Single-Phase Soft-Switching Unified Power Quality Conditioner Based on Three-Arm Converter

This paper presents a soft-switching single-phase unified power quality conditioner (UPQC) based on a three-arm converter. The topology uses a soft-switching series and shunt active power filter with a shared arm to reduce the number of main switches and employs simple resonant units to reduce switching losses and improve system efficiency. The soft-switching series active power filter can compensate for the grid voltage fluctuation such as voltage swell, voltage sag, over-voltage, under-voltage, and harmonics. The soft-switching shunt active power filter can mitigate the harmonic current and achieve a unity power factor at the grid side. Besides, using simple resonant units, all main switches of the high-frequency arm operate at zero-voltage switching (ZVS) turn-on, while all auxiliary switches operate at zero-current switching (ZCS) turn-off; otherwise, the low-frequency arm operates at line frequency switching can reduce the switching losses significantly. Finally, some experimental results are presented to verify the performance of the proposed system.