ECE317 : Feedback and Control

Lecture 1
Introduction

Dr. Richard Tymerski

Dept. of Electrical and Computer Engineering
Portland State University

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 Outline
• Introduction of the course
• Automatic control
• Open-loop system and closed-loop system
• Goal of the course

2
 What is “Control”?
• Make some object behave as we desire.
• In control engineering, the controlled object is
called system, or plant, or process.
• Imagine “control” around you!
• Room temperature control
• Car driving, bicycle riding
• Voice volume control
• Balance of bank account
• “Control” (move) the position of the pointer
• etc.

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 What is “Automatic Control”?
• Not manual!
• Why do we need automatic control?
• Convenient (room temperature control, laundry
machine)
• Dangerous (hot/cold places, space, bomb removal)
• Impossible for human (nanometer scale precision
positioning, work inside the small space that human
cannot enter, huge antennas control, elevator)
• It exists in nature. (human body temperature control)
• High efficiency (engine fuel-injection control)
• Many examples of automatic control around us

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 Outline
• Introduction of the course
• Automatic control
• Open-loop system and closed-loop system
• Goal of the course

5
 Example: Toaster
• A toaster toasts bread, by setting timer.

Setting of timer Toasted bread

Toaster

• A toaster does not measure the color of

bread during the toasting process.
• What happens if your setting is wrong....
• However, a toaster would be more expensive
with:
• Sensors to measure the color, and
• Actuators to adjust the timer based on the
measured color.

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 Example: Laundry machine
• A laundry machine washes clothes, by
setting a program.
Program setting Washed clothes
Machine

• A laundry machine does not measure

how clean the clothes become.
• Control without measuring devices
(sensors) is called open-loop control.

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 Ex: Automobile direction control
• Change the direction of the automobile. Block diagram
Steering
Desired Error wheel Direction
direction
angle
Brain Hand Auto

Eye

• Control with measuring devices (sensors) is called

closed-loop (feedback) control.
• Manual (not-automatic) control

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 Ex: Automobile cruise control
• Maintain the speed of the automobile. Disturbance (wind,
bumpy road, etc.)
Error Acceleration
Desired
speed Speed
Controller Actuator Auto

Sensor
• Cruise control can be both manual and automatic.
• When the controlled system is “Automobile”, input and
output depend on control objectives, and not unique!

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 Ex: Room temperature control
• Maintain the temperature in a room.
Disturbance
Error Heating
Desired switch
temp. state Temperature
Controller Actuator Room

Sensor

• Temperature control can be automatic.

• Note the similarity of the diagram above to the
diagram in the previous slides!

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 Ex: Water level control
• Maintain the water level in a tank.
Disturbance
Error Valve
Desired
level state Water level
Controller Actuator Tank

Sensor

• Water level control can be automatic.

• Other examples : autopilot, catching a ball, etc

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12
 Automatic feedback control systems:
Elements and design objective
Error Disturbance
Reference Input Output
Controller Actuator Plant

Sensor

• Control system design objective is to design a

controller such that the output follows the
reference in a “satisfactory” manner even in the
face of disturbances.

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 Features of feedback control
• Advantage: Strong, or robust, against
• uncertainty
• unpredictable disturbance
• variation of plant etc.
• Disadvantage:
• The action is taken after some undesirable event
happens.
• Stability issues

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 Outline
• Introduction of the course
• Automatic control
• Open-loop system and closed-loop system
• Goal of the course

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 Systematic controller design process
Disturbance
Reference Input Output
Controller Actuator Plant

Sensor

4. Implementation 1. Modeling

Controller Mathematical model

2. Analysis
3. Design
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 Goal of this course
To learn basics of feedback control systems
• Modeling as a transfer function and a block diagram
• Laplace transform (Mathematics!)
• Electrical, mechanical
• Example system: DC-to-DC switching converter
• Analysis
• Stability: Pole Locations, Routh-Hurwitz criterion
• Time response (transient and steady state)
• Frequency response, Bode diagram
• Design
• frequency response technique, Bode diagram
• frequency compensation,
Theory, simulation with Matlab and PECS, practice in laboratories

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 Course roadmap
Modeling Analysis Design
Laplace transform
Stability
Design specs
• Pole locations
Transfer function
• Routh-Hurwitz
Frequency domain
Block Diagram
Time response
Linearization Bode plot
• Transient
• Steady state (error)
Models for systems Compensation
• electrical
Frequency response
• mechanical Design examples
• Bode plot
• example system

Matlab & PECS simulations & laboratories

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