Environmental Engineering Reference
In-Depth Information
3.
The rear wind rotor reaches the maximum rotational speed at the rated wind
velocity. Under the rated wind velocity, both wind rotors work at the best
effi ciencies. Over the rated wind velocity, the rated operation mode starts,
where the output is kept constant regardless of the wind velocity.
With more increment of the wind velocity, the rear wind rotor decreases its
4.
rotational speed gradually, stops, then it begins to rotate in the same direction
of the front wind rotor, so as to its rotational torque coincides with the larger
rotational torque of the front wind rotor. When the rear wind rotor rotates in the
same direction to the front wind rotor, the fl ow in the blowing mode suppresses
the abnormal rotation of the front wind rotor.
The above operating conditions enable successfully not only to increase the
output but also to guarantee the quality of the electric power, namely power supply
frequency at the rated operation without the traditional brake and/or the pitch con-
trol mechanisms. That is, the relative rotational speed between the front and the
rear wind rotors affects directly the quality of the electric power. The power supply
frequency can be kept constant when the wind rotors are designed so as to keep the
relative rotational speed constant. The output can also be kept constant when the
wind rotors are designed so as to keep the value, determined by the relative rota-
tional speed and torque, constant. Moreover, the counter-rotation under the rated
wind velocity makes the output higher in the poor wind circumstances, as reviewed
before. That is a remarkable advantage for area which has no acceptable wind
circumstance in the power generation.
4 Preparation of double rotational armature type generator
4.1 Double-fed induction generator with double rotational armatures
The doubly fed induction generator is installed in the large-scale wind power unit
for the grid-connected electric power system [9]. Figure 8 shows the system dia-
gram where the tandem wind rotors rotate the double rotational armature type gen-
erator. It is not necessary to control the wind rotor speeds, namely the rotational
frequency
f
W
, mechanically because the revolving electromagnetic fi eld is induced
from the grid-connected electricity and its speed can be adjusted freely by the
frequency
f
2
modulation (the inverter) for the inner armature, namely the second-
ary feed. Besides, the system output
P
and voltage
E
can also be adjusted with the
input
P
2
and voltage
E
2
for the secondary feed. That is, it is easy to keep the output,
the frequency and the voltage constant as required in the grid system.
Figure 9 shows the trial model of the double rotational armature type doubly fed
induction generator. The rated output is
P
= 1.2 kW at the synchronous rotational
speed of 900 min
− 1
, while the output voltage is
E
= 200 V, the current is
I
= 3.5 A,
the frequency is
f
= 60 Hz and the number of the pole is 8.
Figure 10 shows the bench tests for the trial model. The work of the tandem
wind rotors was replaced by the motor. The motor shaft was connected to the shaft
of the inner armature while the shaft of the outer armature was kept stationary
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