Soft-stall control for variable-speed stall-regulated wind turbines

A variable-speed, fixed-pitch wind turbine control strategy was investigated to evaluate the feasibility of constraining rotor speed and power output without the benefit of active aerodynamic control devices. A strategy was postulated to control rotational speed by specifying the demanded generator torque. By controlling rotor speed in relation to wind speed, the aerodynamic power extracted by the blades from the wind was manipulated. Specifically, the blades were caused to stall in high winds. In low and moderate winds, the demanded generator torque and the resulting rotor speed were controlled and the wind turbine operated near maximum efficiency. Turbine models were developed and simulations of operation in turbulent winds were conducted. Results indicated that rotor speed and power output were well regulated. Preliminary investigations of system dynamics (E. Muljadi, K. Pierce, P. Migliore, A conservative control strategy for variable-speed stall-regulated wind turbines, AIAA-2000-31 A Collection of the 2000 ASME Wind Energy Symposium Technical Papers presented at the 38th AIAA Aerospace Sciences Meeting and Exhibit, Reno, NV, January 2000). Showed that, compared to fixed-speed operation, variable-speed operation caused cyclic loading amplitude to be reduced for the turbine blades and low-speed shaft and slightly increased for the tower loads. This result suggests that implementation of the proposed control strategy will have a favorable impact on the turbineʹs fatigue life. The concept was implemented on a 275 kW wind turbine test bed (K. Pierce, P. Migliore, Maximizing the energy capture of fixed-pitch variable-speed wind turbines, AIAA-2000-0032 ASME Wind Energy Symposium Technical Papers presented at the 38th AIAA Aerospace Sciences Meeting and Exhibit, Reno, NV, January 2000). Test data show that the wind turbine performance matches the predicted simulation results. The control concept was shown to operate the wind turbine near maximum efficiency in low-to-moderate wind speeds, while stalling the rotor in the high winds to regulate speed and output power.