Re: PID question

hondgm@xxxxxxxxx wrote:

I'm working on a linear bench power supply using a microcontroller. My
plan is to have a DAC set the output voltage, which will be regulated
by a simple op-amp circuit.
An analog input on the micro will monitor load current. I plan on
using this value to provide current limiting, via a PID algorithm
controlling the set voltage. Some general PID tuning advice in a
Microchip PDF says to first set Kp (with Ki and Kd set to 0) so the
system is as stable as possible.

With only Kp set, the voltage output just follows the error. Not too
helpful. Things got better when I added Ki. I'm not sure if I need
Kd. This seems like a somewhat difficult problem because anything can
be connected as a load.

I've searched the Internet, but nobody seems to be using PID in this
way. I'm sure it is being done, however. What is some general advice
on tuning this PID system? So much information out there seems to be
related to motors and heaters.


The task at hands is going to be similar to motors and heaters, just in different timing ranges. One of the engineers here in the NG (Tim Wescott) has written a nice article about it:

http://www.embedded.com/2000/0010/0010feat3.htm

--
Regards, Joerg

http://www.analogconsultants.com
.

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