Low-Order Space Harmonic Modeling of Asymmetrical Six-Phase Induction Machines

Multiphase machines are commonly analyzed using vector space decomposition modeling technique, where the original phase variables are decomposed into multiple orthogonal subspaces. The machine torque production and, therefore, its dynamic response are mainly decided from the α - β fundamental subspace. In the available literature, other non-fundamental subspaces are commonly regarded as the non-flux/torque producing subspaces while mainly contributing to the extra winding joule losses. Although the primitive harmonic-free models are usually assumed for these secondary subspaces in the asymmetrical six-phase induction machines, a clear evidence to include or discard the effect of the low-order space harmonics of the air gap flux distribution under different neutral configurations has not been established so far. To this end, this paper investigates the effect of the induced air gap harmonics mapped to the x - y and zero subspaces on the dynamic modeling and, hence, the dynamic response of an asymmetrical six-phase induction machine. An improved space harmonic model is, then, proposed to better explore/simulate their effect under both healthy as well as fault conditions. The proposed model is experimentally validated using a 1.5-kW prototype induction machine.