Open-loop vs closed-loop control in Power Electronics - Visual Side-by-Side Comparison

Concept Flow - Open-loop vs closed-loop control

Start Control Process

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Open-loop Control

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Send Control Signal

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System Responds

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No Feedback Used

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Closed-loop Control

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Send Control Signal

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System Responds

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Measure Output

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Compare Output to Desired

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Adjust Control Signal

↩Back to Send Control Signal

Open-loop control sends commands without checking results; closed-loop control measures output and adjusts commands to reach the goal.

Execution Sample

Power Electronics

Desired Speed = 100 RPM
Open-loop: Set motor voltage to fixed value
Closed-loop: Measure speed, adjust voltage to keep 100 RPM

Shows how open-loop sets a fixed input, while closed-loop adjusts input based on measured output.

Analysis Table

Step	Control Type	Action	Measured Output	Adjustment Made	Result
1	Open-loop	Set voltage to 5V	Speed unknown	No adjustment	Motor runs at approx 90 RPM
2	Open-loop	No feedback	Speed unknown	No adjustment	Speed may vary with load
3	Closed-loop	Set initial voltage 5V	Measure speed = 85 RPM	Increase voltage	Speed moves closer to 100 RPM
4	Closed-loop	Adjust voltage to 5.5V	Measure speed = 98 RPM	Small increase	Speed near target
5	Closed-loop	Adjust voltage to 5.6V	Measure speed = 100 RPM	Fine tune	Speed stabilized at 100 RPM
6	Closed-loop	Maintain voltage	Measure speed = 100 RPM	No adjustment	Speed steady despite load changes
7	End	Process complete	-	-	-

💡 Open-loop stops after setting input; closed-loop continues adjusting until output matches desired value.

State Tracker

Variable	Start	After Step 1	After Step 3	After Step 4	After Step 5	Final
Voltage (V)	0	5	5	5.5	5.6	5.6
Speed (RPM)	0	Approx 90	85	98	100	100
Adjustment	None	None	Increase	Increase	Fine tune	None

Key Insights - 3 Insights

Why does open-loop control not adjust the voltage after the first step?

Because open-loop control does not use feedback, it sends a fixed input and does not measure or adjust based on output, as shown in execution_table rows 1 and 2.

How does closed-loop control know when to stop adjusting the voltage?

Closed-loop control measures the output and compares it to the desired value; it stops adjusting when the output matches the target, as seen in execution_table rows 5 and 6.

Why might the motor speed vary in open-loop control under different loads?

Because open-loop control does not measure output, it cannot compensate for changes like load variations, so speed can drift, shown in execution_table row 2.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what action does closed-loop control take after measuring speed?

A Keep voltage the same

B Increase voltage to raise speed

C Decrease voltage to lower speed

D Stop the motor

💡 Hint

Refer to execution_table row 3 under 'Adjustment Made' column.

At which step does the closed-loop control first reach the desired speed of 100 RPM?

A Step 3

B Step 4

C Step 5

D Step 6

💡 Hint

Check execution_table 'Measured Output' column for speed closest to 100 RPM.

If the open-loop control voltage was set higher initially, how would the motor speed change in the execution_table?

A Speed would likely increase but still not adjust

B Speed would decrease automatically

C Voltage would adjust to maintain speed

D Motor would stop

💡 Hint

Open-loop control does not adjust voltage after setting it, see variable_tracker Voltage and Adjustment rows.

Concept Snapshot

Open-loop control sends fixed commands without feedback.
Closed-loop control measures output and adjusts commands.
Closed-loop is more accurate and adapts to changes.
Open-loop is simpler but less precise.
Used in systems where feedback is or isn't possible.

Full Transcript

Open-loop control works by sending a fixed control signal to a system without checking the result. For example, setting a motor voltage and not measuring speed means the system cannot adjust if conditions change. Closed-loop control measures the output, compares it to the desired value, and adjusts the input to reach the target. This feedback loop allows the system to maintain performance despite disturbances. The execution table shows open-loop setting voltage once and not adjusting, while closed-loop measures speed and changes voltage until the speed matches the desired 100 RPM. Variables like voltage and speed change step-by-step in closed-loop but remain fixed in open-loop. Beginners often wonder why open-loop doesn't adjust or how closed-loop knows when to stop; the key is feedback and comparison to the goal. Quizzes test understanding of these steps and differences.