Mahmoud Reza Shakarami

Ph.D. Thesis Defense Session

Abstract

Nowadays, because of economic problems on restructured power systems, also environmental pollution problems, interconnected power systems are operated close to their stability limits. These power systems are called stressed power systems. In large power systems, high power may be transferred between generating stations through weak transmission lines. This subject may produce low frequency oscillations ranging 0.2 to 0.8 Hz in power system facing a disturbance. These oscillations appear in oscillating of angles of a group of generators in an area against angels of generators in other or others areas. Inter-area oscillations with no sufficient damping cause major problems in the power systems. They can fatigue in turbine-generator axis of electrical machines or threaten security of power systems. Also, they have negative effects on power quality, like as flicker. Power system stabilizers (PSSs) are the oldest devices to improve damping of these oscillations. Studies shows that in stressed power systems, these oscillations cannot be damped effectively by only PSSs. Nowadays, FACTS devices with high speed of performance have shown their ability to damp these oscillations effectively. Static synchronous series compensator (SSSC) is one of the new FACTS devices that generates a series voltage synchronized with transmission line voltage. Unlike others FACTS devices, less attention has been done on SSSC to damp electromechanical, particularly inter-area, oscillations. Modeling of SSSC to study of dynamic stability in a multi-machine power system, presentation of a method to design of a lead-lag stabilizer for SSSC and its coordination with PSSs have been studied in this dissertation. Also, analysis and studying on SSSC stabilizer in different control channels on damping inter-area oscillations, investigation on different operation modes of SSSC and analysis of effect of SSSC stabilizers in these modes on damping inter-area oscillations in large and small samples of multi-machine power systems are studied in this research. Studies show that, in the stressed power systems, modal interactions can affect noticeably on dynamic behavior and performance of stabilizers. One of the methods to analysis modal interactions phenomenon is modal series (MS) method. In this dissertation, for the first time, the MS method is expanded to a power system installed with a SSSC stabilizer. Modal interactions between an inter-area mode and control modes related to SSSC stabilizers are studied in the samples of stressed multi-machine power systems. A method to design of SSSC stabilizer and its coordination with PSS to improve damping inter-area oscillations considering modal interactions is presented and tested on IEEE 4 and 50-machine power System.

Date: Oct. 27, 2010, 17:00

Place: Department of Electrical Engineering, Room: 305