This research attempts to quantify the complex interactions between HVDC transmission schemes in a multi-infeed configuration, particularly with regard to the voltage interactions and the commutation failure phenomena. The in-depth analysis of multi-infeed HVDC systems discussed in this research shows the application of several indices such as the MIIF, MIESCR, and CFII, that can provide researchers and planning engineers in the area of HVDC transmission with the necessary tools for their system studies. It shows that these indices are applicable in a multi-infeed system comprising HVDC schemes with different ratings. The Multi-Infeed Interaction Factor (MIIF) quantifies the level of voltage interactions between converter ac buses. The Multi-Infeed Effective Short Circuit Ratio (MIESCR) index is an indicator of ac system strengths with regard to the assessment of the transient overvoltage (TOV) and the power-voltage stability of multi-infeed HVDC systems. The Commutation Failure Immunity Index (CFII) utilizes electromagnetic transient simulation programs to evaluate the immunity of an HVDC converter to commutation failures. The CFII takes into account the ac system strength and the HVDC controls and evaluates their impact on the commutation process. The immunity of both single-infeed and multi-infeed systems to commutation failure phenomena are accurately evaluated and quantified by the CFII. Using the CFII, it is shown that the current commutation in multi-infeed HVDC schemes could fail under circumstances in which the probability of failure had been perceived to be low. The causes of, the effects of, and the remedial actions needed to deal with such anomalous commutation failures are discussed in this thesis. The capability of the new indices to provide an insight into the interactions phenomena in multi-infeed systems are clearly demonstrated by examples that show their application in the analysis of an actual multi-infeed HVDC system that is in the planning phase in the province of Alberta in Canada.

This research attempts to quantify the complex interactions between HVDC transmission schemes in a multi-infeed configuration, particularly with regard to the voltage interactions and the commutation failure phenomena. The in-depth analysis of multi-infeed HVDC systems discussed in this research shows the application of several indices such as the MIIF, MIESCR, and CFII, that can provide researchers and planning engineers in the area of HVDC transmission with the necessary tools for their system studies. It shows that these indices are applicable in a multi-infeed system comprising HVDC schemes with different ratings. The Multi-Infeed Interaction Factor (MIIF) quantifies the level of voltage interactions between converter ac buses. The Multi-Infeed Effective Short Circuit Ratio (MIESCR) index is an indicator of ac system strengths with regard to the assessment of the transient overvoltage (TOV) and the power-voltage stability of multi-infeed HVDC systems. The Commutation Failure Immunity Index (CFII) utilizes electromagnetic transient simulation programs to evaluate the immunity of an HVDC converter to commutation failures. The CFII takes into account the ac system strength and the HVDC controls and evaluates their impact on the commutation process. The immunity of both single-infeed and multi-infeed systems to commutation failure phenomena are accurately evaluated and quantified by the CFII. Using the CFII, it is shown that the current commutation in multi-infeed HVDC schemes could fail under circumstances in which the probability of failure had been perceived to be low. The causes of, the effects of, and the remedial actions needed to deal with such anomalous commutation failures are discussed in this thesis. The capability of the new indices to provide an insight into the interactions phenomena in multi-infeed systems are clearly demonstrated by examples that show their application in the analysis of an actual multi-infeed HVDC system that is in the planning phase in the province of Alberta in Canada.

[pt] Os Sistemas de Energia Elétrica (SEE) operam de acordo com limites de segurança definidos pelo planejamento da operação através de simulações computacionais. Portanto, os componentes da rede elétrica devem ser devidamente modelados para garantir uma operação segura e econômica. A tecnologia dos sistemas de medição fasorial sincronizada permite a obtenção de registros de distúrbios reais, que podem ser comparados com simulações para verificar sua aderência. Tem-se verificado nos atuais SEE diferenças entre os registros e as simulações computacionais dos eventos observados. Tais diferenças têm ocorrido também no Sistema Interligado Nacional (SIN), principalmente em relação ao desvio de frequência, sendo a resposta simulada menos severa quando comparada ao comportamento observado, podendo levar o SIN a operar em um ponto inseguro com risco de atuação de esquemas regionais de alívio de carga. Nesta dissertação são avaliados os modelos de usinas hidráulicas e termoelétricas e os parâmetros que podem influenciar significativamente a resposta das simulações, com ênfase no desempenho da frequência. Distúrbios que ocorreram no SIN são reproduzidos utilizando casos de tempo real, construídos a partir dos dados de estimadores de estado, em conjunto com uma base de modelos dinâmicos. Os resultados das simulações são comparados com os registros reais obtidos pelas PMUs (Phasor Measurement Unit) instaladas no SIN. Parâmetros como altura de queda, resposta dos reguladores de velocidade e modelagem dinâmica e estática das cargas são investigados. Impactos e simulações do fenômeno multi-infeed são apresentados. Os resultados obtidos mostram a necessidade de melhorias nos modelos e nos parâmetros de entrada das simulações de transitórios eletromecânicos do SIN. Ressalta-se a importância da contínua validação sistêmica e específica dos modelos para o planejamento da operação do SIN. / [en] Electric power systems (EPS) operate according to safety limits defined by the operation planning assessed through computer simulations. Therefore, the components of the electrical grid must be properly represented to ensure secure and economical operation. The technology of synchronized phasor measurement systems allows to obtain records of actual faults, which can be compared to simulation results to check their accuracy. Differences between records and computer simulations of the observed events have been verified in the current EPS. Such differences have also occurred in the Brazilian interconnected system (BIS), mainly related to frequency deviations, with the simulated response being less severe when compared to the observed performance. This may lead the BIS to operate under unsafe conditions, with risk of activating regional protection schemes for load shedding; a possible hasty and undesirable action. In this dissertation, the models of hydraulic and thermoelectric power plants and other parameters that can significantly influence the response of simulations are evaluated, with an emphasis on frequency performance. Disturbances that occurred in the BIS are reproduced using real-time cases, built from state estimator data, together with a collection of dynamic models. The simulation results are compared with the actual records obtained by PMUs (Phasor Measurement Units) installed in the BIS. Parameters such as hydropower head, response of speed regulators and dynamic and static modeling of loads are explored. Impacts and simulations of the multi-infeed phenomenon are also presented. The results show the need for improvements in the models and simulation input parameters of electromechanical transient studies of the BIS. There is a continuous need to observe the systemic and specific validation of models for planning and operation of the BIS.

The Brazilian transmission system covers a large area, with a high concentration of consumer centres in the Southeast region and abundant hydro generation in the North. To connect these regions, some of the transmission lines might reach 2500 km length, creating a challenging situation. In this context, system planners have been defining the use of HVDC systems as the most feasible choice of transmission investment. It is so, recognized that the connections of power plants in the Northern region to the load centres in the Southeast will require a significant number of bipoles and, until the present moment, all the operational and planned HVDC lines are based on the converter technology known as LCC (Line Commutated Converter) and consequently subject to commutation failure. Currently, the Brazilian system has four LCC bipoles, with two other bipoles under construction. Although the Southeast grid is strong, the connection of two additional bipoles is a concern as the interaction between these inverters may cause strong effects on one another, a phenomenon known as multi-infeed interaction. In such a situation, the assessment of the system operation, possible outages and possible mitigation methods are of paramount importance. This document presents a different methodology for the analysis of the multi-infeed system mentioned and focuses on its validation by analysing operation under normal conditions and with the implementation of established mitigation methods. The investigation was carried out with EMT, power flow, short-circuit and electromechanical softwares in a very large AC system composed by 100 buses on EMT and full Brazilian system on the rest. The effects of faults were analysed and the areas containing the buses where a fault leads to multiple commutation failures were identified. / O sistema de brasileiro de transmissão abrange uma área ampla, com uma alta concentração de consumo na região Sudeste e abundante geração hidrelétrica no Norte. Para conectar essas regiões, algumas das linhas de transmissão podem alcançar comprimentos de 2500 km, criando uma situação desafiadora. Neste contexto, os planejadores de sistemas têm definido o uso de sistemas HVDC como a escolha mais viável de investimento em transmissão. É então reconhecido que as conexões de usinas na região Norte aos centros consumidores no Sudeste exigirão um número significativo de bipolos e, até o momento presente, todas as linhas HVDC operacionais e planejadas são baseadas na tecnologia de conversão conhecida como LCC (Line Commutated Converter) e consequentemente sujeito a falha de comutação. Atualmente, o sistema brasileiro tem quatro bipolos LCC, com outros dois bipolos em construção. Embora a rede do Sudeste seja considerada forte, a conexão de dois bipolos adicionais é uma preocupação, pois a interação entre esses inversores pode causar efeitos danosos uns sobre os outros, um fenômeno conhecido como interação multi-infeed. Em tal situação, a avaliação da operação do sistema, possíveis interrupções e possíveis métodos de mitigação são de suma importância. Este documento apresenta uma metodologia diferente para a análise do sistema multi-infeed mencionado e foca em sua validação, analisando a operação em condições normais e com a implementação de métodos de mitigação conhecidos. A investigação foi realizada com softwares EMT, de curto circuito, fluxo de potência e estabilidade eletromecância em um sistema CA muito grande composto por 100 barras em EMT e sistema brasileiro completo no resto. Os efeitos das falhas foram analisados e as áreas que contêm as barras onde uma falha leva a múltiplas falhas de comutação foram identificadas.

The Brazilian transmission system covers a large area, with a high concentration of consumer centres in the Southeast region and abundant hydro generation in the North. To connect these regions, some of the transmission lines might reach 2500 km length, creating a challenging situation. In this context, system planners have been defining the use of HVDC systems as the most feasible choice of transmission investment. It is so, recognized that the connections of power plants in the Northern region to the load centres in the Southeast will require a significant number of bipoles and, until the present moment, all the operational and planned HVDC lines are based on the converter technology known as LCC (Line Commutated Converter) and consequently subject to commutation failure. Currently, the Brazilian system has four LCC bipoles, with two other bipoles under construction. Although the Southeast grid is strong, the connection of two additional bipoles is a concern as the interaction between these inverters may cause strong effects on one another, a phenomenon known as multi-infeed interaction. In such a situation, the assessment of the system operation, possible outages and possible mitigation methods are of paramount importance. This document presents a different methodology for the analysis of the multi-infeed system mentioned and focuses on its validation by analysing operation under normal conditions and with the implementation of established mitigation methods. The investigation was carried out with EMT, power flow, short-circuit and electromechanical softwares in a very large AC system composed by 100 buses on EMT and full Brazilian system on the rest. The effects of faults were analysed and the areas containing the buses where a fault leads to multiple commutation failures were identified. / O sistema de brasileiro de transmissão abrange uma área ampla, com uma alta concentração de consumo na região Sudeste e abundante geração hidrelétrica no Norte. Para conectar essas regiões, algumas das linhas de transmissão podem alcançar comprimentos de 2500 km, criando uma situação desafiadora. Neste contexto, os planejadores de sistemas têm definido o uso de sistemas HVDC como a escolha mais viável de investimento em transmissão. É então reconhecido que as conexões de usinas na região Norte aos centros consumidores no Sudeste exigirão um número significativo de bipolos e, até o momento presente, todas as linhas HVDC operacionais e planejadas são baseadas na tecnologia de conversão conhecida como LCC (Line Commutated Converter) e consequentemente sujeito a falha de comutação. Atualmente, o sistema brasileiro tem quatro bipolos LCC, com outros dois bipolos em construção. Embora a rede do Sudeste seja considerada forte, a conexão de dois bipolos adicionais é uma preocupação, pois a interação entre esses inversores pode causar efeitos danosos uns sobre os outros, um fenômeno conhecido como interação multi-infeed. Em tal situação, a avaliação da operação do sistema, possíveis interrupções e possíveis métodos de mitigação são de suma importância. Este documento apresenta uma metodologia diferente para a análise do sistema multi-infeed mencionado e foca em sua validação, analisando a operação em condições normais e com a implementação de métodos de mitigação conhecidos. A investigação foi realizada com softwares EMT, de curto circuito, fluxo de potência e estabilidade eletromecância em um sistema CA muito grande composto por 100 barras em EMT e sistema brasileiro completo no resto. Os efeitos das falhas foram analisados e as áreas que contêm as barras onde uma falha leva a múltiplas falhas de comutação foram identificadas.

Voltage stability is a challenging problem in the design and operation of terrestrial and shipboard power systems. DC links can be integrated in the AC systems to increase the transmission capacity or to enhance the distribution performance. However, DC links introduce voltage stability issues related to the reactive power shortage due to power converters. Multi-infeed DC systems make this existing phenomenon more complicated. In addition, shipboard power systems have unique characteristics, and some concepts and methodologies developed for terrestrial power systems need to be investigated and modified before they are extended for shipboard power systems. One goal of this work was to develop a systematic method for voltage stability assessment of hybrid AC/DC systems, independent of system configuration. The static and dynamic approaches have been used as complementary methods to address different aspects in voltage stability. The other goal was to develop or to apply voltage stability indicators for voltage stability assessment. Two classical indicators (the minimum eigenvalue and loading margin) and an improvement (the 2nd order performance indicator) have been jointly used for the prediction of voltage stability, providing information on the system state and proximity to and mechanism of instability. The eliminated variable method has been introduced to calculate the partial derivatives of AC/DC systems for modal analysis. The previously mentioned methodologies and the associated indicators have been implemented for the application of integrated shipboard power system including DC zonal arrangement. The procedure of voltage stability assessment has been performed for three test systems, the WSCC 3-machine 9-bus system, the benchmark integrated shipboard power system, and the modified I RTS-96. The static simulation results illustrate the critical location and the contributing factors to the voltage instability, and screen the critical contingencies for dynamic simulation. The results obtained from various static methods have been compared. The dynamic simulation results demonstrate the response of dynamic characteristics of system components, and benchmark the static simulation results.