Improved sensorless direct torque control method using adaptive flux observer

A simple structure and a quick and robust response of the direct torque control (DTC) makes it attractive in ac drives. However, in sensorless applications, a precise estimation of the rotor speed is a crucial issue as along with the torque and flux estimation. In this paper an adaptive flux observer is introduced with a stator current and flux vector components as state variables and rotor speed as an unknown parameter which is estimated by using an adaptive scheme. A non-linear inverter model is proposed to obtain a more accurate response. Also, torque, flux and current pulsations, during the steady-state conditions, are considered as the disadvantages of the classical DTC method. A combined DTC and space vector modulation strategy is presented by using fuzzy logic control (FLC). FLCs are designed to obtain a fast response in the transients, and a high accuracy during the steady-state conditions.