A comparison of commonly used input signals for power oscillation damping

Electromechanical oscillations in power systems often exhibit poor damping when the power transfer over a corridor is high relative to the transmission strength. Traditional approaches to aid the damping of power system oscillations include the use of power system stabilisers (PSS). Off late, the capability of flexible AC transmission systems (FACTS) controllers in damping power system oscillations has been explored and proven. Unlike PSS, for a remotely located FACTS controller, it is desired to extract an input signal from the locally measurable quantities at the controller location. The responsiveness of the input signal to the swing modes to be damped-commonly known as "observability" is an important criteria for input signal selection. Analysis of four basic input signals-line current, active power, bus voltage and bus frequency for an example single machine infinite bus (SMIB) system installed with a static VAr compensator (SVC) shows that line current signal enables substantial positive damping to be attained for all operating conditions. This is confirmed by eigenvalue analysis and dynamic simulation using MATLAB.