Nonlinear parameter optimization of PI observer for highly accurate SOC estimation of Li-ion batteries

An effective optimization of proportional integral observer for SOC estimation of lithium ion batteries is done in order to get a very high accuracy. During experimentation, a negligible error band of just 0.6% was found which is the quite high efficiency yet reported in the research area of state of charge estimation of Li-ion batteries. The worth mentioning improvements covered in this paper are the variable selection of value of coulombic efficiency instead of constant one to minimize the error, intelligent identification of parameters for more accurate modeling of nature of Li-ion battery, and non-linear gain scheduling for SOC and open circuit voltage relationship to boost the efficiency. Firstly, the simple PI observer is implemented and tested; then, after specific optimization and improvement, the optimized proportional integral observer is designed. The real time calculated data of Li-ion battery is used to compare the results, and to verify the high efficiency and robustness of proposed design. The most prominent features of new optimized PI observer include the very high efficiency, enhanced robustness and an immediate estimation of current SOC without any requirements of initial value of SOC.