Quote:
Originally Posted by EricVanWyk
I'm wondering if there are any useful side effects to this method...
|
The only thing I can see that would be different is that the integral capping method would be easier to understand and maybe handle some situations a bit differently. I think it might give a slightly better response at full power.
With standard PID, I've always set the limit on I such that I is only in the range from +- u_max / K_i. I justify this as keeping the I term from trying to apply more power than is available.
With Alan's method, you can easily just limit the integrator at the output of the PD controller to be +- u_max.
From block diagram manipulation of Alan's form to the other form, it looks like the equivalent capping of the integrator in the I part of the PI controller (assuming the integrator is before the Ki gain) is to keep it within the range, [(u_max - Kd * error)/Ki, (-u_max - Kd * error)/Ki].
I got there by writing out the block diagram with the integrator directly after the sum block at the output of the PID controller (adding the terms together), writing down the conditions that cap the integrator, and then splitting the integrator and moving it before the sum block. I made sure to rewrite the conditions such that the two integrators would still have the same effective cap as the original integrator. The integrator and differentiator in the Kd part of Alan's form cancel, giving the range above.