Static VAR system auxiliary controllers for damping torsional oscillations

A new concept is presented according to which a midpoint-located static VAR system ( S VS) with appropriate auxiliary control can be simultaneously employed for damping torsional oscillations and enhancing the steady state power transfer limit. Two new SVS auxiliary control signals designated as computed internal frequency (CIF) and computed rotor frequency (CRF), which can be locally synthesized, are proposed. Various locally available signals for SVS control are examined in respect of their ability to stabilize all the torsional modes. It is shown from eigenvalue analysis that with a suitable choice of signal and SVS auxiliary controller parameters, the desired objective can be achieved even when the transmission line is compensated at a level where one of the torsional modes is critically destabilized