Robust State of Charge Estimation of Lithium-Ion Batteries Using a Nonlinearity-Aware PID Observer

An accurate estimation of state of charge (SOC) is crucial for the safe and reliable operation of Lithium-ion batteries (LIBs). However, the complex and intermittent nature of LIBs against dynamic operating conditions makes this task highly challenging. Therefore, a novel nonlinearity-aware PID observer is proposed to ensure enhanced robustness and improved accuracy in dynamic scenarios. The proposed observer is designed using a second-order equivalent circuit model (ECM) whose observability is rigorously discussed. A strategy to detect nonlinearity is integrated with the proposed design to adapt to the most suitable mechanism in highly dynamic situations. An experimental testbench, using an INR21700 cell whose parameters are identified experimentally, is constructed to verify the practicability of the proposed design. Furthermore, comparative results against highly dynamic loadfiles underscore improved accuracy, enhanced robustness, and faster convergence, demonstrating the proposed design's effectiveness in practical scenarios.