曝光臺 注意防騙 網曝天貓店富美金盛家居專營店坑蒙拐騙欺詐消費者

the magnitude and phase angle of the transfer function G(s) (with s = jr.o) and
are given by
M8 - IG( jto)l
                                 Z~g = ZG(jw)
Taking the inverse Laplace transforms in Eq. (5.109), we get
                              Yoo(t) =  M2M   [e-/M +*r +ou) + ej~ +48 +wr)]
                                 = MtMg cos(~t + 4g + tot)
or, in phasor notation,
(5.110)
(5.111)
(5.112)
(5.113)
Mco/~   -. M,M8/(~/ + 48)                         (5.114)
'J
~
{
~
*
i
t,
ii
J1
         ~
    r.
L.
    :l
     J
    H
  -.
Mt =~
4/ = -t  -':~
458            PERFORMANCE, STABILITY, DYNAMICS, AND CONTROL
~&,  with frequency is called the frequency response of the system. In other words,
the ffequency response of a system whose transfer function is G(s),s -  jw iS
nothing but the variation of Mg and 4g with frequency co.
    One of the most widely usc~'methods of obtainin~ the frequency response of
a transfer function is the Bode plot It consists of two parts: the magnitude plot
in decibels where one decibel of M  = 20 1o9io M and the phase plot in degrees,
both plotted against frequency co, which is usually expressed in radians/second.
      Gevnerally, the Bode plotis drawn for open-loop transfer function G(s). Further-
more,if the transfer function contains a variable gain k, then the Bode plotis made
for k -.  1. For any other value of k, the corresponding Bode plot can be easily
obtained by shifting the entire Bode plot by 20 1o9io k. vfhe plot shifts upward if
k > O and downward if k < 0. We willillustrate the'method of drawing a Bode
plot with the help of Example 5.1.
                                             Example 5.1
Draw the Bode plot for a system given by
                                         G(s) = (, ,k/(S~S3l_ 2)
  So/ution.  The first step is to assume k-l and rewrite the given transfer
function in the following form:
      ~(3+1)
                                               G(s) = s(s +1)(2 +1)
             '1(S)
                         = G,(,)GG,(()G,(,)
where
                                        Gi(s) = (3+1)
                                           G2(S) :s
                                                                   G3(s) -. (s + 1)
                                      G4(S) = (2+1)
　
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