Definition check: What type of power-electronic conversion does a cycloconverter perform? Choose the correct classification for a cycloconverter.

Introduction / Context:
Cycloconverters are important in high-power variable-frequency drives for large motors (e.g., rolling mills). They directly change AC at one frequency to AC at another frequency without an intermediate DC link.

Given Data / Assumptions:

• Line-commutated, phase-controlled devices.
• Output frequency is typically a submultiple of the input frequency.

Concept / Approach:

By phase-controlling groups of thyristors, cycloconverters synthesize a low-frequency AC waveform directly from a higher-frequency AC source, hence ac-to-ac conversion. This differentiates them from rectifier-inverter DC-link systems.

Step-by-Step Solution:

Verification / Alternative check:

Standard power-electronics textbooks list cycloconverters under ac-ac converters (direct frequency converters).

Why Other Options Are Wrong:

ac-dc, dc-ac, dc-dc are different categories. ac-dc-ac with a DC link is not a cycloconverter (that is a converter-inverter system).

Common Pitfalls:

Confusing cycloconverters with matrix converters (also ac-ac but using bidirectional switches) or with DC-link inverters.

Final Answer:

ac-ac converter