Definition:
Cycloconverter is a device which converts input power at one frequency to output power at a different frequency with only one stage conversion. It is also known as cycloinverter.
A cycloconverter (CCV) is basically a one-stage frequency changer. Here, one stage conversion means that input AC supply is directly converted to variable frequency output with the use of power electronic switches such as thyristors. The thyristors are switched ON and OFF in such a manner to synthesize variable frequency AC output. It does not require any intermediate DC link. This is reason, it is very efficient.
The input power of this device is fixed AC voltage having a particular frequency. However, the output of the device is variable voltage & variable frequency. The output voltage and frequency of this device is controllable.
A cycloconverter is different from an AC voltage Controller. In AC voltage controller, a fixed input AC voltage is converted to variable AC voltage without any change in frequency. While in CCV, the frequency of input AC supply is changed.
There are mainly two types of cycloconverter:
- Step-up CCV
- Step-down CCV
In step-up type of cycloconveter, the output frequency (fo) is more than the input supply frequency (fs) i.e. fo>fs. This type of CCV is not widely used. Forced commutation is used in this type which make it complex. However, in step-down type, the output frequency is lower than the supply frequency i.e. fo<fs. This is more common and widely used. Line or natural commutation is used to switch off a thyristor in this type of CCV which makes it simple.
Application of Cycloconverter:
The general use of cycloconverter is to provide either a variable frequency power from a fixed input frequency power as in AC motor speed control or a fixed frequency power from a variable frequency power as in aircraft or wind generators.
Some of the major applications of cycloconverter are as follows:
- Speed control of high power AC drives
- Induction heating
- Static VAR compensation
- It is used for converting variable speed alternator voltage to constant frequency output voltage for use as power supply in aircrafts or shipboards.