Direct Torque Control for induction machines: A technology status review

Among all control methods for induction motor drives, Direct Torque Control (DTC) is considered particularly interesting being independent of machine rotor parameters and requiring no speed or position sensors. The basic DTC scheme is characterized by the absence of 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. However, the presence of hysteresis controllers for flux and torque lead to torque and current ripple and variable switching frequency operation for the voltage source inverter. This paper is aimed to briefly recall DTC principles and their intrinsic problems, and to discuss possible control strategies to improve the operating characteristics. Due to its basic principle, DTC technique is well suited for exploiting the improved number of voltage vectors available with multilevel and multiphase converters. A discussion is also carried out in order to emphasize the potentiality of induction motor drives based on these new power converter topologies.