High Performance Direct Torque Controlled Induction Motor Drive for Adjustable Speed Drive Applications

Among all control methods for induction motor drives, Direct Torque Control (DTC) seems to be particularly interesting being independent of machine rotor parameters and requiring no speed or position sensors. The DTC scheme is characterized by the absence of PI regulators, coordinate transformations, current regulators and PWM signals generators. In spite of its simplicity, DTC allows a good torque control in steady state and transient operating conditions to be obtained. This paper is aimed to analyze DTC principles, the strategies and the problems related to its implementation and the possible improvements using Space Vector Pulse Width Modulation (SVPWM). In SVPWM for each sampling period the switching instants of different space vectors are determined to reduce torque ripple. The time durations of two adjacent voltage space vectors and the corresponding zerovoltage space vectors are determined in this method depending on maximum and average switching frequency, allowable for the switching devices in the three phase inverter. Simulation studies have been carried out for different operating conditions of the drive system. The results have been presented and compared with those of the conventional method.