Open-loop vs closed-loop systems in Simulink - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define an open-loop system block in Simulink.

Simulink

open_loop = sim('[1]');

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

Aopen_loop_model

Bclosed_loop_model

Cfeedback_system

Dcontrol_system

Attempts:

3 left

💡 Hint

Common Mistakes

Using the closed-loop model name instead of the open-loop model.

Confusing the feedback system with open-loop.

The open-loop system is simulated using the model named 'open_loop_model'.

2fill in blank

medium

Complete the code to add a feedback loop in Simulink for a closed-loop system.

Simulink

closed_loop = feedback([1], 1);

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

Aopen_loop

Bdisturbance

Ccontroller

Dplant

Attempts:

3 left

💡 Hint

Common Mistakes

Using the open-loop system instead of the plant.

Using the disturbance as the forward path.

The feedback function uses the plant model as the forward path to create a closed-loop system.

3fill in blank

hard

Fix the error in the code to simulate a closed-loop system response.

Simulink

response = step([1]);

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

Aopen_loop

Bclosed_loop

Cdisturbance

Dcontroller

Attempts:

3 left

💡 Hint

Common Mistakes

Calling step on the open-loop system instead of closed-loop.

Using controller or disturbance as input to step.

The step response should be called on the closed-loop system to observe its behavior.

4fill in blank

hard

Fill both blanks to create a dictionary of system types and their descriptions.

Simulink

systems = [1]: 'No feedback control', [2]: 'Uses feedback to adjust output'}

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

A'open_loop'

B'closed_loop'

C'feedback'

D'feedforward'

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up open-loop and closed-loop keys.

Using 'feedback' or 'feedforward' as keys instead of system types.

'open_loop' corresponds to no feedback control, and 'closed_loop' uses feedback to adjust output.

5fill in blank

hard

Fill all three blanks to create a comprehension that filters systems with feedback.

Simulink

feedback_systems = {name: desc for name, desc in systems.items() if [1] [2] [3]

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

A'loop'

Bin

C'closed'

D'open'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'closed' instead of 'open' for filtering feedback systems.

Incorrect order of keywords in the condition.

The comprehension filters system names containing 'closed' in 'loop' to identify feedback systems.

Practice

1. Which of the following best describes an open-loop system in Simulink?

easy

A. A system that uses sensors to monitor output and correct errors.

B. A system that continuously adjusts output based on feedback.

C. A system that operates without using feedback to adjust its output.

D. A system that always maintains a constant output regardless of input.

Solution

1. Step 1: Understand open-loop system definition

   An open-loop system works without feedback; it does not adjust based on output.

2. Step 2: Compare options to definition

   A system that operates without using feedback to adjust its output. matches this definition exactly, while others describe feedback or constant output.

3. Final Answer:

   A system that operates without using feedback to adjust its output. -> Option C

4. Quick Check:

   Open-loop = no feedback [OK]

Hint: Open-loop means no feedback used to adjust output [OK]

Common Mistakes:

• Confusing open-loop with closed-loop systems
• Thinking open-loop uses feedback
• Assuming open-loop always maintains constant output

2. Which Simulink block is typically used to create a closed-loop system?

easy

A. Gain block

B. Sum block with feedback connection

C. Constant block

D. Scope block

Solution

1. Step 1: Identify closed-loop system structure

   Closed-loop systems require feedback, often created by feeding output back to input using a Sum block.

2. Step 2: Match blocks to feedback role

   Sum block with feedback connection allows error calculation, enabling closed-loop control.

3. Final Answer:

   Sum block with feedback connection -> Option B

4. Quick Check:

   Feedback needs Sum block [OK]

Hint: Closed-loop needs feedback; Sum block enables feedback loop [OK]

Common Mistakes:

• Choosing Gain block which only scales signals
• Selecting Constant or Scope blocks which don't create feedback
• Ignoring the feedback connection requirement

3. Consider this Simulink setup: a Gain block with gain 2 connected directly to input, no feedback. What is the output if input is 3?

medium

A. 3

B. 1.5

C. 0

D. 6

Solution

1. Step 1: Identify system type and operation

   The system is open-loop (no feedback). Output = input * gain.

2. Step 2: Calculate output value

   Output = 3 * 2 = 6.

3. Final Answer:

   6 -> Option D

4. Quick Check:

   Output = input x gain = 6 [OK]

Hint: Multiply input by gain for open-loop output [OK]

Common Mistakes:

• Assuming feedback changes output
• Using input value directly without gain
• Confusing gain with division

4. You have a closed-loop system in Simulink but the output does not stabilize and keeps oscillating. What is the most likely cause?

medium

A. Gain value is too high causing instability

B. Feedback loop is missing

C. Input signal is zero

D. Sum block is not connected

Solution

1. Step 1: Understand oscillation cause in closed-loop

   Oscillations often occur when gain is too high, causing the system to overreact and become unstable.

2. Step 2: Eliminate other options

   Feedback loop missing or Sum block not connected would stop feedback, not cause oscillations. Zero input does not cause oscillations.

3. Final Answer:

   Gain value is too high causing instability -> Option A

4. Quick Check:

   High gain causes oscillation [OK]

Hint: High gain in feedback causes oscillations [OK]

Common Mistakes:

• Thinking missing feedback causes oscillations
• Assuming zero input causes oscillations
• Ignoring gain effect on stability

5. You want to design a Simulink model to maintain room temperature at 22°C despite outside temperature changes. Which system type and feature should you use?

hard

A. Closed-loop system with temperature sensor feedback

B. Open-loop system with timer-based heater control

C. Open-loop system with fixed heater power

D. Closed-loop system without feedback

Solution

1. Step 1: Identify control needs for stable temperature

   Maintaining temperature despite changes requires feedback to adjust heater power.

2. Step 2: Choose system type with feedback

   Closed-loop system with temperature sensor feedback adjusts output based on actual room temperature.

3. Final Answer:

   Closed-loop system with temperature sensor feedback -> Option A

4. Quick Check:

   Stable control needs feedback loop [OK]

Hint: Use feedback to adjust for changing conditions [OK]

Common Mistakes:

• Choosing open-loop which can't adjust to changes
• Ignoring need for sensor feedback
• Selecting closed-loop without feedback