Dagens samhälle har stort beroende av central elförsörjning för att ha kapacitet att fungera. Beroendet av centrala produktionsenheter kopplade till stamnätet kan i sin tur göra det svenska elnätet mer sårbart och ostabilt. En potentiell lösning för att göra nätet mer resilient och stabilt är att bygga ut nätet med mindre lokala nät kompletterade av lokala energilager. Dessa energilager kan bestå av villabatterier men även genom att utnyttja elbilar via olika integrationer av V2X. På grund av det ovanliga jordningssystemet i Sverige, utan lokala jordtag i hemmen, är kravet på jordtag en mycket viktig fråga att undersöka för att inte förhindra utvecklingen och utökningen av energilager. Det EU-direktiv som idag gäller vid inmatning från generatorer, RfG, inkluderar uttryckligen inte energilager. Detta skapar en ”lucka” i regelverket där det saknas tydliga krav för energilager och elbilar. Historiskt sett har kraven för ödrift grundats i kraven för reservkraftsystem med en teknik som skiljer sig från den kraftelektronik med växelriktare som existerar idag. Denna studie syftar till att kartlägga de krav som finns för inmatning till det centrala nätet eller det lokala önätet via växelriktare. Det syftar även till att undersöka huruvida de krav som identifierats är applicerbara på modern teknik eller om de behöver uppdateras. Kraven identifierades genom en litteraturgenomgång av det svenska regelverket för el och genom 17 intervjuer med aktörer från myndigheter, organisationer, nätbolag, tillverkare och högskolor där ”krav-kartan”, se nedan bild, även förankrades och utvecklades. Studien visade att det finns en uppdelning för vilka funktioner som relaterar till vilka krav där den tydligaste skillnaden är att kravet på lokalt jordtag endast existerar för anläggningar som är förutsatta att drivas i ödrift. Studien visar även att ett flertal av de krav som identifierats inte är helt applicerbara på det svenska perspektivet eller på modern kraftelektronik och behöver uppdateras. / Todays society has a great dependence on central power production in order to function. The reliance on central production on the main grid exposes the Swedish power grid and makes it more vulnerable and unstable. One potential solution to make the grid more resilient is to expand the network with local micro grids with energy storage. These microgrids can be powered by home batteries but there is also the potential of utilizing electric vehicles through various V2X integrations. Due to the unusual grounding system in Sweden without local earth electrodes in the homes, the requirement for earthing is a very important issue to investigate to prevent any hinders on the development of local energy storages. The EU directive that regulates the requirements for generators, RfG, explicitly does not include energy storage requirements, creating a void in the regulations where there are no clear requirements for energy storages and electric vehicles. Historically, the requirements for island operations have been decided on the requirements for reserve/backup power system which utilizes generators that differs from the power electronics with inverters that are utilized today. This study aims to identify the requirements for feeding while “grid connected” and while in island mode. It also aims to investigate whether the identified requirements are applicable to modern technology or if they need to be updated. The requirements were identified through a literature overview of the Swedish regulations for electricity and through 17 interviews with stakeholders from authorities, organizations, grid companies, manufacturers, and universities, where the "map of requirements" was also discussed and developed. The study showed that there is distinction what requirement relate to what function, where the clearest difference is that the requirement for local earth electrodes only exists for buildings intended for island-operations. The study also shows that several of the identified requirements are not fully applicable to the Swedish perspective or to modern power electronics and need to be updated.

Energy security, global warming, and climate change have been a major source of global discussions and development. Likewise, the rising cost of electricity for consumers and exponential demand for energy are major factors driving the incremental growth and integration of sustainable forms of energy generation into power the system cycle. Distributed generation resources are majorly integrated into the electricity distribution system at the medium voltage (MV) and low voltage (LV) level of the utility grid system. Unexpected power outages on an electricity distribution network can lead to an islanding situation, in which a distributed generation system continues to supply power to the electricity grid. It is highly recommended by operational standards that, under such conditions, a distributed generation system is disconnected from the grid within a short period to prevent damage to power equipment and ensure personnel safety. The decoupling process requires an islanding detection method (IDM). Such detection methods are implemented in grid-tied power electronic converters (PEC) to detect and prevent islanding conditions.  The thesis investigates and describes an active islanding detection method, the active frequency drift with positive feedback. It also covers the parameter design and the analysis of the non–detection zone. The effectiveness of the method was verified through MATLAB/SIMULINK simulation

Recently, a lot of research work has been dedicated toward enhancing performance, reliability and integrity of distributed energy resources that are integrated into distribution networks. The problem of islanding detection and islanding prevention (i.e. anti-islanding) has stimulated a lot of research due to its role in severely compromising the safety of working personnel and resulting in equipment damages. Various Islanding Detection Methods (IDMs) have been developed within the last ten years in anticipation of the tremendous increase in the penetration of Distributed Generation (DG) in distribution system. This work proposes new IDMs that rely on transient and distributed behaviors to improve integrity and performance of DGs while maintaining multi-DG islanding detection capability. In this thesis, the following questions have been addressed: How to utilize the transient behavior arising from an islanding condition to improve detectability and robust performance of IDMs in a distributive manner? How to reduce the negative stability impact of the well-known Sandia Frequency Shift (SFS) IDM while maintaining its islanding detection capability? How to incorporate the perturbations provided by each of DGs in such a way that the negative interference of different IDMs is minimized without the need of any type of communication among the different DGs? It is shown that the proposed techniques are local, scalable and robust against different loading conditions and topology changes. Also, the proposed techniques can successfully distinguish an islanding condition from other disturbances that may occur in power system networks. This work improves the efficiency, reliability and safety of integrated DGs, which presents a necessary advance toward making electric power grids a smart grid.

The future power grid will effectively utilize renewable energy resources and distributed generation to respond to energy demand while incorporating information technology and communication infrastructure for their optimum operation. This dissertation contributes to the development of real-time techniques, for wide-area monitoring and secure real-time control and operation of hybrid power systems. To handle the increased level of real-time data exchange, this dissertation develops a supervisory control and data acquisition (SCADA) system that is equipped with a state estimation scheme from the real-time data. This system is verified on a specially developed laboratory-based test bed facility, as a hardware and software platform, to emulate the actual scenarios of a real hybrid power system with the highest level of similarities and capabilities to practical utility systems. It includes phasor measurements at hundreds of measurement points on the system. These measurements were obtained from especially developed laboratory based Phasor Measurement Unit (PMU) that is utilized in addition to existing commercially based PMU’s. The developed PMU was used in conjunction with the interconnected system along with the commercial PMU’s. The tested studies included a new technique for detecting the partially islanded micro grids in addition to several real-time techniques for synchronization and parameter identifications of hybrid systems. Moreover, due to numerous integration of renewable energy resources through DC microgrids, this dissertation performs several practical cases for improvement of interoperability of such systems. Moreover, increased number of small and dispersed generating stations and their need to connect fast and properly into the AC grids, urged this work to explore the challenges that arise in synchronization of generators to the grid and through introduction of a Dynamic Brake system to improve the process of connecting distributed generators to the power grid. Real time operation and control requires data communication security. A research effort in this dissertation was developed based on Trusted Sensing Base (TSB) process for data communication security. The innovative TSB approach improves the security aspect of the power grid as a cyber-physical system. It is based on available GPS synchronization technology and provides protection against confidentiality attacks in critical power system infrastructures.

This master thesis examines technical requirements for small hydro power plants (HPP) to operate proximate parts of the power grid in island mode. The work examines how small hydropower can be modified and complemented with additional technologies to achieve sufficient frequency control capabilities. A case study was performed within the concession area of power grid operator Ålem Energy. One of the HPPs, located in Skälleryd, is owned by Ålem Energy and became the focal point of the study. Relevant parts of the concession area were surveyed for properties such as system inertia, electric load and available power. Furthermore, a model of Kaplan turbine 1 in Skälleryd HPP was created with the purpose of studying the benefits of bypassing regulation control from the wicket gates directly to the runner. The method was tested in an off-grid islanding test. Frequency control of the turbine was tested powering electric heaters and, using a new method, controlling a virtual power grid. Finally, a theory was developed to estimate the transient disturbance resilience (TDR) of a power grid. The theory was applied to the HPP in Skälleryd to suggest modifications for the plant to achieve sufficient islanding capabilities. The survey of the power system revealed a promising potential for the HPPs to operate in island mode, especially at later stages when the grid spans several HPPs for more system inertia. The available power from the HPPs was however strongly seasonal which imposes flexibility on a future plan of action for engaging the grid in island mode. The method of controlling the turbine power from the runner proved to have several difficulties. Firstly, the current hydraulics system was not able to freely control the runner as the hydrodynamic forces on the runner blades were too large. Secondly, the method was found to be unstable due to inherent amplification of speed deviations. Furthermore, the low inertia at Skälleryd is likely detrimental to the lone frequency control of the turbine. Therefore other methods for improving frequency control were suggested. The developed theory for TDR was used to create charts describing the TDR for various combinations of system inertia and regulation speed. By studying the proprieties of Skälleryd HPP in the charts the necessary modifications could be rationally chosen. A frequency regulating dummy load was found to be the simplest option. A control scheme was suggested with the dummy load performing primary frequency control and the turbines at Skälleryd performing secondary control, restoring the dummy load to its nominal state.

O ilhamento em sistemas elétricos contendo geração distribuída ocorre quando parte da rede elétrica torna-se eletricamente isolada da concessionária e o subsistema isolado continua a ser energizado por geradores distribuídos. É importante detectar essa condição, que pode, por exemplo, levar a problemas como alteração da qualidade da energia elétrica e religamento automático fora de sincronismo, causando danos irreversíveis aos equipamentos da rede elétrica. Uma forma de detecção do ilhamento é o uso de funções de proteção de frequência e suas variações, tais como a função de taxa de variação de frequência e a função de deslocamento de fase (ou salto de vetor). Neste contexto, é importante que se tenham modelos computacionais e analíticos confiáveis dessas funções de proteção para que sejam executadas simulações, permitindo validar ajustes e verificar condições anormais de operação. O objetivo desta dissertação é desenvolver e validar modelos computacionais e analíticos das funções de proteção de sub/sobre frequência, taxa de variação de frequência e deslocamento de fase, empregados na detecção de ilhamento de geradores distribuídos. Os modelos computacionais são desenvolvidos em uma plataforma que permite realizar simulações dinâmicas em tempo real. A validação dos modelos é efetuada utilizando funções de proteção existentes em relés comerciais. A avaliação de desempenho dos modelos em relação à proteção anti-ilhamento é realizada utilizando o conceito das curvas de desempenho, as quais foram obtidas a partir de simulações computacionais em tempo real e em malha fechada pelo uso de um simulador digital em tempo real. Os resultados permitem comprovar a efetividade dos modelos para representar as funções de proteção dos relés comerciais ensaiados, com erros abaixo de 3% para uma ampla faixa de pontos de operação do sistema elétrico e do gerador distribuído. / Islanding in power distribution systems with distributed generators occurs when part of the electrical network becomes isolated from the electrical company and the isolated area is still energized by distributed generation. It is important to detect this condition which can lead to problems such as low power quality levels and out of step reclosing, causing severe equipment damages. One of the island detection methods is the use of frequency protection functions and their variations, such as the rate of change of frequency relay and phase shift relay (or vector surge relay). In this context, it is important to obtain reliable relay computational and analytical models to execute simulations that allow verifying and validating settings, and investigating abnormal operation conditions. This dissertation aims to develop and validate computational and analytical models of under and over frequency, rate of change of frequency and phase shift protection functions applied to distributed generation islanding detection. The computational model development is performed on a real time dynamic simulation platform. The model validations are performed using protection functions of commercial relays. The models performance evaluation and validation were carried out by using the performance curves, which are obtained through real time closed loop simulations using a real time digital simulator. The results prove the model effectiveness to represent commercial protection functions, with errors below 3% for a wide range of distribution system and distributed generator operating conditions.

O ilhamento em sistemas elétricos contendo geração distribuída ocorre quando parte da rede elétrica torna-se eletricamente isolada da concessionária e o subsistema isolado continua a ser energizado por geradores distribuídos. É importante detectar essa condição, que pode, por exemplo, levar a problemas como alteração da qualidade da energia elétrica e religamento automático fora de sincronismo, causando danos irreversíveis aos equipamentos da rede elétrica. Uma forma de detecção do ilhamento é o uso de funções de proteção de frequência e suas variações, tais como a função de taxa de variação de frequência e a função de deslocamento de fase (ou salto de vetor). Neste contexto, é importante que se tenham modelos computacionais e analíticos confiáveis dessas funções de proteção para que sejam executadas simulações, permitindo validar ajustes e verificar condições anormais de operação. O objetivo desta dissertação é desenvolver e validar modelos computacionais e analíticos das funções de proteção de sub/sobre frequência, taxa de variação de frequência e deslocamento de fase, empregados na detecção de ilhamento de geradores distribuídos. Os modelos computacionais são desenvolvidos em uma plataforma que permite realizar simulações dinâmicas em tempo real. A validação dos modelos é efetuada utilizando funções de proteção existentes em relés comerciais. A avaliação de desempenho dos modelos em relação à proteção anti-ilhamento é realizada utilizando o conceito das curvas de desempenho, as quais foram obtidas a partir de simulações computacionais em tempo real e em malha fechada pelo uso de um simulador digital em tempo real. Os resultados permitem comprovar a efetividade dos modelos para representar as funções de proteção dos relés comerciais ensaiados, com erros abaixo de 3% para uma ampla faixa de pontos de operação do sistema elétrico e do gerador distribuído. / Islanding in power distribution systems with distributed generators occurs when part of the electrical network becomes isolated from the electrical company and the isolated area is still energized by distributed generation. It is important to detect this condition which can lead to problems such as low power quality levels and out of step reclosing, causing severe equipment damages. One of the island detection methods is the use of frequency protection functions and their variations, such as the rate of change of frequency relay and phase shift relay (or vector surge relay). In this context, it is important to obtain reliable relay computational and analytical models to execute simulations that allow verifying and validating settings, and investigating abnormal operation conditions. This dissertation aims to develop and validate computational and analytical models of under and over frequency, rate of change of frequency and phase shift protection functions applied to distributed generation islanding detection. The computational model development is performed on a real time dynamic simulation platform. The model validations are performed using protection functions of commercial relays. The models performance evaluation and validation were carried out by using the performance curves, which are obtained through real time closed loop simulations using a real time digital simulator. The results prove the model effectiveness to represent commercial protection functions, with errors below 3% for a wide range of distribution system and distributed generator operating conditions.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-04-20T13:39:03Z No. of bitstreams: 1 pedromachadodealmeida.pdf: 13436160 bytes, checksum: 84c66613dade0766ae9ea2bdc8be9f91 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-04-20T14:45:37Z (GMT) No. of bitstreams: 1 pedromachadodealmeida.pdf: 13436160 bytes, checksum: 84c66613dade0766ae9ea2bdc8be9f91 (MD5) / Made available in DSpace on 2017-04-20T14:45:37Z (GMT). No. of bitstreams: 1 pedromachadodealmeida.pdf: 13436160 bytes, checksum: 84c66613dade0766ae9ea2bdc8be9f91 (MD5) Previous issue date: 2011-04-29 / Esta dissertação apresenta uma estratégia de controle para sistemas de geração fotovoltaicos, de único estágio, trifásicos, conectados à rede elétrica de distribuição. São desenvolvidos modelos matemáticos para representar as características dinâmicas dos painéis fotovoltaicos, do conversor fonte de tensão (VSC -“Voltage Source Converter”) e da rede de distribuição. A modelagem do sistema de geração disperso (SGD) é feita no sistema de coordenadas síncrono (dq), fornecendo um sistema de equações diferenciais que pode ser usado para descrever o comportamento dinâmico do sistema quando as tensões da rede estão equilibradas ou desequilibradas. O conversor é controlado no modo de corrente, através da estratégia de modulação vetorial (Space Vector Modulation - SVM). São projetadas duas malhas de controle em cascata para controlar o conversor estático. A malha interna controla a corrente injetada na rede enquanto que a externa controla a tensão no barramento CC do conversor. O controle da tensão CC permite rastrear o ponto de máxima potência do painel PV além de controlar a quantidade de potência ativa injetada na rede CA. Um método ativo de detecção de ilhamento baseado na injeção de corrente de sequência negativa é incorporado ao sistema de controle. Resultados de simulações digitais obtidos com o programa ATP (Alternative Transient Program ) são utilizados para validar os modelos matemáticos e as estratégias de controle. Finalmente, um protótipo experimental de pequena escala é montado em laboratório. Todo o sistema de controle do protótipo experimental foi implementado no DSP TMS320F28212. Os resultados obtidos demonstram o funcionamento do sistema e podem ser usados para validar a estratégia de controle utilizada. / This dissertation presents a control strategy for a single-stage, three-phase, photovoltaic systems to be connected to a distribution network. Mathematical models are developed to represent the dynamic characteristics of the photovoltaic panels, the voltage-source converter (VSC) and the distribution network. The modeling of the dispersed generation system (DGS) is done in the synchronous reference frame (dq), providing a system of differential equations that describes the dynamic behavior of the system when the network voltages are balanced or unbalanced. The converter is controlled in current mode through the space vector modulation (SVM) strategy. Two control loops are designed to control the static converter. The inner loop controls the injected current into the network while the external loop controls the converter DC bus voltage. The DC voltage regulator allows to track the PV maximum power point and to control the active power injected into the AC grid. An active islanding detection method based on negative-sequence current injection is incorporated into the control system. Digital simulations results obtained with Alternative Transients Program (ATP) is used to validate the mathematical models and the control strategies. Finally, a small-scale experimental prototype is implemented in the laboratory. The whole control system of the experimental prototype was programmed in DSP TMS320F2812 of Texas Instruments. The results demonstrate that the operation of the system can be used to validate the applied control strategy.

Classically, wide-area synchronized power system monitoring has been an expensive task requiring significant investment in utility communications infrastructures for the service of relatively few costly sensors. The purpose of this research is to demonstrate the viability of power system monitoring from very low voltage levels (120 V). Challenging the accepted norms in power system monitoring, the document will present the use of inexpensive GPS time synchronized sensors in mass numbers at the distribution level. In the past, such low level monitoring has been overlooked due to a perceived imbalance between the required investment and the usefulness of the resulting deluge of information. However, distribution level monitoring offers several advantages over bulk transmission system monitoring. First, practically everyone with access to electricity also has a measurement port into the electric power system. Second, internet access and GPS availability have become pedestrian commodities providing a communications and synchronization infrastructure for the transmission of low-voltage measurements. Third, these ubiquitous measurement points exist in an interconnected fashion irrespective of utility boundaries. This work offers insight into which parameters are meaningful to monitor at the distribution level and provides applications that add unprecedented value to the data extracted from this level. System models comprising the entire Eastern Interconnection are exploited in conjunction with a bounty of distribution level measurement data for the development of wide-area disturbance detection, classification, analysis, and location routines. The main contributions of this work are fivefold: the introduction of a novel power system disturbance detection algorithm; the development of a power system oscillation damping analysis methodology; the development of several parametric and non-parametric power system disturbance location methods, new methods of power system phenomena visualization, and the proposal and mapping of an online power system event reporting scheme. / Ph. D.