Study on failure of PSS caused by instability of close mode shapes

Low frequency oscillation has been a serious threat to the security and stability of power system operation today. PSS is an effective damping controller to inhibit low frequency oscillation and has been widely used in power system. Location installation of PSS is mostly determined by the participation factors which can be calculated by right eigenvectors (lower frequency oscillation mode shapes) and left eigenvectors. However, in an n-machine system, there are n-1 low frequency oscillation modes whose frequencies are distributed in a small range of 0.2-3.0Hz, which leads close mode may occur. Study has shown that close mode shapes are sensitive to system structural parameters, that is, a small change of structural parameters may lead a big change of close mode shapes. This paper first theoretically analyze the failure of PSS led by the instability of close mode shapes, then New England 10-machine system is employed to validate the conclusion.