What is Sinusoidal PWM?

A PWM method for making a near-sinusoidal AC output with an inverter. A sine wave at the desired output frequency (the reference) is compared with a triangular wave of much higher frequency (the carrier); the upper switch is on while the reference is larger and the lower switch while it is smaller. The ratio of the reference amplitude to the carrier amplitude is the modulation index, and as long as it is 1 or less, the fundamental of the output voltage is proportional to it. Overmodulation beyond 1 increases low-order harmonics.

Read the beginner explainer: What Is an Inverter? DC to AC for Air Conditioners and EVs

Japanese name: 正弦波PWM

Sinusoidal PWM appears in 4 practice questions across 1 topic, including Power Electronics Circuits.

Field: Power Electronics Circuits

Try it: questions about Sinusoidal PWM

In sinusoidal PWM for an inverter, which of the following correctly describes how the switches are turned on and off?

AThe switches change state only once per half cycle of the desired output frequency
BWithout a carrier, the on and off states of the switches are chosen at random so that the average of many pulses approaches a sine wave
CThe desired sine wave (reference) is compared with a triangular wave (carrier), and the upper switch is on while the reference is larger

Show answer and explanation

Answer: C. The desired sine wave (reference) is compared with a triangular wave (carrier), and the upper switch is on while the reference is larger

Sinusoidal PWM compares a sine-wave reference at the desired output frequency with a triangular carrier of much higher frequency. Turning on the upper switch while the reference is larger than the carrier and the lower switch while it is smaller gives a voltage whose pulse widths follow the sine wave. When this voltage is smoothed, for example by the inductance of the motor windings, a sinusoidal component proportional to the reference remains. Switching only once per half cycle is called a square-wave inverter, whose output contains many low-order harmonics.

An inverter leg on a 600 V DC supply is operated with sinusoidal PWM at a modulation index of 0.8. Which of the following is the amplitude (peak) of the fundamental of the leg output voltage with respect to the midpoint of the DC supply?

A240 V
B300 V
C480 V

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Answer: A. 240 V

The modulation index m is the reference amplitude divided by the carrier amplitude. In the linear range with m of 1 or less, the amplitude of the fundamental of the leg output voltage is m × E/2, which here is 0.8 × 600/2 = 240 V. At m = 1 it reaches its maximum of 300 V (E/2), and a higher voltage cannot be produced while staying with sinusoidal PWM. Changing the modulation index adjusts the magnitude of the AC output voltage without changing the DC voltage.

Sinusoidal PWM in the explanations

Sinusoidal PWM compares a sine-wave reference at the desired output frequency with a triangular carrier of much higher frequency.
In sinusoidal PWM for an inverter, which of the following c…
At m = 1 it reaches its maximum of 300 V (E/2), and a higher voltage cannot be produced while staying with sinusoidal PWM.
An inverter leg on a 600 V DC supply is operated with sinus…