In a three-phase semi-converter, at a time one SCR and one diode conduct simultaneously. With SCR T1 conducting which diode(s) is most likely to conduct along with T1?

In a three-phase semi-converter, when SCR T1 is conducting, the diode that is most likely to conduct along with T1 is the diode connected to the phase that is negative at that instant. For example, if T1 is connected to phase A, and the phase order is A, B, C with A being positive, then diode D2 (connected to phase B) would likely conduct, as it would be reverse-biased during T1’s conduction, while diode D3 (connected to phase C) would be forward-biased and capable of conducting.

Therefore, with SCR T1 conducting, the most likely diode to conduct is the one associated with the phase that is at the most negative potential at that time.