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Item Cascaded- and Modular-Multilevel Converter Laboratory Test System Options: A Review: A Review(2021-03) Heath, Theodor; Barnes, Mike; Judge, Paul D.; Chaffey, Geraint; Clemow, Phil; Green, Tim C.; Green, Peter R.; Wylie, James; Konstantinou, Georgios; Ceballos, Salvador; Pou, Josep; Belhaouane, Mohamed Moez; Zhang, Haibo; Guillaud, Xavier; Andrews, Jack; POWER ELECTRONICS AND SYSTEM EQUIPMENTThe 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.Item Low-frequency voltage ripples in the flying capacitors of the nested neutral-point-clamped converter(Institute of Electrical and Electronics Engineers Inc., 2016-05-10) Ghias, Amer M.Y.M.; Pou, Josep; Ceballos, Salvador; Agelidis, Vassilios G.; POWER ELECTRONICS AND SYSTEM EQUIPMENTThe flying capacitors (FCs) of the nested neutral-point-clamped (NNPC) converter show an inherent voltage ripple at fundamental frequency. This ripple can be significantly large under some operating conditions of the converter. In this paper, the amplitudes of the low-frequency voltage ripples in the FCs are determined. An averaged model of the NNPC converter is introduced and used in the analysis. The amplitudes of the capacitor voltage ripples are provided using normalized variables so that this information can be used to size the FCs of the converter in different applications. The results of the analysis are validated experimentally in a laboratory prototype.