Cycloconverter commutation types Assertion (A): A cycloconverter may be line-commutated or forced-commutated. Reason (R): A step-up cycloconverter requires forced commutation.

Introduction / Context:
Cycloconverters synthesize low-frequency AC directly from line AC using phase-controlled devices. Their commutation method (line versus forced) depends on the required output frequency and power factor demands.

Given Data / Assumptions:

• Line-commutated (natural) commutation is standard for step-down frequency conversion.
• Forced commutation is possible using auxiliary circuits/transistorized switches.
• Step-up cycloconversion (f_out > f_in) cannot be realized with simple line commutation.

Concept / Approach:
Line commutation relies on natural current zeroes of the grid voltage and is suited to step-down operation. To achieve step-up or to control at times when the line does not naturally commutate, external commutation (forced) is required. Thus, cycloconverters may be built in either mode, and specifically the step-up type requires forced commutation.

Step-by-Step Solution:
Validate A: Both line-commutated and forced-commutated cycloconverters are used → A is true.Validate R: Step-up operation needs device turn-off independent of line zeros → forced commutation → R is true.Causality: R explains why one class (step-up) must be forced-commutated → adequately supports A.

Verification / Alternative check:
Drive textbooks distinguish step-down (line-commutated) vs step-up (forced-commutated) cycloconverters explicitly.

Why Other Options Are Wrong:

• Saying R is not the explanation ignores the direct need for forced commutation in step-up conversion.
• Claiming R or A is wrong conflicts with established practice.

Common Pitfalls:

• Confusing cycloconverters with matrix converters; the latter can synthesize wider frequency ranges with bidirectional switches.

Final Answer:
Both A and R are correct and R is correct explanation of A