A rapid online calculation method for state of health of lithium-ion battery based on coulomb counting method and differential voltage analysis

Accurate estimation of state of health (SOH) is crucial for battery management system in ensuring the reliability and safety for system operation. For SOH estimation, the model-based methods require sophisticated battery models while the data-driven methods need huge battery data and computation burden. To avoid these drawbacks, a model-free SOH calculation method by fusion of coulomb counting method and differential voltage analysis (DVA) is proposed, realizing rapid online SOH calculation under constant current discharging stage. Firstly, the conventional coulomb counting method is converted to calculate SOH, which needs two state of charge (SOC) and corresponding measurement time to further proceed. Subsequently, DV curves are obtained based on the battery measurable parameters without smoothing or function fitting, then the x-axis of DV curves is replaced by SOC axis to get SOC based DV curves. Using discrete analysis, two SOC feature points are identified from SOC based DV curves, whose corresponding measurement time and mean SOC are used to compute SOH directly. In addition, the SOH calculation accuracy of the proposed method is verified by experimental data. The validation results indicate that this method can provide online accurate SOH calculation under constant current discharging stage with low computation.