Single-phase full-bridge inverter for an R–L load For a single-phase full-bridge inverter feeding an R–L (inductive) load, what is the minimum practical device set required to ensure proper current paths?

Introduction / Context:
An H-bridge inverter must provide paths for inductive load current during both active switching and freewheeling intervals. This question checks familiarity with antiparallel diodes (commonly called feedback or freewheel diodes) required with thyristor or transistor switches when supplying R–L loads.

Given Data / Assumptions:

• Topology: single-phase full-bridge (H-bridge).
• Load is inductive; current cannot change instantaneously.
• Switch technology: thyristors (SCRs) without inherent body diodes.

Concept / Approach:

When one diagonal pair of SCRs turns off or the applied voltage reverses, the inductor forces current to continue. Without a diode path antiparallel to each controlled device, dangerous overvoltage can occur. Therefore, each of the four SCRs needs a diode in antiparallel to carry reactive current and provide safe commutation/freewheeling paths.

Step-by-Step Solution:

Verification / Alternative check:

Equivalent IGBT/MOSFET implementations use intrinsic/body diodes for the same function, confirming the need for antiparallel conduction.

Why Other Options Are Wrong:

Using no diodes or only two diodes leaves incomplete current paths; eight thyristors is unnecessary and costly for a single-phase bridge.

Common Pitfalls:

Assuming resistive-load rules apply to inductive loads; forgetting that SCRs do not conduct reverse current without diodes.

Final Answer:

4 thyristors and 4 diodes