Cascaded- and Modular-Multilevel Converter Laboratory Test System Options: A Review

The increasing importance of cascaded multilevel converters (CMCs), and the sub-category of modular multilevel converters (MMCs), is illustrated by their wide use in high voltage DC connections and in static compensators. Research is being undertaken into the use of these complex pieces of hardware and software for a variety of grid support services, on top of fundamental frequency power injection, requiring improved control for non-traditional duties. To validate these results, small-scale laboratory hardware prototypes are often required. Such systems have been built by many research teams around the globe and are also increasingly commercially available. Few publications go into detail on the construction options for prototype CMCs, and there is a lack of information on both design considerations and lessons learned from the build process, which will hinder research and the best application of these important units. This paper reviews options, gives key examples from leading research teams, and summarizes knowledge gained in the development of test rigs to clarify design considerations when constructing laboratory-scale CMCs.This work was supported in part by The University of Manchester supported by the National Innovation Allowance project ``VSC-HVDC Model Validation and Improvement'' and Dr. Heath's iCASE Ph.D. studentship supported through Engineering and Physical Sciences Research Council (EPSRC) and National Grid, in part by the Imperial College London supported by EPSRC through the HubNet Extension under Grant EP/N030028/1, in part by an iCASE Ph.D. Studentship supported by EPSRC and EDF Energy and the CDT in Future Power Networks under Grant EP/L015471/1, in part by University of New South Wales (UNSW) supported by the Solar Flagships Program through the Education Infrastructure Fund (EIF), in part by the Australian Research Council through the Discovery Early Career Research Award under Grant DECRA_DE170100370, in part by the Basque Government through the project HVDC-LINK3 under Grant ELKARTEK KK-2017/00083, in part by the L2EP research group at the University of Lille supported by the French TSO (RTE), and in part by the Hauts-de-France region of France with the European Regional Development Fund under Grant FEDER 17007725

A comprehensive review on modular multilevel converters, submodule topologies, and modulation techniques

The concept of the modular multilevel converter (MLC) has been raising interest in research in order to improve their performance and applicability. The potential of an MLC is enormous, with a great focus on medium- and high-voltage applications, such as solar photovoltaic and wind farms, electrified railway systems, or power distribution systems. This concept makes it possible to overcome the limitation of the semiconductors blocking voltages, presenting advantageous characteristics. However, the complexity of implementation and control presents added challenges. Thus, this paper aims to contribute with a critical and comparative analysis of the state-of-the-art aspects of this concept in order to maximize its potential. In this paper, different power electronics converter topologies that can be integrated into the MLC concept are presented, highlighting the advantages and disadvantages of each topology. Nevertheless, different modulation techniques used in an MLC are also presented and analyzed. Computational simulations of all the modulation techniques under analysis were developed, based on four cascaded full-bridge topologies. Considering the simulation results, a comparative analysis was possible to make regarding the symmetry of the synthesized waveforms, the harmonic content, and the power distribution in each submodule constituting the MLC.This work has been supported by FCT—Fundação para a Ciência e Tecnologia, within the R&D Units Project Scope UIDB/00319/2020. Mr. Luis A. M. Barros is supported by the doctoral scholarship PD/BD/143006/2018, granted by the Portuguese FCT foundation

Emerging Converter Topologies and Control for Grid Connected Photovoltaic Systems

Continuous cost reduction of photovoltaic (PV) systems and the rise of power auctions resulted in the establishment of PV power not only as a green energy source but also as a cost-effective solution to the electricity generation market. Various commercial solutions for grid-connected PV systems are available at any power level, ranging from multi-megawatt utility-scale solar farms to sub-kilowatt residential PV installations. Compared to utility-scale systems, the feasibility of small-scale residential PV installations is still limited by existing technologies that have not yet properly address issues like operation in weak grids, opaque and partial shading, etc. New market drivers such as warranty improvement to match the PV module lifespan, operation voltage range extension for application flexibility, and embedded energy storage for load shifting have again put small-scale PV systems in the spotlight. This Special Issue collects the latest developments in the field of power electronic converter topologies, control, design, and optimization for better energy yield, power conversion efficiency, reliability, and longer lifetime of the small-scale PV systems. This Special Issue will serve as a reference and update for academics, researchers, and practicing engineers to inspire new research and developments that pave the way for next-generation PV systems for residential and small commercial applications

Thermal regulation and balancing in modular multilevel converters

Modular multilevel converters (MMCs) are envisaged as the key power electronic converter topology to enable a multi-terminal pan-European high voltage direct current (HVDC) Supergrid for the interconnection of offshore wind farms and exchange of energy between different countries. A key feature of MMCs in the large number of semiconductor devices employed in each converter station, distributed over a stack of series-connected sub-modules (SMs). These semiconductors possess strict thermal limits, which can constrain the operating range on the converter by limiting its capability of providing enhanced functionalities to the AC grid such as short-term power overloads. Furthermore, due to different loading conditions and ageing, significant temperature differences can exist between SMs which can lead to a very different lifetime expectancies for the semiconductor modules. This thesis proposes active thermal control methodologies to act of two distinct converter levels. Firstly, two novel dynamic rating strategies are proposed to define the converter current injection limit as a response to the maximum semiconductor temperature feedback. This enables the exploitation of the semiconductors thermal headroom to provide short-term power overloads, which can be used for the improvement of the frequency support of a power-distressed AC grid. Secondly, a SM-level temperature regulation and balancing algorithm is proposed, aiming at the equalisation of the maximum semiconductor die temperature in all the SMs of an MMC arm. The proposed methods are validated in a detailed and combined electro-thermal simulation model with 3 and 10 SMs per arm developed in MATLAB®/Simulink® using PLECS® Blockset. An experimental platform has been designed and utilised to verify the effectiveness of the dynamic rating strategies and the SM temperature regulation and balancing strategy

Anuário Científico – 2009 & 2010 Resumos de Artigos, Comunicações, Teses, Patentes, Livros e Monografias de Mestrado

O Conselho Técnico-Científico do Instituto Superior de Engenharia de Lisboa (ISEL), na senda da consolidação da divulgação do conhecimento e da ciência desenvolvidos pelo nosso corpo docente, propõe-se publicar mais uma edição do Anuário Científico, relativa à produção científica de 2009 e 2010. A investigação, enquanto vertente estratégica do Instituto Superior de Engenharia de Lisboa (ISEL), tem concorrido para o seu reconhecimento nacional e internacional como instituição de referência e de qualidade na área do ensino das engenharias. É também nesta vertente que o ISEL consubstancia a sua ligação à sociedade portuguesa e internacional através da transferência de tecnologia e de conhecimento, resultantes da sua atividade científica e pedagógica, contribuindo para o seu desenvolvimento e crescimento de forma sustentada. São parte integrante do Anuário Científico todos os conteúdos com afiliação ISEL resultantes de resumos de artigos publicados em livros, revistas e atas de congressos que os docentes do ISEL apresentaram em fóruns e congressos nacionais e internacionais, bem como teses e patentes. Desde 2002, ano da publicação da primeira edição, temos assistido a uma evolução crescente do número de publicações de conteúdos científicos, fruto do trabalho desenvolvido pelos docentes que se têm empenhado com afinco e perseverança. Contudo, nestes dois anos (2009 e 2010) constatou-se um decréscimo no número de publicações, principalmente em 2010. Uma das causas poderá estar diretamente relacionada com a redução do financiamento ao ensino superior uma vez que limita toda a investigação no âmbito da atividade de I&D e da produção científica. Na sequência da implementação do Processo de Bolonha em 2006, o ISEL promoveu a criação de cursos de Mestrado disponibilizando uma oferta educativa mais completa e diversificada aos seus alunos, mas também de outras instituições, dotando-os de competências inovadoras apropriadas ao mercado de trabalho que hoje se carateriza mais competitivo e dinâmico. Terminados os períodos escolar e de execução das monografias dos alunos, os resumos destas são igualmente parte integrante deste Anuário, no que concerne à conclusão dos Mestrados em 2009 e 2010.A fim de permitir uma maior acessibilidade à comunidade científica e à sociedade civil, o Anuário Científico será editado de ora avante em formato eletrónico. Excecionalmente esta edição contempla publicações referentes a dois anos – 2009 e 2010