how to add uncertainty in the plant ? and how to design controller for this ?

Hello I have done code and simulink model of LQG controller with internal model , now i want to simulate it with uncertainty ..how should i add uncertainty in the internal model or plant ?

my code is

**************% Plant *******

A = [0 1;-50 -10];

B = [0;1];

C = [20 0];

D = 0;

G = ss(A,B,C,D)

%******* Disturbance model or internal model ******

An = [0 8*pi; -8*pi 0];

Gn = [0;1];

Cn = [1000 0];

Dn = 0;

g1 = [0 1]';

z = ss(An,Gn,Cn,Dn)

%*********** Augmented system Plant + Disturbance model *********

Aaug = [A g1*Cn;zeros(2) An]

Baug = [B;zeros(2,1)];

Gaug = [zeros(2,1);Gn];

Caug = [C zeros(1,2)];

Daug = 0;

Saug = ss(Aaug,Baug,Caug,Daug)

% ****** controller gain********

QX = [1 0 0 0;0 0 0 0;0 0 0 0;0 0 0 0]

R = 10^-8

[Kc,S,E] = lqr(Aaug,Baug,QX,R)

%*****estimator gain *******

QW = 0.01;

QV = 0.01;

L= lqe(Aaug,Gaug,Caug,QW,QV)

*****************************

my simulink model

upper part is disturbance model

mid part is plant model

thank you

[Aniket]

Hello , Any one knows about this ? it will help me a lot for my project.

Thank you