Multi-mode control system for wind turbines

In a control system for a wind turbine, said wind turbine having a wind driven rotor with variable pitch angle blades, the improvement comprising:

• closed loop control means responsive to system operating conditions for producing a control signal indicative of desired rate of change of blade pitch angle,
• rate limiter means receiving said control signal for maintaining said control signal within predetermined limits,
• electronic integrator means for producing from said control signal a signal indicative of desired blade pitch angle, said integrator means including pitch angle limiter means for maintaining said desired blade pitch angle signal within predetermined maximum and minimum limits,
• and blade pitch change means responsive to said desired blade pitch angle signal for varying the blade pitch angle.

In a wind turbine having a wind driven rotor with a plurality of variable pitch angle blades, means for maintaining a substantially constant rate of change of rotor speed during start up and shut down of said wind turbine comprising:

• means for sensing the actual speed of said rotor and producing a rotor speed signal indicative thereof,
• rate sensor means for producing from said rotor speed signal a signal indicative of the actual rate of change of rotor speed,
• means producing a reference signal proportional to a rotor speed rate of change limit,
• comparator means comprising said actual rate of change of rotor speed signal with said reference signal and producing an error signal proportional to the difference therebetween,
• and means responsive to said error signal for varying the pitch angle of said rotor blades.

In a wind turbine having a wind driven rotor with a plurality of variable pitch angle blades, said rotor being adapted to be connected to a generator via a shaft means, means for controlling the power output from said generator comprising:

• means for sensing the actual speed of said rotor and producing a rotor speed signal indicative thereof,
• means for sensing the actual speed of said generator and producing a generator speed signal indicative thereof,
• means for comparing said rotor speed signal with said generator speed signal and producing a speed error signal variable with the difference therebetween,
• signal compensating means responsive to said speed error signal for producing therefrom a signal proportional to the rate of change of speed error,
• means for measuring the torque of said shaft means and producing a shaft torque signal indicative thereof,
• means for producing a reference signal proportional to a desired shaft torque,
• means for comparing said shaft torque signal with said reference signal and producing a shaft torque error signal variable with the difference therebetween,
• means for summing said rate of change of speed error signal with said shaft torque error signal to produce a rate of change of shaft torque signal,
• and means responsive to said rate of change of shaft torque signal for varying the pitch angle of said rotor blades.