S-plane and Transient Response: Poles, Zeros, and Inverse Laplace Transform, Study notes of Automatic Controls

The concept of the s-plane in control systems engineering, including the definitions of zeros and poles, system characteristic polynomial and equation, and pole-zero patterns. It also covers the transient response and inverse laplace transform, as well as graphical determination of residues and root locus gain.

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2011/2012

Uploaded on 07/19/2012

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1 The s-plane
We write
C(s)= G(s)R(s)
where C, G and R are each ratios of polynomials in s, i.e. G(s)=
num G .
den G
Consider the following definitions:
zeroes of C, G and R are
poles of C, G and R are
system zeroes and poles are
system characteristic polynomial is
system characteristic equation is
Note that the roots of the C.E. are
Since, the polynomials have real coefficients, the poles and zeros are
2
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pf5

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1 The s-plane

We write

C(s) = G(s)R(s)

where C, G and R are each ratios of polynomials in s, i.e. G(s) =

num G . den G

Consider the following definitions:

  • zeroes of C, G and R are
  • poles of C, G and R are
  • system zeroes and poles are
  • system characteristic polynomial is
  • system characteristic equation is

Note that the roots of the C.E. are

Since, the polynomials have real coefficients, the poles and zeros are

We plot the poles and zeros in the s(σ + jω) plane.

Example:

1 Assume R(s) = s

. Then the pole-zero pattern of C(s) = R(s)G(s) is the

superposition of the patterns of R(s) and G(s):

K(s + 2) C(s) = s(s + 4)

3 Graphical determination of residues (real

poles)

(a) Typical factor in PFE is

(a is positive and b is negative)

We can write

where b − (−a) is

So in the s-plane:

(b) The general expression for K 1 in the example above is

(c) Using the actual values, we have:

and for K 2 :

(d) So as before,

− 4 t c(t) = K( + e ) 2 2