An estimation method of Li-ion battery impedance using z-transform

An estimation method of circuit parameters of a Lithium-ion battery model is proposed in this paper. The model consists of a DC voltage source and an internal impedance. The proposed method gives the circuit parameters from a measured voltage and current waveforms during its operation. The internal voltage is a function of the State Of Charge (SOC). The internal impedance can be expressed by a resistor, which expresses the voltage drop in a high frequency region, and some RC parallel circuits, which express the transient characteristic of the battery. Their parameters are estimated from the impedance in z-domain. The proposed method gives satisfactory accurate parameters without initial values. The accuracy of the proposed method is confirmed by a comparison with the measured transient characteristic of a battery.