Design Of Six-phase Inverter And Research Of Harmonic Injection Method

The use of six-phase induction motor for drivers presents several advantages over the conventional three-phase drivers,such as improved relialiry,reduction on the power ratings and harmanic reduction.For these reasons,six-phase motors are widely used in high power applicatons. A typical construction of six-phase motor drives includes an induction machine with dual three-phase connection,where two three-phase groups are spatially shifted 30°,a six-leg inverter and control circuit.By controlling the phase currents of the machine,harmonic elimination and torque ripple reduction techniques can be implmentd.This paper presents a method of injecting third harmaonic,zero sequence current components to improve the machine torque density. The torque density improvement is obtained from two basic factors.First,the third harmonic zero sequence components are in quadrature in each three-phase winding group.This creates an additonal rotating field in synchrnism 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.This paper presents MMF of a six-phase motor by means of fourier analysis and winding function, and the mathmatical model of six-phase motor considering the third harmaonic.Based on it, simulation waveform are compared when in the winding is injecting the third harmonic current and when it is not. And a conclusion the third harmonic current can output can output higher torque density.Analytical,emulation and experimental results are presented to show the system operation and to demonstrate the improvement on the torque density.