Load-commutated chopper: commutating elements In a load-commutated (auxiliary commutated) thyristor chopper, which set of components typically forms the commutation network to force turn-off?

Introduction / Context:
Thyristors cannot turn off by gate command; current must be forced to zero for a finite time. In DC–DC choppers, where line commutation is unavailable, forced (auxiliary) commutation networks are employed. Understanding the typical commutation components is central to chopper design and classification.

Given Data / Assumptions:

• Thyristor-based chopper (not self-commutated IGBT/MOSFET).
• Load-commutated topology using an auxiliary path.
• Intent is to create a reverse or zero current through the main SCR for its turn-off time.

Concept / Approach:

Classic forced commutation employs an LC network pre-charged via switching. At the desired instant, an auxiliary SCR connects the charged capacitor so that reverse current flows through the main SCR, reducing its current to zero and applying reverse bias during the turn-off interval.

Step-by-Step Solution:

Verification / Alternative check:

Standard commutation classes (A–E for choppers) show auxiliary SCR plus LC for many load-commutated schemes.

Why Other Options Are Wrong:

A capacitor alone cannot provide controlled resonant current; an LC without the auxiliary device lacks the switching action; transformer-only is not standard forced-commutation here.

Common Pitfalls:

Assuming gate control is enough for SCR turn-off; ignoring the need for reverse bias time (t_q).

Final Answer:

A capacitor, an inductor, and an auxiliary thyristor