变论域双模糊控制器在锂电池均衡策略仿真中的应用

Application of Variable Universe Double Fuzzy Controller in Simulation of Lithium Battery Equilibrium Strategy

针对固定阈值均衡策略和传统模糊均衡策略在电池组充放电末期易造成过压或欠压保护误动作而不能全程均衡,并且在电池间存在较大差异时均衡力度不足的问题,提出变论域双模糊控制器(VDF)均衡策略。以NCR18650B型三元锂电池充放电实验数据建立锂电池仿真模型,以单体锂电池的荷电状态(SOC)作为一级模糊控制器输入,将其输出与锂电池工作电流的乘积用于调节二级模糊控制器输出论域;以单体锂电池SOC与电池组平均SOC的差及其变化率作为二级模糊控制器输入,其输出作为均衡电流;以电池组内单体电池间SOC极差表征电池间的不一致性,以极差首次收敛至0.05确定均衡时间。Simulink仿真结果表明:VDF均衡策略可以有效降低电压保护误动作;与传统模糊均衡策略相比,在恒流充放电工况和自定义动态应力测试工况下,VDF均衡策略均衡速度可以提高30%以上;在电池间存在较大差异时,均衡结束后VDF均衡策略的一致性可以提高20%以上。

The fixed threshold equalization strategy and the traditional fuzzy equalization strategy usually result in overvoltage or undervoltage protection to malfunction at the end of the battery pack charge and discharge,and it is difficult to be fully balanced,because a large difference between the batteries makes the balance insufficient.A variable universe double fuzzy controller(VDF)equalization strategy is thus proposed.The lithium battery simulation model is established according to the experimental data of charged and discharged NCR18650 Bternary lithium battery.The state of charge(SOC)of the single lithium battery is used as the input of the first-level fuzzy controller,and its output multiplied by the lithium battery working current value is used to adjust the output domain of the second-level fuzzy controller;the difference between the SOC of a single lithium battery and the average SOC of the battery pack and its rate of change are used as the input of the second-level fuzzy controller,and its output is used as the equalizing current;the extreme difference of SOC between the single cells in the battery pack represents the inconsistency,and the equilibrium time is determined by the first convergence of the extreme difference to 0.05.The simulation results from Simulink show that the VDF equalization strategy effectively reduces the voltage protection malfunction.With constant charge and discharge current and in custom dynamic stress test(DST),VDF equalization strategy is compared with the traditional fuzzy equalization strategy,and the results show that the equalization rate increases by above 30%,and as a large difference exists between the batteries,the consistency increases by above 20%after the end of the equalization.