Study of Inter Area Oscillations Using Phasor Measurement Units

Abstract

Low-frequency oscillations in the power system have major repercussions on power system stability and the objective of maximum power transfer. Local and global control strategies have been developed to dampen and impede these oscillations. A modern local control strategy is supplying the automatic voltage regulation (AVR) of the generator with a power system stabilizer (PSS). Modern global control strategies include supplying the tie lines with flexible alternating current transmission systems devices (FACTS) and a power oscillation damper (POD).

Including global signals in conjunction with local signals as an input on the generators PSS has been studied, but follows the same problems as PSSs tuned to enhance damping of the inter-area mode. Once satisfactory results are achieved on the inter-area mode, local modes of the machines involved in the inter-area mode tend to become less stable, or unstable. This type of interaction has caused most of the latest problems regarding damping of the inter-area mode with the use of the generators PSS.

The following thesis investigates the impact on inter-area oscillations of including global measurements from phasor measurement units (PMU) in conjunction with local measurements as an input signal on a FACTS-device installed on the tie-line between two interconnected areas. A remote measurement feedback controller has been designed, tuned, and placed on the two-area; four-machine system, created for studying inter-area oscillations. Phasor measurements from optimally located measurement units were shown to improve the damping of the local and inter-area, low-frequency oscillations. The advantages of damping the before-mentioned oscillations were apparent through the ability to increase the power transfer capability in the tie-lines between the two areas following the implementation of the control method. The robustness of the suggested control method was analyzed through a small-signal stability test increasing tie-line power transfer, and a transient stability test using time-domain simulations of a severe fault, more specific a three-phase short circuit on the tie-lines.