EL 625 Lecture 1
1
EL 625 Lecture 1
Definition
:
A
physical system
is an interconnection of
physical components that perform a specific function.
These
components may be electrical, mechanical,hydraulic,thermal and
so forth.
System
S
-
u
1
-
u
2
•
•
•
-
u
r
-
y
1
-
y
2
•
•
•
-
y
m
Inputs
or
excitations
Outputs
or
responses
Inputs
:
signals that can be directly changed with time in order
to effect indirectly desired changes in some other signals of the
system which are of particular interest (which are called
out-
puts
)
Using vector notation,
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EL 625 Lecture 1
2
u
(
t
) =
u
1
(
t
)
u
2
(
t
)
u
3
(
t
)
.
.
.
u
r
(
t
)
y
(
t
) =
y
1
(
t
)
y
2
(
t
)
y
3
(
t
)
.
.
.
y
m
(
t
)
System
S
-
u
(
t
)
-
y
(
t
)
y
(
t
) =
S
{
u
(
t
)
}
‘Input-output relation’
y
e
=
S
{
u
e
}
y
e
and
u
e
represent the entire time functions
y
and
u
respectively.
EL 625 Lecture 1
3
Classification of Systems
Type of system
Brief Description
Dynamic
system has memory; output at time t de-
pends on inputs at times other than t
Static
System has no memory (zero memory) ;
output at time t depends on input only at
time t
MIMO
Multi-Input-Multi-Output - many inputs
and outputs
SISO
Single-Input-Single-Output - one input and
one output
Continuous-time
differential equations
Discrete-time
difference equations
Causal
System is not predictive - output depends
only on past values of input
Non-causal
output depends on future values of input
also
Linear
Superposition holds
Non-linear
‘not linear’ - Superposition does not hold
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EL 625 Lecture 1
4
Finite-Dimensional
finite number of states required to charac-
terize the system - ‘lumped’ system
Infinite-Dimensional
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