asdf44
Advanced Member level 4
If I wanted to control the current of an unknown and potentially very large inductance how do I approach that? Or more generally, how can you control any system with unknown and potentially large inertia (like a voltage source and large C).
So to state some possibly obvious control theory facts:
1) I've got 360 degrees to work with
2) My error amplifier consumes 180 of those degrees
3) The pole created by the inductor will create a 90 degree phase shift at a frequency that's realistically lower than where I want to cross over my compensator
4) So in theory I've got 90 degrees left to work with for my controller (and 45 would ideally be left as margin)
At first I thought I'd investigate various lead compensation schemes (like Type III compensation) however:
a) These have fixed zeros which can't be well tailored to my unknown pole frequency and inevitably crossover at roughly 90 degrees minimum anyway (correct?)
b) Or in general I'd like to push the phase as high as possible at compensator crossover however for the compensator to cross over a pole must be pushing it there, and that means ~90 degree phase shift (correct?)
c) So it appears that I can't do much better than a single pole compensator which shifts from ~0->~90 (leaving razor thin phase margins)
So where does that leave me?
A) Am I misunderstanding my options?
B) Can I live with razor thin phase margins in this application?
C) Is there no generalized solution to potentially infinite inertia?
So to state some possibly obvious control theory facts:
1) I've got 360 degrees to work with
2) My error amplifier consumes 180 of those degrees
3) The pole created by the inductor will create a 90 degree phase shift at a frequency that's realistically lower than where I want to cross over my compensator
4) So in theory I've got 90 degrees left to work with for my controller (and 45 would ideally be left as margin)
At first I thought I'd investigate various lead compensation schemes (like Type III compensation) however:
a) These have fixed zeros which can't be well tailored to my unknown pole frequency and inevitably crossover at roughly 90 degrees minimum anyway (correct?)
b) Or in general I'd like to push the phase as high as possible at compensator crossover however for the compensator to cross over a pole must be pushing it there, and that means ~90 degree phase shift (correct?)
c) So it appears that I can't do much better than a single pole compensator which shifts from ~0->~90 (leaving razor thin phase margins)
So where does that leave me?
A) Am I misunderstanding my options?
B) Can I live with razor thin phase margins in this application?
C) Is there no generalized solution to potentially infinite inertia?