This preview shows page 1. Sign up to view the full content.
Unformatted text preview: ve
mathematical model is never accurate.
How to measure relative stability?
Use a “distance” from the critical point -1.
Gain margin (GM) & Phase margin (PM)
15 2008/09 MECH466 : Automatic Control 16 4 Gain margin (GM) Examples of GM
Im Phase crossover
Gain margin (in dB)
Gain Indicates how much
OL gain can be
violating CL stability.
2008/09 Im Re Nyquist plot of L(s)
L(s) MECH466 : Automatic Control 17 2008/09 Reason why GM is inadequate
Same gain margin,
but different relative stability MECH466 : Automatic Control Gain crossover
frequency ωg: Gain margin is often inadequate
to indicate relative stability 19 Nyquist plot of L(s)
L(s) Indicates how much
OL phase lag can be
violating CL stability. Phase margin!
MECH466 : Automatic Control 18 Phase margin (PM) Phase margin
Phase 2008/09 Re 2008/09 MECH466 : Automatic Control 20 5 An example Notes on Nyquist plot
Nyquist plot can be used for study of closed-loop
closedstability, for open loop systems which is unstable and
Controller design on Nyquist plot is difficult.
(Controller design on Bode p...
View Full Document
This document was uploaded on 03/05/2014 for the course MECH 466 at University of British Columbia.
- Fall '08