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Unformatted text preview: Control 19 2008/09 MECH466 : Automatic Control 20 5 Guidelines to choose z and p How to design lag compensator The zero and the pole of a lag compensator
should be close to each other, for
other, For the desired CL pole
For The pole of a lag compensator should be close
to the origin, to have a large ratio z/p, leading to
a large ramp-error constant Kv.
However, the pole of a lag compensator too
close to the origin may be problematic:
Slow settling (due to closed-loop pole near the origin)
closed- 2008/09 MECH466 : Automatic Control 21 Root locus
With lead compensator 1.2
Imaginary Axis 22 1.4 10 0 MECH466 : Automatic Control Ro o t L o c u s Desired pole 5
Imaginary Axis 2008/09 Comparison of step responses 15 10 Lead-lag controller
Lead- With lead-lag compensator
lead- Ro o t L o c u s 15 Take a small p (by trial-and-error!)
trial- and- 0.8 0 -5 -5 0.4 -10 -10 Uncompensated 0.6 0.2 With lead compensator
With lead-lag compensator
-6 -4 -2 0 -15
-6 R e a l A x i...
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- Fall '08