Three-Phase Four-Wire Unified Power Quality Conditioner Based on AC-DC-AC Nine-Leg Converter and Shunt Converter

In this paper, a three-phase transformerless unified power quality conditioner (UPQC) based on a nine-leg converter and a four-wire shunt converter is proposed and investigated. The system ensures grid power factor compensation with low harmonic content and feeds the load with a sinusoidal waveform. The shunt converter provides balanced currents with reactive and harmonic compensation, which allows the nine-leg converter to operate with a wide range of unbalanced loads. In addition, the shared-leg currents are minimized, reducing the power losses. The system model, pulse-width modulation (PWM) techniques, and control strategy are discussed in this work. Experimental results are presented to confirm the feasibility of the proposed structure.