PhD Defence by Fukiko Kawai
29.11.2018 kl. 13.00 - 16.00
“Disturbance Feedback Control for Industrial Systems: Practical Design with Robustness”
The Japanese company Fuji Electric Co., Ltd. (Fuji) first introduced and patented the concept of Disturbance Feedback Control (DFC) in 1980, for the purpose of attenuating drop impact disturbances in rolling mill processes at steel plants. Since then, DFC has been applied to dampen oscillations in electric motors with backlash, compensate for dead-time voltage errors in power electronics, as well as several other industrial applications.
A controller with DFC can be categorized as a two-degree-of-freedom controller, in the sense that one controller is designed as an ordinary reference-following controller, while the DFC itself is designed specifically to deal with unwanted disturbances, thus enhancing the performance of the overall control loop. Even though DFC as mentioned has been applied with success in various contexts, there are still some issues that remain to be resolved in a systematic way, in particular robustness guarantees, constraint handling, and anti-windup.
The aim of the present study is thus to propose practical design methods using robust control theory in order to improve the stability and performance of existing industrial controllers.
To address this aim, a design methodology is proposed, in which the plant to be controlled, a nominal model of it, and the existing controller are considered together as an extended plant. The DFC is designed for this extended plant using robust control techniques such as optimization via Linear Matrix Inequalities (LMIs).
Specifically, optimization problems are formulated to minimize the effect of disturbances while maintaining stability and performance for a range of model uncertainties.
Two very different case studies, refrigeration systems and gantry cranes, are chosen from Fuji's product portfolio for evaluating the feasibility of the design methodology.
In the first case study, a conventional controller for a commercial refrigeration system is designed, tested and then augmented with DFC. A two-step design procedure is proposed; first, a set of LMIs is solved to design a robust DFC without taking saturation into account, and then a second set of LMIs is solved to yield an anti-windup compensator to accommodate for actuator saturation.
The proposed design is compared with the conventional control system, both in simulation and through practical experiments.
The results indicate that both robustness and performance can be improved in the presence of model uncertainties, and the proposed design is able to avoid wind-up phenomena when the control inputs are saturated.
The second case study considered in the thesis concerns gantry cranes, which are widely used in factory automation, construction and shipping contexts.
For this case study, an anti-sway control scheme is proposed, in which a robust DFC is designed using the same fundamental approach as in the first case study to minimize the sway angle and trolley position errors via LMI optimization.
The robust DFC is added to an existing crane control system composed of a feedforward and state feedback control. Both simulation and lab test results show improvements in control performance when the gantry load is subjected to impulse force disturbances for a wide range of rope lengths.
Associate Professor Hans Henrik Niemann, Danmarks Tekniske Universitet, Kgs. Lyngby, Denmark
Professor Shiro Masuda, Tokyo Metropolitan University, Japan
Associate Professor Mohsen Soltani, Aalborg University, Denmark (chairman)
Associate Professor Jan Dimon Bendtsen, Aalborg University, Denmark
Associate Professor Palle Andersen, Aalborg University, Denmark
Associate Professor John-Josef Leth, Aalborg University, Denmark
After the defence there will be a reception at Fredrik Bajers Vej 7, C3-203
Free of charge
Automation and Control Section, Department of Electronic Systems
Aalborg University, Fredrik Bajers Vej 7, B3-104