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This paper deals with modeling and stability analysis of a doubly-fed induction generator (DFIG)-based wind-power unit that is interfaced with the grid via a series-compensated transmission line. A detailed mathematical model is developed in this paper that takes into account dynamics of the flux observer, phase-locked loop (PLL), controllers of the power-electronic converter, and wind turbine. Using the model and based on eigenvalue/participation-factor analysis, the system and controller parameters that substantially influence the system stability have been identified. The developed model is validated through a comprehensive set of simulation studies in the Matlab/Simulink and PSCAD/EMTDC software environments. Index Terms--Control, doubly-fed induction generator (DFIG), eigenvalue analysis, participation factor, power electronics, series compensation, small-signal analysis, wind power.

The rapid growth of wind power systems worldwide will likely see the integration of large wind farms with electrical networks that are series compensated for ensuring stable transmission of bulk power. This may potentially lead to subsynchronous-resonance (SSR) issues. Although SSR is a well-understood phenomenon that can be mitigated with flexible ac transmission system (FACTS) devices, scant information is available on the SSR problem in a series-compensated wind farm. This paper reports the potential occurrence and mitigation of SSR caused by an induction-generator (IG) effect as well as torsional interactions, in a series-compensated wind farm. SSR suppression is achieved as an additional advantage of FACTS controllers which may already be installed in the power system for achieving other objectives. In this study, a wind farm employing a self-excited induction generator is connected to the grid through a series-compensated line. A static var compensator (SVC) with a simple voltage regulator is first employed at the IG terminal in addition to the fixed shunt capacitor for dynamic reactive power support. The same SVC is shown to effectively damp SSR when equipped with an SSR damping controller. Also, a thyristor-controlled series capacitor (TCSC) that is actually installed to increase the power transfer capability of the transmission line is also shown to damp subsynchronous oscillations when provided with closed-loop current control. While both FACTS controllers--the SVC and TCSC--can effectively mitigate SSR, the performance of TCSC is shown to be superior. Extensive simulations have been carried out using EMTDC/PSCAD to validate the performance of SVC and TCSC in damping SSR. Index Terms--Flexible ac transmission systems (FACTS), self-excited induction generator (SEIG), series compensation, static VAR compensator (SVC), subsynchronous resonance (SSR), thyristor-controlled series capacitor (TCSC), wind power systems.

This paper presents a comparative study of the performance of distance relays for transmission lines compensated by shunt connected flexible ac transmission system (FACTS) controllers/devices. The objective of this study is to evaluate the performance of various distance protection schemes on transmission lines with shunt-FACTS devices applied for midpoint voltage control. The impact of two types of shunt FACTS devices, static var compensator (SVC) and static synchronous compensator (STATCOM) on the transmission line distance protection schemes is studied for different fault types, fault locations and system conditions. The power system elements and the shunt-FACTS devices with their associated controllers are modeled using RSCAD/RTDS software. The results are based on the performance of commercial distance relays using a real time digital simulator (RTDS). Index Terms--Distance channel aided schemes, distance protection relay, flexible ac transmission system (FACTS), power system protection, real time digital simulator, shunt compensation, static synchronous compensator (STATCOM), static var compensator (SVC).

This paper presents a study of the performance of distance protection relays when applied to protect shunt Flexible AC Transmission System (FACTS) compensated transmission lines. The objective of this study is to evaluate the performance of distance relays on transmission lines with FACTS devices applied for mid point voltage control. Effect of two types of shunt FACTS devices, Static Var Compensators (SVC) and Static Synchronous Compensators (STATCOM) are studied. The study is conducted in three stages. First the situation is studied analytically, where the errors introduced in the impedance measurement due to the presence of shunt FACTS devices on the line are analyzed. In the second stage, the situation is simulated using transient simulation software, EMTDC. In this method, the response of FACTS devices for different fault conditions and system conditions is also modeled. This method brings out some unique problems that would be experienced by the distance relays due to some specific characteristics of the FACTS devices. Finally, the findings are confirmed by testing a commercial distance relay using a Real Time Digital Simulator (RTDS). The results obtained by testing the commercial relay validate the analytical and simulation studies. Index Terms--Distance protection relay, flexible ac transmission system (FACTS), power system protection, real-time digital simulator (RTDS), shunt compensation, static synchronous compensators (STATCOM), static var compensators (SVC).

This paper describes a fundamental study into modeling the effects of frequency variation on network and shunt impedances in long term power system stability simulations. The focus is on extreme post-fault situations where significant generation-load mismatch causes wide excursions in system frequency. A novel application of singular perturbations is presented. This method is compared with the 'constant reactance' technique, the 'variable reactance' method in which the network reactances are varied with system frequency, and a method in which the network transients are fully simulated. Stability simulations for an interconnected two-area system employing the different modeling techniques show that a two time scale analysis using the singular perturbation method is a feasible technique for accurate prediction of long term post fault system behaviour. Keywords - Long Term Dynamics, Singular Perturbation Method, Network Modeling, Two Time Scale Analysis

Byline: Ran Peng, Rajiv K. Varma, Jin Jiang Rapid advances in Wide-Area Measurement (WAM) and communication technologies have made the use of remote system data/signals for effective control and operation of power systems possible. This paper presents a new concept of damping control of Static Var Compensator (SVC) based on rotor speeds of remotely located generators. The concept is demonstrated in three study systems: a single machine infinite bus system, a two-area four-machine 11-bus system, and the Western System Coordinating Council (WSCC) three-machine nine-bus meshed system. The performance of the proposed remote generator speed signal is compared with the traditionally utilised local signals for SVC damping control through nonlinear time domain simulations. It is shown that the rotor speed of the remotely located generator that significantly participates in the lightly or negatively damped electromechanical mode of oscillation is the most effective SVC control signal in damping electromechanical oscillations in a power system.