PWM generation in Simulink

Introduction

PWM (Pulse Width Modulation) helps control power to devices by turning signals on and off quickly. Simulink lets you create and test PWM signals easily without hardware.

Controlling motor speed in a simulation before building a real controller

Testing how changing PWM duty cycle affects power delivery in circuits

Simulating LED brightness control using PWM signals

Learning how PWM signals work in electronics and control systems

Syntax

Simulink

1. Use a 'Pulse Generator' block to create a square wave.
2. Set the pulse width to control the duty cycle.
3. Connect the output to your system or scope to observe the PWM signal.

The 'Pulse Generator' block frequency controls how fast the PWM switches.

The pulse width percentage sets how long the signal stays ON in each cycle.

Examples

This example sets a PWM signal that is ON half the time and OFF half the time at 1 kHz frequency.

Simulink

% Create a PWM signal with 50% duty cycle at 1 kHz
pulseWidth = 50; % percent
frequency = 1000; % Hz
% In Simulink, set Pulse Generator block parameters:
% Amplitude: 1
% Period: 1/frequency = 0.001 seconds
% Pulse Width: pulseWidth = 50

This PWM signal stays ON for 25% of each cycle, useful for lower power output.

Simulink

% Create a PWM signal with 25% duty cycle at 500 Hz
pulseWidth = 25; % percent
frequency = 500; % Hz
% Set Pulse Generator block parameters accordingly.

Sample Program

This code opens a Simulink model named 'pwm_example' that contains a Pulse Generator block configured for PWM. Running the simulation displays the PWM signal on a Scope.

Simulink

% Open Simulink model
model = 'pwm_example';
open_system(model);

% In the model, a Pulse Generator block is set with:
% Amplitude = 1
% Period = 0.002 (500 Hz)
% Pulse Width = 50 (50%)

% Run the simulation
sim(model);

% The Scope block connected to Pulse Generator shows the PWM waveform.

Important Notes

You can adjust the pulse width dynamically using other blocks to simulate changing PWM duty cycles.

Use the Scope block to visually check the PWM waveform shape and timing.

Summary

PWM signals switch ON and OFF quickly to control power.

Simulink's Pulse Generator block creates PWM by setting pulse width and frequency.

Use simulation to test PWM effects before hardware implementation.

Practice

1. What does PWM stand for in Simulink and what is its main purpose?

easy

A. Pulse Wave Measurement; it measures signal frequency.

B. Power Width Management; it manages battery power levels.

C. Pulse Width Modulation; it controls power by switching signals ON and OFF quickly.

D. Pulse Width Memory; it stores signal data.

Solution

1. Step 1: Understand PWM meaning

   PWM stands for Pulse Width Modulation, a method to control power by changing signal ON/OFF times.

2. Step 2: Identify PWM purpose in Simulink

   In Simulink, PWM controls power by switching signals ON and OFF quickly to adjust power delivery.

3. Final Answer:

   Pulse Width Modulation; it controls power by switching signals ON and OFF quickly. -> Option C

4. Quick Check:

   PWM = Pulse Width Modulation controlling power [OK]

Hint: PWM controls power by fast ON/OFF switching [OK]

Common Mistakes:

• Confusing PWM with measuring signals
• Thinking PWM stores data
• Mixing PWM with battery management

2. Which Simulink block is commonly used to generate PWM signals?

easy

A. Pulse Generator block

B. Gain block

C. Integrator block

D. Scope block

Solution

1. Step 1: Recall Simulink blocks for PWM

   The Pulse Generator block is designed to create pulses with adjustable width and frequency.

2. Step 2: Match block to PWM function

   Since PWM requires pulses with specific widths, the Pulse Generator block is the correct choice.

3. Final Answer:

   Pulse Generator block -> Option A

4. Quick Check:

   Pulse Generator block creates PWM pulses [OK]

Hint: Pulse Generator creates PWM signals in Simulink [OK]

Common Mistakes:

• Choosing Gain block which scales signals
• Selecting Integrator block which sums signals
• Picking Scope block which only displays signals

3. Given a Pulse Generator block with Amplitude=5, Period=10, Pulse Width=30%, what is the ON time duration of the PWM signal?

medium

A. 3 seconds

B. 5 seconds

C. 7 seconds

D. 10 seconds

Solution

1. Step 1: Calculate ON time from pulse width and period

   ON time = Pulse Width (%) x Period = 30% x 10 = 0.3 x 10 = 3 seconds.

2. Step 2: Confirm units and values

   Period is in seconds, so ON time is 3 seconds.

3. Final Answer:

   3 seconds -> Option A

4. Quick Check:

   ON time = 30% x 10 = 3 seconds [OK]

Hint: ON time = pulse width % x period [OK]

Common Mistakes:

• Using amplitude instead of period for calculation
• Confusing pulse width percentage with time
• Calculating OFF time instead of ON time

4. You set the Pulse Generator block with Pulse Width = 110%. What will happen during simulation?

medium

A. The block will generate an error and stop simulation.

B. The block will generate a continuous ON signal (always high).

C. The block will generate a continuous OFF signal (always low).

D. The block will ignore the pulse width and use default 50%.

Solution

1. Step 1: Understand pulse width limits

   Pulse Width should be between 0% and 100%. Values above 100% mean the signal is ON all the time.

2. Step 2: Predict simulation behavior

   With 110%, the block treats it as always ON, so the output stays high continuously.

3. Final Answer:

   The block will generate a continuous ON signal (always high). -> Option B

4. Quick Check:

   Pulse Width > 100% means always ON [OK]

Hint: Pulse Width >100% means signal always ON [OK]

Common Mistakes:

• Expecting simulation error for >100% pulse width
• Thinking signal stays OFF
• Assuming default pulse width is used

5. You want to simulate a PWM signal that controls a motor speed with a frequency of 50 Hz and a duty cycle of 40%. How do you set the Pulse Generator block parameters in Simulink?

hard

A. Set Period = 0.02 seconds, Pulse Width = 50%, Amplitude = motor voltage level

B. Set Period = 50 seconds, Pulse Width = 40%, Amplitude = motor voltage level

C. Set Period = 0.04 seconds, Pulse Width = 40%, Amplitude = motor voltage level

D. Set Period = 0.02 seconds, Pulse Width = 40%, Amplitude = motor voltage level

Solution

1. Step 1: Calculate period from frequency

   Period = 1 / Frequency = 1 / 50 = 0.02 seconds.

2. Step 2: Set pulse width and amplitude

   Duty cycle is 40%, so Pulse Width = 40%. Amplitude should match motor voltage level to control speed.

3. Final Answer:

   Set Period = 0.02 seconds, Pulse Width = 40%, Amplitude = motor voltage level -> Option D

4. Quick Check:

   Period = 1/50 = 0.02s, Pulse Width = 40% [OK]

Hint: Period = 1/frequency; set pulse width as duty cycle % [OK]

Common Mistakes:

• Using period equal to frequency value
• Setting wrong pulse width different from duty cycle
• Confusing period units (seconds vs milliseconds)