1. CONTROL SYSTEMS THEORY
Assessment
Mini Project
Lab Report
Test
20%
20%
20%
Final Exam
Total
40%
100%

2. Teaching plan
Week Chapter
1
2-3
4
5-7
8
9-10
Introduction to control systems
System representation
Response analysis in time domain
Stability analysis in time domain
Test
Controller design
11-12 Response analysis in frequency domain
13-14 Stability analysis in frequency domain

3. CONTROL SYSTEMS
THEORY
Basic Control Systems Concept
Chapter 1
STB 35103

4. Objectives
 To
understand the concept of control
systems engineering.
 To
evaluate the characteristic responses of
a certain automatically controlled system.

5. Introduction
What is control system?
A
control systems is an integral part of our society.
It is used in an automatically controlled systems
Definition:
Subsystem
Control
Control System
Output of
the process
Process
A control system consists of subsystems and processes
assembled for the purpose of controlling the output of the
process

6. Purpose of building control system
We build control systems for four primary reasons
1.
Power amplification
2.
Remote control
3.
Convenience of input form
4.
Compensation from disturbances

7. Figure 1.1 a
Elevators
Early elevators were controlled
by hand ropes or an elevator
operator. Here, a rope is cut
to demonstrate the safety
brake, an innovation in early
elevators;
Photos courtesy of United
Technologies Otis Elevator.

8. Figure 1.1 b
Elevators
Modern Duo-lift elevators
make their way up the Grande
Arche in Paris, driven by one
motor, with each car
counterbalancing the other.
Today, elevators are fully
automatic, using control
systems to regulate position
and velocity.

9. Other examples
 ASIMO-created
by Honda

10. Other examples
 Car
cruise control
http://auto.howstuffworks.com/cruise-control3.htm
Cables
Electronicallycontrolled
Vacuum actuator

11. Other examples

Anti-lock braking system (ABS)

Major components of the typical ABS system
four speed sensors (one at each wheel)
 electronic control unit (ABS computer)
 a hydraulic control unit

http://www.samarins.com/glossary/abs.html

12. Other examples

Vehicle suspension system

a system that will absorb the energy of the
vertically accelerated wheel, allowing the frame
and body to ride undisturbed while the wheels
follow bumps in the road
http://auto.howstuffworks.com/car-suspension.htm

13. 
Advantages & disadvantages?

14. Response characteristic
Input: Our desired response
Output: The actual response that we get from
the system
E.g. Using the elevator.

15. Response characteristic
Elevator:
We need to push the button of
our desired floor. Elevator rise to
the floor with speed and floorleveling accuracy that is
comfortable to the passenger.
Input - Push of the floor button
- can be represented by a
step command
- represents what we
would like the output to
be after the elevator
stops

16. Figure 1.3
Elevator input and output

17. Response characteristic
Transient response:
The state changes through a path that is related to
the physical device and the way it acquires and
dissipate energy.
E.g.
The elevator undergoes a gradual change as it rises
from the ground to our selected floor. We call this
part of the response the transient response.

18. Figure 1.3
Elevator input and output

19. Response characteristic
Steady state response:
Approximation to the commanded or desired
response.
E.g.
This response occurs when the elevator reaches our
desired floor.

20. Response characteristic
Steady state error:
The difference between the input and the output.
Often steady-state error is inherent in the designed
system. It is up to the engineer to determines
whether or not that error leads to significant
degradation of systems function.
E.g.
Accuracy of the elevator’s leveling with the floor.

21. Type of systems
Control system configuration can be categorized
into two:
1)Open-Loop
Input
Control System
Output
2)Closed-Loop
Input
Control System
Output

22. Type of systems
Open-loop system
A generic open-loop system
Input transducer: Converts the form of input to that used by
controller
Controller:
Drives a process or plant

23. Type of systems
Open-loop system
A generic open-loop system
Plant:
Air conditioning system
Controller: Remote control
Input:
???
Output:
???

24. Type of systems
Open-loop system
A generic open-loop system
Open loop-system characteristic
Cannot compensate for any disturbances that add
to the controller’s driving signal.
Signal that drives plant is corrupted by
disturbance. The output is also corrupted.

25. Open loop control

Missile launcher system

26. Type of systems
Open-loop system
Advantage of
Open-loop system
Simple
Cheap

27. Type of systems
Open-loop system
Disadvantage of
Open-loop system
Sensitive to
disturbance
Solution
Use closed-loop system
Inability to correct
for disturbance

28. Type of systems
Closed-loop system
A generic closed-loop system

29. Type of systems
Closed-loop system
Input transducer:
Converts the form of the input to the form used by
controller.
Output transducer (sensor):
Measures the output response and converts it into
the form used by the controller.

30. Type of systems
Closed-loop system
Output transducer (sensor):
Measures the output response and converts it into
the form used by the controller.
E.g.
Valves of a temperature control system:
Input position
+
output temperature
→electrical signals

31. Type of systems
Closed-loop system
Valves of a temperature control system:
Input position  potentiometer (variable resistor)
output temperature  thermistor Electrical resistance
changes with
temperature

32. Type of systems
Closed-loop system
A generic closed-loop system

33. Type of systems
Closed-loop system
First summing junction adds the signal from the
input to the signal from the output which arrives
via the feedback path (return path from output to
summing junction).

34. Type of systems
Closed-loop system
Actuating signal: Input and output have different
gain
Error:
Input and output transducers
have unity gain (transducers
amplifies its input by 1)

35. Type of systems
Closed-loop system
Closed-loop system compensates for disturbance by:
•Measure output response
•Feeding the measurement back to summing junction
•If there is difference between two responses, the system
drives the plant. If no difference, the system does not drive
the plant.

36. Closed loop feedback control

Missile launcher system

37. Type of systems
Closed-loop system
Advantage of
Closed-loop system
Less sensitive to
noise, disturbances
and changes in
environment
Transient response
and steady-state error
can be controlled
easily
Transient response and steady-state error can be controlled
by redesigning the controller. The process of redesigning is
called compensating the system and the resulting hardware
is a compensator

38. Type of systems
Closed-loop system
Disadvantage of
Closed-loop system
More complex
More expensive

39. Type of systems
Open loop vs. Closed-loop system

How do we choose OL or CL?

Criticality of application
The need to monitor output
 The need to control the output
 The need for reduced error or zero error
 Cost / budget
 Safety


40. Analysis and design objectives
3 major
objectives
Transient
Response
Steady-state
response
Stability

41. Analysis and design objectives
Transient response
A very important aspect in control systems.
E.g.
Elevator. Slow transient response makes
passengers impatient. Rapid transient response
makes them uncomfortable.

42. Analysis and design objectives
Steady-state response
This response resembles the input. We are
concerned about the accuracy of the steady-state
response.
E.g.
An elevator must be level enough with the floor for
the passengers to exit.

43. Analysis and design objectives
Stability
Total response of a system is the sum of natural
response and forced response.
Total response = Natural response + Forced response
c ( t ) = cforced ( t ) + cnatural ( t )
A useful control system has a natural response that
1. Eventually approaches zero, leaving only the forced
response.
2. Oscillates.

44. Design process
Determine a
physical system
and specifications
from the
requirements
Analyze, design
and test to
ensure
requirements
are met
Draw
functional
block
diagram
Reduce
block
diagrams if
necessary
Transform
physical
system into
a schematic
Obtain block
diagram,
signal flow
diagram,
state-space
representation