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obscont Scilab Group Scilab Function obscont
NAME
obscont - observer based controller
CALLING SEQUENCE
[K]=obscont(P,Kc,Kf)
[J,r]=obscont(P,Kc,Kf)
PARAMETERS
P : syslin list (nominal plant) in state-space form, continuous
or discrete time
Kc : real matrix, (full state) controller gain
Kf : real matrix, filter gain
K : syslin list (controller)
J : syslin list (extended controller)
r : 1x2 row vector
DESCRIPTION
obscont returns the observer-based controller associated with a nominal
plant P with matrices [A,B,C,D] (syslin list).
The full-state control gain is Kc and the filter gain is Kf. These gains
can be computed, for example, by pole placement.
A+B*Kc and A+Kf*C are (usually) assumed stable.
K is a state-space representation of the compensator K: y->u in:
xdot = A x + B u, y=C x + D u, zdot= (A + Kf C)z -Kf y +B u, u=Kc z
K is a linear system (syslin list) with matrices given by:
K=[A+B*Kc+Kf*C+Kf*D*Kc,Kf,-Kc].
The closed loop feedback system Cl: v ->y with (negative) feedback K
(i.e. y = P u, u = v - K y, or xdot = A x + B u, y = C x + D u, zdot = (A
+ Kf C) z - Kf y + B u, u = v -F z) is given by Cl = P/.(-K)
The poles of Cl ( spec(cl('A')) ) are located at the eigenvalues of
A+B*Kc and A+Kf*C.
Invoked with two output arguments obscont returns a (square) linear
system K which parametrizes all the stabilizing feedbacks via a LFT.
Let Q an arbitrary stable linear system of dimension r(2)xr(1) i.e.
number of inputs x number of outputs in P. Then any stabilizing
controller K for P can be expressed as K=lft(J,r,Q). The controller which
corresponds to Q=0 is K=J(1:nu,1:ny) (this K is returned by
K=obscont(P,Kc,Kf)). r is size(P) i.e the vector [number of outputs,
number of inputs];
EXAMPLE
ny=2;nu=3;nx=4;P=ssrand(ny,nu,nx);[A,B,C,D]=abcd(P);
Kc=-ppol(A,B,[-1,-1,-1,-1]); //Controller gain
Kf=-ppol(A',C',[-2,-2,-2,-2]);Kf=Kf'; //Observer gain
cl=P/.(-obscont(P,Kc,Kf));spec(cl('A')) //closed loop system
[J,r]=obscont(P,Kc,Kf);
Q=ssrand(nu,ny,3);Q('A')=Q('A')-(maxi(real(spec(Q('A'))))+0.5)*eye(Q('A'))
//Q is a stable parameter
K=lft(J,r,Q);
spec(h_cl(P,K)) // closed-loop A matrix (should be stable);
SEE ALSO
ppol, lqg, lqr, lqe, h_inf, lft, syslin, feedback, observer
AUTHOR
F.D.
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