Sinusoidal PWM (SPWM) technique in Power Electronics - Step-by-Step Execution

Concept Flow - Sinusoidal PWM (SPWM) technique

Start

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Generate Reference Sine Wave

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Generate High-Frequency Carrier Triangle Wave

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Compare Sine and Triangle Waves

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Output PWM Signal

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Control Motor or Load

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End

The SPWM technique compares a low-frequency sine wave with a high-frequency triangle wave to create a PWM signal that controls power devices.

Execution Sample

Power Electronics

ref_wave = sin(pi * f * t)
carrier = triangle_wave(freq=fc, t)
if ref_wave > carrier:
    output = HIGH
else:
    output = LOW

This code generates a PWM signal by comparing a sine wave reference with a triangle carrier wave.

Analysis Table

Step	Time (t)	Reference Sine Value	Carrier Triangle Value	Condition (ref > carrier)	PWM Output
1	0 ms	0.0	0.5	False	LOW
2	1 ms	0.31	0.3	True	HIGH
3	2 ms	0.59	0.7	False	LOW
4	3 ms	0.81	0.2	True	HIGH
5	4 ms	0.95	0.9	True	HIGH
6	5 ms	1.0	0.4	True	HIGH
7	6 ms	0.95	0.8	True	HIGH
8	7 ms	0.81	0.6	True	HIGH
9	8 ms	0.59	0.7	False	LOW
10	9 ms	0.31	0.3	True	HIGH
11	10 ms	0.0	0.5	False	LOW

💡 After one sine wave period (10 ms), the PWM cycle repeats.

State Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	After 6	After 7	After 8	After 9	After 10	Final
ref_wave	0.0	0.31	0.59	0.81	0.95	1.0	0.95	0.81	0.59	0.31	0.0	0.0
carrier	0.5	0.3	0.7	0.2	0.9	0.4	0.8	0.6	0.7	0.3	0.5	0.5
output	LOW	HIGH	LOW	HIGH	HIGH	HIGH	HIGH	HIGH	LOW	HIGH	LOW	LOW

Key Insights - 3 Insights

Why is the PWM output HIGH when the sine wave value is less than the triangle wave at some points?

The PWM output is HIGH only when the sine wave value is greater than the triangle wave value, as shown in the execution_table rows where the condition is True. If the sine wave is less, output is LOW.

Why does the PWM output change multiple times within one sine wave period?

Because the triangle wave frequency is much higher than the sine wave frequency, the comparison happens many times per sine period, creating multiple PWM pulses as seen in the execution_table steps.

What happens to the PWM output at the start and end of the sine wave period?

At the start and end (0 ms and 10 ms), the sine wave value equals zero and is less than the carrier, so the PWM output is LOW, matching the execution_table rows 1 and 11.

Visual Quiz - 3 Questions

Look at the execution_table at step 4. What is the PWM output and why?

A HIGH because sine (0.2) > carrier (0.81)

B HIGH because sine (0.81) > carrier (0.2)

C LOW because sine (0.81) < carrier (0.2)

D LOW because sine (0.2) < carrier (0.81)

💡 Hint

Check the 'Condition (ref > carrier)' column at step 4 in execution_table.

At which step does the PWM output first become LOW after being HIGH?

A Step 2

B Step 5

C Step 3

D Step 9

💡 Hint

Look for the first row where output changes from HIGH to LOW in the output column.

If the carrier wave frequency increased, how would the PWM output change in the execution_table?

A More PWM pulses per sine wave period

B Fewer PWM pulses per sine wave period

C PWM output stays the same

D PWM output becomes constant HIGH

💡 Hint

Higher carrier frequency means more comparisons per sine period, increasing PWM pulse count.

Concept Snapshot

Sinusoidal PWM (SPWM) compares a low-frequency sine wave (reference) with a high-frequency triangle wave (carrier).
When sine > triangle, output is HIGH; else LOW.
This creates PWM pulses that approximate a sine wave.
Used to control AC motors and inverters.
Carrier frequency controls PWM resolution.
Sine frequency controls output waveform frequency.

Full Transcript

Sinusoidal PWM (SPWM) technique works by generating a low-frequency sine wave as a reference and a high-frequency triangle wave as a carrier. At each time step, the sine wave value is compared to the triangle wave value. If the sine wave is greater, the PWM output is set HIGH; otherwise, it is LOW. This process repeats many times per sine wave period, creating a PWM signal that approximates a sine wave. The PWM signal can then be used to control power devices like motors or inverters. The carrier frequency determines how many PWM pulses occur per sine wave cycle, affecting the smoothness of the output. The sine wave frequency sets the output waveform frequency. This technique is widely used in power electronics for efficient and precise control of AC power.