Can't get the PID controller to work

[Doven]

I'm having problems getting the PID controller in Multisim to work.  Attached is a simple Buck converter with a PID controller wired into a PWM that drives the MOSFET.

If I were doing this in MatLab Simulink, I would set up a Constant as the reference and use a voltage sensor for the output voltage and feed those into the PID.  However, I don't see a clear way to do that in Multisim.  So instead, I tried using an actual DC source as the reference, but that doesn't seem to work.

In the attached schematic, the PID output (net 2) stays at 0 V.  Unfortunately, the Help documentation is useless, as it doesn't even show a sample circuit for the PID controller, so I don't know what Multisim expects for the setup.


Can someone tell me what I'm doing wrong here?

[RichieTheBard]

The way you have it wired seems to be correct, since it should just be the error obtained from the feedback signal, and the desired value. Without actually being able to look into the circuit and how it is configured, my first thought would be to check what is the voltage in the other portion of the circuit, and make sure that they are behaving as expected.

If you can share this example circuit you posted, we might be able to take a better look at it, and see what may be happening here.

Cheers,

[Doven]

Sure, thank you.  The file is attached.

[RichieTheBard]

First thing that I noted is the parameters of the PID in your circuit, I don't know what you want them  to be exactly, but I can't imagine they are correct with the current values, specially the maximum and minimum voltage outputs they allow, since it is completely unable to output any negative voltage the way it is configured. I don't know what you would need to change those values to, but that would be my first guess in this case.