11 research outputs found

    Analysis and mitigation of DC voltage imbalance for medium-voltage cascaded three-level neutral-point-clamped converters

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    The cascaded three-level neutral-point-clamped (3L-NPC) converter and the modular multi-level converter (MMC) are attractive solutions for medium-voltage direct-current (MVDC) applications. Due to their low cost compared to MMCs, cascaded 3L-NPC converters have been adopted in ANGLE-DCa 30 MVA MVDC link demonstration project in North Wales, UK. DC voltage imbalance across submodules (SMs) is a common challenge for both types of MVDC converters. Such imbalance is topology dependent and remains under-researched for cascaded 3L-NPC converters. In this paper, small-signal model-based analysis has been done to reveal that the dc voltage imbalance in cascaded 3L-NPC converters is caused by an unstable system pole. Two voltage balancing methods are presented. The first method is based on PI controllers to precisely regulate SMs voltages without influencing output power. However, it relies on communication between a central controller and local controllers within SMs. The second method uses inverse-droop based control to take over the dc voltage regulation upon loss of communication. Both balancing methods are experimentally validated using a 30 kVA testbed based on the ANGLE-DC project. It has been demonstrated that the dc voltages of SMs can be effectively balanced with both methods during changes of load conditions and dc bus voltages

    Decentralized control for multi-terminal cascaded medium-voltage converters considering multiple crossovers

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    Decentralized control with multiple droop characteristics can significantly improve the accuracy of power flow in medium-voltage direct-current (MVdc) networks. However, multiple crossovers caused by different control characteristics can lead to the drifts of power and voltage and instability issues. When this type of control is implemented in the cascaded three-level neutral-point-clamped (C3L-NPC) converters, on one hand, the mechanism of such the power and voltage drifts was not investigated. On the other hand, power control accuracy, dc voltage balancing across submodules (SMs) and multiple crossovers should all be considered, which requires suitable control methods. To address the challenges, firstly, the mechanism behind the power and dc voltage drifts is analyzed. Secondly, a control scheme is presented to improve the power control accuracy and dc voltage balancing and concurrently, to avoid the multiple crossovers. This is achieved by suitable droop gain design and adding a secondary power compensator. The presented control scheme is verified in MATLAB/Simulink simulation and experimentally validated in a three-terminal MVdc testbed. Results show that the accuracy of steady-state power flow is improved by 15% due to the elimination of multiple crossovers, while the power accuracy at dynamics improved by 13% with the secondary power compensato

    Active control of medium-voltage cascaded three-level neutral-point-clamped converters

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    Three-Level Neutral-Point-Clamped (3L-NPC) converters have been widely used in the high-power motor drives. In recent years, a novel cascaded 3L-NPC converter has been developed and adopted in the ANGLE-DC project − a 30 MVA MVDC link demonstration project in North Wales, UK. This cascaded configuration provides exceptional waveform quality, modular design and a cost-effective solution to MVDC applications. Although the control strategy for a single 3L-NPC converter has been well established, control of the cascaded 3L-NPC converter is still under-researched. The potential challenges to control strategy design arising from their cascaded connections need to be specifically explored. In particular, due to the series DC connection, the voltage imbalance across 3L-NPC submodules (SMs) may occur and influence the system stability. This issue may occur in converter stations where power is controlled in either point-to-point or multi-terminal systems. Beyond the electric characteristic, thermal characteristic is also vital to the performance of system. Thermal imbalance of 3L-NPC SMs may occur in a cascaded 3L-NPC converter even the voltage and power are equally shared, which poses great challenges to the system reliability. To address aforementioned challenges, this thesis developed suitable control schemes for the cascaded 3L-NPC converter system and demonstrated their operation using a 30 kVA MVDC testbed based on the real ANGLE-DC project. The DC voltage imbalance was analysed through a small-signal model-based approach. Two DC voltage balancing methods with and without communications were presented. The PI-based method can automatically switch to the droop-based method upon failures of communication. The DC voltage imbalance of the cascaded 3L-NPC converter is further investigated in a three-terminal MVDC network in consideration together with the interactions of control characteristics between different converter stations and the power control accuracy. Then suitable control scheme was proposed. Multiple crossovers due to the interactions are avoided while DC voltage balance and power control accuracy are achieved as well. To mitigate the thermal imbalance, a thermal sharing controller was superposed on the DC voltage balancing controller to regulate the active and reactive power of each SM according to their individual junction temperatures. The thermal stresses are hence equally shared in presence of mismatched component parameters and cooling system failures. The effectiveness of presented methods in the thesis has been verified in MATLAB/Simulink simulation and experimentally validated

    Modular DC/DC converter topologies for off-shore DC collection point

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    PhD ThesisWith the development of the economy, the demand for energy has been substantially growing. Wind power, particularly from offshore wind farms, is one of the best solutions. In Europe, installed capacity had exceeded 8GW by 2105 and will probably reach 40GW in 2020. These ambitious plans require the establishment of large-scale wind farms with more efficient transmission systems. The high voltage direct current (HVDC) transmission system is an effective way to deliver large-scale energy over long distances with lower power losses. However, due to the growth of large-scale offshore wind energy system, the connection between the farms and HVDC transmission lines is more challenging. Medium-voltage DC (MVDC) collection networks are a promising technology for such integration, aiming to eliminate voltage difference. High-voltage high-power DC/DC converters are the key enabler for MVDC grids. But the present lack of suitable high-voltage high-power DC/DC converter topologies is preventing the development of DC networks. Several high-voltage high-power topologies have proposed in previous studies, but most such topologies involve design compromises in terms of switching losses, limited conversion ratios, and lack of modular design, lack of electrical isolation features. This thesis presents three novel modular DC/DC topologies, which are developed based on the conventional modular multilevel converter (MMC), to enable the integration of off-shore wind farms with high voltage direct current (HVDC) transmission systems. The first topology is a unidirectional single-phase modular DC/DC converter, and the second is a unidirectional threephase modular DC/DC converter consisting of a windfarm-side three-phase modular multilevel (MMC) inverter and a series-connected diode rectifier module linked by a special decoupled medium frequency transformer. The third topology is a bidirectional three-phase modular DC/DC converter where a three-phase MMC inverter produces a controllable AC voltage connected at the primary side of a three-phase decoupled medium frequency transformer. The secondary output voltages decoupled into three identical but 120-degree phase-shifted voltages. Simulations using MATLAB/Simulink are reported to demonstrate the effectiveness of the proposed converters. Moreover, a low voltage scaled-down prototype of the unidirectional II single-phase modular DC/DC converter is developed to validate its feasibility experimentally. Keywords: Modular multilevel converter, offshore wind farm, unidirectional/bidirectional modular DC/DC converters, HVDC system.Scottish Energ

    Analysis and Development of Multiple Phase Shift Modulation in A SiC-Based Dual Active Bridge Converter

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    Renewable energy adoption is a popular topic to release the stress of climate change caused by greenhouse gas. Electricity is ideal secondary energy for clean primary energy such as nuclear, wind, photovoltaic, and so on. To extend the application of electricity and reduce fossil energy consumption by transportation sectors, electric vehicles (EVs) become promising technology that can further inspire the development of renewable energy. Battery as the core in an EV provides the energy to the motor and all on-board electric equipment. The battery charger is mainly composed of a power factor correction (PFC) and isolated DC-DC converter. Therefore, power electronics equipment plays an important role in automotive products. Meanwhile, in recent years, the market capacity for wide band-gap devices, SiC MOSFET, continues to increase in EV applications. Dual active bridge (DAB) is an excellent candidate for isolated DC-DC converter in EV battery charger. The characteristics include an easy control algorithm, galvanic isolation and adjustable voltage gain. Different modulation strategies are developed to improve the performance and stability by using multiple phase shift (MPS) control. This thesis focuses on the utilization of different modulation strategies to realize smooth transition among MPS control in full operational range with securing zero-voltage-switching (ZVS) to eliminate the crosstalk in the hard-switching process. The influence of MPS control on ZVS resonance transient is also addressed to find out the accurate minimum required energy of the inductor to finish the ZVS transition. Furthermore, a general common-mode voltage model for DAB is proposed to analyze the impact of MPS control on the common-mode performance

    Fault Tolerant DC–DC Converters at Homes and Offices

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    The emergence of direct current (DC) microgrids within the context of residential buildings and offices brings in a whole new paradigm in energy distribution. As a result, a set of technical challenges arise, concerning the adoption of efficient, cost-effective, and reliable DC-compatible power conditioning solutions, suitable to interface DC microgrids and energy consuming elements. This thesis encompasses the development of DC–DC power conversion solutions, featuring improved availability and efficiency, suitable to meet the requirements of a comprehensive set of end-uses commonly found in homes and offices. Based on the energy consumption profiles and requirements of the typical elements found at homes and offices, three distinctive groups are established: light-emitting diode (LED) lighting, electric vehicle (EV) charging, and general appliances. For each group, a careful evaluation of the criteria to fulfil is performed, based on which at least one DC–DC power converter is selected and investigated. Totally, a set of five DC–DC converter topologies are addressed in this work, being specific aspects related to fault diagnosis and/or fault tolerance analysed with particular detail in two of them. Firstly, mathematical models are described for LED devices and EV batteries, for the development of a theoretical analysis of the systems’ operation through computational simulations. Based on a compilation of requirements to account for in each end-use (LED lighting, EV charging, and general appliances), brief design considerations are drawn for each converter topology, regarding their architecture and control strategy. Aiming a detailed understanding of the two DC–DC power conversion systems subjected to thorough evaluation in this work – interleaved boost converter and fault-tolerant single-inductor multiple-output (SIMO) converter – under both normal and abnormal conditions, the operation of the systems is evaluated in the presence of open-circuit (OC) faults. Parameters of interest are monitored and evaluated to understand how the failures impact the operation of the entire system. At this stage, valuable information is obtained for the development of fault diagnosis strategies. Taking profit of the data collected in the analysis, a novel fault diagnostic strategy is presented, targeting interleaved DC–DC boost converters for general appliances. Ease of implementation, fast diagnostic and robustness against false alarms distinguish the proposed approach over the state-of-the-art. Its effectiveness is confirmed through a set of operation scenarios, implemented in both simulation environment and experimental context. Finally, an extensive set of reconfiguration strategies is presented and evaluated, aiming to grant fault tolerance capability to the multiple DC–DC converter topologies under analysis. A hybrid reconfiguration approach is developed for the interleaved boost converter. It is demonstrated that the combination of reconfiguration strategies promotes remarkable improvements on the post-fault operation of the converter. In addition, an alternative SIMO converter architecture, featuring inherent tolerance against OC faults, is presented and described. To exploit the OC fault tolerance capability of the fault-tolerant SIMO converter, a converter topology targeted at residential LED lighting systems, two alternative reconfiguration strategies are presented and evaluated in detail. Results obtained from computational simulations and experimental tests confirm the effectiveness of the approaches. To further improve the fault-tolerant SIMO converter with regards to its robustness against sensor faults, while simplifying its hardware architecture, a sensorless current control strategy is presented. The proposed control strategy is evaluated resorting to computational simulations.O surgimento de micro-redes em corrente contínua (CC) em edifícios residenciais e de escritórios estabelece um novo paradigma no domínio da distribuição de energia. Como consequência disso, surge uma panóplia de desafios técnicos ligados à adopção de soluções de conversão de energia, compatíveis com CC, que demonstrem ser eficientes, rentáveis e fiáveis, capazes de estabelecer a interface entre micro-redes em CC e as cargas alimentadas por esse sistema de energia. Até aos dias de hoje, os conversores CC–CC têm vindo a ser maioritariamente utilizados em aplicações de nicho, que geralmente envolvem níveis de potência reduzidos. Porém, as perspectivas futuras apontam para a adopção, em larga escala, destas tecnologias de conversão de energia, também em equipamentos eléctricos residenciais e de escritórios. Tal como qualquer outra tecnologia de conversão electrónica de potência, os conversores CC–CC podem ver o seu funcionamento afectado por falhas que degradam o seu bom funcionamento, sendo que essas falhas acabam por afectar não apenas os conversores em si, mas também as cargas que alimentam, limitando assim o tempo de vida útil do conjunto conversor + carga. Desta forma, é fulcral localizar a origem da falha, para que possam ser adoptadas acções correctivas, capazes de limitar as consequências nefastas associadas à falha. Para responder a este desafio, esta tese contempla o desenvolvimento de soluções de conversão de energia CC–CC altamente eficientes e fiáveis, capazes de responder a requisitos impostos por um conjunto alargado de equipamentos frequentemente encontrados em habitações e escritórios. Com base nos perfis de consumo de energia eléctrica e nos requisitos impostos pelas cargas tipicamente utilizadas em habitações e escritórios, são estabelecidos três grupos distintos: iluminação através de díodos emissores de luz, carregamento de veículo eléctrico (VE) e aparelhos eléctricos em geral. Para cada grupo, é efectuada uma avaliação cuidadosa dos critérios a respeitar, sendo com base nesses critérios que será escolhida e investigada pelo menos uma topologia de conversor CC–CC. No total, são abordadas cinco topologias de conversores CC–CC distintas, sendo que os aspectos ligados ao diagnóstico de avarias e/ou tolerância a falhas são analisados com particular detalhe em duas dessas topologias. Inicialmente, são estabelecidos modelos matemáticos descritivos do comportamento das principais cargas consideradas no estudo – díodos emissores de luz e baterias de VEs – visando a análise teórica do funcionamento dos sistemas em estudo, suportada por simulações computacionais. Com base numa compilação de requisitos a ter em conta em cada aplicação – iluminação através de díodos emissores de luz, carregamento de veículo eléctrico (VE) e aparelhos eléctricos em geral – são estabelecidas considerações ligadas à escolha de cada topologia de conversor não isolado, no que respeita à sua arquitectura e estratégia de controlo. Visando o conhecimento aprofundado das duas topologias de conversor CC–CC alvo de particular enfoque neste trabalho – conversor entrelaçado elevador e conversor de entrada única e múltiplas saídas, tolerante a falhas – quer em funcionamento normal, quer em funcionamento em modo de falha, é avaliado o funcionamento de ambas as topologias na presença de falhas de circuito aberto nos semicondutores activos. Para o efeito, são monitorizados e analisados parâmetros úteis à percepção da forma como os modos de falha avaliados neste trabalho impactam o funcionamento de todo o sistema. Nesta fase, é obtida informação fundamental ao desenvolvimento de estratégias de diagnóstico de avarias, particularmente indicadas para avarias de circuito aberto nos semicondutores activos dos conversores em estudo. Com base na informação recolhida anteriormente, é apresentada uma nova estratégia de diagnóstico de avarias direccionada a conversores CC–CC elevadores entrelaçados utilizados em aparelhos eléctricos, em geral. Facilidade de implementação, rapidez e robustez contra falsos positivos são algumas das características que distinguem a estratégia proposta em relação ao estado da arte. A sua efectividade é confirmada com recurso a uma multiplicidade de cenários de funcionamento, implementados quer em ambiente de simulação, quer em contexto experimental. Por fim, é apresentada e avaliada uma gama alargada de estratégias de reconfiguração, que visam assegurar a tolerância a falhas das diversas topologias de conversores CC–CC em estudo. É desenvolvida uma estratégia de reconfiguração híbrida, direccionada ao conversor entrelaçado elevador, que combina múltiplas medidas de reconfiguração mais simples num único procedimento. Demonstra-se que a combinação de múltiplas estratégias de reconfiguração introduz melhorias substanciais no funcionamento do conversor ao longo do período pós-falha, ao mesmo tempo que assegura a manutenção da qualidade da energia à entrada e saída do conversor reconfigurado. Noutra frente, é apresentada e descrita uma arquitectura alternativa do conversor de entrada única e múltiplas saídas, com tolerância a falhas de circuito aberto. Através da configuração proposta, é possível manter o fornecimento de energia eléctrica a todas as saídas do conversor. Para tirar máximo proveito da tolerância a falhas do conversor de entrada única e múltiplas saídas, uma topologia de conversor indicada para sistemas residenciais de iluminação baseados em díodos emissores de luz, são apresentadas e avaliadas duas estratégias de reconfiguração do conversor, exclusivamente baseadas na adaptação do controlo aplicado ao conversor. Os resultados de simulação computacional e os resultados experimentais obtidos confirmam a efectividade das abordagens adoptadas, através da melhoria da qualidade da energia eléctrica fornecida às diversas saídas do conversor. São assim asseguradas condições essenciais ao funcionamento ininterrupto e estável dos sistemas de iluminação, já que a qualidade da energia eléctrica fornecida aos sistemas de iluminação tem impacto directo na qualidade da luz produzida. Por fim, e para aprimorar o conversor de entrada única e múltiplas saídas tolerante a falhas, no que respeita à sua robustez contra falhas em sensores, é apresentada uma estratégia de controlo de corrente que evita o recurso excessivo a sensores e, ao mesmo tempo, simplifica a estrutura de controlo do conversor. A estratégia apresentada é avaliada através de simulações computacionais. A abordagem apresentada assume vantagens em múltiplos domínios, sendo de destacar vantagens como a melhoria da fiabilidade de todo o sistema de iluminação (conversor + carga), os ganhos atingidos ao nível do rendimento, a redução do custo de implementação da solução, ou a simplificação da estrutura de controlo.This work was supported by the Portuguese Foundation for Science and Technology (FCT) under grant number SFRH/BD/131002/2017, co-funded by the Ministry of Science, Technology and Higher Education (MCTES), by the European Social Fund (FSE) through the ‘Programa Operacional Regional Centro’ (POR-Centro), and by the Human Capital Operational Programme (POCH)

    3단 구성을 가지는 단상 반도체 변압기의 신뢰성 향상을 위한 분산 제어 방법

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    학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2017. 2. 조보형.본 논문에서는 단상 SST의 신뢰성 제고 방안에 대해서 연구하였다. 중앙 제어기가 담당하는 역할을 최소화하는 분산 제어 방법을 제안하고 이를 검증하여 SST 신뢰성 향상에 기여하고자 하였다. 연구의 대상이 된 회로는 CHB 컨버터의 AC-DC단, 다중 모듈 DAB 컨버터의 DC-DC단, 인버터의 DC-AC단으로 이루어진 3단 구성 SST이다. 단, 분산 제어를 통한 신뢰성 향상은 다중 모듈인 경우에만 검증이 가능하므로 통상 단일 모듈로 구성되는 DC-AC단을 제외한 AC-DC단과 DC-DC단을 논의의 대상으로 한정하였다. CHB 컨버터의 분산 제어 방법으로 피드포워드 기반의 간접 전류 제어 방법을 제안하였다. 제안한 방법에서는 간접 전류 제어를 통한 분산 제어 방법으로 n개 모듈의 (n+1)개의 상태 변수(1개의 입력 전류 + n개의 DC-link 전압)를 제어할 수 있다. 단, 제안한 방법을 통해 각 CHB 모듈의 출력 전압이 기준 전압으로 수렴하기 위해서는 각 CHB 모듈이 전력을 전달 받는 속도가 모두 달라야 한다. 이를 달성하기 위하여 간접 전류 제어를 위한 피드포워드 계수를 도입하였다. 그 결과, 각 CHB 모듈의 출력 전압이 기준 전압으로 수렴할 수 있다. 제안하는 방법의 성능에 대해서는 CHB 컨버터의 소신호 모델을 기반으로 분석을 수행하였다. 한편, 각 CHB 모듈이 DC-link 전압을 제어하고 있는데 모듈 간 전력 균등 분배가 이루어지지 않을 경우에 전력 변환의 품질이 떨어질 수 있다. 또한 과도하게 전력을 공급하는 모듈의 고장 확률이 증가하여 시스템의 신뢰성이 떨어지게 된다. 이에 다중 모듈 DAB 컨버터에 대해서는 CHB 컨버터와 DAB 컨버터의 전력 전달 원리를 이용한 분산 제어 방법을 제안하여 모듈 간 전력 균등 분배를 달성하고자 하였다. CHB 컨버터에서 간접 전류 제어 시 d축 제어 지령 정보는 DAB 컨버터의 전력 정보를 가지게 된다. 따라서 DAB 컨버터는 CHB 컨버터의 d축 제어 지령을 피드백 정보로 이용하여 모듈 간 전력 균형을 달성할 수 있다. 제안한 제어의 성능을 분석하였으며, 이를 바탕으로 피드백 계수의 설계가 가능하도록 하였다. 제안된 분산 제어 방법들의 유효성을 3개 모듈로 이루어진 하드웨어를 구축하여 실험으로 검증하였다. 그 결과 CHB 컨버터 단에서는 d축 상 전압 제어와 q축 피드포워드 입력을 통해 지령의 입력 전류가 형성되는 것을 확인하였다. 또한 1이 아닌 역률을 이용해 제어 지령 공유 없이 3개 모듈이 각각의 출력 전압을 기준 전압으로 잘 제어하고 있음을 확인하였다. 다중 모듈 DAB 컨버터 단에서는 CHB 컨버터 단의 d축 제어 지령 정보를 이용하여 제어 지령 공유 없이 3개 모듈 간 전력 분배 특성을 크게 향상 할 수 있음을 확인하였다. 이상의 제안된 분산 제어 방법들을 통해 중앙 제어기가 담당하는 역할을 전체 시스템 운영 지침 전달 및 모듈 고장 정보 관장 등의 보조 기능들로 축소할 수 있다. 그 결과 백업 시스템 구축이 간편해져 SST 시스템의 신뢰성 향상, 단순화 및 비용 저감 등의 효과를 기대할 수 있을 것으로 판단된다.제 1 장 서론 1 1.1 연구의 배경 1 1.1.1 반도체 변압기의 활용과 전망 1 1.1.2 반도체 변압기의 과제 5 1.2 연구의 목적 및 범위 10 1.3 논문의 구성 13 제 2 장 반도체 변압기의 기존 연구 14 2.1 회로 구성 14 2.1.1 중전압 교류 대응 방법에 따른 분류 14 2.1.2 전력 변환단 수에 따른 분류 21 2.1.3 본 논문의 연구 대상이 될 회로 구성 25 2.2 제어 방법 26 2.2.1 반도체 변압기의 기존 제어 방법론 27 2.3 신뢰성 향상 방안 33 2.3.1 시스템 구성에 따른 신뢰도 특성 33 2.3.2 기존 신뢰성 향상 방안의 한계점 38 2.3.3 제안하는 신뢰성 향상 방안 40 제 3 장 CHB 컨버터에 적용 가능한 신뢰성 향상 방안 43 3.1 dq 동기 좌표계에서의 CHB 컨버터 모델링 43 3.1.1 dq 변환 43 3.1.2 CHB 컨버터 모델링 44 3.2 제안한 분산 제어 방법 49 3.2.1 H-Bridge 컨버터의 간접 전류 제어 50 3.2.2 CHB 컨버터의 간접 전류 제어 54 3.2.3 제안한 방법의 성능 분석 59 3.3 소신호 분석 및 제어기 설계 61 3.3.1 소신호 모델 입력단의 디커플링화 63 3.3.2 CHB 컨버터의 제어 분석 65 3.3.3 개별 모듈의 제어 분석 74 3.4 멀티 레벨 동작을 위한 PWM 동기화 80 3.5 모의 실험 결과 84 3.5.1 제안한 방법 동작 확인에 대한 모의 실험 85 3.5.2 특정 모듈 고장 탈락 상황에 대한 모의 실험 91 제 4 장 다중 모듈 DAB 컨버터에 적용 가능한 신뢰성 향상 방안 100 4.1 전력 균등 분배의 필요성 100 4.2 DAB 컨버터 103 4.2.1 동작 원리 103 4.2.2 PSM 기법 106 4.3 제안한 분산 제어 방법 109 4.3.1 다중 모듈 DAB 컨버터의 분산 제어 방법 110 4.3.2 제안한 방법의 성능 분석 111 4.4 모의 실험 결과 114 4.4.1 kDAB = 2 x 10-5인 경우 114 4.4.2 kDAB = 2 x 10-4인 경우 116 제 5 장 실험 및 결과 119 5.1 시스템 구성 119 5.2 제안한 방법의 설계 122 5.3 실험 결과 124 5.3.1 PLL 동작 확인 124 5.3.2 CAN 통신 동작 확인 126 5.3.3 CHB 컨버터의 분산 제어 실험 결과 129 5.3.4 다중 모듈 DAB 컨버터의 분산 제어 실험 결과 131 제 6 장 결론 및 향후 과제 137 6.1 결론 137 6.2 향후 과제 139 참고문헌 142 부 록 160 Abstract 168Docto

    Operation, Monitoring, and Protection of Future Power Systems: Advanced Congestion Forecast and Dynamic State Estimation Applications

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    The electrical power systems are undergoing drastic changes such as increasing levels of renewable energy sources, energy storage, electrification of energy-efficient loads such as heat pumps and electric vehicles, demand-side resources, etc., in the last decade, and more changes will be followed in the near future. The emergence of digitalization and advanced communication in the case of distribution systems to enhance the performance of the electricity infrastructure also adds further complexities. These changes pose challenges such as increased levels of network congestion, voltage variations, protection mis-operations, increased needs for real-time monitoring, and improved planning practices of the system operators. These challenges will require the development of new paradigms to operate the power grids securely, safely, and economically. This thesis attempted to address those challenges and had the following main contributions:First, the thesis started by presenting a comprehensive assessment framework to address the distribution system operators’ future-readiness and help the distribution system operators to determine the current status of their network infrastructures, business models, and policies and thus identify the pathways for the required developments for the smooth transition towards future intelligent distribution grids.Second, the thesis presents an advanced congestion forecast tool that would support the distribution system operators to forecast and visualize network congestion and voltage variations issues for multiple forecasting horizons ranging from close-to-real time to a day-ahead. The tool is based on a probabilistic power flow that incorporates forecasts of solar photovoltaic production and electricity demand, combined with advanced load models and different operating modes of solar photovoltaic inverters. The tool has been integrated to an existing industrial graded distribution management system via an IoT platform Codex Smart Edge of Atos Worldgrid. The results from case studies demonstrated that the tool performs satisfactorily for both small and large networks and can visualise the cumulative probabilities of network congestion and voltage variations for a variety of forecast horizons as desired by the distribution system operator.Third, a dynamic state estimation-based protection scheme for the transmission lines which does not require complicated relay settings and coordination has been demonstrated using an experimental setup at Chalmers power system laboratory. The scheme makes use of the real-time measurements provided by advanced sensors which are developed by Smart State Technology, The Netherlands. The experimental validations of the scheme have been performed under different fault types and conditions, e.g., unbalanced faults, three-phase faults, high impedance faults, hidden failures, inductive load conditions, etc. The results have shown that the scheme performs adequately in both normal and fault conditions and thus the scheme would work for transmission line protection by avoiding relay coordination and settings issues.Finally, the thesis presents a decentralized dynamic state estimation method for estimating the dynamic states of a transmission line in real-time. This method utilizes the sampled measurements from the local end of a transmission line, and thereafter dynamic state estimation is performed by employing an unscented Kalman filter. The advantage of the method is that the remote end state variables of a transmission line can be estimated using only the local end variables and, hence, the need for communication infrastructure is eliminated. Furthermore, an exact nonlinear model of the transmission line is utilized and the dynamic state estimation of one transmission line is independent of the other lines. These features in turn result in reduced complexity, higher accuracy, and easier implementation of the decentralized estimator. The method is envisioned to have potential applications in transmission line monitoring, control, and protection

    2016 Oklahoma Research Day Full Program

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    This document contains all abstracts from the 2016 Oklahoma Research Day held at Northeastern State University
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