Characterization of Ultracapacitors for Transient Load Applications

Ultracapacitors (UCs) are of increasing interest in different application areas, such as microgrids and transportation, which demand high transient power and are growing in capability every day. New power system architectures have been proposed that may be well suited to reliably and efficiently supply power to these previously unseen applications. Among the architectures that hold a great deal of promise are hybrid energy storage modules that integrate energy dense batteries with power dense UCs into a single power supply that augments traditional generation technologies. Within such architecture, the UC is the element that may be utilized to sink and source power quickly, at the leading or falling edge of a transient event. Considerable advances have been made to increase both the power and energy density, respectively, of UCs. Significant reduction of the internal impedance has resulted in an increased power capability that makes UCs well suited for use in these applications. Hybrid UC technologies, such as lithium-ion capacitors, have been developed, which have much higher energy density with nearly the same power density. In an effort to better understand and validate the capabilities of new UC technologies, a series of experiments has been performed on cells from four different manufacturers. Novel experimental testbeds and methods have been used to measure each technology's internal impedance and power density. The experimental testbed utilized, along with the results collected to date, will be presented.