Automated design of multi-mode fuzzy controllers

[摘要] ENGLISH ABSTRACT:A standard fuzzy logic controller is not robust enough to guarantee consistent closed-loopperformance for highly non-linear plants. A finely tuned closed-loop response loses relevance asthe system dynamics change with operating conditions. The self-adaptive fuzzy logic controller cantrack changes in the system parameters and modify the controller parameters accordingly. In mostcases, self-adaptive fuzzy logic controllers are complex and rely on some form of mathematicalplant model.The multi-mode fuzzy logic controller extends the working range of a standard fuzzy logiccontroller by incorporating knowledge of the non-linear system dynamics into the control rule-base.The complexity of the controller and difficulty in finding control rules have limited the applicationof multi-mode fuzzy logic controllers.An automated design algorithm is proposed for the design of a multi-mode control rule-base usingqualitative plant knowledge. The design algorithm is cost function-based. The closed-loopresponse, local to a domain of the non-linear state space, can be tuned by manipulation of the costfunction weights. Global closed-loop response tuning can be done by manipulation of the controllerinput gains. Alternatively, a self-learning or self-adaptive algorithm can be used in a modelreference adaptive control architecture to optimise the control rule-base. Control rules responsiblefor unacceptable closed-loop performance are identified and their consequences modified.The validity of the proposed design method is evaluated in five case studies. The case studiesillustrate the advantages of the multi-mode fuzzy logic controller. The results indicate that theproposed self-adaptive algorithm can be used to optimise a rule-base given a required closed-loopspecification. If the system does not conform to the model reference adaptive architecture then theintuitive nature of the cost function based design algorithm proves to be an effective method forrule-base tuning.

[发布机构] Stellenbosch University