State of the art in generator technology for offshore wind energy conversion systems

This paper presents an overview and analysis of the state-of-the-art generator technology for offshore wind energy conversion systems (WECS) in order to identify the current technology frontier. First, classification of the drive train solutions in use obtained by thorough investigation of all the offshore wind farms in operation is presented. Then, Key Performance Indicators (KPI) for the drive train evaluation are discussed and two KPI are chosen for in-depth investigation: total drive train efficiency and generator weight. Comparative study of drive train efficiency for different system topologies has been carried out and presented. A novel way of comparison of various generator technologies on weight in the form of a map `power density vs. torque density´ is proposed. The map allows showing the technology state of art and frontier for all the existing generator solutions independent of speed and power. To create the map, characteristics of over 90 wind power generators have been collected, analyzed and classified. Finally, design and integration issues as well as the technology trends for directly driven offshore WECS are discussed.