@article {OA5328, title = {Analysis of Characteristic Hysteresis Loops of Magnetic Shielding Inductive Fault Current Limiters}, journal = {IEEE Transactions on Applied Superconductivity}, volume = {23}, number = {3}, year = {2013}, note = {n/a}, pages = {5601004{\textendash}5601004}, abstract = {

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.

}, url = {http://oa.uninova.pt/5328/}, author = {Pedro Arsenio and Tiago Silva and Nuno Vilhena and Jo{\~a}o Pina and Anabela Pronto} } @conference {OA5053, title = {Lumped Parameters Equivalent Circuit of a Superconducting Hysteresis Motor}, booktitle = {EUCAS Conference 2011}, volume = {36}, year = {2012}, note = {n/a}, pages = {975{\textendash}979}, abstract = {

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.

}, url = {http://oa.uninova.pt/5053/}, author = {David In{\'a}cio and Jo{\~a}o Pina and Martins, Jo{\~a}o and M{\'a}rio Ventim Neves and Alfredo {\'A}lvarez} } @article {OA5102, title = {Modelling and Simulation of Inductive Fault Current Limiters}, journal = {Physics Procedia}, volume = {36}, year = {2012}, note = {n/a}, pages = {1248{\textendash}1253}, abstract = {

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.

}, url = {http://oa.uninova.pt/5102/}, author = {Jo{\~a}o Pina and Pedro Pereira and A. Gon{\c c}alves Pronto and Pedro Ars{\'e}nio and Tiago Silva} } @conference {OA5058, title = {Towards an energy model for supporting real time building energy management}, booktitle = {2012 IEEE 16th International Conference on Intelligent Engineering Systems (INES)}, year = {2012}, note = {n/a}, pages = {203{\textendash}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.

}, url = {http://oa.uninova.pt/5058/}, author = {Oliveira-Lima, Jose A. and Jo{\~a}o F. Martins and Lima, Celson and Delgado-Gomes, Vasco and Jo{\~a}o Pina and Grzegorz Benysek} } @article {OA4734, title = {Experimental Characterization of a Conventional (Aluminum) and of a Superconducting (YBCO) Axial Flux Disc Motor}, journal = {IEEE Transactions on Applied Superconductivity}, year = {2011}, note = {n/a}, month = {January}, abstract = {

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{\textquoteright} behavior. From the performed tests, the parameters of both motors{\textquoteright} models were deduced. A variable load was used to obtain both motor{\textquoteright}s characteristics (conventional and superconducting). Experimental obtained characteristics of both motors are compared with the ones predicted from parameters{\textquoteright} calculation. The HTS motor provides high efficiency then the conventional ones.

}, url = {http://oa.uninova.pt/4734/}, author = {D In{\'a}cio and Jo{\~a}o Pina and Go{\cn}alo Luis and J. F. Martins and Ventim-Neves, M. and Alfredo Alvarez} } @article {OA5068, title = {Experimental Characterization of a Conventional (Aluminum) and of a Superconducting (YBCO) Axial Flux Disc Motor}, journal = {IEEE Transactions on Applied Superconductivity}, volume = {21}, number = {3}, year = {2011}, note = {n/a}, pages = {1146{\textendash}1150}, abstract = {

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{\textquoteright} behavior. From the performed tests, the parameters of both motors{\textquoteright} models were deduced. A variable load was used to obtain both motor{\textquoteright}s characteristics (conventional and superconducting). Experimental obtained characteristics of both motors are compared with the ones predicted from parameters{\textquoteright} calculation. The HTS motor provides high efficiency then the conventional ones.

}, url = {http://oa.uninova.pt/5068/}, author = {David In{\'a}cio and Jo{\~a}o Pina and Go{\cn}alo Luis and Jo{\~a}o F. Martins and M{\'a}rio Neves and Alfredo Alvarez} } @conference {OA5148, title = {Home Electric Energy Monitoring System: Design and Prototyping}, booktitle = {Technological Innovation for Sustainability}, series = {IFIP Advances in Information and Communication Technology}, volume = {349}, year = {2011}, note = {n/a}, pages = {437{\textendash}444}, abstract = {

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.

}, url = {http://oa.uninova.pt/5148/}, author = {Jo{\~a}o Gil Josu{\'e} and Jo{\~a}o Pina and M{\'a}rio Neves} } @conference {OA5158, title = {Numerical Design Methodology for an All Superconducting Linear Synchronous Motor}, booktitle = {Technological Innovation for Sustainability}, series = {IFIP Advances in Information and Communication Technology}, volume = {349}, year = {2011}, note = {n/a}, pages = {553{\textendash}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{\textquoteright} 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.

}, url = {http://oa.uninova.pt/5158/}, author = {Jo{\~a}o Pina and M{\'a}rio Ventim Neves and Alfredo {\'A}lvarez and Amadeu Le{\~a}o Rodrigues} } @conference {OA1950, title = {High Temperature Superconducting Fault Current Limiters as Enabling Technology in Electrical Grids with Increased Distributed Generation Penetration}, booktitle = {Doctoral Conference on Computing, Electrical and Industrial Systems - DoCEIS{\textquoteright}10}, year = {2010}, note = {n/a}, month = {February}, pages = {427{\textendash}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.

}, url = {http://oa.uninova.pt/1950/}, author = {Jo{\~a}o Pina and M{\'a}rio Neves and Alfredo {\'A}lvarez and Amadeu Rodrigues} } @booklet {OA2496, title = {Polyphase Motor with Variable Number of Poles}, year = {2010}, note = {n/a}, month = {February}, 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.

}, url = {http://oa.uninova.pt/2496/}, author = {Jo{\~a}o Pina} } @article {OA2534, title = {Research and Development of Alternative Concepts in HTS Machines}, journal = {IEEE Transactions on Applied Superconductivity}, volume = {21}, number = {3}, year = {2010}, note = {n/a}, month = {December}, pages = {1141{\textendash}1145}, publisher = {IEEE}, abstract = {

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{\textquoteright} 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{\textquoteright} number approach, is applied to a superconducting hysteresis disk motor. All these concepts are being investigated and simulation and experimental results are presented.

}, url = {http://oa.uninova.pt/2534/}, author = {Jo{\~a}o Pina and David In{\'a}cio and Gon{\c c}alo Luis and Jos{\'e} M. Ceballos and Pedro Pereira and Martins, Jo{\~a}o and Ventim-Neves, M. and Alfredo Alvarez and A. Le{\~a}o Rodrigues} } @article {OA2428, title = {Reverse engineering of inductive fault current limiters}, journal = {Journal of Physics: Conference Series}, volume = {234}, number = {3}, year = {2010}, note = {n/a}, pages = {1{\textendash}9}, publisher = {IOP Publishing}, abstract = {

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{\textquoteright} hysteresis loops and consequently their dynamic behavior. Previous models based on the separate analysis of the limiters{\textquoteright} components were already derived, e.g. in transformer like equivalent models. Nevertheless, the assumptions usually made may limit these models{\textquoteright} application, as shown in the paper. The proposed methodology obviates these limitations. Results are validated through simulations.

}, url = {http://oa.uninova.pt/2428/}, author = {J M Pina and P Su{\'a}rez and M Ventim Neves and A {\'A}lvarez and A L Rodrigues} } @unpublished {OA2153, title = {Energia nuclear no panorama nacional: benef{\'\i}cios vs custos e an{\'a}lise de sustentabilidade}, year = {2009}, note = {n/a}, month = {May}, publisher = {FCT-UNL}, abstract = {n/a}, url = {http://oa.uninova.pt/2153/}, author = {Jer{\'o}nimo Cunha}, editor = {Amadeu Rodrigues and Jo{\~a}o Pina} } @unpublished {OA1962, title = {Impacto do mercado ib{\'e}rico de electricidade (MIBEL) no comportamento competitivo dos agentes produtores de energia el{\'e}ctrica}, year = {2009}, note = {n/a}, month = {May}, publisher = {FCT-UNL}, abstract = {

A presente Disserta{\c c}{\~a}o consiste num estudo do comportamento competitivo de entidades, produtoras e comercializadoras de energia el{\'e}ctrica, num per{\'\i}odo de tempo antes e ap{\'o}s a entrada em vigor do Mercado Ib{\'e}rico de Electricidade (MIBEL). Esse per{\'\i}odo de tempo engloba os meses entre Abril de 2007 e Abril de 2008, sendo que o MIBEL teve in{\'\i}cio a 1 de Julho de 2007. O estudo incide principalmente no grau de competitividade ou aus{\^e}ncia da mesma, que as referidas entidades adoptaram ap{\'o}s o come{\c c}o do MIBEL. Para poder efectuar essa avalia{\c c}{\~a}o, recorre-se a uma abordagem baseada em varia{\c c}{\~o}es conjecturais, que constituem um indicador desse grau de competitividade. Ou seja, as varia{\c c}{\~o}es conjecturais representam a convic{\c c}{\~a}o que determinada empresa X tem face ao comportamento que outra empresa Y adoptar{\'a} ap{\'o}s uma ac{\c c}{\~a}o efectuada pela empresa X. Por ac{\c c}{\~a}o depreende-se, por exemplo, uma redu{\c c}{\~a}o ou um aumento da quantidade de produ{\c c}{\~a}o de uma empresa. Se o valor da vari{\'a}vel conjectural for 0, as empresas encontram-se a concorrer {\`a} Cournot. Caso seja -1, as empresas encontram-se em concorr{\^e}ncia perfeita. Por outro lado, se o valor da varia{\c c}{\~a}o conjectural for superior a 0 pode existir uma situa{\c c}{\~a}o de conluio entre as empresas. De modo a obter estes valores das varia{\c c}{\~o}es conjecturais, utiliza-se e readapta-se um simulador de mercado di{\'a}rio, denominado SiMEC - Simulador do Mercado El{\'e}ctrico e do Carbono. Este simulador, que anteriormente simulava apenas per{\'\i}odos temporais precedentes ao MIBEL, foi reajustado de modo a incluir dados p{\'o}s MIBEL. Finalmente, s{\~a}o ent{\~a}o realizados gr{\'a}ficos comparativos e retiradas conclus{\~o}es acerca do comportamento das entidades face a altera{\c c}{\~o}es na estrutura do mercado de electricidade.

}, url = {http://oa.uninova.pt/1962/}, author = {Alexandra Tavares}, editor = {M{\'a}rio Neves and Jorge Sousa and Jo{\~a}o Pina} } @unpublished {OA2101, title = {Controlo de Geradores de Indu{\c c}{\~a}o Duplamente Alimentados em Turbinas E{\'o}licas}, year = {2009}, note = {n/a}, month = {July}, publisher = {FCT-UNL}, abstract = {

A instala{\c c}{\~a}o em larga escala de turbinas e{\'o}licas equipadas com um gerador de indu{\c c}{\~a}o duplamente alimentado (GIDA) tem vindo a promover a realiza{\c c}{\~a}o de v{\'a}rios estudos relacionados com potenciais solu{\c c}{\~o}es para a sua integra{\c c}{\~a}o na rede el{\'e}ctrica. Nesta tese apresenta-se uma t{\'e}cnica de controlo que permite regular as pot{\^e}ncias activa e reactiva do GIDA de forma est{\'a}vel e independente. A sua viabilidade {\'e} suportada n{\~a}o s{\'o} por um estudo te{\'o}rico pr{\'e}vio mas tamb{\'e}m pelos resultados da simula{\c c}{\~a}o de modelos desenvolvidos usando o software Matlab?Simulink?. Apesar de este sistema funcionar a velocidade vari{\'a}vel (ainda que dentro de certos limites), continua a existir a necessidade de limitar a pot{\^e}ncia fornecida pela turbina e{\'o}lica quando a velocidade do vento assume valores superiores ao nominal. Assim, faz-se tamb{\'e}m uma breve an{\'a}lise de alguns m{\'e}todos de regula{\c c}{\~a}o de pot{\^e}ncia activos e passivos.

}, url = {http://oa.uninova.pt/2101/}, author = {Jorge Ferreira}, editor = {M{\'a}rio Neves and Jo{\~a}o Pina} } @unpublished {OA2137, title = {Electrifica{\c c}{\~a}o de servi{\c c}os prim{\'a}rios em povoados remotos africanos recorrendo a sistemas solares fotovoltaicos (PV)}, year = {2009}, note = {n/a}, month = {July}, publisher = {FCT-UNL}, abstract = {

A presente disserta{\c c}{\~a}o surge pelo interesse em estudar a adequa{\c c}{\~a}o do uso de sistemas solares fotovoltaicos na electrifica{\c c}{\~a}o de servi{\c c}os prim{\'a}rios em povoados remotos nos pa{\'\i}ses Africanos mais carenciados. A abordagem te{\'o}rica tem como objectivo principal reflectir sobre a import{\^a}ncia destas aplica{\c c}{\~o}es intervindo naquelas que s{\~a}o consideradas as maiores dificuldades dos pa{\'\i}ses subdesenvolvidos, ou seja, saneamento b{\'a}sico, servi{\c c}os de sa{\'u}de e meios de comunica{\c c}{\~a}o adequados. Nesse contexto estuda-se a viabilidade de alimentar com energia el{\'e}ctrica produzida localmente unidades sanit{\'a}rias na prov{\'\i}ncia de Sofala (Mo{\c c}ambique). O trabalho exigiu por isso um estudo de caso baseado numa dessas unidades. Mediante a an{\'a}lise das amostras recolhidas para esta investiga{\c c}{\~a}o elaborou-se atrav{\'e}s de ferramentas inform{\'a}ticas um dimensionamento e uma modela{\c c}{\~a}o adequadas ao sistema fotovoltaico a ser implementado. Os resultados obtidos de acordo com os requisitos da unidade sanit{\'a}ria permitiram dimensionar os elementos do sistema bem como, simular hora a hora o seu funcionamento di{\'a}rio ao longo do ano. Uma vez provada a sua viabilidade incluiuse ainda neste trabalho um anteprojecto da instala{\c c}{\~a}o.

}, url = {http://oa.uninova.pt/2137/}, author = {Ricardo Leote}, editor = {M{\'a}rio Neves and Jo{\~a}o Pina} } @conference {OA1789, title = {Conventional and HTS Disc motor with pole variation control}, booktitle = {2nd International Conference on Power Engineering, Energy and Electrical Drives (POWERENG{\textquoteright}2009)}, year = {2009}, note = {n/a}, pages = {513{\textendash}518}, abstract = {

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{\textquoteright}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{\textquoteright}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{\textquoteright} 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{\textquoteright}s computed are compared. Considerations about the systems overall efficiency, including cryogenics, are also discussed.

}, url = {http://oa.uninova.pt/1789/}, author = {D In{\'a}cio and J. A. In{\'a}cio and J. Pina and S Valtchev and M. Neves and J. Martins and A. Rodrigues} } @unpublished {OA1222, title = {Compara{\c c}{\~a}o num{\'e}rica e experimental das caracter{\'\i}sticas dos Motores de Histerese Convencional e Supercondutor}, year = {2008}, note = {n/a}, month = {September}, publisher = {FCT-UNL}, abstract = {

Os motores de histerese s{\~a}o muito atraentes, numa ampla gama de aplica{\c c}{\~o}es devido {\`a} caracter{\'\i}stica bin{\'a}rio - velocidade e simplicidade de constru{\c c}{\~a}o. {\'E} 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 t{\^e}m-se mostrado como, provavelmente, a melhor m{\'a}quina el{\'e}ctrica usando materiais SAT. Ambos os motores, quer convencional quer supercondutor (com SAT), s{\~a}o motores de histerese, mas apresentam diferentes fen{\'o}menos f{\'\i}sicos para o seu funcionamento: o comportamento de histerese nos materiais ferromagn{\'e}ticos convencionais {\'e} devido {\`a} falta de linearidade das suas propriedades magn{\'e}ticas dos materiais ferromagn{\'e}ticos enquanto a histerese nos materiais supercondutores de alta temperatura {\'e} de natureza ohmica e est{\'a} relacionada com din{\^a}mica de v{\'o}rtices. Nesta tese aspectos te{\'o}ricos, experimentais e simulados de ambos os motores s{\~a}o discutidos, real{\c c}ando-se o princ{\'\i}pio de funcionamento de cada um e as caracter{\'\i}sticas mais relevantes de cada um. As caracter{\'\i}sticas 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 electromec{\^a}nicos e a efici{\^e}ncia dos sistemas, incluindo a criogenia para os dispositivos supercondutores de alta temperatura.

}, url = {http://oa.uninova.pt/1222/}, author = {David In{\'a}cio}, editor = {M{\'a}rio Neves and Anabela Gon{\c c}alves and Jo{\~a}o Pina} } @unpublished {OA1223, title = {Projecto de uma caixa de velocidades el{\'e}ctrica por meio da varia{\c c}{\~a}o do n{\'u}mero de p{\'o}los para motores em disco de rotor em alum{\'\i}nio e em materiais supercondutores de alta temperatura (SAT)}, year = {2008}, note = {n/a}, month = {May}, publisher = {FCT-UNL}, abstract = {

Nesta disserta{\c c}{\~a}o apresenta-se um motor em disco polif{\'a}sico inovador bem como uma estrat{\'e}gia de controlo com base no m{\'e}todo de varia{\c c}{\~a}o de velocidade por comuta{\c c}{\~a}o do n{\'u}mero de pares de p{\'o}los. A configura{\c c}{\~a}o das bobinas aliada {\`a} escolha das correntes e tens{\~o}es que se injectam nas bobinas dos estatores, permite comutar electronicamente o n{\'u}mero de p{\'o}los do motor entre 2, 4 6 e 8 p{\'o}los, conseguindo-se controlar a caracter{\'\i}stica bin{\'a}rio?velocidade do motor. O motor em disco possui a bobinagem feita em cobre com dois semi-estatores, em que quando utiliza o rotor em alum{\'\i}nio (com condutividade diferente de zero) comporta-se como um motor de indu{\c c}{\~a}o convencional. Quando se substitui o rotor em alum{\'\i}nio por um constitu{\'\i}do por um supercondutor de alta temperatura (SAT), o dispositivo comporta-se como um motor de histerese. O princ{\'\i}pio de funcionamento do motor em disco convencional {\'e} baseado na indu{\c c}{\~a}o de for{\c c}a electromotrizes no rotor e, consequentemente, uma vez que o alum{\'\i}nio {\'e} bom condutor el{\'e}ctrico, correntes el{\'e}ctricas induzidas, originadas por haver um campo magn{\'e}tico vari{\'a}vel que {\'e} criado pelos semi-estatores. O comportamento deste tipo de motores, no que diz respeito a principais caracter{\'\i}sticas (como o bin{\'a}rio?velocidade para os diferentes n{\'u}meros de pares de p{\'o}los), circuito equivalente de Steinmetz, entre outras teorias associadas {\'e} j{\'a} conhecido h{\'a} bastante tempo. O princ{\'\i}pio de funcionamento do motor SAT {\'e} diferente do apresentado anteriormente, funciona com base na din{\^a}mica de v{\'o}rtices e devido ao facto de aparecer o fen{\'o}meno de ancoragem de fluxo (flux pinning) nos supercondutores de alta temperatura. Como o campo magn{\'e}tico varia, ent{\~a}o o disco roda. Este motor tem um princ{\'\i}pio de funcionamento muito mais complexo que o motor de indu{\c c}{\~a}o sendo a obten{\c c}{\~a}o do modelo do motor SAT complicada. A obten{\c c}{\~a}o do modelo do motor SAT n{\~a}o {\'e} abordado nesta disserta{\c c}{\~a}o. Os comportamentos e modos de opera{\c c}{\~a}o do motor com disco de alum{\'\i}nio e em materiais SAT s{\~a}o simulados atrav{\'e}s de um programa comercial de elementos finitos, nesta disserta{\c c}{\~a}o, sendo a supercondutividade simulada com base na rela{\c c}{\~a}o entre o campo el{\'e}ctrico e a densidade de corrente pela lei da potencia{\c c}{\~a}o (E-J power law). Com as simula{\c c}{\~o}es pretende-se comparar o rendimento electromec{\^a}nico de ambos os motores.

}, url = {http://oa.uninova.pt/1223/}, author = {Steve In{\'a}cio}, editor = {M{\'a}rio Neves and Jo{\~a}o Pina and Stanimir Valtchev} } @article {OA1764, title = {An electrical gearbox by means of pole variation for induction and superconducting disc motor}, journal = {Journal of Physics: Conference Series}, volume = {97}, year = {2008}, note = {n/a}, pages = {012221}, abstract = {

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{\textquoteright}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{\textquoteright}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{\textquoteright} 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.

}, url = {http://oa.uninova.pt/1764/}, author = {S In{\'a}cio and D In{\'a}cio and J M Pina and Stanimir Valtchev and M V Neves and A L Rodrigues} } @article {OA1816, title = {Power electronics performance in cryogenic environment: evaluation for use in HTS power devices}, journal = {Journal of Physics: Conference Series}, volume = {97}, year = {2008}, note = {n/a}, pages = {012219}, publisher = {iopscience}, 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{\textquoteright} 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.

}, url = {http://oa.uninova.pt/1816/}, author = {P Pereira and S Valtchev and J. Pina and A Gon{\c c}alves and M Ventim Neves and A L Rodrigues} } @article {OA1817, title = {A test rig for thrust force measurements of an all HTS linear synchronous motor}, journal = {Journal of Physics: Conference Series}, volume = {97}, year = {2008}, note = {n/a}, pages = {012220}, publisher = {IOPScience}, 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{\textquoteright}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.

}, url = {http://oa.uninova.pt/1817/}, author = {J. Pina and P Pereira and S Valtchev and A Gon{\c c}alves and M Ventim Neves and A Alvarez and L Rodrigues} } @conference {OA1045, title = {Numerical and Experimental Comparison of Electromechanical Properties and Efficiency of HTS and Ferromagnetic Hysteresis Motors}, booktitle = {8th European Conference on Applied Superconductivity (EUCAS)}, year = {2007}, note = {n/a}, month = {September}, abstract = {

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{\textquoteright}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{\textquoteright}s non-linear magnetic properties, while in HTS materials the hysteresis has an ohmic nature and is related with vortices{\textquoteright} 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{\textquoteright}s electromechanical performances but also the overall systems efficiency, including cryogenics for the HTS device.

}, url = {http://oa.uninova.pt/1045/}, author = {David In{\'a}cio and Jo{\~a}o Pina and Anabela Gon{\c c}alves and M{\'a}rio Neves and Amadeu Rodrigues} } @conference {OA1044, title = {Power Electronics Performance in Cryogenic Environment: Evaluation for Use in HTS Power Devices}, booktitle = {8th European Conference on Applied Superconductivity (EUCAS)}, year = {2007}, note = {n/a}, month = {September}, 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{\textquoteright} 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

}, url = {http://oa.uninova.pt/1044/}, author = {Pedro Pereira and S Valtchev and Jo{\~a}o Pina and Anabela Gon{\c c}alves and M{\'a}rio Neves and Amadeu Rodrigues} } @conference {OA881, title = {Case Study in the Design of HTS Machines: an All Superconducting Linear Synchronous Motor}, booktitle = {1st International Conference on Power Engineering, Energy and Electrical Drives, POWERENG}, year = {2007}, note = {n/a}, month = {April}, pages = {185{\textendash}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.

}, keywords = {High Temperature Superconductivity, Ironless Linear Motor, superconducting machines}, url = {http://oa.uninova.pt/881/}, author = {Jo{\~a}o Pina and M{\'a}rio Neves and Amadeu Rodrigues} } @conference {OA1792, title = {An Electrical Gearbox by means of pole variation for induction and superconducting disc motor}, booktitle = {8th European Conference on Applied Superconductivity (EUCAS)}, year = {2007}, note = {n/a}, abstract = {

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{\textquoteright}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{\textquoteright}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{\textquoteright} 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.

}, url = {http://oa.uninova.pt/1792/}, author = {S In{\'a}cio and D In{\'a}cio and J. Pina and S Valtchev and M Ventim Neves and A. Rodrigues} } @conference {OA1769, title = {Fuel Cells as Clean Electrical Energy Sources}, booktitle = {XCLEEE - X Portuguese-Spanish Conference in Electrical Engineering}, year = {2007}, note = {n/a}, abstract = {n/a}, url = {http://oa.uninova.pt/1769/}, author = {A. Rodrigues and M{\'a}rio Neves and Jo{\~a}o Pina} } @conference {OA1773, title = {High Performance, Environment Friendly, Modular and Fault Tolerant Renewable Energy Microgrid}, booktitle = {12th International Energy Conference \& Exhibition (ENERGEX2007)}, year = {2007}, note = {n/a}, abstract = {n/a}, url = {http://oa.uninova.pt/1773/}, author = {Jo{\~a}o Pina and C. Caracaleanu and A Gon{\c c}alves and Pedro Pereira and S Valtchev and M{\'a}rio Neves and A. Rodrigues} } @conference {OA790, title = {Magnetisation System and Thrust Force Measurement of an All Superconducting Linear Synchronous Motor}, booktitle = {X Portuguese-Spanish Congress in Electrical Engineering}, year = {2007}, note = {n/a}, abstract = {n/a}, url = {http://oa.uninova.pt/790/}, author = {Jo{\~a}o Pina and M{\'a}rio Neves and Alfredo {\'A}lvarez and Amadeu Rodrigues} } @conference {OA792, title = {Pilhas de Combust{\'\i}vel como Fonte Limpa de Energia El{\'e}ctrica}, booktitle = {X Portuguese-Spanish Congress in Electrical Engineering}, year = {2007}, note = {n/a}, abstract = {n/a}, url = {http://oa.uninova.pt/792/}, author = {Amadeu Rodrigues and M{\'a}rio Neves and Jo{\~a}o Pina} } @conference {OA789, title = {Study in the Design of HTS Machines: an All Superconducting Linear Synchronous Motor}, booktitle = {POWERENG 2007 - International Conference on Power Engineering, Energy and Electrical Drives}, year = {2007}, note = {n/a}, abstract = {n/a}, url = {http://oa.uninova.pt/789/}, author = {Jo{\~a}o Pina and M{\'a}rio Neves and Amadeu Rodrigues} } @conference {OA1813, title = {A test rig for thrust force measurements f an all HTS linear synchronous motor}, booktitle = {8th European Conference on Applied Superconductivity (EUCAS)}, year = {2007}, note = {n/a}, 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{\textquoteright}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.

}, url = {http://oa.uninova.pt/1813/}, author = {Jo{\~a}o Pina and Pedro Pereira and S Valtchev and A Gon{\c c}alves and M{\'a}rio Neves and A. Rodrigues} } @conference {OA791, title = {Topology of an Electrical Gearbox with Variable Poles for Induction and Superconducting Disc Motors}, booktitle = {X Portuguese-Spanish Congress in Electrical Engineering}, year = {2007}, note = {n/a}, abstract = {n/a}, url = {http://oa.uninova.pt/791/}, author = {In{\'a}cio Steve and Jo{\~a}o Pina and Stanimir Valtchev and M{\'a}rio Neves and Amadeu Rodrigues} } @article {OA352, title = {Design of a Linear Synchronous Motor With High Temperature Superconductor Materials in the Armature and in the Field Excitation System}, journal = {Journal of Physics: Conference Series}, volume = {43}, year = {2006}, note = {n/a}, pages = {804{\textendash}808}, publisher = {IOP}, abstract = {n/a}, url = {http://oa.uninova.pt/352/}, author = {Jo{\~a}o Pina and M{\'a}rio Neves and M. McCulloch and Amadeu Rodrigues} } @conference {OA354, title = {Design of a Linear Synchronous Motor With High Temperature Superconductor Materials in the Armature and in the Field Excitation System}, booktitle = {European Conference on Applied Superconductivity, EUCAS?05}, year = {2005}, note = {n/a}, month = {September}, abstract = {n/a}, url = {http://oa.uninova.pt/354/}, author = {Jo{\~a}o Pina and M{\'a}rio Neves and M. McCulloch and Amadeu Rodrigues} } @conference {OA378, title = {Multipole Superconducting Synchronous Generator}, booktitle = {6th European Conference on Applied Superconductivity (EUCAS)}, year = {2003}, note = {n/a}, month = {September}, abstract = {n/a}, url = {http://oa.uninova.pt/378/}, author = {M. Caserza Magro and M{\'a}rio Neves and Athanasis Sfetsos and Jo{\~a}o Pina and Anabela Gon{\c c}alves} } @article {OA359, title = {Flux Modelling of Reluctance Machines with Bulk Superconducting Materials}, journal = {Electromotion Review}, year = {2003}, note = {n/a}, abstract = {n/a}, url = {http://oa.uninova.pt/359/}, author = {Athanasis Sfetsos and Jo{\~a}o Pina and Anabela Gon{\c c}alves and M{\'a}rio Neves and Amadeu Rodrigues} } @article {OA1882, title = {A glass furnace operation system using fuzzy modelling and genetic algorithms for performance optimisation}, journal = {Engineering Applications of Artificial Intelligence}, volume = {16}, number = {7-8}, year = {2003}, note = {n/a}, pages = {681{\textendash}690}, abstract = {

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.

}, url = {http://oa.uninova.pt/1882/}, author = {J. Pina and PU Lima} } @article {OA360, title = {Torque Modelling of a Superconducting Reluctance Machine}, journal = {Electromotion Review}, year = {2003}, note = {n/a}, abstract = {n/a}, url = {http://oa.uninova.pt/360/}, author = {Amadeu Rodrigues and B. A. Potter and Jo{\~a}o Pina and Anabela Gon{\c c}alves and M{\'a}rio Neves} } @unpublished {OA511, title = {Opera{\c c}{\~a}o e Controlo de um Forno de Vidro}, year = {2002}, note = {n/a}, publisher = {IST - Instituto Superior T{\'e}cnico}, abstract = {n/a}, url = {http://oa.uninova.pt/511/}, author = {Jo{\~a}o Pina}, editor = {Pedro Lima} }