The output power variability of intermittent renewable sources can cause significant fluctuations in distribution system voltages. A local linear controller that exploits the capability of a photovoltaic inverter to provide both real and reactive power is described. This controller substitutes reactive power for real power when fluctuations in the output of the photovoltaic source are experienced. In this way, the inverter can help mitigate distribution system voltage fluctuations. In order to provide real and reactive to the grid, a three-phase grid-connected single-stage photovoltaic system with maximum power point tracking and power control is described. A method of reducing the current harmonic caused by resonance of the LC filter and transformer is presented. The local linear controller is examined using an example distribution system, and it is found that the controller is effective at mitigating voltage violations. The photovoltaic control system is examined using three-phase single-stage PV inverter system. The power control and damping system show good performance and stability under rapid change of irradiance.

In this dissertation, the generalized averaging method models for inverters, reactive power control methods for photovoltaic inverters, and a noise immunity improvement for hybrid position observers for brushless dc motor drives are studied. Models of inverters and other converters based on averaging have been widely used in numerous simulation applications. Generalized averaging can be applied to model both average and switching behavior of converters while retaining the faster run times associated with average-value models. Herein, generalized average models for single- and three-phase pulse width modulation inverters are proposed. The modulation signal for the proposed model could be either a sinusoidal waveform without high order harmonics or a sinusoidal waveform with third-harmonic injection. And this generalized average models also can apply for modeling three-phase pulse width modulation inverters with varying modulation signal frequency in the reference frame. These models are based on a quasi-Fourier series representation of the switching functions that includes fundamental and switching frequency components as well as sideband components of the switching frequency. The proposed models are demonstrated both in simulation and experimentally and are found to accurately portray both the fundamental and the switching behavior of the inverter. In particular, the use of sideband components allows accurate representation of the variation in switching ripple magnitude that occurs in the steady state. The generalized average models are found to have simulation run times that are significantly faster than those associated with detailed models. Therefore, the proposed generalized average models are suitable for simulation applications in which both accuracy (including the switching behavior) and fast run times are required (e.g., long simulation times, systems with multiple converters, and repeated simulations). Variations in the output power of intermittent renewable sources can cause significant fluctuations of distribution system voltage magnitudes. Reactive power control methods that employ the reactive power capability of photovoltaic three-phase inverters to mitigate these fluctuations are proposed. These control methods cause the three-phase inverters to substitute reactive output power for real output power when fluctuations in the solar power are experienced, allowing the fluctuations to be controlled. Performance metrics for assessing the ability of these controllers to perform this mitigation are defined. The controllers are examined using the IEEE 123-bus feeder distribution system, and it is found that the controllers can effectively mitigate voltage magnitude fluctuations and that the appropriate choice of controller depends on the performance metrics of interest. Finally, a noise immunity improvement for hybrid position observers for brushless dc motor drives is proposed. A finite state machine is used to detect Hall-effect sensor transitions to determine if these transitions are true transitions or the result of momentary glitches. This filter causes a delay in the detection of the Hall-effect sensors that is compensated in the proposed observer. The proposed observer is compared in simulations with the original hybrid position observer under both non-noisy and noisy conditions for both constant and variable speed operation, and it has good performance even under high noise and variable speed conditions.

Orientadores: Ernesto Ruppert Filho, Marcelo Gradella Villalva / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-24T10:01:12Z (GMT). No. of bitstreams: 1 Oliveira_LeonardoRuffeilde_M.pdf: 3470428 bytes, checksum: 7972e30772adc6b114e71c8f464265b8 (MD5) Previous issue date: 2013 / Resumo: O objetivo deste trabalho é a construção de um conversor eletrônico de potência monofá-sico completo para conexão à rede elétrica de distribuição de baixa tensão alimentado por painel fotovoltaico Painéis fotovoltaicos comerciais geram uma tensão contínua que varia entre 20 e 50V, dependendo do tipo de painel e da ocorrência ou não de conexão entre os mesmos; sendo necessário, portanto, a adequação dos níveis de tensão gerados pelo painel com o nível de tensão da rede elétrica de distribuição, na qual ele será conectado. O conversor eletrônico de potência utilizado neste trabalho é constituído de dois estágios sendo o primeiro CC ¿ CC e o segundo, um inversor, CC ¿ CA. Ele será controlado de duas maneiras: a primeira será responsável pelo con-trole da tensão de entrada do conversor CC - CC e pela injeção de potência no conversor CC - CA o qual, além de ser o responsável pela transformação da tensão contínua em alternada também é responsável pelo sincronismo do conversor CC - CA com a rede elétrica. São apresentados resultados de simulação do funcionamento do conversor para geração fotovoltaica de energia elétrica, sua malha de controle e o funcionamento do sistema elétrico completo. O projeto com-pleto dos conversores e dos circuitos auxiliares bem como os resultados experimentais obtidos em laboratório são apresentados / Abstract: The objective of this work is the construction of a complete single-phase power electronic converter for grid connection of low voltage distribution powered by photovoltaic panels. Photo-voltaic panels generates a DC voltage that varies between 20 and 50V, depending on the type of panel and presence or absence of connection between them, it is necessary, therefore, the ade-quacy of voltage levels generated by the panel with the voltage level of the electrical distribution network, in which it is connected. The power electronic converter used in this study consists of two stages with the first is a dc ¿ dc converter and the second is a dc-ac converter, frequency inverter. It will be controlled in two ways: the first is responsible for controlling the input voltage of the dc-dc converter and the power injection in the ac-dc converter which, besides being res-ponsible for the transformation into alternating voltage is also responsible by the synchronism of the converter dc-ac with the utility grid. Simulation results of the converter operation connected to the utility grid are presented, its network control and operation of the complete electrical sys-tem. The complete design of converters and auxiliary circuits and the experimental results obtai-ned in the laboratory are presented / Mestrado / Energia Eletrica / Mestre em Engenharia Elétrica

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L'émergence et le développement des systèmes électriques de ces vingt dernières années nous ont conduits à l'élaboration d'architectures de plus en plus complexes. Nous les retrouvons notamment au niveau d'applications embarquées ainsi qu'au cœur de réseaux de distribution isolés. L'intégration de nombreux équipements de différentes natures soulève la problématique de la stabilité. C'est dans ce contexte que s'insèrent ces travaux de thèse, qui aboutissent sur la mise en œuvre de méthodes d'analyse de la stabilité et de la qualité des réseaux distribués de puissance. Les études menées au cours de ces travaux reposent sur des expressions analytiques représentant le comportement fréquentiel de réseaux continus. Ces modèles sont ensuite associés au critère de Routh-Hurwitz, afin de permettre les études de stabilité selon les évolutions de leurs paramètres. L'analyse des résultats obtenus au niveau d'architectures présentant plusieurs équipements permet d'affiner nos connaissances sur le fonctionnement de ces systèmes. Les phénomènes de couplage, la disposition d'un réseau en fonction du nombre et de la puissance des charges, du point de vue de la stabilité, sont notamment développés. Les recherches de dimensionnements optimaux de plusieurs éléments indéterminés, combinant les notions de stabilité et de qualité et réalisées à l'aide d'algorithmes d'optimisation, sont également présentées. Enfin, les parties fondamentales de ces travaux, que constituent la modélisation ainsi que l'étude de la stabilité, sont validés par une approche expérimentale. / The emergence and the development of electrical systems during these last twenty years have led us to the elaboration of more and more complex architectures. They can be particularly found on embedded applications as well as in the heart of isolated distribution networks. The integration of several equipments with various natures raises the problem of stability. Thesis work presented here fits in with this context, leading to the implementation of stability and quality analysis methods, applied to distributed power networks. Studies led during this work are based on analytical expressions representing the continuous networks frequency behaviour. These models are then associated to the Routh-Hurwitz criterion in order to allow stability studies, according to their parameter values evolution. Analysis of results obtained on networks architectures using several equipments allows the refinement of our knowledge on these systems operation. Coupling phenomena, network layout according the loads number and power from a stability point of view, are particularly developed. Optimal sizing research for several undetermined elements, merging stability and quality criteria and carried out using optimization algorithms, is also presented. Finally, fundamental parts of this work which correspond to models building as well as stability studies are validated by an experimental approach.

Satellite power systems can be understood as islanded dc microgrids supplied by specialized and coordinated solar cell arrays augmented by electrochemical battery systems to handle high-power loads and periods of eclipse. The periodic availability of power, the limited capacity of batteries, and the dependence of all mission service on power consumption create a unique situation in which temporal power and energy scarcity exist. A multi-period model of an orbital satellite power system’s performance over a mission’s duration can be constructed. A modular power system architecture is used to characterize the system’s constraints. Using mathematical programming, an optimization problem can be posed such that the optimal power and energy ratings for the power system are determined for any load schedule imposed by a given mission’s requirements. The optimal energy trajectory of the electrical power system over a mission’s duration is also determined when the mathematical programming problem is solved. A generic set of mission requirements is identified to test this approach, but the objective function of the resulting optimization problem can be modified to return different results. These results can provide a clear illustration of the trade-offs that designers of such power systems consider in the design process.

This thesis presents a distributed power-management architecture for concentrating photovoltaic (CPV) systems. Specifically, the Δ-conversion scheme with voltage equalization is analyzed and verified for the CPV system from Morgan Solar, Inc. This architecture uses inverting buck-boost converters, denoted Δ-converters, which equalize the voltages of neighbouring CPV cells in a series-connected string of cells and improve the systems tolerance to parameter variations. The power benefits of Δ-conversion and the Δ-converter current distributions are investigated using statistical simulations. The effectiveness of Δ-conversion in the presence of randomly distributed mismatches is demonstrated, and current cascading is identified as the main design challenge. The Δ-converter is modelled and compensated using Middlebrook's Extra Element Theorem. Analysis of measured data from a six-cell CPV system demonstrate the benefits of Δ-conversion under realistic scenarios. Experimental results from prototype systems show up to 31% power benefits in the presence of mismatches.

In this thesis, we analyze allocation of two separate resources in wireless networks: transmit power and buffer space. Controlled allocation of power can provide good performance for both users and the network. Although centralized mechanisms are possible, distributed power control algorithms are preferable for efficient operation of the network. Viewing distributed power allocation as the collection of rational decisions of each user, we make game theoretic problem formulations, devise distributed algorithms and analyze them. First, equilibrium analysis of a vector power control game based on network energy efficiency in a multiple access point wireless network is presented. Then, a distributed mechanism is proposed that can smooth admission control type power control so that every user can stay in the system. Introducing a new externality into utility function, a game theoretic formulation that results in desired distributed actions is made. Next, the proposed externality is investigated in a control theoretic framework. Convergence of gradient based iterative power updates are investigated and stability of corresponding continuous time dynamical system is established. In the final part of the thesis, allocation of buffer space is addressed in a wireless downlink using a queueing theoretic framework. An efficient algorithm that finds optimal buffer partitioning is proposed and applications of the algorithm for different scenarios are illustrated. Implications of the results about cross layer design and multiuser diversity are discussed.

A new Markov chain based energy storage model to evaluate the power supply availability of microgrids with renewable energy generation for critical loads is proposed. Since critical loads require above-average availability to ensure reliable operation during extreme events, e.g., natural disasters, using renewable energy generation has been considered to diversify sources. However, the low availability and high variability of renewable energy sources bring a challenge in achieving the required availability for critical loads. Hence, adding energy storage systems to renewable energy generation becomes vital for ensuring the generation of enough power during natural disasters. Although adding energy storage systems would instantaneously increase power supply availability, there is another critical aspect that should be carefully considered; energy storage sizing to meet certain availability must be taken into account in order to avoid oversizing or undersizing capacity, which are two undesirable conditions leading to inadequate availability or increased system cost, respectively. This dissertation proposes to develop a power supply availability framework for renewable energy generation in a given location and to suggest the optimal size of energy storage for the required availability to power critical loads. In particular, a new Markov chain based energy storage model is presented in order to model energy states in energy storage system, which provides an understanding of the nature of charge and discharge rates for energy storage that affect the system's power output. Practical applications of the model are exemplified using electrical vehicles with photovoltaic roofs. Moreover, the minimal cut sets method is used to analyze the effects of microgrid architectures on availability characteristics of the microgrid power supply in the presence of renewable energy sources and energy storage. In addition, design considerations for energy storage power electronics interfaces and a comparison of various energy storage methods are also presented. / text

This thesis presents a distributed power-management architecture for concentrating photovoltaic (CPV) systems. Specifically, the Δ-conversion scheme with voltage equalization is analyzed and verified for the CPV system from Morgan Solar, Inc. This architecture uses inverting buck-boost converters, denoted Δ-converters, which equalize the voltages of neighbouring CPV cells in a series-connected string of cells and improve the systems tolerance to parameter variations. The power benefits of Δ-conversion and the Δ-converter current distributions are investigated using statistical simulations. The effectiveness of Δ-conversion in the presence of randomly distributed mismatches is demonstrated, and current cascading is identified as the main design challenge. The Δ-converter is modelled and compensated using Middlebrook's Extra Element Theorem. Analysis of measured data from a six-cell CPV system demonstrate the benefits of Δ-conversion under realistic scenarios. Experimental results from prototype systems show up to 31% power benefits in the presence of mismatches.