0
$\begingroup$

I am learning Control Theory and i have a confusion about whether the following PID controllers are interchangeable or similar.

  1. Are they equivalent? Why?
  2. Is there any difference in how i would implement both of them in code? I have to program this in Arduino.

Here is the first control loop which is the normal definition of a PID controller:

pid1

And here is the changed one with the negative feedback changed to positive and the setpoint changed from positive to negative.

pid2

$\endgroup$
1
  • $\begingroup$ I wouldn't necessarily call this positive feedback. Most definitions of positive feedback generally assume that the setpoint and measurement/feedback are added in phase (typically both with a plus sign). $\endgroup$
    – user883521
    Jul 2 '19 at 17:02
1
$\begingroup$

No, you can't change that willy-nilly.

The second diagram is perfectly valid, however, if the plant tends to operate in reverse from normal. If you have a plant whose output gets more negative when its input goes positive then you'd use the second one.

$\endgroup$
1
  • $\begingroup$ They can of course be made equivalent if you are allowed to specify negative gains. I have not (yet) seen that implemented in practice... $\endgroup$
    – user883521
    Jul 2 '19 at 16:53

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.