PWM generation in Simulink - Mini Project: Build & Apply

PWM Generation in Simulink

📖 Scenario: You are working on a simple control system that requires generating a Pulse Width Modulation (PWM) signal. PWM signals are used in many real-world applications like controlling motor speed or LED brightness by switching the signal on and off rapidly with varying duty cycles.

🎯 Goal: Build a Simulink model that generates a PWM signal with a fixed frequency and a configurable duty cycle.

📋 What You'll Learn

Create a sine wave or constant block as the reference signal

Add a PWM generator using a comparator block

Configure the PWM frequency and duty cycle using parameters

Display the PWM output waveform

💡 Why This Matters

🌍 Real World

PWM signals are widely used in electronics to control power delivery to devices like motors, LEDs, and heaters by adjusting the duty cycle.

💼 Career

Understanding PWM generation is essential for engineers working in embedded systems, robotics, and control systems design.

1

Create the Reference Signal

In your Simulink model, add a Sine Wave block. Set the Amplitude to 1 and the Frequency to 50 Hz. This will be the reference signal for PWM generation.

Simulink

# Add a Sine Wave block with Amplitude 1 and Frequency 50 Hz
# Your code here

Hint

Use the Simulink library to drag a Sine Wave block into your model. Double-click it to set the amplitude and frequency.

2

Add the PWM Carrier Signal

Add a Repeating Sequence block to your model to act as the carrier signal for PWM. Set its output to a sawtooth waveform that goes from 0 to 1 with a period of 0.02 seconds (which corresponds to 50 Hz frequency).

Simulink

% Step 1: Add Sine Wave block with Amplitude 1 and Frequency 50 Hz
% Step 2: Add Repeating Sequence block with sawtooth from 0 to 1 and period 0.02
# Your code here

Hint

The Repeating Sequence block can be configured to output a sawtooth by setting its time and output vectors accordingly.

3

Create the PWM Signal Using a Comparator

Add a Relational Operator block to compare the Sine Wave output and the Repeating Sequence output. Set the operator to <. This block will output 1 when the sine wave is greater than the carrier, generating the PWM signal.

Simulink

% Step 1: Add Sine Wave block with Amplitude 1 and Frequency 50 Hz
% Step 2: Add Repeating Sequence block with sawtooth from 0 to 1 and period 0.02
% Step 3: Add Relational Operator block with operator '<'
# Your code here

Hint

Use the Relational Operator block and set its operator to < to compare the two signals.

4

Display the PWM Output

Add a Scope block to your model and connect it to the output of the Relational Operator block. Run the simulation for 0.1 seconds and observe the PWM waveform on the scope.

Simulink

% Step 1: Add Sine Wave block with Amplitude 1 and Frequency 50 Hz
% Step 2: Add Repeating Sequence block with sawtooth from 0 to 1 and period 0.02
% Step 3: Add Relational Operator block with operator '<'
% Step 4: Add Scope block and connect to Relational Operator output
# Your code here

Hint

Use the Scope block to visualize the PWM output. Set the simulation stop time to 0.1 seconds.

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)