Fig. 3 Single-phase to single-phase cycloconverter waveforms
a) input voltage
b) output voltage for zero firing angle
c) output voltage with firing angle p/3 rad.
d) output voltage with varying firing angle
The frequency of the output voltage, vo in Fig. 3b is 4 times less than that of vs, the input voltage, i.e. fo/fi=1/4. Thus, this is a step-down cycloconverter. On the other hand, cycloconverters that have fo/fi>1 frequency relation are called step-up cycloconverters. Note that step-down cycloconverters are more widely used than the step-up ones.
The frequency of vo can be changed by varying the number of cycles the positive and the negative converters work. It can only change as integer multiples of fi in 1f-1f cycloconverters.
With the above operation, the 1f-1f cycloconverter can only supply a certain voltage at a certain firing angle a. The dc output of each rectifier is: