Two-phase inverter/induction motor drive

Much interest is shown nowadays in the use of variable-speed ac motor drives in applications which previously have been the domain of the de motor supplied from a controlled rectifier or chopper. This interest is due mainly to improvements in semiconductor switching technology and the consequent increased reliability of the de-link inverter, together with the cost-effectiveness and the long-term reliability of ac machines, especially squirrel-cage induction motors. This thesis presents a recently developed form of variable-speed ac motor drive, comprising a 2-phase induction motor fed by a 2-phase inverter. A detailed mathematical model for the drive is developed and this is used to predict the dynamic and steady-state performance of a 300W experimental arrangement under various operating conditions and for both square-wave and sinusoidal PWM modes of operation. The validity and accuracy of the model are confirmed by the close agreement obtained in both shape and value between the experimental and predicted results. The harmonic content of the drive waveforms and the levels of torque and speed pulsations resulting from the inverter supply for both the square-wave and PWM modes of operation are evaluated, and the effects of load-torque and operating frequency variations on the drive performance are also considered. It is concluded in the thesis that this drive arrangement offers the advantages of relative simplicity, high reliability and little maintenance, and can provide a reasonably good performance and efficiency over a wide speed range. Consequently, it is a viable alternative for many variable-speed drive applications.