Research On Available Capacity Estimation Method For Lithium-ion Batteries Of Electric Vehicle

Affected by environmental pollution and energy crisis, new energy vehicle is listed as the key support industry of China. The occupancy of new energy vehicles is increasing year by year. Lithium-ion battery is attractive for applications varying from electric vehicles (EVs) and hybrid electric vehicles (HEVs) due to the excellent characteristics. Lithium-ion batteries’ state parameters, such as SOC and SOH, are difficult to be measured directly because of the intrinsic characteristics. So the research of battery model and battery state parameters has always been the hot spot of the industry. The battery management system, as an important part of new energy vehicles, is the guarantee of Evs’ safety work and the equipment platform of battery state parameters estimation. Battery state parameters accurately estimate in the battery management system still be a technical problem. This dissertation proposed a approach based on battery management and test platform system to estimate the available capacity and SOH of power batteris.Firstly, the working principle and structure characteristics of lithium-ion battery are studied, and the basic working characteristics of the battery and the influencing factors of lithium-ion battery capacity attenuation are analysed.Secondly, the lithium-ion battery modeling is selected by comparing the advantages and disadvantages of other equivalent circuit models. The second-order RC equivalent circuit model are adopted to simulate the performance of the battery, and the battery model parameters identification is based on RLS algorithm. It can be obtained estimated parameters for the available capacity of battery estimates.Then, This dissertation studies several commonly estimation methods of battery available capacity. The battery SOC is estimated based on the selected battery model using the extended kalman filter method. Combined the EKF achieved real-time SOC values and the SOC value of coulomb counting method, it can obtain the SOC value of the current moment. Available capacity is obtained by the relationship of SOC and battery capacity.Finally, the experimental platform is setted up to verify the battery model is practical.Through the results of the experiment of battery cell and battery pack to validate the proposed method, we can see the selected estimation method has great improvement in the precision and a good experimental effect.