| The use of six-phase induction motor for industrial drives presents several advantages over the conventional three-phase drive, such as improved reliability, reduction on the power ratings for the static converters and harmonic reduction. For these reasons, six-phase induction motors are widely used in high power applications.; A typical construction of six-phase induction motor drives includes an induction machine with dual three-phase connection, where two three-phase groups are spatially shifted thirty degrees, a six-leg inverter and control circuit. By controlling the phase currents of the machine, harmonic elimination and torque ripple reduction techniques can be implemented.; This work presents a technique of injecting third harmonic, zero sequence current components in the phase currents to improve the machine torque density. The torque density improvement is obtained from two basic factors. First, in a six-phase machine, the third harmonic zero sequence components are in quadrature in each three-phase winding group. This creates an additional rotating field in synchronism to the fundamental field. Second, as in a conventional third harmonic injection technique for PWM modulation signals, but now applied to the flux distribution of the machine, the fundamental flux component is increased.; Analytical, finite element and experimental results are presented to show the system operation and to demonstrate the improvement on the torque density. |
