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Design Of Fuzzy Controllers

Design of a fuzzy controller requires more design decisions than usual, for example regarding rule base, inference engine, defuzzification, and data pre- and post processing. This tutorial paper identifies and describes the design choices related to single-loop fuzzy control, based on an international standard which is underway. | Design Of Fuzzy Controllers Jan Jantzen jj@iau.dtu.dk 1 Abstract Design of a fuzzy controller requires more design decisions than usual for example regarding rule base inference engine defuzzification and data pre- and post processing. This tutorial paper identifies and describes the design choices related to single-loop fuzzy control based on an international standard which is underway. The paper contains also a design approach which uses a PID controller as a starting point. A design engineer can view the paper as an introduction to fuzzy controller design. Contents 1 Introduction 2 2 Structure of a fuzzy controller 6 2.1 Preprocessing 6 2.2 Fuzzification 7 2.3 Rule Base 7 2.4 Inference Engine 13 2.5 Defuzzification 15 2.6 Postprocessing 16 3 Table Based Controller 17 4 Input-Output Mapping 19 5 Takagi-Sugeno Type Controller 22 6 Summary 24 A Additive Rule Base 26 1 Technical University of Denmark Department of Automation Bldg 326 DK-2800 Lyngby DENMARK. Tech. report no 98-E 864 design 19 Aug 1998. 1 1. Introduction While it is relatively easy to design a PID controller the inclusion of fuzzy rules creates many extra design problems and although many introductory textbooks explain fuzzy control there are few general guidelines for setting the parameters of a simple fuzzy controller The approach here is based on a three step design procedure that builds on PID control 1. Start with a PID controller. 2. Insert an equivalent linear fuzzy controller 3. Make it gradually nonlinear. Guidelines related to the different components of the fuzzy controller will be introduced shortly. In the next three sections three simple realisations of fuzzy controllers are described a table-based controller an input-output mapping and a Takagi-Sugeno type controller. A short section summarises the main design choices in a simple fuzzy controller by introducing a check list. The terminology is based on an international standard which is underway IEC 1996 . Fuzzy controllers are used to