Ngoc Tham Tran

A Padé Approximate Model of Lithium Ion Batteries

We present a reduced order model for a lithium ion battery in which Pade approximants are used to simplify complex, transcendental, transfer functions associated with the linearized, pseudo 2-dimensional (P2D) electrochemical model of the battery. The resulting transfer functions take the form of simple, rational polynomial functions, which can be used to compute any variable at any location within a one-dimensional representation of the battery domain. Corrections for nonlinear behavior are also incorporated into the reduced model. The results obtained using the reduced model compare favorably to those from the full (nonlinear) P2D model and the computational time required to produce these results is significantly reduced. Importantly, the form of the reduced model means that variables can be evaluated at specific discrete locations within the cell domain, without the need to compute all values of the variable at all discrete locations, as is the case with the spatial discretization methods most commonly used to implement the P2D model. We show that this results in further significant time savings and enhances the suitability of the model for variety of applications.

An equivalent circuit model of li-ion battery based on electrochemical principles used in grid-connected energy storage applications

Based on basic electrochemical principles, an equivalent circuit model of a Li-ion battery is developed. The eventual aim of the work is to use such a model in the accurate control of power flow for a battery energy storage system (BESS) in grid-scale applications. The model developed here allows one to monitor the BESS internal states, by taking into consideration the internal dynamics of the battery including Li-ion concentration, overpotential and degradation. Comparison of the results obtained from the developed model with more established but computationally expensive models shows that the developed model performs well in terms of both external electrical characteristics and major internal chemical dynamics for the studies of grid-scale BESS.