WIP, Description in progress
In this section, we treat the problem of designing a full-order state observer for system such that the effect of the disturbance to the estimate error is
prohibited to a desired level.
The system is following
where
are respectively the state vector, the measured
output vector, and the output vector of interests.
are the disturbance vector and control vector , respectively.
are the system coefficient matrices of
appropriate dimensions.
For the system, we introduce a full-order state observer in the following form:
where is the state observation vector and is the observer gain. Obviously,
the estimate of the interested output is given by
which is desired to have as little affection as possible from the disturbance .
Using system dynamics,
Denoting
.
The transfer function of the system is clearly given by
.
With the aforementioned preparation, the problems of state
observer designs can be stated as follows.
( state observers) Given system (9.22) and a positive scalar ,
find a matrix such that
.
( state observers) Given system (9.22) and a positive scalar ,
find a matrix such that
As a consequence of the requirements in the previous problems, the error system
is asymptotically stable, and hence we have
This states that is an asymptotic estimate of .
Regarding the solution to the problem of H∞ state observers design, we have the
following theorem.
The state observers problem 1 has a solution
if and only if there exist a matrix and a symmetric positive definite matrix
such that
When such a pair of matrices W and P are found, a solution to the problem is
given as
With a prescribed attenuation level, the problem of H∞ state observers design is
turned into an LMI feasibility problem in the form problem stated before. The problem with a
minimal attenuation level can be sought via the following optimization problem:
min
s.t.
The state observers problem 2 has a solution
the following 2 conclusions hold.
1.It has a solution if and only if there exists a matrix W, a symmetric matrix Q,
and a symmetric matrix X such that
,
,
.
When such a triple of matrices are obtained, a solution to the problem is
given as
.
2. It has a solution if and only if there exists a matrix V, a symmetric matrix Z,
and a symmetric matrix Y such that
,
,
trace.
When such a triple of matrices are obtained, a solution to the problem is
given as
.
In applications, we are often concerned
with the problem of finding the minimal attenuation level . This problem can be
solved via the optimization
min
s.t. ,
,
,
or
min
trace
When a minimal ρ is obtained, the minimal attenuation level is .
WIP, additional references to be added
A list of references documenting and validating the LMI.