ISEL - Eng. Electrotécn. - Artigos
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- Adaptive and predictive controllers applied to onshore wind energy conversion systemPublication . Viveiros, Carla; Melicio, Rui; Mendes, Victor; Igreja, JoséThis paper presents a simulation of onshore energy conversion system connected to the electric grid and under an event-based supervisor control based on deterministic version of a finite state machine. The onshore energy conversion system is composed by a variable speed wind turbine, a mechanical transmission system described by a two-mass drive train, a gearbox, a doubly fed induction generator rotor and by a two-level converter. First, mathematical models of a variable speed wind turbine with pitch control are studied, followed by the study of different controller types such as adaptive controllers and predictive controllers. The study of an event-based supervisor based on finite state machines is also studied. The control and supervision strategy proposed for the onshore energy conversion system is based on a hierarchical structure with two levels, execution level where the adaptive and predictive controllers are included, and the supervision level where the event-based supervisor is included. The objective is to control the electric output power around the reference power and also to analyze the operational states according to the wind speed. The studied mathematical models are integrated into computer simulations for the onshore energy conversion system and the obtained numerical results allow for the performance assessment of the system connected to the electric grid. A comparison of the onshore energy conversion system performance without or with the supervisor is carried out to access the influence of the control and supervision strategy on the performance.
- An artificial neural network approach for short-term wind power forecasting in PortugalPublication . Catalão, João Paulo da Silva; Pousinho, Hugo Miguel Inácio; Mendes, VictorThis paper presents an artificial neural network approach for short-term wind power forecasting in Portugal. The increased integration of wind power into the electric grid, as nowadays occurs in Portugal, poses new challenges due to its intermittency and volatility. Hence, good forecasting tools play a key role in tackling these challenges. The accuracy of the wind power forecasting attained with the proposed approach is evaluated against persistence and ARIMA approaches, reporting the numerical results from a real-world case study.
- An exploratory study of training intensity in EEG neurofeedbackPublication . Esteves, Inês; Nan, Wenya; Alves, Cristiana P.; Calapez, Alexandre; Melicio, Fernando; Rosa, AgostinhoNeurofeedback training has shown benefits in clinical treatment and behavioral performance enhancement. Despite the wide range of applications, no consensus has been reached about the optimal training schedule. In this work, an EEG neurofeedback practical experiment was conducted aimed at investigating the effects of training intensity on the enhancement of the amplitude in the individual upper alpha band. We designed INTENSIVE and SPARSE training modalities, which differed regarding three essential aspects of training intensity: the number of sessions, the duration of a session, and the interval between sessions. Nine participants in the INTENSIVE group completed 4 sessions with 37.5 minutes each during consecutive days, while nine participants in the SPARSE group performed 6 sessions of 25 minutes spread over approximately 3 weeks. As a result, regarding the short-term effects, the upper alpha band amplitude change within sessions did not significantly differ between the two groups. Nonetheless, only the INTENSIVE group showed a significant increase in the upper alpha band amplitude. However, for the sustained effects across sessions, none of the groups showed significant changes in the upper alpha band amplitude across the whole course of training. The findings suggest that the progression within session is favored by the intensive design. Therefore, based on these findings, it is proposed that training intensity influences EEG self-regulation within sessions. Further investigations are needed to isolate different aspects of training intensity and effectively confirm if one modality globally outperforms the other.
- Application of a configurable model for risk assessment in the work sitesPublication . Nunes, FernandoThis paper presents a configurable model for occupational risk analysis, supported in decision matrix risk assessment with variable indexes dimensions and weightings. The formulation proposed seeks to overcome typical limitations such as range compression effect, mistakenly over classification of smaller risks and subjective input information. Also it allows its customization for each type of risk as a function of input information available in order to minimize subjectivity, while normalizing output for the calculated risk levels with a percent scale. This approach facilitates the implementation of models built to go along with the life of installations with periodically updates to fulfill accumulated data. To avoid discontinuation of procedures and practices implemented in the organizations, the model also enables the easy incorporation of risk assessment and control procedures based on risk classification matrixes, already in use regardless of their size and sector of activity.
- Application of adaptive neuro-fuzzy inference for wind power short-term forecastingPublication . Pousinho, Hugo Miguel Inácio; Mendes, Victor; Catalão, João Paulo da SilvaThe increased integration of wind power into the electric grid, as nowadays occurs in Portugal, poses new challenges due to its intermittency and volatility. Hence, good forecasting tools play a key role in tackling these challenges. In this paper, an adaptive neuro-fuzzy inference approach is proposed for short-term wind power forecasting. Results from a real-world case study are presented. A thorough comparison is carried out, taking into account the results obtained with other approaches. Numerical results are presented and conclusions are duly drawn. (C) 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.
- Artificial vision in renewable photovoltaic systems: a review and vision of specific applications and technologiesPublication . Amaral, Tito G.; Cordeiro, Armando; Fernao Pires, VitorRenewable energy resources have become extremely important in the current context of air pollution and the production of significant amounts of greenhouse gas emissions that contribute to global warming. One of the most important renewable energy sources that has shown the highest growth in recent years is photovoltaic (PV) systems. Due to their significance, this research presents a review of the applications in which artificial computer vision can be used in photovoltaic systems. From the results presented in this review, it will be evident that artificial vision can be applied for several different purposes. The advantages of using this technique will also be highlighted. Additionally, a systematic literature review is presented on the research associated with this topic. Through this review, it will be evident that many advanced algorithms related to image acquisition equipment have been proposed to ensure high reliability and fast results. This review does not merely focus on a specific topic or algorithms associated with image processing applied to photovoltaic systems. Rather, this work presents a broad and comprehensive review detailing all viable applications and associated computer vision technologies that can be deployed within these systems. Besides that, the review will clearly specify which work one is based on public datasets. To allow future reproducibility or research, the links to all public datasets utilized in the works based on them are included.
- Assessing the value of demand response in microgridsPublication . Gomes, Isaías; Melício, Rui; Mendes, VictorThis paper presents a computer application to assist in decisions about sustainability enhancement due to the effect of shifting demand from less favorable periods to periods that are more convenient for the operation of a microgrid. Specifically, assessing how the decisions affect the eco nomic participation of the aggregating agent of the microgrid bidding in an electricity day-ahead market. The aggregating agent must manage microturbines, wind systems, photovoltaic systems, energy storage systems, and loads, facing load uncertainty and further uncertainties due to the use of renewable sources of energy and participation in the day-ahead market. These uncertainties can not be removed from the decision making, and, therefore, require proper formulation, and the proposed approach customizes a stochastic programming problem for this operation. Case studies show that under these uncertainties and the shifting of demand to convenient periods, there are opportunities to make decisions that lead to significant enhancements of the expected profit. These enhancements are due to better bidding in the day-ahead market and shifting energy consumption in periods of favorable market prices for exporting energy. Through the case studies it is concluded that the proposed approach is useful for the operation of a microgrid.
- Assessment and optimization of wind energy integration into the power systems: application to the portuguese systemPublication . Faias, Sérgio Miguel Redondo; Sousa, Jorge A. M.; Reis, Francisco S.; Castro, R.The increasing integration of wind energy in power systems can be responsible for the occurrence of over-generation, especially during the off-peak periods. This paper presents a dedicated methodology to identify and quantify the occurrence of this over-generation and to evaluate some of the solutions that can be adopted to mitigate this problem. The methodology is applied to the Portuguese power system, in which the wind energy is expected to represent more than 25% of the installed capacity in a near future. The results show that the pumped-hydro units will not provide enough energy storage capacity and, therefore, wind curtailments are expected to occur in the Portuguese system. Additional energy storage devices can be implemented to offset the wind energy curtailments. However, the investment analysis performed show that they are not economically viable, due to the present high capital costs involved.
- Assessment and optimization of wind energy integration into the power systems: application to the portuguese systemPublication . Faias, Sérgio; Sousa, Jorge A. M.; Reis, Francisco Silva; Castro, RuiThe increasing integration of wind energy in power systems can be responsible for the occurrence of over-generation, especially during the off-peak periods. This paper presents a dedicated methodology to identify and quantify the occurrence of this over-generation and to evaluate some of the solutions that can be adopted to mitigate this problem. The methodology is applied to the Portuguese power system, in which the wind energy is expected to represent more than 25% of the installed capacity in a near future. The results show that the pumped-hydro units will not provide enough energy storage capacity and, therefore, wind curtailments are expected to occur in the Portuguese system. Additional energy storage devices can be implemented to offset the wind energy curtailments. However, the investment analysis performed show that they are not economically viable, due to the present high capital costs involved.
- Automatic synthesis of VHDL Hardware Components from IOPT Petri Net modelsPublication . Pereira, Fernando; Gomes, LuísThe IOPT Petri net class, designed to implement embedded system controllers, combining the well known properties of Petri nets with input and output functions, provides a set of capabilities suitable to specify digital controller systems. This paper presents an automatic code generation tool used to create VHDL controller implementations of IOPT models and describes the underlying code generation strategies. The new tool is integrated under the Web based IOPT-Tools framework (accessible at http://gres.uninova.pt), containing a complete tool-chain ranging from interactive model design and edition, model checking and simulation tools to automatic code generation, allowing the design of embedded system controllers using only graphical tools and without the need to manually write any hardware description or software code.