A combination of open and closed-loop control for disturbance rejection

A control strategy for rejecting disturbances consisting of predictable and unpredictable components is presented. This control strategy implements a switching mechanism so that an adaptive internal model principle (IMP) controller switches between open loop and closed-loop modes. A wideband disturbance controller is active in both modes to minimize unpredictable disturbances. The adaptive IMP controller operates in closed-loop mode when it is determined that there is a predictable disturbance not being perfectly cancelled. Otherwise its input is removed and it continues to cancel the identified disturbance in an open loop manner. With this control strategy, the wideband controller can be made more aggressive in minimizing the unpredictable disturbance while maintaining the stability margins and control actions.