Analysis of Power Flow in UPQC during Voltage Sag and Swell Conditions for Selection of Device Ratings

This paper deals with the steady state analysis of unified power quality conditioner (UPQC). The UPQC, a combination of shunt and series active power filter (APF), is one of the best solutions towards the mitigation of voltage sags and swells problems on distribution network. The mathematical analysis is based on active and reactive power flow through the shunt and series APF, wherein series APF can absorb or deliver the active power whereas the reactive power requirement is totally handled by shunt APF alone during all conditions. The derived relationship between source current and % of sag/swell variation shows shunt APF plays an important role in maintaining the overall power balance in the entire network. The digital simulation is carried out to verify the analysis done. The simulation results support the mathematical analysis. The effect of load VAR variation and the impact of % sag/swell on the kVA ratings of both shunt and series APF are also analyzed. This analysis can be very useful for selection of device ratings for both shunt and series APFs