Re: PID question


John Popelish wrote:
hondgm@xxxxxxxxx wrote:
John Popelish wrote:
hondgm@xxxxxxxxx wrote:


digitally regulating voltage.

Understood. In PID controller terminology, the DAC produces
a setpoint for the voltage regulator. The regulator acts as
a follower to copy the reference as the voltage output
(possibly with a scaling factor).

I'll be able to set the voltage via a
user interface (as well as current), but the PID controller will have
the capability of forcing the voltage lower to meet a current setpoint.

a lot like preventing integral wind up in the master control
of a cascade control strategy (the voltage control, in this
case) when it loses control of the slave (the current
controller). In effect, you need some way to limit the
error at the input of the error amplifier, once the output
ceases to have an effect (the moment the current limit
process takes over), so that voltage control resumes
smoothly and quickly, once the current falls below the limit
value. Limiting the integral windup causes the voltage
controller output to match the current limit setpoint at the
moment that the current falls below the current limit value.

Yes, integrator windup, I just read about that after I wrote the email.
That part I now understand. But I'm unclear about a couple things in
the topology. Here's a drawing of how I understand it:
http://www.yourfilehost.com/media.php?cat=image&file=Drawing1.jpg

I wasn't sure about where the feedback goes. One problem, if the
feedback path is correct as I have it, is that my current range is
0-2500 and the current range is 0-4000. Maybe it just has to be scaled.

.

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