Abstract

Abstract
This paper addresses the problem of robustly tuning power system stabilisers (PSSs) in systems with large wind power integration. PSSs installed in wind energy conversion systems, namely in doubly fed induction generators, are used in this research to provide additional damping to the electromechanical modes of oscillation. A new method that aims to reduce the computational effort required to find a robust solution that is suitable for a very large set of operating conditions is also proposed.

Abstract
This paper proposes an optimized dispatch control strategy for active and reactive powers delivered by a doubly fed induction generator in a wind park. In this control approach, wind turbines are supposed to operate over a deloaded maximum power extraction curve and with respond to a supervisory wind farm control after a request from a system operator for adjusting the outputs of the wind park. The definition of the active and reactive powers operating points, for each wind turbine, is defined from an optimization algorithm that uses the primal-dual predictor corrector interior point method. The control strategy used at the wind generator level exploits a combination of pitch control and control of the static converters to adjust the rotor speed for the required operation points. A small wind park is used to illustrate the effectiveness of the developed approach.

Abstract
This paper describes the design of a Power System Stabilizer synthesized by a static Artificial Neural Network. The patterns used to train the neural network are sets of controller parameters, previously calculated for several system operation points using a pole-shifting method. This neural network stabilizer then operates, in a gain-scheduling scheme, in accordance with the values of active and reactive powers furnished by the generator to the power system, but with soft transition variations of the controller parameters. The trained neural network presents, as its main characteristic, almost uniform values for all the stabilizer parameters when the system synchronous machine is generating reactive power, but these same parameters suffer great variations when the machine is absorbing reactive power. Simulation tests presented show very good performance for the proposed Neural PSS, when compared with a fixed-parameter stabilizer, corroborating the main characteristic of the proposed stabilizer. (C) 2005 Published by Elsevier Ltd.

Abstract
This paper presents a new candidate method for on-line transient security assessment and enhancement based on pattern recognition techniques. Transient state variables are used as primary features and the classifier is obtained in two phases, through the combination of an optimum discriminant transformation together with a probabilistic procedure. The proposed security functions can be further refined by means of a second level classifier based on an optimal discrimination plane and using a weighted K nearest neighbor rule. It is shown that this method provides also an efficient and simple tool for on-line preventive control. Results obtained for several contingencies in the CIGRE test system are discussed.

Abstract
This work presents a control strategy applied to a doubly fed induction machine (DFIM) for wind generation in a medium power system. In order to control the active power and reactive power exchange between the machine and the grid, the rotor is fed by a link of AC-DC-AC converters modeled as voltage and controlled current sources, respectively. The control of the rotor-side converter is realized by fuzzy controllers whose performances are compared with that of conventional Proportional-Integral controllers. The control of the grid-side converter is carried out by a control block based on the instantaneous power theory and it is controlled to maintain the DC link voltage constant and to improve the power factor of the system. Some design considerations of the control schemes are discussed. A multimachine model is used in digital simulations to assess the dynamic behavior of the power system control scheme proposed in this work.