Load-commutated chopper topology How many thyristors are typically used in a load-commutated chopper configuration?

Introduction / Context:
Load-commutated choppers use the energy stored in the load (often an R–L or motor with back-emf) to assist in commutation. The standard arrangement employs a bridge allowing current to be redirected so that a device naturally turns off when current transfers to another path.

Given Data / Assumptions:

• Bidirectional current capability through the load for commutation.
• Typical implementation uses an H-bridge with thyristors and diodes as needed.
• Basic topology, not multi-pulse expansions.

Concept / Approach:

An H-bridge comprises four controlled devices. By gating diagonally opposite devices, current is steered in either direction through the load. Commutation occurs as the load energy assists in transferring current from one device pair to another, turning devices off without auxiliary LC networks.

Step-by-Step Solution:

Verification / Alternative check:

Canonical references depict load-commutated choppers with four SCRs; more complex versions add diodes or snubbers but retain four primary controlled devices.

Why Other Options Are Wrong:

One or two thyristors cannot steer bidirectional current; six devices would be characteristic of three-phase bridges, not a basic DC chopper.

Common Pitfalls:

Confusing current-commutated (Class C/D) with load-commutated (bridge-type) topologies.

Final Answer:

Four thyristors