Voltage Sag/Swell Controller by Means of D-UPFC in the Distribution System

A power quality issue, especially, voltage problem is the vital concern in most distribution system today. So far, the voltage problem is mainly from under-voltage (voltage sag) condition due to a short circuit or fault. Recently, renewable energy such as photovoltaic (PV) system affects over-voltage (voltage swell) condition caused by its reverse power flow at daylight. In this paper, proposed distribution-unified power flow controller (D-UPFC) for preventing both voltage sag and swell conditions is discussed. The proposed scheme consists of an AC chopper, a switch and a series transformer. The AC chopper generates compensation power when voltage sag or swell condition happens. The secondary and tertiary parts of a series transformer connect with switches for controlling voltage sag or swell. D-UPFC does not need any energy storage devices such as large capacitors or inductors and it provides fast compensation. Simulation results show D-UPFC controls voltage concerns in the distribution system