Three-phase to single-phase full-wave bridge cycloconverter How many thyristors are used in a 3-phase to 1-phase full-wave bridge cycloconverter (positive and negative converter groups included)?

Introduction / Context:
A cycloconverter produces a low-frequency AC output directly from a higher-frequency AC supply using phase-controlled thyristor bridges. Device counting is a common exam check for understanding converter structure and gating requirements.

Given Data / Assumptions:

• Input: three-phase AC supply.
• Output: single-phase AC (both positive and negative half-cycles synthesized).
• Full-wave bridge operation in each group (positive and negative).

Concept / Approach:

To synthesize a single-phase output, a cycloconverter typically uses two three-phase controlled rectifier bridges: one bridge generates the positive portions (positive converter), and another generates the negative portions (negative converter). Each three-phase full-wave controlled bridge requires 6 thyristors. Using two such bridges results in 6 + 6 = 12 devices, often linked via intergroup reactors to prevent circulating currents.

Step-by-Step Solution:

Verification / Alternative check:

Standard textbooks depict two 6-pulse bridges feeding a single-phase load through intergroup reactors. This architecture is ubiquitous in low-frequency large drives.

Why Other Options Are Wrong:

8 devices correspond to some single-phase bridges; 18 or 36 devices match higher-pulse or multioutput arrangements, not the basic 3-phase to 1-phase full-wave case.

Common Pitfalls:

Confusing 3-phase to 3-phase cycloconverters (which require more devices) with the 3-phase to 1-phase variant.

Final Answer:

12