Industrial electronics
Explainer
Sinusoidal PWM: Making a Clean Sine Wave
A square-wave inverter is full of harmonics. Sinusoidal PWM fixes that.
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Lesson notes
Key points
- A plain square-wave inverter output contains strong low-order harmonics, like the third and fifth, which heat motors and transformers.
- In sinusoidal PWM, a sine reference wave is compared with a fast triangular carrier wave to decide switching instants.
- Whenever the sine is above the carrier the switch is on, so pulse widths widen and narrow following the sine.
- The modulation index, reference peak divided by carrier peak, sets output amplitude, while the reference frequency sets output frequency.
Definitions
- Harmonics
- Unwanted frequency components at whole multiples of the fundamental output frequency.
Takeaway: SPWM compares sine with triangle; modulation index sets amplitude.
Quick check: In SPWM, what quantity mainly sets the output voltage amplitude?
- Carrier frequency
- Modulation index
- DC link polarity
Amplitude scales with the ratio of reference peak to carrier peak.
HarmonicsCarrier comparisonPulse widthModulation index
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