Harmonic mitigation in a Virtual Air Gap Variable Reactor via control current modulation

A Virtual Air Gap Variable Reactor is a device that is capable of producing a continuously variable reactance with a better dynamic response and without introducing the harmonics created by the thyristor switching of a TCR. This paper presents a method of harmonic mitigation that can be applied to a laboratory prototype Virtual Air Gap Variable Reactor (VAG-VR) which further improves on the low harmonics already achieved. The method utilizes control current modulation such that the DC auxiliary current is modulated with a 2nd harmonic component. It is seen that the 3rd harmonic can be reduced in the range of 60% - 96% as compared to using the DC auxiliary current without modulation. The 5th and 7th harmonics also show a modest reduction. This improvement is in addition to the improvements that have already been achieved by the VAG-VR as compared to the thyristor controlled reactor (TCR).