Blade pitch control of a wind turbine

Claim 2

A control system for adjusting the pitch of variable-pitch angle blades in a wind turbine generating electric power and for maintaining dynamic stability under all conditions, wherein at low wind speeds said control system maintains the pitch of said blades at an angle close to the value providing maximum torque, and at high wind speeds said control system adjusts the pitch of said blades to maintain rated power, said control system comprising: a. means for adding a signal proportional to the rate of change of electric power generated by said wind turbine and a nominal blade control signal; and b. means, coupled to said adding means, for generating a control signal from the output of said adding means to control the pitch of said variable-pitch blades, said generating means including means for ensuring that the values of said control signal remain above a minimum level needed to ensure the blade pitch at said angle close to the value for providing maximum torque.

Claim 3

A control system as described in claim 1 wherein said nominal blade control signal remains constant at said minimum level.

Claim 4

A control system as described in claim 1, further comprising: a. means for subtracting a predetermined reference power signal from a signal representing the electric power generated by said wind turbine; and b. means, coupled to said subtracting means, for generating from the output of said subtracting means said nominal blade control signal, said nominal blade control signal generating means including means for maintaining said nominal blade control signal above said minimum level.

Claim 5

A control system for adjusting the pitch of variablepitch angle blades in a wind turbine for generating electric power, said control system comprising: a. means for subtracting a signal corresponding to the electric power output generated by said wind turbine and a predetermined power reference signal; b. means, coupled to the output of said subtracting means, for generating a first blade control signal greater than a minimum level which corresponds to a predetermined minimum blade angle for said variable-pitch angle blades; c. means, coupled to said first blade control signal and said subtracting means, for generating a second blade control signal greater than said minimum level; and d. means, coupled to said second blade control signal and to a signal proportional to the rate of change of electric power generated by said wind turbine, to generate a third blade control signal greater than said minimum level, said third blade control signal being used to adjust the pitch of said variablepitch angle blade.

Claim 6

A control system for adjusting the pitch of variablepitch angle blades in a wind turbine for generating electric power, said control system comprising: a. means for subtracting a signal corresponding to the electric power output generated by said wind turbine and a predetermined power reference signal; b. means, coupled to the output of said subtracting means, for generating a first blade control signal greater than a minimum level which corresponds to a predetermined minimum blade angle for said variable-pitch angle blades; c. means, coupled to said first blade control signal and said subtracting means, for generating a second blade control signal greater than said minimum level; and d. means, coupled to said second blade control signal and to a signal proportional to the rate of change of electric power generated by said wind turbine, to generate a third blade control signal greater than said minimum level, said third blade control signal being used to adjust the pitch of said variablepitch angle blade.

Claim 7

The control system in claim 4 wherein each of said means for generating said first, second and third blade control signals includes a limiter.

Claim 8

The control system in claim 5 wherein said means for generating said first blade control signal and the means for generating said second blade control signal each includes an adder.

Claim 9

The control system in claim 6 wherein said means for generating said first blade control signal includes an integrator.

Claim 10

A control system for adjusting the pitch of variable-pitch angle blades in a wind turbine for generating electric power, said control system comprising: a. a subtractor for generating a difference signal representing the difference between a signal proportional to the electric power generated by said wind turbine and a predetermined power reference signal; b. an integrator coupled to said substractor for integrating said difference signal; c. a first limiter coupled to said integrator to keep the output from said integrator greater than a minimum level representing a desired minimum blade angle for said variable-pitch angle blades; d. a first adder coupled to said subtractor and said first integrator for adding the output of said first limiter and said difference signal; e. a second limiter coupled to said first adder to keep the output from said first adder above said minimum level; f. a second adder coupled to said second limiter for adding the output of said second limiter and a signal proportional to the rate of change of electric power generated by said wind turbine; and g. a third limiter coupled to said second adder to keep the output of said second adder above said minimum level, the output from said third being used to control the pitch of said variable-pitch angle blades.

Claim 11

A control system for adjusting the pitch of variable-pitch angle blades in a wind turbine for generating electric power, said control system comprising: a. a subtractor for generating a difference signal representing the difference between a signal proportional to the electric power generated by said wind turbine and a predetermined power reference signal; b. an integrator coupled to said substractor for integrating said difference signal; c. a first limiter coupled to said integrator to keep the output from said integrator greater than a minimum level representing a desired minimum blade angle for said variable-pitch angle blades; d. a first adder coupled to said subtractor and said first integrator for adding the output of said first limiter and said difference signal; e. a second limiter coupled to said first adder to keep the output from said first adder above said minimum level; f. a second adder coupled to said second limiter for adding the output of said second limiter and a signal proportional to the rate of change of electric power generated by said wind turbine; and g. a third limiter coupled to said second adder to keep the output of said second adder above said minimum level, the output from said third being used to control the pitch of said variable-pitch angle blades.

Claim 12

A wind turbine for generating electric power comprising: a. a plurality of variable-pitch angle blades; b. means for generating electric power from the rotation of said plurality of variable-pitch angle blades caused by wind; and c. means for controlling the pitch of each of said plurality of variable-pitch angle blades, said controlling means including: i. means for subtracting a signal corresponding to the electric power output generated by said wind turbine and a predetermined reference signal; ii. means, coupled to the output of said subtracting means, for generating a first blade control signal greater than a minimum level which corresponds to a predetermined minimum blade angle for said variable-pitch angle blades; iii means coupled to said first blade control signal and said subtracting means, for generating a second blade control signal greater than said minimum level; and iv. means, coupled to said second blade control signal and to a signal proportional to the rate of change of power generated by said wind turbine, to generate a third blade control signal greater than said preset minimum level, said third blade control signal being used to adjust the pitch of said variable-pitch angle blade.

Claim 13

A wind turbine for generating electric power comprising: a. a plurality of variable-pitch angle blades; b. means for generating electric power from the rotation of said plurality of variable-pitch angle blades caused by wind; and c. means for controlling the pitch of each of said plurality of variable-pitch angle blades, said controlling means including: i. means for subtracting a signal corresponding to the electric power output generated by said wind turbine and a predetermined reference signal; ii. means, coupled to the output of said subtracting means, for generating a first blade control signal greater than a minimum level which corresponds to a predetermined minimum blade angle for said variable-pitch angle blades; iii means coupled to said first blade control signal and said subtracting means, for generating a second blade control signal greater than said minimum level; and iv. means, coupled to said second blade control signal and to a signal proportional to the rate of change of power generated by said wind turbine, to generate a third blade control signal greater than said preset minimum level, said third blade control signal being used to adjust the pitch of said variable-pitch angle blade.

Claim 14

A wind turbine system for generating electric power, comprising: a. a plurality of variable-pitch angle blades; b. means for varying the pitch of said variable-pitch angle blades, said varying means being controlled by a blade angle output signal; c. means for generating electrical power from the rotation of said plurality of variable-pitch angle blades; d. means for sensing the output power from said generating means; e. means for sensing the rate of change of output power from said generating means; and f. means for controlling the pitch of said variablepitch angle blades, said controlling means including: i. means for subtracting the output of said output power sensing means and a predetermined reference signal; ii. means, coupled to the output of said subtracting means, for generating a first blade control signal greater than a minimum level which corresponds to a predetermined minimum blade angle for said variable-pitch angle blades; iii. means coupled to said first blade control signal and said subtracting means, for generating a second blade control signal greater than said minimum level; and iv. means, coupled to said second blade control signal and to the output of said output power rate sensing means for generating said blade angle output signal.

Claim 15

A wind turbine system for generating electric power, comprising: a. a plurality of variable-pitch angle blades; b. means for varying the pitch of said variable-pitch angle blades, said varying means being controlled by a blade angle output signal; c. means for generating electrical power from the rotation of said plurality of variable-pitch angle blades; d. means for sensing the output power from said generating means; e. means for sensing the rate of change of output power from said generating means; and f. means for controlling the pitch of said variablepitch angle blades, said controlling means including: i. means for subtracting the output of said output power sensing means and a predetermined reference signal; ii. means, coupled to the output of said subtracting means, for generating a first blade control signal greater than a minimum level which corresponds to a predetermined minimum blade angle for said variable-pitch angle blades; iii. means coupled to said first blade control signal and said subtracting means, for generating a second blade control signal greater than said minimum level; and iv. means, coupled to said second blade control signal and to the output of said output power rate sensing means for generating said blade angle output signal.