Intelligent wind power unit with tandem wind rotors - Wind Power Generation and Wind Turbine Design - page 334

2. It is necessary to equip the wind rotor with the brakes and/or the pitch control

mechanisms, to suppress the abnormal rotation and the overload at the strong
wind. To keep good quality of the electric power by increasing the rotational
speed of the armature, it is necessary to prepare the large-sized generator with
multi-poles or the accelerating gearbox.
There are few areas applicable to the traditional wind turbine with the rated

3.

mode at the wind velocity faster than 11 m/s. It is desired, for the next leap of
the wind turbine technologies, to get the fruitful output at not only rich but also
poor wind circumstances.

To overcome above weak points, the authors invented the superior wind power
unit called “intelligent wind power unit”. This unit is composed of the large-sized
front wind rotor, the small-sized rear wind rotor and the peculiar generator with the
inner and the outer rotational armatures without the traditional stator. The front and
the rear wind rotors drive the inner and the outer armatures in the upwind type or
drive the outer and the inner armatures in the downwind type, respectively. The rota-
tional direction and speed of both wind rotors/armatures are free, and automatically
and smartly adjusted pretty well in response to the wind circumstances. This unit is
applicable to the area with not only rich wind circumstances such as Middlegrunden
offshore [1], but also poor circumstances having weak and/or fl uctuating wind.

2 Previous works on tandem wind rotors

The idea of the tandem wind rotors has been proposed [2], and Ushiyama et al.
could also increase the output using the model tandem wind rotors, as follows [3].
The front wind rotor consists of six blades with the diameter of 0.8 m, and the rear
wind rotor consists of three blades with the diameter of 1.2 m, as shown in Fig. 1.
The front and the rear wind rotors are connected directly to the stator casing and
the armature of the traditional generator, respectively. The outputs against the rela-
tive rotational speed are shown in Fig. 2. The maximum outputs are 2.6 W at the
wind velocity V = 6 m/s, 19.8 W at V = 8 m/s, and 38.9 W at V = 10 m/s, in the
experimental results. This paper discusses the output in the followings. The rated
output of the generator is 36 W at the rotational speed N T = 950 min − 1 but the
actual output is 38.9 W with N T = 768 min − 1 at 10 m/s. That is, the output is higher
than the rated output even if the rotational speed is slower than the rated speed,
and the relative rotational speed is increased by the counter-rotation. As a result,
this paper concluded that the experimental results of the model demonstrated the
technical possibility of the counter-rotating-type wind turbine generator. Jang and
Heo brought recently the above ideas into his researches and has proposed the
tandem type composed of the small-sized front wind rotor and the large-sized rear
wind rotor [4].
In 2002, Appa Technology Initiative developed the counter-rotating type wind
turbine (CRWT) and the prototype was supplied to the fi eld tests in California. The
prototype composed of tandem wind rotors, whose diameters are 4 m and blade
numbers are 2 with the tip speed ratio l = 6, and the isolated traditional generator