Single-phase full-wave AC voltage regulator with resistive load Considering a purely resistive load, what is the average load current over one full cycle for a single-phase full-wave AC regulator (antiparallel SCRs with phase control)?

Introduction / Context:
Full-wave AC voltage regulators using antiparallel SCRs control the RMS voltage applied to a resistive load by delaying turn-on within each half cycle. For resistive loads, current is in phase with voltage and reverses direction every half cycle, which determines the average current value over a full period.

Given Data / Assumptions:

• Load is purely resistive.
• Full-wave control, triggering in each half cycle.
• No DC bias present in the source.

Concept / Approach:

Average (DC) current is the time-average of instantaneous current over a full cycle. With a resistive load on an AC source, instantaneous current i(t) = v(t)/R follows the polarity of v(t). Positive and negative half cycles are equal in magnitude and opposite in sign, so the net average over a full cycle is zero regardless of firing angle (provided conduction occurs symmetrically in both halves).

Step-by-Step Solution:

Verification / Alternative check:

Even with phase control, provided both halves are triggered equally, the symmetry ensures zero DC component; only the RMS value changes.

Why Other Options Are Wrong:

• “Cannot be zero / always positive”: contradict symmetry for a resistive AC load.
• “May be sometimes zero”: it is always zero under the stated conditions.

Common Pitfalls:

Confusing average (DC) with RMS; a regulator changes RMS value but not the fact that the average over a full cycle is zero for resistive AC loads.

Final Answer:

is always zero