MATLAB: How to create discrete transfer functions in Simulink

controllerdiscretepid

Hello,

I have created a control system with PID controller in continuous domain. Now I want to discretise the whole model ( controller + plant ). I brought the controller in the discrete domain first and did multi domain simulation. I got the result, which I required. Now, I want to bring the plant in discrete domain.

My plant is a simple PT-1 element with a delay time of 10 micro seconds.

G(s) = K* e^(-sT_t)/(s+a) , where T_t is the delay time.

I want to ask how can I create this transfer function in Discrete Transfer function block? ( For simplicity it is possible to neglect delay time )

In discrete domain, after neglecting the delay time:

G(z) : k* z / (z – e^-a*T) , T is the sampling time

Thanks in advance.

Best Answer

Hi,

You want to create discrete transfer functions in Simulink for above G(z), right?

You can create it in Simulink using Discrete Transfer Fcn Simulink block.

Kindly check the attached block.

Regards,

Abdulmanan Butt

Related Solutions

MATLAB: How to include a time delay in Simulink of the type exp(-Ts)

Hi Francois,

Instead of using Continuous 'Transfer fcn' block, use the 'LTI System' block present in Control System toolbox to simulate LTI systems with delays. In the LTI system variable, specify your system description. For example, if you have a LTI system with unit gain and pole at -1, the LTI system variable will be tf([1],[1 1],'ioDelay',5). Note that you can also use state space description of your system here i.e ss(A,B,C,D,'ioDelay',5) - with A,B,C,D matrices defined appropriately.

You will require the Control System Toolbox to use 'LTI System' block.

MATLAB: Moving from z domain to w domain, transfer function

MATLAB control system toolbox have d2c function to convert transfer function from discrete (z-domain) to continuous (s-domain). However, you need to specify the sample time period in the discrete domain. Try this

ts = 0.1;
z = tf('z', 0.01);
Gz = (0.003569*z+0.003395)/(z^2-1.861*z+0.8607);
Gw = d2c(G);
Gz
Gw

Result

Gz =
 
  0.003569 z + 0.003395
  ----------------------
  z^2 - 1.861 z + 0.8607
 
Sample time: 0.01 seconds
Discrete-time transfer function.
Gw =
 
  -2.348e-07 s + 0.7499
  ---------------------
  s^2 + 1.5 s - 0.03231
 
Continuous-time transfer function.

s-domain is equivalent to w-domain when

Best Answer

Related Solutions

MATLAB: How to include a time delay in Simulink of the type exp(-Ts)

MATLAB: Moving from z domain to w domain, transfer function

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