Figure $3$: Three phase semicontrolled converter circuit for Question $3$

$($a$)$ Draw vd waveform and identify the devices that conduct during various

intervals. You are expected to make appropariate selection of the values

of vs$,$ Ls and Id$.$

$($b$)$ What is the function of the diode Df $.$

$($c$)$ Repeat part $($a$)$ assuming that diode Df is not present in the converter

of Figure $3.$