Advantages & Disadvantages of Cyclo-converter
Fig: Single-phase to single-phase cycloconverter (using thyristor bridges)
Advantages of Cycloconverter:
1. In a cyclo-converter, ac power at one frequency is converted directly to a lower frequency in a single conversion stage.
2. Cyclo-converter functions by means of phase commutation, without auxiliary forced commutation circuits. The power circuit is more compact, eliminating circuit losses associated with forced commutation.
3. Cyclo-converter is inherently capable of power transfer in either direction between source and load. It can supply power to loads at any power factor, and is also capable of regeneration over the complete speed range, down to standstill. This feature makes it preferable for large reversing drives requiring rapid acceleration and deceleration, thus suited for metal rolling application.
4. Commutation failure causes a short circuit of ac supply. But, if an individual fuse blows off, a complete shutdown is not necessary, and cyclo-converter continues to function with somewhat distorted waveforms. A balanced load is presented to the ac supply with unbalanced output conditions.
5. Cyclo-converter delivers a high quality sinusoidal waveform at low output frequencies, since it is fabricated from a large number of segments of the supply waveform. This is often preferable for very low speed applications.
6. Cyclo-converter is extremely attractive for large power, low speed drives.
Disadvantages of Cycloconverter:
1. Large number of thyristors is required in a cyclo-converter, and its control circuitry becomes more complex. It is not justified to use it for small installations, but is economical for units above 20 kVA.
2. For reasonable power output and efficiency, the output frequency is limited to one-third of the input frequency.
3. The power factor is low particularly at reduced output voltages, as phase control is used with high firing delay angle.