3. (30 points) Consider the single-input single-output nonlinear control system:
i = x - r^2
y = x + u
Prove that:
(a) E is globally asymptotically stabilizable by a smooth state feedback controller:
(x1,2) = x + x^2 + x1
Determine the parameters α, β, and γ. Hint: try the Lyapunov function V(r1,r) = (r1^2 + r2^2).
(b) There does not exist any linear output feedback control law:
u = ky + kE + ϵ
which renders the equilibrium (x1, x2) = (0, 0) locally asymptotically stable.
(c) Although E is not stabilizable by static output feedback, it can be locally stabilized by the dynamic output compensator:
u = y^5 - φ = n
at x1,2 = 0,0,0
Hint: for (b)-(c), try the center manifold theory.