Three Phase to Three phase Cycloconverter

Power Electronics, Cycloconverter, AC to AC converter, Three phase to Three phase Cycloconverter

1. 1. Circuit Diagram

2. 2.1 Working of the circuit The firing schedules of thyristors in phase groups B and C are same as that of group A but lag by 120 o and 240 o respectively. The average value of output voltage can be varied by varying the firing angles of the SCRs on conduction, whereas the frequency of the output voltage can be varied by changing the sequence of firing of the SCRs.

3. 2.2 Working of the circuit From the circuit diagram, it is evident that one group of thyristors (group of 3) is responsible for producing positive alterations (known as group P) and the other group (known as group N) is responsible for negative alterations. Each group consists of 3 SCRs, thus in total 6 SCRs per phase. This means, in all 18 SCRs are required for the whole circuit.

4. 2.3 Working of the circuit With a balanced load, the neutral connection is no longer necessary and may be omitted. It has been assumed that the output frequency of cycloconverter is less than the supply frequency.

5. 3.1 Waveform for Phase R (Wire A)

6. 3.2 Waveform for Phase R (Wire B)

7. 3.3 Waveform for Phase R (Wire C)

8. 3.4 All Output Waveforms