Air-gap MMF Analysis of Fifteen-phase Induction Motor With Non-sinusoidal Supply

The magneto-motive forces(MMFs) resulting from the different order harmonic currents of fifteen-phase induction motor under the non-sinusoidal supply may be of the same rotating speeds,which shows that 3-order harmonic MMF can be utilized to decrease the amplitude of the fundamental MMF and improve the performance indexes of the machine. 3-order harmonic exciting current is also obtained for minimizing the amplitude of the superposed MMF. By Fourier analysis,the non-sinusoidal current of the induction motor is resolved into fundamental component and a series of harmonic components,from which the resulted space MMFs are calculated. The fact that the harmonic MMF from the same order harmonic current rotates at the synchronous speed is discovered. Based on the mathematical expression for the superposed MMF,the amplitude of it is achieved by means of the derivation. The direct search method is performed to yield the minimum amplitude,thus also determining the effective value and phase angle of the corresponding 3-order harmonic exciting current. The reasons that the performance indexes of the machine are improved and the power density is increased are presented,which provides the theoretical foundation for optimization design of fifteen-phase induction motors.