Line-commutated AC–DC converters: commutation class Which commutation method (class) is associated with conventional AC–DC line-commutated converters (thyristor rectifiers)?

Introduction / Context:
Thyristor rectifiers that are tied directly to the AC mains rely on the line voltage reversal to turn devices off. This form of natural commutation is categorized under a specific commutation class used in standard power-electronics nomenclature.

Given Data / Assumptions:

• AC–DC converter without auxiliary resonant circuits.
• Thyristors are turned off by the AC supply going through current zero.

Concept / Approach:

In line commutation, the AC source itself provides the necessary current zero and reverse voltage to recover each thyristor. This is contrasted with load or auxiliary commutation that requires LC or forced circuits to achieve turn-off.

Step-by-Step Solution:

Verification / Alternative check:

Standard converter classifications list line-commutated rectifiers under Class F, widely used in HVDC and industrial drives prior to widespread self-commutated devices.

Why Other Options Are Wrong:

Classes A, C, D, E all require specific LC or auxiliary switching, not natural line reversal. Thus they do not describe standard AC–DC mains commutation.

Common Pitfalls:

Confusing forced commutation (for DC–AC inverters or DC choppers) with natural, line-provided commutation.

Final Answer:

Class F (line commutation)