Operation of a single-phase dual converter (circulating-current mode) When a single-phase dual converter operates in circulating-current mode, which statement is correct about the two converters?

Introduction / Context:
Dual converters provide reversible DC voltage and current. In the circulating-current mode, both bridges are gated, allowing instantaneous reversal without gaps in conduction and improved dynamic response.

Given Data / Assumptions:

• Two fully controlled bridges connected antiparallel on the DC side.
• A series reactor limits circulating current.
• Firing angles are set such that one bridge rectifies while the other inverts.

Concept / Approach:
To create a controllable average DC voltage around zero, one converter is biased to produce positive DC voltage (rectifier) while the other is biased to produce negative DC voltage (inverter). Their slight voltage difference creates circulating current through the reactor while enabling instantaneous polarity transitions at the load.

Step-by-Step Solution:
Set Converter 1 with α < 90° → positive Vdc (rectifier).Set Converter 2 with α > 90° → negative Vdc (inverter).Operate both simultaneously; the reactor carries the circulating current.Hence, one rectifies while the other inverts.

Verification / Alternative check:
Phase control equations Vdc ∝ cos α confirm opposite polarities with complementary firing angles.

Why Other Options Are Wrong:

• Both rectifying or both inverting would not provide the necessary polarity balance.
• “only one converter conducts” describes non-circulating mode, not circulating mode.

Common Pitfalls:

• Insufficient reactor inductance causing excessive ripple and stress.
• Mis-synchronization leading to large loop currents.

Final Answer:
one converter works as a rectifier while the other works as an inverter