Performance analysis of a speed-sensorless induction motor drive based on a constant-switching-frequency DTC scheme

A control technique, which utilizes the stator flux components as control variables, has been applied to a speed-sensorless induction motor drive. The scheme may be regarded as a development of a direct torque control scheme, aimed at achieving a constant-switching-frequency operation. At each sampling period the required voltage vector is calculated on the basis of the error between the reference and the estimated stator flux vector. The problems related to the voltage-source inverter dead time and the stator flux estimation at low speed have been analyzed, and an efficient solution has been proposed. The performance of the drive system has been verified by experimental tests, and good results have been achieved in both steady-state and transient operating conditions.