A new state observer for sensorless DTC control

High-efficiency sensorless direct torque control (DTC) of an induction motor is proposed. A new robust state observer is elaborated which gives a correct flux estimation even in the low frequency range. For this purpose the stator and rotor resistances are estimated on-line. A dynamic optimisation of the hysteresis bandwidths allows a full utilisation of the inverter and it minimises the harmonic distortion of currents. Finally sensorless speed estimation techniques are proposed, which can work in the entire speed region, including the low speed region. Simulation results are given to validate the new scheme.