MATLAB CONTROL SYSTEM TOOLBOX 9 Guide de l'utilisateur télécharger pdf (Page 570)

100

101

rlocfind

11-180

11rlocfind

Purpose Select feedback gain from root locus plot

Syntax [k,poles] = rlocfind(sys)

[k,poles] = rlocfind(sys,p)

Description rlocfind returns the feedback gain associated with a particular set of poles on

the root locus.

rlocfind works with both continuous- and discrete-time SISO

systems.

[k,poles] = rlocfind(sys) is used for interactive gain selection from the

root locus pl ot of the SISO system

sys generated by rlocus. The function

rlocfind puts up acrosshair cursoron t h e root locus plott hat youuse to select

a particular pole location. The root locus gain associated with this point is

returned in

k and the column vector poles contains the closed-loop poles for

this gain. To use this command, the root locus o f the SISO open-loop model

sys

must be present in the current figure window.

[k,poles] = rlocfind(sys,p) takes a vector p of desired root locations and

computes a root locus gain for each of these locations (that is, a gain for which

one of the closed-loop roots is near the desired location). The

jth entry of the

vector

k gives the computed gain for the pole location p(j),andthejth column

of the matrix

poles lists the resulting closed-loop poles.

Example Determine a feedback gain such that the closed-loop poles of the system

have damping r atio ζ =0.707.

h = tf([2 5 1],[1 2 3]);

rlocus(h) % Plot the root locus

k = rlocfind(h) % Select pole with ζ=.707 graphically

Algorithm [k,poles] = rlocfind(sys,p) calculates the gain k from the following

formula.

k = abs(d(p)/n(p))

hs()

5s 1++

2s3++

-------------------------------=

1 2 ... 565 566 567 568 569 570 571 572 573 574 575 ... 648 649

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MATLAB CONTROL SYSTEM TOOLBOX 9 Guide de l'utilisateur Page 570

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