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时间:2010-05-31 02:36来源:蓝天飞行翻译 作者:admin
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LINEAR SYSTEMS, THEORY, AND DESIGN: A BRIEF REVIEW       509
Fig. 5.40    Schematic diagram of state-space representation.
(t)
In other words, given the initial conditions x(0), the state transition matrix enables
us to predict the state vector at t > O.
    Substituting for x(t) from Eq. (5.178) into state Eq. (5.176), we obtain
<P(t)x(0) - AQ(t)x(0)                        (5.179)
                                   [<i>(t) - Aq>(t)]x(0) = 0                        (5.180)
If this identity is to hold for fdl arbitrary values of x(0), we must have
                                                     <P(t) - AtP(t) : 0                                     (5.181)
This shows that the state transition matrix q>(t) is a solution to the homogeneous
state Eq. (5.176).
   Determination of state transition matrix.   Take the Laplace transformation
of Eq. (5.176),
sx(s) - x(0) : Ax(s)
(5.182)
                                          x(s) = (sl - A)-lx(0)                             (5.183)
Here, we assume that (sl - A)-] exists,i.e., (sl - A) is nonsingular. Then,
                                   x(t) = L-l[(sl - A)-llx(0)                       (5.184)
for t > O. Comparing Eqs. (5.184) and (5.178), we get
                                      q>(t) = L-l[(sl - A)-l]                          (5.185)
Let
                                       x(t) = eArx(0)                             (5.186)
The matrix exponentialis given by
                [ntn
                       eA' =I+At+ A2   +...+ A~+--              (5.187)
rr
j
 L
 s
 t
;t
 ain
 a2n
 a3n
            N
            .
 ann
510          PERFORMANCE, STABILITY, DYNAMICS, AND CONTROL
where I is the identity matrix. We note that Eq. (5.186) satisfies the homogeneous
state Eq. (5.176). Hence,
                  A2t2       A t
(p(t) = eAr = I+At +   2~ + " '+ r7r +- "            (5.188)
Using this, the solution of the complete nonhomogeneous state Eq. (5.171) can be
expressed as1.3
 
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