Undefined function 'hinfnorm' for input arguments of type 'tf'.

I am trying to calculate the H inf norm of a transfer function. The code is

theta=0;
kp=0.2;
kd=0.7;
tau=0.1;
h=0.5;


s=tf('s');

Gamma=(exp(-theta*s)*s^2*((0.6*s)+1)+(kd*s)+kp)/((h*s+1)*(s^2*((0.1*s)+1)+(kd*s)+kp));

ninf=hinfnorm(Gamma);

I do have the control system toolbox but I do not know why am I getting this error?

Answer 1

[Paul]

Hi Kashish,

If you don't have the Robust Control Toolbox for hinfnorm(), you can probably use sigma() from the Control Systems Toolbox

Example from the Question:

theta=0;
kp=0.2;
kd=0.7;
tau=0.1;
h=0.5;
s=tf('s');
Gamma=(exp(-theta*s)*s^2*((0.6*s)+1)+(kd*s)+kp)/((h*s+1)*(s^2*((0.1*s)+1)+(kd*s)+kp));
ninf=hinfnorm(Gamma)

ninf = 1.0753

sv = sigma(Gamma);
max(sv(1,:))

ans = 1.0736

MIMO example from doc page for hinfnorm()

G = [0 tf([3 0],[1 1 10]);tf([1 1],[1 5]),tf(2,[1 6])];
ninf = hinfnorm(G)

ninf = 3.0150

sv = sigma(G);
max(sv(1,:))

ans = 2.9976

See the doc page for sigma() for more info to see if it will suit your needs.

Note that, unilke hinfnorm(),sigma() doesn't check for stability of the system.