Periods of Conduction and Freewheeling in a Single Phase Semiconverter with a Freewheeling Diode

In a single-phase semiconverter, a freewheeling diode is used to provide a path for the current flow when the thyristor is turned off. This diode allows the current to flow through the load during the freewheeling period. The firing angle, denoted by 'a', determines the time at which the thyristor is triggered to conduct the load current.

Conduction Period:
- The conduction period starts when the thyristor is triggered to conduct the load current and ends when the thyristor is turned off.
- During the conduction period, the load current flows through the thyristor and the load.
- The conduction period is given by the difference between the firing angle and the angle at which the thyristor turns off.
- Therefore, the conduction period is 'p - a', where 'p' represents the period of the AC supply waveform.

Freewheeling Period:
- The freewheeling period starts when the thyristor is turned off and ends when the next firing pulse is given to the thyristor.
- During the freewheeling period, the load current flows through the freewheeling diode and the load.
- The freewheeling period is given by the difference between the firing angle of the next thyristor and the angle at which the thyristor turns off.
- Since the freewheeling diode conducts the load current during this period, the angle at which the thyristor turns off is the same as the angle at which the freewheeling diode starts conducting.
- Therefore, the freewheeling period is 'p - a', where 'p' represents the period of the AC supply waveform.

Conclusion:
- The periods of conduction and freewheeling in a single-phase semiconverter with a freewheeling diode are both 'p - a', where 'p' represents the period of the AC supply waveform.
- This means that the thyristor conducts the load current for a certain duration determined by the firing angle, and during the remaining duration, the freewheeling diode conducts the load current.