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This article investigates the effect of airgap length on the electromagnetic performance of direct-drive surface mounted permanent magnet Vernier (SPM-V) machines with different power ratings. Using 3 kW machine as an example, its performance is comprehensively compared with a conventional SPM machine with the same airgap lengths using two-dimensional finite-element analysis. For each airgap length, the slot/pole number combination for the SPM-V machine is investigated to achieve the optimal performance compared to the conventional SPM machine. In order to make the study more generic, the slot/pole number and the airgap length variations are expressed as normalized pole pitch, i.e., $\overline {{{\boldsymbol{\tau }}_{\boldsymbol{r}}}} $ (ratio of rotor pole pitch to electromagnetic airgap length). The results show that for 3 kW machines, $\overline {{{\boldsymbol{\tau }}_{\boldsymbol{r}}}} $ >2.2 is a good design criterion for the SPM-V machines to achieve higher average torque and efficiency than the conventional SPM machines. In addition, a reasonably good power factor (>0.9 in this case) can be achieved. Although the power factor of SPM-V machines drops significantly at multi-MW power level, i.e., 3 and 10 MW, the criterion $\overline {{{\boldsymbol{\tau }}_{\boldsymbol{r}}}} $ >2.2 still results in achieving a performance closest to their optimal capability. However, when $\overline {{{\boldsymbol{\tau }}_{\boldsymbol{r}}}} $ >2.2, special consideration should be paid to avoid potential irreversible magnet demagnetization at multi-MW power levels. [ABSTRACT FROM AUTHOR]

This paper combines the use of multi-phase configurations and current harmonic injection methods to achieve significantly improved performance for doubly salient synchronous reluctance machines (DS-SRMs). In order to understand the torque production mechanism of multi-phase DS-SRMs with current harmonic injection, some general analytical torque models have been developed. The models are based on Fourier Series analysis of self- and mutual-inductances. It has been established that with current harmonic injection, the torque ripple of both 5-phase and 6-phase DS-SRMs can be significantly reduced and the average torque can be enhanced. It contrast, harmonic injection always has a detrimental impact on 4-phase machines. The investigations of losses and dynamic performance with current harmonic injection for multi-phase machine have also been carried out and demonstrated that the proposed method can improve the efficiency in constant torque region and maintain comparable performance to fundamental current supply in the flux weakening region. Experimental validation based on single layer, 6-phase, DS-SRM has been performed. [ABSTRACT FROM AUTHOR]

This article investigates some novel modular consequent pole PM machines (CPMs) with E-core and C-core stators. Different slot-pole number combinations including 12-slot/10-pole (Ns>2p) and 12-slot/14-pole (Ns<2p) have been investigated. Their static and dynamic electromagnetic performances have been investigated, e.g. the phase back-EMF, on-load torque, torque-speed curves, power factor-speed curves and also efficiency maps are compared. It is found that the existence of flux gaps (FGs) can improve the average torque of the 12-slot/14-pole E-core modular CPMs while the C-core structure can be a better candidate where relatively low torque ripple is desirable. Moreover, by selecting proper FG width, the 12-slot/14-pole E-core modular CPMs can achieve better flux-weakening capability and higher efficiency while the 12-slot/10-pole C-core modular CPMs can have higher power factors over the whole speed range. The finite element simulation results have been validated by a series of experiments using 12-slot/14-pole modular CPMs with both C-core and E-core stators. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of concentrated winding configurations and stator core structures on torque performance of fractional-slot surface-mounted permanent magnet (SPM) machines. From analyzing the separated torque components of prototype SPM machines with 12-slot/10-pole (12S/10P) combination by frozen permeability (FP) method, it can be found that the torque ripple is closely related with local saturation in fully closed slot (FCS) machines. Besides, the heavier local saturation will also jeopardize the merit of using alternate teeth wound windings, such as obtaining higher average torque than electrical machines with all teeth wound windings. The further analysis of stator tooth relative permeability variation over one electrical period demonstrates that the major reason for torque ripple difference among these electrical machines with different stator topologies is the asymmetric saturation between the adjacent teeth. Both the subharmonic due to armature reaction (determined by winding connection and current value) and the asymmetry of stator core structure contribute to such asymmetric saturation. In order to more clearly verify this, the complementary slot/pole number combination (12S/14P) is also analyzed. The conclusion is effective for electrical machines with other slot/pole number combinations as well. Experiments have been carried out to validate the predictions. [ABSTRACT FROM PUBLISHER]

This paper investigates the influence of pole number and stator outer diameter on the performance of superconducting (SC) generators. The SC generator has an iron-cored rotor topology. First, the generator structure is introduced and the optimization procedure is described. Then, the influence of design parameters on performance, in terms of generator volume, weight, SC wire utilization, active material cost, etc., is presented. Some relationships for the optimal combinations for different performance attributes are established. In addition, the influence of SC material price on the determination of optimal stator outer diameter and pole number is discussed. Finally, the influence of SC coil area per pole on performance is also investigated. [ABSTRACT FROM PUBLISHER]

This paper presents single-layer modular permanent-magnet machines with either wound or unwound teeth with tooth tips. The structures with wound teeth having tooth tips are suitable for modular machines with slot number higher than pole number to compensate for the drop in winding factor due to the flux gaps in alternate stator teeth, accordingly to maintain or even to increase their average torques. However, the structures with unwound teeth having tooth tips are suitable for modular machines with slot number lower than pole number to increase the winding factor and hence to further improve the machine performance. The phase back-EMF, on-load torque, iron and copper losses, as well as efficiency have been calculated using FE analysis for different slot/pole number combinations, and for different flux gap and tooth tip widths. It is found that by properly choosing the flux gap and tooth tip widths, both the on-load torque performance and the efficiency can be optimized for the investigated machines with different slot/pole number combinations. Experiments have been carried out to validate the FE results. [ABSTRACT FROM PUBLISHER]

This paper presents four types of three-phase permanent magnet (PM) machines, that is, modular and unequal teeth (UNET) machines either with or without tooth tips. Two-dimensional finite element (FE) modeling has been carried out to analyze the influences of flux gaps (in alternate stator teeth) and UNET widths. These influences are mainly on winding factors, air-gap flux density due to PMs, flux linkage, back-electromotive force, and electromagnetic torques. For UNET machines without tooth tips, it has been found that the UNET widths affect both winding factor and air-gap flux density due to PMs. However, for UNET machines with tooth tips, the UNET widths have no effect on machines’ electromagnetic performance. Nevertheless, for modular machines, the flux gaps influence three parameters: winding factor, air-gap flux density due to PMs, and flux focusing/defocusing. Meanwhile, for different slot/pole number combinations, the influences of flux gap and UNET widths are different. Several general rules concerning these influences have been established. These general rules can be extended to other single or dual three-phase modular or UNET machines with different slot/pole number combinations. Prototypes of modular machines have been built, and the predictions and conclusions have been validated. [ABSTRACT FROM PUBLISHER]