Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: This thesis is a description of how the first magnetically geared axial flux permanent magnet generator (MGAFG) is designed, constructed and experimentally evaluated. Magnetic gears (MGs) allow for contact-less power transfer and lubricant free operation, which may solve the reliability concerns with current mechanically geared wind energy converters. However, the complex structure of MGs may present serious challenges to its design. Thus, special care should be given to the mechanical layout and the electromagnetic influence of every component. The MGAFG can be configured to be magnetically coupled or decoupled. In the coupled configuration the permanent magnets (PMs) of the MG contribute to the total flux linkage in the PM generator (PMG). The coupled configuration is therefore more efficient. The processing time required to optimise the decoupled configuration is however much faster, since the MG and the PMG can be optimised separately. The optimised results show that a torque density in excess of 100kNm/m3 could be achieved, which is significantly higher than any of known electrical machines. However, owing to excessive losses in the mechanical support structures, the prototype exhibited lower torque density and poor efficiency. The design related aspects and issues are analysed and discussed in detail in an attempt to outline problem areas in the design process. Relevant recommendations are also given for future design improvements. The costs of magnetic material accounts for over fifty percent of the total cost of the prototype. Therefore to make the manufacturing of the MGAFG more economically viable magnetic material should be minimised in the design process. / AFRIKAANSE OPSOMMING: In hierdie tesis word die eerste magnetiese geratte aksiale vloed permanente magneet generator (MGAVG) ontwerp, vervaardig en eksperimenteel geëvalueer. In magnetiese ratte (MR) is daar geen kontak tussen werkende dele nie, daarom word geen smeermiddels benodig nie. Dit dra by tot die betroubaarheid van die ratkaste in wind energie generators en kan onderhoud grotendeels uitskakel. Die komplekse struktuur van magnetiese ratte kan egter die betroubaarheid van die ontwerp juis verswak. Daarom moet die meganiese uitleg noukeurig beplan word sodat dit nie die elektromagnetiese werking ondermyn nie. Die magnetiese rat (MR) en die permanente magneet generator (PMG) van die masjien kan magneties of sonder magnetiese koppeling verbind word. In die gekoppelde konfigurasie dra all die permanente magnete van die MR gesamentlik by tot die totale vloed-koppeling in die PMG. Wat die magnetiese gekoppelde konfigurasie meer doeltrefend maak. Minder tyd word benodig om die nie magnetiese gekoppelde konfigurasie te optimaliseer omdat die MR en die PMG apart geoptimaliseer kan word. Die optimale resultate toon dat ’n wringkrag van meer as 100kNm/3 bereik kan word, wat aansienlik beter is as die van bekende elektriese masjiene. Maar as gevolg van oormatige verliese in die meganiese strukture, toon die prototipe lae wringkrag digtheid en swak doeltreffendheid. Die ontwerp probleme word ontleed en bespreek in ’n poging om probleem areas in die ontwerp te identifiseer. Relevante aanbevelings word gegee vir toekomstige ontwerp verbeterings. Die koste van die magnetiese material verteenwoordig meer as vyftig persent van die vervaardigings koste van die prototipe. Koste kan bespaar word op die vervaardiging van die MGAVG deur die hoeveelheid magnete wat gebruik word te beperk.

The growing demand of electrified light duty trucks, including sports utility vehicles (SUV) require high performance motors to surpass form their internal combustion engine counterparts. The Axial Flux Permanent Magnet (AFPM) Motor is expected to be one of the leading technologies to meet the demands of these industries due to its efficenct and high torque and power density. Designing a robust thermal management system for this motor is key to utilizing these performance benefits. To meet these demanding conditions, additive manufacturing is expected to play a critical role in enhancing performance. Additively manufactured hollow coil is a cooling strategy to extract heat directly from the hottest part of the motor, the stator. The following research assesses the viability of the design in a prototype motor. ANSYS CFX is used to characterize the pressure drop and flowrate, and a test setup is used to validate the results. The challenges associated with integrating the solution into a motor is highlighted as well as design issues during design development. Finally, the integration of a parallel hybrid SUV using an AFPM motor is documented and the challenges with integration into a vehicle is explained. / Thesis / Master in Advanced Studies (MAS)

A Thesis Submitted to the School of Graduate Studies in Partial Fulfillment of the Requirements for the Degree of Master of Applied Science in Mechanical Engineering / In the wake of the rising global demand for more electric transportation, aerospace electrification is becoming a highly active research area as commercial fully electric aircrafts are becoming a reality. The transportation electrification industry is challenged to develop powerful, safe, and compact-sized machines that can replace fossil fuel powered engines in aircrafts. Axial Flux Permanent Magnets (AFPM) machines are currently being intensively developed as a great candidate for this purpose due to their inherently higher power density compared to other machine electric machines topologies. The efforts of further increasing AFPM machines power density add more thermal challenges as intensive cooling is required at a relatively small machine package to avoid machine failure. One of the most concerning failure modes in these machines is power output reduction due to overheating of the rotor-mounted permanent magnets or even complete failure due to irreversible demagnetization. This research discusses the design process of an integrated rotor air cooling system for a 100 kW AFPM machine designed for an electric aircraft propulsion system. The embedded cooling system allows the rotor to be self-cooled at a sufficient cooling rate while minimizing the impact on machine efficiency due to windage power losses. The presented design process includes several stages of cooling enhancement including the addition and fine-tuning of rotor fan blades and rotor vents design. These enhancements are done by studying the air flow over the rotor surfaces in conjunction with heat transfer through Conjugate Heat Transfer (CHT) Computational Fluid Dynamics (CFD) analyses. In an initial study, different rotors with different combinations of rotor cooling features are studied and their thermal performance is compared. The results show that using rotor embedded fan blades in throughflow ventilated rotor geometry offers the best performance balance, achieving sufficient rotor cooling rate within a reasonable increase of windage power loss. A parametric study is performed to improve the rotor blade geometry for a higher ratio of heat transfer to windage losses. Another study is performed where the rotor and the enclosure geometries are fine-tuned simultaneously to reduce the negative effect on rotor heat transfer imposed by the enclosure. The final geometry of the rotor enclosure assembly is generated based on the research results and the design is integrated into the final machine prototype to be tested. / Thesis / Master of Applied Science (MASc) / Axial-flux permanent magnets (AFPM) machines are gaining the transportation electrification industy attention as a greener alternative to combustion engines in aircraft propulsion systems due to their high power and torque density. The intense endeavors of the current research to further improve AFPM machines power densities brings thermal design challenges to ensure the safe operation of the machine. Rotor permanent magnets failure due to demagnetization as a result of overheating can impose a great risk to the machine operation and safety. Accordingly, special attention should be paid to rotor thermal management. This research discusses the design process of an integrated rotor air cooling system for an AFPM machine designed for an electric aircraft. The machine mechanical and thermal design parameters are used to set an initial rotor design with different rotor cooling features based on literature findings. Rotor fan blades and air vents are selected as the main rotor cooling features for the design. Several design iterations are then made to fine-tune the rotor geometry targeting low operating temperature of the permanent magnets at a low cost of windage losses. The thermal performance of the different designs is assessed and compared to each other using conjugate heat transfer (CHT) computational fluid dynamics (CFD) analyses. Safe operating temperature of the magnets is achieved at an acceptable windage losses value with the final design, and it is selected for prototyping.

Traffic congestion in large urban and metropolitan areas is a substantial problem plaguing these areas. Not only are commuters losing valuable time, but greenhouse gas emissions are substantially worse because of congestion. Considerable research and development into next generation electrified aircraft is ongoing to introduce air mobility as a viable new means of transporting people and goods across long commutes. This development extends into commercial aviation as a whole as a means of reducing the industry’s carbon footprint with new aircraft designs that employ electrified propulsion systems. Many electrified aircraft projects are currently underway, ranging from small commuter aircraft all the way to large twin-aisle aircraft, and part of the development scope for alot of these projects is creating highly robust and power dense electric machines that replace the current state-of-the-art. The axial flux permanent magnet synchronous machine is an exciting candidate for aircraft propulsion due to its exceptional torque density and compact axial nature. In this thesis, the mechanical design for three generations of axial flux permanent magnet synchronous machines is discussed. These machines serve as development phase prototypes for machines that are ultimately intended for propulsion applications in commercial aviation, particularly for eVTOL aircraft. The motivation for electrification in the commercial aviation industry is discussed, followed by an overview of the development landscape for electrified propulsion systems in commercial aviation, focusing primarily on electric machines that are currently state-of-the-art or are set to be in the near future, as well as what is required for future electric machines in terms of power output and power density. The axial flux architecture is then presented, including a high-level comparison to the radial-flux architecture, an overview of the various axial flux machine designs and topologies, and a discussion of the inherent mechanical design challenges associated with the axial flux architecture. The yokeless and segmented armature axial flux permanent magnet synchronous machine design was selected for the machines developed as part of the research for this thesis, and the discussion of the mechanical design of these machines is broken up into the two core sub assemblies: stator assembly and rotating assembly. High-level design methodologies are introduced for both sub-assemblies, which is further broken down into different approaches pertaining to each generation. The first and second generation designs are presented at a high level, followed by deep-dives into the complete mechanical design for the third generation stator, the bearing selection, arrangement, and analysis for the third generation rotating assembly, and adhesive characterization trials used to guide adhesive selection for rotor magnetics retention in the second and third generation machines. The current status of the machines and any outcomes from testing that has been conducted thus far, particularly with respect to performance, is presented at the end. / Thesis / Master of Applied Science (MASc)

Axial flux permanent magnet (AFPM) machines have recently attracted significant attention due to several reasons, such as their specific form factor, potentially higher torque density and lower losses, feasibility of increasing the number of poles, and facilitating innovative machine structures for emerging applications. One such machine design, which has promising, high efficiency particularly at higher speeds, is of the coreless AFPM type and has been studied in the dissertation together with more conventional AFPM topologies that employ a ferromagnetic core. A challenge in designing coreless AFPM machines is estimating the eddy current losses. This work proposes a new hybrid analytical and numerical finite element (FE) based method for calculating ac eddy current losses in windings and demonstrates its applicability for axial flux electric machines. The method takes into account 3D field effects in order to achieve accurate results and yet greatly reduce computational efforts. It is also shown that hybrid methods based on 2D FE models, which require semi-empirical correction factors, may over-estimate the eddy current losses. The new 3D FE-based method is advantageous as it employs minimum simplifications and considers the end turns in the eddy current path, the magnetic flux density variation along the effective length of coils, and the field fringing and leakage, which ultimately increases the accuracy of simulations. After exemplifying the practice and benefits of employing a combined design of experiments and response surface methodology for the comparative design of coreless and conventional AFPM machines with cores, an innovative approach is proposed for integrated design, prototyping, and testing efforts. It is shown that extensive sensitivity analysis can be utilized to systematically study the manufacturing tolerances and identify whether the causes for out of specification performance are detectable. The electromagnetic flux path in AFPM machines is substantially 3D and cannot be satisfactorily analyzed through simplified 2D simulations, requiring laborious 3D models for performance prediction. The use of computationally expensive 3D models becomes even more challenging for optimal design studies, in which case, thousands of candidate design evaluations are required, making the conventional approaches impractical. In this dissertation a new two-level surrogate assisted differential evolution multi-objective optimization algorithm (SAMODE) is developed in order to optimally and accurately design the electric machine with a minimum number of expensive 3D design evaluations. The developed surrogate assisted optimization algorithm is used to comparatively and systematically design several AFPM machines. The studies include exploring the effects of pole count on the machine performance and cost limits, and the systematic comparison of optimally designed single-sided and double-sided AFPM machines. For the case studies, the new optimization algorithm reduced the required number of FEA design evaluations from thousands to less than two hundred. The new methods, developed and presented in the dissertation, maybe directly applicable or extended to a wide class of electrical machines and in particular to those of the PM-excited synchronous type. The benefits of the new eddy current loss calculation and of the optimization method are mostly relevant and significant for electrical machines with a rather complicated magnetic flux path, such is the case of axial flux and of transvers flux topologies, which are a main subject of current research in the field worldwide.

Tato dizertační práce se zabývá návrhem původního motor-generátoru s axiálním tokem a buzením permanetními magnety, zkonstruovaným specificky pro hybridní elektrický autobus. Návrhové zadání pro tento stroj přineslo požadavky, které vedly k této unikátní topologii tak, aby byl dosažen výkon, účinnost a rozměry stroje. Tato partikulární topologie motor-generátoru s axiálním tokem je výsledkem literární rešerše, kterou následoval výběr koncepce stroje s představeným návrhem jako výsledkem těchto procesů. Přístup k návrhu stroje s axiálním tokem sledoval „multi-fyzikální“ koncepci, která pracuje s návrhem elektromagnetickým, tepelným, mechanickým, včetně návrhu řízení, v jedné iteraci. Tím je v konečném návrhu zajištěna rovnováha mezi těmito inženýrskými disciplínami. Pro samotný návrh stroje byla vyvinuta sada výpočtových a analytických nástrojů, které byly podloženy metodou konečných prvků tak, aby samotný návrh stroje byl přesnější a spolehlivější. Modelování somtného elektrického stroje a celého pohonu poskytlo představu o výkonnosti a účinnosti celého subsytému v rozmanitých operačních podmínkách. Rovněž poukázal na optimizační potenciál pro návrh řízení subsystému ve smyslu maximalizace účinnosti celého pohonu. Bylo postaveno několik prototypů tohoto stroje, které prošly intensivním testováním jak na úrovni sybsytému, tak systému. Samotné výsledky testů jsou diskutovány a porovnány s analytickými výpočty parametrů stroje. Poznatky získané z prvního prototypu stroje pak sloužily k představení možností, jak zjednodušit výrobu a montáž stroje v příští generaci. Tato práce zaznamenává jednotlivé kroky během všech fází vývoje elektrického stroje s axiálním tokem, počínaje výběrem konceptu stroje, konče sumarizací zkušeností získaných z první generace prototypu tohoto stroje.

Les travaux de recherche présentés dans cette thèse concernent les petites machines à aimants permanents, à flux axial et à auto-commutation électronique ayant la topologie d’un rotor intérieur discoïdal avec des aimants Nd-Fe-B montés en surface et de deux stators extérieurs identiques, chacun avec enroulement triphasé distribué dans des encoches. Après l’examen des topologies candidates pour applications d’entraînement direct basse-vitesse, une modélisation électromagnétique analytique de pré-dimensionnement d’un prototype de telles machines est réalisée. Ensuite, une approche numérique originale est développée et couplée à l’optimisation géométrique des aimants rotoriques en vue de réduire les harmoniques d’espace de l’induction magnétique dans l’entrefer et aussi les ondulations du couple électromagnétique. Des nombreux tests expérimentaux sont effectués sur le prototype de machine pour vérifier son dimensionnement ainsi que pour valider la stratégie d’auto-commutation électronique et de contrôle de base / The research work presented in this thesis is concerned with small electronically-commutated axial-flux permanent-magnet (AFPM) machines having the double-sided topology of an inner rotor with surface-mounted Nd-Fe-B magnets, sandwiched between two outer slotted stators with distributed three-phase windings. After reviewing the small double-sided AFPM machine candidate topologies for low-speed direct-drive applications, the thesis hinges on the size equations and the analytical electromagnetic design of the inner-rotor AFPM (AFIPM) machine topology under study. Original methods of modelling and design optimization of a small prototype AFIPM machine are then proposed with the view to reducing the airgap flux density space-harmonics and the torque ripple by rotor-PM shape modification. Extensive experimental tests are carried out on the small three-phase AFIPM machine prototype in order to validate its proper design and to check its electronic commutation and basic control technique

Dans un contexte automobile électrique et hybride, la part des machines synchrones à aimants permanents s'est accrue exponentiellement. Cette évolution s'accompagne d'exigences en termes d'émissions vibro-acoustiques. En termes de dimensionnement de la chaîne de traction, l'analyse multiphysique du moteur s'avère être un enjeu crucial pour son développement. La nécessité de disposer de codes informatiques de conception possédant des temps de calcul faibles pour une précision maximale se fait ressentir pour l'exploration de solutions potentiellement performantes dans les premières étapes du processus de dimensionnement. A ce titre, les aspects vibratoires et acoustiques sont modélisés analytiquement et par éléments finis dans la présente thèse. Ainsi, au moyen du modèle magnétique, l'analyse magnéto-vibro-acoustique faiblement couplée (résolution itérative des différentes physiques) peut être réalisée.La thèse est découpée en quatre parties. La première expose un état de l’art sur les émissions vibro-acoustiques des machines et notamment la modélisation du bruit d’origine magnétique. Les problématiques de la modélisation sont détaillées. Dans une deuxième partie, les modèles sont largement décrits. Les modèles éléments finis sont validés expérimentalement. Une troisième partie se propose de valider les modèles analytiques par éléments finis, en complexifiant progressivement la géométrie d’une machine à aimants montés en surface à flux radial. Enfin, la dernière partie utilise les modèles éléments finis pour étudier des machines non-conventionnelles comme les machines à commutation de flux et les machines à aimants en surface à flux axial. / The proportion of permanent magnets synchronous motors used for electric and hybrid automotive traction has exponentially increased during the past decade. This evolution comes with ever-demanding low noise and vibrations requirements. Multi-physics analysis of the motor is a decisive issue for the development of the powertrain. For the exploration of potentially efficient motor solutions in first design steps, it is thus a necessity to have at disposal fast and accurate computer codes. In this respect, acoustic and vibratory aspects are modeled using finite element and analytical models in this thesis. As a result, using an electromagnetic model, the weakly-coupled magneto-vibro-acoustic analysis (iterative solving of each physic) can be performed.The thesis is divided into four parts. The first part states the art on machine vibro-acoustic emissions and focuses on noise of magnetic origins modeling. Issues of modeling are detailed. Then, models are described to a great extent in the second part. Finite element models are favorably compared to experimental measures. A third part validates analytical models in comparison to finite element analysis, by gradually complicating the geometry of a surface permanent magnets radial flux machine. Finally, a fourth part uses finite element models to study non-conventional machines such as flux switching radial flux machines and surface permanent magnets axial flux machines.