WindsofChangeforPowerandControl.docVIP

Winds of Change for Power and Control Drives and controls aspect of wind power technology provides new engineering challenges and lessons as more multi-megawatt, utility-scale wind turbines come online. Frank J. Bartos, P.E., Control Engineering -- Control Engineering, 8/1/2009 ? At home on sweeping plains, arid deserts, remote mountain sides—and more recently moving offshore—growing numbers of multi-megawatt (MW) wind turbines are producing clean electric power. Wind turbine size is rising to take advantage of proportionately higher power generation-to-cost ratios obtainable. The American Wind Energy Association (AWEA) puts average size of turbines installed in 2008 at 1.67 MW. Meanwhile, the top end of rated capacity is 5-6 MW, intended for offshore sites. Still larger wind turbines are in planning. Except in some European countries, wind power historically has been a small contributor to electricity production relative to long-established sources. However, winds of change are starting to blow. The U.S. took the lead in installed wind power capacity at the end of 2008 with 25.2 gigawatt (GW), followed by Germany (23.9 GW), Spain (16.8 GW), and China (12.2 GW), according to the Global Wind Energy Council (GWEC). China is expected to take the lead in the near future. These giant wind turbines house electric, hydraulic, and mechanical drives, various subsystems, plus electronic controls in a nacelle atop a tower that stands as high as 135-m (450 ft). Rotor (blade) diameters can measure well over 100 m. Installed equipment must withstand harsh ambient conditions, on/off cycling due to high or low winds, and nacelle vibrations without undue maintenance. Pitch and yaw control Arguably, the most critical, costliest parts of the system are the turbine blades, which must be controlled and protected. Blade-pitch control regulates the amount of power and torque extracted from the wind by optimally orienting blades to the air flow, while yaw control keeps the nacelle pointing