A new closed-loop voltage model flux observer for sensorless DTC method

Direct torque control (DTC) is a well-known method for ac induction motor (IM) drive systems. This approach is based on estimating stator flux and torque. So, accurate flux estimation is one of the fundamental key components of DTC drives. In this paper, an improved stator flux estimation technique based on the voltage model with stator flux and stator current errors as feedbacks is introduced. The goal of the novel observer is compensating the conventional voltage model based flux observer shortcomings such as, integration drift and integrator saturation problems. In proposed reduced-order flux observer, stator flux and current errors are applied to the integrator through static gains in order to shift poles of the observer transfer function to the left in the complex plane. So, the stability of the flux observer and consequently the DTC operation is improved. The robustness and dynamic performance of the novel observer are evaluated by means of simulations under critical loads.