Speaker: Academician Radu-Emil Precup
Title: Issues in the Design and Application of Two-Degree-of-Freedom Fuzzy Controllers
Time: 14:30-15:30, May 19, 2023 (Friday)
Website: Teams Link
Abstract:
As highlighted in various classical papers on control, the extension of the controllers from one-degree-of-freedom (1-DOF) ones to two-degree-of-freedom (2-DOF) ones actually helps in the separate design and tuning with respect to the reference input (or the set-point) and the disturbance input (usually of load-type) in terms of a feedforward connection and appropriate additional block inserted in the controller (and thus control system) structure. This allows the design and tuning of control systems with good performance with respect to both the reference input and the disturbance input, namely good set-point tracking and good disturbance rejection. The transition of the results specific to linear controllers is coined back to Precup and Preitl in 1999 and 2003 leading to 2-DOF fuzzy controllers, which were initially called fuzzy controllers with non-homogenous dynamics with respect to the input channels. These controllers were further developed in the later papers published 2009 and 2012 and applied to servo systems and electrical drives. This transition allows the enhancement of the control system performance indices especially if the controllers cope with nonlinear processes.In the context of metaheuristic (optimization) algorithms, nature-inspired optimization algorithms (NIOAs), became very popular as they are much better in terms of efficiency and complexity than classical algorithms. Using the tuning parameters of the fuzzy controllers as variables in appropriately defined optimization problems, NIOAs are successfully applied to the optimal tuning of the parameters of fuzzy controllers. This is a viable approach to ensure the systematic design and tuning of fuzzy controllers and successful in the control of nonlinear processes, where the nonlinear feature of both the processes and the fuzzy controllers affect the efficient solving of the optimization problems and can lead to local solutions.An advantage of NIOAs is the performance improvement for complicated optimization problems where analytical solutions cannot be found. Three shortcomings of NIOAs are: (i) there are not yet methods to know the best parameters of NIOAs to solve problems that can be set at the beginning when using the algorithms, (ii) sensitivity with respect to the parameters of the algorithms, and (iii) large number of evaluations of the objective functions.The stable design of fuzzy controllers is another approach to ensure their systematic design. The stability conditions derived in the context of the stability analysis give useful information in the tuning of the controllers and can also be employed as inequality-type constraints in the optimization problems. This lecture presents several issues concerning the design, tuning and implementation of 2-DOF fuzzy controllers focusing on 2-DOF PI-fuzzy controllers and 2-DOF PID-fuzzy controllers in their Mamdani and Takagi-Sugeno-Kang forms. The tuning is based on mapping the parameters of the linear PI and PID controllers to the parameters of the fuzzy controllers in terms of the modal equivalence principle. The linear controllers are tuned by Preitl’s and Precup’s Extended Symmetrical Optimum method (1999). The classical algebraic approach based on Diophantine equations and mapping the parameters of the 2-DOF linear controllers to the parameters of the 2-DOF fuzzy ones will be treated as well. The lecture also treats aspects concerning the NIOA-based tuning of fuzzy controllers and their stable design, and highlights a part of the results obtained by the Process Control group of the Politehnica University of Timisoara, Romania, in representative applications of the group’s labs.
Personal Introduction:
Radu-Emil Precup is currently a Director of the Council of Doctoral Studies of the Politehnica University of Timisoara, Romania, a member of the Council of the Doctoral School Automatic Control and Computers, Politehnica University of Bucharest, Romania, a member of the Computers, information technology and systems engineering committee as part of the CNATDCU, a director of the Automatic Systems Engineering Research Centre with the Politehnica University of Timisoara, Romania, a professor with the Department of Automation and Applied (previously named Industrial) Informatics, Faculty of Automation and Computers, Politehnica University of Timisoara, Romania, a reviewer of the Swiss National Science Foundation (SNSF), Bern, Switzerland, CINECA, Bologna, Italy, the National Council of Science and Technology (CONACYT), Ciudad de Mexico, Mexico, and the Mobility and Reintegration Programme (MoRePro) of the Slovak Academy of Sciences, Bratislava, Slovakia, etc. He's current research fields include development and analysis of new control structures and algorithms including conventional control, fuzzy control, data-based control, model-free control, sliding mode control, neuro-fuzzy control; theory and applications of soft computing; systems modelling, identification and optimization (including nature-inspired algorithms); computer-aided design of control systems; applications to mechatronic systems (including automotive systems and mobile robots), embedded systems, control of power plants, servo systems, electrical driving systems, etc. So far, he has published nearly 30 monographs, published more than 380 high-quality papers, and was invited to give 19 academic speeches.
[Editor: Xiaohan Liu]