How do star- (wye) plus delta-connected windings provide a phase change every 30°?
Draw a delta, and draw a star across it from the same three vertices. This is effectively a phasor diagram.

Measure the angle between each leg of the star and either delta from the same vertex. You should find it's 30 degrees.

So between three phases of a delta waveform and three phases of a star waveform, and their six complements, you will find 12 waveforms equally spaced at 30 degrees.

Now, note that a single phase bridge rectifier provides two output pulses per cycle, one from the waveform's peak, and one from its complement (i.e. a positive pulse from the negative peak).