| Summary: | Thesis (PhD)--Stellenbosch University, 2012. === ENGLISH ABSTRACT: In this dissertation a new type of electrical machine, a Radial Flux Air-Cored Permanent Magnet
machine with a Double-sided Rotor and utilising concentrated, non-overlapping windings,
is proposed. The concept of the Double-sided Rotor Radial Flux Air-Cored Permanent Magnet
machine, or RFAPM machine for short, was derived from the Double-sided Rotor Axial Flux
Air-Cored Permanent Magnet (AFAPM) machine. One of the problems that AFAPM machines
experience, is the deflection of the rotor discs due to the strong magnetic pull of the permanent
magnets, especially with double-sided rotor machines. The main advantage of a RFAPM machine
over a AFAPM machine is that the rotor back-iron is cylindrically shaped instead of disk
shaped. Due to the structural integrity of a cylinder, the attraction force between the two rotors
does not come into play any more.
The focus of this dissertation is on a thorough analytical analysis of the Double-Sided Rotor
RFAPM machine. With the RFAPM being an air-cored machine, the feasibility to develop a
linear, analytical model, to accurately predict the radial flux-density and hence the induced
EMF in the stator windings, as well as the accurate calculation of the developed torque of the
machine, needed to be investigated. The need for a thorough analytical examination of the
Double-Sided Rotor RFAPM machine stemmed from the need to reduce the blind reliance on
Finite Element Modelling (FEM) software to calculate the back-EMF and torque produced by
these machines.
Another problem experienced with the FEM software was to obtain accurate torque results.
Excessive ripple torque oscillations were sometimes experienced which took a considerable
amount of time to minimise with constant refinement to the meshing of the machine parts.
Reduction in the mesh element size unfortunately also added to the simulation time. The requirement
for an accurate analytical model of the RFAPM machine was also necessary in order to reduce the amount of time spent on successive FEM simulation to obtain the optimum pole
arc width of the permanent magnet in order to minimise the harmonic content of the radial
flux-density distribution in the the stator windings.
In this dissertation, the use of single-layer and double-layer, non-overlapping, concentrated
winding for the RFAPM machine is also investigated. It was decided to include a comparison of
these two non-overlapping winding configurations with a “hypothetical” concentrated, overlapping
winding configuration. This would allow us to gauge the effectiveness of using nonoverlapping
winding with respect to the reduction in copper losses as well as in the reduction
in copper volume. It would also allow us to investigate the extent of how much the developed
torque is affected by using non-overlapping windings instead of overlapping windings. === AFRIKAANSE OPSOMMING: In hierdie proefskrif word ’n nuwe tipe elektriese masjien, ’n Radiale-vloed Lugkern Permanent
Magneet Masjien met ’n dubbelkantige rotor en nie-oorvleuelende Windings voorgestel.
Die konsep vir die Radiale-vloed Lugkern Permanent Magneet Masjien, of RVLPM vir kort,
is afgelei vanaf die Dubbelkantige Rotor, Aksiale-vloed Lugkern (AVLPM) masjien. Een van
die probleme wat met AVLPM masjiene ondervind word, is die defleksie van die rotorjukke as
gevolg van die sterk aantrekkingskragte van die permanente magnete, veral in dubbelkantige
rotor masjiene. Die hoof voordeel wat die RVLPM masjien inhou bo die AVLPM masjien, is
die feit dat die RVLPM se rotorjukke silindries is in plaas van ronde skywe. As gevolg van die
strukturele integriteit van ’n silinders, speel die aantrekkingskrag van die permanente magnete
nie meer ’n rol nie.
Die fokus van die proefskrif gaan oor die deeglike analitiese analise van die dubbelkantige
RVLPM masjien. Weens die feit dat die RVLPM masjien ’n lugkern masjien is, is daar besluit
om ondersoek in te stel na die moontlikheid om ’n lineêre, analitiese model vir die masjien
op te stel waarmee die radiale-vloeddigtheid, teen-EMK asook die ontwikkelde draaimoment
vir die masjien akkuraat bereken kan word. Die behoefde aan ’n akkurate analitiese model
vir die dubbelkantige rotor RVLPM masjien is om die blinde vertroue te elimineer wat daar in
Eindige-Element Modellering (EEM) sagteware gestel word om die teen-EMK en ontwikkelde
draaimoment van die RVLPM masjien uit te werk.
’n Verdere probleem wat daar met EEM sagteware ondervind is, is die akkurate berekening
van die ontwikkelde draaimoment. Oormatige rimpel draaimoment ossillasies is soms
ondervind wat heelwat tyd geverg het om te minimeer, deur voortdurende verfyning van die
EEM maas in die verskillende dele van die masjien. Soos die maas egter kleiner word, verleng
dit die simulasie tyd van die EEM aansienlik. Nog ’n rede vir ’n akkurate analitiese model van die RVLPM masjien, is om vinnige metode te verkry om die optimale permanente magneet
pool hoekwydte te verkry, wat die minste Totale Harmoniese Vervorming (THV) in die
radiale-vloeddigtheidsdistribusie in die statorgebied sal veroorsaak, sonder om herhaaldelike
EEM simulasies te loop.
In die proefskrif word die gebruik van enkellaag en dubbellaag, nie- oorvleuelende, gekonsentreerde
wikkelings vir die RVLPM masjien ook ondersoek. Daar is besluit om hierdie
twee nie-oorvleuelende windingskonfigurasies met ’n “hipotetiese” gekonsentreerde, oorvleuelende
windingskonfigurasie te vergelyk. Dit behoort ons in staat te stel om die doeltreffendheid
van nie-oorvleuelende windings te bepaal, met betrekking tot die afname in koperverliese
asook die afname in kopervolume. Verder sal dit ons in staat stel om ook mate waartoe die ontwikkelde
draaimoment deur nie-oorvleuelende windings beïnvloed word, te ondersoek.
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