This work proposes an approach to design fractional-slot permanent magnet synchronous machines (FSPMSMs) equipped with phases made up of one coil parallel branches. These machines exhibit attractive potentialities, especially their enhanced open-circuit fault tolerance capability. Beyond their intrinsic fault tolerance, an open-circuit affecting the targeted topologies leads to a torque step-down limited to the one developed by the concerned coil rather than the torque produced by the total phase in FSPMSMs equipped with phases made up of series-connected coils. Furthermore, these topologies are suitably-adapted to low-voltage power supply that makes them viable candidates in automotive applications. This potentiality is by far vital in battery electric vehicles with the risk of electrocution in case of accident totally-eradicated thanks to the reduction of the DC bus voltage. Part 1 of the developed work is aimed at a star of slots-based identification and topological characterization of the FSPMSMs enabling the arrangement of the armature phases according to one coil parallel branches. The study distinguishes the topologies with odd and even number of phases, arranged in single-and double-layer slots. A case study is treated using a 2D finite element analysis and validated by experiments.INDEX TERMS Fractional-slot permanent magnet synchronous machines, phases arranged in one coil parallel branches, start of slots approach, odd and even number of phases, single-and double-layer slots.

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The paper is aimed at a class of fractional-slot permanent magnet-synchronous machines (FSPMSMs) equipped with phases made up of one coil parallel branches, with emphasis on their potential to reject the circulating harmonic currents. Following the identification and topological characterization of this class of machines treated in Part 1, the star of slots approach is extended to the investigation of their back-EMF harmonic content, and the possible resulting circulating harmonic currents. It is found that all identified candidates exhibit the potential to reject the circulating harmonic currents. A case study dedicated to a candidate equipped with three phases made up of six parallel branches of one coil each, is treated. Following an analysis of its back-EMF harmonic content, the torque-speed characteristic is analyticallypredicted and validated by 2D finite element analysis and by experiments. The study is achieved by a special attention paid to the iron loss and thermal analysis.INDEX TERMS Fractional-slot PM synchronous machines, one coil parallel branches made phases, start of slots approach, back-EMF harmonic content, circulating harmonic currents, torque production, power flow and thermal analysis.