Analysis of a Virtual Air Gap Variable Reactor

This paper presents the basic operation of a virtual air gap variable reactor (VAG-VR). Variable reactors have many applications in the power industry. Their use allows control of line power flow, as well as damping of power oscillations and subsynchronous resonances. A variable reactor is most commonly implemented as a thyristor controlled reactor (TCR) by switching in and out a constant reactance to achieve an averaged variable reactance. By using a virtual air gap, implementation of a continuously variable reactance is possible without introducing the harmonics created by the thyristor switching. A high speed of response is achieved by using a power electronics solution to drive the DC control windings. A full bridge dc-dc converter is used to provide the full range of negative and positive voltage required.