Model Identification Of Lithium Ion Batteries

Individual Power System(IPS)supply energy for the individual soldier to perform tasks outdoor.The lithium-ion batteries are selected as the energy storage elements for the IPS.In order to monitor batteries,parameters identification should be performed on battery models.Several normal battery models such as empirical models and Electrical circuit models are included in the article.The characteristics of different models are analyzed.Nernst model,Combined model,the first order RC model and the second order RC model are selected for parameters identification.In order to study the discharging characteristics of batteries,pulse discharging tests are performed under different temperatures and currents.The parameters of different models are identified based on the off-line discharging data.Constant and ladder pulse discharging processes have been simulated.The comparison of simulation results and experimental data validates the methods for parameters identification.Based on the accommodation of the accuracy and simplicity,the first order RC model is selected as the fundamental model for the IPS.The parameters of the first order RC model which are identified under different temperatures and currents are compared.And the effects of temperature and current for the model parameters such as capacity,OCV-SOC curve and impedance are analyzed.An batch-type working manner has been proposed according to the working condition of the IPS.Two online parameters identification methods are proposed based on the batch-type working manner.The first one which is combined with recursive least square(RLS)can only be used to identify the parameters of the cell under relaxation condition.Because RLS method can only handle the time-invariant systems.The second one based on the particle swarm optimization(PSO)can handle the time-variant systems.It can be used to identify parameters in real time.In the end,simulation validation has been performed to verify the two methods.While the further research need to be done to validate the usability of them on the IPS.