PID controller on Nexys3

[shrestha]

does anybody know how to code PID controller? help will be appreciated?

 

[cristian.ignat]

Hello,

 

If you want a controller for a motor then you can use a PI controller (derivative component is not very important in this case). You can start using a very simple PI controller. 

 

The PI controller is running in a loop like on the following C code (see also the link https://batchloaf.wordpress.com/2013/06/11/simple-pi-control-using-the-dspic30f4011/):

 

double setpoint, measured_value, error, output;

double previous_error = 0, integral = 0;

const double dt = 0.00005, Kp = 0.001, Ki = 0.001;

 

While(1)

{

        if(Time_interrupt == 1)

        { 

             Time_interrupt = 0;

             setpoint = read_set_point();

             measured_value = read_measured_value();

             error = setpoint - measured_value;

             integral = integral + error*dt;

             output = Kp*error + Ki*integral;

             previous_error = error;

        }

}

 

You can modify the constants and also the timer. Time_interrupt becomes 1 on each 0.00005 seconds and this is the reason that dt constant is 0.00005 - in seconds. 

 

Regards,

Cristian

[zygot]

This can be quite a complex topic, but I'm assuming that you want something useful but not too didactic. I suggest that you check out the excellent material provided here: http://brettbeauregard.com. You will find an answer that is both practical and easy to understand.

[JColvin]

Here's a slightly more direct link to the material zygot is referring to: http://brettbeauregard.com/blog/2011/04/improving-the-beginners-pid-introduction/

 

I'll echo zygot in the fact that the material is a great place to start for PID control.

[shrestha]

thats link does not work anymore. Do you have other reference?

[JColvin]

The link was gone like you said when I started writing this reply, but it appears to be back up now... hopefully it stays there.

 

But PID control can quickly become a very involved topic, especially if you're not super familiar with some of the math and theory involved behind it, and unfortunately there doesn't seem to be a lot of material out there that explains PID from the ground up. This project goes beyond the scope of what Digilent does as a company, and it's been awhile since I took a process control class, so I will be of limited help. 

 

However, I would recommend checking out these three links that get progressively more in depth on PID here, here, and here. There is also an (apparently) semi-famous article on PID for people with PhD's here that does a decent job on explaining the purpose of the three main parts of PID (proportional, integral, and derivative).

 

Thanks,

JColvin

[shrestha]

thanks Jcolvin, cristain.. I will give a shot.