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In this article, the control technique of an AC variable-speed drive is presented using a modified direct torque control method. The AC motor of the drive is an induction motor, and the modified scheme of the direct torque control uses the space vector modulation technique to create the switching pattern of the inverter. The steady state of operation is investigated in depth as well as the dynamic performance of the system. The results of this modified control scheme are compared to the corresponding results of the classical direct torque control method, leading to the conclusion that the modified scheme is more robust and smoother in comparison to the classical one. [ABSTRACT FROM AUTHOR]

Due to their robust structure, low and constant starting current, constant torque, and smooth and noiseless operation, small- and medium-sized power rating hysteresis motors are commonly employed in high-speed applications. However, hysteresis motors, in general, have a comparatively low power factor, efficiency, and torque density. In this article, a new structure, the coreless dual-rotor disc hysteresis motor, is introduced. Electromagnetic field analysis of the machine is performed, and its steady-state equivalent circuit is deduced. An algorithm employed in a computer simulation predicts the operating characteristics of the new machine. In comparison with common hysteresis machines, the superiority of the coreless dual-rotor disc hysteresis motor in regards to efficiency and power factor is revealed. Moreover, a sensitivity analysis is accomplished, and impacts of some structural parameters on the performance of the machine are illustrated. Simulation and a few experimental results for a prototype machine are given, and these validate the equivalent circuit and proposed model of the coreless dual-rotor disc hysteresis motor. [ABSTRACT FROM AUTHOR]