Fractional Order Parameter Estimation from the Nyquist Plots with Two Distinct Lobes

Equivalent circuit modelling is an important tool to investigate electrochemical processes. This paper presents an analytical technique for the estimation of model parameters from the frequency response (Nyquist plot) of the system, when the plots have two distinct semicircular lobes. The proposed technique is suitable also for fractional order model as it includes the cases where one of the lobes is a depressed semicircle, originated due to the presence of a constant phase element. This method provides a quick estimation of equivalent parameters, thus, would be helpful for online parameter estimation like state-of charge estimation for a Li-ion battery in electrical vehicles.