Automatic Control Systems -Lecture Note 2-
Introduction 2
Type of Control System
◈ Open-loop control system
◈ Closed-loop control system
Concept of Automatic Control
System : a collection of things which operates as a whole with input and output
Plant : a physical object as control target of control system
Process : a plant dealing with chemical, thermodynamic, or fluid dynamics quantity of output like as temperature, pressure, fluid, water level, pH, etc.
Reference input : a command signal output is supposed to track
Terminology
□ Definition of terms
Disturbance : an unexpected external signal which have a negative influence on the output performance of system
Measurement noise : an additive signal to sensor measurement of output
Feedback control : a closed-loop control method whose output signal is fed back to the input of control system
Closed-loop control : = feedback control
Open-loop control : a control method with only the reference control input without any feedback signal
Terminology
Servo system : a control system whose output signal represents physical or mechanical quantity like as position, velocity,
acceleration, etc.
Process control system : a control system which is aiming at managing its whole operation flow and manufacturing process Time-varying system : a system whose input-output characteristic is time variant
Time-invariant system : a system whose input-output transfer characteristic is not variant with time
Linear system : a system whose input-output transfer function model G satisfies
where are inputs and arbitrary constants.
1 2 1 2
( ) ( ) ( )
G u u G u G u
, u
u
,
Terminology
Nonlinear system : a system which is not linear
Control objective : a design goal whose control system is aiming at
Stability
Command following Disturbance rejection Noise reduction
Terminology
Open-loop Control :
u G
input
y
output
<Fig> Constant Gain System
Feedback Concept
□ What and Why?
‧ An Ideal Case : with known constant gain and without disturbance and noise, the open-loop inverse gain control achieves the control objective of tracking
G -1 G
r
Reference input
controller
u y
Control
input output
plant
<Fig> Open-loop control
1
( 1) u G r
y Gu G G r r
Feedback Concept
(1)
‧ Problem : the ideal case does not apply to real system
‧ Uncertainty in system model parameter, external disturbance, and sensor noise exist :
d u
G G
y ( )
Feedback Concept
(2)
•G : nominal gain
•Del G : system modeling parameter error
•d : external disturbance
G
G
d
y
u +
+ +
+
<Fig> Uncertain Constant Gain Plant Assuming the open-loop inverse gain control
1 1
( )
y G G G r d r GG r d
d r GG
r
y ( 1) Tracking error exists
1
G
Feedback Concept
(3)
<Note>
① Gain error ΔG and disturbance d induce control error
② Since ΔG and d are not known, the open-loop control can not achieve the perfect tracking of reference input or
reduction of disturbance
Feedback Concept
G
G r + C
-
e u + + +
+ y
d
<Fig> Feedback Control System
C e
y r
e
) (r y C
Ce
u
( ) ( ) ( )
y G G u d G G C r y d
: controller : control error
(4)
Feedback Concept
C d G r G
C G G
C G y G
) (
1
1 )
( 1
) (
C
When the control gain is large and approaches to infinity
( ) 1
1, 0
1 ( ) 1 ( )
G G C
G G C G G C
(5)
(6)
. r y
implying
Feedback Concept
<Note>
① The larger C, the better tracking performance and lesser effect of disturbance called high gain theorem
② The high gain theorem applies only to the case without the sensor noise of output measurement
Feedback Concept
‧ Feedback Control System with Sensor Noise
G
G r + C
-
e u + + +
+ y
d
+ v
+
<Fig> Feedback Control System
v
Feedback Concept
: sensor noise
High Control Gain implies
‧ How to design controller gain C how to balance the disturbance gain and noise gain
C v G G
C G d G
C G r G
C G G
C G y G
) (
1
) (
) (
1
1 )
( 1
) (
(7)
r v
r
y
Feedback Concept
1 ) |
( 1
)
| ( ) |
( 1
| 1
G G C
C G G
C G G
Idle-Speed Control of Automobile
Control System Example
Sun-Tracking Control of Solar Collectors
Control System Example
Elevators
Control System Example
a. Early elevators were controlled by hand ropes or an elevator operator.
b. Today, elevators are fully automatic, using control systems to regulate position and velocity.
Control System Example
Robots
Control System Example
Video Laser Disc Player
Control System Example
Industrial and Intelligent Service Robot Systems Hybrid Car Motor Control Systems
Semiconductor Process Control Systems Communication Network Control Systems Telecommunication Device Control Systems Embedded Control Systems
Steel Mill Process Control Systems
Automobile Active Suspension Control Systems Intelligent Building Automation Control Systems Flight Guidance Control Systems
Power Plant Distributed Control Systems
