Auxiliary-commutated (forced) chopper device stress In an auxiliary-commutated chopper, the instantaneous peak current in a thyristor equals:

Introduction / Context:
Auxiliary (forced) commutation schemes briefly superimpose a resonant current on the load current to reverse-bias or momentarily reduce current through a main thyristor for turn-off. Understanding peak device current is essential for safe ratings.

Given Data / Assumptions:

• Chopper uses LC commutation applying a reverse or additional current pulse.
• Load current is nonzero at the commutation instant.
• Idealized short commutation interval with low damping.

Concept / Approach:

At commutation, device currents combine vectorially along the same conduction path instant by instant. A thyristor may momentarily conduct both the load current and the resonant capacitor current (depending on topology and which device is carrying which component), producing a peak equal to the sum of those peak magnitudes in the worst case.

Step-by-Step Solution:

Verification / Alternative check:

Design guides recommend sizing SCRs for the algebraic sum during overlap, considering tolerances, since the resonant current pulse adds to the steady load current in a given device path.

Why Other Options Are Wrong:

Considering only one component underestimates device stress; “none of the above” contradicts standard commutation analysis.

Common Pitfalls:

Ignoring simultaneous current paths; assuming the capacitor current always subtracts rather than adds; overlooking timing that can produce additive peaks.

Final Answer:

The sum of the peak load current and the peak commutating capacitor current