Philipe C. Pereira's Bibliography

The paper presents a methodology of analysis for radial power systems using quadripoles for the components representation. Three-phase elements can be represented this way if they can be considered symmetric and symmetrical components transformations are used in order to work with modal quantities instead of the phase ones. The application of the method is presented using several examples derived from real power systems, allowing interesting studies as voltage stability, reactive compensation, P-Q and P-V curves drawing, voltage variation and reactive power flow, among others. It is shown that the proposed tool demands substantially less computational effort, being, thus, very attractive to evaluate disturbances.

The pulses of the PWM waveform synthesized by inverters present ultra-fast variations, whose harmonic components extend up to the MHz range. Their application on the cable that connects the converter to the motor results in a number of undesirable phenomena, which go from problems of electromagnetic interference to physical damage of the motor. The aim of the present study is to discuss and clarify such problems, illustrating them through several measurements performed in both laboratory and the field, obtained over the years of work performed by this research group. Innovative and promising solutions for their attenuation are also presented.

This work presents a thorough survey on the Potential Induced Degradation (PID) of solar panels, describing its actuation mechanisms, influencing factors, resulting damages and impact of the electric system characteristics (grounding type, presence of inverters, cell association, etc) on its severity, among other issues. Along the development of this work, the authors formulated the hypothesis that the common voltage produced by the PWM switching of the inverter bridge could propagate over the photovoltaic installation and be combined with the voltage between the module terminals (poles) and the ground, eventually resulting in substantial voltage shifts. Since the TCO corrosion and the polarization phenomenon are strongly dependent on the poles potential in relation to the (grounded) module frame, the inverter could then worsen the PID. In this context, in order to investigate such suspicion, a computational case study was performed, where a complete photovoltaic system was implemented in Matlab/Simulink, with seven different configurations. For each of them, the common mode voltage and currents, which are produced by the inverter and propagate over the installation, had their profile determined at the connection point of the panels and analyzed under the PID phenomenon context.

Studies involving high frequency quantities require appropriate system modeling for accurate simulated results. Electromagnetic transients and electromagnetic compatibility are traditional fields where high frequency phenomena are present, thus demanding special models. Since power electronic devices represent a permanent source of electric disturbances, such as fast voltage transitions, many problems arise from their operation. In a photovoltaic system, which is the focus of the present paper, important phenomena of this nature take place, such as displacement currents flowing through different paths within the system, stepped voltage manifestation in equipment neutral point and high frequency earth return currents, among others. For their accurate reproduction, the whole photovoltaic installation must be appropriately represented in the simulations, allowing the problem investigation and the development of solutions. In this context, this work is dedicated to the power transformer high frequency modeling, firstly presenting an extensive survey on the topic and, latter, proposing a simple but effective model. Special attention was given to the model parameters determination, being a measuring methodology employed for this aim and an application example presented, for a real case.

The ultra fast variations present in the voltage output of PWM inverters are responsible for several problems in the scope of electromagnetic compatibility. In the case of photovoltaic systems, which is the subject of this work, the major concern relies on the common mode voltage produced by the inverter, whose fast dv/dt's excite all the distributed capacitances of the system devices to the ground, generating unwanted high-frequency currents flowing through different paths. Among other problems, these currents generate conducted electromagnetic interference. The loops for their circulation include the capacitive coupling between (i) the solar cells and the corresponding module frame, (ii) the cable phase conductors and the trays or metallic tubes where they are installed, (iii) internal parts of the transformer and filters and their frame and (iv) the inverter internal devices and the grounded heatsink. In this work, the focus is on the appropriate modeling of the inverter for electromagnetic compatibility studies. A special effort was employed on the development of a measuring methodology of the models parameters, suitable for application in the field.

The stepped common mode voltage generated in the normal operation of a PWM inverter, applied over the distributed capacitive couplings between the electric system devices and the ground, produces high-frequency transient currents that flow through the system earth return path, leading to electromagnetic compatibility problems. In this context, this paper addresses specifically the inverter switching, focusing the generated common-mode voltage and the resulting undesired common mode currents that flow within a photovoltaic installation. Several different PWM techniques are analyzed and compared regarding the corresponding common mode voltage pattern and the correlated ground current. The studied modulation strategies are fully described and latter implemented in the Matlab/Simulink software, being the inverter placed within a detailed representation of the whole photovoltaic system, appropriately modeled for high-frequency studies. The advantages and limitations of the analyzed switching techniques are then pointed out and ranked, with special attention to the common mode quantities generation.

Photovoltaic power systems have been widely spread in the last years, especially for their versatility, the price reductions provided by production scale, the advances in the solar panels conversion efficiency and the incentives for use of renewable sources of energy. However, the power conversion stage necessary to inject the generated power into the grid involves the use of electronic devices whose switching process may generate distorted voltage and current waveforms that interact with other system components, frequently producing unexpected and undesirable effects, related with electromagnetic interferences and power quality issues. This paper proposes to investigate the different particularities of the system which propitiate the occurrence of these phenomena and how to mitigate their effects, focusing 15 kW-150 kW grid-connected PV systems usually installed in commercial buildings and schools, greater than typical residential installations and less than multi MW solar farms.

Driving induction motors with PWM inverters through long distances result in several undesired high frequency phenomena, such as transient overvoltages at the motor terminals, common-mode currents flowing through the system and the presence of a cable charging current, among others. Instead of filters, which represent the traditional method for the mitigation of these problems, in a previous work the authors proposed an alternative solution, where the rectifier and inverter bridges are separated and connected by the long cable, being the latter located right besides the motor. This alternative configuration, based on DC transmission, aside from solving the aforementioned problems, provides the additional benefits of reducing the voltage drop in the cable and providing copper economy for the power transmission. In this context, in the present work a prototype of a long cable motor drive system was built in both configurations (conventional and with DC transmission). Several results involving the transient overvoltages, cable charging and common-mode currents were obtained from each system and compared, in order to demonstrate the effectiveness of the proposed drive system topology in reducing these undesirable phenomena.

This article discusses the actual failure rate of electronic components when these are exposed to harsh environments, which can include vibration, dust, humidity, high temperature and others. It presents a compilation on the physico-chemical effects that can take place when electronic components are stressed and how such effects can reduce the component life. It is also presented a compilation of the results of a thorough and comprehensive research on different standards for reliability prediction, along with a critical and comparative analysis between the methodologies and applications related to each one of them. Furthermore, to provide the reader a broader understanding of the methodology used in these standards, an example employing a typical SV-PWM converter used in motor drive systems, submitted to different environmental stresses, is used as a case study.

Photovoltaic power systems have been widely spread in the last years, especially for their versatility, the price reductions provided by production scale, the advances in the solar panels conversion efficiency and the incentives for use of renewable sources of energy. However, the power conversion stage necessary to inject the generated power into the grid involves the use of electronic devices whose switching process may generate distorted voltage and current waveforms that interact with other system components, frequently producing unexpected and undesirable effects, related with electromagnetic interferences and power quality issues. This paper proposes to investigate the different particularities of the system which propitiate the occurrence of these phenomena and how to mitigate their effects, focusing 15 kW-150 kW grid-connected PV systems usually installed in commercial buildings and schools, greater than typical residential installations and less than multi MW solar farms.

Driving induction motors with PWM inverters through long distances result in several undesired high frequency phenomena, such as transient overvoltages at the motor terminals, common-mode currents flowing through the system and the presence of a cable charging current, among others. Instead of filters, which represent the traditional method for the mitigation of these problems, in a previous work the authors proposed an alternative solution, where the rectifier and inverter bridges are separated and connected by the long cable, being the latter located right besides the motor. This alternative configuration, based on DC transmission, aside from solving the aforementioned problems, provides the additional benefits of reducing the voltage drop in the cable and providing copper economy for the power transmission. In this context, in the present work a prototype of a long cable motor drive system was built in both configurations (conventional and with DC transmission). Several results involving the transient overvoltages, cable charging and common-mode currents were obtained from each system and compared, in order to demonstrate the effectiveness of the proposed drive system topology in reducing these undesirable phenomena.

Dans le cadre du traitement du contact en grands glissements, des techniques d'intégration adaptatives doivent être mises en oeuvre, indispensables pour pouvoir traiter correctement le contact entre deux corps déformables. Une formulation de contact dite continue a été implantée dans Code_Aster, code de thermo-mécanique développé à la R&D d'EDF et diffusé en libre, suite à une collaboration avec le Professeur H. Ben Dhia de l’École Centrale de Paris. Lorsque les points en vis-à-vis du contact se décalent les uns par rapport aux autres, des éléments finis dits tardifs sont créés à la volée et permettent de prendre en compte l'évolution du contact. Ces éléments finis composés des mailles des surfaces de contact en vis-à-vis changent au fur et à mesure de l'évolution du contact et sont recréés à chaque évolution des géométries des surfaces de contact. L'intégration des équations d'équilibre, de contact et de frottement pour ces éléments est délicate. On propose de faire évoluer les schémas d'intégration actuels à terme de façon à créer des sous-éléments pour l'intégration numérique issus de la projection des surfaces de contact l'une sur l'autre. Dans un premier temps on propose d'utiliser une intégration différenciée pour l'équation d'équilibre et les équation de contact et de frottement. Une maquette de travail en 2D a été réalisée, avec les validations associées de façon à montrer les améliorations apportées par cette méthode en terme de précision et de stabilité.

Sistemas de geração fotovoltaica têm se difundido nos últimos anos, especialmente devido à sua versatilidade, às reduções de custos promovidas pela produção em escala, aos avanços tecnológicos que têm promovido um aumento na eficiência de conversão das células e aos incentivos para o uso de fontes renováveis. Entretanto, o estágio de conversão de energia necessário para injetar a energia gerada envolve o uso de dispositivos eletrônicos cujo processo de chaveamento pode gerar formas de tensão e correntes com conteúdo espectral de alta frequência, que interagem com outros componentes do sistema, eventualmente produzindo efeitos indesejáveis, relacionados com interferência eletromagnética conduzida, destacando-se a circulação de correntes de modo-comum. Esse trabalho propõe investigar as diferentes particularidades do sistema que propiciam a ocorrência desses fenômenos e como mitigar seus efeitos, focando sistemas de geração conectados à rede, que podem ser instalados sobre prédios comerciais, escolas e residências.

Photovoltaic power systems have been widely spread in the last years, especially for their versatility, the price reductions provided by production scale, the advances in the solar panels conversion efficiency and the incentives for use of renewable sources of energy. However, the power conversion stage necessary to inject the generated power into the grid involves the use of electronic devices whose switching process may generate voltage and current waveforms with a high frequency spectral content that interacts with other system components, frequently producing unexpected and undesirable effects, related with electromagnetic interferences, mainly the common-mode current flow. This work proposes to investigate the different particularities of the system which propitiate the occurrence of these phenomena and how to mitigate their effects, focusing grid-connected PV systems usually installed in commercial buildings, schools and residential installations.

A proposta desse trabalho é fazer uma análise da conversão magnetohidrodinânica. Num primeiro momento, apresentaremos os princípios básicos que regem esse fenômeno, que nada mais é que a indução de uma corrente elétrica num fluido condutor em movimento quando este atravessa um campo magnético perpendicular a sua velocidade de deslocamento. Reescreveremos a lei de Ohm para um fluido condutor, demonstraremos a relação de Saha, que quantifica a ionização térmica de gás a fim de avaliarmos sua condutividade, e mostraremos as diferentes configurações de um gerador MHD (Faraday e Hall). Enfim, faremos uma análise de dois tipos de gerador MHD a indução, um primeiro que utiliza um campo viajante e outro utilizando um campo alternante.

The proposal of this work is to make an analysis of magnetohydrodynamics conversion. At first, we will introduce the basic principles governing this phenomenon, which consists in inducing an electrical current in a conducting fluid in motion when it passes through a magnetic field perpendicular to its velocity. We rewrite the Ohm's law for a moving conducting fluid, we demonstrate the Saha equation, that quantifies the thermal ionization of gas, and we show the different configurations of a MHD generator (Faraday and Hall). We'll make an analysis of two kinds of induction MHD generator: the first one uses a traveling field and another one uses an alternating field.

Para o estudo de fenômenos de alta freqüência através de simulações computacionais, a representação dos equipamentos elétricos deve ser feita através de modelos específicos. No tocante a cabos elétricos, a modelagem deve, necessariamente, incluir a variação de sua resistência e indutância em função dos efeitos pelicular e proximidade. Dentre as várias alternativas possíveis, o modelo denominado “N-Ramos” vem sendo empregado com bastante êxito, para este propósito. Contudo, apesar de sua larga utilização, seu desempenho ainda não foi avaliado para uma grande gama de situações possíveis, como, por exemplo, para diferentes formas de instalação do cabo, bitolas e arranjo geométricos, dentre outras. Nesse contexto, o objetivo do presente trabalho é o de caracterizar os erros que poderão ser obtidos ao se utilizar o modelo “N-Ramos” para a representação de diferentes tipos de cabo, de forma a orientar o usuário sobre qual desempenho pode ser esperado em cada aplicação.

Os estudos de aterramento de instalações elétricas geralmente levam em conta somente aspectos de proteção contra faltas; contudo, em sistemas que utilizam conversores eletrônicos de potência, as análises devem contemplar também a circulação de correntes de alta frequência pelo terra induzidas pelas rápidas variações de tensão resultantes do processo de chaveamento dos dispositivos eletrônicos. Neste contexto, o presente artigo expõe as principais questões que são pertinentes quando da decisão sobre quais pontos devem ser aterrados num sistema de geração fotovoltaica, com enfoque na avaliação dessas correntes de terra. Além da análise do aterramento de proteção, diferentes configurações para o aterramento funcional da instalação serão comparadas, orientando o projetista sobre como se evitar ou reduzir a circulação indesejada de tais correntes, sem comprometer o funcionamento da instalação.