Analysis of GTO-based static VAr compensators

The growing availability of high-power gate turn-off thyristors (GTOs) has meant that power electronic convertor circuits can be manufactured with the ability to both absorb and generate reactive power. These circuits constitute the next generation of static VAr compensators (SVCs) which may eventually supersede the conventional thyristor-controlled reactors (TCRs) and thyristor-switched capacitors (TSCs) used in power systems at present. The paper gives an analysis of both 6-pulse and 12-pulse GTO-SVCs based on voltage-source convertor circuits, and equations are derived that describe the performance of each circuit. In addition, the conditions leading to circuit resonances are discussed together with possible methods of avoiding the problems.