DC motor modeling in Simulink - Mini Project: Build & Apply

DC motor modeling in Simulink

📖 Scenario: You want to understand how a DC motor works by building a simple model in Simulink. This will help you see how voltage input affects motor speed and current.

🎯 Goal: Build a basic DC motor model in Simulink using blocks for voltage input, motor parameters, and output displays for speed and current.

📋 What You'll Learn

Create a Simulink model with a DC voltage source

Add blocks to represent motor electrical and mechanical parts

Configure motor parameters like resistance and inertia

Connect blocks to simulate motor speed and current

Display motor speed and current using scopes

💡 Why This Matters

🌍 Real World

Modeling DC motors helps engineers design and test motor control systems before building physical prototypes.

💼 Career

Understanding motor modeling is useful for roles in automation, robotics, and control systems engineering.

1

Set up the DC motor parameters

Create variables in the MATLAB workspace for the DC motor parameters: R = 2 (resistance in ohms), L = 0.5 (inductance in henrys), Kb = 0.01 (back EMF constant), Kt = 0.01 (torque constant), J = 0.01 (moment of inertia), and b = 0.1 (friction coefficient).

Simulink

# Define motor parameters in MATLAB workspace
# Your code here

Hint

Use simple assignment statements like R = 2; to set each parameter.

2

Create the Simulink model and add blocks

Open a new Simulink model and add these blocks: DC Voltage Source, Sum, Gain, Integrator, and Scope. Arrange them to start building the motor's electrical circuit.

Simulink

R = 2;
L = 0.5;
Kb = 0.01;
Kt = 0.01;
J = 0.01;
b = 0.1;
% Add Simulink blocks: DC Voltage Source, Sum, Gain, Integrator, Scope
% Your code here

Hint

Use the Simulink Library Browser to drag and drop these blocks into your model.

3

Connect blocks and set motor equations

Connect the blocks to model the motor equations. Use the Gain blocks to represent resistance R and inductance L. Use the Sum block to calculate voltage difference. Add integrators for current and speed. Set gains for torque constant Kt and back EMF constant Kb.

Simulink

R = 2;
L = 0.5;
Kb = 0.01;
Kt = 0.01;
J = 0.01;
b = 0.1;
% Connect blocks to model motor equations
% Set gains for R, L, Kt, Kb
% Use integrators for current and speed
% Your code here

Hint

Think of the motor as two parts: electrical (voltage, current) and mechanical (torque, speed). Use gains and integrators to connect them.

4

Run simulation and display motor speed and current

Run the Simulink simulation for 5 seconds. Use Scope blocks to display the motor speed and current outputs. Make sure the scopes show the changing values over time.

Simulink

R = 2;
L = 0.5;
Kb = 0.01;
Kt = 0.01;
J = 0.01;
b = 0.1;
% Run simulation for 5 seconds
% Connect Scope blocks to motor speed and current
% Your code here

Hint

Use the sim command with your model name and time. Open the scopes to see the results.

Practice

1. What is the main purpose of using Simulink for DC motor modeling?

easy

A. To write code for motor control algorithms

B. To manufacture DC motors automatically

C. To simulate motor behavior before building physical hardware

D. To measure motor speed with physical sensors

Solution

1. Step 1: Understand Simulink's role

   Simulink is a tool for creating visual models and running simulations, not for manufacturing or direct measurement.

2. Step 2: Identify the correct purpose

   Simulink helps simulate motor behavior to predict performance before hardware is built.

3. Final Answer:

   To simulate motor behavior before building physical hardware -> Option C

4. Quick Check:

   Simulate motor behavior = To simulate motor behavior before building physical hardware [OK]

Hint: Simulink simulates, it does not build or measure [OK]

Common Mistakes:

• Confusing simulation with physical measurement
• Thinking Simulink writes hardware code
• Assuming Simulink manufactures motors

2. Which Simulink block is typically used to represent the electrical input voltage to a DC motor?

easy

A. Step block

B. Integrator block

C. Constant block

D. Gain block

Solution

1. Step 1: Identify input voltage representation

   Step block is commonly used to simulate a voltage that changes at a specific time, like turning the motor on.

2. Step 2: Compare other blocks

   Gain scales signals, Constant holds fixed value, Integrator accumulates signals, so Step fits best for input voltage changes.

3. Final Answer:

   Step block -> Option A

4. Quick Check:

   Voltage input changes = Step block [OK]

Hint: Use Step block for voltage changes over time [OK]

Common Mistakes:

• Using Constant block for changing voltage
• Confusing Gain with input source
• Thinking Integrator models voltage input

3. Given this Simulink model snippet for a DC motor, what will the scope display if the input voltage is a step from 0 to 12V at 1 second?

Electrical input: Step block (0 to 12V at t=1s)
Motor speed output connected to Scope

medium

A. Motor speed decreases after 1s

B. Motor speed jumps instantly to max at 1s

C. Motor speed remains zero throughout

D. Motor speed gradually increases after 1s

Solution

1. Step 1: Understand motor response to voltage step

   When voltage steps up, motor speed does not jump instantly due to inertia; it rises gradually.

2. Step 2: Analyze scope output

   Scope shows motor speed increasing smoothly after 1 second, reflecting physical motor acceleration.

3. Final Answer:

   Motor speed gradually increases after 1s -> Option D

4. Quick Check:

   Motor inertia causes gradual speed rise [OK]

Hint: Motor speed changes smoothly, not instantly [OK]

Common Mistakes:

• Expecting instant speed jump
• Thinking speed stays zero
• Assuming speed decreases after voltage step

4. You built a DC motor model in Simulink but the motor speed output stays zero even after applying voltage. What is the most likely error?

medium

A. Step block voltage set to zero

B. Integrator block missing in the mechanical subsystem

C. Scope block not connected to output

D. Gain block value set to negative

Solution

1. Step 1: Check mechanical subsystem setup

   Integrator block models motor speed from acceleration; missing it means speed never changes.

2. Step 2: Evaluate other options

   Voltage zero means no input but question says voltage applied; scope connection affects display but not speed; negative gain affects direction but not zero speed.

3. Final Answer:

   Integrator block missing in the mechanical subsystem -> Option B

4. Quick Check:

   Missing integrator means no speed change [OK]

Hint: Mechanical integrator needed to get speed from acceleration [OK]

Common Mistakes:

• Ignoring missing integrator effect
• Assuming scope connection causes zero speed
• Confusing gain sign with zero output

5. You want to model a DC motor in Simulink that includes both electrical and mechanical dynamics with load torque changing over time. Which approach is best?

hard

A. Use separate electrical and mechanical subsystems connected by torque and speed signals, with a time-varying load torque input

B. Model only electrical subsystem and ignore mechanical load

C. Use a single Gain block to represent entire motor behavior

D. Apply a Constant block for load torque and ignore time variation

Solution

1. Step 1: Understand modeling requirements

   Electrical and mechanical parts affect motor behavior; load torque changes over time must be included.

2. Step 2: Choose modeling approach

   Separate subsystems allow clear representation and connection via torque and speed signals; time-varying load torque input models real conditions.

3. Step 3: Evaluate other options

   Ignoring mechanical or load dynamics oversimplifies; Gain or Constant blocks cannot capture dynamics properly.

4. Final Answer:

   Use separate electrical and mechanical subsystems connected by torque and speed signals, with a time-varying load torque input -> Option A

5. Quick Check:

   Separate subsystems + time-varying load = Use separate electrical and mechanical subsystems connected by torque and speed signals, with a time-varying load torque input [OK]

Hint: Model electrical + mechanical parts separately with load input [OK]

Common Mistakes:

• Ignoring mechanical subsystem
• Using constant load torque only
• Oversimplifying motor as single Gain block