A new rotor time constant adaptation method for a VSI fed indirect field oriented induction motor drive

Field oriented control of an induction motor requires the rotor time constant as an essential parameter to calculate both the magnitude and phase of the rotor flux vector. Therefore it becomes necessary to adapt the rotor time constant. A simple method based on current measurements alone is proposed. Since this method uses current measurements, which are smoother, compared to the voltage waveforms in a VSI-fed drive, the implementation is easy and noise free. The method also works during transients. The stator direct and quadrature current components are predicted, assuming a perfect value of rotor time constant in the control side. This is compared with the measured currents. A mismatch in this comparison, is an indication of an error in phase of the rotor flux. This information is used to correct the control side rotor time constant