237-00156 SofTec Microsystems SRL, 237-00156 Datasheet - Page 18

• Manufacturer Part Number: 237-00156
• Description: BOARD ISOLATION FOR ST7
• Manufacturer: SofTec Microsystems SRL
• Type: Optoisolation Boardr

Specifications of 237-00156

• Contents: *
• For Use With/related Products: STMicro ST7FMC Motor Control Device
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

AK-ST7FMC User's Manual
rotates while the conductors remain stationary. In the DC commutator motor,
the current polarity is altered by the commutator and brushes. On the
contrary, in the brushless DC motor, the polarity reversal is performed by
power transistors switching in synchronization with the rotor position.
1
Therefore, BLDC motors often incorporate either internal or external position
sensors to sense the actual rotor position or the position can be detected
without sensors.
The BLDC motor is driven by rectangular voltage strokes coupled with the
given rotor position. The generated stator flux interacts with the rotor flux,
(which is generated by a rotor magnet) and defines the torque and thus
speed of the motor. The voltage strokes must be properly applied to the two
phases of the three-phase winding system so that the angle between the
stator flux and the rotor flux is kept close to 90° to get the maximum
generated torque. Due to this fact, the motor requires electronic control for
proper operation.
1.4 The AC Induction Motor
The AC induction motor is a rotating electric machine designed to operate
from a three-phase source of alternating voltage. The stator is a classic three
phase stator with the winding displaced by 120°. The most common type of
induction motor has a squirrel cage rotor in which aluminum conductors or
bars are shorted together at both ends of the rotor by cast aluminum end
rings. When three currents flow through the three symmetrically placed
windings, a sinusoidally distributed air gap flux generating the rotor current is
produced. The interaction of the sinusoidally distributed air gap flux and
induced rotor currents produces a torque on the rotor. The mechanical
angular velocity of the rotor is lower then the angular velocity of the flux
wave by so called slip velocity.
In adjustable speed applications, AC motors are powered by inverters. The
inverter converts DC power to AC power at the required frequency and
amplitude. The inverter consists of three half-bridge units where the upper
and lower switches are controlled complimentarily. As the power device's
turn-off time is longer than its turn-on time, some dead-time must be inserted
between the turn-off of one transistor of the half-bridge and turn-on of it's
complementary device. The output voltage is mostly created by a pulse
width modulation (PWM) technique. The three-phase voltage waves are
shifted 120° to each other and thus a three-phase motor can be supplied.
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