## Cycloconverter

• It is an apparatus or device which convert constant AC voltage, constant frequency input supply into variable voltage, variable frequency supply.

### Principle of operation

• The Cycloconverter is made of two converters in which one converter works as a positive converter and second converter works as negative converter. The firing angle of both converters are set such that
• αPN  = π

Where

• αP = Firing angle of positive converter and
• αN = Firing angle of negative converter
• The firing angle of both converters is set such that it will change the output frequency.
• The P – converter and N – converter is made by series connection of variable alternating supply and diode.
• The output voltage of each converter becomes equal in the P – type converter and N – type converter of the ideal Cycloconverter.
• The output voltage at the terminal of the Cycloconverter is either of the alternating voltage of the converter because each converter has equal alternating voltage amplitude, phase as well as frequency.

• The power flows from either load to converter to converter to load by controlling the firing angle of each converter.
• The unidirectional property of the P – converter and N – converter results in P – converter works in positive half cycle of alternating supply and N – converter works in negative half cycle of alternating supply.
• It does not depend upon phase between load voltage and load current.

### Effect of Load Displacement On Working of Cycloconverter

• The voltage and current waveform for the ideal Cycloconverter for different load displacement is shown in the figure B. ( Displacement angle – It is angle between fundamental current and voltage of load current.)

• The current flows through converters when both converters are operated in the rectifier mode.
• Figure B shows waveforms for each converter.

• Both converters operate in inverting mode when the load displacement angle is 180o
• As the load is regenerative, the power flows from load terminal to output terminal of Cycloconverter.

#### Load displacement angle 80o lagging

• The converter operates in the rectifier mode during 100o of the positive half cycle from its first zero.
• The power flows from Cycloconverter to load during this mode.
• The converter operates in the inverter mode during 80o of the remaining positive half cycle of the alternating supply.