Improved Method for Characterization of Ultracapacitorby Constant Current Charging

Abstract

Ultracapacitors are creating new horizons in the field of energy storage systems (ESS). The reason behind the popularity is its unmatched characteristics like very high power density, long cycle life, deep discharge capacity, high efficiency and low ESR. Hence these types of devices can be effectively used in pulse power applications in power system, communication system and hybrid electrical vehicles. Different types of Ultracapacitor models have been analysed and proposed since many years. This paper introduces a simplified three branch dynamic model of Ultracapacitor using constant current charging method .The detailed test procedure for 150 farad and 350 farad ultracapacitors was followed in the laboratory to develop dynamic model of ultracapacitors under charging current of 5A .The model includes R-C branches along with an inductance, EPR (Equivalent Parallel Resistor) and ESR (equivalent series resistance). Ultracapacitor equivalent model is built with the consideration of linear and nonlinear factors, temperature variation & effect of leakage current. The experiment has been implemented with simple laboratory instrument like constant current supply, voltage & current data logger and computer. Computational time required for parameters calculation is minimum & simple compared to other methods followed by different authors. Final results are verified by comparing experimental results with results obtained by simulating the derived equivalent circuit model in MATLAB/Simulink. Finally some applications of ultracapacitor are discussed.