Dissertations / Theses on the topic 'Multi-phase machine'

Transportation electrification has experienced a significant growth in recent years, and the electrification of the powertrain – namely hybridization – is considered the most viable solution seen by car manufacturers to achieve the challenging emission targets. Among the hybrid electrical powertrain topologies, the mild-hybrid configuration with the 48 V battery system offers the best ratio cost versus CO2 improvements. In particular, the 48 V technology does not require electrical shock protection whilst allows to leverage a variety of fuel saving functions such as electrical boost and regenerative braking. The thesis is focused on the electromagnetic and thermal design of a Belt-driven Starter Generator, BSG, for 48 V mild-hybrid powertrains. In the BSG layout, the starter-generator replaces the conventional alternator with a low impact on the engine compartment layout, even if a redesign of the belt tensioner is required. It is noteworthy to keep in mind that the electrical machine shall provide high starting torque and wide constant power speed range, both in motor and generator mode. Furthermore, the application imposes the adoption of low cost materials and the electrical machine is located in a harsh environment. As a consequence, the design is challenging from the electromagnetic, thermal and mechanical point of view. The novelties of the research lie in the 48 V automotive applications, by describing the practical difficulties to fulfill the design specifications through a suitable material selection, the identification of the cooling system and the available technological solutions. The first section of the thesis reports results from a literature review on electrical machine for mild-hybrid application aiming to highlight different criteria for the selection of the electrical machine. In this context the advantages in terms of fault tolerance and stator current splitting of multiphase drives are investigated. Furthermore, in this section the required performances and the constraints imposed by the specific application are analyzed. Among the different motor technologies, a dual three-phase induction machine having two stator winding sets shifted by 60 electrical degrees is selected as a suitable candidate. The second part of the thesis reports electromagnetic and mechanical issues addressed during the design stage, with special focus on stator winding layout, pole number and rotor slot. The adopted six-phase machine uses a four-layer bar stator winding that has been demonstrated as a good solution to improve the slot fill factor and thermal behavior. In addition, the thesis reports a comparison supported by experimental tests between open and closed rotor slots solutions; the focus is to maximize the machine electromagnetic performance according to the mechanical limits imposed by the rotating speed. Finally, predicted and measured performance of the prototypes are reported and discussed for validation purposes. The third part of the thesis deals with the thermal assessment of the BSG with particular emphasis on accurate winding temperature prediction as well as the cooling system selection. Since the stator-winding region is very sensitive to thermal issues and is usually attributed as being the main heat source within the machine body, its thermal modeling is of major importance. In these regards, a simplified stator winding thermal model was developed for the temperature prediction during transient condition. Moreover, considering that the driving cycle is characterized by time variable loss distribution, an effective cooling system must be mandatorily adopted together with high temperature class insulation material. In this context, the development of heat extraction through forced convection is experimentally investigated on the BSG prototype. As a main outcome of this research activity, it has been demonstrated the feasibility of the proposed design solution with respect to electromagnetic and thermal requirements.

The ever increasing demand for electrical energy has meant that electrical power systems have evolved to be the highly complex networks that are in existence today, where the transient interactions that take place between large synchronous generators have been the focus of advanced research for many decades. More recently, the proliferation of synchronous and asynchronous generators of comparatively small rating, which are not centrally planned, has added new impetus to this area of research. At a time when not only technical but also economic and environmental concerns must be carefully assessed, more realistic models of the individual power plant transient response and its interaction with the rest of the network become mandatory to achieve more accurate analysis of the network operation and prevent wastage of technical and economical resources. The main thrust of this research project is to develop comprehensive models of rotating machinery with which to assess the transient response of electrical power networks that undergo severe unbalanced operation due to faulty conditions developing anywhere in the power network, including the rotating machinery’s windings. To achieve an unrivalled speed of response, a nodal-based model of the electrical power network has been developed, enabling the study of power networks of any size and topological formation with the utmost flexibility and efficiency. The rotating machinery addressed in this research work is the three-phase synchronous generator and the three-phase asynchronous (induction) machine. In multi-machine power systems transient studies, it is common to look at all the rotating machinery in the network as being healthy units having an idealized sinusoidally distributed stator winding – the possibility of a severe unbalanced condition internal to the machine due to internal fault or the effect of space harmonics, has, so far, not been addressed in a multi-machine environment. In this research work, new EMTP type models, with enhanced numerical properties, are constructed for the simulation of internal and external machine fault phenomena with different levels of details including the effects of saturation and space harmonics. Advanced numerical methods are employed to improve on the numerical stability of the network model allowing the use of larger time steps than what otherwise is possible with traditional numerical methods, enabling the new model to execute faster than existing models and yet to exhibit the same degree of numerical accuracy with an unrivalled degree of modelling flexibility. A case in point is an application made to model the transient response of a Variable Frequency Transformer (VFT) undergoing internal faults on its stator side. The rotating machinery models with internal fault representation developed in this research lend themselves to an application in the area of condition monitoring, where a new method is developed to detect internal faults in the stator side of three phase rotating machinery. The method is shown to be highly effective when applied to machines operating in an isolated environment as well as in a multi-machine power system, performing very well when applied to different types of equipment and various kinds of internal faults.

Les machines électriques à aimants, appréciées pour leurs densités énergétiques volumique et massique, équipent la majorité des véhicules électrifiés. Par contre, dans la zone à puissance constante d’un système de propulsion, les commander à pertes maîtrisées, cela en démagnétisant les aimants mais de façon réversible, reste une gageure, particulièrement sous environnement thermique changeant. Les solutions simples pour se prémunir d’une démagnétisation irréversible sont coûteuses: surdimensionner ou ajouter une terre très très rare (Dysprosium).Cette thèse propose d’ajouter à l’approche de la démagnétisation réversible universellement utilisée, celle d’une boite de vitesse électromagnétique. Pour cela on conçoit une machine pentaphasée à aimants.Passer de trois à cinq phases permet alors d’augmenter les paramètres de réglage de l’alimentation électrique et, moyennant approximation, de disposer de deux machines fictives à p et 3p paires de pôles, chacune pouvant contribuer de façon équivalente à la production du couple. Pratiquement, l’utilisation optimale de ces deux machines permet de reconstituer la fonction de boite de vitesse
Permanent Magnet electrical machines , appreciated for their high power density, equip the majority of the electrified vehicles. However, controlling these machines, in the constant power range of the propulsion system while mastering the losses, with PM reversible demagnetization remains a challenge especially under varying thermal environnement. Proposed solutions aim for protecting PM from irreversible demagnetization are costly: oversizing or using very rare earth PM (Dysprosium).In this thesis, we proposed to add on the reversible demagnetization approach universally used , that of a electromagnetic gearbox. Thus, we design a five phase PM machine.Increasing the phase number from three to five, increases the adjustment parameter of the electrical supply, and allows to have two fictitious machines with p and 3 p poles. Each fictitious machine contributes equivalently in producing torque. Practically, the optimal use of these two machines leads to reconstructing the gearbox function

The need for efficiency, reliability and continuous operation has lead over the years to the development of fault-tolerant electrical drives for various industrial purposes and for transport applications. Permanent-magnet synchronous machines have also been gaining interest due to their high torque-to-mass ratio and high efficiency, which make them a very good candidate to reduce the weight and volume of the equipment.

In this work, a multidisciplinary approach for the design of fault-tolerant permanent-magnet synchronous machine drives is presented.

The drive components are described, including the electrical machine, the IGBT-based two-level inverter, the capacitors, the sensors, the controller, the electrical source and interfaces. A literature review of the failure mechanisms and of the reliability model of most of these components is performed. This allows understanding how to take benefit of the redundancy generally introduced in fault-tolerant systems.

A necessary step towards fault tolerance is the modelling of the electrical drive, both in healthy and faulty operations. A general model of multi-phase machines (with a number of phases equal to or larger than three) and associated converters is proposed. Next, control algorithms for multi-phase machines are derived. The impact of a closed-loop controller upon the occurrence of faults is also examined through simulation analysis and verified by experimental results.

Condition monitoring of electrical machines has expanded these last decades. New techniques relying on various measurements have emerged, which allow a better planning of maintenance operations and an optimization of the uptime of electrical machines. Regarding drives, a number of sensors are inherently present for control and basic protection functions. The utilization of these sensors for advanced condition monitoring is thus particularly interesting since they are available at no cost.

A novel fault detection and isolation scheme based on the available measurements (phase currents, DC-link voltage and mechanical position) is developed and validated experimentally. Change-detection algorithms are used for this purpose. Special attention is paid to sensor faults as well, what avoids diagnosis errors.

Fault-tolerant control can be implemented with passive and active approaches. The former consists in deriving a control scheme that gives acceptable performance for all operating conditions, including faulty conditions. The latter consists in applying dedicated solutions upon the occurrence of faults, i.e. by reconfiguring the control. Both approaches are investigated and implemented.

Finally, design considerations are discussed throughout the thesis. The advantages and drawbacks of various topologies are analyzed, which eventually leads to the design of a five-phase fault-tolerant permanent-magnet synchronous machine.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

There are many applications, such as paper mills, locomotive traction and machine tools, which require high performance control of more than one electric motor. These multi-motor drives are generally available in two configurations. The first one consists of a number of three-phase voltage source inverters (VSI) connected in parallel to a common DC link, each inverter feeding a three-phase AC motor. This configuration allows independent control of all machines by means of their own three-phase VSIs. The second method comprises one inverter, which feeds multiple parallel-connected three-phase motors. However, this configuration does not allow independent control of each motor and is suitable only for traction. This thesis explores a novel concept for multi-motor drive systems, based on utilization of multi-phase machines and VSIs, and series connection of all the machines in the group. Application of a single multi-phase VSI in conjunction with multi-phase machines generates additional degrees of freedom. The research presented here utilises these additional degrees of freedom to control a number of machines independently within a novel multi-phase multi-machine drive. The concept is based on the fact that independent flux and torque control of any AC machine, regardless of the number of stator phases requires control of only two stator current components. This leaves the remaining current components free to control other machines within the group. It is shown that it is possible to connect the machines in such a way that what one machine sees as the flux/torque producing components the other machines see as non-flux/torque producing components, and vice versa. Therefore it is possible to connect in series a number of multi-phase machines and independently control each machine while supplying them from a single multi-phase inverter. Different configurations of the multi-motor drive are possible depending on certain properties of the supply phase number. In general, higher the supply phase number is, higher the number of connectable machines is. However, some phase numbers are more favourable than others, as discussed in detail in the thesis. Simulation studies are provided for five, six, seven, nine, ten and fifteen phase configurations in order to verify the concept. It is shown that the concept is independent of the type of AC machines used and the only requirement is that they all have sinusoidal distributed magnetomotive force. Current control in both the stationary and rotating reference frames is considered and it is concluded that current control in the rotating reference frame requires compensation of the additional voltage drops caused by the series connection. Two possible methods of compensating for these voltage drops are suggested and verified by simulation. Finally, a laboratory rig is described, which utilises two three-phase inverters connected in such a way as to form a single six-phase inverter. A six-phase two-motor drive comprising a symmetrical six-phase induction machine and a three-phase induction machine or a three-phaseP MSM is investigatede xperimentally. An analysis of the performance of the two-motor drive is presented and it is shown that decoupled control of each machine is achieved.

La fatigue occasionne 90% des ruptures des pièces en service. Les états de contraintes sont généralement multiaxiaux mais paradoxalement les critères qui permettent de juger de la sécurité sont peu nombreux et s'avèrent peu satisfaisants soit dans le principe,soit dans la commodité d'exploitation. Le présent mémoire propose un critère de fatigue multi axiale basé sur la moyenne quadratique des amplitudes des contraintes tangentielles et normales. Ce critère est satisfaisant dans son principe et toutes les conséquences (diagramme de HAIGH en traction et torsion en particulier) en sont tirées. Le domaine de validité est tel que τ(-1)/σ(-1) est compris entre 0,577 et 0,866. Un programme général de calcul a été développé. La validation du critère est faite à l'aide d'essai de la littérature selon une méthode originale de validation statistique consistant à comparer lès distributions de la contrainte équivalente et de la limite de fatigue σ(-1) par la méthode de MONTE CARLO. Le critère est validé pour 70% à 80% des essais étudiés
Fracture of mechanical parts in operation are induced mainly by fatigue ( 90%). The stress state are generally multiaxial but surprisingly,criteria which permit safety evaluation are few and not well based in theory and not well suited for practice. The multiaxial fatigue criterion proposed in this report is based on quadratic average of the intensity of tangential and normal stress. This criterion satisfies theoretical requirements and all practical consequences as diagrams of HAIGH in traction and torsion are deduced from it. The validity domain in τ(-1)/σ(-1) is between 0,577 and 0,866. A general program of calculation has been developed. The criterion has been validated by tests found in the technical literature following an original method of statistical validation applied to the comparison of the equivalent stress and of fatigue limit σ(-1). The criterion is qualified for 70 to 80 % of studied tests

Over the past decades, attention has been brought to the importance of indoor air quality and the serious threat of bio-aerosol contamination towards human health. A novel idea to transport hazardous particles away from sensitive areas is to automatically control bio-aerosol concentrations, by utilising airflows from ventilation systems. Regarding this, computational fluid dynamics (CFD) may be employed to investigate the dynamical behaviour of airborne particles, and data-driven methods may be used to estimate and control the complex flow simulations. This thesis presents a methodology for machine-learning based control of particle concentrations in turbulent gas-solid flow. The aim is to reduce concentration levels at a 90 degree corner, through systematic manipulation of underlying two-phase flow dynamics, where an energy constrained inlet airflow rate is used as control variable. A CFD experiment of turbulent gas-solid flow in a two-dimensional corner geometry is simulated using the SST k-omega turbulence model for the gas phase, and drag force based discrete random walk for the solid phase. Validation of the two-phase methodology is performed against a backwards facing step experiment, with a 12.2% error correspondence in maximum negative particle velocity downstream the step. Based on simulation data from the CFD experiment, a linear auto-regressive with exogenous inputs (ARX) model and a non-linear ARX based neural network (NN) is used to identify the temporal relationship between inlet flow rate and corner particle concentration. The results suggest that NN is the preferred approach for output predictions of the two-phase system, with roughly four times higher simulation accuracy compared to ARX. The identified NN model is used in a model predictive control (MPC) framework with linearisation in each time step. It is found that the output concentration can be minimised together with the input energy consumption, by means of tracking specified target trajectories. Control signals from NN-MPC also show good performance in controlling the full CFD model, with improved particle removal capabilities, compared to randomly generated signals. In terms of maximal reduction of particle concentration, the NN-MPC scheme is however outperformed by a manually constructed sine signal. In conclusion, CFD based NN-MPC is a feasible methodology for efficient reduction of particle concentrations in a corner area; particularly, a novel application for removal of indoor bio-aerosols is presented. More generally, the results show that NN-MPC may be a promising approach to turbulent multi-phase flow control.

Nowadays we are witnessing a strong growth in the full electric vehicle market. In the field of traction the requirements are low weight, small dimensions and low cost, without renouncing reliability and good performances. The high power density requirement is pushing the research towards integrated drive solutions. A particular drive that allows to obtain more insightful integrated solutions is the multi-phase one. In fact, in multi-phase structures it is possible to realize a converter as a combination of standard modules with an equal subdivision of the current. The resulting power electronics modules meet the needs of an integrated solution: smaller and widely distributed. Although road electric vehicles primarily adopt 3-phase drives, the multi-phase version could represent a good alternative not only for its integration capability but also for other features like reduced weight and volume, high efficiency, low vibrations and noise, robustness and, overall, fault tolerance. The aim of this thesis is to investigate a particular category of multiphase machines, characterized by a very simple structure that allows to match manufacturing and performance standards. In Chapter 1, the subcategory of multiphase machine object of the investigation is identified. Considering a simple stator structure, as the tooth-coil wound, a general algorithm to identify the right stator-rotor coupling in multiphase machine is presented. In Chapter 2, an analytical and generalized formulation of the harmonic fields at the air gap for the multi-n-phase solutions chosen is reported allowing to understand and quantify the harmonic compensation in the MMF. Starting from the Lorenz Force Law an analytical formulation of the torque and torque ripple is then proposed. The model proposed has been then verified by Finite Element Analysis (FEA). In Chapter 3, the main issues tackled in the design of a nine phase machine are reported. Between the possible solutions a 9 slot 10 poles PM-inset machine has been chosen. The chapter reports the evaluation of the performance conducted by the time stepping FEA. The chapter reports the experimental results that were conducted on a prototype. A description of the control infrastructure is reported. In Chapter 4, a simple modulation strategy that allows to reduce the DC-link stress for a triple-3-phase drive is presented. The analysis of the benefits introduced by the PWM phase shifting are evaluated by steady state simulations ,using the software Pspice, in all the possible operating conditions. A worst case approach has been chosen in order to find the best angle of shifting between carriers to reduce the DC-link rms current in multi-3-phase drives. The results of the experimental validation are reported. The same analysis has been extended to sectored multiphase. In Chapter 5, a mathematical model is proposed in order to evaluate the torque and the torque ripple in fractional slot tooth-coil wound (TCW) Synchronous Reluctance (SyR) machines. Considering a generic harmonic field and an ideal SyR rotor, the rotor magnetic potential is modelled and the torque equations are calculated starting from the Lorenz Force Law. Time stepping FEA results are reported in order to verify the formulations. Appendix A reports the mathematical demonstration that defines the rotor reaction for an ideal SyR rotor together with the methodologies used to design the SyR constant permeance rotor. Appendix B reports the manufacturing process of the machine. Appendix C reports the COOL-TIE concept: a cooling devices for the electrical machine compatible with the power electronic integration

Multiphase electronically commutated dc machine is a new non-conventional machine and converter topology aimed at dc power generation and delivery systems. This thesis presents a detailed analysis of two multiphase electronically commutated dc machine topologies, firstly, the two level topology then the multilevel topology. Electronic current commutation processes in these topologies are analysed and electrical machine parameters that influence current commutation and the design of the electronic commutator are exposed. The behaviour of the power electronic commutator circuit is shown to be tightly coupled to that of the electrical machine connected to it and to be inductively dominated during current commutation. Performance, efficiency, footprint and cost are all affected by design considerations arising from the interaction of electronic commutator switching devices and electrical machine. Thus there is an incentive to ensure that the designs of power electronic commutator circuits and electrical machines are matched, allowing the requirements of the system as a whole to be satisfied. Since these machine and converter topologies depart from the conventional machine and converter topologies, an alternative modelling approach that lends itself well to modelling of the machine and its associated power electronics is presented. The models are used to evaluate the operational attributes of the machine and its associated electronic commutator power electronic circuit and the proposed control schemes. Results from two prototype laboratory drives built to practically access the viability and fully characterise the operational behavior of these topologies together with the simulation results are presented. Conclusions are drawn concerning the proposed topologies and their associated control strategies.

Je jasné, že nejúspěšnější konstrukce zahrnuje postup vícefázového řízení, ve kterém každá fáze může být považována za samostatný modul. Provoz kterékoliv z jednotek musí mít minimální vliv na ostatní, a to tak, že v případě selhání jedné jednotky ostatní mohou být v provozu neovlivněny. Modulární řešení vyžaduje minimální elektrické, magnetické a tepelné ovlivnění mezi fázemi řízení (měniče). Synchronní stroje s pulzním tokem a permanentními magnety se jeví jako atraktivní typ stroje, jejíž přednostmi jsou vysoký kroutící moment, jednoduchá a robustní konstrukce rotoru a skutečnost, že permanentní magnety i cívky jsou umístěny společně na statoru. FS-PMSM jsou poměrně nové typy střídavého stroje stator-permanentní magnet, které představují významné přednosti na rozdíl od konvenčních rotorů - velký kroutící moment, vysoký točivý moment, v podstatě sinusové zpětné EMF křivky, zároveň kompaktní a robustní konstrukce díky umístění magnetů a vinutí kotvy na statoru. Srovnání výsledků mezi FS-PMSM a klasickými motory na povrchu upevněnými PM (SPM) se stejnými parametry ukazuje, že FS-PMSM vykazuje větší vzduchové mezery hustoty toku, vyšší točivý moment na ztráty v mědi, ale také vyšší pulzaci díky reluktančnímu momentu. Pro stroje buzené permanentními magnety se jedná o tradiční rozpor mezi požadavkem na vysoký kroutící moment pod základní rychlostí (oblast konstantního momentu) a provozem nad základní rychlostí (oblast konstantního výkonu), zejména pro aplikace v hybridních vozidlech. Je předložena nová topologie synchronního stroje s permanentními magnety a spínaným tokem odolného proti poruchám, která je schopná provozu během vinutí naprázdno a zkratovaného vinutí i poruchách měniče. Schéma je založeno na dvojitě vinutém motoru napájeném ze dvou oddělených vektorově řízených napěťových zdrojů. Vinutí jsou uspořádána takovým způsobem, aby tvořila dvě nezávislé a oddělené sady. Simulace a experimentální výzkum zpřesní výkon během obou scénářů jak za normálního provozu, tak za poruch včetně zkratových závad a ukáží robustnost pohonu za těchto podmínek. Tato práce byla publikována v deseti konferenčních příspěvcích, dvou časopisech a knižní kapitole, kde byly představeny jak topologie pohonu a aplikovaná řídící schémata, tak analýzy jeho schopnosti odolávat poruchám.

Dans les avions et lanceurs, des systèmes entraînés par l’énergie hydraulique, mécanique ou pneumatique sont progressivement remplacés par des systèmes électriques pour des raisons techniques et industrielles. Cependant, ces nouveaux systèmes doivent répondre aux contraintes économiques et de poids concernant ces domaines tout en garantissant une certaine fiabilité. Dans ce contexte industriel, des topologies innovantes multi-machines multi-convertisseurs à haut niveau de fiabilité sont comparées ici à des structures plus standards toujours tolérantes aux défaillances. Ainsi, des topologies avec des machines polyphasées couplées électriquement en série ont été choisies pour ce travail de thèse. La mise en série permet la mutualisation des bras d’onduleurs, réduisant ainsi leur nombre, et augmente la résistance totale du système. La valeur crête du courant est alors réduite lors de l’apparition de certains défauts avec, comme contrepartie, une augmentation inéluctables des pertes Joule globales. Pour que le contrôle de ces machines couplées électriquement en série soit indépendant, il est mis en évidence pourquoi le nombre de phase de ces machines doit être supérieur à 3 et avec de plus une connexion électrique spéciale permutant les phases. Une nouvelle topologie brevetée est tout particulièrement étudiée et testée expérimentalement. Apres validation du concept, des stratégies de contrôle plus complexes et des reconfigurations de la commande après le défaut sont appliquées afin de juger des potentialités d’amélioration des systèmes Pour les comparaisons, des simulations et des essais expérimentaux ont été réalisés. Les critères choisis pour cette comparaison ont été la puissance de dimensionnement de l’onduleur, servant d’image de son coût et de son poids, les pertes Joule et le couple pulsatoire, tous les trois pour un fonctionnement en mode dégradé
In airplanes and launch vehicles, hydraulics, mechanical and pneumatic systems are progressively being replaced by electric systems for technical and industrial reasons. However, these new electric systems have to take into account the economical and weight reliability constraints of the aeronautics industry, ensuring the required reliability. Therefore, novel high reliability multi-machine and multi-converter topologies are compared to standard structures looking forward to find solutions that can be industrially implemented. Then, series-coupled machine topologies were chosen for this work. The series-coupling mutualizes the inverter legs, reducing their number, and increases the total electrical resistance of the system. As a consequence, the peak-current after the occurrence of certain faults is reduced, but the total copper losses are higher. In order to independently control the series-coupled machines, it is highlighted the reason why the number of phases must be higher than 3 and with a special electric coupling that permutes the machine’s phases. A new patented topology is deeply analyzed with experimental tests. After a validation of the studied system, more complex control strategies and control reconfiguration after a fault are also implemented in order to evaluate the potential improvements on the system performance in degraded mode. Simulation and experimental results were used on this study. For this analysis the dimensioning power of the inverter, the copper losses and the torque ripple, all of them in degraded mode, are the compared criterions

Nowadays, embedded systems are more and more numerous that impacted strongly energy conversion systems. Associated constraints translates into a reduction of the masses and the losses to improve energy efficiency in the conversion chain. This is the case in the field of aeronautics or the concept of ″More Electric Aircraft″ now becomes a reality. Therefore, the permanent magnet synchronous machine becomes an actuator of excellence because of its important mass power, its low maintenance cost and its dynamic qualities. When these machines are associated to carry out cooperative functions (for example flight surfaces) can still reduce the mass embedded in pooling power electronics. It is precisely in this context that localizes our work by offering structures power electronics-based, reduced to power for two or more electric machines in parallel and providing control laws aimed at improving energy efficiency. We we are interested specifically in the Predictive Control of two Synchronous Machines connected in parallel with a 3-Phase Converter. These machines have identical characteristics and must follow a same velocity profile with a torque of different load and in any case independent. The predictive control approach leads us to consider the voltage inverter as a device having a finite number of input states and we need to select every moment the best control solution to minimize a cost function. This cost function on one or two machines, is composed of a portion which represents the quality of the produced torque (Iq current) and another party representative quality of the conversion via produced losses (Id current). This approach works naturally for variable switching frequency. Thus the document state of different solutions studied showing the limits of such an approach both dynamic in terms of losses. To improve this basic solution we develop an approach based on the use of virtual vector which increase the possibilities of control and led to operation at constant frequency through a SVM solution. The search for an optimum virtual vector is proposed and applied to a device consisting of two low-power machines. The various proposals are validated through numerical simulation and consolidated by experimental results.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Neu, Richard; Committee Member: Damm, E. Buddy; Committee Member: Gall, Ken; Committee Member: Gokhale, Arun; Committee Member: McDowell, David; Committee Member: Zhou, Min

碩士
中華大學
資訊工程學系碩士班
101
Live migration technology of virtual machine enables real machines to become more flexible in terms of its functions, thus raising the utilization of resources in clouds. The key technology of using live migration of virtual machine lies in the pre-copy strategy; through which virtual machine can perform live migrate with no interruption of service provided by virtual machine. In order to have an efficient live migration, it is imperative that the migration of virtual machines’ memories is not limited by bandwidth and lower the downtime of the virtual machines. Presently, the live migration algorithm provided by Xen would perform repetitive transfer of memory pages, resulting in waste of bandwidth and hence decreased of migration efficiency. Therefore, how to formulate an efficient algorithm of live migration is an important issue. This thesis presents a live migration algorithm, termed as Multi-Phase Pre-Copy (MPP). In the iterative pre-copy stage, memory pages will be transmitted only if the predefined thresholds were met. In such way, the repetitiveness migration of memory pages can be significantly reduced. In addition, we also implemented a virtual machine image transformation interface, which is able to convert an image format. Advantage of the transformation tool is that a user can run different VMs on single physical machine. As a result, cost for h/w investment can be significantly reduced. The simulation of Multi-Phase Pre-Copy algorithm has demonstrated a dramatic reduction of live migration time. In the best case, it can reduce 84% transmission of memory pages.

Induction machine (IM) is the workhorse of several industries due to its low cost and minimal maintenance. Power electronic converters play a major role in driving IMs which give better flexibility in these applications. With the advancement of production levels and effi ciency, the power-level demands of the industries are going up day by day. To meet this increased power-demand, the required ratings of the power converter components are also increased which sometimes can't be realized with the existing technologies. Due to this limitation, induction machines with more than three phases are becoming popular where the power handled by each phase is reduced compared to three-phase machine for the same power rating of IM. These machines are called multi-phase machine and six-phase machine is one of the most popular multi-phase machines. Six-phase machine is of two types: Symmetrical and Asymmetrical. In symmetrical six-phase machine, all the six stator windings are spatially displaced by 60 electrical. Asymmetrical six-phase machine, also known as split-phase induction machine (SPIM), has two sets of balanced three-phase windings which are displaced by 30 degree electrical. The later confi guration has become popular due to its less susceptibility to the time-harmonic components present in the excitation waveform. This thesis is aimed at studying the modulation strategies of SPIM driven by the power-electronic converter. There are two types of power-converters to drive SPIM: DC-AC (Inverter) and AC-AC (matrix converter). The thesis provides detailed discussions on winding structure, nature of excitation, dynamic modeling and steady-state equivalent circuit of SPIM which are required to investigate the modulation strategies of power-converter fed SPIM drive. The dynamic model of SPIM reveals that the fundamental component and a selective group of odd harmonics can contribute to the air-gap flux and hence participate in electromagnetic energy transfer and torque production. The equivalent circuit seen by the fundamental component and the above group of harmonics is similar to the equivalent circuit of three-phase IM. There is another group of odd harmonics which doesn't contribute to the air-gap flux and the equivalent circuit seen by this group consists of stator resistance and leakage inductance. So the excitation of SPIM with these harmonics will cause a large amount of harmonic currents due to low impedance of the equivalent circuit. These harmonic currents don't contribute to the air-gap flux or torque ripple but cause copper losses. So the objective of SPIM modulation is to excite the machine with fundamental component and zero or minimal injection of harmonics belonging to the first or second group. Vector Space Decomposition (VSD) technique, which exists in the literature, modulates the SPIM without injecting any harmonics in the line-neutral voltage. In this thesis, the modulation index of inverter fed SPIM drive has been de fined as the ratio of peak fundamental line-neutral voltage and DC-bus voltage. This thesis provides the derivation of the maximum modulation index achieved by VSD technique. This work tries to unify the understandings behind the existing modulation techniques by proposing a new way of modeling of six-phase inverter. The existing Conventional Space Vector PWM (CSVPWM) technique modulates the SPIM by keeping air-gap flux sinusoidal and it attains the modulation index higher than the maximum modulation index achieved by VSD technique by injecting signifi cant amount of second group of harmonics. Although this group of harmonics doesn't create any torque ripple in the machine, higher injection results into reduction in the efficiency of the SPIM drive modulated by CSVPWM technique. To overcome this, two novel modulation techniques have been proposed in this thesis for the modulation index higher than the maximum modulation index obtained by VSD technique and these two techniques have much-reduced injections of the second group of harmonics compared to CSVPWM. One of these two techniques is able to attain the complete range of modulation index as can be achieved by the CSVPWM and this technique solves a constraint optimization problem in order to minimize the second group of harmonics injection. Another technique is easy to implement but it doesn't attain the whole range of modulation index as achieved by CSVPWM. Within the sub-range, the performance of the second technique is close to the performance of the first technique. The thesis also explores the modulation of matrix converter (MC) fed SPIM drive. Although MC is a promising candidate for drive applications due to high power density and extended lifetime in absence of DC-link electrolytic capacitor, modulation technique of MC fed SPIM drive doesn't exist in the literature. A modulation technique of MC fed SPIM drive has been proposed in this work and this technique keeps the air-gap flux sinusoidal without injecting any harmonics in the line neutral voltage. The proposed modulation techniques have been veri fied by the experiments performed on laboratory prototype hardware built and tested in the lab. The design details of these hardware prototypes are included in this thesis.

Dissertação de Mestrado Integrado em Engenharia Electrotécnica e de Computadores apresentada à Faculdade de Ciências e Tecnologia
O Mundo está em grande mudança. Existe atualmente uma clara viragem do ponto de vista energético. A crescente aposta em energias renováveis, eficiência energética, mobilidade elétrica, entre outros, faz com que a inovação e desenvolvimento nestes setores esteja em alto crescimento. Obviamente que para isto, existe uma simbiose entre a indústria e a ciência. As publicações nestas áreas multiplicam-se e esta dissertação surgiu com o intuito de colmatar referências na área das máquinas elétricas, nomeadamente das Máquinas Multifásicas de Ímanes Permanentes. O trabalho realizado teve como objetivo principal perceber o estado da arte quanto aos métodos de diagnóstico de falhas nos ímanes permanentes de máquinas multifásicas de ímanes permanentes e, a partir de simulações criadas para o efeito, avaliar a possibilidade da criação de novas abordagens relativamente ao diagnóstico desta falha. O Capítulo 1 menciona o enquadramento do tema da dissertação, bem como, qual a motivação para a elaboração deste documento. O Capítulo 2 aborda quais os tipos de falhas que se podem encontrar nas máquinas em estudo, referindo as falhas elétricas, mecânicas e magnéticas. É apresentado também uma revisão geral dos métodos de diagnóstico já existentes, onde são abordados os diversos sinais já estudados e quais as conclusões retiradas para as máquinas em estudo, terminando com uma comparação entre eles. O Capítulo 3 inicia a descrição da máquina estudada, bem como qual foi o procedimento adotado para a realização das diversas simulações e análises aos diferentes estados simulados. Primeiramente, é descrita as duas falhas que induzimos na máquina, desmagnetização de um conjunto de ímanes de um polo e a sua totalidade, referindo qual o método utilizado para a criação de ambas. Numa segunda fase, são estudados quatro sinais: tensão do estator, tensão de neutros, corrente i_dq, fluxo encadeado e os erros de predição de corrente. O Capítulo 4 conclui este trabalho, enunciando as vantagens e desvantagens dos vários métodos, sumarizando as conclusões obtidas no Capítulo 3 relativas à variação dos métodos estudados com a velocidade da máquina, regime de carga e a severidade da carga, essencialmente. Por fim, são apontados quais os métodos que apresentam melhores características quanto ao diagnóstico de falha por desmagnetização dos ímanes permanentes para a máquina estudada, avaliação da tensão de neutros e os erros de predição de corrente.
The world is undergoing great change. There is currently a clear shift from an energy point of view. The growing bet on renewable energies, energy efficiency, electric mobility, amongst others means that innovation and development in these sectors are booming. Due to this, there is a symbiosis between industry and science. There are numerous publications in this area and this dissertation aims to add more knowledge in the field of electrical machines, namely multiphase permanent magnet machines. The main objective of the work carried out was to understand the state-of-the-art methods regarding diagnosing damage in the permanent magnets of permanent magnet multiphase machines and, based on simulations created for this purpose, to try to understand the possibility of creating new approaches regarding this malfunction. Chapter 1 mentions the framework and motivation that led us to carry out this dissertation, as well as the objectives outlined initially. Chapter 2 begins by addressing the types of malfunctions we can find in the machine's understudy, then referring to a general review of existing diagnostic methods, ending with a comparison between them based on various aspects. Chapter 3 begins with a complete description of the machine that we studied and what was the procedure adopted to carry out the different simulations and analyzes the different simulated states. Firstly, we describe the two faults that we induced in the machine, the demagnetization of a set of magnets from a pole and its entirety, referring to the method used to create both. In a second phase, four signals are studied: stator voltage, the voltage between neutrals, i_dq current, chained flux, and current prediction errors. Chapter 4 concludes this work, listing the advantages and disadvantages of the different methods, summarizing the conclusions obtained in Chapter 3 regarding the variation of the studied methods with the machine speed, load regime, and failure severity. Finally, it is pointed out which methods have the best characteristics regarding the fault diagnosis by demagnetization of the permanent magnets for the studied machine, evaluation of the neutral voltage, and current prediction errors.