Over the past decade, modular multilevel converters have evolved as the preferred choice for high voltage conversion systems. The design of the converter poses a computational challenge to the classical electromagnetic transient simulation techniques, for which the existing literature proposes numerous simplified and computationally-efficient equivalent representations. Despite the extensive collection of proposed models, the literature lacks a systematic comparison of these representations, which could enable their appropriate selection based on the specific simulation objectives. In light of these requirements, this article presents a comprehensive review of MMC models and discusses their applicability for parallel and real-time simulation. Using PSCAD/EMTDC simulations, the models are objectively compared with regards to computational efficiency and accuracy for various transient conditions. In addition, the paper also presents a brief account of MMC operation and the associated control and modulation system.

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Abstract. The Southern Ocean has a profound impact on the Earth's climate system. Its strong winds, intense currents, and fierce waves are critical components of the air-sea interface and contribute to absorbing, storing, and releasing heat, moisture, gasses, and momentum. Owing to its remoteness and harsh environment, this region is significantly under sampled, hampering the validation of prediction models and large scale observations from satellite sensors. Here, an unprecedented data set of simultaneous observations of winds, surface currents, and ocean waves is presented, to address the scarcity of in situ observations in the region – https://doi.org/10.26179/5ed0a30aaf764 (Alberello et al., 2020c), and https://doi.org/10.26179/5e9d038c396f2 (Derkani et al., 2020). Records were acquired underway during the Antarctic Circumnavigation Expedition (ACE), which went around the Southern Ocean from December 2016 to March 2017 (Austral summer). Observations were obtained with the wave and surface current monitoring system WaMoS-II, which scanned the ocean surface around the vessel using marine radars. Measurements were assessed for quality control and compared against available satellite observations. The data set is the most extensive and comprehensive collection of observations of surface process for the Southern Ocean and has the potential to support further theoretical and numerical research on lower atmosphere, air-sea interface and upper ocean processes.