Disturbance rejection control for non-minimum phase systems with optimal disturbance observer

Area of Science:

• Control Systems Engineering
• Systems Theory

Background:

• Non-minimum phase (NMP) systems with time delays present significant control challenges.
• Disturbance rejection is crucial for maintaining system performance in the presence of uncertainties.

Purpose of the Study:

• To develop a robust disturbance observer (DOB) based control strategy for stable NMP systems with time delays.
• To propose a novel DOB configuration strategy that synthesizes multiple critical design requirements.

Main Methods:

• A robust DOB is employed to compensate for plant uncertainties, transforming the uncertain plant into a nominal one.
• A prefilter is designed for desired performance based on the compensated nominal plant.
• A novel DOB configuration strategy is developed by formulating an optimization function that integrates internal/robust stability, relative order, and mixed sensitivity.

Main Results:

• The proposed DOB-based control structure effectively compensates for uncertain plants, including those with unstable zeros and time delays.
• The novel DOB configuration strategy successfully synthesizes stability, performance, and robustness requirements.
• Optimal solutions are obtained using standard H∞ theory, guaranteeing the specified design requirements.

Conclusions:

• The developed robust DOB-based control strategy offers an effective solution for disturbance rejection in stable NMP systems with time delays.
• The proposed DOB configuration methodology provides a systematic approach to designing controllers that meet complex performance and stability criteria.