Motor startup and braking simulation in Simulink - Mini Project: Build & Apply

Motor startup and braking simulation

📖 Scenario: You are working as an engineer to simulate how a motor starts up and then brakes. This helps understand how the motor behaves in real life when it is turned on and then stopped.

🎯 Goal: Create a simple model that simulates a motor starting up with a constant voltage and then braking by applying a braking torque. You will set up the motor parameters, configure the startup and braking phases, run the simulation, and observe the motor speed over time.

📋 What You'll Learn

Create a DC motor model

Set motor parameters: resistance, inductance, torque constant, inertia

Add a voltage input to start the motor

Add a braking torque input to stop the motor

Simulate motor speed over time

Plot motor speed to see startup and braking behavior

💡 Why This Matters

🌍 Real World

Simulating motor startup and braking helps engineers design motor controllers and predict motor behavior in machines like electric vehicles or industrial equipment.

💼 Career

Understanding motor dynamics and simulation is important for roles in electrical engineering, control systems, and automation industries.

1

Set up motor parameters

Create variables in the MATLAB workspace for the motor parameters: R (resistance) = 2 ohms, L (inductance) = 0.5 H, Kt (torque constant) = 0.1 Nm/A, and J (inertia) = 0.01 kg.m^2.

Simulink

% Define motor parameters
% Your code here

Hint

Use simple assignment statements to create each variable with the exact values.

2

Configure startup and braking inputs

Create two time vectors: t_startup from 0 to 2 seconds and t_brake from 2 to 4 seconds. Create a voltage input vector V that is 24 volts during startup and 0 volts during braking. Create a braking torque vector Tb that is 0 during startup and 0.5 Nm during braking.

Simulink

R = 2;  % Resistance in ohms
L = 0.5;  % Inductance in henrys
Kt = 0.1; % Torque constant in Nm/A
J = 0.01; % Inertia in kg.m^2
% Create time vectors and input signals
% Your code here

Hint

Use ones and zeros functions to create constant vectors for voltage and braking torque.

3

Simulate motor speed using differential equation

Write code that calculates motor speed omega over time using the equations: J * d(omega)/dt = Kt * I - Tb and L * dI/dt = V - R * I - Kt * omega. Use Euler's method with time step 0.01 seconds to simulate from 0 to 4 seconds. Store the speed values in omega.

Simulink

R = 2;  % Resistance in ohms
L = 0.5;  % Inductance in henrys
Kt = 0.1; % Torque constant in Nm/A
J = 0.01; % Inertia in kg.m^2
t_startup = 0:0.01:2;  % Time from 0 to 2 seconds
 t_brake = 2.01:0.01:4; % Time from 2.01 to 4 seconds
V = [24*ones(size(t_startup)) zeros(size(t_brake))];  % Voltage input
Tb = [zeros(size(t_startup)) 0.5*ones(size(t_brake))];  % Braking torque
% Simulate motor speed omega over time
% Your code here

Hint

Use a for loop from 2 to N to update current and speed using Euler's method.

4

Plot motor speed over time

Plot the motor speed omega against time vector t which combines t_startup and t_brake. Label the x-axis as 'Time (s)' and y-axis as 'Motor Speed (rad/s)'.

Simulink

R = 2;  % Resistance in ohms
L = 0.5;  % Inductance in henrys
Kt = 0.1; % Torque constant in Nm/A
J = 0.01; % Inertia in kg.m^2
t_startup = 0:0.01:2;  % Time from 0 to 2 seconds
 t_brake = 2.01:0.01:4; % Time from 2.01 to 4 seconds
V = [24*ones(size(t_startup)) zeros(size(t_brake))];  % Voltage input
Tb = [zeros(size(t_startup)) 0.5*ones(size(t_brake))];  % Braking torque

dt = 0.01;
N = length(V);
omega = zeros(1, N);
I = 0;
for k = 2:N
    dI = (V(k-1) - R*I - Kt*omega(k-1))/L;
    I = I + dI*dt;
    domega = (Kt*I - Tb(k-1))/J;
    omega(k) = omega(k-1) + domega*dt;
end

% Plot motor speed
% Your code here

Hint

Use plot(t, omega) and label axes with xlabel and ylabel. Add a title and grid for clarity.

Practice

1. What is the main purpose of using a Step input block in a motor startup simulation in Simulink?

easy

A. To apply braking force to the motor

B. To simulate the motor turning on at a specific time

C. To measure the motor speed

D. To display the motor speed graphically

Solution

1. Step 1: Understand the role of Step input block

   The Step input block provides a sudden change in input value at a specified time, simulating an event like turning the motor on.

2. Step 2: Relate Step input to motor startup

   In motor startup simulation, the Step input triggers the motor to start running at a chosen time.

3. Final Answer:

   To simulate the motor turning on at a specific time -> Option B

4. Quick Check:

   Step input = motor start trigger [OK]

Hint: Step input means sudden start signal for motor [OK]

Common Mistakes:

• Confusing Step input with braking action
• Thinking Step input measures speed
• Assuming Step input displays graphs

2. Which of the following is the correct way to connect a Brake block in Simulink to simulate motor braking?

easy

A. Connect Brake block input to motor speed output

B. Connect Brake block input to motor torque output

C. Connect Brake block output to motor speed input

D. Connect Brake block output to motor torque input

Solution

1. Step 1: Identify Brake block connections

   The Brake block takes motor speed as input to apply braking force based on speed.

2. Step 2: Match correct input-output connection

   Motor speed output should connect to Brake block input to simulate braking effect properly.

3. Final Answer:

   Connect Brake block input to motor speed output -> Option A

4. Quick Check:

   Brake input = motor speed output [OK]

Hint: Brake block input must receive motor speed [OK]

Common Mistakes:

• Connecting Brake output to motor speed input
• Using motor torque instead of speed as input
• Reversing input and output connections

3. Given this Simulink setup: a Step input turns the motor on at 1 second, and a Brake block applies braking at 5 seconds. What will the Scope block show for motor speed over 10 seconds?

medium

A. Speed rises at 1s, stays constant, then drops after 5s

B. Speed stays zero until 5s, then rises sharply

C. Speed rises at 1s and remains constant without change

D. Speed drops immediately at 1s and stays low

Solution

1. Step 1: Analyze Step input effect at 1 second

   The Step input causes motor speed to increase starting at 1 second, simulating startup.

2. Step 2: Analyze Brake block effect at 5 seconds

   At 5 seconds, the Brake block applies braking, causing speed to decrease after that time.

3. Final Answer:

   Speed rises at 1s, stays constant, then drops after 5s -> Option A

4. Quick Check:

   Step start then brake drop = Speed rises at 1s, stays constant, then drops after 5s [OK]

Hint: Motor speed rises at start, drops when brake applied [OK]

Common Mistakes:

• Thinking speed rises after brake time
• Assuming speed never changes after start
• Confusing timing of speed changes

4. You run a motor startup and braking simulation but the Scope shows motor speed never decreases after braking is applied. What is the most likely error?

medium

A. Step input time is set after braking time

B. Motor speed is set to zero initially

C. Scope block is not connected to motor speed

D. Brake block input is not connected to motor speed output

Solution

1. Step 1: Identify why braking has no effect

   If motor speed does not decrease after braking, the Brake block likely does not receive correct speed input.

2. Step 2: Check Brake block connections

   Brake block input must be connected to motor speed output to apply braking properly.

3. Final Answer:

   Brake block input is not connected to motor speed output -> Option D

4. Quick Check:

   Brake input missing = no speed drop [OK]

Hint: Check Brake input connection if speed doesn't drop [OK]

Common Mistakes:

• Ignoring Brake block wiring
• Mixing Step input and Brake timing
• Assuming Scope connection causes braking issue

5. You want to simulate a motor startup that ramps speed gradually over 3 seconds, then apply braking that stops the motor smoothly over 2 seconds. Which Simulink blocks and settings should you use?

hard

A. Use a Pulse Generator for startup and no Brake block

B. Use a Step block for startup and a Brake block with constant force

C. Use a Ramp block for startup and a Brake block with a time-based brake force

D. Use a Constant block for startup and a Step block for braking

Solution

1. Step 1: Choose startup block for gradual speed increase

   A Ramp block increases motor speed smoothly over a set time, perfect for gradual startup over 3 seconds.

2. Step 2: Choose braking method for smooth stop

   A Brake block with time-based brake force can apply braking gradually over 2 seconds to stop smoothly.

3. Final Answer:

   Use a Ramp block for startup and a Brake block with a time-based brake force -> Option C

4. Quick Check:

   Ramp for smooth start + timed brake = Use a Ramp block for startup and a Brake block with a time-based brake force [OK]

Hint: Ramp for smooth start, Brake with timed force for smooth stop [OK]

Common Mistakes:

• Using Step block for gradual startup
• Applying constant brake force for smooth stop
• Omitting Brake block for stopping