Initial SOC Error Recovery with a CC-RLS-PI Hybrid Estimator

Coulomb counting (CC) is open-loop and cannot correct a wrong initial State of Charge (SOC). A scheme that adds recursive least squares (RLS) parameter identification and a proportional-integral (PI) correction to CC was proposed for a 260 mAh cell. This study examines that scheme with Thevenin parameters identified offline and held fixed, using Panasonic 18650PF data under static 1C, HWFET and UDDS profiles, initial errors of −2, −20 and −35 percentage points of SOC, and a comparison with CC and with open-circuit-voltage (OCV) initialization. The hybrid estimator first entered the ±2% error band within 1–389 s but never stayed in it. Its mean absolute error (MAE) was 1.5–4.0%, rising to 5.0–7.7% below 40% SOC on the static and HWFET profiles, and it beat CC only when the initial error was at least 2–4 points. In starts at mid-SOC under load without rest, it had a lower MAE than OCV initialization in 7 of 9 cases. The identified polarization resistance changed more than threefold with the forgetting factor. The scheme suits recovery from large initial errors when OCV initialization is unreliable, within an accuracy limit of about 2–4%.