Back EMF Harmonic Analysis of Permanent Magnet Magnetic Geared Machine

Permanent magnet magnetic geared machine (PM-MGM) is widely researched as a potential core component of electrical continuously variable transmission system. Due to the dual mechanical port structure, back electromotive force (EMF) characteristics of PM-MGMs are quite different from that of conventional permanent magnet (PM) machines. In this article, back EMF harmonic features of PM-MGMs are thoroughly analyzed. The back EMF harmonic amplitude and order are analytically deduced, it can be found that both of them are variable and related with normalized speed ratio. A simulation/experiment method is proposed to separate and calculate different flux linkage components. A novel distortion factor criterion for PM-MGMs is defined to evaluate the variable back EMF distortion value. Different from existing criteria, the proposed criterion is a function of normalized speed ratio, hence it is more comprehensive for PM-MGM back EMF comparison and machine design. The torque ripple caused by back EMF harmonics is also analyzed. A PM-MGM prototype has been manufactured, and back EMF features as well as validity of the proposed distortion factor are verified by experiment.