aiming at the balance capability brought by the MMC balance topology and the balance loop adjustment adopted,and the balance efficiency problem caused by the voltage regulator loop.The existing MMC balance topology has been improved,and the balance and voltage regulation are independently controlled.Analysis of the factors influencing the optimal equilibrium time of the improved MMC equilibrium topology,the results show that the optimal equilibrium time is composed of the number of single cells in the battery pack,the number of single balanced bypass batteries,charge and discharge current,the initial dispersion of remaining power,and The battery capacity is determined jointly.Finally,the factors that affect the equilibrium time of the battery pack are simulated in MATLAB.The simulation results show the correctness of the theoretical analysis.Based on the analysis of the influencing factors of the optimal equilibrium time of the MMC equilibrium topology,the optimal time equilibrium control strategy is designed for the two working states of charging and discharging.In order to unify the two sets of control of charge and discharge,and at the same time ensure the output voltage of the equalizer is stable,an equalization control strategy based on model predictive control is proposed.The charge-discharge controller of the bidirectional DC/ DC converter at the back stage is designed,and the battery is simulated by constant current and constant voltage charging to verify the feasibility of the proposed control strategy and the designed charge-discharge controller.The experimental prototype was built,and the three-string three-parallel battery pack was used for experimental verification.First,the constant current discharge equalization experiment was carried out.The experiment verified the feasibility of the equilibrium topology and the proposed algorithm.In order to further verify the operation effect of the balanced topology in actual operating conditions,the battery pack was tested in FUDS conditions.The experimental results also showed the feasibility of the improved balanced topology and control strategy.In more severe cases,the balance effect using the remaining power as the balance indicator is better than the voltage as the balance indicator.