Step response analysis in Simulink - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a step input signal in Simulink.

Simulink

stepSignal = [1]('Step');

Drag options to blanks, or click blank then click option'

Atimeseries

Bstep

Csignalbuilder

Dsim

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'timeseries' incorrectly for step input creation.

Confusing simulation commands with signal creation.

The step function creates a step input signal in MATLAB, which can be used in Simulink.

2fill in blank

medium

Complete the code to simulate the model named 'myModel' for 10 seconds.

Simulink

simOut = sim('[1]', 'StopTime', '10');

Drag options to blanks, or click blank then click option'

AmyModel

BsimulinkModel

CstepResponse

DmodelSim

Attempts:

3 left

💡 Hint

Common Mistakes

Using variable names instead of the model name string.

Passing incorrect model names.

The sim function runs the Simulink model specified by its name as a string. Here, the model is 'myModel'.

3fill in blank

hard

Fix the error in extracting the step response data from simulation output.

Simulink

stepData = simOut.[1].signals.values;

Drag options to blanks, or click blank then click option'

AstepResponse

Boutput

Clogsout

Dyout

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect property names that do not exist in the simulation output.

Confusing logsout with yout.

The simulation output stores logged signals in the yout property by default, which contains the signal values.

4fill in blank

hard

Fill both blanks to plot the step response data with time on the x-axis and output on the y-axis.

Simulink

plot(simOut.tout, simOut.[1].signals.[2]);

Drag options to blanks, or click blank then click option'

Ayout

Bvalues

Ctime

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Using time or data instead of values.

Mixing up the properties of the simulation output.

The tout property contains time points, and yout.signals.values contains the output data to plot the step response.

5fill in blank

hard

Fill all three blanks to create a dictionary of step response characteristics: rise time, settling time, and overshoot.

Simulink

stepInfo = struct('RiseTime', [1], 'SettlingTime', [2], 'Overshoot', [3]);

Drag options to blanks, or click blank then click option'

Astepinfo(stepData, simOut.tout).RiseTime

Bstepinfo(stepData, simOut.tout).SettlingTime

Cstepinfo(stepData, simOut.tout).Overshoot

Dstepinfo(stepData, simOut.tout).Peak

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect property names like 'Peak' instead of 'Overshoot'.

Not passing both data and time to stepinfo.

The stepinfo function returns a structure with step response metrics. We extract RiseTime, SettlingTime, and Overshoot to analyze the response.

Practice

1. What does the step function in Simulink primarily show about a system?

easy

A. The system's output response to a sudden input change

B. The frequency response of the system

C. The system's steady-state error only

D. The system's input signal over time

Solution

1. Step 1: Understand the purpose of the step function

   The step function simulates how a system reacts when a sudden input (step input) is applied.

2. Step 2: Identify what the output represents

   The output shows how the system's output changes over time after the step input, revealing speed and stability.

3. Final Answer:

   The system's output response to a sudden input change -> Option A

4. Quick Check:

   Step response = output after sudden input [OK]

Hint: Step function shows output after sudden input change [OK]

Common Mistakes:

• Confusing step response with frequency response
• Thinking it shows only steady-state error
• Assuming it plots input signal instead of output

2. Which of the following is the correct syntax to plot the step response of a transfer function sys in MATLAB?

easy

A. response.step(sys)

B. plotstep(sys)

C. sys.step()

D. step(sys)

Solution

1. Step 1: Recall MATLAB step response syntax

   The standard MATLAB command to plot step response is step(sys), where sys is the system model.

2. Step 2: Check other options for correctness

   Options B, C, and D are not valid MATLAB commands for step response plotting.

3. Final Answer:

   step(sys) -> Option D

4. Quick Check:

   Use step(sys) to plot response [OK]

Hint: Use step(sys) to plot step response in MATLAB [OK]

Common Mistakes:

• Using incorrect function names like plotstep
• Trying object method calls not supported
• Confusing syntax with other toolboxes

3. Given the following MATLAB code, what is the approximate settling time of the system's step response?

sys = tf([1], [1 3 2]);
info = stepinfo(sys);
settling_time = info.SettlingTime;

medium

A. About 2 seconds

B. About 1 second

C. About 3 seconds

D. About 4 seconds

Solution

1. Step 1: Analyze the transfer function

   The system has poles at -1 and -2, so it is stable and expected to settle quickly.

2. Step 2: Use stepinfo to find settling time

   The stepinfo function calculates settling time, which for this system is approximately 2 seconds.

3. Final Answer:

   About 2 seconds -> Option A

4. Quick Check:

   Settling time from stepinfo ≈ 2 sec [OK]

Hint: Use stepinfo(sys).SettlingTime for settling time [OK]

Common Mistakes:

• Confusing settling time with rise time
• Ignoring system poles location
• Assuming default values without calculation

4. Identify the error in the following MATLAB code for plotting step response:

sys = tf([1 2], [1 4 5]);
step(sys)
title('Step Response')
xlabel('Time')
ylabel('Output')

medium

A. Missing semicolon after tf definition

B. No error; code runs correctly

C. The transfer function numerator and denominator are reversed

D. Step function should be called as step_response(sys)

Solution

1. Step 1: Check transfer function syntax

   The numerator and denominator vectors are correctly placed in tf([1 2], [1 4 5]).

2. Step 2: Verify step function and plot commands

   The step(sys) command is correct, and titles and labels are properly set.

3. Final Answer:

   No error; code runs correctly -> Option B

4. Quick Check:

   Code syntax is correct and runs [OK]

Hint: Check tf and step syntax carefully [OK]

Common Mistakes:

• Thinking numerator and denominator are swapped
• Expecting semicolon is mandatory (optional)
• Using incorrect step function names

5. You want to compare the step responses of two systems sys1 = tf([1], [1 2 1]) and sys2 = tf([2], [1 3 2]). Which MATLAB code snippet correctly plots both responses on the same graph for comparison?

hard

A. step(sys1); step(sys2);

B. plot(step(sys1), step(sys2));

C. step([sys1 sys2]);

D. step(sys1 + sys2);

Solution

1. Step 1: Understand how to plot multiple step responses

   Using step([sys1 sys2]) plots both systems' step responses on the same figure for easy comparison.

2. Step 2: Evaluate other options

   step(sys1); step(sys2); overwrites the first plot without hold on; plot(step(sys1), step(sys2)); is invalid syntax; step(sys1 + sys2); plots sum system, not comparison.

3. Final Answer:

   step([sys1 sys2]) -> Option C

4. Quick Check:

   Use step([sys1 sys2]) for combined plot [OK]

Hint: Use step([sys1 sys2]) to plot both responses together [OK]

Common Mistakes:

• Trying to add systems instead of plotting separately
• Using plot() on step outputs incorrectly
• Forgetting hold on/off when plotting separately