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Registered Member #816
Joined: Sun Jun 03 2007, 07:29PM
Location:
Posts: 156
Well kind of thought as the typical voltage mode typeIII compensation network had 3 terms it was already approaching something similar to a PID loop, though the proportional gain at dc, often seem to be set at infinite.
Apologies if I have got it wrong or misunderstood what you meant, have a lot to learn about power design myself.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Electra wrote ...
Well kind of thought as the typical voltage mode typeIII compensation network had 3 terms it was already approaching something similar to a PID loop, though the proportional gain at dc, often seem to be set at infinite.
Apologies if I have got it wrong or misunderstood what you meant, have a lot to learn about power design myself.
Electra, you did get my correct meaning. However as for Sulaiman's comments, i fail to see why PID's would cuase bad behavior... my curiosity lies with how the typical C||(R,C) circuit that lays across the out and the in op-amp on all those IC's would be modded to accept A PID sYstem.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
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Posts: 1546
The PID could handle thermal regulation quite well, and if you think about it the root of Ohms law is just heat handling. At least while we cant make superconductor SMPSs.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
A PID can control anything, it is the general case of all linear control loops.
Proportional gain at DC makes no sense. It's the integral gain that does that. As soon as you set the integral gain greater than zero, you get infinite gain at DC.
The standard SMPS compensation circuit is equivalent to a PI controller, which is of course a PID with the D set to 0. The extra little capacitor across the whole thing isn't part of the PI scheme. It's just there to slug noise at the switching frequency, it is too small to affect the loop dynamics. (if you make it big enough to affect the dynamics, its effect is destabilising)
Lately people here have been experimenting with non-linear control schemes like bang-bang and delta modulation, and claim better transient response than linear PWM. One advantage of these schemes is, it's almost impossible to screw up the compensation because instability is actually the way they work.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Steve Conner wrote ...
A PID can control anything, it is the general case of all linear control loops.
yep, precisly. a PID loop will always work (even without the "plant" devices being known), however there are more optimised solutions if the interior of the device can be defined.
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PID Loops for SMPS's.
