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Fuzzy-logic-based algorithms are widely employed in variable-speed drives. However, although they provide an excellent speed-control performance, they may result in significant current harmonics. These may be reduced by employing a non-linear distribution of fuzzy sets in the membership function of the output variable, albeit with some deterioration in the speed-control performance. A simple adaptive fuzzy logic control algorithm, in which the speed-error threshold may be either fixed or self-tuned, is proposed. Simulations and measurements on vector-controlled permanent-magnet brushless AC drives confirm that the proposed adaptive fuzzy logic control results in an excellent speed-control performance and robustness to parameter variations, while current harmonics are reduced. Its performance is compared with that which is achieved when conventional fuzzy logic and PI speed control are employed. [ABSTRACT FROM AUTHOR]