Need help with transfer function in VHDL

[Bustigo]

I am implementing a control system in VHDL. Now I am facing a couple of problems. For the controller itself, I used two inputs - error and change of error. Now I have to pass the controller output to a plant which has the transfer function of 1/(ks^2+s), where k is a real number.

I don't know how to implement this s-domain transfer function in VHDL. And my supervisor doesn't want me to use any kind of add-ons, I have to implement everything by myself. I thought of converting this s-domain function to z-domain, but then again, I don't know how to code z-domain TF in VHDL either.

And for the second input to the controller, how do I calculate derivative? Is it (e(t)-e(t-1))/T, where T is the sampling period?

I currently have no clue whatsoever. Any help would be greatly appreciated. Thanks in advance.

 

[shaiko]

Try to look at written code in this field

https://opencores.org/project,pid_controler

 

[TrickyDicky]

First of all, if your supervisor doesnt want you to use "add ons", then forget about real numbers. Without the floating point IP blocks you'll have to implement the complicated floating point operation blocks, which would be a chore. Think about fixed point and look up tables instead, because fixed point it just integer arithmatic.

 

[shaiko]

TrickyDicky,

Have you ever implemented a PID controller in a FPGA?