João Murta Pina

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.

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.

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.

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.

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.

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.

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.

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.