All,
I'm trying to implement a PID control scheme for a plant that has an extremely slow time constant (1.25 seconds). I'm running the simulation using Simulink's "fixed step" solver with a "fixed step size" of 1ms to mimic the 1 kHz processing speed of the digital controller.
The strange thing is that I cannot get the system to stabilize by tuning the PID gains at a step size of 1ms...however, when I slow down the controller loop time by increasing the fixed step size to 8ms, I can easiy maintain system stability with PID control. Am I doing something wrong...the faster step size should make controlling the system easier?? Any help/suggestions is appreciated.
Thanks in advance,
-weg