Battery Modelling For Large Current Pulses

Non-linearity due to high current pulses and frequency should be accounted for and included in the electrical equivalent circuit model of a battery cell; apart from its dependence on state of charge (SOC) and temperature. In order to obtain a large current pulse characterisation of a given cell, a current pulse testing circuit with both the high current and high frequency range capabilities is designed. The test circuit is built in a printed circuit board with the controlled switches and a provision to set the current pulse width using a microcontroller. The desired current magnitude is obtained by using a resistor designed from a copper sheet. Also, pretests are carried out on the given cell to determine state of charge (SOC) vs. open circuit voltage (OCV) characteristics at different temperatures. The cell is tested with the current pulses of different magnitude and time duration at a selected SOC level and temperature. Impedance behaviour over current magnitude and time duration respectively are deduced and mathematically fitted to the piecewise parameterised models. The obtained model parameters are in accordance with the Electrochemical Impedance Spectroscopy (EIS) results. Hence, the developed test circuit used for the battery modelling is validated