I would like to generate variable duty cycle PWM signal in Simulink based on the value of manipulated value of PID block. The sampling time and relevant parameters of PWM block must be user defined. Is there any specific block which I can use? Or is there any other way in command line. Thank you.
Regards,
Ankur Gajjar
You can use Matlab function block. Check the picture and code:
function y = fcn(signal, klok, period)
%#codegen
minValue=0.0;
maxValue=100.0;
duty=(signal-minValue)/(maxValue-minValue);
intvalue=floor(klok/period);
cduty=klok/period-intvalue;
if cduty
You can use Matlab function block. Check the picture and code:
function y = fcn(signal, klok, period)
%#codegen
minValue=0.0;
maxValue=100.0;
duty=(signal-minValue)/(maxValue-minValue);
intvalue=floor(klok/period);
cduty=klok/period-intvalue;
if cduty
Dear Dajic,
Thank you for your reply. I would like to ask that since I want to convert the input signal having the range of 0 to 100 into PWM signal, in my case max Amplitutude will be 100? And can provide some more details regarding clock and constant you have used in the picture? An explanation of the code would also be great. Awaiting your response.
Regards,
Ankur Gajjar
OK. I edited the code slightly, so now you can set both: minValue and maxValue. The constant is PWM period in seconds (in this case it's 2). The clock is a block which gives current simulation time in seconds. In 'Simulation parameters' set a 'fixed step' as simulation time: for example 0.001 (though it will work with default option 'variable step' too, but we want to guarantee fixed simulaton step). We use that simulation time and period to calculate current position in the current PWM period (cduty, can be from 0 to 1). We use signal, minValue and maxValue to calculate required duty cycle (duty, can be from 0 to 1). Than we compare cduty with duty and create output as 1 or 0.
Alternatively you can create a sub-block that consists of the following.
Input: duty
Output: pwm
Create a saw-tooth waveform using a "Repeating Sequence" block. Set the period to 1/fs, where fs is your frequency. And set the output value to go from your minimum to maximum duty cycle, e.g. 0-100.
Then use a logic block to compare the input, "duty" to the saw-tooth waveform created by the "Repeating Sequence" block, i.e. test if "duty>sawtooth" The output from this logic block is your "pwm" output.
If you want you can make a mask for your sub-block that lets the user specify fs.
This image should explain how this setup creates a PWM signal. http://en.wikipedia.org/wiki/File:Pwm.svg
In principle this is exactly the same as what Dajic's code is doing.
- Badges
- Science topic