Basic series inverter: source current waveform quality In a basic series inverter (resonant L–C with R load), the source (DC link) current generally has what harmonic content?

Introduction / Context:
Series inverters rely on resonance of the L–C series branch with the load to shape current. Understanding the harmonic nature of current is crucial for filter design and source sizing.

Given Data / Assumptions:

• Series R–L–C tuned near the fundamental of operation.
• Thyristor commutation via natural resonance.
• Quasi-sinusoidal current when tuned correctly.

Concept / Approach:

At or near series resonance, the impedance to the fundamental is low while it is higher for off-resonant harmonics. Thus, current tends toward a sinusoid dominated by the fundamental component, leading to lower harmonic content compared with square-wave switched currents.

Step-by-Step Solution:

Verification / Alternative check:

Practical waveforms from resonant inverters show rounded, near-sinusoidal current pulses compared to hard-switched square-wave inverters.

Why Other Options Are Wrong:

“High” or “zero” are extremes; properly tuned series inverters do not yield zero harmonics but typically achieve comparatively low distortion. Firing angle alone does not dictate harmonic profile; resonance tuning is key.

Common Pitfalls:

Assuming current is square just because devices commutate; ignoring that the series L–C shapes the current waveform strongly.

Final Answer:

Low harmonic content