Control of dynamic VAR compensator based on current source converter

Abstract

The paper proposes a current source based Dynamic VAR Compensator (DVC) control strategy. The switching unit in this DVC topology is composed of series connected switch and diode also termed as the “current switch”. The proposed controller has been designed to force discontinuous conduction mode operation thus fundamentally different from the traditional constant current source based control system operation. This naturally facilitates zero current turn-on, zero voltage switch overlap and zero current turn off. Two of the switches undergo hard switched turn off only once in a switching time period. The switching scheme has been managed in such a way that the diodes are always turned off at zero voltage thereby minimizing the reverse recovery loss and stress. This effectively reduces the switching losses and allows the switching frequency to be designed considerably higher. High Switching frequency facilitates faster response and high power density. An average model of this DVC converter has been used in an IEEE-34 BUS system to validate the VAR compensation capability. It has been shown that this effectively improves the feeder voltage profile. The ill effects of partial clouding over roof-top PV cells have also been shown, and its mitigation by the DVC. The proposed VAR compensator algorithm can adjust capacitive reactive power as well as inductive reactive power, which can be adapted to a wide range of load.