Three-phase bridge inverter – device current in 180° vs 120° conduction All other parameters being the same, how does the peak thyristor current in a 3-phase bridge inverter operating in 180° conduction mode compare with that in 120° conduction mode?

Introduction / Context:
Inverters can be modulated for 120° or 180° conduction per device. The conduction interval and number of devices simultaneously conducting determine how phase and line currents split among devices, influencing peak device current ratings.

Given Data / Assumptions:

• Same DC link voltage and load conditions.
• Bridge inverter using thyristors (or ideal switches).
• Comparison strictly between conduction schemes.

Concept / Approach:

With 180° conduction, two devices in each leg can conduct, and three devices are typically on at any instant, changing the current sharing relative to 120° mode (two devices on at a time). The distribution leads to higher peak current demands on individual devices in 180° mode for the same load current envelope.

Step-by-Step Solution:

Verification / Alternative check:

Device current waveforms in standard references show increased peak in 180° mode for identical load conditions when compared to 120° mode.

Why Other Options Are Wrong:

• “Same” ignores conduction overlap differences.
• “Lower” contradicts typical current sharing outcomes.
• “Any of the above” is non-deterministic and incorrect.

Common Pitfalls:

Conflating RMS and peak values; depending on load nature, RMS may change differently, but the question asks about peak device current.

Final Answer:

has higher peak thyristor current than in 120° mode of operation