Intelligent wind power unit with tandem wind rotors - Wind Power Generation and Wind Turbine Design - page 341

because the electric characteristics depend only on the relative rotational speed
between both armatures. The rotational speed of the motor which represents the
relative speed (in this case, rotational speed of inner armature) was controlled by
the inverter. Another inverter and the transformer were used to control the input
frequency f 2 and voltage E 2 of the secondary feed of the generator. The input to the
generator, namely the output of the tandem wind rotors, was estimated with the
rotational speed and torque. The output was measured by the power meter and
consumed through electric bulbs (lamps).
In the bench test, the output frequency f = f 1 was kept constant at 60 Hz, and the
output voltage E = E 1 was also kept constant at 200 V, regardless of the external
bulb load P bulb .
Figure 11 shows the characteristics in keeping the output voltage E 1 and fre-
quency f 1 constant as described just above, where N T is the relative rotational speed
(= N F N R , N F and N R are the outer and the inner rotational speed, and give the

positive value in the N F direction). The input frequency f 2 is in inverse proportion
to the relative rotational speed N T irrespective of the external load P bulb , though the
phase must be changed at the higher relative speed than the synchronous speed
900 min − 1 . The input voltage E 2 depends not only on N T but also on P bulb , namely
the output P 1 . The input P 2 comes to be negative at the higher rotational speed than
the synchronous speed 900 min − 1 , as shown in Fig. 12. That is, P 2 changes fruitfully
from the input to the output, and the net output from the generator is P = P 1

−

P 2 .
The output and/or the input are given in Fig. 13, for instance, when the tandem
wind rotors with the relative rotational speed N T and the rotational torque T against

−

90

f 1

60

30

f 1 , E 1

f 2 , E 2 P bulb

0

90 W
450 W
940 W
1200 W
1650 W

f 2

-30

300

E 1

200

100

E 2

0

0 200 400 600 800 1000 1200 1400

N T min -1

Figure 11: Effect of the external load and the relative rotational speed on the
input frequency f 2 and voltage E 2 .