# Nyquist Stability

• posted

I've got a question on the Nyquist Stability criterion.

Consider a unity negative feedback system with plant L(s) and gain K in the forward loop.

A nyquist plot is to be generated for this system to meet the following criteria:

1) L(s) has one unstable right half plane pole

2) The closed loop system is stable for (1/3 < K < 2) and unstable for K=1/3 and K=2.

3) Phase margin of 30 degrees

4) Zero steady state error to a step reference input.

Help !

• posted

I don't generally do homework here and i won't do yours. I will point pit, though, that somebody probably left something out. The phase margin is clearly a function of gain. (The zero steady-state error implies that the system contains an integrator.)

Jerry

• posted

Just as a hint. Sketch a prototype/known Nyquist plot and evaluate each of your criteria for this known plot. Then work backwards to find a answer. Ray

• posted

Dnia 09-07-2010 o 06:02:28 Mohit napisa=B3(a):

You are asking for help because.... you are tired of thinking? You don't like it and you think that thinking is bad and dirty?

Make your muscles grow. Become a person.

You are asking for help because....?

• posted

Assuming that this is a class, go over your notes or the recent reading assignments in the book -- it may have been done as an example already; that will tell you your instructor's expectations.

If you're doing self-study then review the chapter of the book out of which this problem comes.

There _are_ ways to do this by construction, but we'd have to know how much you know before we could tell you how to do it that way.

• posted

1: What feature does L(s) need to have to stabilize that unstable pole? 4: What feature does L(s) need to have to have zero steady state error to a step input? 2: What does the Nyquist plot have to have to make the system stable for the given gain range? 3: What feature does the Nyquist plot have to have for 30 degrees phase margin?