Section 7–3 / Polar Plots 435
v
Im
Re
Im
(^0) Re
0
0
Im
Re
Im
(^00) Re
Im
Re
Im
(^0) Re
Im
Im
Im
Im
Re
Re
Re
Re
0
0
0
0
1
0
v
v v
v
(^00)
v v
0 0
v =
v =
v =
v =
v =
v =
v =
1
jv
1
1
1
1 +jvT
jvT
jv 1 +jvT
jvT
1 +jvT
1
a
v =
v = 0 v = 0
v = 0
v = 0
v = 0
1
(jv)^2
1 +jvT
1 +jvaT
(a 1 )
1
(1+jvT 1 ) (1 +jvT 2 ) (1 +jvT 3 )
vn^2
jv[(jv)^2 + 2 zvn(jv)+vn^2 ]
1 + jvT 1
jv (1+jvT 2 ) (1 +jvT 3 )
1
Table 7–1 Polar Plots of Simple Transfer Functions
Drawing Nyquist Plots with MATLAB. Nyquist plots, just like Bode diagrams,
are commonly used in the frequency-response representation of linear, time-invariant,
feedback control systems. Nyquist plots are polar plots, while Bode diagrams are
rectangular plots. One plot or the other may be more convenient for a particular opera-
tion, but a given operation can always be carried out in either plot.
The MATLAB command nyquistcomputes the frequency response for continuous-
time, linear, time-invariant systems. When invoked without left-hand arguments,nyquist
produces a Nyquist plot on the screen.
