The forecasting of solar irradiance in photovoltaic power generation is an important tool for the integration of intermittent renewable energy sources (RES) in electrical utility grids. This study ...evaluates two machine learning (ML) algorithms for intraday solar irradiance forecasting: multigene genetic programming (MGGP) and the multilayer perceptron (MLP) artificial neural network (ANN). MGGP is an evolutionary algorithm white-box method and is a novel approach in the field. Persistence, MGGP and MLP were compared to forecast irradiance at six locations, within horizons from 15 to 120 min, in order to compare these methods based on a wide range of reliable results. The assessment of exogenous inputs indicates that the use of additional weather variables improves irradiance forecastability, resulting in improvements of 5.68% for mean absolute error (MAE) and 3.41% for root mean square error (RMSE). It was also verified that iterative predictions improve MGGP accuracy. The obtained results show that location, forecast horizon and error metric definition affect model accuracy dominance. Both Haurwitz and Ineichen clear sky models have been implemented, and the results denoted a low influence of these models in the prediction accuracy of multivariate ML forecasting. In a broad perspective, MGGP presented more accurate and robust results in single prediction cases, providing faster solutions, while ANN presented more accurate results for ensemble forecasting, although it presented higher complexity and requires additional computational effort.
The paper presents a comparative study of two solar string inverters based on the Quasi-Z-Source (QZS) network. The first solution comprises a full-SiC two-level QZS inverter, while the second design ...was built based on a three-level neutral-point-clamped QZS inverter with Silicon based Metal–Oxide–Semiconductor Field-Effect Transistors (Si MOSFETs). Several criteria were taken into consideration: the size of passive elements, thermal design and size of heatsinks, voltage stress across semiconductors, and efficiency investigation. The Photovoltaic (PV)-string rated at 1.8 kW power was selected as a case study system. The advantages and drawbacks of both solutions are presented along with conclusions.
This work proposes a design method for robust state feedback H∞ grid current controller applied to single‐phase grid‐connected photovoltaic (PV) systems. The proposed method achieved high system ...reliability even dealing with grid distorted voltages and other power quality issues. The robustness of the H∞ controller was verified in the face of parametric uncertainties at the first‐order output filter, and also a satisfactory disturbance rejection performance was achieved. The proposed design is based on linear matrix inequalities associated with constraints involving H∞ optimisation and a pole placement analysis on the continuous‐time domain. A discrete‐time analysis is also presented in order to indicate the simplicity of its implementation by a microcontroller or similar devices. Based on the presented results and in order to validate the proposed controller, its robust performance was compared with two linear and well‐known control methods: a classical PI controller, in terms of robustness; and a robust H∞ resonant controller, regarding the power quality at the connection point with the grid‐utility. Although the conclusions were listed regarding a low voltage PV grid‐interactive multilevel power converter, the proposed H∞ control design (and its concepts) can be applied to a great variety of renewable energy resources systems.
This paper describes the tuning process of the proportional-resonant controller, taking into account the significant computational delay from the digital control system. Different structures of the ...controller and related contradicting results are discussed. Particular attention is paid to the stability domain and its dependence on different parameters of the proportional-resonant controller. The main outcome of this paper consists in the tuning approach guidelines for selection of controller parameters in case of significant digital system delay. An optimal controller structure and start-up current optimization are proposed. All results are confirmed by simulation and experimental setup.
This work proposes a design method for robust state feedback $H_{\infty }$H∞ grid current controller applied to single-phase grid-connected photovoltaic (PV) systems. The proposed method achieved ...high system reliability even dealing with grid distorted voltages and other power quality issues. The robustness of the $H_{\infty }$H∞ controller was verified in the face of parametric uncertainties at the first-order output filter, and also a satisfactory disturbance rejection performance was achieved. The proposed design is based on linear matrix inequalities associated with constraints involving $H_{\infty }$H∞ optimisation and a pole placement analysis on the continuous-time domain. A discrete-time analysis is also presented in order to indicate the simplicity of its implementation by a microcontroller or similar devices. Based on the presented results and in order to validate the proposed controller, its robust performance was compared with two linear and well-known control methods: a classical PI controller, in terms of robustness; and a robust $H_{\infty }$H∞ resonant controller, regarding the power quality at the connection point with the grid-utility. Although the conclusions were listed regarding a low voltage PV grid-interactive multilevel power converter, the proposed $H_{\infty }$H∞ control design (and its concepts) can be applied to a great variety of renewable energy resources systems.
Orientador: José Antenor Pomilio
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação
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Previous issue date: 2011
Resumo: Este trabalho aborda as características que envolvem o gerenciamento da operação de um sistema monofásico de geração distribuída. Embora tais características possam ser expandidas para sistemas trifásicos e de potência elevada, o sistema proposto está relacionado com aplicações de geração distribuída em baixa tensão ou naquelas que envolvam consumidores residenciais. O funcionamento do sistema proposto é baseado em um conversor eletrônico de potência elaborado a partir da estrutura multinível na topologia cascata assimétrica de 19 níveis. Nesta topologia, as tensões dos barramentos CC devem ser isoladas e desiguais entre si. Tal condição permite o envolvimento, nos barramentos CC do inversor, de múltiplas ou diferentes fontes alternativas de energia elétrica tais como sistemas fotovoltaicos, sistemas de células a combustível ou sistemas eólicos associados com conversores CC/CC. Com o sistema em operação, busca-se uma injeção apenas de potência ativa no sistema de distribuição alimentador e um fornecimento ininterrupto de energia elétrica para uma carga local mesmo quando nesta predominar características não-lineares de alimentação. Assim, de acordo com os seus objetivos, o sistema proposto opera de forma contínua e intercalada entre os modos ilhado e compartilhado. Detalhes sobre tais modos de operação e suas respectivas transições são apresentadas. As transições envolvem a detecção de ilhamento e o êxito no sincronismo. Em função disso, é apresentado um método ativo de detecção de condições de ilhamento. Tal método representa a adaptação de um método ativo já existente (AFDPF) aos requisitos de operação do sistema proposto neste trabalho. Justificativas e detalhes dessa adaptação do método ativo AFDPF são apresentados. Com relação à outra transição, um método de sincronismo baseado em técnicas PLL é apresentado. Tal método de sincronismo atende os requisitos estabelecidos em IEEE Std 1547-2003, diminuindo os impactos de uma possível religação com o sistema de distribuição. Para permitir um melhor funcionamento sob diferentes requisitos, também são descritas as etapas que envolvem os métodos de projeto dos controladores adotados: controlador PI de corrente de saída; controlador PI de potência média injetada; e controlador P+Ress de tensão na carga. Em especial, é apresentada uma nova metodologia de projeto do controlador proporcional e ressonante (P+Ress) de tensão baseada na sua resposta em malha fechada observada no domínio do tempo, em contrapartida ao seu método clássico de projeto baseado no domínio da freqüência. Um modelo matemático para simulações computacionais e um protótipo experimental utilizando o DSP TMS320F2812 foram considerados. Resultados de simulações computacionais e experimentais são comparados e permitem a verificação do comportamento do sistema proposto sob condições normais e anormais de operação
Abstract: This work regards the issues related to the operation management of a single-phase distributed generation system. Although these issues can be applied three-phase systems and high power systems, the proposed system is related to low voltage distributed generation applications or related to residential consumers. The operation of the single-phase proposed system is based on an utility-interactive power electronics converter which is composed by an asymmetrical cascaded multilevel inverter. This topology is able to create an output signal with up to 19 levels and it is supplied by DC voltage power sources that must be isolated and unequal from each other. By this demand it is possible to combine multiple and/or different alternative DC voltage power supplies as photovoltaic, fuel cells or wind energy systems into the DC buses of the single-phase multilevel inverter. During the operation of the proposed system, an injection of only active power into the grid utility and an uninterrupted load supply are achieved even when the local load (or group of local loads) has predominant nonlinear characteristics. For those reasons the proposed system operates continuously and alternately between two operation modes: grid-connected mode and stand-alone mode. Details about them and its transitions are also presented. The transitions are related to a correct detection of islanding situations and also to an effective synchronization method. The islanding detection is achieved by adaptations on an already known active method (AFDPF) to accomplish the project's goals. The reasons and details about these adaptations are presented. Furthermore the synchronization method is described and it is based on PLL techniques. Both transition methods meet the IEEE Std 1547-2003 requirements and it decreases the impacts from the proposed system into grid utility. To guarantee a suitable operating under several conditions, a wide range of operation points can be found by using the design methods described to each proposed controller: PI output current controller; PI injected active power controller; and a P+Ress load voltage controller. In highlights it is proposed a new design method to proportional and resonant controller (P+Ress) based on its closed-loop time response, instead of the classical method based on its open-loop frequency response. A mathematical model for simulations and an experimental low power prototype based on DSP TMS320F2812 have been considered. Simulation and experimental results are compared and they allow examining the performance of the proposed system operating under normal and abnormal conditions
Doutorado
Energia Eletrica
Doutor em Engenharia Elétrica
Orientador: Jose Antenor Pomilio
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e Computação
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Previous issue date: 2006
Resumo: Este trabalho aborda a implementação de um filtro ativo de potência utilizando um inversor multinível com topologia em cascata assimétrica. Justificativas para utilização de estruturas multiníveis são discutidas. O sistema de controle utilizado garante um fornecimento nulo de potência ativa pelo filtro ativo e que a corrente fornecida pela fonte de alimentação tenha a mesma forma de onda da tensão de alimentação. Com isso, o fator de potência visto pela fonte é próximo de seu valor unitário e a fonte fornece apenas potência ativa à carga. Resultados de simulações e experimentais validam o esquema adotado. Também é descreva uma proposta para se realizar o controle das tensões CC da topologia em cascata assimétrica. Palavras-chave: Eletrônica de Potência, Inversor Multinível, Qualidade da Energia Elétrica, Filtro Ativo de Potência, Controle Digital
Abstract: This work regards a shunt active power filter implementation using an asymmetrical cascaded multilevel convel1er. Reasons for using multilevel structures are discussed. The system control guarantees that the active power filter does not supply active power and the source current has the same waveform of the source voltage. Consequently, the power factor from the source side is almost one and the source only supplies active power to the load. Simulation and experimental results validate the applied scheme. A proposal for controlling the DC voltages from the asymmetrical cascaded topology is also described.
Mestrado
Energia Eletrica
Mestre em Engenharia Elétrica
Este artigo apresenta uma aplicação de compensação série para mitigação de efeito “flicker”. A compensação se baseia na síntese de indutância negativa, ao invés da aplicação de capacitores. A ...vantagem deste método é que se impede o surgimento de ressonâncias em situações transitórias que podem surgir devido à interação dinâmica da linha com o elemento de compensação. A indutância negativa é sintetizada utilizando a técnica de Síntese Direta de Reatâncias, enquanto sua realização é feita por meio da topologia de conversores multiníveis em cascata assimétrica. Mostra-se que é possível eliminar as variações de tensão no ponto de acoplamento comum causadas por variações na corrente da carga e comprova-se a não ocorrência de ressonâncias nos transitórios. Um arranjo experimental de baixa potência foi implementado para validar o funcionamento do sistema, com o controle realizado por meio de um Processador Digital de Sinais.
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