Powder alignment system for anisotropic bonded NdFeB Halbach cylinders

A Halbach cylinder, fabricated from pre-magnetized sintered NdFeB magnet segments, is proposed for the powder aligning system during the compression or injection moulding of anisotropic bonded Halbach oriented NdFeB ring magnets. The influence of leading design parameters of the powder aligning system, viz. the number of magnet segments per pole, their axial length and radial thickness, and their clearance from the mould, is investigated by finite element analysis, and validated experimentall

Analysis of anisotropic bonded NdFeB Halbach cylinders accounting for partial powder alignment

An analytical technique is developed for predicting the performance of a bonded Halbach oriented anisotropic magnet, with due account of partial alignment of the NdFeB powder during injection molding. The predicted performance of a 12-pole injection molded, Halbach oriented magnet is compared with measuremen

Novel modular switched reluctance machines for performance improvement

Compared to non-modular machines, modular topologies become increasingly attractive due to their simplified manufacture process, better fault tolerant capability and potentially reduced material consumption. In order to maintain or even enhance the machine performance while achieving high fault tolerant capability, novel modular, single layer winding switched reluctance machines (SRMs) with different pole numbers are proposed, which are supplied by rectangular wave current with different conduction angles. The influences of the pole number and flux gap width between E-core segmented stators on the electromagnetic performance have been investigated in terms of self- and mutual inductances, electromagnetic torque, copper loss, iron loss, and radial force. It has been found that the modular structures with higher rotor pole numbers than stator slot numbers (12-slot/14-pole and 12-slot/16-pole SRMs) can maintain and even improve the average torque due to the nature of self- and mutual inductances. In addition, the torque ripple for modular machines are significantly reduced (below 50%), so do the iron loss and radial force, leading to higher efficiency albeit with potentially lower vibration and acoustic noise. Two prototypes with 12-slot/8-pole and 12-slot/14-pole combinations have been built with both non-modular and modular structures to validate the predictions in terms of inductances and static torques

Investigation on contribution of inductance harmonics to torque production in multiphase doubly salient synchronous reluctance machines

This paper investigates the contribution of each order inductance harmonic to the torque (both average torque and torque ripple) of multiphase doubly salient synchronous reluctance machines (DS-SRMs). Such machines are similar to switched reluctance machines but supplied with sinewave currents. The investigations in this paper are as follows: first, a general analytical torque model based on Fourier Series analysis of inductances has been built for machines with different phase numbers, slot/pole number combinations and also winding configurations. The instantaneous torque for DS-SRMs with any given phase number can then be accurately predicted. Using such model, contribution of each order inductance harmonic to torque can be investigated separately. It is found that the torque ripple frequency of the DS-SRM only depends on phase number. For example, for a m-phase machine, there will be m×kth order torque ripple if mod(mk,2)=0, where m is phase number and k is a natural number. This study also explains why certain phase numbers inherently produce lower torque ripple than others. The findings in this paper provide a future direction for potential torque ripple reduction methods either from machine design or advanced control. The simulations have been validated by experiments using a 6-phase DS-SRMs

Influence of Conduction Angles on Single Layer Switched Reluctance Machines

This paper investigates the influence of conduction angles on the performances of two 3-phase 12-slot/8-pole short pitched switched reluctance machines (SRMs): single layer SRM with conventional winding (SL-CSRM), and single layer SRM with mutually coupled winding (SL-MCSRM). Both unipolar and bipolar excitations are employed for the SRMs with different conduction angles such as unipolar 120° elec., unipolar 180° elec., bipolar 180° elec., bipolar 240° elec., and bipolar 360° elec. Their flux distributions, self- and mutual-flux linkages and inductances are analyzed, and followed by a performance comparison in terms of on-load torque, average torque, torque ripple, using two-dimensional finite element method (2D FEM). Copper loss, iron loss and machine efficiency have also been investigated with different phase currents and rotor speeds. The predicted results show that the conduction angle of unipolar 120° elec. is the best excitation approach for SL-CSRM at low current and also modest speed, as its double layer counterpart. However, at high current, the higher average torque is achieved by a conduction angle of unipolar 180° elec. For SL-MCSRM, bipolar 180° elec. conduction is the most appropriate excitation method to generate a higher average torque but lower torque ripple than others. The lower iron loss is achieved by unipolar excitation, and the SLCSRM with unipolar 120° elec. conduction produces the highest efficiency than others at 〖10A〗_rms. In addition, the performances of single layer machines have been compared with the established double layer SRMs with conventional and mutually-coupled windings. The prototype SRMs, for both SL-CSRM and SL-MCSRM, have been built and tested to validate the predictions

Performance comparison of doubly salient reluctance machine topologies supplied by sinewave currents

This paper comprehensively investigates the electromagnetic performance of 3-phase, 12-slot, and 8-pole switched reluctance machines (SRMs) with different winding configurations, i.e. double/single layer, short pitched (concentrated) and fully pitched (distributed). These SRMs are supplied by sinewave currents so that a conventional 3-phase converter can be employed, leading to behavior which is akin to that of synchronous reluctance type machines. Comparisons in terms of static and dynamic performances such as d- and q-axis inductances, on-load torque, torque-speed curve, efficiency map, etc. have been carried out using two-dimensional finite element method (2-D FEM). It is demonstrated for the given size of machine considered, that for same copper loss and without heavy magnetic saturation, both single and double layer mutually coupled SRMs can produce higher on-load torque compared to conventional SRMs. Additionally, double layer mutually coupled SRM achieved the highest efficiency compared to other counterparts. When it comes to single layer SRMs, they are more suitable for middle speed applications and capable of producing higher average torque while lower torque ripple than their double layer counterparts at low phase current. Two prototype SRMs, both single layer and double layer, are built to validate the predictions

Investigation on synchronous reluctance machines with different rotor topologies and winding configurations

This paper investigates the influence of rotor topologies and winding configurations on the electromagnetic performance of 3-phase synchronous reluctance machines with different slot/pole number combinations, e.g. 12-slot/4-pole and 12-slot/8-pole. Transversally laminated synchronous reluctance rotors with both round flux barrier and angled flux barrier have been considered, as well as the doubly-salient rotor as that used in switched reluctance machines. Both concentrated and distributed winding configurations are accounted for, i.e., single layer and double layer conventional and mutually coupled windings, as well as fully-pitched winding. The machine performance in terms of d- and q-axis inductances, on-load torque, copper loss, and iron loss have been investigated using 2-D finite-element analysis. With appropriate rotor topology, 12-slot/4-pole and 12-slot/8-pole machines with fully-pitched and double layer mutually coupled windings can achieve similar torque capacity, which are higher than the machines with other winding configurations. In addition, the synchronous reluctance machine with round flux barrier can have lower iron loss than doubly salient reluctance machine under different working conditions. The prototypes of 12-slot/8-pole single layer and double layer, doubly salient synchronous reluctance machines have been built to validate the predictions in terms of inductances and torques

Comparative Study of Torque Production in Conventional and Mutually Coupled SRMs Using Frozen Permeability

This paper investigates the influence of mutual fluxes (inductances) on the resultant torque in three-phase conventional switched-reluctance machine (CSRM) and mutually coupled SRM (MCSRM) using the frozen permeability (FP) method. Under saturation conditions, the FP method allows accurately separating the torques due to self-flux and mutual flux, hence quantifying their contributions to torque generation. Then, appropriate current waveforms (unipolar or bipolar, square wave or sinewave) can be established to maximize the output torques. It is well known that the mutual torque of CSRM can be negligible. However, this paper has shown that when sinewave current is employed and under full or overload conditions, the torque will be significantly reduced due to non-negligible negative mutual torques. Different from CSRM, the self-torque and the mutual torque of MCSRM can be added if current waveform is properly chosen, e.g., sinewave currents. This can significantly boost the resultant torque. The predictions have been validated by experiments

Recent Development of Reluctance Machines with Different Winding Configurations, Excitation Methods, and Machine Structures

This paper reviews the performances of some newly developed reluctance machines with different winding configurations, excitation methods, stator and rotor structures, and slot/pole number combinations. Both the double layer conventional (DLC-), double layer mutually-coupled (DLMC), single layer conventional (SLC-), and single layer mutuallycoupled (SLMC-), as well as fully-pitched (FP) winding configurations have been considered for both rectangular wave and sinewave excitations. Different conduction angles such as unipolar120º elec., unipolar/bipolar 180 ºelec., bipolar 240 º elec. and bipolar 360ºelec. have been adopted and the most appropriate conduction angles have been obtained for the SRMs with different winding configurations. In addition, with appropriate conduction angles, the 12-slot/14-pole SRMs with modular stator structure is found to produce similar average torque, but lower torque ripple and iron loss when compared to non-modular 12-slot/8-pole SRMs. With sinewave excitation, the doubly salient synchronous reluctance machines with the DLMC winding can produce the highest average torque at high currents and achieve the highest peak efficiency as well. In order to compare with the conventional synchronous reluctance machines (SynRMs) having flux barriers inside the rotor, the appropriate rotor topologies to obtain the maximum average torque have been investigated for different winding configurations and slot/pole number combinations. Furthermore, some prototypes have been built with different winding configurations, stator structures, and slot/pole combinations to validate the predictions