Enhancement of Three-Phase Four-Wire UPQC Topology for Power Quality Problems-Sags and Swells

Abstract

The unified power quality conditioner (UPQC) is a custom power device, which mitigates voltage and currentrelated PQ issues in the power distribution systems. In this paper, a UPQC topology for applications with non-stiff
source is proposed. The proposed topology enables UPQC to have a reduced dc-link voltage without compromising its
compensation capability. This proposed topology also helps to match the dc-link voltage requirement of the shunt and
series active filters of the UPQC. The topology uses a capacitor in series with the interfacing inductor of the shunt active
filter, and the system neutral is connected to the negative terminal of the dc-link voltage to avoid the requirement of the
fourth leg in the voltage source inverter (VSI) of the shunt active filter. The average switching frequency of the switches
in the VSI also reduces, consequently the switching losses in the inverters reduce. The main purpose is to compensate for
voltage imbalance,reactive power, negative sequence current and harmonics.