Handout 3: Gain and Phase Margins for unstable
systems
Eric Feron
Feb 9, 2004
Gain and Phase Margins exist for all systems, including the
1
unstable ones Example1: H(s) =
1 ? s/1
Sketch the Bode plot (Gain and Phase) to the left of next page. Sketch
root-locus to the right of the page, above the Nyquist plot.
Phase margin for K = ?1.3 is
1
2
s
2
+ 0.2s + 3
H(s) =
3(s ? 0.1)(s
2
+ 0.2s + 1)
Figure 1: 1 cm of space
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