Unified power quality conditioner for distribution system without reference calculations

Power quality is an important measure of the performance of electric power system. The main concerns include voltage quality and the current quality. The voltage may contain amplitude errors, harmonics, phase unbalance, sag/dips, swells, flicks, impulses and interrupt/outage. As for the current quality is concerned, harmonics, reactive component, unbalance, excessive neutral/zero-sequence current are the main issues. This paper proposes a unified power quality conditioner (UPQC) with one cycle control (OCC) to deal with most of the problems identified above as a whole. The proposed OCC-UPQC consists of a serial three-phase three-leg and a parallel three-phase four-leg converter. The OCC-UPQC has the advantages of no reference calculation that results in simplicity, vector operation for reduced losses, modular approach with the flexibility to work in both three-wire or four-wire systems, in addition to the inherent features of fast transient response, high precision, constant switching frequency, etc. The principle of the proposed UPQC is provided in details. The performances of both voltage and current quality improvement are verified to be excellent with experiment results.