Speed sensorless direct torque control implementation in a current source inverter fed induction motor drive

Abstract

In the paper one speed sensorless direct torque control (DTC) implementation in a current source inverter (CSI) fed induction motor drive is proposed. DTC of a CSI fed induction motor drive involves the direct control of the rotor flux linkage and the electromagnetic torque by applying the optimum current switching vectors. For sensorless control of the drive, an improved estimator is applied using stator voltages and currents. The stator current, voltage and resistance are not measured, but determined by a reconstruction from DC link measurements and the inverter switches states. This reduces the count of the sensors in the drive since the inputs for the flux estimator are reconstructed motor voltage and current obtained from the measured DC link values. An EMS offset estimator using simple technique based on the knowing states of the inverter switches compensates the offset of the pure integrator in the flux estimator. The angle of the rotor flux space vector, needed for the switching table, is determined from the referred rotor flux values and motor parameters used in the control algorithm are only the stator resistance and the transient inductance. Experiments are provided to confirm the performance of the proposed control algorithm.