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# Nyquist Plot & stability

## Nyquist Plot & stability

(OP)
Can any one explain how Nyquist plot is assosciated with predicting Stability of a system

### RE: Nyquist Plot & stability

If you have a system with transfer function H(s) and negative feedback loop with function G(s), then overall system is
H(s)/[1+G(s)H(s)].

As can be seen from the equation, the system will blow up when the product G(s)H(s) approaches -1.  If you plot trajectory on the nyquist plot you can see how close it comes to the -1 point. Gain margin is how far below |1| the gain was when angle passed through 180. Phase margin is how much ahead of 180 was the phase when gain decreased through the magnitude |1| circle. Same info can be gained from Bode plot.  There's lot's more that can be said....

### RE: Nyquist Plot & stability

(OP)
Thanks pete,

Further, will u be able to qoute some websites/ URL's for reference

regards,

kashyap

### RE: Nyquist Plot & stability

My favorite search engine is dogpile.com.
It gives you back results from a large number of other search engines.

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