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Nonlinear Control Sy.. - Free

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302 CHAPTER 11. NONLINEAR OBSERVERS<br />

To see that I has an asymptotically stable equilibrium point at the origin, consider the<br />

Lyapunov function candidate:<br />

but<br />

and<br />

V iPi + iPx<br />

_ -2TQ2+22TP[f(i+2,u) - f(2,u)]<br />

pTQiII Amin(Q)II.t1I2<br />

II2xT P[f [(.i+ x, u) - f(, u)jjj J12±TPII II f p+ x, u) - f p, u) jj<br />

< 2y\,,<br />

Therefore, V is negative definite, provided that<br />

or, equivalently<br />

Amin(Q)II:i1I2 > 2yAmax(P)jjill2<br />

Example 11.4 Consider the following system:<br />

Setting<br />

we have that<br />

Solving the Lyapunov equation<br />

y<br />

)'min (Q)<br />

2A""' (P)<br />

LX2J=[12J[x2J+[<br />

y=[10][ 2<br />

A-LC=<br />

L=[°<br />

[ 0<br />

1<br />

1<br />

2<br />

0<br />

2 I<br />

P(A - LC) + (A - LC)T P = -Q<br />

0

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