Current harmonic compensation for n-phase machines with asymmetrical winding arrangement

Abstract

Multiphase machines (MPMs) have become serious contenders in several applications, such as offshore wind energy and electric vehicles. Low-order current harmonics arise in actual drives due to converter and machine nonlinearities, thus producing losses and torque ripple. In comparison to three-phase machines, in MPMs this effect is aggravated because of the existence of low-impedance subspaces. To cancel these harmonics, a multiple resonant controller (RC) (MRC) structure has recently been proposed for MPMs, which combines RCs and synchronous frames (SFs). The MRC scheme allows a significant computational saving in comparison to the multiple SF (MSF) strategy, which includes a proportional-integral controller in an SF per each harmonic. However, such MRC method is only suitable for MPMs with symmetrical winding arrangement (SWA), while asymmetrical winding arrangement (AWA) is also a common choice. In this paper, the MRC strategy is extended to MPMs with AWA. Different neutral configurations, whose effect on the harmonic mapping is more complicated than for SWAs and has hardly been studied so far, are considered. The optimum combinations of frequencies at which the RCs and the SFs should be tuned for AWAs are assessed. Simulation results are provided.