Consideration on SVC control instability with detailed model and verification on stabilization by on-line gain adjustment function

Abstract

The AC system voltage sensitivity is shown to be affected by the SVC operation point change in addition to the AC system short circuit capacity change. Then, an SVC detailed model is proposed considering the dead times in the digital control and the phase controlled thyristors. With this model, the control instability characteristics is discussed based on the root locus calculation. In this discussion, it is indicated that the instability possibly appears in a real AC system and that the oscillation frequency is in a narrow range. Then, based on the discussion, a fast on-line automatic gain adjustment function is proposed. The instability and its oscillation frequency are confirmed to be consistent with the discussion results through the simulation test with the actual SVC controller and through the field test in the actual AC system and the SVC facility. Furthermore, the automatic gain adjustment function is also confirmed to show good performance as designed in these tests.