Closed Logarithmic Nyquist plot

Function for plotting Nyquist diagram on a logarithmic scale

A new logarithmic Nyquist plot is proposed where the amplitude is in a logarithmic scale and the diagram is entirely contained in a circle of finite radius. This method does not need different levels of magnification of the plot as happens using linear Nyquist diagram which often, in particular when poles at the origin are present, hide the behavior of the frequency response in the areas very close to or very far from the origin of the complex plane. All the considerations made by Nyquist stability criterion can be done with this plot which maintains all the properties of polar plots such as gain and phase margins, intersection points with the real axis, encirclements of the critical point.

This work has been submitted to the European Control Conference 2014 for possible publication.