Speed setting system and method for a stall-controlled wind turbine
View Patent ↗A speed setting system that generates a speed control command for controlling the rotational speed of a stall-controlled wind turbine of a wind-powered machine. The speed setting system generates the speed command as a function of performance variation of the wind turbine due to environmental and/or other factors. The speed setting system utilizes a performance-compensation term that is slowly adjusted to compensate for relatively long-term performance variation. In one example, the performance-compensation term is adjusted only when the current power output of the wind turbine is at least 80% of the rated output power to ensure the wind speed is sufficiently high.
1. A controller for controlling rotational speed of a stall-controlled wind turbine of a wind-powered machine having a speed control system for controlling the rotational speed, wherein the stall-controlled wind turbine has a power-coefficient curve, the controller comprising:
a speed setting system operatively configured to provide a speed control command to the speed control system, said speed setting system including:
a power speed block that determines the speed control command based on a speed limit curve derived as a function of a performance-compensation term raised to the power of a compensator exponent, said compensator exponent being determined as a function of the power-coefficient curve.
2. A controller according to claim 1 , wherein the stall-controlled wind turbine has a rotational speed limit, a radius and a power limit, and said speed limit curve is defined by the equation:
ω
L
=
K
o
×
P
L
a
r
5
/
3
×
κ
b
wherein:
ω L is the rotational speed limit of the stall-controlled wind turbine;
P L is the power limit of the stall-controlled wind turbine;
K 0 is a constant chosen to match the power-coefficient curve approximately;
κ is the performance-compensation term;
a is a power limit exponent;
b is the compensator exponent; and
r is the radius of the wind turbine.
3. A controller according to claim 2 , wherein each of the power limit exponent a and the compensator exponent b are approximately equal to one-third.
4. A method of controlling rotational speed of a stall-controlled wind turbine of a wind-powered machine having a speed control system for controlling the rotational speed, wherein the stall-controlled wind turbine has a power-coefficient curve, the method comprising:
receiving a power limit signal corresponding to an output power limit P L for the stall-controlled wind turbine;
determining a speed limit command based on a speed limit curve that is a function of: 1) the output power limit P L and 2) a performance-compensation term raised to the power of a compensator exponent, said compensator exponent being determined as a function of the power-coefficient curve; and
outputting the power speed limit command to the speed control system.
5. A method according to claim 4 , further comprising defining the speed limit curve by the equation:
ω
L
=
K
o
×
P
L
a
r
5
/
3
×
κ
b
wherein:
ω L is the rotational speed limit of the stall-controlled wind turbine;
K 0 is a constant chosen to match the power-coefficient curve approximately;
κ is the performance-compensation term;
a is a power limit exponent;
b is the compensator exponent; and
r is the radius of the wind turbine.
6. A method according to claim 5 , wherein said defining the speed limit curve includes setting each of the power limit exponent a and the compensator exponent b equal to about one-third.
7. A machine-readable storage medium containing machine-executable instructions for implementing a method of controlling rotational speed of a stall-controlled wind turbine of a wind-powered machine having a speed control system for controlling the rotational speed, wherein the stall-controlled wind turbine has a power-coefficient curve, said machine-executable instructions comprising:
a first set of machine-executable instructions for receiving a power limit signal corresponding to an output power limit P L for the stall-controlled wind turbine;
a second set of machine-executable instructions for determining a speed limit command based on a speed limit curve that is a function of: 1) the output power limit P L and 2) a performance-compensation term raised to the power of a compensator exponent, said compensator exponent being determined as a function of the power-coefficient curve; and
a third set of machine executable instructions for outputting the power speed limit command to the speed control system.
8. A machine-readable medium according to claim 7 , further comprising machine-executable instructions defining the speed limit curve by the equation:
ω
L
=
K
o
×
P
L
a
r
5
/
3
×
κ
b
wherein:
ω L is the rotational speed limit of the stall-controlled wind turbine;
K 0 is a constant chosen to match the power-coefficient curve approximately;
κ is the performance-compensation term;
a is a power limit exponent;
b is the compensator exponent; and
r is the radius of the wind turbine.
9. A method according to claim 8 , further comprising machine-executable instructions setting each of the power limit exponent a and the compensator exponent b equal to about one-third.