To integrate large volumes of renewables and use electricity more efficiently, many industrial trials are on-going around the world that aim to realize decentralized or hierarchical control of renewable and distributed energy resources, flexible loads and monitoring devices. As the cost and complexity involved in the centralized communications and control infrastructure may be prohibitive in controlling millions of these distributed energy resources and devices, distributed optimization methods are expected to become much more prevalent in the operation of future electric power systems, as they have the potential to address this challenge and can be applied to various applications such as optimal power ow, state estimation, voltage control, and many others. While many distributed optimization algorithms are developed mathematically, little effort has been reported so far on how these methods should actually be implemented in real-world large-scale systems. The challenges associated with this include identifying how to decompose the overall optimization problem, what communication infrastructures can support the information exchange among subproblems, and whether to coordinate the updates of the subproblems in a synchronous or asynchronous manner. This research is dedicated to developing mathematical tools to address these issues, particularly for solving the non-convex optimal power flow problem. As the first part of this thesis, we develop a partitioning method that defines the boundaries of regions when applying distributed algorithms to a power system. This partitioning method quantifies the computational couplings among the buses and groups the buses with large couplings into one region. Through numerical experiments, we show that the developed spectral partitioning approach is the key to achieving fast convergence of distributed optimization algorithms on large-scale systems. After the partitioning of the system is defined, one needs to determine whether the communications among neighboring regions are supported. Therefore, as the second part of this thesis, we propose models for centralized and distributed communications infrastructures and study the impact of communication delays on the efficiency of distributed optimization algorithms through network simulations. Our findings suggest that the centralized communications infrastructure can be prohibitive for distributed optimization and cost-effective migration paths to a more distributed communications infrastructure are necessary. As the sizes and complexities of subproblems and communication delays are generally heterogeneous, synchronous distributed algorithms can be inefficient as they require waiting for the slowest region in the system. Hence, as the third part of this thesis, we develop an asynchronous distributed optimization method and show its convergence for the considered optimal power flow problem. We further study the impact of parameter tuning, system partitioning and communication delays on the proposed asynchronous method and compare its practical performance with its synchronous counterpart. Simulation results indicate that the asynchronous approach can be more efficient with proper partitioning and parameter settings on large-scale systems. The outcome of this research provides important insights into how existing hardware and software solutions for Energy Management Systems in the power grid can be used or need to be extended for deploying distributed optimization methods, which establishes the interconnection between theoretical studies of distributed algorithms and their practical implementation. As the evolution towards a more distributed control architecture is already taking place in many utility networks, the approaches proposed in this thesis provide important tools and a methodology for adopting distributed optimization in power systems.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-04-20T17:56:56Z No. of bitstreams: 1 luisguilhermedasilvacosta.pdf: 5093972 bytes, checksum: 6380895e21a76520d3f4a10aad5a3371 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-04-24T16:50:02Z (GMT) No. of bitstreams: 1 luisguilhermedasilvacosta.pdf: 5093972 bytes, checksum: 6380895e21a76520d3f4a10aad5a3371 (MD5) / Made available in DSpace on 2017-04-24T16:50:02Z (GMT). No. of bitstreams: 1 luisguilhermedasilvacosta.pdf: 5093972 bytes, checksum: 6380895e21a76520d3f4a10aad5a3371 (MD5) Previous issue date: 2012-02-24 / Atualmente, há um grande interesse no desenvolvimento de transceptores PLC (power line communication) para a transmissão banda larga e banda estreita de dados visando, sobretudo, aplicações smart grids e de acesso banda larga. Para o avanço da tecnologia PLC, há grande demanda pela introdução de acopladores com características e desempenhos que viabilizem a conexão dos tranceptores PLC `as redes de energia elétrica, com o mínimo de distorção possível. Neste contexto, a presente contribuição versa sobre o estudo, a investigação, especificação, projeto e análise de acopladores capacitados para transceptores PLC SISO (single input single output) banda larga e banda estreita. Para tanto, são introduzidos acopladores PLC nas seguintes faixas de frequências: de 9 kHz `a 2 MHz, de 1,7 MHz `a 100 MHz e de 1,7 MHz `a 150 MHz. As análises dos projetos e dos protótipos dos acopladores, concebidos para operar nas referidas bandas, mostram as dificuldades encontradas para garantir que as especificações de projeto sejam atendidas quando os componentes passivos são comerciais e a faixa de frequência de operação do acoplador aumenta. Além disso, as análises confirmam a necessidade de consideração de técnicas de prototipação de placas de circuitos impresso para sinais de frequência elevada. Finalmente, os resultados de medição mostram que os acopladores para baixa frequência discutidos podem ser utilizados em sistemas de medição de canais PLC. / Currently, there is a great interest to develop power line communications (PLC) transceivers for broadband and narrowband data communications for smart grids and network access. However, for advancing PLC technologies, there is a great demand for introduction of couplers for connecting the PLC tranceivers to the electric energy circuits with minimum distortion. This contribution addresses the study, investigation, specification, design, and analysis of capacitive couplers for single input single output (SISO), broadband and narrowband PLC transceivers. Capacity and SISO PLC couplers covering the following frequencies bandwidth are addressed: from 9 kHz up to 2 MHz, from 1,7 MHz up to 100 MHz and from 1,7 MHz up to 150 MHz. The analysis performance of the designed and prototyped PLC couplers for operating in the aforementioned frequencies bandwidths, shows the inherent difficulties to guarantee that the design specifications are fulfilled when passive components are commercial ones and the frequency bandwidth increase. Additionally, the analysis confirms the need for taking into account advancing prototyping techniques for dealing with high-frequency signals. Finally, the measurements show that the discussed narrowband PLC couplers can be used in a PLC channel system.