State of charge estimation for pulse discharge of a LiFePO₄ battery by a revised Ah counting

Tracing the battery's state of charge (SOC) accurately in real-time is a vital requirement for safe and reliable battery management. This paper proposes a revised Ah counting method for SOC estimation by correlating the available capacity with the amount of dischargeable lithium (Li) in the electrode particles. The revised Ah counting method can capture the dynamic responses of SOC during the pulse discharge operations. The calculated discharge capacities for a LiPFeO₄ battery with the revised Ah counting method are in close agreement with the measured values giving the maximum error by 1.1%. The changes in the unavailable Li in a carbon particle are analyzed. The results show that the variation of unavailable capacity is a gradual process during the pulse discharge. The accuracy of the traditional Ah counting and the revised Ah counting for SOC estimation are evaluated with the constant current pulse and the variable current pulses at different environment temperatures. The results indicate that the revised Ah counting method performs better synchronism than that of traditional Ah counting method. The maximum error of the estimated discharge time with the proposed method is less than 3.8% compared to the experimental measurement.