Research On State Of Charge Estimation And Balance Management Of Lithium-ion Capacitors

Lithium-ion capacitors(LICs)are identified as a new type of energy storage device,which have the performance characteristics of double-layer capacitors and lithium-ion batteries.Based on higher energy density and power density,LICs can be widely used in the fields of electric vehicles and trams.As one of the key components of electric vehicles,the battery management system plays a vital role in the efficiency,reliability and safety of electric vehicle systems.This paper takes lithium-ion capacitors as the research object.The state-of-charge(SOC)estimation and balance management in the management system of lithium-ion capacitors are studied,in which the main research contents and results of this paper are as follows:Performance test and equivalent model of LICs.Due to the lack of research on the performance of lithium-ion capacitors,LICs are identified as the research object in this dissertation.By using a battery test system platform,the characteristics of LICs are studied and analyzed by experiential tests,including voltage,current characteristics,internal resistance characteristics and self-discharge characteristics.Based on the particularity of the internal reaction mechanism of lithium-ion capacitors,a second-order RC equivalent model was established that model can not only reflect the characteristics of supercapacitors,but also characterize the chemical reactions of lithium batteries.In Hybrid Pulse Power Characteristic(HPPC)conditions,the simulation verifies the accuracy of the established equivalent model.Model parameter identification and SOC estimation of LICs.Recursive Least Squares with forgetting factor(FFRLS)is used to identify model parameters,which can update and correct model parameters in real time.Based on the results of online identification,the SOC is estimated by utilizing the method of joint estimation combining adaptive extended Kalman filter(AEKF)algorithm with online parameter identification algorithm.In HPPC and self-defined cycle working conditions,MATLAB simulation verifies the effectiveness of the method.SOC balancing management of LICs.This paper introduces the topology matrix to characterize the relationship between the equilibrium current and the SOC of the monomer in the equilibrium topology.The linear programming method is used to analyze the common balanced topological structure.On the basis of the traditional Buck-boost converter,the multiple level idea is induced,and the bidirectional hierarchical balanced topological structure of lithium-ion capacitor is proposed.The model predictive control algorithm(MPC)is used to construct the global optimization problem of lithium-ion capacitors.Besides,the SOC balance of the lithium-ion capacitor balancing system is completed by the effective set online optimization algorithm.In the three states of standing,charging and discharging,the SOC balance is simulated by the MPC online optimization algorithm and the fuzzy logic control(FLC)algorithm.By comparing the results of simulation,it can be known that the MPC algorithm has advantages of faster equalization speed and shorter equalization time.