Modeling and Validation of a Lithium-Ion Battery Pack

Batteries are part of an extremely nonlinear electrochemical system, and their performance is determined by various key factors such as law of thermodynamics, electrode kinetics, ion transport, and diffusion. To develop an accurate model of a battery, it is important to take into consideration both the internal and external conditions that would determine both the battery dynamics and its performance. Electrochemical, mathematical, and electrical equivalent circuit models are three common ways to model the electrochemical battery system. However, using these models involves certain limitations such as increased computation, empirical equations, and components (both active and passive). A simple electrical battery model with a voltage source and a resistor is insufficient to attain the desired level of accuracy in the model. To overcome these limitations, this study presents an electrothermal model that has been designed by adding "n" number of resistance capacitance (RC) pairs connected parallelly to ensure both dynamics and accuracy. An electrothermal model of a lithium-ion cell with a one-RC model and two-RC model has been developed, and a performance comparison has also been made to check the voltage accuracy of all the models. The electrical and thermal parameters (Em (state of charge [SOC], T), RO (SOC, T), R1 (SOC, T), R2 (SOC, T), C1 (SOC, T), C2 (SOC, T)) required for an RC model have been extracted through the pulse charge-discharge test. A battery pack of 55 V, 50 Ah using the RC model based on the Indian driving cycle condition has also been developed. Pulse charge-discharge and constant current-constant voltage profiles have been applied to the developed battery pack model to simulate and validate the accuracy of voltage in a real-time scenario.