Dual converter operating types and reasoning Assertion (A): A dual converter (two controlled rectifier bridges connected in anti-parallel) may be of the circulating-current type or the non–circulating-current type. Reason (R): In a circulating-current dual converter, only one converter can be operated at a time.

Introduction / Context:
Dual converters are widely used in DC drives to achieve four-quadrant operation (both motoring and braking in forward and reverse). Understanding the difference between circulating-current and non–circulating-current configurations is essential for selecting reactors, sizing devices, and ensuring smooth reversal of current without supply disturbances.

Given Data / Assumptions:

• A dual converter consists of two fully controlled rectifier bridges connected back-to-back across the same DC load.
• Bridges are phase-controlled to set the average DC voltage magnitude and polarity.
• Circulating-current configuration uses interbridge reactors to limit internal current.

Concept / Approach:

There are two operating types: (1) non–circulating-current type, where only one bridge conducts at a time and reversal is achieved by disabling one bridge and enabling the other after dead time; (2) circulating-current type, where both bridges are biased simultaneously with slightly different firing angles and an interbridge reactor limits the circulating current, giving fast and smooth reversal at the cost of extra losses and hardware.

Step-by-Step Solution:

Verification / Alternative check:

Standard DC drive texts show current overlap between the two bridges in the circulating-current mode, controlled by an inductor to prevent excessive loop current.

Why Other Options Are Wrong:

Options (a) and (b) assume R is true; it is not. Option (d) assumes A is false; it is true. Option (e) says both are wrong; incorrect.

Common Pitfalls:

Learners often swap the definitions, thinking “circulating” means alternately enabling bridges. In fact, circulating means both bridges are biased simultaneously with a reactor in between.

Final Answer:

A is correct but R is wrong