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Featured Application: The results of this work can be included in the design stage of interior permanent-magnet synchronous motors for aircraft drive applications. The torque performance of the interior permanent-magnet synchronous motor (IPMSM) must be further improved to satisfy the growing demand of aircraft drive application. To this end, this article focuses on the design optimization of the IPMSM structure in the aircraft drive systems to improve the torque density and reduce the torque ripple. A special fractional-slot winding and ∇-type magnetic-pole rotor topology are proposed as the optimized IPMSM structure compared with the structure of an existing motor. The simulations of the original and optimized structures at different current values reveal the variance of the torque in the average and ripple, mechanical and external characteristics, efficiency and steady-state temperature. The performance of an optimized prototype is analyzed by experimental testing, and the results show that an optimized motor has a higher torque density and lower torque ripple than the original one at the same speed and rated power, but it also has a higher temperature rise. However, the temperature rise value is acceptable in the experimental testing condition, so the validity of the design optimization method for the proposed structure is verified. [ABSTRACT FROM AUTHOR]

The torque performance of the interior permanent-magnet synchronous motor (IPMSM) must be further improved to satisfy the growing demand of aircraft drive application. To this end, this article focuses on the design optimization of the IPMSM structure in the aircraft drive systems to improve the torque density and reduce the torque ripple. A special fractional-slot winding and ∇-type magnetic-pole rotor topology are proposed as the optimized IPMSM structure compared with the structure of an existing motor. The simulations of the original and optimized structures at different current values reveal the variance of the torque in the average and ripple, mechanical and external characteristics, efficiency and steady-state temperature. The performance of an optimized prototype is analyzed by experimental testing, and the results show that an optimized motor has a higher torque density and lower torque ripple than the original one at the same speed and rated power, but it also has a higher temperature rise. However, the temperature rise value is acceptable in the experimental testing condition, so the validity of the design optimization method for the proposed structure is verified.

There are many space harmonics in the stator magnetomotive force (MMF) of fractional-slot concentrated winding (FSCW). These harmonics will produce high eddy current losses in the permanent magnet (PM), which will reduce motor efficiency and affect motor performance. Aiming at the above problems, the harmonic components of traditional stator MMF are first analyzed in this article, and then, a novel space-shifted unequal-turn winding structure is proposed for dual three-phase fractional-slot permanent magnet synchronous motors (PMSMs). Meanwhile, the sub- and super-harmonics in the stator MMF can be simultaneously eliminated using the proposed winding structure. To verify the effectiveness of the proposed structure, an 18-slot/8-pole motor and a 30-slot/14-pole dual three-phase fractional-slot PMSM with low space harmonic are designed by using the proposed space-shifted unequal-turn winding structure based on the analysis of nine-slot/eight-pole and 15-slot/14-pole motors. Finally, by comparing the finite element analysis (FEA) results, it is verified that the dual three-phase PMSM motor with the proposed structure has smaller eddy current losses in PM and better motor performance. [ABSTRACT FROM AUTHOR]

This paper proposes a novel 24-slot/10-pole dual three-phase (DTP) fractional-slot overlapped winding, which can simultaneously achieve the goals of low non-working space harmonics and stator modularization. Moreover, the proposed winding inherits the majority of the merits of conventional fractional-slot concentrated winding (FSCW), such as low cogging torque, low torque ripple and short end-windings. The winding configuration of the proposal is described first, and then its magnetomotive force (MMF) analysis is conducted to calculate the winding factors by using the star of slots. According to the theoretical analysis, the harmonic reduction mechanism of the proposal is expounded in depth. In addition, a specific case of a permanent magnet synchronous machine (PMSM) equipped with the proposal is analyzed and compared with two PMSMs equipped with DTP-FSCW and two-slot-pitch fractional-slot winding (TSP-FSW) respectively by finite element method (FEM) in terms of no-load back electromotive force (EMF), cogging torque, armature reaction field, on-load torque, efficiency, and fault tolerance. A prototype with the proposed winding is built and tested to verify the theoretical analysis and numerical simulations.

Recently, fractional-slot windings with two-slot coil pitch are receiving more and more attention due to their lower space harmonic contents in stator magnetomotive force (MMF) compared with the widely-used fractional-slot nonoverlapping counterparts. To further reduce the detrimental space harmonics for this type of winding, various solutions featured by varied coil turn ratios are investigated in this paper. Firstly, all the feasible slot and pole number combinations for fractional-slot windings with two-slot coil pitch are discussed. Secondly, two types of Slot Harmonic Only Windings (SHOW), i.e., SHOW I and SHOW II, are illustrated on the 18-slot/10-pole (18S10P) and 24S10P windings, through which only the main harmonic and its slot harmonics will be present in stator MMF harmonics. Then, to overcome the drawback of reduced main harmonic magnitude owing to both the decreased winding factor and poor slot area utilization associated with the SHOW, two solutions, i.e., 6-0 solution and 5-1 solution for 18S10P and four alternatives, i.e., 7-1 solution, 6-2 solution, 5-3 solution and 4-4 solution for 24S10P, are proposed based on the SHOW I or SHOW II. It is found that the 5-1 solution for 18S10P and 5-3 solution for 24S10P winding are the most desirable ones considering the tradeoff between larger main harmonic magnitude and lower harmonic contents. Furthermore, electromagnetic performance comparisons are carried out between 24S10P permanent magnet (PM) machines with 5-3 solution and 12S10 two layer and 24S10P two layer machines. Although the average torque of the 24S10P machine with 5-3 solution has a slight decrease, its torque ripple and radial magnetic force density rotor eddy-current losses are greatly suppressed compared with the two layer counterparts.

Fractional-slot slot harmonic only windings (SHOW), featured by multi-layer and varied coil turn ratios, contain only the torque-generating component and its slot harmonics in stator magnetomotive force (MMF), which makes them attractive. This paper establishes general design principles of SHOW considering different slot/pole combinations and makes detailed comparisons between SHOW and double layer (DL) windings for surface-mounted permanent magnet (SPM) machines. Firstly, fractional slot windings are classified into several categories. Similarity in distribution factors of MMF harmonics is illustrated, based on which, harmonics elimination principle of SHOW is explained. Then, general equations for calculating optimal coil turn ratios for SHOW are derived. Practical ratios approximating the optimal ones are also presented and evaluated. Furthermore, in order to show the superiorities of SHOW, 12-slot/10-pole (12s10p) and 24S10P SPM machines with SHOW are comprehensively studied and compared with their DL counterparts in terms of torque ripple, overload capability, rotor magnet loss, stator iron loss and radial electromagnetic force harmonics. Finally, 12S10P and 24S10P prototypes with SHOW are fabricated and tested for verifications. [ABSTRACT FROM AUTHOR]

If multi-phase machines equipped with tooth-concentrated winding with half a slot per pole and per phase offer interesting characteristics (simplified manufacturing, no space subharmonic, fault-tolerant ability), their low fundamental winding factors make their designs and controls challenging. The paper addresses the case of a seven-phase Surface-mounted Permanent Magnet (SPM) machine which has a fundamental winding factor lower than the third. This so-called bi-harmonic specificity is considered in order to achieve good torque quality (average value and ripples). Regarding the design, the magnet layer is segmented into two identical radially magnetized tiles that cover about three-quarters the pole arc. Regarding the control, the rated Maximum Torque Per Ampere (MTPA) supply strategy (h1h3 control) aims at generating a third harmonic current component greater than the fundamental. A prototype has been manufactured: the ability of the machine to provide smooth torque is experimentally confirmed through the implementation of a simple MTPA control which copes with high distortion in no-load voltage. [ABSTRACT FROM AUTHOR]

The need for higher efficiency motors is becoming more relevant due to recent policies adopted in most advanced economies, which are adopting new minimum energy performance standards. A great effort to optimize several parts of rotating electric machines is being done to fulfill that requirement. Recent studies focus on stator winding optimization, because of its high loss share. In this paper, a general multilayer winding configuration is proposed for winding design optimization for multiphase symmetrical machines, by combining multilayer integer-slot, fractional-slot, and fractional-slot concentrated windings. The constrained minimization of the airgap magnetomotive force harmonic distortion and winding resistance is solved by the hybridization of differential evolution with a non-dominating sorting algorithm. A framework is provided for replication purposes. An experimental application example of standard and optimized windings is included for performance assessment. The optimized winding leads to a significant motor efficiency gain, while reducing the amount of copper needed for manufacturing. [ABSTRACT FROM AUTHOR]

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The comparison of permanent magnet motors with integer and fractional number of slots per pole and phase was made. The torque developed by the motor and the torque ripples level were chosen as the major criterions. The comparison was made according to the results of equations of numerical calculation of magnetic field in active motors volumes using the finite element analysis. The recommendations on the choice of the most suitable option are given. [ABSTRACT FROM AUTHOR]

A 6-phase fractional-slot-per-pole-per-phase interior permanent magnet (IPM) machine having a novel topology of 18-slot, 8-pole and a 6-phase, 48-slot, 8-pole IPM with distributed windings, both designed for a segment-A electric vehicle, are assessed for the risk of partial irreversible demagnetization under various fault conditions. This paper describes a more accurate approach of demagnetization assessment based on 2-D transient finite-element analysis. It is shown that due to the presence of low-order space harmonics in the fractional-slot IPM machine, the demagnetization risks across all pole pairs are different. Compared with the distributed wound machine, the fraction-slot machine is less vulnerable to demagnetization due to relatively high winding inductance, although its demagnetized regions are not uniform in each pole. It is also shown that although the demagnetizing current of one 3-phase short-circuit (SC) is greater than that of 6-phase SC, the resultant demagnetization risk is lower than that of 6-phase SC in the fractional-slotmachine. [ABSTRACT FROM AUTHOR]

The interest for fractional-slot permanent-magnet (PM) synchronous machines has been more and more increasing in recent years. Particularly attractive is the interior PM (IPM) machine, since it is characterized by two torque components: the PM torque and the reluctance torque. Owing to this feature, the IPM machine is able to operate under flux-weakening conditions, as required by many applications, such as automotive, machine tools, washing machines, and so on. Another feature is that the rotor position can be detected without sensor even at zero speed, by means of techniques based on high-frequency signal injection. The aim of this paper is to investigate the torque components and the sensorless position detection capability of an IPM dual three-phase machine equipped with two fractional-slot windings. These two windings are designed to be supplied by two separate converters, yielding an increase of the fault-tolerant capability of the machine. The analysis and the tests deal with the capability of the machine when it operates under healthy as well as faulty conditions, i.e., when the supply of one three-phase winding set is switched off and only one winding continues to be supplied. [ABSTRACT FROM AUTHOR]