Quote:
Originally Posted by Alan Anderson
But for speed control instead of position control, you probably don't need to care about I.
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Quite the contrary! In order to achieve perfect tracking in steady state in speed control, it is imperative that integral control is used - when considering position control, there's no need for it, except if deadzone compensation is of interest.
This is explained by the internal model principle: the unstable modes of the reference signal must be included in the loop in order to achieve perfect tracking; a step change's Laplace transform is 1/s (an unstable pole at the origin), so we must include this pole in the loop. A position control system already has a pole at the origin (because position is speed integrated over time), so there's no need for integral control. That isn't true for a speed control system, which is why we must add integral control to cancel the unstable mode of the reference signal. If you were using a sine source as the reference things would be different, of course.
More info than you'd ever like to know (in a seminal academical paper, though):
http://www.sciencedirect.com/science...search type=a