Effect of source inductance (overlap) in a three-phase fully controlled bridge converter What is the principal effect on the output when finite source inductance causes commutation overlap?

Introduction / Context:
In controlled rectifiers, source (or supply) inductance prevents instantaneous current transfer between device pairs, creating an overlap interval during which both outgoing and incoming thyristors conduct. This overlap reduces the effective output voltage because a portion of the line-to-line voltage is “lost” in the commutation process.

Given Data / Assumptions:

• Three-phase fully controlled bridge (six-pulse) under continuous current.
• Finite source inductance causes a commutation angle μ > 0.
• Device drops neglected for first-order understanding.

Concept / Approach:

During overlap, two line phases simultaneously feed the DC link, effectively shorting part of the line-to-line voltage across source inductances. The DC output sees a lower instantaneous voltage than the ideal case. Averaging across the cycle yields a DC output smaller than the ideal value (at the same firing angle). Current generally is determined by the load (e.g., E–L–R), not directly increased by overlap.

Step-by-Step Solution:

Verification / Alternative check:

Measured waveforms show flattened notches during commutation and reduced DC average proportional to μ; analytical models compute ΔV ≈ (ωL_s) * I_d * (constant), confirming the drop.

Why Other Options Are Wrong:

Claimed increases in output voltage contradict physics of overlap; statements about increased current are not generally true without specifying load dynamics.

Common Pitfalls:

Assuming overlap only adds ripple; ignoring that it also lowers mean output voltage and can impact control range near inversion.

Final Answer:

Decrease in the average output voltage