
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 "Settings->Frequency units".
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 in
"Settings->Frequency units".
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.

