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Tavares, Alexandra Impacto do mercado ibérico de electricidade (MIBEL) no comportamento competitivo dos agentes produtores de energia eléctrica. Eds. Mário Neves, Jorge Sousa, and João Pina. FCT-UNL, 2009. Abstract

A presente Dissertação consiste num estudo do comportamento competitivo de entidades, produtoras e comercializadoras de energia eléctrica, num período de tempo antes e após a entrada em vigor do Mercado Ibérico de Electricidade (MIBEL). Esse período de tempo engloba os meses entre Abril de 2007 e Abril de 2008, sendo que o MIBEL teve início a 1 de Julho de 2007. O estudo incide principalmente no grau de competitividade ou ausência da mesma, que as referidas entidades adoptaram após o começo do MIBEL. Para poder efectuar essa avaliação, recorre-se a uma abordagem baseada em variações conjecturais, que constituem um indicador desse grau de competitividade. Ou seja, as variações conjecturais representam a convicção que determinada empresa X tem face ao comportamento que outra empresa Y adoptará após uma acção efectuada pela empresa X. Por acção depreende-se, por exemplo, uma redução ou um aumento da quantidade de produção de uma empresa. Se o valor da variável conjectural for 0, as empresas encontram-se a concorrer à Cournot. Caso seja -1, as empresas encontram-se em concorrência perfeita. Por outro lado, se o valor da variação conjectural for superior a 0 pode existir uma situação de conluio entre as empresas. De modo a obter estes valores das variações conjecturais, utiliza-se e readapta-se um simulador de mercado diário, denominado SiMEC - Simulador do Mercado Eléctrico e do Carbono. Este simulador, que anteriormente simulava apenas períodos temporais precedentes ao MIBEL, foi reajustado de modo a incluir dados pós MIBEL. Finalmente, são então realizados gráficos comparativos e retiradas conclusões acerca do comportamento das entidades face a alterações na estrutura do mercado de electricidade.

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Steve, Inácio, João Pina, Stanimir Valtchev, Mário Neves, and Amadeu Rodrigues. "Topology of an Electrical Gearbox with Variable Poles for Induction and Superconducting Disc Motors." X Portuguese-Spanish Congress in Electrical Engineering. 2007. Abstract
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Sfetsos, Athanasis, João Pina, Anabela Gonçalves, Mário Neves, and Amadeu Rodrigues. "Flux Modelling of Reluctance Machines with Bulk Superconducting Materials." Electromotion Review (2003). AbstractWebsite
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Rodrigues, Amadeu, B. A. Potter, João Pina, Anabela Gonçalves, and Mário Neves. "Torque Modelling of a Superconducting Reluctance Machine." Electromotion Review (2003). AbstractWebsite
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Rodrigues, Amadeu, Mário Neves, and João Pina. "Pilhas de Combustível como Fonte Limpa de Energia Eléctrica." X Portuguese-Spanish Congress in Electrical Engineering. 2007. Abstract
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Rodrigues, A., Mário Neves, and João Pina. "Fuel Cells as Clean Electrical Energy Sources." XCLEEE - X Portuguese-Spanish Conference in Electrical Engineering. 2007. Abstract
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Pina, João, Mário Neves, M. McCulloch, and Amadeu Rodrigues. "Design of a Linear Synchronous Motor With High Temperature Superconductor Materials in the Armature and in the Field Excitation System." Journal of Physics: Conference Series. 43 (2006): 804-808. AbstractWebsite
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Pina, João, Mário Neves, and Amadeu Rodrigues. "Study in the Design of HTS Machines: an All Superconducting Linear Synchronous Motor." POWERENG 2007 - International Conference on Power Engineering, Energy and Electrical Drives. 2007. Abstract
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Pina, J. M., P. Suárez, Ventim M. Neves, A. Álvarez, and A. L. Rodrigues. "Reverse engineering of inductive fault current limiters." Journal of Physics: Conference Series. 234 (2010): 1-9. AbstractWebsite

The inductive fault current limiter is less compact and harder to scale to high voltage networks than the resistive one. Nevertheless, its simple construction and mechanical robustness make it attractive in low voltage grids. Thus, it might be an enabling technology for the advent of microgrids, low voltage networks with dispersed generation, controllable loads and energy storage. A new methodology for reverse engineering of inductive fault current limiters based on the independent analysis of iron cores and HTS cylinders is presented in this paper. Their electromagnetic characteristics are used to predict the devices' hysteresis loops and consequently their dynamic behavior. Previous models based on the separate analysis of the limiters' components were already derived, e.g. in transformer like equivalent models. Nevertheless, the assumptions usually made may limit these models' application, as shown in the paper. The proposed methodology obviates these limitations. Results are validated through simulations.

Pina, João, C. Caracaleanu, A. Gonçalves, Pedro Pereira, S. Valtchev, Mário Neves, and A. Rodrigues. "High Performance, Environment Friendly, Modular and Fault Tolerant Renewable Energy Microgrid." 12th International Energy Conference & Exhibition (ENERGEX2007). 2007. Abstract
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Pina, João, David Inácio, Gonçalo Luis, José M. Ceballos, Pedro Pereira, João Martins, M. Ventim-Neves, Alfredo Alvarez, and Leão A. Rodrigues. "Research and Development of Alternative Concepts in HTS Machines." IEEE Transactions on Applied Superconductivity. 21 (2010): 1141-1145. AbstractWebsite

High temperature superconducting (HTS) machines are recognized to offer several advantageous features when comparing to conventional ones. Amongst these, highlights the decrease in weight and volume of the machines, due to increased current density in conductors or the absence of iron slots' teeth; or the decrease in AC losses and consequent higher efficiency of the machines, even accounting for cryogenics. These concepts have been already demonstrated and some machines have even achieved commercial stage. In this paper, several alternative approaches are applied to electrical motors employing HTS materials. The first one is an all superconducting linear motor, where copper conductors and permanent magnets are replaced by Bi-2223 windings and trapped flux magnets, taking advantage of stable levitation due to flux pinning, higher current densities and higher excitation field. The second is an induction disk motor with Bi-2223 armature, where iron, ironless and hybrid approaches are compared. Finally, an innovative command strategy, consisting of an electronically variable pole pairs' number approach, is applied to a superconducting hysteresis disk motor. All these concepts are being investigated and simulation and experimental results are presented.

Pina, João, Mário Neves, and Amadeu Rodrigues. "Case Study in the Design of HTS Machines: an All Superconducting Linear Synchronous Motor." 1st International Conference on Power Engineering, Energy and Electrical Drives, POWERENG. 2007. 185-190. Abstract

The electric and magnetic properties of high temperature superconductors and the possibility to cool them by cheap liquid nitrogen makes them attractive in power applications. An all superconducting linear synchronous motor is presented in this paper in order to quantify the benefits and disadvantages of such applications. The term ?all superconducting? is related with the absence of copper conductors and iron parts. Certain characteristics of the superconducting materials impose severe restrictions when used, e.g., as armature windings. A numerical method for deriving the thrust and lift forces developed in such a motor, driven by a typical current inverter, is presented.

Pina, J., P. Pereira, S. Valtchev, A. Gonçalves, Ventim M. Neves, A. Alvarez, and L. Rodrigues. "A test rig for thrust force measurements of an all HTS linear synchronous motor." Journal of Physics: Conference Series. 97 (2008): 012220. AbstractWebsite

This paper presents the design of a test rig for an all HTS linear synchronous motor. Although this motor showed to have several unattractive characteristics, its design raised a number of problems which must be considered in future HTS machines design. HTS electromagnetic properties led to the development of new paradigms in electrical machines and power systems, as e. g. in some cases iron removal and consequent assembly of lighter devices. This is due to superconductor's ability to carry high currents with minimum losses and consequent generation in the surrounding air of flux densities much higher than the allowed by ferromagnetic saturation. However, severe restrictions in HTS power devices design that goes further beyond cryogenic considerations must be accounted in. This is usually the case when BSCCO tapes are used as conductors. Its bending limitations and the presence of flux components perpendicular to tape surface, due to the absence of iron, have to be considered for it may turn some possible applications not so attractive or even practically unfeasible. An all HTS linear synchronous motor built by BSCCO tapes as armature conductors and two trapped-flux YBCO bulks in the mover was constructed and thrust force measurements are starting to be performed. Although the device presents severe restrictions due to the exposed and other reasons, it allowed systematising its design. A pulsed-field magnetiser to generate opposite fluxes for both YBCO bulks is also detailed. Thrust force numerical predictions were already derived and presented.

Pina, João, Pedro Pereira, Gonçalves A. Pronto, Pedro Arsénio, and Tiago Silva. "Modelling and Simulation of Inductive Fault Current Limiters." Physics Procedia. 36 (2012): 1248-1253. AbstractWebsite

Inductive superconducting fault current limiters have already demonstrated their technical viability in electrical networks. Its architecture and robustness make them potentially adequate for distribution networks, and this type of devices is considered as an enabling technology for the advent of embedded generation with renewable energy sources. In order to promote the growth and maturity of these superconducting technologies, fast design tools must be developed, allowing simulating devices with different materials in grids with diverse characteristics. This work presents advances in the development of such tool, which, at present stage, is an effective alternative to software simulations by finite elements methods, reducing dramatically computation time. The algorithms are now compared with experimental results from a laboratory scale prototype, showing the need to refine them.

Pina, João, Mário Neves, M. McCulloch, and Amadeu Rodrigues. "Design of a Linear Synchronous Motor With High Temperature Superconductor Materials in the Armature and in the Field Excitation System." European Conference on Applied Superconductivity, EUCAS?05. 2005. Abstract
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Pina, João, Mário Neves, Alfredo Álvarez, and Amadeu Rodrigues. "Magnetisation System and Thrust Force Measurement of an All Superconducting Linear Synchronous Motor." X Portuguese-Spanish Congress in Electrical Engineering. 2007. Abstract
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Pina, João Polyphase Motor with Variable Number of Poles., 2010. Abstract

The invention consists in a polyphase motor and operating system thereof that allows obtaining an arbitrary relation of the number of magnetic poles without mechanical commutations within the stator. The number of slots of the latter is ideally given by the least common multiple between the required pole relations. The stator is polyphasic, and the rotor is that of an induction or hysteresis motor. The motor is designed for applications where a large range of operation requiring maximum yield and?or smooth speed?torque (or force, depending on whether the motor is rotary or linear) transitions. This is the case of electric vehicle traction. The operating system receives control references via a controller that compares them with the signals read by the sensor(s). The control action feeds a polyphase inverter for generating the voltages or currents that feed the stator. The speed, torque, or position values are measured in the rotor.

Pina, J., and PU Lima. "A glass furnace operation system using fuzzy modelling and genetic algorithms for performance optimisation." Engineering Applications of Artificial Intelligence. 16 (2003): 681-690. AbstractWebsite

An architecture for the operation of a recuperative-type glass furnace is introduced in this paper. It is based on a hierarchical scheme, with two main parts: process optimisation and process modelling. Process optimisation is carried out by an expert controller, and uses genetic algorithms to solve a multiobjective optimisation problem. Process modelling is performed by a learning system, based on a fuzzy learning-by-examples algorithm. Results of real and simulated experiments with the glass manufacturing process are presented.

Pina, João, Pedro Pereira, S. Valtchev, A. Gonçalves, Mário Neves, and A. Rodrigues. "A test rig for thrust force measurements f an all HTS linear synchronous motor." 8th European Conference on Applied Superconductivity (EUCAS). 2007. Abstract

This paper presents the design of a test rig for an all HTS linear synchronous motor. Although this motor showed to have several unattractive characteristics, its design raised a number of problems which must be considered in future HTS machines design. HTS electromagnetic properties led to the development of new paradigms in electrical machines and power systems, as e. g. in some cases iron removal and consequent assembly of lighter devices. This is due to superconductor's ability to carry high currents with minimum losses and consequent generation in the surrounding air of flux densities much higher than the allowed by ferromagnetic saturation. However, severe restrictions in HTS power devices design that goes further beyond cryogenic considerations must be accounted in. This is usually the case when BSCCO tapes are used as conductors. Its bending limitations and the presence of flux components perpendicular to tape surface, due to the absence of iron, have to be considered for it may turn some possible applications not so attractive or even practically unfeasible. An all HTS linear synchronous motor built by BSCCO tapes as armature conductors and two trapped-flux YBCO bulks in the mover was constructed and thrust force measurements are starting to be performed. Although the device presents severe restrictions due to the exposed and other reasons, it allowed systematising its design. A pulsed-field magnetiser to generate opposite fluxes for both YBCO bulks is also detailed. Thrust force numerical predictions were already derived and presented.

Pina, João, Mário Neves, Alfredo Álvarez, and Amadeu Rodrigues. "High Temperature Superconducting Fault Current Limiters as Enabling Technology in Electrical Grids with Increased Distributed Generation Penetration." Doctoral Conference on Computing, Electrical and Industrial Systems - DoCEIS'10. 2010. 427-434. Abstract

Amongst applications of high temperature superconductors, fault current limiters are foreseen as one of the most promising in power systems. Several topologies have been developed in the last years, taking advantage of different superconductors? properties. Increasing distributed generation (DG) penetration, based on renewable energy, adds new short-circuit sources to electrical grids, which brings several energy quality and protection issues. Superconducting fault current limiters can obviate these problems, representing thus an enabling technology for DG penetration. In this paper current limiter topologies are presented, its operations principles, strengths and weaknesses, in the context of these DG grids. In the end, future trends are discussed.

Pina, João, Mário Ventim Neves, Alfredo Álvarez, and Amadeu Leão Rodrigues. "Numerical Design Methodology for an All Superconducting Linear Synchronous Motor." Technological Innovation for Sustainability. Vol. 349. IFIP Advances in Information and Communication Technology, 349. 2011. 553-562. Abstract

One potential advantage of the application of superconducting materials in electrical machines is the possibility to build lighter and compact devices by removing iron. These machines find applications, e.g., in systems where cryogenics is already available, or in naturally cryogenic environments. The design of motors with high temperature superconductors (HTS) presents issues unconsidered in classical machines, besides considerations on cryogenics, such as HTS brittleness or mechanical restrictions. Moreover, HTS' electromagnetic properties also degrade due to flux density components, which arise if there is no iron to guide magnetic flux. Several aspects must thus be considered in the design stage, as applications may turn less attractive or even unfeasible. In this paper these issues are detailed, and a numerical methodology for the design of an all superconducting (without iron or conventional conductors) linear synchronous motor is presented.

Pina, João Operação e Controlo de um Forno de Vidro. Eds. Pedro Lima. IST - Instituto Superior Técnico, 2002. Abstract
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Pereira, P., S. Valtchev, J. Pina, A. Gonçalves, Ventim M. Neves, and A. L. Rodrigues. "Power electronics performance in cryogenic environment: evaluation for use in HTS power devices." Journal of Physics: Conference Series. 97 (2008): 012219. AbstractWebsite

Power electronics (PE) plays a major role in electrical devices and systems, namely in electromechanical drives, in motor and generator controllers, and in power grids, including high-voltage DC (HVDC) power transmission. PE is also used in devices for the protection against grid disturbances, like voltage sags or power breakdowns. To cope with these disturbances, back-up energy storage devices are used, like uninterruptible power supplies (UPS) and flywheels. Some of these devices may use superconductivity. Commercial PE semiconductor devices (power diodes, power MOSFETs, IGBTs, power Darlington transistors and others) are rarely (or never) experimented for cryogenic temperatures, even when designed for military applications. This means that its integration with HTS power devices is usually done in the hot environment, raising several implementation restrictions. These reasons led to the natural desire of characterising PE under extreme conditions, e. g. at liquid nitrogen temperatures, for use in HTS devices. Some researchers expect that cryogenic temperatures may increase power electronics' performance when compared with room-temperature operation, namely reducing conduction losses and switching time. Also the overall system efficiency may increase due to improved properties of semiconductor materials at low temperatures, reduced losses, and removal of dissipation elements. In this work, steady state operation of commercial PE semiconductors and devices were investigated at liquid nitrogen and room temperatures. Performances in cryogenic and room temperatures are compared. Results help to decide which environment is to be used for different power HTS applications.

Pereira, Pedro, S. Valtchev, João Pina, Anabela Gonçalves, Mário Neves, and Amadeu Rodrigues. "Power Electronics Performance in Cryogenic Environment: Evaluation for Use in HTS Power Devices." 8th European Conference on Applied Superconductivity (EUCAS). 2007. Abstract

Power electronics (PE) plays a major role in electrical devices and systems, namely in electromechanical drives, in motor and generator controllers, and in power grids, including high-voltage DC (HVDC) power transmission. PE is also used in devices for the protection against grid disturbances, like voltage sags or power breakdowns. To cope with these disturbances, back-up energy storage devices are used, like uninterruptible power supplies (UPS) and flywheels. Some of these devices may use superconductivity. Commercial PE semiconductor devices (power diodes, power MOSFETs, IGBTs, power Darlington transistors and others) are rarely (or never) experimented for cryogenic temperatures, even when designed for military applications. This means that its integration with HTS power devices is usually done in the hot environment, raising several implementation restrictions. These reasons led to the natural desire of characterising PE under extreme conditions, e. g. at liquid nitrogen temperatures, for use in HTS devices. Some researchers expect that cryogenic temperatures may increase power electronics' performance when compared with room-temperature operation, namely reducing conduction losses and switching time. Also the overall system efficiency may increase due to improved properties of semiconductor materials at low temperatures, reduced losses, and removal of dissipation elements. In this work, steady state operation of commercial PE semiconductors and devices were investigated at liquid nitrogen and room temperatures. Performances in cryogenic and room temperatures are compared. Results help to decide which environment is to be used for different power HTS applications

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Oliveira-Lima, Jose A., João F. Martins, Celson Lima, Vasco Delgado-Gomes, João Pina, and Grzegorz Benysek. "Towards an energy model for supporting real time building energy management." 2012 IEEE 16th International Conference on Intelligent Engineering Systems (INES). 2012. 203-208. Abstract

Building energy management may simultaneously integrate multiple energy areas and sources of information. The coordination of synergies allow better-informed decisions, such as performing forecasts and adjustments of energy production and storage, while adapting electrical loads to off-peak times, when energy rates are lower. This work targets the improvement and optimization of energy management operations in buildings and large complexes, by introducing a conceptual model for supporting real-time advanced reasoning and inference towards efficient energy management.