Current and voltage control system designs with EKF-based state-of-charge estimator for the purpose of LiFePO4 battery cell charging

This paper presents two designs of constant-current/constant voltage battery charging control systems in the form of a cascade control system arrangement with the superimposed proportional-integral (PI) controller commanding the battery charging current reference to the inner PI controller-based current control loop. The superimposed control level can be realized as: (i) battery terminal voltage limiting control loop, or (ii) battery state-of-charge (SoC) control loop based on SoC estimation using an extended Kalman filter, which augments the battery terminal voltage control loop in a straightforward way. The design of such modular control system is based on the suitable control-oriented model of the battery charging process and utilization of damping optimum criterion. The effectiveness of the proposed battery charging control system has been verified by means of simulations using the readily available experimentally-obtained model of a lithium-iron-phosphate (LiFePO4) battery cell, which has shown notable potential for charging process speedup when traditional battery voltage limiting control is augmented with the SoC control loop.