In power-electronics practice, which commutation method is typically employed in an inverter that converts DC to AC?

Introduction / Context:
Commutation is the process by which a switching device is turned off and current is transferred to another path. Inverters convert DC to AC and therefore must periodically switch current direction. This question probes whether an inverter relies on the AC supply for device turn-off (line commutation) or needs an internal method (forced commutation).

Given Data / Assumptions:

• Stand-alone DC source feeding an inverter.
• General inverter topologies using thyristors, MOSFETs, or IGBTs.
• No external AC mains available for natural current zero crossings.

Concept / Approach:

Line (natural) commutation uses the natural zero of an AC source current/voltage to turn devices off. Forced commutation creates the required reverse bias or current zero by auxiliary circuits (LC networks, snubbers, or self-commutating transistors) because a DC source has no natural zero crossings. Modern transistor inverters are self-commutated; thyristor inverters use auxiliary forced-commutation methods when not tied to an AC grid.

Step-by-Step Solution:

Verification / Alternative check:

Grid-tied line-commutated inverters do exist (called line-commutated converters), but typical stand-alone DC-AC inverters for motor drives, UPS, and PV use forced/self-commutation (PWM with IGBTs or forced-commutated SCRs).

Why Other Options Are Wrong:

Line commutation requires an external AC source zero; option “both simultaneously” is not standard practice; “no commutation” contradicts switching fundamentals.

Common Pitfalls:

Confusing rectifiers (often line-commutated) with inverters; assuming thyristors can naturally turn off on DC without auxiliary networks.

Final Answer:

Forced commutation