Partially-Coupled d–q–0 Components of Magnetically-Isolated FSCW IPM Machines With Open-End-Winding Drives

Fractional-slot concentrated winding interior permanent magnet (FSCW-IPM) machines have been designed with very low winding mutual inductance for magnetic isolation features required for improving their fault-tolerant capabilities. These magnetically-isolated FSCW-IPM machines no longer adhere to the preconditions required for a conventional abc-to-dq0 transformation. As a result, it is found in this article that d-, q-axes could couple with 0-axis in magnetically-isolated FSCW-IPM machines. Considering the second-order reluctance component, this phenomenon leads to third-harmonic injection in phase voltages during normal operation, which can be cancelled out in terms of line-to-line voltage for Y-connected three-phase system. However, for open-end-winding machine drives without winding neutral point constraint, these voltage harmonics will show up in the winding voltage waveforms. Study shows that the amplitudes of these extra harmonics are determined by both saliency ratio and zero-axis current. The bandwidth of the proportional integral (PI) current regulator as well as switching frequency should be carefully determined to be able to take into account the major harmonics injected in phase voltages. Experimental verification on a 12-slot/10-pole prototype machine with spoke PMs has been carried out to show the impact of this phenomenon.