Preliminary results on identification of an electro-thermal model for low temperature and high power operation of cylindrical double layer ultracapacitors

The capability of ultracapacitors in delivering high power at low temperature applications such as cold starting is the motivation of this paper. A two state equivalent electric circuit model coupled with a two state thermal model is defined and parameterized to develop a four state control oriented electro-thermal model for cylindrical double layer ultracapacitors. The proposed two state equivalent electric circuit model mimics the terminal voltage dynamics and could be used to evaluate the power capability and efficiency of the cell. The electric model parameters are estimated by pulse-relaxation tests for sub-zero temperatures as low as -40 °C. The two state thermal model provides a tool to estimate the surface and core temperature dynamics. The two models are then coupled through the reversible plus irreversible heat generation and also via temperature dependence of the equivalent circuit model parameters. The modeled terminal voltage and surface temperature dynamics are in good agreement with experimental observations for fixed environmental temperature with forced air cooling.