UBC Theses and Dissertations

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UBC Theses and Dissertations

A nonlinear circuit model for lithium-ion batteries Ren, Shengru


A lithium ion battery model is required for proper design of battery powered systems such as marine applications. The various existing models lack of the nonlinear aspect of the batteries being studied, suffer from high complexity and are not quite suitable for system level simulation. Therefore the scope of this thesis is to produce a battery model capable of capturing the nonlinearity of the battery for system level design. The Randle circuit model is selected as the base model to build upon and the electrochemical impedance spectroscopy is chosen as the fundamental test method for extracting the model parameters. The nonlinearity is accounted for by defining the equivalent circuit model elements’ parameters functions of the state of charge. Since lithium-ion batteries are prone to be affected by the changes in temperature, all the experiments are done under controlled temperature. The proposed model is a modified Randle circuit model in time domain implemented in MatLAB/SIMULINK. The model’s validity is verified using test data. It is concluded that this final version of model proposed in this thesis can be used directly in system level simulation while offering reasonable accuracy. However the proposed model does suffer from its dependency on the cell chemistry, which will limit its applications.

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