Capacitive behavior and stored energy in supercapacitors at power line frequencies

Allagui A.
Elwakil A.S.
Fouda M.E.
Radwan A.G.

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. © 2018 Elsevier B.V.