Three-phase bridge inverter in 180° conduction mode At any instant in steady-state 180° conduction, how many thyristors conduct simultaneously?

Introduction / Context:
In a six-step, three-phase bridge inverter, switching patterns define how many devices conduct at a time. The 180° conduction mode is a standard gating scheme where each device conducts for half a cycle, with overlaps forming line-to-line square-wave segments to the load.

Given Data / Assumptions:

• Three-phase full bridge with six thyristors or transistors.
• 180° conduction per device; commutation every 60° electrical.
• Balanced three-phase load (usually star or delta connected).

Concept / Approach:
In 180° conduction, at any instant one device from the upper group and two devices from the lower group (or vice versa) conduct, producing three nonzero phase connections to the DC bus. The switching sequence ensures that exactly three devices conduct together, maintaining a nearly rectangular line-to-line voltage across the load phases.

Step-by-Step Solution:
Each device conducts for 180°, with turn-on events every 60°.Conduction sets: at each 60° interval, three devices share conduction (one from one leg and two from the other legs), keeping the current paths complete.Hence, the number of simultaneously conducting devices is 3.

Verification / Alternative check:
Standard six-step inverter timing tables (gating sequence A+, B−, C+, etc.) show three switches on at all times in 180° mode, confirming the count.

Why Other Options Are Wrong:

• 1 or 2 devices cannot form all three phase connections.
• 4 or 6 devices would short parts of the DC bus or overconstrain paths in this mode.

Common Pitfalls:

• Confusing 180° conduction with 120° conduction (where two devices conduct at a time).

Final Answer:
3