Predictive flux control for induction motor drives with modified disturbance observer for improved transient response

Abstract

This paper proposes an extended model based predictive flux control (MPFC) with modified disturbance observer speed loop for induction motors. The main advantages of the proposed method are the improvement of load estimation, the suppression of current overshoot at step changes in reference speed and the removal of weighting factor in the newly formulated cost function. Weighting factor is removed by using extended reference transformation which translates reference torque, generated by the speed controller, into equivalent stator flux vector eliminating the challenging task of gain tuning at different points of operation. Then, the load torque is considered as an unknown disturbance and the accuracy of load estimation during speed jumps is improved by using a reduced order PI observer (ROPIO) with low-pass filter (LPF) for improved integration. The observer is combined with disturbance rejection based control to design a composite speed controller replacing conventional PI loop. The effectiveness of the proposed method is validated on a two-level three-phase inverter fed induction motor drive using dSpace DS1104 controller board. The dynamic response of the proposed method is compared to previously proposed disturbance observer based controller (DOBC) for predictive torque control method. The load estimation error of the proposed method at speed jumps is reduced by 66% while current surges are also suppressed effectively.