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Niel144
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Join Date: Jul 2013
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Control System Engineering

08/16/2013 11:09 AM

Does a system being absolute unstable mean that it is unstable for all values of 's' and relative stability mean its stability at particular values of s?can anyone show me physical significance of instability in terms of a dc servo position control system and relate that to relative stability parameters in s domain.
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lyn
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#1

Re: control system engineering

08/16/2013 12:00 PM

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Tom_Consulting
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#2
In reply to #1

Re: control system engineering

08/17/2013 8:14 AM

Lyn must be right...we know he's "absolutely unstable"!

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PWSlack
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#3

Re: Control System Engineering

08/17/2013 8:32 AM

Recommended textbook: "Process Systems Analysis and Control", by Coughanowr and Koppel, any edition.

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WoodwardDL
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#4

Re: Control System Engineering

08/17/2013 11:44 AM

All systems are sets of poles and zeros (i.e. the Laplace transform). If the damping of ANY pole becomes positive, the system will be unstable. In aerospace world, when the damping of a wing becomes positive, it starts fluttering, and if speed is not reduced the wing can break off.

I don't know about "absolute" vs. "relative" stability, but it is a fact that energy has to be applied at the frequency of a specific pole to force it into positive damping. It is possible to use a system with a nearly unstable pole if the forcing functions do not excite that specific pole.
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