A new active speed stall control compared to pitch control for a direct-drive wind turbine

The objective of this paper is to assess 10 MW directdrive permanent-magnet (DDPM) generator systems with different control strategies namely pitch control and active speed stall control. In the active speed stall control concept, there is no pitch mechanism, and the rotor speed is actively controlled by the generator to control the output power. The active speed stall control wind turbine with the DDPM generator system may be an attractive concept especially for offshore. This turbine has high potential because the wear, the maintenance and the failures of the pitch mechanism and the gearbox are omitted. The different DDPM generator systems are designed roughly, and the dimensions, weights, cost and performance of the systems are compared. To enable the active speed stall control concept, it is necessary to increase the weight and cost of generator system compared to the pitch control concept. Index Terms-wind turbine, permanent-magnet, generator, direct-drive, stall control, pitch control