Ripple Current Reduction for Fuel-Cell-Powered Single-Phase Uninterruptible Power Supplies

Abstract

A well-known issue of fuel-cell-powered single-phase uninterruptible power supplies (UPS) is that the input current from the dc source is coupled with the second-order current ripple due to the ac-side instantaneous power pulsating at twice the line frequency. The low-frequency ripple component has been confirmed to have detrimental impacts on fuel cell's reliability and lifespan. To solve this issue, a boost inverter that can work in both differential mode (DM) and common mode (CM) operations is adopted by this paper. The DM operation achieves active power conversion and a well-regulated ac output voltage. Meanwhile, the CM operation ensures effective dc current ripple reduction. In addition to operating with linear loads, the proposed control method extends its working scope to nonlinear loads, where meticulously designed repetitive controllers are employed to handle the multiple low-harmonic situations. Moreover, the proposed control method also introduces an interleaved pulse-width modulation to further reduce the switching frequency ripple in the dc current. The stability of the proposed control system is stringently examined. Finally, presented experimental results validate the theoretical analysis as well as the effectiveness of the proposed method in current ripple reduction.