Development of a Lithium-ion Battery Model and State of Charge Estimation Algorithm with Hardware-in-the-loop Validation

A fill-order Linear Observer is designed to estimate the State of Charge using a model of a Lithium-ion 18650 cell. The battery model consists of an Equivalent Circuit Network with parameters from test data of an actual cell provided as a function of State of Charge, temperature and Open Circuit Voltage. The model is validated against a current and voltage profile obtained from a real-world drive scenario. The observer is designed as a linearization of the state-space representation of the Equivalent Circuit Network and offline simulation is used to verify its robustness. With a Hardware-in-the-loop setup, the battery model and observer are implemented and results compared against the offline simulations showing strong agreement; thus, validating in real-time the estimation algorithm. Analysis of the results suggest that battery degradation affects the accuracy of the observer thus noting the need to update its parameters in real-time.