Final answer:
The maximum ripple current through the output filter inductor in an H-Bridge converter occurs under bipolar modulation at a duty cycle of 0.5. This configuration causes both positive and negative swings, inducing maximum changes in the inductor.
Step-by-step explanation:
The question pertains to the ripple current through the output filter inductor of an H-Bridge converter and when it is at a maximum, under different modulation schemes and duty cycles. Ripple current is affected by the switching frequency, duty cycle (D1), and whether the modulation is unipolar or bipolar. In a bipolar modulation scheme, both the positive and negative swings contribute to the ripple, while in unipolar modulation, only one type of swing (either positive or negative) contributes to the ripple.
In the scenario given, the maximum ripple current would occur with the bipolar modulation when D1=0.5 because this setting operates the converter switches at their maximum rate, inducing maximum current changes in the inductor. While with unipolar modulation, the ripple is generally lower due to the fact that the switches do not change states from positive to negative as frequently as they do in bipolar modulation.
Discussion for (a) and (d)
For the given options (a) bipolar modulation with D1=0.5 and (d) unipolar modulation with D1=0.25, option (a) presents a case where the ripple current is maximum due to the largest amount of current change induced in the inductor. The correct answer to the student's question would be option B. (bipolar modulation and when D1=0.5).