As the stator voltage is reduced the air gap flux and torque also reduced .
The torque is proportional to the square of the stator supply voltage and a reduction of the stator voltage can produce a reduction in the speed .
Where , b< 1
The range of speed control depends on the slip for maximum torque Smax .
the induced voltage is proportional to the flux , frequency and r.m.s air gap flux .
For a low slip motor , the speed range is very narrow.
For a low slip motor , the speed range is very narrow.
This type of voltage control is not suitable for a constant torque load and is normally applied to applications requiring low starting torque and narrow range of speed control at retivily low slip .
where , Km is constant and depends on the number of turns of the stator winding.
- The stator voltage can be varied by :
- AC voltage controller
- Voltage-fed variable DC link inverter
- pulse width modulation (PWM) inverter
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