Three Phase to Single Phase Bridge Cycloconverter

Three Phase to Single Phase Bridge Cycloconverter

• The circuit diagram of a three phase to single phase bridge cycloconverter is as shown in Figure A. Here two ac to dc converter 3-phase bridges (P-converter and N-converter) are connected to a common resistive load.
• Figure B shows the waveforms for f_o = 1 / 3 f_{in. The} thyristors from P-converter operate in pairs 16, 12, 32, 34, 54 and 56 to produce a 6-pulse positive output which corresponds to one full cycle of input but only the positive half cycle of the output.

Circuit Diagram of Three Phase to Single Phase Bridge Cycloconverter :

Figure A

• Then the thyristors from N-converter are gated in the sequence 1’6′, 1’2′, 2’3′, 3’4′, 4’5′ and 5’6′ to produce a 6-pulse negative output voltage which corresponds to one full cycle of input but only the negative half cycle of the output as shown in Figure B. Hence the waveforms of Figure B show the cycloconverter output for f_{o = 1 / 3} f_in.
• _{The type of load is purely resistive.}
• _{When either P or N converter is conducting they simply behave as 3-phase AC-DC bridge converter.} 
• _For α < 60° the load current will be continuous whereas for α ≥ 60° it will be discontinuous.
• Thyristors from both converters should never be turned on simultaneously, other AC supply will be short circuited.

Output Waveform of Three Phase to Single Phase Bridge Cycloconverter :

Figure B

Gating Sequence of Three Phase to Single Phase Bridge Cycloconverter :