Ripple frequency of three phase half bridge converter

[jaus tail]

Homework Statement

Homework Equations

Three phase half controlled bridge rectifier can have 3 pules at output or 6 pulses depending on firing angle.

The Attempt at a Solution

Ripple frequency is m times the input frequency where m is number of pulses.
It can be 3 or 6. So why have they marked A as right answer? I think there can be two right answers.

 

[Baluncore]

If “half-controlled” meant half wave rectification, then the answer is (A)3 times.
If “half-controlled” meant full wave with only say a diode below and a controlled rectifier above then the reference output would be the lowest voltage from the diodes and the output would be the controlled phase making three per cycle so the answer would still be (A)3 times.
But all things are relative.
If the three phase transformer is not centre tapped with the neutral acting as the reference, the diodes would produce the half wave reference, not output pulses.