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How do the speed of AC induction motor is controlled?
In this method, speed of an induction motor is controlled by injecting a voltage in rotor circuit. If we inject emf which is in phase with the rotor induced emf, rotor resistance will decrease. Thus, by changing the phase of injected emf, speed can be controlled.
How are AC motors controlled?
An AC motor controller is known as the device that controls the speed of the AC motor. The rectifier converts AC input into DC (direct current), while the inverter switches the DC voltage to an adjustable frequency AC output voltage. The inverter can also be used to control output current flow if needed.
What causes power to flow through an AC motor?
As the coils are energized, the magnetic field they produce between them induces an electric current in the rotor. The interaction between the two fields causes the rotor to turn. As the magnetic field alternates between the red and blue coils, it effectively rotates around the motor.
Why is starting current high in a motor?
This high current in the rotor will create its own magnetic field which opposes the main stator magnetic field, this weakens the stator magnetic field so the back EMF in the stator will drop and the supply voltage will be much higher than the stator back EMF and so the supply current increases to a high value.
Where is VFD used?
The most common uses of a VFD are for control of fans, pumps and compressors, and these applications account for 75% of all drives operating globally. Soft starters and across-the-line contactors are other, less sophisticated types of motor controllers.
How does a TRIAC phase triggering circuit work?
This type of AC motor speed control gives a fully variable and linear control because the voltage can be adjusted from zero to the full applied voltage as shown. This basic phase triggering circuit uses the triac in series with the motor across an AC sinusoidal supply.
What happens when a TRIAC switch is moved to position B?
If the switch is moved to position B gate current flows at every half cycle the same as before and full power is drawn by the lamp as the triac operates in modes Ι+ and ΙΙΙ–. However this time when the switch is connected to position C, the diode will prevent the triggering of the gate when MT2 is negative as the diode is reverse biased.
What are the four modes of operation of a TRIAC?
And these four modes in which a triac can be operated are shown using the triacs I-V characteristics curves. In Quadrant Ι, the triac is usually triggered into conduction by a positive gate current, labelled above as mode Ι+. But it can also be triggered by a negative gate current, mode Ι–.
When does triac turn off at end of half cycle?
As we have seen above, the triac turns-OFF automatically at the end of the half-cycle and the VR1 – C1 triggering process starts again on the next half cycle.