Search

This paper presents a cost estimation study for several rail power conditioner (RPC) topologies based on an indirect modular multilevel converter (MMC), in which these topologies are combined with V/V or Scott power transformers. The RPC topologies under interest in this paper are: the RPC based on a full-bridge MMC (RPC based on MMC4), the RPC based on two-phase three-wire MMC (RPC based on MMC3), and the RPC based on a half-bridge MMC (RPC based on MMC2). These RPC systems operate at medium voltage levels in the interconnection to 25 kV-50 Hz catenary sections to solve power quality problems, such as the current harmonics and the negative sequence components (NSCs) of currents. Along the paper are described the V/V and the Scott power transformers, the RPC main architectures, and the estimated cost of implementation for each RPC topology considering V/V or Scott implementations. As main contribution, the presented results could help in the selection procedure of the RPC topology, giving the best economical solution according to the used power transformer (V/V or Scott)., This work has been supported by FCT – Fundação para a Ciência e Tecnologia within the Project Scope: UID/CEC/00319/2019. This work has been supported by FCT within the Project Scope DAIPESEV – Development of Advanced Integrated Power Electronic Systems for Electric Vehicles: PTDC/EEI-EEE/30382/2017. Mohamed Tanta is supported by the doctoral scholarship with a reference PD/BD/127815/2016 granted by the Portuguese FCT agency.

The Modular Multilevel Converter (MMC) has become progressively an attractive solution for the medium-power and the high-power applications, due to its modularity, flexibility of redundancy or scalability, high efficiency and low production of harmonic contents. However, in order to have a reliable and robust MMC system, different concerns should be observed in terms of the converter control complexity and the required effective protection system. In this context, this paper presents a novel hardware protection topology for the MMC half-bridge submodule. The introduced scheme is based on new sensors technology that can be assembled near the power hardware, resulting in less perturbation and a very low signal delay. This allows the protection system to respond quickly to fault situations. The proposed protection scheme of half-bridge MMC submodules is a new contribution given the steadily increasing popularity of the MMC and that just a few scientific publications treat in detail the protection mechanisms of half-bridge submodules for MMC. The experimental results confirm the effectiveness of the proposed scheme after creating the fault overvoltage and overcurrent conditions on one MMC half-bridge submodule., This work has been supported by national funds through FCT – Fundação para a Ciência e Tecnologia within the Project Scope: UID/CEC/00319/2019. This work has been supported by FCT Project DAIPESEV PTDC/EEI-EEE/30382/2017 and by the ERDF – European Regional Development Fund through the Operational Programme for Competitiveness and Internationalisation – COMPETE 2020 Programme, and by National Funds through the Portuguese funding agency, FCT, within project SAICTPAC/0004/2015 – POCI –01–0145–FEDER–016434. Mohamed Tanta was supported by FCT PhD grant with a reference PD/BD/127815/2016.

Programa doutoral em Engenharia Electrónica e de Computadores, Railway systems have progressively been developed since James Watt presented a technique of converting steam power into a circular movement back in 1763. With the novelty of steam engines at that time and the increasing of railway networks, railway industry quickly became an economic catalyst throughout the world due to the advantages of passenger and freight transport. In 1879, Siemens & Halske company introduced the world’s first electric train in the city of Berlin, consisting of a locomotive and three wagons, and supplied via an insulated third rail with 150 V direct current (DC). From that time, the world has begun to recognize the important transition from steam power to electric power, and the potential of the electrified railway as a mode of mass transport. Due to the plenty of fuel in the last century, Diesel trains were not only common, but they also dominated the railway sector for a few decades. Consequently, the development in the infrastructures of electric trains decelerated, and the path to having fully electrified trains was long enough. In this context, electric trains have introduced progressively, in which Diesel and electric power have been combined to create hybrid locomotives. However, and with the increased demand for transportation and the higher fuel prices in the last decades, electric trains can substantially offer lower operating costs and lower emissions compared with the Diesel-powered trains. Nowadays, most of the high-speed electric trains use alternating current (AC) power supply for their traction power systems, which provide better performance under long-distance power transmission than DC power supply. However, as the need for railway transportation increases due to more passengers and higher mobility requirements, more flexible and efficient traction systems are always needed. In Europe, AC traction power systems are mainly classified according to the voltage and frequency parameters (15 kV, 16.7 Hz) or (1×25 kV or 2×25 kV, 50 Hz). In all cases, railway operators have an absolute interest to run the electrified trains with the lowest possible operation and maintenance costs. In this context, power quality improvement at the three-phase power grid, associated with the AC electrified railway has drawn more attention in the last decades, especially after the evolution in the Power Electronics field. Subsequently, various solutions based on Power Electronics converters have been proposed to improve power quality in the electrified railway, e.g., the flexible AC transmission systems (FACTS). The rail power conditioner (RPC) is one of the FACTS devices that can be used to improve power quality by compensating harmonic contents, reactive power and negative sequence components of currents generated by the railway system. Among the other possible multilevel power converters, the modular multilevel converter (MMC) is an attractive solution for medium-voltage applications due to harmonics reduction, lower switching losses, and higher flexibility, scalability and reliability. Therefore, the MMC has been enhanced to be combined with the FACTS family. Taking into consideration the existing opportunities in the railway industry, not only in the development of the electric train itself, but also on the power quality improvement in the electrified railway, there is a strong investment in technological development for electrified railway systems. Therefore, this work presents a new topology of Power Electronics converter (RPC based on MMC) that compensates power quality problems associated with traction power systems, thus, reducing the operating costs of the electrified trains and increasing the power capacity of the electric traction grid. The main innovations of the RPC based on MMC are the integration of the MMC topology to operate as a railway power quality conditioner, benefiting from the advantages of the MMC in the traction power supply system. In this context, the research work proposed and developed in this Ph.D. thesis aimed to design, develop and validate a reduced-scale laboratory prototype of the RPC based on MMC, including all the necessary control algorithms and simulation models that are important to support the correct operation of the proposed system. Under simulation conditions, this work developed control algorithms for different RPC topologies, (full-bridge, half-bridge, three-wire, etc.) for demonstrating the general capabilities of the RPC system, and also for two different transformers connections (V/V and Scott). The most favorable RPC based on MMC topology (based on half-bridge MMC) was deeply and extensively simulated, namely employing predictive control approach. The experimental results obtained from a developed reduced-scale prototype confirm the validity of the presented control theory, as well as the power quality improvement capability of the proposed solution., Os sistemas ferrovias foram progressivamente desenvolvidos desde que James Watt apresentou uma técnica de conversão da energia a vapor para um movimento circular em 1763. Com a novidade dos motores a vapor e a sua implementação nas redes ferroviárias, a indústria ferroviária rapidamente se tornou um catalisador econômico em todo o mundo devido às vantagens no transporte de passageiros e mercadorias. Em 1879, a empresa Siemens & Halske introduziu o primeiro comboio elétrico do mundo na cidade de Berlim, consistindo numa locomotiva com três vagões, alimentado por um terceiro trilho isolado alimentado com corrente contínua em 150 V (CC). A partir desse momento, o mundo começou a reconhecer a importante transição da energia a vapor para a energia elétrica e o potencial na ferrovia eletrificada como um meio de transporte de massa. Devido à abundância de combustível fóssil no século passado, os comboios a Diesel não eram apenas comuns, mas também dominaram o setor ferroviário. Consequentemente, o desenvolvimento das infraestruturas dos comboios elétricos desacelerou, e o caminho para haver comboios totalmente eletrificados tornou-se bastante longo. Nesse contexto, os comboios elétricos começaram a impor-se progressivamente, inicialmente pela combinação do motor Diesel e do motor elétrico, resultando numa locomotiva híbrida. No entanto, com o aumento da demanda pelo transporte, e com o aumento do preço dos combustíveis nas últimas décadas, os comboios elétricos afirmaram-se por poderem oferecer custos operacionais mais baixos, assim como melhor desempenho ambiental. Atualmente, a maioria dos comboios elétricos de alta velocidade utilizam sistema de tração em corrente alternada (CA), que oferece melhor desempenho na transmissão de energia a longa distância do que sistema de tração em corrente contínua CC. No entanto, o aumento do transporte ferroviário requer a melhoria da eficiência energética devido a haver mais passageiros e maiores requisitos de mobilidade. Na Europa, os sistemas de tração elétrica são classificados principalmente de acordo com os parâmetros de tensão e frequência (15 kV, 16,7 Hz) ou (1×25 kV ou 2×25 kV, 50 Hz). Em ambos os casos, os operadores ferroviários têm interesse absoluto em otimizar os custos. Nesse contexto, a melhoria da qualidade de energia elétrica na ferrovia suscitou mais atenção nas últimas décadas, principalmente pela introdução da eletrônica de potência. Posteriormente, várias soluções baseadas em conversores de eletrônica de potência foram propostas para melhorar a qualidade de energia elétrica na ferrovia, como por exemplo, os sistemas flexíveis de transmissão CA (FACTS – Flexible AC Transmission Systems). O condicionador ativo de potência ferroviário (RPC – Rail Power Conditioner) é um dos dispositivos FACTS que pode ser usado para melhorar a qualidade da energia elétrica, compensando o conteúdo harmônico, a potência reativa e os componentes de sequência negativa das correntes. Por outro lado, o conversor multinível modular (MMC – Modular Multilevel Converter) é uma solução atraente para aplicações de média tensão, devido à redução dos harmónicos e das perdas de comutação, e ao aumento da flexibilidade, confiabilidade e escalabilidade. Deste modo, o MMC foi aprimorado para ser integrado na família FACTS. Levando em consideração as oportunidades existentes no setor ferroviário, não apenas no desenvolvimento do próprio comboio elétrico, mas também na melhoria da qualidade de energia elétrica na ferrovia, existe um forte investimento no desenvolvimento tecnológico para os sistemas ferroviários eletrificados. Assim sendo, este trabalho apresenta uma nova topologia de conversor de eletrônica de potência (RPC baseado em MMC) que compensa os problemas de qualidade de energia elétrica associados aos sistemas de tração, reduzindo os custos operacionais dos comboios elétricos e otimizando a qualidade de energia da rede elétrica. As inovações principais do RPC baseado em MMC são a integração da topologia do MMC para operar como condicionador de qualidade de energia elétrica na ferrovia, beneficiando das vantagens do MMC. Neste contexto, o trabalho de investigação proposto e desenvolvido nesta tese apontou como objetivo projetar, desenvolver e validar um protótipo laboratorial em escala reduzida do RPC baseado em MMC, incluindo todos os algoritmos de controlo necessários e os modelos de simulação que são importantes para suportar a operação correta do sistema. Sob condições de simulação, este trabalho desenvolveu algoritmos de controlo para diferentes topologias do RPC (ponte completa, meia ponte, três fios, etc.), para demonstrar as capacidades gerais do sistema do RPC, e também para dois transformadores diferentes (V/V e Scott). O RPC mais favorável baseado na topologia do MMC (baseado no MMC de meia ponte) foi profunda e extensivamente simulado, nomeadamente utilizando uma abordagem de controlo preditivo. As simulações e os resultados experimentais confirmam a validade da teoria de controlo apresentada, bem como a capacidade de melhoria da qualidade de energia elétrica na solução proposta., Fundação para a Ciência e a Tecnologia – FCT), which allowed me to continue my studies with the PD/BD/127815/2016 Ph.D. scholarship under the Innovation in Railway Systems and Technologies Doctoral Program – iRail.