On the torque accuracy of stator flux observer based induction machine control

Due to the nonlinear nature of the induction machine model parameters, accurate torque control of induction machine drives that targets a deviation below five percent becomes a challenging task. In field oriented or direct torque control algorithms, the use of a voltage model stator flux observer may be considered as a very promising approach to achieve superior torque accuracy, because the voltage model is basically only sensitive to stator resistance deviation. In this paper, the torque accuracy of a direct field oriented control algorithm, based on a Gopinath-style stator flux observer, is analyzed. The sensitivity to parameter deviation, model accuracy and inverter related inaccuracies is separated. Measurements show, that torque accuracy is limited. Possible causes for the remaining torque deviation and the limits of the control algorithm are discussed.