how to make a PWM with a variable duty cycle, one duty cycle fixed during a time and after the second one?

Dear community,

I’ve got a problem, even if I try many things; I have to admit that I don’t know how to solve it. It’s the first I face of timing problem.

The problem:

I want to generate a pwm with a variable duty cycle, the frequency is fixed. If the condition is true (‘1’): From t=0 to t=200ms the duty cycle is 50% from t=200ms to condition is not true the duty cycle is 10%. If the condition is false (‘0’): duty cycle is 0.

Why I do this? I want to control a motor with a variable duty cycle to save energy, I just need more current at the start to move and after less current just to keep the move.

So I try something like this but I really no sure that it is the good way I developed a Simulink diagram: http://img4.hostingpics.net/pics/883426image001.png

Pwm_gen1

http://img4.hostingpics.net/pics/631225image002.png

In the FCN, I try several codes but they didn’t work, I don’t know if it’s better to use another block or way to do it… Code inside FCN

function y = fcn(u)

%#eml

if (u >= 1)

   y = 0.5;

%I want to wait here 200ms before changing the duty cycle

   y = 0.1;

else

y=0;

end

I try to put wait () instruction but it seems not compatible inside “embedded matlab function” block. I try another think, I counted the rising edge of the duty cycle (using ‘detect rise positive’ block)and when I reach a value equivalent to 200ms, I change the duty cycle but I didn’t manage it, I think I have a problem with initiate a value for a counter (first time I do it).

Does someone has some idea to help me to solve this problem? Does someone face of this kind of problem?

Thanks in advance community.

p.s I used Matlab-Simulink R2009a.

[Jordan Monthei]

You could create your own Level 2 S-function that outputs a square wave, and then based on its input changes what the duty cycle of that square wave is.

If you were willing to attempt this approach, i have already built a custom S-function block that is somewhat near to what you are trying to do and could edit it into something workable.