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Catalao J.P.S.,University of Beira Interior | Catalao J.P.S.,Center for Innovation in Electric and Energy Engineering | Pousinho H.M.I.,University of Beira Interior | Pousinho H.M.I.,Center for Innovation in Electric and Energy Engineering | Mendes V.M.F.,Polytechnic Institute of Lisbon
IEEE Transactions on Power Systems | Year: 2011

A novel hybrid approach, combining wavelet transform, particle swarm optimization, and adaptive-network-based fuzzy inference system, is proposed in this paper for short-term electricity prices forecasting in a competitive market. Results from a case study based on the electricity market of mainland Spain are presented. A thorough comparison is carried out, taking into account the results of previous publications. Finally, conclusions are duly drawn. © 2010 IEEE.


Catalao J.P.S.,University of Beira Interior | Catalao J.P.S.,Center for Innovation in Electric and Energy Engineering | Pousinho H.M.I.,University of Beira Interior | Mendes V.M.F.,Polytechnic Institute of Lisbon
Energy | Year: 2011

In this paper, a novel mixed-integer nonlinear approach is proposed to solve the short-term hydro scheduling problem in the day-ahead electricity market, considering not only head-dependency, but also start/stop of units, discontinuous operating regions and discharge ramping constraints. Results from a case study based on one of the main Portuguese cascaded hydro energy systems are presented, showing that the proposed mixed-integer nonlinear approach is proficient. Conclusions are duly drawn. © 2010 Elsevier Ltd.


Pousinho H.M.I.,University of Beira Interior | Mendes V.M.F.,Polytechnic Institute of Lisbon | Catalao J.P.S.,University of Beira Interior | Catalao J.P.S.,Center for Innovation in Electric and Energy Engineering
Energy Conversion and Management | Year: 2011

The increased integration of wind power into the electric grid, as nowadays occurs in Portugal, poses new challenges due to its intermittency and volatility. Wind power prediction plays a key role in tackling these challenges. The contribution of this paper is to propose a new hybrid approach, combining particle swarm optimization and adaptive-network-based fuzzy inference system, for short-term wind power prediction in Portugal. Significant improvements regarding forecasting accuracy are attainable using the proposed approach, in comparison with the results obtained with five other approaches. © 2010 Elsevier Ltd. All rights reserved.


Batista N.C.,University of Beira Interior | Melicio R.,University of Évora | Matias J.C.O.,University of Beira Interior | Catalao J.P.S.,University of Beira Interior | Catalao J.P.S.,Center for Innovation in Electric and Energy Engineering
Energy | Year: 2013

The actual electric grid was developed to offer electricity to the clients from centralized generation, so with large-scale distributed renewable generation there is an urgent need for a more flexible, reliable and smarter grid. The wireless technologies are becoming an important asset in the smart grid, particularly the ZigBee devices. These smart devices are gaining increased acceptance, not only for building and home automation, but also for energy management, efficiency optimization and metering services, being able to operate for long periods of time without maintenance needs. In this context, this paper provides new comprehensive field tests using open source tools with ZigBee technologies for monitoring photovoltaic and wind energy systems, and also for building and home energy management. Our experimental results demonstrate the proficiency of ZigBee devices applied in distributed renewable generation and smart metering systems. © 2012 Elsevier Ltd.


Catalao J.P.S.,University of Beira Interior | Catalao J.P.S.,Center for Innovation in Electric and Energy Engineering | Pousinho H.M.I.,University of Beira Interior | Mendes V.M.F.,Polytechnic Institute of Lisbon
Renewable Energy | Year: 2011

This paper proposes artificial neural networks in combination with wavelet transform 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. Results from a real-world case study are presented. A comparison is carried out, taking into account the results obtained with other approaches. Finally, conclusions are duly drawn. © 2010 Elsevier Ltd.


Fernao Pires V.,Polytechnic Institute of Setúbal | Fernao Pires V.,Center for Innovation in Electric and Energy Engineering | Martins J.F.,New University of Lisbon | Hao C.,China University of Mining and Technology
Solar Energy | Year: 2012

A fast and robust control strategy for a multilevel inverter in grid-connected photovoltaic system is presented. The multilevel inverter is based on a dual two-level inverter topology. There are two isolated PV generators that feeding each bridge inverter. The output of each inverter is connected to a three-phase transformer. The active and reactive powers flowing into the grid are controlled by a sliding mode algorithm. An alfa-beta space vector modulator is also used. The inverters DC voltages are also controller by a sliding mode controller. In this way, a fast and robust system controller is obtained. Several test results are presented in order to verify the effectiveness of the proposed system controller. © 2012 Elsevier Ltd.


Santos J.,Center for Innovation in Electric and Energy Engineering | Lopes B.,Center for Innovation in Electric and Energy Engineering | Branco P.J.C.,Center for Innovation in Electric and Energy Engineering
Sensors and Actuators, A: Physical | Year: 2010

The ionic polymer-metal composite (IPMC) is a new functional material that, being flexible and capable of operating in air and in liquid environments, is a new candidate for diaphragms in micropump devices. In this paper, two different IPMC diaphragms have been fabricated and experimentally tested. Their stroke volume was examined with different values of electric current supplied for each IPMC diaphragm. The novel results showed that both diaphragms have an asymmetric behaviour of their upward and downward displacements mainly imposed by the electrode layer, which becomes more brittle as the IPMC diaphragm moves up and down. Stroke volumes up to 80 μl were obtained and a flow rate of about 8.02 μl/s was achieved for an operating frequency of 0.1 Hz. The results clearly show that there are significant differences between the obtained dynamic characteristics when it is used FEM simulations to study IPMCs diaphragms and when they are experimentally test in real operating conditions. © 2010 Elsevier B.V.


Faria J.A.B.,Center for Innovation in Electric and Energy Engineering | Das Neves M.G.,Center for Innovation in Electric and Energy Engineering
IEEE Transactions on Power Delivery | Year: 2011

The high-frequency domain characterization of overhead three-phase cables is a critical issue as far as power line carrier communications is concerned. In many instances a detailed knowledge of the electric and magnetic parameters of the cable is not available. Even if manufacturer cable-data are available, strong proximity effects among cable conductors do inhibit the utilization of closed-form expressions for the determination of the cable constitutive parameters, namely, the entries of the per-unit-length R, L, G , and C matrices. However, the determination of such parameters can always be made experimentally. In this paper, new measurement principles based on the cable excitation by independent propagation modes are presented and discussed. In the case of symmetric cables, the eigenvectors associated to the propagation modes are frequency independent, however, the propagation constants and surge impedances are not. The entries of the frequency-dependent R, L, G , and C matrices are retrieved from open and short-circuit cable measurements involving information on the modal propagation constants and modal surge impedances. For exemplification purposes, experimental results concerning a shielded three-phase cable for low voltage applications are provided. The results in this paper do not apply to buried cables where ground return phenomena would need to be accounted © 2010 IEEE.


Barros J.D.,University of Madeira | Silva J.F.A.,Center for Innovation in Electric and Energy Engineering | Jesus E.G.A.,University of Madeira
IEEE Transactions on Industrial Electronics | Year: 2013

The development of high-processing-capability microprocessors allows the implementation of new digital control methods for neutral-point-clamped (NPC) multilevel converter in power-electronic applications. This paper presents a new predictive digital control method for multilevel converters, called fast predictive. This method computes the optimal vector using the NPC three-phase multilevel dynamic model equations just once in each control cycle, while current predictive methods need 27 calculations. The closest vector to the optimal vector is found by minimizing the distance between each one of the 27 available vectors to the optimal vector. Space vector modulation could be also used. The obtained performance is similar to the predictive optimal control that uses the converter model to find all the 27 responses of the multilevel and then searches for the vector that minimizes control errors. Relative to predictive optimal control, the fast predictive improves digital processing speed by at least 150% in multilevel converters with 27 vectors. This speed improvement would allow multilevel converters with five or higher number of levels (125 instead of 27 vectors) to be controlled using the same sampling frequency of the three-level inverter. The fast-predictive controller is used in a multilevel rectifier with near-unity power factor to enforce the ac currents. Fast predictive control is also used in the rectifier dc voltage to reduce sensitivity of the dc voltage to dc load disturbances. The simulation and experimental results show that the fast-predictive controller is able to control the ac currents of a three-phase multilevel rectifier, achieving nearly 1.5% total harmonic distortion while balancing the capacitors' dc voltages. The use of predictive control to regulate the dc voltage shows an improvement of approximately 7% compared to a proportional-integral controller. © 2012 IEEE.


Henriques T.,Center for Innovation in Electric and Energy Engineering | Cesar B.,Center for Innovation in Electric and Energy Engineering | Branco P.J.C.,Center for Innovation in Electric and Energy Engineering
Applied Energy | Year: 2010

Portable fuel cells are receiving great attention today mainly because their energy density is higher than any portable battery solution. Among other types, portable polymer electrolyte membrane (PEM) fuel cells are an established technology where research on increasing their efficiency is leading product development and manufacturing. The objective of this work was to study and evaluate the redesign of a commercial portable fuel cell, improving its efficiency. A three-dimensional model of the original PEM fuel cell with parallel plus a transversal flow channel design was developed using Comsol Multiphysics, including the effects of liquid water formation and electric current production. Using this model, the effects of different channel geometries and respective cathode flow rates on the cell's performance, including the local transport characteristics, were studied. Laboratory tests with various fuel cell stacks using the new channels structure were effectuated for an evaluation of the fuel cell's performance, showing improvements in its efficiency of up to 26.4%. © 2009 Elsevier Ltd. All rights reserved.

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