Analysis of the Fractional Dynamics of an Ultracapacitor and Its Application to a Buck-Boost Converter

Abstract

This work studies the fractional dynamics of an ultracapacitor which is used in a Buck-Boost power electronic converter as energy storage unit. Ultracapacitors are used in applications such as hybrid vehicles, UPS, power electronic converters connected to the grid, etc, because of their higher energy density. Nevertheless, they exhibit more complex dynamics than standard capacitors due to the diffusion phenomena, which causes a dynamic fractional behaviour in such capacitors. In this work, the fractional behaviour of the ultracapacitor used in the Buck-Boost converter has been identified by means of an experimental test. Then, the impact of the fractional dynamics of the ultracapacitor on the power electronic converter is analysed. Simulation results are provided in order to compare the ultracapacitor fractional behaviour with an equivalent standard capacitor in terms of voltage dynamics in the Buck-Boost converter.