A novel fuzzy knowledge based flux observer for induction motor drives

The paper deals with the estimation of the air gap flux amplitude of an induction motor fed by a voltage source PWM inverter. The estimation is carried out by a fuzzy knowledge based (FKB) observer which infers the flux level from easily measurable quantities as the stator frequency, the stator current amplitude and the power factor as well as from the shape of the peak-to-peak value of the current ripple due to the PWM switching. Actually it has been found that the current ripple is rich in information about the saturation level of the motor iron core and therefore about the magnitude of the air gap flux. The use of a FKB observer, which is the key feature of this work, allows an effective use of such information, yielding a quite accurate flux estimation, in spite of the uncertainty in the motor parameters and of the nonlinearity due to the iron saturation