Single-phase series converter made from two semi-converters Two identical semi-converters are connected in series to form a single-phase series converter supplied by v(t) = V_m sin(ωt). Let the firing angles be equal (α1 = α2 = α). If α1 = α2 = 0°, what is the average DC output voltage?

Introduction / Context:
A series converter formed by two semi-converters is used to improve input current symmetry and power factor compared to a single semi-converter. Understanding its average DC output at specific firing angles helps compare it with standard rectifier topologies.

Given Data / Assumptions:

• Input: v(t) = V_m sin(ωt).
• Two identical semi-converters in series, α1 = α2 = α.
• Consider α = 0° (immediate firing at each half-cycle start).
• Ideal devices; continuous, non-overlapping commutation considered.

Concept / Approach:
For a single semi-converter, the average output is V_dc,semi = (V_m / π) * (1 + cos α). With a properly phased series converter using equal angles, the resulting average voltage equals that of a full-controlled bridge at the same α for α within the practical range; at α = 0°, this reduces to V_dc = 2 V_m / π.

Step-by-Step Solution:
Recall: full-controlled bridge at α = 0° gives V_dc = 2 V_m / π.The series arrangement of two semi-converters with α1 = α2 yields an equivalent average characteristic matching the full bridge at α = 0°.Therefore, at α = 0°, V_dc = 2 V_m / π.

Verification / Alternative check:
Comparative plots of V_dc vs α show the series-converter curve coinciding with the full bridge at the end conditions, including α = 0°.

Why Other Options Are Wrong:

• (0) or (V_m/π): undervalue the rectified average at zero firing angle.
• (4 V_m/π): double counts; not supported by the series topology.
• (V_m/2): unrelated to average rectified values.

Common Pitfalls:

• Assuming two semi-converters simply add outputs arithmetically without considering conduction sequence.
• Confusing peak V_m with RMS values or misapplying scaling.

Final Answer:
(2 V_m / π)