Thyristor commutation classification Which commutation method explicitly uses an external pulse source to force the current to zero in the thyristor (external pulse commutation)?

Introduction / Context:
Commutation in thyristor converters refers to turning the device off by forcing its current to zero and reverse-biasing its junctions. Various classes categorize how this is achieved. Recognizing the class that uses an external pulse source is important for high-performance or special-purpose converters.

Given Data / Assumptions:

• Standard commutation classes A through F.
• Device is a line-commutated or force-commutated SCR.

Concept / Approach:

Class E commutation employs an external pulse (often via a pulse transformer or an auxiliary supply) to apply a reverse current or reverse voltage across the SCR to turn it off, independent of the main load network resonance or the line voltage zero-crossing.

Step-by-Step Solution:

Verification / Alternative check:

Commutation taxonomy: A (load), B (resonant), C (auxiliary with complementary SCR), D (impulse or parallel capacitor), E (external pulse), F (line/natural).

Why Other Options Are Wrong:

(a) and (b) rely on load/auxiliary resonant networks; (d) is natural at line zero-crossings, not via external pulses.

Common Pitfalls:

Mixing auxiliary commutation (Class C) with external pulse commutation (Class E); the former uses internal commutating components tied to the main supply.

Final Answer:

Class E (External pulse commutation)