A Novel Unified Power Flow Controller with Sub-Synchronous Oscillation Damping

The unified power flow controller (UPFC) as a multi-objective flexible ac transmission system (FACTS) controller, can be utilized to control active and reactive power flows in a transmission line in addition to the bus voltage. Also UPFC can be utilized as a stabilizer in cooperation with the PSS which is discussed here. This paper scrutinizes the detailed analysis of sub-synchronous resonance (SSR) and torsional torques, arising from a power system employing Voltage Sourced Converter (VSC)-based FACTS such as UPFC. Also the main purpose of this paper is to present a damping control of VSC Back to Back (BIB) to relieve SSR in FACTS with series compensation. Furthermore a power controller loop is designed to power flow and reactive power control; both of two control loops are added to an UPFC in a transmission system. Concisely, this work presents the role of supplemental control of an existing VSC -BtB in SSR of a series compensated transmission power system. The supplemental controller is added to an existing VSC-based BtB tie in a transmission grid. The analysis considers different operating modes of the converters. The robustness of the considered supplemental control is tested by time domain nonlinear transient simulation, frequency analysis and also modal analysis. Moreover the frequency analysis is based on the alpha-beta model and the transient simulation considers the alpha-beta frame model and the three-phase detailed model of VSC. The influences of the operating modes of the converters and generator model are involved in this investigation. Copyright (C) 2011 Praise Worthy Prize S.r.l. - All rights reserved.