This paper presents a novel type of variable speed wind turbine with a new drive train different from the variable speed wind turbine commonly used nowadays. In this concept, a synchronous generator is directly coupled with the grid, therefore, the wind turbine transient overload capability and grid voltage support capability can be significantly improved. An electromagnetic coupling speed regulating device (EMCD) is used to connect the gearbox high speed shaft and synchronous generator rotor shaft, transmitting torque to the synchronous generator, while decoupling the gearbox side and the synchronous generator, so the synchronous generator torque oscillations during a grid fault are not transmitted to the gearbox. The EMCD is composed of an electromagnetic coupler and a one quadrant operation converter with reduced capability and low cost. A control strategy for the new wind turbine is proposed and a 2 MW wind turbine model is built to study the wind turbine fault ride-through capability. An integrated simulation environment based on the aeroelastic code HAWC2 and software Matlab/Simulink is used to study its fault ride-through capability and the impact on the structural loads during grid three phase and two phase short circuit faults.

The Center for Ocean Energy Research (COER) at the University of Maynooth in Ireland organized a hydrodynamic modeling competition in conjunction with OMAE2015. Researchers were challenged to predict the dynamic response of a floating rigid-body device that was experimentally tested in a series of wave-tank tests. Specifically, COER set up a blind competition, where the device specifications and test conditions were released, but the experimental results were kept private until all competition participants submitted their numerical simulation results. The National Renewable Energy Laboratory and Sandia National Laboratories entered the competition and modeled the experimental device using both the WEC-Sim and FAST numerical modeling tools. This paper describes the numerical methods used to model the device and presents the numerical modeling results. The numerical results are also compared to the experimental results provided by COER at the completion of the competition.

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