> -----Original Message-----
> From: Donovan Parks [SMTP:dparks@UVIC.CA]
> Sent: Monday, September 15, 2003 10:32 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      [EE]: Tuning a PID Algorithm
>
> My question: how do I tune a PID algorithm?  There were some positive
> response to this question last time I asked and some people that were
> willing to help me learn the 'art' of PID algorithms.
>
> I have been reading about PID in depth from textbooks and on the web,
> but am starting to feel more and more like tuning it is an art and not a
> science.  In addition, there is some fundamental questions I have that I
> can not find answers for.
>
Tuning PID loops for the absolute best performance is indeed something of an
art.  However, getting ballpark gains for the P,I and D sections isn't
overly difficult using a technique know as "Ziegler-Nichols".  A search on
this name should bring up many hits, but the basic technique is to set the
Integral and Derivative gains to zero, and then increase the Proportional
gain until the system is just sustaining an oscillation (lets call it k).
You than measure the period of the oscillation (call it t), which is used to
derive ballpark gains for the I and D terms.

P = k/1.7
I = t/2
D = t/8

Remember these values are a starting point, the loop response is most
unlikely to be optimised at this stage.  However, with your simulator you
should be able to tweak the values to see what effect each parameter has
which should give you a good feeling for tuning the system in the actual
AUV.

As a rule of thumb increasing the I term to get the loop to home into the
setpoint more quickly will tend to increase overshoot.  Increasing the D
term will compenstate for this to some extent.

HTH

Mike




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