It is well known that multi-phase machines exhibit better performance (efficiency, torque density, fault tolerance, etc.) than 3-phase machines. From the manufacturing point of view, it is interesting to have the possibility of improving a machine design by just conducting minor changes in the production process. In this regard, 6-phase machines emerge as the natural choice to improve a design without modifying the active parts. This paper presents an optimal procedure to shift from a 3-phase to a 6-phase induction motor design by just rearranging the coil connections. By starting from a 3-phase winding design, different 6-phase winding arrangements are analyzed. A methodology to define all the possible 6-phase winding arrangements is presented. Discard criteria based on balanced radial forces and impedances are defined. Afterwards, selected winding candidates are compared in terms of analytical calculations and later on, based on FE simulations for a 690 V, 1 MW induction machine design. Different possible configurations are evaluated in terms of stator Joule losses, torque ripple, power factor and electromagnetic efficiency both under healthy and faulted inverter conditions. Finally, a 6-phase machine prototype is tested in order to verify the improvement in machine characteristics, thus validating the proposed method.

This paper presents a review of the state of the art in electric propulsion for regional aircraft in the MW range. The implications surrounding the implementation of this technology, such as the need of high-power density or the use of high-voltage at high-altitude, are presented. Along with the challenges, the available technologies to face them are reviewed. Those are, as follows, the emerging new motor topologies for this purpose, the winding technologies, the materials employed for electric motors for aircraft propulsion and the ground-breaking use of high-temperature superconductors (HTS) as a high-power density enabler. Finally, a conclusion is presented gathering the main ideas of the paper.

This paper obtains analytical expressions for the calculation of the slot leakage inductance for fractional-slot concentrated-winding (FCSW) machines with one-, two-, or four-layer windings. The formulas are derived from solving the 2-D Poisson problem associated with the slot region, making them more accurate than classically used expressions that assume a leakage flux path parallel to the placement of the conductors in the slot. Explicit formulas are given in the case of one- and two-layer FSCWs with a number of phases ranging from 3 to 7. The obtained analytical expressions are validated by a finite-element analysis, showing excellent agreement between both calculation methods, even for large slot-opening-to-slot-pitch ratios. A brief comment with regard to the fault-tolerant capability of permanent-magnet FSCW machines with respect to the number of layers is also given.

This paper studies the feasibility of using synchronous reluctance machines (SynRM) for low speed–high torque applications. The challenge lies in obtaining low torque ripple values, high power factor, and, especially, high torque density values, comparable to those of permanent magnet synchronous machines (PMSMs), but without resorting to use permanent magnets. A design and calculation procedure based on multistatic finite element analysis is developed and experimentally validated via a 200 Nm, 160 rpm prototype SynRM. After that, machine designs with different rotor pole and stator slot number combinations are studied, together with different winding types: integral-slot distributed-windings (ISDW), fractional-slot distributed-windings (FSDW) and fractional-slot concentrated-windings (FSCW). Some design criteria for low-speed SynRM are drawn from the results of the study. Finally, a performance comparison between a PMSM and a SynRM is performed for the same application and the conclusions of the study are summarized.