Three-phase four-leg active power quality conditioner without references calculation

Due to the use of diverse electric loads, the power quality problem in the power distribution systems can be very complex, especially in three-phase three-wire or four-wire distribution systems. This paper proposes a unified power quality conditioner (UPQC) with one cycle control (OCC) that has the functions of harmonic suppression, reactive power compensation, unbalanced load correction, and source neutral/zero-sequence current limitation. The advantages of this UPQC include no need for reference calculation, vector operation, and flexible structure for three-wire or four-wire system. Experimental and simulation results from a prototype confirmed the feasibility of the proposed approach.