## With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, tutorials, and more.

No credit card required

### 6.6.  NYQUIST DIAGRAMS USING MATLAB[7]

In the previous section, several Nyquist diagrams were illustrated which were hand drawn. They were based on the transformation of the contour drawn in the s-plane to the G(s)H(s) plane. In this section, the MATLAB utility used for obtaining the Nyquist diagram is identified, and it is applied.

#### A.  Drawing Nyquist Diagrams of Systems Defined by Transfer Functions

If the system is defined by a transfer function, the Control System Toolbox command which determines the Nyquist plot is:

nyquist.

The Nyquist diagram can be used with polynomial transfer functions, defined as G(s) = num(s)/den(s) where “num” and “den” contain the polynomial coefficients, if invoked with three right-hand arguments as follows

[re,im] = nyquist(num,den,w)

where

re       = real part on the Nyquist diagram

im      = imaginary part on the Nyquist Diagram

num   = row matrix format representing the numerator of the polynomial

den    = row matrix format representing the denominator of the polynomial