6. Operation and Control of Wind Energy Converters

Power output from wind energy converters depends upon the power curve of the machine and the controls exercised to operate it. Pitch controlled machines are used more often than yaw controlled and stall controlled machines. The capacity factor of wind turbines, which represents utilization of the installed capacity, usually does not exceed 40 %. Controlling the rotational speed of the blades is necessary in some designs for keeping the frequency constant; however, this forces the turbine to run in non-maximum power output regime for most of the time. Therefore, modern converters run with variable rotation and produce a constant frequency by specific asynchronous generators or by using electronic converters. Due to heavy fluctuations in wind speed, wind energy converters are not suitable for stand alone applications unless provided with storage or backed-up system.