Ultracapacitor: Modelling and Characterization for Electric Vehicle Application

Ultracapacitors (UCs) are characterized by its high power storage capacity, Low Equivalent Series Resistance (ESR) which leads to an efficient high charging / discharging currentat a wide range of operating temperatures. UCs are successfully utilized as a supplementary energy sources for electric vehicles (EVs). According to their high power densities they are adopted to operate in quick acceleration, hill-climbing and regenerative braking. So they have been considered for transient power supply and recovery in EVs. An UC-battery combination system can effectively smooth the power fluctuation caused by periodic acceleration and deceleration for different driving cycles. In this paper, the performance characterization of an UC is recorded including measuring the capacitance, equivalent series resistance and the output terminal voltage. The characterization is verified experimentally at different loading conditions in order to model the performance of the UC under different loading and operating conditions. A simplified Fuzzy modelling technique is adopted for capacitance estimation based on the charging/discharging currents and the surrounding temperature. The estimated capacitance from the fuzzy model is very close to the actual value that proofs the high efficiency of the proposed model. The ESR, terminal voltage, and SOC are estimated from the introduced model. The available charge after charging or discharging is estimated based on the estimated terminal voltage and capacitance.