Environmental Engineering Reference
In-Depth Information
e ðÞ¼ X g X g ; rated :
ð 11 : 6 Þ
The proportional and integral gains are scheduled such as the rotor DOF has the
same response of a closed-loop system defined by the natural frequency x 0 and
the damping ratio f 0 at each wind speed in the full load region. The scheduling
gains are calculated using the following equations
K P ðÞ¼ 2I D X r ; rated f 0 x 0
N dP
dh
ð 11 : 7 Þ
K I ðÞ¼ I D X r ; rated x 0
N dP
dh
ð 11 : 8 Þ
where I D is the drive-train inertia, X r ; rated is the rated rotor speed, N is the gearbox
ratio, and d dh represents the sensitivity of the rotor aerodynamic power to the
scheduling parameter (e.g., collective blade pitch angle). For further details on
how the sensitivity is converted into a function of the scheduling parameter, the
reader is referred to [ 4 ].
11.2.3.2 Generator Torque Control
The generator torque control is basically used in the under-rated region to follow
the maximum power production by changing the rotor speed as the wind speed
changes. In the above-rated region, two approaches are presently used, the first one
uses constant generator torque (rated value), with this approach the power will be a
function of the fluctuations of the rotor speed about its rated value as the wind
speed changes, these speed fluctuations are minimized by the pitch controller. The
second approach is to use a constant generator power, which means to adapt the
generator torque within certain limits to the changes of the rotor speed in order to
produce constant output power. This second approach assumes that the generator
torque can move above its rated value to some maximum value, and the fluctua-
tions are constrained to a maximum torque rate.
Considering maximum power production in the partial load region, the gen-
erator torque is a function of the rotor speed such as
T g ¼ pqR 5 C P ; max
2k 2 N 3
X g
ð 11 : 9 Þ
where q is the air density, R the rotor radius, C P ; max is the maximum power coef-
ficient, k is the tip speed ratio corresponding to C P ; max . Considering the constant
output power approach for the full load region, the generator torque is given as
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