Methods of Overcoming Fluctuations of Power
Wind turbines are designed to yield maximum output at a wind speed of 15 m/s. If the wind speed is more, the excess energy is wasted. But the rotor is to be protected from damage. This is done by power control mechanism. The important methods used in power control are described below.
1. Pitch control :
The power output of the turbine is constantly checked by an electronic measuring unit. When the power output becomes too high, it actuates the blade pitch mechanism which turns the rotor blades out of the wind. This reduces the power output. When the wind velocity reduces and the power output falls, the blade is turned back to the original position and the power again increases. The mechanism is operated hydraulically.
2. Passive stall control :
In this control the blade is fixed at a fixed angle. When the wind speed increases, it creates turbulence on the side opposite to that facing the wind reduces the angle of attack. This will reduce the lift force developed and hence reduces the power output. It is much sampler method than the pitch control method but it less accurate.
3. Active stall control :
There two have blades with changeable pitch angles. When the wind speed reduces, it pitches the blades, so that wind power output increases. But when the power reaches the rated power, the blade is pitched in the opposite direction to that of pitch control so that the angle of attack increases.
4. Yaw control :
This is yet another method in which the turbine is rotated about a vertical axis facing or away from the wind. This method is used only in small wind turbines power plants 1 kW or less.