Variable-Speed Wind Turbine

A variable speed wind turbine is designed to operate across a wide range of rotor speeds rather than the roughly constant rotation of a fixed speed turbine, which lets it capture more of the available aerodynamic power as wind conditions change. Turbine efficiency, expressed as the power coefficient, is optimized by holding the tip speed ratio, the ratio of blade tip speed to wind speed, near its ideal value, so as wind speed changes the rotor speed must also change to stay near peak efficiency. Every grid connected wind turbine from the first one in 1939 until the 1970s was a fixed speed design; the 1.5 megawatt Gamma 60 turbine is credited as the first variable speed grid connected wind turbine, built with a teetering hub. Variable speed turbines are controlled either by stall regulation, which manages power by letting the airfoil stall and reducing rotor speed at high wind, or by pitch regulation, which actively adjusts blade angle for finer control of power output.