Synchronous reluctance motors with fractional slot-concentrated windings

PhD ThesisToday, high efficiency and high torque density electrical machines are a growing research interest and machines that contain no permanent magnet material are increasingly sought. Despite the lack of interest over the last twenty years, the permanent magnet-free synchronous reluctance machine is undergoing a revival and has become a research focus due to its magnet-free construction, high efficiency and robustness. They are now considered a potential future technology for future industrial variable speed drive applications and even electric vehicles. This thesis presents for the first time a synchronous reluctance motor with fractional slot-concentrated windings, utilizing non-overlapping single tooth wound coils, for high efficiency and high torque density permanent magnet-free electric drives. It presents all stages of the design and validation process from the initial concept stage through the design of such a machine, to the test and validation of a constructed prototype motor. The prototype machine utilizes a segmented stator core back iron arrangement for ease of winding and facilitating high slot fill factors. The conventional synchronous reluctance motor topology utilizes distributed winding systems with a large number of stator slots, presenting some limitations and challenges when considering high efficiency, high torque density electrical machines with low cost. This thesis aims to present an advancement in synchronous reluctance technology by identifying limitations and improving the design of synchronous reluctance motors through development of a novel machine topology. With the presented novel fractional slot concentrated winding machine design, additional challenges such as high torque ripple and low power factor arise, they are explored and analysed - the design modified to minimise any unwanted parasitic effects. The electrical and electromagnetic characteristics of the developed machine are also explored and compared with that of a conventional machine. A novel FEA post-processing technique is developed to analyse individual air-gap field harmonic torque contributions and the machines dq theory also modified in order to account for additional effects. The developed machine is found to be lower cost, lower mass and higher efficiency than an equivalent induction or conventional synchronous reluctance motor, but does suffer higher torque ripples and lower power factor. The prototype is validated using static and dynamic testing with the results showing a good match with finite element predictions. The work contained within this thesis can be considered as a first step to developing commercial technology based on the concept for variable speed drive applications.Financial assistance was provided by was provided by the UK Engineering and Physical Sciences Research Council (EPSRC) in the form of a Doctoral Training Award and additional financial assistance was kindly provided by Cummins Generator Technologies, Stamford, UK, through industrial sponsorship of this wor

SRM drives for electric traction

"GAECE" -- PortadaDescripció del recurs: 11 maig 2020GAECE (Grup d’accionaments elèctrics amb commutació electrònica). The group of electronically commutated electrical drives is a research team of Universitat Politècnica de Catalunya (UPC BARCELONATECH), which conducts investigation in four areas: electrical drives, power electronics, mechanics and energy and sustainability. Regarding electrical drives, research focuses on the development of new reluctance, permanent magnet and hybrid electrical drives. The main goal of those electrical drives is the integration of the power converter/controller and the mechanical transmission, being specially intended for the traction of light electric vehicles. That research is carried out by using the analysis of finite elements, taking into account eco-design criteria, considering new materials and new control strategies.First editio

Flux switching machines using segmental rotors

Flux switching machines (FSM) employing a segmental rotor have field and armature systems on the stator and a presentation of an unexcited rotor with isolated segments. The single-tooth winding arrangement on the stator provides a potential for material and energy savings. The principle for producing bipolar flux in the armature stator teeth relies on the natural switching of the armature tooth flux, accomplished by the moving segments of the rotor. Three phase configurations have been studied, from conception and design to construction and testing, with field excitation provided by either a field winding or permanent magnets (PM). Flux switching machines have shown characteristics that are peculiar when employing a segmental rotor, significantly affecting the symmetry of the induced armature EMF waveform and parity of magnitudes of the positive and negative torques. For three phase operation, six topologies are feasible when employing a 12-tooth stator and two other topologies may be produced on a 24-tooth stator. An optimum topology on the 12/8-configuration and another proof-of-principle topology on the 12/5-configuration, using field-windings and permanent-magnets, have been designed and constructed, while applying modern practices and considerations for manufacture. The characteristics of FSMs employing a segmental rotor, initially predicted by finiteelement (FE) modelling, have been verified by measurements. The FSM employing a field-winding is found to have a specific torque output which is similar to the conventional switched reluctance motor and still substantially higher than that of the synchronous reluctance motor. Although the PM adaptation of the FSM produces specific torque output which is nearly twice that of the wound-field FSM and about 64% that of an equivalent permanent-magnet synchronous motor (PMSM) with surface or insert magnets, accounting for the usage of the magnets reflects its specific torque output to be about 1.48 times higher than the PMSM. Although the FSM is operated as an AC machine with sinusoidal three-phase currents, its dq-equivalent representation shows significant differences from that of the conventional AC machine. In the prediction of the performance, it is found, in both the wound-field and PM configurations, that the dq model is more dependable if the coupling dq inductance is taken into account.EThOS - Electronic Theses Online ServiceCommonwealth Scholarship Commission of UKGBUnited Kingdo

Analysis, design optimisation and experimental performance of synchronous reluctance and permanent magnet assisted synchronous reluctance machines

The research studies, in detail, the synchronous reluctance machine (SynRM) and permanent magnet assisted synchronous reluctance machine (PMSynRM) to improve the machine performances. In this study, the SynRM analytical models are revisited, and functional characteristics are mathematically developed to improve the machine performance. The performance parameters such as torque density, power factor, and efficiency are investigated along with torque ripples. SynRM is known for its high torque density in a compact size. Its improvement is analytically studied further by optimising rotor properties. The power factor of these machines is rather low compared with its equivalent AC machines. Although the machine’s power factor can be improved using control techniques, it is still not high enough. The machine has gone through significant development over the years since J.K Kostko published the first paper on reluctance machines back in 1923. The researchers have tested various types of anisotropies, such as axially laminated and transversally laminated. The machine torque and power factor depend on its saliency ratio. Although the axially laminated structure offers high saliency ratio due to the naturally distributed flux barrier structure, it has mechanical constraints. The axial rotor segments are fixed together by specially designed bolts that are conductive material in nature. This mechanical arrangement increases quadrature axis inductance, consequently reduces the saliency ratio of the machine. On the other hand, the transversally laminated structure is more mechanically feasible and offers comparatively high performance. One of the primary focus of this study is to improve the power factor. It has been comprehensively investigated. The SynRM machine is also known for high torque ripples. The non-linear structure and its reluctance path along the air-gap make the machine highly susceptible to torque pulsation. The cross induction due to the D and Q axis along the air-gap increases the machine’s ripples. Besides, poor stator winding (both sinusoidal and step excitation) also increases the machine torque ripples. The existing ripple reduction practices are revisited in this study to further understand the torque ripples of this machine. The rotor of SynRM is redesigned and optimised to reduce the ripples effect. The causes of ripples are also analytically studied in detail, and mathematical models are developed and presented for understanding the phenomena. Two different ways of analysing the ripple effects are considered, and the pros and cons of both methods are discussed. The SynRM is simulated using an advanced finite element analysis (FEM) software to verify the analytical models as well as optimise the machine performance. Firstly, primitive rotor structures are developed so that they can be automatically varied during parameterisation and optimisation. Four flux barrier shapes are analysed to determine the optimum shape for high performance by investigating flux’s natural path. From the results, a multi-barrier arrangement is studied with an advanced algorithm for three and four-layer designs, and an optimum rotor is proposed based on the simulations. Using a single-objective and multi-objective optimisation techniques, the SynRM is optimised from the simulated design. An advanced topology is developed for automated optimisation that can offer flexibility in varying optimisation variables as part of this research. The optimised design’s performance is analysed in detail and compared with analytical models. The torque ripples are discussed in detail, and an advanced torque ripple minimisation topology is developed. Then the design is optimised for two types of barrier shapes. A number of designs are prototyped for experimental verification. Finally, the current trend in rare-earth magnets is investigated with its cost per volume ratio. The rare-earth neodymium magnets are focused on this study for improved performance with optimum volume. The analytical model of PM assisted design is studied in detail, and its performance parameters are compared with SynRM. A PMSynRM with a linear-barrier is simulated for a detailed analysis of the machine that discusses different PM volumes and the impact on machine performance due to the volume of PM and location. The performance parameters, discussed in the analytical model, are compared with the simulation results. The improvement in power factor and torque density is investigated using various designs. The optimisation is performed in two ways. The first one is adding PMs to the optimised SynRM. Single-objective and multi-objective optimisation are performed using an advanced optimisation algorithm. Secondly, the topology of SynRM is modified for PMSynRM in such a way the entire machine can be automated during optimisation by adding the PM’s variables to the existing one. The performances of the two optimised designs have been compared. PMSynRM prototypes are developed to verify the simulation results. The eight SynRM designs are prototyped to report the practical results. Six of them are to verify various performance parameters of SynRM and two of them to test the ripples effect. Moreover, two PMSynRM prototypes are fabricated to verify the simulation results. The saliency of each SynRM is measured and compared with simulated results. Then, each design is tested experimentally in all possible scenarios and compared. Extensive testing is performed on all prototypes under various operating conditions and reported

Design and control of a synchronous reluctance machine drive

This thesis investigates the design, performance and control of a synchronous reluctance machine (Synchrel) drive. The Synchrel machine is proposed for variable speed drives because of its advantages over other machines. The rotor has no cage winding, brushes or slip rings. The torque ripple levels are lower in the Synchrel machine than the switched reluctance machine as it operates from a standard sine wave supply. An axially laminated rotor was designed based on finite element analysis, with the aim of producing the same output power as obtained from an induction motor (M) with a similar stator. Using vector control, the developed torque is controlled by regulating the stator current vector. Two vector control schemes are used, maximum torque per ampere and constant current in the direct axis. The output torque characteristics of the machine have been confirmed by finite element analysis. Slotine's approach of sliding mode control is used for position control of the vector controlled synchronous reluctance machine. A comparison is undertaken between the performance of a fixed gain controller with two sliding mode controllers, for both the regulator and servo cases. Invariant performance is obtained using Slotine's sliding mode control approach, unlike with a fixed gain controller. Robustness to parameter variation is an important feature of this technique. This robustness can be achieved through the control law design, assuming parameter variation bounds are known. These improvements are demonstrated for variations in load inertia. Inductance ripple affects machine performance, for example decreasing output torque and increasing core losses. A state space model for the machine that incorporates this inductance effect, yields drive simulation results that agree with experimental results

Investigation of performance improvement of doubly salient synchronous reluctance machine with current harmonic injection

This thesis investigates some novel current harmonic injection methods to improve the electromagnetic performance of doubly salient synchronous reluctance machines (DS-SRMs). These machines will have different winding configurations, slot/pole number combinations and phase numbers. The theoretical analyses (both static and dynamic) are carried out based on Fourier Series analysis, and validated by 2-dimensional finite element method and also experiments using several prototype machines. Based on the analytical torque model in abc-axis frame, a powerful insight into the mechanism of torque generation of the DS-SRMs with pure sinewave current supply can be achieved. The electromagnetic torque (both magnitude and phase angle) produced by each order of inductance harmonic can be predicted, which allows us to obtain the dominant torque ripple components for such machines. Therefore, the appropriate current harmonic (3rd, 5th and 7th) can be injected to generate torque ripple components in order to compensate that produced by the fundamental current, and hence to achieve an overall reduced torque ripple. On the other hand, the average torque of the DS-SRMs can also be improved by properly selecting the current harmonics in terms of harmonic order, amplitude and phase angle. However, it is found that the current harmonics, although can improve torque performance, will often cause extra losses (both copper and iron losses) and undesirable distortion in the phase voltages, which could lead to negative impact on the machine efficiency and dynamic performance. Therefore, in order to fully evaluate the potential of the proposed harmonic current injection method, comprehensive studies about losses, efficiency and dynamic performances such as torque-speed curves of 3-phase and multi-phase DS-SRMs have been carried out. In order to simplify the investigation of dynamic performance analyses such as the torque speed curves and efficiency maps, novel analytical torque model in dq0-axis frame has also been proposed. The findings in this thesis can provide some useful guidelines for torque performance improvement of DS-SRMs using harmonic current injections

Sizing, optimisation and thermal evaluation of an axial flux permanent magnet motor in comparison with a radial flux motor

LAUREA MAGISTRALEQuesto elaborato è basato su un'iniziativa del Piano Nazionale di Ripresa e Resilienza (PNRR). Il progetto triennale, di cui questa tesi costituisce il primo capitolo, è finalizzato a sviluppare prototipi di motori per applicazioni automobilistiche con l'obiettivo di promuovere la transizione verso i veicoli elettrici e migliorarne l'efficienza. Il focus del progetto è stato l'ottimizzazione dei parametri e la valutazione termica di un motore a flusso assiale con un confronto diretto con un motore a flusso radiale. Il primo passo fondamentale per questo progetto ha coinvolto lo sviluppo di un motore elettrico innovativo, in cui il flusso del campo magnetico è stato direzionato parallelamente all'asse di rotazione, ottenendo così una struttura chiamata a flusso assiale. Per la realizzazione efficiente di un prototipo, è stato implementato un algoritmo di minimizzazione delle "objective function" con vincoli, utilizzando MATLAB. I parametri sono stati successivamente validati attraverso una serie di fasi utilizzando software di analisi a elementi finiti. Per il modello del motore a flusso radiale, è stato utilizzato il software user-friendly Ansys MotorCAD, mentre per il modello a flusso assiale, più complesso, sono stati impiegati Ansys Maxwell e MotorXP-AFM. I risultati delle prestazioni di entrambi i motori sono stati comparati per identificare i rispettivi vantaggi e svantaggi. Per completare il progetto, è stata condotta un'analisi termica approfondita dei due motori. Per il motore a flusso radiale, è stato progettato un involucro alettato, poiché le sue dimensioni maggiori permettono una dissipazione termica più efficiente senza la necessità di raffreddamento a liquido. Per il motore a flusso assiale, invece, data la sua compattezza e le elevate prestazioni, è stata proposta una soluzione di raffreddamento a liquido a fronte della potenziale generazione di temperature elevate a lungo termine. In entrambi i casi i risultati sono stati validati: utilizzando Ansys MotorCAD per il motore a flusso radiale e Ansys Fluent per il motore a flusso assiale. Questa ricerca contribuisce alla conoscenza nel campo della progettazione di motori elettrici per veicoli, offrendo un'analisi dettagliata e comparativa tra i motori a flusso radiale e assiale, con particolare attenzione alla dimensione, all'efficienza termica e alle prestazioni. Il valore aggiunto di questo lavoro risiede nella progettazione e validazione di motori innovativi, nonché nell'ottimizzazione delle soluzioni di raffreddamento, fornendo dati preziosi per il futuro sviluppo di veicoli elettrici più efficienti e sostenibili.This work is based on an initiative of the National Recovery and Resilience Plan (PNRR). The three-year project, of which this thesis constitutes the first chapter, aims to develop prototypes of engines for automotive applications with the goal of promoting the transition to electric vehicles and improving their efficiency. The project focus was on optimising parameters and thermal evaluation of an axial flux motor with a direct comparison to a radial flux motor. The first fundamental step for this project involved the development of an innovative electric motor, in which the magnetic field flow was directed parallel to the axis of rotation, resulting in a structure called axial flux motor. For the efficient realisation of a prototype, an "objective function" minimisation algorithm with constraints was implemented using MATLAB. The parameters were subsequently validated through a series of phases using finite element analysis software. For the radial flux motor model, the user-friendly software Ansys MotorCAD was used, while for the more complex axial flux model, Ansys Maxwell and MotorXP-AFM were employed. The performance results of both motors were compared to identify their respective advantages and disadvantages. To complete the project, a comprehensive thermal analysis of the two motors was conducted. For the radial flux motor, a finned enclosure was designed, as its larger dimensions allow for more efficient thermal dissipation without the need for liquid cooling. For the axial flux motor, given its compactness and high performance, a liquid cooling solution was proposed due to the potential generation of elevated temperatures over the long term. In both cases the results were validated: using Ansys MotorCAD for the radial flux motor and Ansys Fluent for the axial flux motor. This research contributes to knowledge in the field of electric motor design for vehicles by providing a detailed and comparative analysis between radial and axial flux motors, with a focus on size, thermal efficiency, and performance. The added value of this work lies in the design and validation of innovative motors, as well as the optimisation of cooling solutions, providing valuable data for the future development of more efficient and sustainable electric vehicles

Investigation of Doubly Salient Stator Slot Permanent Magnet Machines

Variable flux reluctance machines (VFRMs), which have both field and armature windings on the stator, are novel types of magnetless machines with a simple and robust mechanical structure and a low manufacturing cost. However, their electromagnetic performance, especially their overloading capability, is limited by high magnetic saturation due to field excitation. Therefore, circumferentially magnetized permanent magnets (PMs) are placed in the stator slot openings in order to (a) alleviate the magnetic saturation and (b) increase the torque capability based on VFRM, which leads to novel machine topologies, i.e. hybrid excited stator slot PM machines (HESSPMs) and stator slot PM machines (SSPMs). The effects of PMs in the stator slot openings are comparatively investigated for VFRMs, HESSPMs and SSPMs together with the discussion of the unique fault tolerant feature in stator slot PM machines. Furthermore, the overlapping winding (OW) layouts with coil pitches of 3 stator slot pitches are proposed in the three machine topologies in order to enhance the torque density. The electromagnetic performance of each machine topology, with OW and non-overlapping winding (NOW) and various feasible stator slot/rotor pole number combinations, is comparatively studied by finite element method. It shows that the proposed OW layout can improve the average torque of VFRM, HESSPM and SSPM with the optimal stator/rotor pole number combination. The proposed OW layout will be more competitive for the machines with a longer axial length and reduced end-effect. Prototype machines for these three machine topologies with both NOW and OW are built and tested to validate the finite element predicted results

Segmental rotor switched reluctance machines for use in automotive traction

PhD ThesisThis thesis explores the development of the Segmental Rotor Switched Reluctance Machine (SRM) to provide electric vehicle traction. This electrical machine, which has a topology distinct from the conventional SRM and has been previously shown to offer enhanced torque density, is selected based on its potential to offer a low cost, sustainable alternative to today’s state-of-the-art electric vehicle traction motors. With the launch, as long ago as 1997, of the Toyota Prius Hybrid Electric Vehicle and of the more recent Nissan Leaf Electric Vehicle in 2010, volume produced vehicle traction drives are an established reality. However hurdles remain in order to reduce the cost of electric and hybrid electric vehicles so that they become cost-competitive with more conventional vehicles. From an electrical machine perspective, one clear cost driver stands out; the rare-earth metals which form the key ingredient in today’s class leading electrical machines. These materials are both expensive (>100USD/kg) and, as was seen in 2011 / 2012, subject to significant price volatility. Equally the mining and refinement of rare-earth materials, such as Neodymium, Dysprosium and Samarium, has been shown to have a much higher environmental footprint than that of the other materials typically used in electrical machines. Beyond the elimination of rare-earths, the thesis looks to further improve the sustainability and cost of the Segmental Rotor SRM. Copper conductors, expensive and difficult to recycle at an electrical machine’s end-of-life, are replaced by more easily recycled aluminium. Aluminium windings are compressed, prior to assembly with the electrical machine, in order to achieve very high fill factors to overcome their relatively low electrical conductivity. Methods are also sought to reduce overall material waste and simplify assembly processes; these include computer based optimisation of the motor structure along with the use of modular manufacturing techniques. With the Nissan Leaf’s Neodymium Iron Boron based Interior Permanent Magnet machine selected as a comparator, an 80kW Segmental Rotor SRM is constructed and tested. The design is shown to have promise and a number of industrially funded follow-on projects are now underway in order to develop the technology further for use in a volume electric vehicle application