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 120o and 240o 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