Power control strategy for variable-speed fixed-pitch wind turbines

Variable-speed fixed-pitch (VSFP) wind turbine is widely used in small-to-medium scale wind turbine markets due to its simple structure, low cost and high reliability features. However, power control, especially maximum power limitation control at high wind velocities, of such turbine concept is hard to realize and it has not been studied much in existing researches so far. To overcome this difficulty, we propose a simple power control strategy for VSFP wind turbines, covering the entire range of wind velocity. The proposed strategy contains a novel maximum power point tracking (MPPT) control method, a constant-speed (CS) soft-stalling control method and a constant-power (CP) soft-stalling control method. These three sub-control methods are appropriately combined in a way to realize seamless transitions among different operational modes (MPPT, CS and CP). The system structure and operational principle of the proposed strategy are thoroughly analyzed. Theoretical analysis is verified by simulation and experimental results performed by a 1.2kW fixed-pitch variable-speed wind turbine prototype.