Civil Engineering Reference
In-Depth Information
FIGURE 5-14
Maximum power operation using rotor tip-speed control scheme.
have significant error particularly in a large wind farm with shadow effects.
Being sensitive to the changes in the blade surface, the optimum TSR grad-
ually changes. The computer reference TSR must be changed accordingly
many times over the life. This is expensive. Besides, it is difficult to determine
the new optimum tip-speed ratio with changes that are not fully understood,
nor easily measured.
5.6.2
Peak Power Tracking Scheme
The power versus speed curve has a single well-defined peak. If we operate
at the peak point, a small increase or decrease in the turbine speed would
result in no change in the power output, as the peak point locally lies in a
flat neighborhood. Therefore, a necessary condition for the speed to be at
the maximum power point is as follows:
dP
d
ω
=
0
(5-3)
This principle is used in the control scheme (
Figure 5-15
)
. The speed is
increased or decreased in small increments, the power is continuously mea-
sured, and
is continuously evaluated. If this ratio is positive, meaning
we get more power by increasing the speed, the speed is further increased.
On the other hand, if the ratio is negative, the power generation will reduce
if we change the speed any further. The speed is maintained at the level
where
∆
P
/
∆ω
is close to zero. This method is insensitive to the errors in local
wind speed measurement, and also to the wind turbine design. It is, there-
fore, the preferred method. In a multiple machine wind farm, each turbine
must be controlled by its own control loop with operational and safety
functions incorporated.
∆
P
/
∆ω
