Design of an optimised dual fuzzy logic speed controller for high performance electric drives

The paper describes a novel method for the design of an optimised fuzzy logic speed controller. The approach is based on the analysis of the system behaviour in the error state-space. The final control structure, in a form of a dual fuzzy logic controller, is arrived at in two stages. The first stage encompasses design of a PID-like fuzzy controller, while the second stage consists of placing an additional fuzzy controller in parallel with the PID-like fuzzy controller. The resulting dual controller is characterised with high performance in the wide range of operating conditions, and with small number of parameters that can be adjusted using optimisation methods. Tuning can be performed either independently for the PID-like fuzzy controller and the additional fuzzy controller (using a simple Nelder-Mead optimisation method), or simultaneously (using genetic algorithms). Both possibilities are discussed and the results are compared. The controller is developed and tested for a plant comprising a vector controlled induction motor drive.