Multirate strong tracking extended Kalman filter and its implementation on lithium iron phosphate (LiFePO4) battery system

Lithium Iron phosphate (LiFePO4) battery has obtained extensive attention of researchers for its high energy density, little contamination and ready availability. In this paper, different numbers of RC branches in the equivalent Thevenin circuit model are explored by comparing accuracy of curve fitting with in-house experimental data. Besides, battery system with 6 cells of second order equivalent circuit is modeled using Matlab/Simscape. A multirate strong tracking extended filter (MRSTEKF) is proposed by introducing the multirate control strategy and lifting technology into strong tracking extended Kalman filter (STEKF) to improve tracking stability and estimation precision of state of charge (SOC). Root mean square error (RMSE) is exploited to evaluate the performance of the algorithms of extended Kalman filter (EKF), STEKF and MRSTEKF. Simulation results demonstrate that the proposed MRSTEKF is faster than EKF and STEKF by 55.34% and 49.51%, and is more precise by 52.66% and 33.88%.