An online capacity estimation method for LiFePO4 battery module with incremental capacity curve processed by tracking differentiator under noises

Incremental capacity (IC) analysis is an effective and widely used approach to evaluate the lithium-ion battery remaining capacity. A limitation for IC based capacity estimation is that it requires a consistent constant charging current for each test and demands a large amount of data to be stored, which hinder its use in practical conditions. To address the issues, this paper proposes an online capacity estimation method for battery module with incremental capacity curves processed by tracking differentiator. Specifically, the IC features, such as peak voltage, peak amplitude, are analyzed for the battery module empirically and theoretically. The analytic linear relationship between the IC features and capacity are formulated. As a basis, the calculation of dQ/dV is converted to the derivative of terminal voltage, which is obtained by a designed tracking differentiator. For the iteratively derived IC curve, a realtime peak detection algorithm is proposed to detect the second peak voltage without the requirement to store any historical data. The proposed method is not sensitive to noise and applicable to common charging conditions. Experimental results with cycle data for a commercial 206Ah battery module reveals the superiority of the proposed method.