F. M. Hughes

Control of DFIG-based wind generation for power network support

This paper addresses the design and implementation of a novel control scheme for a doubly fed induction generator (DFIG), of the type employed with wind turbines, to provide support to power system operation. It is shown that this controller provides a DFIG-based wind farm with operational and control compatibility with conventional power stations, the ability to contribute to voltage support and recovery following network faults, the ability to provide a power system stabilizer capability that improves overall system damping, and the capability of contributing short-term frequency support following loss of network generation. A simple but realistic test network that combines synchronous and wind farm generation has been modeled and used to assess dynamic performance. Simulation results are presented and discussed that demonstrate the capabilities and contributions of the new DFIG controller to network support.

A power system stabilizer for DFIG-based wind generation

A power system stabilizer (PSS) for a wind turbine employing a doubly fed induction generator (DFIG) is presented. It is shown that this PSS can significantly influence the contribution that a DFIG-based wind farm can make to network damping. A simple, generic test network that combines synchronous and wind farm generation is used to demonstrate system performance contributions. The results of both eigenvalue analysis and time response simulation studies are presented to illustrate contributions to network dynamic and transient performance that the DFIG controller with its PSS can make. Performance capabilities superior to those provided by synchronous generation with automatic voltage regulator and PSS control are demonstrated.

Overview and Comparative Analysis of Gas Turbine Models for System Stability Studies

Gas turbines have become increasingly popular in the different power systems, due to their lower greenhouse emission as well as the higher efficiency, especially when connected in a combined cycle setup. With increasing installations of gas turbines scheduled in different countries, the dynamics of the gas turbines become increasingly more important. In order to study such dynamics, accurate models of gas turbines are needed. This paper presents a comparative analysis and an overview of various models of gas turbines published in different literature.

Influence of Tower Shadow and Wind Turbulence on the Performance of Power System Stabilizers for DFIG-Based Wind Farms

The aim of the paper is to demonstrate the way in which mechanical power variations, due to tower shadow and wind turbulence, influence control performance of power system stabilizer (PSS) loops for doubly-fed induction generators (DFIGs). The PSS auxiliary loops are applied on a specific DFIG control scheme, the flux magnitude and angle controller (FMAC). However, since the PSS signal is applied at the output of the basic controller, the PSS performance characteristics displayed are deemed typical for DFIG control schemes in general. The relative capabilities of PSS controllers based on stator power, rotor speed, and network frequency, when the DFIG turbine is subjected to aerodynamic torque variations, are investigated via simulation studies. A two-generator aggregate model of a wind farm is introduced, which enables the influence of tower shadow and wind turbulence on both an individual turbine and on the overall wind farm itself to be assessed.

Validated Models for Gas Turbines Based on Thermodynamic Relationships

Many different types of gas turbines (GTs) are currently in use in power systems worldwide. These gas turbines can be broadly classed as single shaft GT (heavy duty GT) or twin shaft GT (aero-derivative). Due to the different construction of the two types of GT, their responses to the same operational disturbances can differ widely. Modern electronic governors offer wide scope for utilizing the GT to provide a contribution to network support in terms of damping provision and post-fault recovery, features that currently are not included in governor control performance specifications. In order to assess such capability, models capable of yielding more detailed information about GT dynamic behavior than those presently available are needed. This paper presents validated GT models developed from first principles based on the underlying physical processes that dictate the dynamic responses of GTs. The models are validated against manufacturer factory test data and differences in the dynamic behavior of the two major types of GTs are explored. In addition, phase compensated governors are implemented to explore the feasibility of employing such devices in a realistic GT operational scenario.

Comparative Analysis and Reconciliation of Gas Turbine Models for Stability Studies

Gas turbines have become increasingly popular in recent years in different power systems, due to their lower greenhouse emission as well as the higher efficiency, especially when connected in a combined cycle setup. With increasing installations of gas turbines scheduled in different countries, the dynamics of the gas turbines become increasingly more important. In order to study such dynamics, accurate models of gas turbines are needed. This paper presents a comparative analysis of two most widely used mathematical models, namely the IEEE and Rowens model. Efforts were also made to reconcile the two models and to obtain a hybrid model which uses characteristics derived from the IEEE model.