PWM generation in Simulink - Step-by-Step Execution

Concept Flow - PWM generation in Simulink

Set Reference Signal

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Set Carrier Signal (Triangle Wave)

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Compare Reference and Carrier

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Generate PWM Output

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Output PWM Signal

PWM generation compares a reference signal with a carrier wave to create a pulse-width modulated output.

Execution Sample

Simulink

Reference = 0.6;
Carrier = (sawtooth(2*pi*1000*t, 0.5) + 1)/2;
PWM = Reference > Carrier;

This code compares a constant reference with a triangle wave carrier to produce a PWM signal.

Execution Table

Step	Time (ms)	Reference Value	Carrier Value	Condition (Reference > Carrier)	PWM Output
1	0.0	0.6	0.0	True	1
2	0.1	0.6	0.3	True	1
3	0.2	0.6	0.7	False	0
4	0.3	0.6	1.0	False	0
5	0.4	0.6	0.7	False	0
6	0.5	0.6	0.0	True	1
7	0.6	0.6	0.3	True	1
8	0.7	0.6	0.7	False	0
9	0.8	0.6	1.0	False	0
10	0.9	0.6	0.7	False	0
11	1.0	0.6	0.0	True	1

💡 Simulation ends at 1.0 ms, completing one full carrier wave cycle.

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	After 6	After 7	After 8	After 9	After 10	Final
Reference	0.6	0.6	0.6	0.6	0.6	0.6	0.6	0.6	0.6	0.6	0.6	0.6
Carrier	0.0	0.3	0.7	1.0	0.7	0.0	0.3	0.7	1.0	0.7	0.0	0.0
PWM Output	1	1	0	0	0	1	1	0	0	0	1	1

Key Moments - 2 Insights

Why does the PWM output switch from 1 to 0 when the carrier value exceeds the reference?

Because the PWM output is 1 only when the reference is greater than the carrier (see execution_table rows 2 and 3). When carrier > reference, condition is false, so output is 0.

Why does the PWM output repeat its pattern every 1 ms?

The carrier is a triangle wave with a 1 kHz frequency, so it completes a cycle every 1 ms, causing the PWM pattern to repeat (see execution_table time column).

Visual Quiz - 3 Questions

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

A 0, because carrier equals 1.0 which is greater than reference

B 1, because reference is greater than carrier

C 1, because carrier is less than reference

D 0, because reference is zero

💡 Hint

Check the 'Condition' and 'PWM Output' columns at step 4 in the execution_table.

At which time does the PWM output first become 0?

A 0.1 ms

B 0.2 ms

C 0.0 ms

D 0.5 ms

💡 Hint

Look at the 'PWM Output' column in execution_table and find the first 0.

If the reference value increased to 0.8, how would the PWM output change at 0.7 ms?

A PWM output would be 0 because carrier is 1.0

B PWM output would be 0 because 0.8 < 0.7

C PWM output would be 1 because 0.8 > 0.7

D PWM output would be 1 because carrier is 0.3

💡 Hint

Compare new reference 0.8 with carrier at 0.7 ms from execution_table.

Concept Snapshot

PWM generation in Simulink:
- Use a reference signal and a carrier triangle wave.
- Compare reference > carrier at each time step.
- Output 1 if true, else 0.
- PWM duty cycle depends on reference level.
- Carrier frequency sets PWM frequency.

Full Transcript

PWM generation in Simulink works by comparing a reference signal with a carrier triangle wave. At each time step, if the reference is greater than the carrier, the PWM output is 1; otherwise, it is 0. This creates a pulse-width modulated signal where the width of the pulses depends on the reference value. The carrier wave frequency determines how often the PWM signal repeats. For example, with a 1 kHz carrier, the PWM pattern repeats every 1 millisecond. This method is visualized step-by-step by tracking the reference, carrier, condition, and PWM output values over time.