Variable-speed wind turbines are a promising concept for large offshore wind farms. The variable-speed concept can be realised with multi-pole synchronous generators (MPSG) excited by permanent magnets. The main advantages of this concept are that (i) the wind turbines are gearless and (ii) the electrical excitation system is replaced by permanent magnets. The electromagnetic construction of the permanent magnet generators (PMG) is, however, more complex than in conventional concept generators. The PMG are grid-connected through and controlled by their frequency converters. The converter control can be used to stabilise the large wind farm at transient events in the grid to complete the grid specifications of the power system controllers. This article gives an overview of the structural concepts of PMG and explains modelling details of the PMG and their frequency converters.

The oceans cover more than two-thirds of the planet, representing the vastest part of natural resources. Nevertheless, only a fraction of the ocean depths has been explored. Within this context, this article presents the H2020 ENDURUNS project that describes a novel scientific and technological approach for prolonged underwater autonomous operations of seabed survey activities, either in the deep ocean or in coastal areas. The proposed approach combines a hybrid Autonomous Underwater Vehicle capable of moving using either thrusters or as a sea glider, combined with an Unmanned Surface Vehicle equipped with satellite communication facilities for interaction with a land station. Both vehicles are equipped with energy packs that combine hydrogen fuel cells and Li-ion batteries to provide extended duration of the survey operations. The Unmanned Surface Vehicle employs photovoltaic panels to increase the autonomy of the vehicle. Since these missions generate a large amount of data, both vehicles are equipped with onboard Central Processing units capable of executing data analysis and compression algorithms for the semantic classification and transmission of the acquired data.

Abstract-This paper deals with the problems related to an islanding experiment performed at Rejsby Hede in Denmark. During the experiment several interesting observations were made in connection to distortion of voltages and currents. Observations were also made in connection to variation of frequency and phase. In this paper the data are analyzed in three different manners and the results are related to the physics of the electric system.

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