Efficient Methods for the Study of Eddy-Currents Effects in Medium-Voltage Rotating Electrical Machines

Lo scopo di questa tesi \ue8 presentare alcuni metodi efficienti (dal punto di vista computazionale) per il calcolo degli effetti dovuti alle correnti parassite (eddy currents) in macchine elettriche rotanti in media tensione. Due applicazioni in particolare sono state considerate nel dettaglio. Inizialmente viene analizzato il fenomeno delle correnti parassite indotte nell'albero di motori asincroni a due poli e il conseguente effetto sulle prestazioni della macchina, focalizzandosi in particolare sul fattore di potenza. La seconda parte della tesi concentra la sua attenzione sullo studio dell'avviamento da rete di motori sincroni con rotore massiccio. Per ciascuna applicazione vengono introdotte alcune procedure di calcolo, facenti uso di opportuni modelli numerici basati sul metodo degli elementi finiti, per mezzo delle quali vengono adeguatamente calcolati i parametri dei circuiti equivalenti di macchina, tenendo conto degli effetti legati alle correnti parassite. I modelli numerici sono opportunamente definiti, in modo tale da ridurre al massimo la complessit\ue0 delle geometrie e il conseguente onere computazionale. I risultati delle procedure innovative qui proposte sono confrontati con i dati provenienti da prove sperimentali sulle macchine oggetto di studio e con analoghi risultati di calcolo dedotti tramite le procedure comunemente utilizzate. Il confronto fra questi dati ha dimostrato che gli approcci di calcolo introdotti in questa tesi permettono di ottenere risultati con un elevato livello di accuratezza e una netta riduzione dell'onere computazionale.The efficient computation of eddy-current effects in medium voltage electric machines is discussed in this dissertation. Two particular cases are considered. Firstly, the effects of shaft eddy-currents on two-pole induction motor performance is addressed, with special focus on the power factor. In the second part of the thesis the start-up calculation of a large synchronous motor with solid rotor is analyzed. For each application a special calculation procedure is introduced. These procedures adopt a set of suitable finite-element models to properly compute the machine equivalent circuit parameters that are mainly influenced by eddy-current-related phenomena. By suitably choosing finite-element models boundary conditions and excitations their geometry is simplified to the maximum possible extent, in order to reduce the computational burden. The results of the new calculation methods are compared with experimental data and with analogous results obtained from commonly-adopted calculation procedures. The comparison proves that the proposed approaches can lead to high accuracy levels with very remarkable computational savings

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

The integration of input filters in electrical drives

PhD ThesisThe integration of passive components such as inductors and capacitors has gained significant popularity in integrated drive research, and future power electronics systems will require more integrated and standardised packages. These give rise to better power density and improved performance. However, packaging techniques and passive components have been considered a technological barrier which is limiting advances in power electronics. The focus on size reduction should be turned towards the passive components, such as converter chokes, DC-link capacitors and electromagnetic interference (EMI) filters, and achieving greater power density depends on innovative integration concepts, flexibility in structures and extended operating temperature ranges while system integration and modularity are not mutually exclusive. This research considers the possibility of integrating input power filter components into electric machines. Particular attention is paid to the integration of electromagnetic line filter inductors to give better utilisation of the motor volume and envelope. This can be achieved by sharing the machine’s magnetic circuit. An LCL line filter has been chosen to be integrated with a gridconnected permanent magnet synchronous machine. Machines have been proposed in this study for low speed (3000 RPM) and high speed (25000 RPM) operation. The two machines have similar dimensions, but the low-speed machine is less challenging in terms of losses and filter integration, so attention is directed more to the high-speed machine. Both are supplied with low- and high-power drives at power ratings of 4.5 kW and 38 kW respectively. Several novel techniques have been investigated to integrate filter inductors into the electrical machines to produce a single mechanically packaged unit without significant increases in size and losses. Different approaches have been simulated using finite element analysis (FEA) to assess the effectiveness of the integration of passives within the machine structure. Each design has been iteratively optimised to determine the best mass of copper and core for the integrated filter inductors, targeting parity in power density when compared to traditional separate packages. The research demonstrates that an approach utilising a double-slot stator machine (named the integrated double slot (IDS) machine) with input filters wound into the outermost slots is the most appropriate choice in terms of achieving higher power density. The integrated filter inductors mimic the electromagnetic behaviour of the discrete industrially packaged inductors but with a volume reduction of 87.6%. A prototype of the IDS machine design of a 38 kW, 25000 RPM, including filter inductors was manufactured and testedthe General Electricity Company of Libya (GECOL), the Engineering and Physical Sciences Research Council (EPSRC), and the Engineering Doctorate scheme at Newcastle University

Conceptual design study of a nuclear Brayton turboalternator-compressor

A comprehensive analysis and conceptual design study of the turboalternator-compressor components using HeXe as the working fluid was performed. The study was conducted in three phases: general configuration analysis (Phase 1), design variations (Phase 2), and conceptual design study (Phase 3). During the Phase 1 analysis, individual turbine, alternator, compressor, and bearing and seal designs were evaluated. Six turboalternator-compressor (TAC) configurations were completed. Phase 2 consisted of evaluating one selected Phase 1 TAC configuration to calculate its performance when operating under new cycle conditions, namely, one higher and one lower turbine inlet temperature and one case with krypton as the working fluid. Based on the Phase 1 and 2 results, a TAC configuration that incorporated a radial compressor, a radial turbine, a Lundell alternator, and gas bearings was selected. During Phase 3 a new layout of the TAC was prepared that reflects the cycle state points necessary to accommodate a zirconium hydride moderated reactor and a 400 Hz alternator. The final TAC design rotates at 24,000 rpm and produces 160 kWe, 480 V, 3-phase, 400 hertz power

Potassium Turboalternator /KTA/ preliminary design study. Volume 2 - Alternator parametric design

Potassium turboalternator design study - alternator parametric desig

Fluid bearing spindles for data storage devices

Ph.DDOCTOR OF PHILOSOPH

Fabrication and test of a space power boiler feed electromagnetic pump. Part 1: Design and manufacture of pump

A three-phase helical induction electromagnetic (EM) pump has been designed and built. This pump was designed for use as the boiler-feed pump of a potassium Rankine-cycle space electric power system. The pump is constructed of high temperature materials including a T-111 duct, Hiperco 27 magnetic material, nickel clad silver conductor wire, and a completely inorganic insulation system. The pump is designed to deliver 3.25 lb/sec potassium at 1000 F with a developed head of 240 psi while being cooled by 800 F NaK. At these conditions, the overall pump efficiency is expected to be 18%

Potassium Turboalternator /KTA/ preliminary design study. Volume 3 - Phase 2 KTA final design

Potassium turboalternator design study - final desig