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Pancake Resolvers >> Brush Type Motors >>
Brushless DC Motors
devices. Hall effect elements, sine cosine
resolvers, optical encoder, electromagnetic
and electrostatic pickups, magneto-resistors,
and magneto-diodes are currently being
used as rotor position sensors.
The specific requirements of each application
usually dictate the position sensing system
selections.The linear Hall effect ele
ment is the sensing systems most frequently
used because of its small size, low cost, and
simplified processing electronics. Figure 9 is
a functional control circuit for a two phase
brushless DC torque motor with linear Hall
effect rotor positions sensing. To obtain Hall
device output voltages proportional to the
sine and cosine of the rotor’s position, the
Hall devices are mechanically displaced 90
electrical degrees from each other, and are
V C
Control
Input
voltage
_
+
Hall Current Control Amplifier
K AMP
1(
V )
I C
H1 H2 H3
K2 _
VH +
K2 _
VH (800) 777-3393
then align with the stator’s BEMF or
torque waveform.The magnitude and
direction of the motor drive current is regulated
by varying the magnitude and polarity
of the Hall device control current.
The control equations are as follows:
(Refer to Fig. 9)
I C =K IV C
V H =K HI CBCos
Where
Ic = Hall device control current(Amp)
Vc = Input control Voltage (Volt)
K1 = Current amplifier gain (Amp/Volt)
V H = Hall device output voltage (Volt)
K H = Hall constant (Volt/Amp-KGauss)
B = Rotor permanent magnet field vector
V ( V )
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+
K2 _
VH +
V ( V )
V ( V )
Differential Amplifiers
_
+
_
+
_
+
K 3
K 3
K 3
Power Amplifiers
( )
Figure-10. Functional control circuit for a three phase brushless DC torque motor with Hall Effect positioning
sensor. positioning sensing.
AMP
V
10C
10B
0A
0C
0A
0B
Commutating Brushless DC Motors