A Study Of Wind Powered Turbine Generation

4.2    INTEGRATION AND CONTROL
As the need to stabilize the nation’s energy resources and electricity demand there is a cause to improve the method of possible impact on system operation and control.
The schedule may be implemented either electrically or by a suitable programmed digital computer. The gain in the speed, torque and power loop controls is schedule as a function of average wind velocity to optimize stability and response.
This inversion relates to the use of wind energy to drive a wind turbine for the production of electrical power and specifically to a control system which automatically modulates the pitch angle of wind turbine in order to regulate either electrical output power, shaft torque or speed in order to minimize the effect on wind quota (a sudden, strong, rush of air carried by wind) and turbulence (the state of being irregular or violent movement of the air) and to reduce stress on the blades and other mechanical components
It has been found that the control necessary to produce electrical power from a synchronous generator, driven by a wind turbine, can be provided by varying the pitch angle of the wind turbine blade. During start-up and short down of the wind turbine the blade pitch angle is scheduled by open loop control as a function of rotor speed and wind velocity. During normal operation the pitch angle of the wind turbine blade is controlled in a closed loop manner to maintain either a constant generator speed for isolated power generating station or when the generator is synchronized to the load or constant generator output power or shaft torque when the generator is connected to an electrical grid. This loop contains proportional, integral and derivative control signals in addition to lead compensation.
This gain in the closed loop control is continuously varied as a function of wind velocity to optimize stability and transient response. Wind velocity may be sensed directly or synthesized as a function of system operation condition. The control system for blade pitch angle is very responsive to the wind quest and reacts rapidly via an anticipation control signal, which is summed with the close loop control signal during rapid changes in wind conditions to minimize mechanical stress. An integration in the closed loop is forced via a feedback loop to track the blade pitch angle even when the closed loop controls are inactive.