ECE 1001 Intro. to Electrical

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ECE 1001 Intro. to Electrical Computer
Engineering-Introduction to Control Systems-

• Dr. Jiann-Shiou Yang
• Department of Electrical Computer Engineering
• University of Minnesota
• Duluth, Minnesota

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Outline

• Examples of Control System Applications
• What is a Control System?
• What is Feedback and What are its Effects?
• Mathematical Foundations for Automatic Control -
  (Math 3280, Math 3298 and ECE 2111)
• MATLAB Software (will be covered and used in ECE
  2111 and ECE 3151 courses For details, check
  http//www.mathworks.com)

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• What is a Control System? A control system is
  an interconnection of components forming a
  system configuration to provide a desired system
  response.
• Basic Control System Components
• Plant or Process -The portion of a system
  which is to be controlled-

Process
Input
Output
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• Actuators -An actuator is a device that
  provides the motive power to the process (i.e.,
  the device that causes the process to provide
  the output)-
• Sensors
• Controller(s)
• Examples of Control Applications
• Aircraft Autopilot
• Disk drive read-write head positioning system
• robot arm control system
• automobile cruise control system
• etc.

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Open-Loop Control Systems An open-loop control
system utilizes an actuating device to control
the process directly without using feedback.
Desired Output response
Output
Property The system outputs have no effect upon
the signals entering the process (i.e., the
control inputs are not influenced by the process
outputs)
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Closed Loop (Feedback) Control Systems
A closed-loop control system uses a measurement
of the output and feedback of this signal to
compare it with the desired input ( i.e.,
reference or command) Example Turntable Speed
Control (Open-loop vs. Closed-loop) Many modern
devices use a turntable to rotate a disk at a
constant speed. For example, a computer disk
drive and a CD player all require a constant
speed of rotation in spite of motor wear and
variation and other component changes. For the
turntable speed control, the goal is to design a
controller that will ensure that the actual speed
of rotation is within a specified percentage of
the desired speed despite all possible
uncertainties.
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Speed
Turntable
Adjustable Battery
DC Amplifier
DC motor
(a)
Desired speed (voltage)
Control Device
Process
Actuator
Actual Speed
Amplifier
DC motor
Turntable
(b)
Turntable speed control open-loop
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Speed
Turntable
Adjustable Battery
DC Amplifier

DC motor
Speed setting
_
Tachometer
(a)
Error
Desired speed (voltage)
Control Device
Actuator
Process

Actual Speed
Amplifier
_
DC motor
Turntable
Sensor
Tachometer
Measured Speed (voltage)
(b)
Turntable speed controlclosed-loop
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• Motivations for Feedback
• The main reasons for using feedback are the
  following
• Reducing the sensitivity of the performance to
  parameter variations of the plant and
  imperfections of the plant model used for design
• Reducing the effects of external disturbances and
  sensor noises
• Feedback can also
• Improve transient response characteristics
• Reduce steady -state errors
  

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Controller
Process
Comparison
Output
Desired Output Response
Measurement
Closed-loop general form
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• Effect of Feedback on Sensitivity
• -For the open-loop system shown below, if K2 is
  halved, then the system gain is also halved (that
  is, the overall system gain reduces to 50 of
  its original gain).
• Lets close the loop (with negative unity
  feedback). (a) Assume K1K21. If K2 is halved,
  then the overall system gain reduces to 67 of
  the original gain. (b) If K1K29, then the
  overall system gain becomes 91 of the original
  gain. (Note that for simplicity, we assume that
  K1 and K2 constant this requirement is not
  necessary. In general, they are frequency
  dependent)
• Conclusion The sensitivity is reduced as the
  loop gain (i.e., K1K2) is increased. - (0ne
  advantage of using feedback)

plant
controller
R
K1
K2
C