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Control System Basics
ELEC 312
Control System Definition
Consists of subsystems and processes
assembled for the purpose of obtaining an
output with desired performance, given a
specified input
What are the measures of performance?
Purposes of control systems: tracking
power amplification, remote control,
convenience of input form, and
compensation for disturbances.
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Terminology
Plant : a system (physical object) whose
output is to be controlled
e.g. CD player, disk drive mechanics,
engine, aircraft, missile, car suspension,
computer network, elevator, industrial
process, etc.
Sensor: a system used to measure the
quantity to be controlled (output
of the plant)
e.g. radar altimeter, strain gauge, GPS,
tachometer, microphone, transducers, etc.
Terminology
Actuator: a device (usually mechanical)
for controlling the plant by
influencing its input
e.g. hydraulic, pneumatic, electric motors,
pumps, heaters, solenoid, etc.
Disturbances: uncontrollable signals to the
plant that tend to adversely
affect the plant’s output
e.g. wind gusts, earthquakes, external
shaking & vibration, road surface, etc.
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Terminology
Controller: A device that processes the
sensor signal to generate an
input to drive the actuator
(also called control processor)
e.g. human, mechanical device, electro-
mechanical, microcontroller, digital signal
processors, etc.
Control law: the scheme or algorithm used
by the controller to derive the
actuator signal
Automatic Control
The process of causing a system to
behave in a prescribed manner
The process of causing a controlled
variable (plant’s output) to conform to
some reference (desired) input
Objective: control y by using u such that
y follows r
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Open-Loop Control
The control input u(t) is synthesized based
on the a priori knowledge of the system
(plant) and the reference input r(t)
The control system does not measure the
output, and there is no comparison of the
output to make it conform to the desired
output (reference input).
Closed-Loop Control
The control input, u(t), is synthesized based
on the a priori knowledge of the system
(plant), the reference input r(t), and the error
signal, e(t)
The control system measures the output, and compares it to the desired output (reference input) through a feedback path to generate an error signal
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Shock Absorber
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A DC Servomotor System
Antenna Azimuth Position Control System
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Detailed Layout
Schematics
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Functional Block Diagram
Microcomputer-based Control
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A Bread-making Machine
Types of Controllers
Two-position or on-off Controllers
Proportional Controllers
Integral Controllers
Proportional-plus-integral Controllers
Proportional-plus-derivative
Controllers
Proportional-plus-integral-plus-
derivative Controllers
Lead, Lag, Lag-lead
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Proportional Control
)()( teKtu p= pKsE
sU=
)(
)(
Kp = proportional gain
Integral Control
=t
i teKtu0
)()( s
K
sE
sU i=)(
)(
Ki = adjustable constant
Control Action: Proportional (P)
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)(
)()(
RR
RR
sV
sVsG
i
o ==
Control Action: Integral (I)
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4 1
)(
)()(
CsRR
R
sV
sVsG
i
o ==
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Proportional-plus-Integral Control
+=t
i
p
p teT
KteKtu
0
)()()(
+=
sTK
sE
sU
ip
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)(
)(
Ti = integral time
Proportional-plus-derivative
Control
dt
tdeTKteKtu dpp
)()()( +=
( )sTKsE
sUdp += 1
)(
)(
Td = derivative time
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Control Action: Proportional+Integral (PI)
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1
2
3
4 1
)(
)()(
CsR
CsR
R
R
R
R
sV
sVsG
i
o +==
Control Action: Proportional+Derivative (PD)
)1()(
)()( 11
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2
3
4 +== CsRR
R
R
R
sV
sVsG
i
o
Proportional-plus-integral-plus-
derivative Control
++=t
i
p
dpp teT
K
dt
tdeTKteKtu
0
)()(
)()(
++= sT
sTK
sE
sUd
ip
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)(
)(
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Control Action: Proportional+Integral+Derivative (PID)
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2211
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2
3
4 )1)(1(
)(
)()(
CsR
CsRCsR
R
R
R
R
sV
sVsG
i
o ++==
Control Action: Lead or Lag
)1(
)1(
)(
)()(
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11
1
2
3
4
+
+==
CsR
CsR
R
R
R
R
sV
sVsG
i
o
Control Action: Lag-Lead
]1)()[1(
)1](1)([
)(
)()(
42211
22311
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+++
+++==
RRsCCsR
CsRRRsC
R
R
R
R
sV
sVsG
i
o
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