Industrial electronics
Explainer
How Inverters Fake a Smooth Sine Wave
Your inverter only outputs on or off, so where does the sine wave come from?
Quick check · tap an answer to continue
Lesson notes
Key points
- In sinusoidal PWM, a sine reference wave is compared with a fast triangular carrier wave.
- When the sine is above the triangle the upper switch is on, so pulses widen near the sine peak.
- The modulation index, reference amplitude divided by carrier amplitude, sets the fundamental output voltage.
- The motor or filter inductance averages the pulses, so current follows a near-sinusoidal shape at the reference frequency.
Takeaway: SPWM: compare sine with triangle, and the pulses average into a sine.
Quick check: In SPWM, what sets the frequency of the output fundamental?
- The carrier frequency
- The DC bus voltage
- The reference frequency
The output follows the sine reference; the carrier only sets switching rate.
Carrier comparisonPulse widthModulation indexFiltering
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