Desperate about Nyquist Diagrams

[nebbione]

Hi everyone! I searched all over the web and nobody/nothing gives a good explanation on how to plot nyquist diagrams... can somebody help with these ? I can't go forward in my study of control engineering without knowing these and I'm stucked...

How are nyquist diagrams plotted starting from a transfer function or from bode diagrams?

Can somebody explain in a detailed way or link me a site where it's explained step by step ?

Thank you

 

[jedishrfu]

These two references may help:

http://en.wikipedia.org/wiki/Nyquist_plot

and

http://www.facstaff.bucknell.edu/mastascu/econtrolhtml/Freq/Freq6.html

 

[nebbione]

Already viewed, but it doesn't help...

 

[SteamKing]

How about this link:

http://mmae.iit.edu/~mpeet/Classes/MMAE443/443Lecture23.pdf

 

[Runei]

A nyquist plot is simply plotting the whole function G(jω).

You have G(s) => G(jω), and then for each ω, you plot the resulting complex number in the complex plain. Normally this is done by using a polar plot, where instead of x and y (or Re and I am in the complex plain), we use r (the distance from origin to the point) and θ (the angle of the line from origin to that point, measured from the real axis of course, and counter-clockwise).

Now for a complex number, the r is simply the magnitude of the number, and θ is the phase.

So for the function G(jω), you simply plot each result as an r and θ. That is, you look at mag(G) and angle(G), and the you plot that.

 

[nebbione]

I already viewed even that link but cannot understand... ok i understand that I'm plotting G(jω) but what is the domain ? how much i havef to draw ? how can i know from which module to which module e from which fase to which fase ? Isn't there some place where this is well explained ?

 

[NascentOxygen]

The domain goes from f=0 Hz to f=∞ Hz, you make your own judgement on how many points to plot and their spacing.

http://www.facstaff.bucknell.edu/mastascu/econtrolhtml/Freq/Freq6.html

Oops. Someone has already posted that link.