The input voltage, vs is an ac voltage at a frequency, fi as shown in Fig. 3a. For easy
understanding assume that all the thyristors are fired at a=0° firing angle, i.e. thyristors act like diodes. Note that the firing angles are named as aP for the positive converter and aN for the negative converter.
Consider the operation of the cycloconverter to get one-fourth of the input frequency at the output. For the first two cycles of vs, the positive converter operates supplying current to the load. It rectifies the input voltage; therefore, the load sees 4 positive half cycles as seen in Fig. 3b. In the next two cycles, the negative converter operates supplying current to the load in the reverse direction. The current waveforms are not shown in the figures because the resistive load current will have the same waveform as the voltage but only scaled by the resistance. Note that when one of the converters operates the other one is disabled, so that there is no current circulating between the two rectifiers.