Abstract

This thesis deals with Flexible AC Transmission Systems (FACTS) based on Voltage Source Converters (VSC). In particular, the emphasis is on series-connected VSC into transmission lines, known as Static Synchronous Series Compensator (SSSC) and Interline Power Flow Controller (IPFC). These are modern series compensators with fast response and high performance. The SSSC and IPFC applications are simulated with the help of EMTP-RV software, where detailed models of the power system and controllers are implemented and the dynamic performances are considered. The proposed VSC is based on a 3-level Neutral-Point-Clamped (NPC) VSC employing PWM techniques to generate firing pulses for the VSC switches. The VSC main circuit configuration, function and operating principles are first described. The proposed VSC is used as the major building block of the SSSC. The detailed model of SSSC (with two different control strategies) is then presented. The controllers are designed to regulate the transmission line impedance by injecting a set of 3-phase voltages with controllable magnitude and phase angle.The stability of the proposed SSSC under various system conditions is investigated and the two different control strategies are compared. Finally, two SSSCs with a common DC-link are used to configure an IPFC. The proposed IPFC is applied to two parallel transmission lines to regulate their impedances. The validity of the proposed control techniques under various system conditions is also investigated