SISTEMA FOTOVOLTAICO DE PEQUENO PORTE INTERLIGADO À REDE ELÉTRICA by Eldin Mario Miranda Terán Dissertação submetida à Universidade Federal do Ceará como parte dos requisitos para obtenção do grau de Mestre em Engenharia Elétrica. Orientador: Prof. Dr. René Pastor Torrico Bascopé

INTRODUÇÃO GERAL 

Em meados do século XVIII a Grã Bretanha presenciou o inicio da Revolução Industrial: um conjunto de avanços tecnológicos que mudaram todo o sistema produtivo conhecido até então. O motor a vapor e depois o motor a combustão foram os principais atores nesta revolução. Esta revolução espalhou-se rapidamente pela Europa, pelos Estados Unidos e pelo mundo todo no século XIX. Paralelamente, grandes avanços na área da eletricidade foram realizados e a máquina elétrica foi desenvolvida. Já no século XX muitos países atingiram altos níveis de industrialização enquanto a energia elétrica mudou o estilo de vida da humanidade toda. A energia primária que foi usada para impulsionar esta revolução e que ainda continua alimentando o sistema produtivo do planeta é baseada em combustíveis fósseis e carvão. No ano de 2009 aproximadamente 88% do consumo energético mundial teve origem nestas fontes (petróleo, carvão e gás natural) [1]. É sabido que esta dependência global dos combustíveis fósseis tem provocado sérios problemas no clima do planeta e que no futuro o custo da sua produção vai aumentar mais e mais, a medida que seja mais complexo realizar a exploração destes recursos, ocasionando problemas econômicos e sociais. Diante deste panorama, as fontes de energia renovável, como a solar, hidráulica e eólica entre outras, perfilam-se a ser a solução à demanda energética no futuro, sendo uma resposta tecnicamente viável e amigável com o meio ambiente, porém cara, quando comparada com as tecnologias convencionais na atualidade, precisando de subsídios e apoio dos governos para serem implementadas1 [2]. Em países altamente desenvolvidos como Espanha, Alemanha, Itália, Japão e outros, há diversos incentivos tributários a produção de energia renovável, entretanto, na América do Sul ainda não se conta com legislações que incentivem a produção de energia renovável em grande escala. A eletrônica de potência desempenha um papel importante na atividade de processamento da energia renovável, particularmente das energias fotovoltaica e eólica. No caso da energia fotovoltaica tem-se uma fonte de corrente contínua que deve ser transformada em corrente alternada para ser interligada aos sistemas elétricos e às cargas elétricas convencionais. Este processamento de energia é realizado mediante o uso da eletrônica de potência, através de conversores estáticos. Assim, neste trabalho foi desenvolvido um sistema de energia fotovoltaica de pequeno porte interligado à rede elétrica, formado por dois estágios de processamento de energia:  O primeiro estágio é um conversor cc-cc elevador (Boost) responsável por aumentar a tensão entregue pelos painéis fotovoltaicos a uma tensão adequada para ser transformada em corrente alternada e, por extrair a máxima potência elétrica disponível nos painéis fotovoltaicos.  O segundo estágio é um conversor cc-ca Full-Bridge (ponte completa) responsável por transformar a corrente continua entregue pelo primeiro estágio em corrente alternada num nível de tensão, frequência e fase úteis à rede elétrica de baixa tensão. No capítulo 1 do trabalho tem-se uma revisão bibliográfica geral focada na área da eletrônica de potência, ou seja, nas topologias de conversores aplicáveis em sistemas fotovoltaicos interligados à rede elétrica. Além disso, apresenta-se informação sobre energia solar fotovoltaica com foco nas técnicas de rastreamento de máxima potência, os objetivos do trabalho e a proposta do estudo. Nos capítulos 2 e 3 são apresentados o primeiro estágio (cc-cc) e segundo estágio (cc-ca) de processamento de energia, respectivamente. As topologias escolhidas são analisadas qualitativa e quantitativamente e os projetos dos conversores são realizados; também é detalhada a técnica de rastreamento de máxima potência (MPPT) usada no primeiro estágio e a metodologia de controle aplicada no segundo estágio. Finalmente, no capitulo 4 são apresentados resultados de simulação complementados com resultados experimentais para validar os estudos teóricos feitos nos capítulos anteriores. 

  LINK: http://www.repositorio.ufc.br/bitstream/riufc/3869/1/2012_dis_emmteran.pdf
 

Design of Delta Primary - Transposed zigzag Secondary (DTz) Transformer to Minimize Harmonic Currents on the Three-phase Electric Power Distribution System Chairul Gagarin Irianto, Rudy Setiabudy, and Chairul Hudaya Department of Electrical Engineering, Universitas Trisakti, Jakarta, Indonesia

 

Design of Delta Primary - Transposed zigzag Secondary (DTz) Transformer to Minimize Harmonic Currents on the Three-phase Electric Power Distribution System Chairul Gagarin Irianto, Rudy Setiabudy, and Chairul Hudaya

Department of Electrical Engineering, Universitas Trisakti, Jakarta, Indonesia

Abstract: The delta primary - transposed zigzag secondary (DTz) transformer has been designed and used to reduce the bad impacts of the harmonic in the distribution power system. The DTz transformer is constructed with delta connection in primary winding and the three transposed windings at the different core legs of secondary winding. The harmonic reduction method of the DTz transformer applies two basic principles. The first principle is to inhibit electromagnetic energy of the harmonic currents by cancelling the phase polarity on the secondary winding. The second is to insulate the remaining of the mmf induction from harmonic current loads and minimize to circulate in the delta windings on the primary side. The triplen harmonics currents generated on the primary and secondary winding of DTz transformer are simulated in this paper. Both balanced and unbalanced loads of the three-phase distribution system are examined. The experiment shows that the total THD current in the secondary winding when balanced loads are applied is about 70.8 %, and in the primary side is 24.3 %. While for unbalanced loads, the average THD in secondary winding is 68.44 % and in delta winding is 26.4 %. It means the DTz transformer has a filter-ability to reduce about 42 - 46 % THD for both balanced and unbalanced loads. By comparing the computer simulation results and data measurements through experiment in the laboratory, it is proved that the use of the proposed DTz transformer is one of the methods to reduce harmonic currents and inhibit them to enter to the supply system.

Keywords: triplen harmonic currents, balanced and unbalanced loads, delta primary - transposed zigzag secondary winding (DTz) transformer, non-linear loads

LINK:https://www.researchgate.net/profile/Chairul_Hudaya/publication/267838702_Design_of_Delta_Primary_-Transposed_zigzag_Secondary_DTz_Transformer_to_Minimize_Harmonic_Currents_on_the_Three-phase_Electric_Power_Distribution_System/links/546d39d30cf26e95bc3caf85/Design-of-Delta-Primary-Transposed-zigzag-Secondary-DTz-Transformer-to-Minimize-Harmonic-Currents-on-the-Three-phase-Electric-Power-Distribution-System.pdf

Mitigation of DC Current Injection in Transformerless Grid-Connected Inverters By Weichi Zhang - School of Engineering Newcastle University United Kingdom

 Mitigation of DC Current Injection in Transformerless Grid-Connected Inverters Weichi Zhang B.Sc., M.Sc. A thesis submitted for the degree of Doctor of Philosophy April 2019 School of Engineering Newcastle University United Kingdom

Abstract With a large number of small-scale PV plants being connected to the utility grid, there is increasing interest in the use of transformerless systems for grid-connected inverter photovoltaic applications. Compared to transformer-coupled solutions, transformerless systems offer a typical efficiency increase of 1-2%, reduced system size and weight, and reductions in cost. However, the removal of the transformer has technical implications. In addition to the loss of galvanic isolation, DC current injection into the grid is a potential risk. Whilst desirable, the complete mitigation of DC current injection via conventional current control methods is known to be particularly challenging, and there are remaining implementation issues in previous studies. For this reason, this thesis aims to minimize DC current injection in grid-connected transformerless PV inverter systems. The first part of the thesis reviews the technical challenges and implementation issues in published DC measurement techniques and suppression methods. Given mathematical models, the performance of conventional current controllers in terms of DC and harmonics mitigation is analyzed and further confirmed in simulations and experiments under different operating conditions. As a result, the second part of the thesis introduces two DC suppression methods, a DC voltage mitigation approach and a DC link current sensing technique. The former method uses a combination of a passive attenuation circuit and a software filter stage to extract the DC voltage component, which allows for further digital control and DC component mitigation at the inverter output. It is proven to be a simple and highly effective solution, applicable for any grid-connected PV inverter systems. The DC link sensing study then investigates a control-based solution in which the dc injection is firstly accurately determined via extraction of the line frequency component from the DC link current and then mitigated with a closed loop. With an output current reconstruction process, this technique provides robust current control and effective DC suppression based on DC link current measurement, eliminating the need for the conventional output current sensor. Results from rated simulation models and a laboratory grid-connected inverter system are presented to demonstrate the accurate and robust performance of the proposed techniques. This thesis makes a positive contribution in the area of power quality control in grid-connected inverters, specifically mitigating the impact of DC injection into the grid which has influences on the network operating conditions and the design and manufacture of the PV power converter itself.

LINK: https://theses.ncl.ac.uk/jspui/bitstream/10443/4594/1/Zhang%20W%202019%20%28added%20to%20dspace%20on%20receipt%29.pdf

Analysis, Design, and Control of a Single-Phase Single-Stage Grid-Connected Transformerless Solar Inverter by Manisha Verma - Department of Electrical and Computer Engineering -Concordia University Montreal, Quebec, Canada.

 Analysis, Design, and Control of a Single-Phase Single-Stage Grid-Connected Transformerless Solar Inverter Manisha Verma A Thesis In the Department of Electrical and Computer Engineering Presented in Partial Fulfillment of the Requirements For the Degree of Master of Applied Science at Concordia University Montreal, Quebec, Canada. June 2019

ABSTRACT

 Analysis, Design, and Control of a Single-Phase Single-Stage Grid-Connected Transformerless Solar Inverter Manisha Verma As energy utilization is increasing with the rise in the world’s power demand, the traditional energy sources are depleting at a high pace. It has led to attention drawn towards inexhaustible energy resources. There is a huge augmentation in the power generation from renewable energy sources (RES) like wind, solar, hydropower, biomass, etc. to reduce the stress on conventional energy sources like fossil fuels, oil, gas, etc. There has been a steep increase in interest for wind and solar energy systems. PV energy has been growing swiftly in the past two decades which made it most demanded power generation system based on RES. This worldwide requirement for solar energy has led to an immense amount of innovation and development in the Photovoltaic (PV) market. The Conventional grid-connected PV inverter was either with DC/DC converter or without DC/DC converter. These inverters were isolated using a transformer either on the grid (AC) side as a low-frequency transformer or as a highfrequency transformer on the DC side. Elimination of the transformer leads to a galvanic connection between the grid and PV module. This gives rise to the flow of leakage current which is disastrous for the system when it exceeds a specific value. Thus, minimization of this leakage current after the removal of the transformer has been an interesting topic explored by many researchers. Many topologies have been proposed targeting reduction in this leakage current either by 1.) Directly connecting the PV negative with neutral of utility grid or 2.) Disconnecting the PV panel side from AC side. This generally involved addition of more switches or diodes or supplementary branches to disconnect during the freewheeling period. Generally, the above-mentioned ways lead to a reduction in efficiency due to increased losses or complex circuitry. The motivation of this thesis is to design a transformerless inverter for single-phase PV grid-tied system with a smaller number of devices and still has minimum ground current. It discusses the prevailing inverter topologies in detail and then explains the modes of operation of the proposed inverter. A simple control strategy has been derived and passive elements of the inverter are designed. The simulation results presented have validated the theoretical claims. The experimental results which are similar to simulation results are evidence that the proposed topology is suitable for PV grid-tied systems. Also, the dynamic modeling of the inverter has been done to derive the plant transfer function. Then, the Proportional Resonant (PR) controller has been designed to ensure the flow of sinusoidal current into the grid with zero steady-state error and constant sinusoidal grid voltage irrespective of load change. The simulation and experimental results achieved high performance which makes this topology successful and promising for grid-tied PV systems.

LINK: https://spectrum.library.concordia.ca/985562/1/Verma_MASc_F2019.pdf

Control Design of a Single-Phase DC/AC Inverter for PV Applications by Haoyan Liu - University of Arkansas, Fayetteville

 Control Design of a Single-Phase DC/AC Inverter for PV Applications A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Electrical Engineering by Haoyan Liu

Harbin University of Science and Technology Bachelor of Engineering in Automation, 2012 May 2016 University of Arkansas

Abstract 

This thesis presents controller designs of a 2 kVA single-phase inverter for photovoltaic (PV) applications. The demand for better controller designs is constantly rising as the renewable energy market continues to rapidly grow. Some background research has been done on solar energy, PV inverter configurations, inverter control design, and hardware component selection. Controllers are designed both for stand-alone and grid-connected modes of operation. For standalone inverter control, the outer control loop regulates the filter capacitor voltage. Combining the synchronous frame outer control loop with the capacitor current feedback inner control loop, the system can achieve both zero steady-state error and better step load performance. For grid-tied inverter control, proportional capacitor current feedback is used. This achieves the active damping needed to suppress the LCL filter resonance problem. The outer loop regulates the inverter output current flowing into the grid with a proportional resonant controller and harmonic compensators. With a revised grid synchronization unit, the active power and reactive power can be decoupled and controlled separately through a serial communication based user interface. To validate the designed controllers, a scaled down prototype is constructed and tested with a digital signal processor (DSP) TMS320F28335.

LINK:https://core.ac.uk/download/pdf/80559559.pdf