A Thévenin circuit modelling approach for sodium metal halides batteries

In this paper a model suitable for representing the electrical dynamic behaviour of Sodium Metal Halides Batteries (SMHBs) has been reported. In particular, the Thevenin circuit approach has been investigated considering the equivalent circuit parameters depending on the State Of Charge (SOC). The proposed SMHB model has been developed referring to the experimental tests conducted on a commercial module with a capacity of 23.5 kWh and a rated discharge power of 7.8 kW. In order to develop the identification of the Thevenin circuit parameters, a numerical processing of the specific measurements of a SMHB test-bench, considering the dynamic analytic solution of Thevenin circuit battery voltage, has been carried out and discussed in detail. The proposed approach allows a significant reduction of steady state errors respect to the numerical fitting procedure. Finally, the optimization of the first step identification process has been performed obtaining a very small variation in the values of the identified parameters by means of the proposed approach. The comparison between the experimental and simulation results has confirmed the good accuracy of the proposed model in a defined SOC range.