Overview of and trends in wind turbine generator systems

This paper gives an overview of wind turbine generator systems and describes some trends. Around 1998, many wind turbine manufacturers changed from constant speed systems to variable speed with doubly-fed induction generators. Since around 2005, they have come with a number of alternative generators systems, mainly to comply with grid requirements as grid-fault ride-through. Most alternatives have brushless generators and full converters. One of them is the direct-drive system. If the availability of permanent magnet materials can be guaranteed, permanent-magnet generators are considered as the most suitable direct-drive generators. The increasing importance of offshore wind energy results in an increasing attention for reliability and availability.