Pulse power characterisation for lithium ion cells in automotive applications - Small and large signal cell impedance analysis

Abstract

The pulse power capability of a Lithium ion cell is an important factor to be considered while dimensioning a traction battery pack. Pulse Power characterization of a Lithium ion cell requires an accurate Equivalent Circuit Model(ECM) in order to describe its dynamic behaviour. The two widely adopted methods for parametrising ECMs are the Current Interruption and Electrochemical Impedance Spectroscopy(EIS) methods. These methods are rarely unified for model development, and therefore this thesis seeks to analyse cells from two different chemistries using both methods in order to draw vital deductions regarding cell impedance behaviour under different operating conditions. The parametrised model obtained is validated using a vehicle driving cycle and a deviation of 30 mV in Root Mean Square Error(RMSE) value between measurement and simulation is obtained. The cell parameters are further used to derive and quantify the pulse power capability of a battery pack which consists of the cells used in this study.