Single-phase full-bridge inverter feeding an RLC load Considering a full-bridge single-phase inverter with antiparallel diodes and an RLC load (allowing current to continue when devices turn off), which devices conduct simultaneously at any instant?

Introduction / Context:
In voltage-source inverters with antiparallel diodes, device conduction patterns depend on the load current polarity and whether forced commutation has just occurred. Understanding which pair conducts at any instant is essential for analyzing output waveforms and device current ratings.

Given Data / Assumptions:

• Full-bridge with four controlled devices (e.g., thyristors) and their antiparallel diodes.
• Load is RLC, so current can lead or lag, and can persist after device turn-off.
• Ideal switches and diodes.

Concept / Approach:

For a full bridge, power is delivered through a diagonal pair of devices. If the commanded polarity matches the load current direction, two thyristors in opposite legs conduct. When current must flow opposite to the commanded device polarity (e.g., due to energy fed back from the reactive load), the antiparallel diodes of the opposite devices conduct, clamping the load and circulating current until the next gating interval. Thus, conduction alternates between a pair of thyristors or a pair of diodes, never all four simultaneously.

Step-by-Step Solution:

Verification / Alternative check:

Textbook current paths show either device–device conduction or diode–diode conduction; mixed thyristor–diode conduction happens transiently at commutation but the steady pairing is as described.

Why Other Options Are Wrong:

• “One thyristor and one diode” (option a): not the dominant simultaneous pair in steady conduction intervals.
• “Two thyristors only” (option b) ignores diode conduction during reactive intervals.
• “All four thyristors” (option d) is impossible for a voltage-source inverter.

Common Pitfalls:

Forgetting that antiparallel diodes provide a path for reactive energy return, which is vital with inductive loads.

Final Answer:

Either two thyristors or two diodes