Comparison of Three-phase and Asymmetrical Six-phase Induction Motors

Abstract

At present, the high-power demand for industrial use is continuously increasing. Three-phase motors are not sufficient to fulfil the demands due to high voltage and current requirements. Six-phase motors are widely introduced for industrial applications due to reduced voltage and current ratings for the same power level compared to the three-phase motors. Due to similar stator and rotor structures, six-phase motors are easy to construct and control. Six-phase machines can be constructed in two different ways symmetrical and asymmetrical. In symmetrical 6 phase machine two sets of 3 phase winding are shifted by 60 degrees electrical and in asymmetrical two sets of 3 phase winding are shifted 30 degrees electrical. In this project report a three-phase induction motor (7.5KW) and a six-phase induction motor (8KW) are compared. For comparison of both motors open loop v/f control with different PWM techniques (SPWM, common mode SVPWM, conventional SVPWM) and vector control are used. For both motors, their current THD and torque pulsations are compared and it is observed that six-phase induction motor gives smooth and better performance.