Fonte ininterrupta de energia trifásica de alto desempenho sem transformador com dupla funcionalidade do estágio de entrada e sistema de controle digital-Venturini, William Alegranci- Dissertação (Mestrado em Engenharia Elétrica) - Universidade Federal de Santa Maria, Santa Maria, 2016.

 

VENTURINI, William Alegranci. High performance three-phase transformerless uninterruptible power supply with double functionality of the input stage and digital control system. 2016. 222 f. Dissertação (Mestrado em Engenharia Elétrica) - Universidade Federal de Santa Maria, Santa Maria, 2016.

 RESUMO

 Esta dissertação de mestrado propõem uma topologia de fonte ininterrupta de energia (UPS - Uninterruptible Power Supplies) trifásica de dupla conversão sem transformador com custo reduzido e sistema de controle digital. A UPS proposta é composta por um estágio de entrada, um banco de baterias, um inversor, um circuito auxiliar e chaves de transferência. O estágio de entrada assume a função de retificador trifásico com filtro LCL em modo normal de operação da UPS e é responsável pela descarga do banco de baterias em modo bateria de operação. Esta configuração reduz o custo do sistema, pois permite que seja aproveitado um circuito disponível e dimensionado para a potência nominal da UPS para a descarga do banco de baterias. Em topologias convencionais de UPSs de dupla conversão o estágio de entrada permanece ocioso durante este modo de operação e um circuito adicional é empregado para este fim. O circuito auxiliar é formado por um indutor e um braço de interruptores e é utilizado como carregador de baterias em modo normal de operação e adicionalmente é utilizado para realizar o equilíbrio das tensões dos capacitores de barramento em modo bateria. Com esta configuração, o circuito auxiliar pode ser dimensionado para apenas uma fração da potência nominal da UPS, propiciando também a redução do custo total do sistema. As chaves de transferência alteram as configurações do estágio de entrada e do circuito auxiliar de acordo com o modo de operação da UPS. É apresentada a operação detalhada da topologia, a modelagem, a estrutura de controle digital utilizada e os resultados obtidos via simulação. Por fim, um protótipo de 20 kVA é implementado e resultados experimentais são adquiridos para a validação da metodologia de projeto empregada bem como da funcionalidade do circuito proposto.

 LINK:https://repositorio.ufsm.br/bitstream/handle/1/8594/VENTURINI%2c%20WILLIAM%20ALEGRANCI.pdf?sequence=1&isAllowed=y

Desenvolvimento de UPS trifásica de alto rendimento utilizando MOSFETS de carbeto de silício Autor Wendell da Cunha Alves. - 2018-Dissertação (mestrado) Universidade Federal de Minas Gerais, Escola de Engenharia.

 

DESENVOLVIMENTO DE UPS TRIFASICA DE ALTO RENDIMENTO UTILIZANDO MOSFETS DE CARBETO DE SILICIO 

AUTOR WENDELL DA CUNHA ALVES 

PROGRAMA DE PÓS-GRADUAÇÃO EM ENGENHARIA ELETRICA UNIVERSIDADE FEDERAL DE MINAS GERAIS- BRASIL

 Resumo

 Com o constante aumento do consumo de energia no mundo, a eficiência dos sistemas e equipamentos está se tornando cada vez mais importante. A UPS é um equipamento que fornece alimentação segura e confiável para sistemas de carga crítica, ou seja, sistemas em que uma interrupção do fornecimento pode levar a perdas econômicas ou até mesmo humanas. A UPS de dupla conversão é a classe UPS mais completa em termos de proteção da carga, regulação, desempenho e confiabilidade, no entanto, tem menor rendimento e maior custo por causa de seu elevado número de conversores eletrônicos de energia. Os dispositivos de Carbeto de Silício estão emergindo como uma oportunidade para construir conversores eletrônicos com maior eficiência e maior densidade de potência. O objetivo principal deste trabalho é projetar um conversor trifásico c.a.-c.c.-c.a. usando Carbeto de Silício para aplicações de UPS de dupla conversão. Para maximizar a eficiência e minimizar o custo, uma comparação é feita para guiar a seleção das topologias de conversor utilizadas. A comparação é feita sob duas condições de operação. Ao final da comparação, dois conversores c.a.-c.c.-c.a. com boa relação custo-benefício são propostos, um para cada condição. Em seguida, um dos conversores propostos é projetado, simulado e construído. As metodologias para dimensionar e escolher os principais componentes de hardware são descritas em detalhes. A operação do conversor e sua técnica de controle são validadas por meio de simulações no software PSIM. Os resultados experimentais obtidos com o protótipo comprovam o alto rendimento alcançável com MOSFETs de Carbeto de Silício. 

Palavras-chave: UPS. Carbeto de Silício. Conversores eletrônicos. Projeto. Alto rendimento.

LINK: https://www.ppgee.ufmg.br/defesas/1583M.PDF

XXIII Congresso Brasileiro de Automática (CBA 2020) 23 e 26 de Novembro de 2020- CONGRESSO VIRTUAL

 

O XXIII Congresso Brasileiro de Automática (CBA 2020) acontecerá entre os dias 23 e 26 de Novembro de 2020, na modalidade de evento virtual.

 A organização é realizada em parceria pela Universidade Federal de Santa Maria (UFSM), Pontifícia Universidade Católica (PUCRS) e a Universidade do Vale do Rio dos Sinos (UNISINOS), vinculado à Sociedade Brasileira de Automática (SBA). O CBA é realizado bianualmente e, desde 1976, é o maior congresso na área de Engenharia Elétrica do Brasil. O congresso conta com a participação expressiva de pesquisadores e profissionais atuantes em diversas áreas da engenharia elétrica, vindos das várias regiões do Brasil e de outros países, promovendo a integração das comunidades científicas, acadêmicas e industriais. O evento tem como base os temas aplicados às áreas que circundam os ramos da engenharia elétrica, com destaque para automação e controle, eletrônica de potência, instrumentação, robótica, sistemas de potência, fontes alternativas de energia, armazenamento de energia, redes elétricas inteligentes, microrredes, mobilidade elétrica e outras áreas afins ao tema central. A edição de 2020 contará com minicursos, sessões plenárias, sessões técnicas, entre outros, com participação de palestrantes renomados e o que há de mais inovador no mundo da engenharia.

LINK PAGINA WEB ORIGINAL: https://cba2020.galoa.com.br/

Multi-powered UPS --Department of Electrical Engineering Graduate School, Chonnam National University Author KIM Jongcheo -Master's Thesis

 Multi-powered UPS KIM Jong Cheol Department of Electrical Engineering Graduate School, Chonnam National University (Supervised by Professor PARK Sungjun)

(Abstract)  As the society develops, load sensitive to power environment such as medical equipment, communication equipment, FA (factory automation) system and data center server is widely used, and reliability and stable supply of power system becomes more important. In particular, electrical equipment used for military purposes is not expected to have any problems in the power supply system during exhibition or operation, so it is becoming necessary to secure a reserve energy source, to duplicate the system or to make surplus system. Even if the reliability of the power supply system is high, momentary power failure due to an accident or a lightning can not be avoided, and there is also a momentary voltage drop (Sag) or a voltage rise (swell) of the power supply. Table 1 below is a definition of the power anomaly phenomenon that appears in the commercial power source shown in IEEE Std 1159TM-2009.

In case of power-sensitive load, it is necessary to prepare for system failure because it can cause fatal damage even in short-term system failure. Therefore, there is a need for an uninterruptible power supply (UPS) [1] [2] to compensate for instantaneous voltage fluctuations as well as for blackout situations.

Automotive UPS systems typically consist of a single module, such as a battery, bi-directional inverter, high-speed switch, and the UPS module is connected to the vehicle generator and critical loads. If the existing UPS system is composed of a single power source and the UPS system is composed of only one power source, it is difficult to cope with the demand of the main load in the long term only by the output of the UPS when the power source is out of power. To solve this problem, connecting several power sources to a load leads to a large increase in cost due to the connection of UPS to each power source. It is an off-line UPS system that is commonly used. The advantage of the off-line method is that when the input power is normal, there is less generation of electromagnetic waves and noise, and the power consumption is low due to high energy efficiency. In addition, it has a simple circuit configuration, high durability, low cost, and miniaturization compared to on-line. The disadvantage of off-line is that momentary power cut-off occurs in the case of power failure, and the output changes according to the input voltage change during non-operation, making it difficult to adjust the voltage and therefore it is not suitable for high-precision load. In the case of Figure 1, it is composed of a single power source, and if the UPS system consists of only one power source, it is difficult to cope with the demand of the main load in the long term only by the output of the UPS when the power source is outage. In particular, in a system having a purpose for use in a command communication terminal of a military, it is difficult to supply stable power because there are many variables in power supply.

In this paper, we propose a multi - power applied UPS system that eliminates the disadvantages of the parallel - connected power supply and has a fast switching time. The UPS system operates in the battery charging mode when the system is in normal operation and operates in the UPS mode, which is the battery discharge mode, in the event of a system failure. In such a mode switching, the follow up of the command voltage should be performed within the shortest time. Since the UPS must supply the same voltage to the load within 4ms in case of a system fault, the switching time and return time must be short when controlling the output voltage and current of the UPS, and the power failure detection time is also important. In addition, since the main loads of the UPS system are mostly time-varying and non-linear loads, it is also necessary to be able to control non-linear loads. Conventionally, a proportional integral (PI) controller has been used as a control method of such a UPS system. The PI controller has a very stable output characteristic in the steady state, but it takes a long time to reach the steady state at the time of mode change or load change due to slow acceleration. Therefore, due to the limit of the transient response characteristic of the controller, it is difficult to perform stable power supply within a short time in the case of a system fault. Also, since the gain of the PI controller affects the response characteristics, response characteristics may be slow or overshoot may occur depending on the gain value selection of the controller. Therefore, in this paper, to compensate the limitation of the proportional integral controller, the controller using the DFT with fast electrostatic sensing characteristics is applied. The control using DFT has an advantage that it can perform fast power failure detection by comparing grid voltage waveform and voltage waveform created by DFT using Schmitt trigger. Therefore, stable power supply is possible when using only PI control in mode switching in UPS system. The multi-power applied UPS system proposed in this paper is finally designed to satisfy the following conditions. In case of system fault, detection method using fast DFT is applied to the electrostatic detection in order to supply stable power to the load in a shorter time than the conventional PI control method. At this time, the switching time of mode switching was set to be less than 4 ms, which is 1/4 of the system cycle, according to KS C 4310 regulation of the uninterruptible power supply in the industry standard council. A 10kW UPS system, in which commercial voltage, vehicle generator, and auxiliary diesel generator can be connected to the proposed switchgear, was tested and validated.

LINK1:http://www.riss.kr/search/detail/DetailView.do?p_mat_type=be54d9b8bc7cdb09&control_no=8f6a0e4c451565dbffe0bdc3ef48d419

LINK2:http://www.mediafire.com/file/0bg7thkijs1736t/MULTIPOWERED+UPS.pdf/file

High Frequency (MHz) Planar Transformers for Next Generation Switch Mode Power Supplies by Radhika Ambatipudi -Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.(Power Electronics)

 High Frequency (MHz) Planar Transformers for Next Generation Switch Mode Power Supplies

by Ambatipudi, Radhika

Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.(Power Electronics) 2013 (English) Doctoral thesis

 ABSTRACT

 Increasing the power density of power electronic converters while reducing or maintaining the same cost, offers a higher potential to meet the current trend in relation to various power electronic applications. High power density converters can be achieved by increasing the switching frequency, due to which the bulkiest parts, such as transformer, inductors and the capacitor's size in the converter circuit can be drastically reduced. In this regard, highly integrated planar magnetics are considered as an effective approach compared to the conventional wire wound transformers in modern switch mode power supplies (SMPS). However, as the operating frequency of the transformers increase from several hundred kHz to MHz, numerous problems arise such as skin and proximity effects due to the induced eddy currents in the windings, leakage inductance and unbalanced magnetic flux distribution. In addition to this, the core losses which are functional dependent on frequency gets elevated as the operating frequency increases. Therefore, this thesis provides an insight towards the problems related to the high frequency magnetics and proposes a solution with regards to different aspects in relation to designing high power density, energy efficient transformers.

The first part of the thesis concentrates on the investigation of high power density and highly energy efficient coreless printed circuit board (PCB) step-down transformers useful for stringent height DC-DC converter applications, where the core losses are being completely eliminated. These transformers also maintain the advantages offered by existing core based transformers such as, high coupling coefficient, sufficient input impedance, high energy efficiency and wide frequency bandwidth with the assistance of a resonant technique. In this regard, several coreless PCB step down transformers of different turn’s ratio for power transfer applications have been designed and evaluated. The designed multilayered coreless PCB transformers for telecom and PoE applications of 8, 15 and 30W show that the volume reduction of approximately 40 - 90% is possible when compared to its existing core based counterparts while maintaining the energy efficiency of the transformers in the range of 90 - 97%. The estimation of EMI emissions from the designed transformers for the given power transfer application proves that the amount of radiated EMI from a multilayered transformer is less than that of the two layered transformer because of the decreased radius for the same amount of inductance.

The design guidelines for the multilayered coreless PCB step-down transformer for the given power transfer application has been proposed. The designed transformer of 10mm radius has been characterized up to the power level of 50W and possesses a record power density of 107W/cm3 with a peak energy efficiency of 96%. In addition to this, the design guidelines of the signal transformer for driving the high side MOSFET in double ended converter topologies have been proposed. The measured power consumption of the high side gate drive circuit together with the designed signal transformer is 0.37W. Both these signal and power transformers have been successfully implemented in a resonant converter topology in the switching frequency range of 2.4 – 2.75MHz for the maximum load power of 34.5W resulting in the peak energy efficiency of converter as 86.5%.

This thesis also investigates the indirect effect of the dielectric laminate on the magnetic field intensity and current density distribution in the planar power transformers with the assistance of finite element analysis (FEA). The significance of the high frequency dielectric laminate compared to FR-4 laminate in terms of energy efficiency of planar power transformers in MHz frequency region is also explored.

The investigations were also conducted on different winding strategies such as conventional solid winding and the parallel winding strategies, which play an important role in the design and development of a high frequency transformer and suggested a better choice in the case of transformers operating in the MHz frequency region.

In the second part of the thesis, a novel planar power transformer with hybrid core structure has been designed and evaluated in the MHz frequency region. The design guidelines of the energy efficient high frequency planar power transformer for the given power transfer application have been proposed. The designed core based planar transformer has been characterized up to the power level of 50W and possess a power density of 47W/cm3 with maximum energy efficiency of 97%. This transformer has been evaluated successfully in the resonant converter topology within the switching frequency range of 3 – 4.5MHz. The peak energy efficiency of the converter is reported to be 92% and the converter has been tested for the maximum power level of 45W, which is suitable for consumer applications such as laptop adapters. In addition to this, a record power density transformer has been designed with a custom made pot core and has been characterized in the frequency range of 1 - 10MHz. The power density of this custom core transformer operating at 6.78MHz frequency is 67W/cm3 and with the peak energy efficiency of 98%.

LINK ORIGINAL NA WEB:

https://www.diva-portal.org/smash/get/diva2:665725/FULLTEXT01.pdf

Étude et élaboration d’un système de surveillance et de maintenance prédictive pour les condensateurs et les batteries utilisés dans les Alimentations Sans Interruptions (ASI) by Mohamed Karim Abdennadher - Study and elaboration of a monitoring and predictive maintenance system for capacitors and batteries used in Uninterruptible Power Supplies (UPS)

 

Étude et élaboration d’un système de surveillance et de maintenance prédictive pour les condensateurs et les batteries utilisés dans les Alimentations Sans Interruptions (ASI) Mohamed Karim Abdennadher

Study and elaboration of a monitoring and predictive maintenance system for capacitors and batteries used in Uninterruptible Power Supplies (UPS)

THESE DE DOCTORAT Présentée devant L’UNIVERSITE CLAUDE BERNARD LYON 1 Pour l’obtention du grade de DOCTEUR de l’UNIVERSITE de LYON 1 (Arrêté du 07 Août 2006) Spécialité : GENIE ELECTRIQUE Préparée au sein de L’ECOLE DOCTORALE ELECTRONIQUE, ELECTROTECHNIQUE, AUTOMATIQUE DE LYON Par M. Mohamed Karim ABDENNADHER

Résumé

 To ensure power quality and permanently, some electronic system supplies exist. These supplies are the Uninterrupted Power Supplies (UPS). An UPS like any other system may have some failures. This can be a cause of redundancy loss. This load loss causes a maintenance downtime which may represent a high cost. We propose in this thesis to work on two of the most sensitive components in the UPS namely electrolytic capacitors and lead acid batteries. In a first phase, we present the existing surveillance systems for these two components, highlighting their main drawbacks. This allows us to propose the specifications which have to be implemented for this system. For electrolytic capacitors, we detail different stages of characterization ; the aging accelerated standard experimental procedure and their associated results. On the other hand, we present the simulation results of monitoring and failure prediction system retained. We discuss the experimental validation, describing the developed system. We detail the electronic boards designed, implemented algorithms and their respective constraints for a real time implementation. Finally, for lead acid batteries, we present the simulation results of the monitoring system adopted to obtain the SOC and SOH. We describe the aging experimental procedure of charging and discharging cycles of the batteries needed to find a simple and accurate electric models. We explain the aging experimental results and in the end we give suggestions for improving our system to get a more accurate SOH.

LINK:  https://tel.archives-ouvertes.fr/tel-00532642v2/document

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

A new high-efficiency single-phase transformerless PV inverter topology Tamás Kerekes, Member, IEEE, Remus Teodorescu, Senior Member, IEEE, Pedro Rodríguez, Member, IEEE, Gerardo Vázquez, Student Member, IEEE, Emiliano Aldabas, Member, IEEE

A new high-efficiency single-phase transformerless PV inverter topology

Tamás Kerekes, Member, IEEE, Remus Teodorescu, Senior Member, IEEE, Pedro Rodríguez, Member, IEEE, Gerardo Vázquez, Student Member, IEEE, Emiliano Aldabas, Member, IEEE

ABSTRACT: There is a strong trend in the photovoltaic (PV) inverter technology to use transformerless topologies in order to acquire higher efficiencies combining with very low ground leakage current. In this paper a new topology, based on the H- Bridge with a new AC bypass circuit consisting in a diode rectifier and a switch with clamping to the DC midpoint is proposed. The topology is simulated and experimentally validated and a comparison with other existing topologies is performed. High conversion efficiency and low leakage current is demonstrated.

I INTRODUCTION Photovoltaic inverters become more and more widespread within both private and commercial circles. These grid connected inverters convert the available direct current supplied by the photovoltaic (PV) panels and feed it into the utility grid. According to the latest report on installed PV power, during 2007 there has been a total of 2.25GW of installed PV systems, out of which the majority (90%) has been installed in Germany, Spain, USA and Japan. At the end of 2007 the total installed PV capacity has reached 7.9 GW of which around 92% is grid connected [1].

There are two main topology groups used in case of grid connected PV systems and they are: with and without galvanic isolation [2]. Galvanic isolation can be on the DC side, in the form of a high frequency DC-DC transformer or on the grid side in the form of a big-bulky AC transformer. Both of these solutions offer the safety and advantage of galvanic isolation, but the efficiency of the whole system is decreased, due to power losses in these extra components. In case the transformer is omitted the efficiency of the whole PV system can be increased with an extra 1-2%. The most important advantages of transformerless PV systems can be observed in Fig. 1, like: higher efficiency, smaller size and weight compared to the PV systems that have galvanic isolation (either on the DC or AC side). 1 Fig. 1 has been made from the database of more than 400 commercially available PV inverters, presented in a commercial magazine about PV systems [3]. Transformerless inverters are represented by the dots (Transformerless), while the triangles represent the inverters that have a low-frequency transformer on the grid side (LF-transformer) and last the stars represent the topologies including a high-frequency DC-DC transformer (HF-transformer), adding a galvanic isolation between the PV and grid. The conclusion drawn from these graphs is that transformerless inverters have higher efficiency, smaller weight and size than their counterparts with galvanic separation. Transformerless PV inverters use different solutions to minimize the leakage ground current and improve the efficiency of the whole system, an issue that has previously been treated in many papers [4]-[11].

LINK: http://seer.upc.edu/material/ficheros_publicaciones/26552ZRV_PV_Inverter.pdf

A Digital Control System for UPS Systems with Smart Grid Capability-Author Mardani Boroujeni, Fatemeh-Faculty Schulich School of Engineering- Institution University of Calgary

 

A Digital Control System for UPS Systems with Smart Grid Capability by Fatemeh Mardani Boroujeni

 

UNIVERSITY OF CALGARY

A THESIS SUBMITTED TO THE FACULTY OF GRADUATE STUDIES IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE GRADUATE PROGRAM IN ELECTRICAL ENGINEERING CALGARY, 

ALBERTA AUGUST, 2019.

  Abstract 

Smart grids have recently become the center of attention for modernizing the grid system. In future smart-grids, energy storage systems are one of the key components, which can complement intermittent renewable energy sources and in turn increase reliability and eciency of the grid system. Modern Uninterruptible Power Supply (UPS) systems can provide storage capacity for future smart grids since they usually include batteries. UPS systems can also provide instant electrical power to sensitive equipment and grid during various events such as brownout, power failures, spikes, voltage surges, EMI/RF noise, and frequency variations.

Future UPS systems require to have much better dynamics in order to deal with transients. The control system of UPS systems mainly determines their dynamical performance and transient response. The existing state-of-the-art UPS control systems are based on linear PI controllers for the most part. Thus, current UPS systems usually show a sluggish transient response and they are not suited for future smart grid applications where instant power is required to maintain the system.

In this thesis, new UPS systems with improved transient response are proposed. The proposed UPS system utilities a new controller that is able to improve the dynamic performance and allows for various smart grid functionalities. The proposed control system is based on the adaptive control theory, which adaptively changes the controller's parameters based on the UPS operating conditions. Furthermore, the proposed control system isolates the double-frequency ripple from the battery in the normal/charging mode as well as in the backup/discharging mode. Therefore, the new UPS system is well-suited for single-phase systems utilizing lithium-ion battery as storage. Mathematical analysis, simulation, and experimental results are presented to verify the performance of the proposed control system and demonstrate its superior performance.

LINK:https://prism.ucalgary.ca/bitstream/handle/1880/110715/ucalgary_2019_mardaniboroujeni_fatemeh.pdf?sequence=2&isAllowed=y