Modeling of Ultracapacitor Short-term and Long-term Dynamic Behavior

Fostering the green energy world has become a hot §topic in recent years. More and more hybrid vehicles §find their way into the consumer market. Batteries §or ultracapacitors are usually employed as the §second energy source in hybrid vehicles. Compared §with batteries, ultracapacitors have more advantages §such as higher energy densities, long life cycles §and environment-friendly. In order to have a good §control strategy in hybrid vehicle to take advantage §of ultracapacitor, its model must be accurate. In §this book, short-term and long-term models have been §developed. For the short-term models, high order §transfer functions consistent with an RC ladder §model are assumed. Transfer function coefficients §are identified by a least squares algorithm based on §experimental data consisting of time-varying current §excitations and the resulting terminal voltage §responses. A long-term model with six RC branches is §developed by fitting the terminal voltage transient §response to an impulse charging current. From the §ultracapacitor models derived, terminal voltages §under different current profiles can be determined §accurately over the time frame of one hour or two §months.