Abstract
In this paper, the development of bidding strategies is investigated for a wind farm owner. The optimization model is characterized by making the analysis of scenarios. The proposed approach allows evaluating alternative production strategies in order to submit bids to the electricity market with the goal of maximizing profits. The problem is formulated as a linear programming problem. An application to a case study is presented Copyright

Abstract
In this paper, a mixed-integer nonlinear approach is proposed to support decision-making for a hydro power producer, considering a head-dependent hydro chain. The aim is to maximize the profit of the hydro power producer from selling energy into the electric market. As a new contribution to earlier studies, a risk aversion criterion is taken into account, as well as head-dependency. The volatility of the expected profit is limited through the conditional value-at-risk (CVaR). The proposed approach has been applied successfully to solve a case study based on one of the main Portuguese cascaded hydro systems. Copyright

Abstract
As wind power generation undergoes rapid growth, lightning and overvoltage incidents involving wind power plants have come to be regarded as a serious problem. Firstly, lightning location systems are discussed, as well as important parameters regarding lightning protection. Also, this paper presents a case study, based on a wind turbine with an interconnecting transformer, for the study of adequate lightning and overvoltage protection measures. The electromagnetic transients circuit under study is described, and computational results are presented Copyright

Abstract
This paper is concerned with the protection of wind energy systems against the direct effects of lightning. As wind power generation undergoes rapid growth, lightning damages involving wind turbines have come to be regarded as a serious problem. Nevertheless, very few studies exist yet in Portugal regarding lightning protection of wind energy systems using numerical codes. A new case study is presented in this paper, based on a wind turbine with an interconnecting transformer, for the analysis of transient phenomena due to a direct lightning strike to the blade. Comprehensive simulation results are provided by using models of the Restructured Version of the Electro-Magnetic Transients Program (EMTP), and conclusions are duly drawn.

Abstract
This paper presents the effect of environmental factors, such as wind speed change, on the classification of power quality (PQ) disturbances in grid-connected wind energy systems. Initially, based on the selection of suitable features and 3-Dimensional feature plots, the PQ disturbances are classified. Further, the disturbances are accurately classified using S-transform based feature extraction followed by classification by modular probabilistic neural network (MPNN), support vector machines (SVMs) and least square support vector machines (LS-SVMs). Different types of sag and swell disturbances due to the change in load and wind speed are created using MATLAB/Simulink and an experimental prototype setup for the classification problem. The results reveal that S-transform based extracted feature data, when trained with MPNN, SVMs and LS-SVM, can effectively classify the PQ disturbances. The accuracy and reliability of the proposed classifier are also validated on signals with noise content. A comparative study is also carried out to determine the robustness of the techniques used. Finally, conclusions are duly drawn.

Abstract
In a competitive electricity market, generation companies have to maximize their profits selecting the best strategy. This paper is on the problem of short-term hydro scheduling, particularly concerning a head-sensitive hydro chain. We propose a method based on nonlinear programming that considers power generation a function of water discharge and also of the head. The proposed method provides a higher profit for the company in comparison with classical optimization methods based on linear programming that ignores head dependence. Numerical results based on a realistic cascaded hydro chain show that this method is adequate for dealing with head-sensitive hydro chains.