Single-phase semiconverter feeding a resistive load If the firing angle is α (in radians), each controlled device (thyristor) conducts for how long per half-cycle?

Introduction / Context:
A single-phase semiconverter (half-controlled bridge) with a resistive load produces a chopped sinusoidal output. The conduction interval of each thyristor depends on the firing angle α and the natural commutation at the next current zero.

Given Data / Assumptions:

• Resistive (R) load, negligible inductance.
• Thyristor is fired at ωt = α in each relevant half-cycle.
• Natural commutation occurs at the next zero crossing of source voltage/current at ωt = π.

Concept / Approach:
In an R-load, current and voltage are in phase. Once the thyristor is triggered at α, it conducts until the source current naturally reaches zero at the end of the half-cycle (ωt = π). Therefore, the conduction interval equals (π − α).

Step-by-Step Solution:
Trigger at ωt = α.Conduction continues to ωt = π (current goes to zero).Thus, conduction duration = π − α.

Verification / Alternative check:
Plotting instantaneous current for an R load confirms conduction ends at the natural current zero coinciding with the voltage zero.

Why Other Options Are Wrong:
π radians: Would imply conduction over the full half-cycle regardless of α.
(π + α): Physically impossible within a half-cycle.
(π − 0.5 α) or α: Do not match natural commutation boundary at π.

Common Pitfalls:
Confusing inductive load behavior (where conduction can extend) with purely resistive load behavior.

Final Answer:
(π − α) radians