Notes on Observable and State Variable Feedback | ECSE 6400, Study notes of Electrical and Electronics Engineering

Material Type: Notes; Class: SYSTEMS ANALYSIS TECHNIQUES; Subject: Electrical & Comp. Sys. Engr.; University: Rensselaer Polytechnic Institute; Term: Fall 2004;

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16. Observers and State
Variable Feedback
Topics
Be ableto
.find the transfer function of the
combined plant-observer-controller
system and explain its significance.
show that the controller and observer
can be designed independently.
.
.determine the effect of feedback on
controllability and observability.
show that sampling may destroy
controllability.
.
Ref: Sections 7.5-7.7. Fall 2004
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16. Observers and State

Variable Feedback

Topics

Be able to

. (^) find the transfer function of the

combined plant-observer-controller
system and explain its significance.
show that the controller and observer
can be designed independently.

. determine the effect of feedback on

controllability and observability.

show that sampling may destroy controllability.

Ref: Sections 7.5-7.7. Fall^2004

A Plant with an Observer and Controller

What is the transfer function of the combined

plant -observer-controller?

Does the observer affect the stability of the overall system? u(t) (^) x(t) =Ax(t) + Bu(t)

  • y(t)^ =^ Cx(t)^ y(t)

i(t) =Ai(t) + Bu(t) + L(y(t) - y(t» y(t) = Ci(t)

. FIG. 7.5-

Find Y(s)/V(s),

system:

observer:

Use the following matrix identity,

[I + C(sl - A)-1 B]-1 = 1 - C(sl - A + BC)-1 B

Use this on the 1st term on the RHS of (4),

Use the identity again (right to left this time) on I - Bk T(s I - A + LC +Bk t) -1I

Rewriting BV(s),

BV(s) =

or BV(s) =[sl - A + LC + BkT - LC]X(s)

and soX(s) = [sl - A + BkT]-1 BV(s)

and Y(s)/V(s) = C [sl - A + BkT]-1 B

What is the transfer function when all the states are measurable?

. The transfer function does not depend on
how quickly the error i (1)goes to zero.

subtract row 1 from row 2,

= det(sI - A + BkT) det(sI - A + LC)

. (^) the modes of the overall system can be made stable.

feedback controller gains do not depend on
observer dynamics.
Conclusion: Controller and Observer can be
designed independently.

State Feedback

. multivariable systems

. with feedback, u(t)=-Kx(t) + Fv(t)

v

FIG. 7.7-

D

  • (^) F u^ B " i.. (^) J x^ c -'"+
    • p+ +

A

-K

effect on controllability (cont):

Test matrix for the closed-loop system is,

E>e= [BF (A-BK)BF (A-BK)2BF.. ... (A -BK)n-l BF]

and for the open-loop system,

ee = [B AB A2B ... An-lB]

Use column operations to show rank (e c) :

rank (ee).

Controllability After

Sampling

Sampling may destroy controllability.

Theorem: If (A,B) is completely controllable then the equivalent discrete system (F,G) is completely controllable if

Im[Aj(A)-Aj(A)]=F21tn/T;n=xl,x2... (*)

whenevertheRe[Aj(A) - Aj(A)] = o.

Example

Xl (t) I 1 1 Xl (t) I 0

    • lu(t)

X2 (t) I l - 1 1 J I X2 (t) I 1

The eigenvalues are 1xj. Evaluating (*):

Show that T == n 7r destroys complete contro liability.