5 Other responses
5.1 Nyquist plot
Nyquist plot of the open loop plant G(s) can be seen by clicking on
``Response ®Nyquist''. The gain and phase margin is displayed on the
plot. If you find that your plot is too coarse or cluttered, you can
change the minimum and maximum frequency in
``Settings ®Nyquist-Nichols plot''. The units for frequency can be
changed in the ``Options'' menu of the Nyquist plot window. You must
close this window to return to the main rltool window.
5.2 Nichols plot
Nichols plot for G(s) is obtained by selecting
``Response ®Nichols''. If the grid (in the main menu) is set to
``on'' you will see the logarithmic grid superimposed on the Nichols
plot. Here too, you can select the desired frequency units. You must
close this window to return to the main rltool window.
5.3 Popov plot
The Popov plot can be used to predict the stability of the closed loop
system with a sector bound nonlinearity in loop. We plot real part of
G(iw) on the real axis and w Imaginary
G(iw) on the imaginary axis. A simple construction then gives
the range of the ``Popov sector'' and the ``multiplier''. Please see
any standard text on nonlinear systems for more details on the Popov
plot.