A robust fuzzy speed estimation for vector control of an induction motor

This work addresses the analysis and the design of an adaptive fuzzy sliding-mode observer applied to vector control of an induction motor. The conception steps for the conventional sliding-mode speed observer (SMO) are laid down clearly. In this work, the drawbacks of SMO in terms of high observer gains and chattering phenomenon due of switching surface are overcome by merging of fuzzy logic with the variable structure to form a fuzzy sliding-mode speed observer (FSMO). The FSMO estimate the rotor speed and rotor flux with minimisation of the high-frequency chattering, and retains the benefits achieved in the conventional sliding observer. The FSMO uses for input and output three membership sets of symmetrical triangular shape, seven fuzzy rules, and the gravity center defuzzification method. The main features of the proposed observer are investigated and compared with those of the conventional (SMO) considering different dynamic operating conditions.The suggested scheme is ideally suited for applications requiring both low and high speed operation, and robust speed field-oriented control even in presence of some key parameter deviations. A comparison of simulation results shows clearly that FSMO is practically free from the chattering problem. Hence it is found to be a suitable replacement of the standard SMO in order to improve industrial drive performances and robustness over a wide speed range at rated load operation.