Comprehensive modeling, testing, and experimental validation of ultracapacitor open circuit voltage characteristics

Abstract

Ultracapacitors (UCs) are the significant component of the energy storage systems (ESS) in the electric traction applications. In the field of electric transportation the UCs need to be modeled dynamically in order to capture real-time characteristics. The model should provide precise estimation of UC responses to various charge/discharge conditions and also predict the behavior of UCs under varied load conditions. In order to incorporate the model for testing purposes in various power electronics/drive simulation toolboxes, it is very important for the model to be accurate. This paper aims at the experimental validation of an accurate parameter identification procedure for an UC model using random charging/discharging current pulses of different magnitudes. The UC model can estimate the output voltage without the extraction of the model's branch parameters. The critical parameters have been estimated dynamically from characteristic equations. The estimation technique for an equivalent RC branch model is simulated and the output voltage response, controlled between Vmin (0V) and Vrated (2.7V) of a single UC cell, has been presented. Finally, the simulation results obtained from the identification technique are validated against the actual charging results obtained from applying charging pulses to a 1200F UC.