Cycloconverter fed to Induction motor

Cyclo converter is a single stage frequency conversion device which converts fixed AC frequency to variable AC frequency. A three phase, three pulse cyclo converter feeding a three phase induction motor is shown below

A cyclo converter fed induction motor drive has following features:

1.The machine operates at its rated flux conditions due to voltage control is made in the converter itself.

2.A cyclo converter operates on line commutation, the losses occurred by forced commutation is eliminated. The converter operates at lag power factor and very poor line power factor for light loads.

3.By modulating thyristors firing angle the high quality sinusoidal waveform is obtained at all frequencies.

4.A cyclo converter is capable of power transfer between AC source to motor load and vice versa.

5.The operation is smooth and efficient due to less significance of torque pulsation and harmonic losses of the machine.

6.At any power factor it can feed power to load with four quadrant operation which is simple and straight forward.

7. The output frequency of cyclo converter is limited to one-third of input frequency. A speed control range of 0-33% of base speed is possible.

8.It requires many thyristors for line commutation, if a thyristor fails no shut down is required and output can be made available without any interruption.

9.Regeneration is inherent in the complete speed range.

Advantages:

1.It has reversibility and four quadrant operation

2.It is justified for large horse power applications

3.Very smooth low speed operation with the least torque ripple

4.Output voltage is replica of reference voltage

5.By using controlled rectifiers and firing angles the output voltage may be controlled

Disadvantages:

1.It requires large number of thyristors

2.At higher ratings the power factor is poor and harmonics are
present in output

3.Converter operates at lagging power factor.

Applications: