Freewheeling diodes in half-bridge inverters In a single-phase half-bridge (voltage source) inverter, freewheeling diodes are required under which load conditions?

Introduction / Context:
In voltage-source inverters, antiparallel (freewheeling) diodes are used to provide a path for reactive load current when the main switches are off or reverse-biased.

Given Data / Assumptions:

• Half-bridge topology with two main switches and corresponding diodes.
• We consider which load types necessitate these diodes for safe operation.

Concept / Approach:
Inductive loads force current continuity. When the applied voltage reverses, the inductor drives current through the antiparallel diode of the opposite switch, preventing overvoltage and current interruption.

Step-by-Step Solution:
Resistive load → current in phase with voltage; diodes are not strictly required for current continuity.Inductive load → lagging current needs a reverse path when switches commutate → diodes required.Capacitive load leads current; in practice, diode conduction is less critical for current continuity, but device antiparallel diodes are commonly present in VSI modules.

Verification / Alternative check:
Standard half-bridge power modules incorporate antiparallel diodes specifically for reactive load handling, predominantly for inductive loads.

Why Other Options Are Wrong:
Always required: Overstated for purely resistive loads.
Inductive or capacitive only: The key need is inductive current continuity.

Common Pitfalls:
Assuming diodes are unnecessary because the load is “mostly resistive”; even small inductance can demand a freewheel path.

Final Answer:
only when the load is inductive