Torque ripple minimization in vector-controlled induction machines

The dynamic response of an induction motor is immensely improved through the use of vector control. However, this controller can inherently and indirectly have an effect on the induction motor's tendency of producing torque ripple. This undesirable tendency can restrict the use of vector controlled induction machines from precision applications such as in robotics and machine tools. A detailed experimental based study on torque ripple production and reduction of induction machines under vector control is presented. A spectral torque ripple model is proposed based on the contribution of dc bias currents and torque harmonics of the actual field frequency. A parameter identification scheme is proposed. The scheme cross correlates digitally generated sine and cosine field functions with the torque ripple in order to determine the unknown parameters of the modeled torque ripple. Once the parameters are determined, the compensator generates a feedforward ripple cancellation term and performs bias current nullification.