MATLAB: How to use SISOTOOL to input systems with delays within Control System Toolbox 7.0 (R2006a)

Control System Toolboxcontrolsdesignestimationltipadesisotools

I want to know if SISO allows to study a transfer function including a delay.

When I execute the following commands:

h = tf(10,[1 3 10],'inputdelay',0.25);
sisotool(h)

I receive the following result

 ??? Error using ==> sisodata.loopdata.checkdata>LocalCheckModelData
 Cannot handle continuous-time models with delays.
 Use PADE to approximate the time delays.

Best Answer

This enhancement has been incorporated in Release 2009b (R2009b). For previous product releases, read below for any possible workarounds:

The ability to input systems with delays in SISOTOOL is not available within Control System Toolbox 7.0 (R2006a).

To workaround this issue, first approximate it using the PADE function.

h = tf(10,[1 3 10],'inputdelay',0.25);
hpade = pade(h,2); % approximate delay with second order pade

Then display this system using SISOTOOL:

sisotool(hpade);

Related Solutions

MATLAB: Is the Krall and Fornaro’s method not implemented to obtain root locus for systems with time delay in the Control Systems Toolbox 8.1 (R2008a)

Control Systems Toolbox 8.1 (R2008a) does not implement the Krall and Fornaro's algorithm for root locus of systems with time delays.

As a workaround, you can obtain a system transfer function using the Pade approximation (see help for PADE command in the Control Systems Toolbox), and then obtain the root locus.

MATLAB: How do i implement (-sexp(-0.1s) + 1 – exp(-0.1s))/(s + exp(-0.1s) -1) as a transfer function in Simulink

This is an irrational transfer function. The best way to implement it would be to create a MATLAB function with 's', the complex frequency as input argument and output the numeric value of transfer function.

Something like the following would do:

function out = Gfcn(s)
  out = (-s*exp(-0.1*s) + 1 - exp(-0.1*s))/(s + exp(-0.1*s) - 1);
end

This function can then be called repeatedly for obtaining the required system characteristics.

Else you can create a transfer function by using pade approximation for transport delays. One simple way will be the following:

    s = tf('s');
    G = (-s*exp(-0.1*s) + 1 - exp(-0.1*s))/(s + exp(-0.1*s) - 1); % This creates a state space model for your system
    Ga = pade(G,2); % Make a rational system using pade approximation for transport delay
    [den, num] = ss2tf(Ga.a, Ga.b, Ga.c, Ga.d); % Obtain numerator and denominator of pade approximated system
    Gtf = tf(num, den) %Transfer function of system with time delays approximated using pade approximation

Best Answer

Related Solutions

MATLAB: Is the Krall and Fornaro’s method not implemented to obtain root locus for systems with time delay in the Control Systems Toolbox 8.1 (R2008a)

MATLAB: How do i implement (-s*exp(-0.1s) + 1 – exp(-0.1s))/(s + exp(-0.1*s) -1) as a transfer function in Simulink

Related Question

MATLAB: How do i implement (-sexp(-0.1s) + 1 – exp(-0.1s))/(s + exp(-0.1s) -1) as a transfer function in Simulink