Superimpose Nichols chart on Nichols plot
The chart relates the complex number H/(1 + H) to H, where H is any complex number. For SISO systems, when H is a point on the open-loop frequency response, then
is the corresponding value of the closed-loop frequency response assuming unit negative feedback.
If the current axis is empty, ngrid generates a new Nichols chart grid in the region –40 dB to 40 dB in magnitude and –360 degrees to 0 degrees in phase. If the current axis does not contain a SISO Nichols frequency response, ngrid returns a warning.
Plot the Nichols response with Nichols grid lines for the following system:
H = tf([-4 48 -18 250 600],[1 30 282 525 60]); nichols(H) ngrid
The right-click menu for Nichols charts includes the Tight option under Zoom. You can use this to clip unbounded branches of the Nichols chart.