Capacitive behavior and stored energy in supercapacitors at power line frequencies

Supercapacitors are commonly viewed and mainly employed as dc electrical energy storage devices. Their behavior at far-from-dc is usually overlooked and not well explored for potential applications. In this work, we investigate analytically and experimentally the performance of supercapacitor at high frequencies, including the 50 Hz/60 Hz power line frequencies. The variation of effective capacitance, power and energy with frequency are analyzed using a fractional-order model consisting of a series resistance and a constant phase element for both pure sinusoidal and full-wave rectified voltage signals. We show that, although supercapacitors drastically loose their dc-rated capacitance at high frequencies (and therefore their energy storage capability), there still exists sufficient capacitive behavior to be used for power line applications. A 220 V/6 V, 50 Hz step-down transformer, a bridge rectifier circuit and a 3 F dc-rated supercapacitor are used in the experimental setup to drive a dc motor taken as a load. The supercapacitor is proven to be able to function as a filtering capacitor during normal operation with a percentage ripple of 0.83%, and as an energy backup device in the event of ac power interruption.