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Science Forum Index » Electronics - Basics Forum » power control system
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| Guest |
 Posted: Wed Feb 07, 2007 12:13 am |
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Let's say you have a closed loop power control system that is making
adjustments every second proportional to the error from a target.
Also,
the readings it gets are delayed by ten seconds. For what values of
the proportional factor is the system stable?
Any help is greatly appreciated.
Thank you. |
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| John Popelish |
| Posted: Wed Feb 07, 2007 12:46 am |
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Guest
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bob@coolgroups.com wrote:
Quote: Let's say you have a closed loop power control system that is making
adjustments every second proportional to the error from a target.
Also,
the readings it gets are delayed by ten seconds. For what values of
the proportional factor is the system stable?
Any help is greatly appreciated.
As long as the loop gain is less than 1, a sustained echo is
impossible. But the loop gain has to include the
proportional gain factor, and the output signal to ultimate
input signal factor.
For example, if 10% change on the output increase produces
an eventual 30% input signal increase, then the proportional
gain on error must be less than 1/3rd. This assumes that
the loop delay is much larger than any time constant that
rolls off high frequencies. A total loop gain of 1/2 is
often near optimum for a dead time dominated loop. This is
because each echo of a disturbance is half as large as the
previous one.
If the controlled process includes, say, a 1 minute time
constant, that filters the output step response as seen by
the process measurement, then higher proportional gain is
useful. For more details on this, you might read the
original Ziegler and Nichols paper on the subject,
reproduced here:
http://www.driedger.ca/Z-N/Z-N.html |
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| Jon Slaughter |
| Posted: Wed Feb 07, 2007 9:04 am |
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<bob@coolgroups.com> wrote in message
news:1170821605.716550.34260@m58g2000cwm.googlegroups.com...
Quote: Let's say you have a closed loop power control system that is making
adjustments every second proportional to the error from a target.
Also,
the readings it gets are delayed by ten seconds. For what values of
the proportional factor is the system stable?
It depends on the signal that your trying to control. If its a slow moving
signal then 10 seconds could be fine. If not then a lot could happen in that
10 seconds so that it actually makes it worse. Your signal might be -1 at
time t = 0 and at time t = 10 its +1. Your control see's -1 but adds a to +1
making it larger. This could happen indefinately and one would get uncontrol
oscillations unless there is some type of dampening(which eventually there
will be). The "adjustments" could always be off and just make the signal
grow without bound. If, say, you know the signal is always positive then
this can't happen. It also can't happen if the frequency your sampling at is
much larger than the bandwidth of the signal. If its periodic then it can
work much better but you still might have issues.
I'm not sure if I understand what your getting at though but maybe this is
close.
Jon |
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| jasen |
| Posted: Thu Feb 08, 2007 4:25 am |
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Guest
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On 2007-02-07, bob@coolgroups.com <bob@coolgroups.com> wrote:
Quote: Let's say you have a closed loop power control system that is making
adjustments every second proportional to the error from a target.
Also,
the readings it gets are delayed by ten seconds. For what values of
the proportional factor is the system stable?
Any help is greatly appreciated.
looks like about .15 loop gain is the limit
..04 seems optimal
no doubt there are equations to describe this system. I got my answers by
plugging your description into a spreadsheet and duplicating it down 1000
rows and then graphing the result.
Bye.
Jasen |
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| Guest |
| Posted: Thu Feb 08, 2007 9:03 pm |
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On Feb 8, 12:25 am, jasen <j...@free.net.nz> wrote:
Quote: On 2007-02-07, b...@coolgroups.com <b...@coolgroups.com> wrote:
Let's say you have a closed loop power control system that is making
adjustments every second proportional to the error from a target.
Also,
the readings it gets are delayed by ten seconds. For what values of
the proportional factor is the system stable?
Any help is greatly appreciated.
looks like about .15 loop gain is the limit
.04 seems optimal
no doubt there are equations to describe this system. I got my answers by
plugging your description into a spreadsheet and duplicating it down 1000
rows and then graphing the result.
Bye.
Jasen
Interesting. Is it possible to devise some type of transfer function
to represent this system?
Thank you. |
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