Rejecting multi-stage and low-frequency resonance with disturbance observer and feedforward control for engine servo

Design and implementation of servo controller for a hydraulic servo system with a load of large inertia, low stiffness and multi-stage resonance is considered. To achieve a set of desired requirements, this paper is divided into three parts of work. First, notch filters and peak filters extracted from the general phase stabilized controller are applied in order to restrain the resonance peak of the load. Second, a disturbance observer in the feedback path is used for rejecting low-frequency disturbance and high-frequency noises. Third, as the complete inversion of the closed-loop dynamics at the whole frequency band does not necessarily give the best performance, low-pass filter, proportional derivative (PD) compensation, and lead correction are adopted in the feedforward path. The work proposed here overcomes the challenge of improving amplitude margin and phase margin while eliminating resonance simultaneously. The effectiveness of the combined control is investigated through simulation and experiment results, which show that the control strategies raised here successfully complete resonance rejection and also give ideal performances that meet the indices.