João Murta Pina

Magnetic shielding inductive fault currentlimiterswith high temperature superconducting cylinders have previously been described by a characteristic (or maximum)hysteresisloop, built from properties of their constitutive parts, which allowed predicting their behavior in electrical grids. These preliminary results were based on finite elements simulations, but posterior experiments suggested limitations in the models. In order to investigate the application of these previous models to real devices, two laboratory scale prototypes were built with different types of superconducting material in the secondary, either bulk cylinder, either tape. Although the behavior of both devices is still approximately defined by a maximumhysteresisloop, differences in the shielding current response, when compared with previous model, must be incorporated in future models.

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.

Os motores de histerese são muito atraentes, numa ampla gama de aplicações devido à característica binário - velocidade e simplicidade de construção. É esperado que o rendimento destes motores seja melhorado aquando do uso de materiais supercondutores de alta temperatura (SAT ? supercondutores de alta temperatura) e, de facto, os motores de histerese têm-se mostrado como, provavelmente, a melhor máquina eléctrica usando materiais SAT. Ambos os motores, quer convencional quer supercondutor (com SAT), são motores de histerese, mas apresentam diferentes fenómenos físicos para o seu funcionamento: o comportamento de histerese nos materiais ferromagnéticos convencionais é devido à falta de linearidade das suas propriedades magnéticas dos materiais ferromagnéticos enquanto a histerese nos materiais supercondutores de alta temperatura é de natureza ohmica e está relacionada com dinâmica de vórtices. Nesta tese aspectos teóricos, experimentais e simulados de ambos os motores são discutidos, realçando-se o princípio de funcionamento de cada um e as características mais relevantes de cada um. As características obtidas, quer por testes experimentais quer por uso do simulador usando elementos finitos (FLUX2D?), foram comparadas com o objectivo de avaliar o rendimento dos motores electromecânicos e a eficiência dos sistemas, incluindo a criogenia para os dispositivos supercondutores de alta temperatura.

A instalação em larga escala de turbinas eólicas equipadas com um gerador de indução duplamente alimentado (GIDA) tem vindo a promover a realização de vários estudos relacionados com potenciais soluções para a sua integração na rede eléctrica. Nesta tese apresenta-se uma técnica de controlo que permite regular as potências activa e reactiva do GIDA de forma estável e independente. A sua viabilidade é suportada não só por um estudo teórico prévio mas também pelos resultados da simulação de modelos desenvolvidos usando o software Matlab?Simulink?. Apesar de este sistema funcionar a velocidade variável (ainda que dentro de certos limites), continua a existir a necessidade de limitar a potência fornecida pela turbina eólica quando a velocidade do vento assume valores superiores ao nominal. Assim, faz-se também uma breve análise de alguns métodos de regulação de potência activos e passivos.

In this paper, a poly-phase disc motor innovative feeding and control strategy, based on a variable poles approach, and its application to a high temperature superconductor (HTS) disc motor, are presented. The stator windings may be electronically commutated to implement a 2, 4, 6 or 8 poles winding, thus changing the motor's torque?speed characteristics. The motor may be a conventional induction motor with a conductive disc rotor, or a new HTS disc motor, with conventional copper windings at its two iron semi-stators and a HTS disc as a rotor. The conventional induction motor's operation principle is related with the induced electromotive forces in the conductive rotor. Its behaviour, characteristics and modelling through Steinmetz and others theories are well known. The operation principle of the motor with HTS rotor, however, is rather different and is related with vortices' dynamics and pinning characteristics; this is a much more complex process than induction, and its modelling is quite complicated. In this paper, the operation was simulated through finite-elements commercial software (FLUX2D), whereas superconductivity was simulated by the E-J power law. The electromechanical performance of both motor's computed are compared. Considerations about the systems overall efficiency, including cryogenics, are also discussed.

In this paper, a poly-phase disc motor innovative feeding and control strategy, based on a variable poles approach, and its application to a HTS disc motor, are presented. The stator windings may be electronically commutated to implement a 2, 4, 6 or 8 poles winding, thus changing the motor's torque?speed characteristics. The motor may be a conventional induction motor with a conductive disc rotor, or a new HTS disc motor, with conventional copper windings at its two iron semi-stators, and a HTS disc as a rotor. The conventional induction motor's operation principle is related with the induced electromotive forces in the conductive rotor. Its behaviour, characteristics (namely their torque?speed characteristics for different number of pole pairs) and modelling through Steinmetz and others theories are well known. The operation principle of the motor with HTS rotor, however, is rather different and is related with vortices' dynamics and pinning characteristics; this is a much more complex process than induction, and its modelling is quite complicated. In this paper, the operation was simulated through finite-elements commercial software, whereas superconductivity was simulated by the E-J power law. The Electromechanical performances of both motors where computed and are presented and compared. Considerations about the systems overall efficiency, including cryogenics, are also discussed.

In this paper, a poly-phase disc motor innovative feeding and control strategy, based on a variable poles approach, and its application to a HTS disc motor, are presented. The stator windings may be electronically commutated to implement a 2, 4, 6 or 8 poles winding, thus changing the motor's torque?speed characteristics. The motor may be a conventional induction motor with a conductive disc rotor, or a new HTS disc motor, with conventional copper windings at its two iron semi-stators, and a HTS disc as a rotor. The conventional induction motor's operation principle is related with the induced electromotive forces in the conductive rotor. Its behaviour, characteristics (namely their torque?speed characteristics for different number of pole pairs) and modelling through Steinmetz and others theories are well known. The operation principle of the motor with HTS rotor, however, is rather different and is related with vortices' dynamics and pinning characteristics; this is a much more complex process than induction, and its modelling is quite complicated. In this paper, the operation was simulated through finite-elements commercial software, whereas superconductivity was simulated by the E-J power law. The Electromechanical performances of both motors where computed and are presented and compared. Considerations about the systems overall efficiency, including cryogenics, are also discussed.

A presente dissertação surge pelo interesse em estudar a adequação do uso de sistemas solares fotovoltaicos na electrificação de serviços primários em povoados remotos nos países Africanos mais carenciados. A abordagem teórica tem como objectivo principal reflectir sobre a importância destas aplicações intervindo naquelas que são consideradas as maiores dificuldades dos países subdesenvolvidos, ou seja, saneamento básico, serviços de saúde e meios de comunicação adequados. Nesse contexto estuda-se a viabilidade de alimentar com energia eléctrica produzida localmente unidades sanitárias na província de Sofala (Moçambique). O trabalho exigiu por isso um estudo de caso baseado numa dessas unidades. Mediante a análise das amostras recolhidas para esta investigação elaborou-se através de ferramentas informáticas um dimensionamento e uma modelação adequadas ao sistema fotovoltaico a ser implementado. Os resultados obtidos de acordo com os requisitos da unidade sanitária permitiram dimensionar os elementos do sistema bem como, simular hora a hora o seu funcionamento diário ao longo do ano. Uma vez provada a sua viabilidade incluiuse ainda neste trabalho um anteprojecto da instalação.

An equivalent model and electromechanical characteristics for the disk motor was obtained based on the Steinmetz parameters. This paper describes a series of tests conducted on an axial flux motor, equipped with an aluminum rotor disc and an YBCO high temperature superconducting rotor disc, at liquid nitrogen temperature (77 K). The rotating magnetic field was produced by a four-pole, three-phase stator winding, at 50 Hz. At asynchronous permanent regime, Steinmetz-type models are able to describe both motors' behavior. From the performed tests, the parameters of both motors' models were deduced. A variable load was used to obtain both motor's characteristics (conventional and superconducting). Experimental obtained characteristics of both motors are compared with the ones predicted from parameters' calculation. The HTS motor provides high efficiency then the conventional ones.

An equivalent model and electromechanical characteristics for the disk motor was obtained based on the Steinmetz parameters. This paper describes a series of tests conducted on an axial flux motor, equipped with an aluminum rotor disc and an YBCO high temperature superconducting rotor disc, at liquid nitrogen temperature (77 K). The rotating magnetic field was produced by a four-pole, three-phase stator winding, at 50 Hz. At asynchronous permanent regime, Steinmetz-type models are able to describe both motors' behavior. From the performed tests, the parameters of both motors' models were deduced. A variable load was used to obtain both motor's characteristics (conventional and superconducting). Experimental obtained characteristics of both motors are compared with the ones predicted from parameters' calculation. The HTS motor provides high efficiency then the conventional ones.

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.

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.

The energy resource management is a major concern worldwide. Energy management activities minimize environmental impacts of the energy production. Therefore, electric energy consumption monitoring has been proposed as an important process which makes immediate reductions in energy use and CO(2) emissions. In recent years, advances in electronics have allowed the implementation of many technological solutions that could help to reduce energy consumption. This paper describes the design and prototyping of a home electric energy monitoring system that provides residential consumers with real time information about their electricity use. The system uses wireless communication and displays the information on a small LCD screen and on a computer.

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.

The potential advantage of using superconducting materials in electrical devices is well described in the literature. The electromagnetic properties of these materials make them unique for several applications, such as, e.g. electrical machines and drives, fault current applications, or superconducting magnetic energy storage. In the development of electromechanical conversion devices, superconducting materials are used foreseeing mainly a decrease in the device dimensions or a performance improvement for the same active volume. To guarantee a good application of this kind of materials it is important to describe and model the phenomena that characterize their operation under different regimes. In this paper, a study based in FEM simulations of a motor with bulk superconductor in the rotor is carried out, with the purpose of understand, quantify and qualify which phenomena are present in the different regimes of the motor, leading to obtaining an equivalent electrical circuit with lumped parameters.

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.

Hysteresis motors are very attractive in a wide range of fractional power applications, due to its torque-speed characteristics and simplicity of construction. This motor's performance is expected to improve when HTS rotors are used, and in fact, hysteresis motors have shown to be probably the most viable electrical machines using HTS materials. While these motors, either conventional or HTS, are both hysteresis motors, they base their operation on different physical phenomena: hysteretic behaviour in conventional ferromagnetic materials is due to the material's non-linear magnetic properties, while in HTS materials the hysteresis has an ohmic nature and is related with vortices' dynamics. In this paper, theoretical aspects of both conventional and HTS hysteresis motors are discussed, its operation principles are highlighted, and the characteristics of both motors are presented. The characteristics, obtained both by experimental tests and numerical simulation (made with commercial software), are compared, in order to evaluate not only the motor's electromechanical performances but also the overall systems efficiency, including cryogenics for the HTS device.