Environmental Engineering Reference
In-Depth Information
14.2.1.5 Actuators: Pitch and Yaw Motors, Torque
The pitch and yaw actuators—see Fig.
14.2
, numbers (5) and (4) respectively- are
NXT motors (see Fig.
14.7
b and [
5
]). They are DC motors and deliver a high
torque thanks to its internal speed reduction gear train (gearing ratio = 1:48).
Because of that, they turn slowly and efficiency is somewhat reduced. Although
each one includes an internal rotation encoder to measure the position of the shaft
with one degree resolution, we use glide wheel angle sensors at the end position of
the actuator drive-train in order to have a direct measurement of the actual angles
(see also Sect.
14.2.1.4
).
The NXT motors consume a current of 60 mA in a no-load situation and up to
2 A in a stalled situation, with a maximum stalled torque of 50 N cm for a few
seconds. The NXT motors are protected by a thermistor (Raychem RXE065 or
Bourns MF-R065). That means that the high 2 A current and associated stalled
torque can be sustained only for a few seconds. They have a non-standard phone
plug type to connect to the NXT microprocessor. At the regular 9 v input the
motors run at 170 revolutions per minute (rpm). For other inputs the motors follow
the linear characteristics:
X
motor
¼ð
170
=
9
Þ
u
ð
14
:
4
Þ
X
motor
¼ð
170
=
50
Þ
T
motor
þ
170
ð
14
:
5
Þ
ð
00
:
94
=
30
Þ
T
motor
þ
0
:
06
ð
for 0
T
motor
30 N.cm
Þ
i
motor
¼
ð
14
:
6
Þ
ð
1
=
20
Þ
T
motor
1
=
2
ð
for T
motor
[ 30 N.cm
Þ
with X
motor
the motor speed in rpm, u the voltage applied to the motor in volts,
T
motor
the motor torque in N. cm and i
motor
the motor current in A [
8
].
14.2.1.6 WT Microprocessors: Real-Time Control for Rotor Speed,
Pitch, Yaw, Torque, Power
The individual wind turbine control system is based on the intelligent NXT 2.0
LEGO
brick, which has a 32-bit microprocessor, a large matrix display, 4 input
and 3 output ports, and Bluetooth and USB communication links. The system is
interchangeable with the new EV3 Intelligent LEGO
Brick [
5
] or the Arduino
microcontroller [
9
].
Each wind turbine has one NXT microcontroller attached to the foundation (see
Fig.
14.2
). It is connected to the pitch and yaw motors (output ports) and the rotor
speed, pitch angle, voltage, and current sensors (input ports). An additional NXT
microcontroller is connected to the four yaw angle sensors (input ports) of the four
wind turbines of the wind farm.
In this way, the wind farm control system presents a hierarchical structure, with
a central computer that runs under Matlab for the Supervisory Control and Data
