Dissertations / Theses on the topic 'High inductions'

The efficiency of electrical machines carries a global impact because they fulfill about three-quarters of global electrical energy consumption. Its improvement requires a sound knowledge of energy loss properties of magnetic materials used in the core of electrical machines, especially non-conventional supply conditions, such as non-sinusoidal, high induction, alternating (1-D) and rotating (2-D) flux waveforms that have been posed with the incorporation of new electronic devices and materials in the systems. For these reasons, novel theoretical models and experimental techniques need to be developed to obtain the loss behavior under these complex flux regimes. To address these issues, experimental investigation and theoretical analysis have been carried out in this thesis on different magnetic materials and a wide ensemble of supply conditions. The aim of the theoretical analysis was to fill the gap between the physicists and the engineers by developing simple models that can be applied to compute the loss under realistic supply conditions. This theoretical frame is rooted in the physical principle of the separation of loss and the Statistical Theory of Loss (STL) by which the loss can be separated into the hysteresis, classical, and excess components. The concept of loss separation has been exploited under 1-D flux and extended to 2-D fluxes, where the relations between alternating and rotational losses have been obtained on a number of different materials, this analysis restricted to the region not influenced by skin effect. The proposed theoretical models have been tested by comparing loss figure of different magnetic materials over a wide range of frequencies, induction levels, and conventional or non-conventional supply conditions. To this purpose, loss characterization of non-oriented Fe-(3.2wt \%)Si steels have been performed using a three phase magnetizer able to generate 1-D and 2-D flux patterns, up to saturation magnetization. Fieldmetric and Thermometric methods have been applied at low and very high induction levels. Loss characterization of other non-oriented Fe-Si and low carbon steels have also been performed under 1-D flux at very low and high sinusoidal inductions using Epstein frame, single sheet tester or ring samples, over frequencies ranging from quasi-static conditions up to 10 kHz. Systematic uncertainties have been observed in measurements using a Single Sheet Tester due to MMF drop in flux closing yoke and a compensated Permeameter has been designed to reduce these uncertainties by compensating the MMF drop in the flux closing yoke.

With our newly proposed dynamical Higgs mechanism and Quantum Induction programme, Higgs mass is predicted at M(H) ≈ 190 GeV by using our modified renormalization group equations. The same procedure also explains the top quark mass correctly.

Within this thesis the principle and application of induction heating will be introduced and the synthesis of magnetic materials, specifically ferrite type materials, via sol-gel methods reported. It is shown that the optimized ferrites demonstrated both excellent catalytic and induction heating properties which can be applied to various reactions. The reaction range can even be extended if magnetic materials are coated with other catalytically active components. Another possible solution which is discussed is the combination of induction heating of bulk metal materials which have been physically blended with an active catalyst. These inductively heated particles then transfer the reaction heat to the surrounding catalyst particles thereby assisting the reaction. The main example used is the oxidative ethylbenzene dehydrogenation reaction. This has been intensively studied over past number of decades as styrene is one of the most useful intermediate compounds for organic synthesis. The combination of induction heating with catalytically active magnetic materials will be introduced here and compared to traditional thermal heating. It will be shown that less deactivation was obtained under induction heating when using CoFe2O4 as a dual functional catalyst. The thesis concludes with an overall discussion and some personal views on potential future directions for this work.

CIVINS
CIVINS
One of the reasons linear motors, a technology nearly a century old, have not been adopted for a large number of linear motion applications is that they have historically had poor efficiencies. This has restricted the progress of linear motor development. The concept of a linear motor as a rotary motor cut and laid out flat with a conventional rotary motor control scheme as a design basis may not be the best way to design and control a high-speed linear motor. End effects and other geometry subtleties of a linear motor make it unique, and a means of optimizing efficiency with both the motor geometry and the motor control scheme will be analyzed to create a High-Speed Linear Induction Motor (LIM) with a higher efficiency than what is possible with conventional motors and controls. This thesis pursues the modeling of a short secondary type Double-Sided Linear Induction Motor (DSLIM) that is proposed for use as an Electromagnetic Aircraft Launch System (EMALS) aboard the CVN-2 1. Mathematical models for the prediction of effects that are peculiar to DSLIM are formulated, and their overall effects on the performance of the proposed machine are analyzed.;3 |a(cont.) These effects are used to generate a transient motor model, which is then driven by a motor controller that is specifically designed to the characteristics of the proposed DSLIM. Due to this DSLIM's role as a linear accelerator, the overall efficiency of the DSLIM will be judged by the kinetic energy of the launched projectile versus the total electric energy that the machine consumes. This thesis is meant to propose a maximum possible efficiency for a DSLIM in this type of role.

Electric vehicles are a key technology in the reduction of our carbon footprint and this has motivated significant research interest. The electrical traction motor is one of the main areas of research in attempts to further improve electric vehicle performance. The permanent magnet motor is the predominant device in this application because of its high specific torque. However, it has suffered from market speculation in the raw magnet materials which has generated efforts to develop electrical machines which have a high specific torque and do not contain rare earth materials. In the past the induction motor used to be the preferred motor for electric vehicles due to its low costs, low maintenance requirements, mature technology and robustness. The induction motor requires a higher specific torque to make it an alternative to permanent magnet machines. For this reason, this research had the primary aim of improving the specific torque of induction machines by undertaking a detailed review of the motor design because this process has conventionally focussed on the requirements for industrial applications. The first stage of the work presented in this thesis consisted of identifying the designs already in use for this purpose and the potential technologies applicable to the induction motor that could be transferred from other electric traction machines. A full review of the design process was also conducted in order to identify the key areas of the process with special reference to the electromagnetic design which used finite element techniques as the main modelling tool. New induction motor designs were developed which showed potential for improving the specific torque; two of these were selected for further refinement, prototyping and testing. Although these designs were modified to facilitate construction, some major difficulties were still encountered during the prototype rotor manufacture. The test results were used to validate the design process and to identify further improvements in the designs. The issues encountered with the rotor manufacture prototype however lead to some overheating during the experimental testing. Comments about the design experience gained during this research are summarized including suggestions for further research.

The fields of nanomaterial and nanostructures are some of the fastest growing fields in material science today. Carbon nanotubes are at the forefront of these fields and their unique mechanical and electrical properties are of great interest to those working in multiple engineering fields. The overall objective of this study was to design and develop a new process and the equipment necessary, to synthesize carbon nanotubes using high voltage and a high-frequency induction field. This was the first time that a high voltage and an induction field have been used simultaneously in high yield production of carbon nanotubes. The source of carbon came from acetylene with cobalt used as the doping agent. The carbon was molded into carbon nanotubes by the high-voltage field. The carbon nanotubes were characterized using electron microscope techniques. Raman spectroscopy was also used to reveal the defects and graphitic structures of the carbon nanotubes.

The aim of this research project was to develop a vector controlled induction motor drive operating without a speed or position sensor but having a dynamic performance comparable to a sensored vector drive. The methodology was to detect the motor speed from the machine rotor slot harmonics using digital signal processing and to use this signal to tune a speed estimator and thus reduce or eliminate the estimator’s sensitivity to parameter variations. Derivation of a speed signal from the rotor slot harmonics using a Discrete Fourier Transform-based algorithm has yielded highly accurate and robust speed signals above machine frequencies of about 2 Hz and independent of machine loads. The detection, which has been carried out using an Intel i860 processor in parallel with the main vector controller, has been found to give predictable and consistent results duing speed transient conditions. The speed signal obtained from the rotor slot harmonics has been used to tune a Model Reference Adaptive speed and flux observer, with the resulting sensorless drive operating to steady state speed accuracies down to 0.02 rpm above 2 Hz (i.e. 60 rpm for the 4 pole machine). A significant aspect of the research has been the mathematical derivation of the speed bandwidth limitations for both sensored and sensorless drives, thus allowing for quantitative comparison of their dynamic performance. It has been found that the speed bandwidth limitation for sensorless drives depends on the accuracy to which the machine parameters are known and that for maximum dynamic performance it is necessary to tune the flux and speed estimator against variations in stator resistance in addition to the tuning mechanism deriving from the DFT speed detector. New dynamic stator resistance tuning algorithms have been implemented. The resulting sensorless drive has been found to have a speed bandwidth equivalent to sensored drives fitted with medium resolution encoders (i.e. about 500 ppr), and a zero speed accuracy of ± 8 rpm under speed control. These specifications are superior to any reported in the research literature.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.
Includes bibliographical references (leaves 97-99).
This project investigates the use of a high speed, squirrel cage induction generator and power converter for producing DC electrical power onboard ships and submarines. Potential advantages of high speed induction generators include smaller size and weight, increased durability, and decreased cost and maintenance. Unfortunately, induction generators require a "supply of reactive power" to run and suffer from variation in output voltage and frequency with any changes to the input reactive power excitation, mechanical drive speed, and load. A power converter can resolve some of these issues by circulating the changing reactive power demanded by the generator while simultaneously controlling the stator frequency to adjust the machine slip and manage the real output power. This combination of real and reactive power control will ensure a constant voltage DC bus over the full load range. Tests were performed on a three horsepower motor to help validate models and simulations at both the two kilowatt and 5 megawatt level. After determining the equivalent circuit of the demonstration motor, it was tested as a generator under grid connected and capacitor excited conditions. A stand-alone five megawatt, 12,000 RPM generator designed specifically to operate at high efficiency and power factor over the full load rang was used to design converter parameters. A variety of reactive power excitation strategies were briefly examined before the flow of reactive currents through a converter was explained using a six step inverter with two different switching schemes.
(cont.) Steady state and transient simulations matched the measured machine performance and illustrated the performance of the control strategy as the load changes. Keywords: induction generator, self-excitation, reactive power, power converter, rectifier.
by Steven Carl Englebretson.
S.M.

Attribute-Oriented Induction of High-level Emerging Pattern(AOI-HEP) is a combination of Attribute Oriented Induction (AOI) and Emerging Patterns (EP). AOI is a summarisation algorithm that compact a given dataset into small conceptual descriptions, where each attribute has a defined concept hierarchy. This presents patterns are easily readable and understandable. Emerging patterns are patterns discovered between two datasets and between two time periods such that patterns found in the first dataset have either grown (or reduced) in size, totally disappeared or new ones have emerged. AOI-HEP is not influenced by border-based algorithm like in EP mining algorithms. It is desirable therefore that we obtain summarised emerging patterns between two datasets. We propose High-level Emerging Pattern (HEP) algorithm. The main purpose of combining AOI and EP is to use the typical strength of AOI and EP to extract important high-level emerging patterns from data. The AOI characteristic rule algorithm was run twice with two input datasets,to create two rulesets which are then processed with the HEP algorithm. Firstly, the HEP algorithm starts with cartesian product between two rulesets which eliminates rules in rulesets by computing similarity metric (a categorization of attribute comparisons). Secondly, the output rules between two rulesets from the metric similarity are discriminated by computing a growth rate value to find ratio of supports between rules from two rulesets. The categorization of attribute comparisons is based on similarity hierarchy level. The categorisation of attributes was found to be with three options in how they subsume each other. These were Total Subsumption HEP (TSHEP), Subsumption Overlapping HEP (SOHEP) and Total Overlapping HEP (TOHEP) patterns. Meanwhile, from certain similarity hierarchy level and values, we can mine frequent and similar patterns that create discriminant rules. We used four large real datasets from UCI machine learning repository and discovered valuable HEP patterns including strong discriminant rules, frequent and similar patterns. Moreover, the experiments showed that most datasets have SOHEP but not TSHEP and TOHEP and the most rarely found were TOHEP. Since AOI- iii HEP can strongly discriminate high-level data, assuredly AOI-HEP can be implemented to discriminate datasets such as finding bad and good customers for banking loan systems or credit card applicants etc. Moreover, AOI-HEP can be implemented to mine similar patterns, for instance, mining similar customer loan patterns etc.

Solid rotor induction machines are suitable for applications which require robustness, reliability and high rotational speed. A literature review of high speed technologies is initially presented. The current limitation and challenges are detailed based on a wide collection of data. The multi-physics aspect related with electrical machines for high speed applications are discussed providing a summary of the current state of the art. The main aim of the research was to develop a multi-physic computational environment for the design and analysis of solid rotor induction machines. The electromagnetic, thermal, structural and rotor dynamics models have been developed targeting reduced computational time and accurate predictions. Numerical techniques are proposed based on the discretisation of the computational domain. The different disciplines are linked together providing a flexible and powerful tool for the characterisation of solid rotor induction machine. Another objective was to investigate the impact of the rotor material on the electromagnetic performances of the machine. Finite Element simulation are used to account for the non linear magnetic properties. The impact on the equivalent circuit parameter is discussed and general criteria for material selection presented. Three dimensional finite element calculation are p erformed targeting the validation of the end region correction factor and select the rotor length. The performances of a 120 [kW]−25000 [rpm] solid rotor machine are compared with a caged rotor induction machine for waste heat recovery application.

Thesis (Ph. D.)--Illinois State University, 1990.
Title from title page screen, viewed November 21, 2005. Dissertation Committee: Patricia H. Klass (chair), Joseph H. Braun, Ronald L. Laymon, Mary Ann Lynn, Patricia O'Connell, Sally B. Pancrazio. Includes bibliographical references (leaves 122-128) and abstract. Also available in print.

Includes bibliographical references.
Advances in power electronic semiconductor technology are making high frequency converters for induction heating more feasible at power levels up to 50kW. This research presents the development and analysis of a solid-state induction-heating system, operating directly off single-phase mains frequency, which enables optimum and efficient operation over a frequency range of 80kHz to 200kHz. The system essentially comprises a DC-DC converter configured as a controlled current source, which feeds a load resonant DC-AC inverter, driving a parallel resonant load circuit. The load circuit comprises an induction-heating coil and a reactive power compensating capacitor. The systems active switching elements comprise power MOSFET's but can be extended to almost any other controlled power devices such as IGBT's, BJT's, SCR's, GTO's or SIT's. An automatic frequency control system ensures that the DC-AC inverter drives the load at its resonant frequency, thereby achieving zero voltage switching of the power semiconductors. This operating mode always ensures maximum power transfer to the load as well as maximum operating efficiency of the DC-AC inverter. Driving the load at resonance presents an essentially resistive load to the DC-DC converter, thereby reducing the losses associated with a reactive load. A compact circuit layout combined with this optimum mode of operation eliminates the need for any snubber circuit components in both the DC-DC and DC-AC converters at this power level. An overview into various applications and technologies of induction-heating is presented in this research. A detailed analysis of the induction-heating coil and work- piece are presented in order to aid the design of the load circuit. The induction-heating technology overview presents various induction-heating power sources, discussing the configurations of various topologies. A brief mathematical analysis is used to describe the operation of power electronic converters employed in the induction-heating system developed for this research. The parallel resonant induction-heating load circuit is characterised mathematically, allowing for the determination of the optimum operating conditions. This is followed by a simulation analysis, which is used to gain insight into the problem of frequency control. The frequency control system is modelled and the steady-state error response evaluated under different input conditions. Experimental results on the system implemented, based on operating waveforms and efficiency measurements of the solid-state induction-heating system are presented along with recommendations for future work. The implemented power source was tested at a maximum power of 2.3kW at 151kHz. A system efficiency of 86% at 1.3kW was measured when operating at 138kHz. This design however, provides for scaling to power levels up to 50kW. The induction-heating system's frequency tracking capability is evaluated by heating a steel work-piece through its Curie transition temperature. The induction-heating system is used to heat a 26mm x 35mm stainless-steel billet (work-piece) to 1200°C in 130 seconds using the calculated power of 1.35kW .

Induction heating has become a popular alternative to other heat sources for stovetop cooking applications due to performance, efficiency, control response, and safety. The main drawback is that extreme difficulty is encountered when trying to head low-resistivity, non-ferromagnetic metals such as aluminum and copper, which are commonly used for cookware in several societies. The lack of ferromagnetic properties, resulting in no hysteresis dissipation, and low resistivity of such metals results in an impractically low resistance reflected through the work coil. The resultant impedance complicates inverter design, as it is too low to be efficiently driven with conventional inverter topologies. The magnitudes of current involved in exciting this impedance also severely impact the efficiency of the coil and resonant components, requiring extreme care in coil design. This work explores various techniques that have been proposed and/or applied to efficiently heat low-resistivity cookware and the associated limitations. A transformer-coupled series-load-resonant topology driven by a full-bridge inverter is proposed as a means of efficiently heating aluminum cookware within practical design constraints. The experimental circuit is built and successfully tested at an output power of 1.66kW. The procedure of optimizing the work coil for improved efficiency is also presented along with the procedure of measuring coil efficiency. An improved circuit incorporating switch voltage detection to guarantee zero-voltage switching is then built in order to overcome limitations of this design.
Master of Science

The thesis discusses the development of closed loop system to control the DC voltage for 200 kW induction generator rated at a speed of 62000 RPM under different load conditions. The voltage regulation has been implemented using PI controller. A gain scheduling control algorithm has been developed to select the appropriate controller gains with respect to the generator load. Further, a relationship between the generator loads and the controller gains has been established. This relationship has been modeled using adaptive control technique to vary the gains automatically at any load condition. The adaptive control technique has been successfully generalized for real time DSP implementation to regulate the DC voltage for high speed induction generators rated from 5 kW to 200 kW.
M.S.
Department of Electrical and Computer Engineering
Engineering and Computer Science
Electrical Engineering

In education, mentoring is pivotal in the early development and long-term success and self-directed efficacy of new teachers. With increasing acknowledgment of the importance of mentoring as the preferred means of induction support for new teachers, mentors can serve to positively impact the overall quality of teaching and learning. Yet, like the induction protocols in other professional occupations, the nature of induction programs in education has taken a variety of forms in more recent years. For mentors, these experiences create added obligations and time away from their own professional responsibilities. Although previous research points to the importance of mentoring and its effectiveness in supporting novices, giving voice to the induction mentor as related to the most effective practices for high quality induction mentoring merits further investigation and an obligation to those who lead them.

The purpose of this study was therefore to contribute to the body of knowledge and literature pertaining to high quality mentoring experiences, specifically as related to the lived experiences and perceptions of effective practices for preparing, developing, and retaining K-12 teacher induction mentors. The participants in this study consisted of K-12 teacher induction mentors at a teacher induction program in Southern California. This study was made possible through the utilization of a phenomenological method, namely through a qualitative phone interview approach.

The findings led to the following five conclusions: (1) prior life and professional experience are pivotal to the manner in which situational learning is acquired and internalized, strongly influencing the way mentors engage in future action; (2) induction mentor preparation and support are crucial to the success of the mentor in their service to new teachers and in their own professional development as educators; (3) time is pivotal to the formulation of and reaping of quality induction experiences; (4) the value of required induction projects is key to the significance of the induction work; and (5) meaningful reflective practices are fundamental to the internal motivation and transformation of the mentor as a professional learner. Implications for policy and recommendations for additional research are discussed at the end of the study.

The aim of this research project was to develop a position controlled induction machine vector drive operating without a speed or position sensor but having a dynamic performance comparable to that of a sensored position vector drive. The methodology relies on the detection of a rotor saliency in the machine by persistent high-frequency voltage injection. The rotor position is then estimated from the resulting stator current harmonics that are modulated by the spatial rotor saliency. This can be a built-in rotor saliency (a designed asymmetry) or the natural saliency due to rotor slotting. This project investigates the demodulation of the extracted high-frequency current spectrum and different topologies for the estimation of rotor position. The tracking of rotor position through rotor saliencies helps to overcome the limitations of model-based approaches that are restricted to speeds above 30rpm on a 4-pole machine and are sensitive to parameter mismatches. The project addresses the difficult problem of separating the modulation effects due to the rotor saliency from distorting modulations due to the saturation saliency and inverter effects. In previous research it had been found that the saturation saliency causes a deterioration of the position estimate that can result in a loss of position and eventually causes the drive to fail. The application of filters to remove the interfering saturation harmonics is not possible. In this research a new approach was developed that compensates online for the saturation effect using pre-commissioned information about the machine. This harmonic compensation scheme was utilized for a 30kW, 4-pole induction machine with asymmetric rotor and enabled the operation from zero to full load and from standstill up to about ±150rpm (±5Hz). The steady-state performance and accuracy of the resulting sensorless drive has been found to operate similarly to a sensored drive fitted with a medium resolution encoder of 600ppr. The project involved studies of the inverter switching deadtime and its distorting effect on the position estimation. A second compensation strategy was therefore developed that is better suited if a large interfering modulation due to the inverter deadtime is present in the machine. The new compensation method was implemented for a second 30kW machine that utilizes the rotor slotting saliency. Good tracking results were obtained with a mean error of less than ±0.5° mechanical under steady-state. The derivation of the position signal for higher speeds introduces an additional speed-dependent error of about 4° mechanical at 170rpm. Sensorless position control was realized for operation from zero to full load for the fully fluxed machine. The performance allowed low and zero speed operation including position transients reaching a speed of 50rpm. The high-frequency modulation introduced by the fundamental currents during transient operation was examined and identified as the main factor limiting the dynamics of the sensorless drive. Two rigs were used for the research. The first rig is build around a network of Transputers, the second rig uses state-of-the-art TMS320C40 and TMS320F240 digital signal processors for the control and was designed and constructed as part of the research.

Induction Assisted Single Point Incremental Forming (IASPIF) is a die-less hot sheet metal forming. The IASPIF does not apply characteristic complex tooling like those applied in deep drawing and bending. In this thesis, induction heating was used to heat up the sheet while simultaneously forming with a tool. The research goal is to improve the formability of high strength steels by heating. The IASPIF consists of non-complicated set up that allows induction heating to be utilized through the coil inductor moved under the sheet and synchronized with the forming tool that moves on the upper side of the sheet. The advanced high strength steel alloys, DP980, DP600 and 22MnB5 steels, were investigated. The influence of induction heating on formability was evaluated by the maximum wall angle that can be achieved in a single pass. Additionally, tool diameter and tool feed rate was also varied. The most influencing parameters were tool feed rate, induction power, and the profile depth. A new forming strategy was also developed by control the heating temperature through coupling the formed profile depth with a successively increased tool feed rate. The forming forces of DP980 steel sheet, were reduced from 7 kN to 2.5 kN when forming process was performed at room and elevated temperature, respectively. Stretching stresses were developed during forming process causing a high reduction in the resulting wall part thickness. New findings in this investigation were the reverse relationship between the step-down depth and the thickness reduction percentage. The smaller the tool diameter, the better was the formability. The finite element simulation of the investigated forming process showed that the increase in heating temperature has a direct effect on rising the plastic strain from 0.2 at room temperature to 1.02 at 800 ◦ C. The maximum true strain achieved in the resulting wall part thickness was determined by FEM simulations and validated with experimental trials. The part shape accuracy was measured and the highest deflection was founded when the part was formed by the highest step-down depth. Moreover, the minimum deflection in the part shape was achieved by utilizing a high induction power in the experiments. Finally, the resulting mechanical properties of the 22MnB5 alloy sheet material were tailored during IASPIF. For this purpose, the sheets were locally heated by induction during the forming process and subsequently quenched at different rates. As a result, the produced tailored parts consist of three different regions, which consist of a ductile, transitional and hardened region. The proposed procedure allows forming and quenching at the same time without transfer and thus, process time was reduced.
Die induktionsgestützte, inkrementelle Blechumformung (englisch: Induction Assisted Single-Point Incremental Forming IASPIF) ist Warmumformprozess, bei dem keine komplexen Werkzeuge wie beim Tiefziehen und Biegen benötigt werden. Inhalt dieser Arbeit ist die inkrementelle Umformung eines Bleches mit gleichzeitig ablaufender induktiver Erwärmung. Das Forschungsziel bestand in der Verbesserung der Umformbarkeit von hochfesten Stahlwerkstoffen wie DP600, DP980 und 22MnB5 durch eine gezielte partielle Erwärmung. Der prinzipielle Aufbau des Versuchsstandes besteht aus einem Spuleninduktor, der unterhalb des umzuformenden Blechs platziert ist, und der synchron mit dem Werkzeug – einem Drückdorn – während des Umformvorganges verfährt. Ein wesentlicher Untersuchungsschwerpunkt bestand in der Ermittlung der Einflussgrößen auf den untersuchten IASPIF-Prozess. Für die Bewertung der Umformbarkeit wurden hierbei der maximal erreichbare Teilwandwinkel und die Profiltiefe, die in einem Umformdurchgang herstellbar waren, ermittelt und ausgewertet. Darüber hinaus konnten im Rahmen der Arbeit die Induktionsleistung des Generators, der Werkzeugdurchmesser und die Werkzeugvorschubgeschwindigkeit als relevante Prozessparameter identifiziert werden. Im Ergebnis der durchgeführten Untersuchungen zeigten die Werkzeugvorschubgeschwindigkeit und die Induktionsleistung einen wesentlichen Einfluss auf die erreichbare Profiltiefe. Aufbauend auf den erzielten Ergebnissen konnte eine prozessangepasste Umformstrategie entwickelt werden, bei der eine konstante Erwärmungstemperatur durch das Koppeln der momentanen Profiltiefe mit einer sukzessiv steigenden Werkzeugvorschubgeschwindigkeit erreicht wird. Weiterhin ließen sich die Kräfte bei der Umformung eines Stahlbleches aus DP980 von 7 kN (bei Raumtemperatur) auf 2,5 kN (bei erhöhter Temperatur) reduzieren. Aufgrund des mit einem Streckziehvorgang vergleichbaren Spannungszustandes während des Umformprozesses war eine starke Verringerung der resultierenden Wanddicke zu beobachten. Als neue Erkenntnis in dieser Untersuchung konnte die umgekehrte Beziehung zwischen der Zustelltiefe und dem Dickenreduktionsprozentsatz abgleitet werden. Aus der Finite - Elemente - Simulation des vorgestellten Umformprozesses wurde erkennbar, dass die Erhöhung der Erwärmungstemperatur einen direkten Einfluss auf die plastische Dehnung von 0,2 (bei Raumtemperatur) auf 1,02 (bei 800 °C) hat. Mittels der numerischen Simulation und der nachfolgenden experimentellen Validierung erfolgte darüber hinaus die Bestimmung der maximalen wahren Dehnung, die in der resultierenden Wanddicke erreicht wurde. Bei den Versuchen mit der größten Zustellung ließ sich durch die Bestimmung der Teileformgenauigkeit die höchste Abweichung von der Sollgeometrie CAD Modell feststellen. Abschließend wurde nachgewiesen, dass der IASPIF Prozess auch zur Einstellung maßgeschneiderter Bauteileigenschaften wie der resultierenden mechanischen Eigenschaften des Blechmaterials aus 22MnB5 einsetzbar ist. Zu diesem Zweck wurden die Bleche während des Umformprozesses lokal induktiv erwärmt und anschließend zur Einstellung des gewünschten Gefüges bei unterschiedlichen Abkühlgeschwindigkeiten abgeschreckt.

With the increasing use of aluminum in naval vessels and the ever-present danger of fires, it is important to have a good understanding of the behavior of aluminum at elevated temperatures. The aluminum samples 5083-H116 and 6061-T651 were examined under a variety of loading conditions and temperatures. Tensile testing was completed on both materials to measure strength properties of elastic modulus, yield strength, and ultimate strength as well as reduction of area from room temperature to 500 deg C taking measurements every 50 deg C. These tests showed how much the material weakened as temperature increases. Low temperatures had a minimal effect on strength while exposure to temperatures between 200 and 300 deg C had the most significant impact. Creep testing was also completed for these materials. These tests were completed at temperatures between 200 and 400 deg C in 50 deg C increments. Stresses for these tests were in the range of 13 to 160MPa for 5083 aluminum and between 13 to 220MPa for 6061 aluminum. These tests showed a significant relationship between stress and temperature and how changes to one can cause a very different resulting behavior. In addition to the creep testing, three creep models were examined as a means of predicting creep behavior. These models included a power law, exponential, and hyperbolic-sine versions and were able to predict creep results with decent accuracy depending on the stress used in the model.
Master of Science

Due to the increasing resistance demonstrated by insects to conventional insecticides, the need for compounds with novel modes of action is becoming more urgent. Also, the discovery and production of new insecticides is vital as regulations and restrictions on conventional insecticides become increasingly stringent (Casida and Quistad 1998). Research in this area requires screening of many candidate compounds which is costly and time-consuming. The goal of this research was to produce in vitro insect neurons from Sf21 insect ovarian cell lines, which could lead to new high throughput screening methods and a way to mass produce insect material for basic research. This study used a culture of Sf21 cells and a mixture of differentiation agents to produce viable neuron-like cells. In the presence of the molting hormone 20-hydroxyecdysone (20-HE), or insulin, in the growth medium, Sf21 cells began to express neuronal morphology, or the production of elongated, axon-like processes within 2-3 days. Maximal differentiation occurred when in the presence of 42 μM 20-HE or 10 μM insulin. Effects were maximal on day 2 for 20-E and day 3 for insulin. Insulin was more potent at day 2 for inducing differentiation (EC₅₀ = 247 nM) than 20-HE (EC₅₀ = 13 μM). In combination, 20-HE and insulin produced apparent synergistic effects on differentiation. Caffeine, a central nervous system (CNS) stimulant, inhibited induction of elongated processes by 20-HE and/or insulin. Caffeine was a potent inhibitor of 42 μM 20-HE, with an IC50 of 9 nM, and the inhibition was incomplete, resulting in about one quarter of the differentiated cells remaining, even at high concentrations (up to 1 mM). The ability to induce a neural phenotype simplifies studies with of insect cells, compared to either the use of primary nervous tissue or genetic engineering techniques. The presence of ion channels or receptors in the differentiated cells remains to be determined. If they are present, high throughput screening for new insecticides will be accelerated and made more economical by the utility of this method.
Master of Science

The objective of this dissertation is to analyse the performance of a linear induction motor suitable to drive a circular saw blade. A selection of analytical methods available from the field of electrical machine theory was used to investigate the particular type of motor. The theoretical analysis is supported by an extensive experimental investigation. Although LIMs have been designed, analyzed and applied in other applications, significant differences exist between those LIMs and the one used for the new application. These include: the annular shaped motor, the smaller air gap, and the rotor which is thin and made of steel. Because of these differences, the methods used by previous investigators were not sufficient to design the LIM required. The theoretical analysis used a selection of methods described in the literature to quantify the effect of the rotor material, the end effect and the edge effect. New methods are described to analyse the effect of the annular shape, the normal forces on the rotor and the coil connection. In addition, a new consideration in the optimisation of these type of motors is described. An extensive experimental program was undertaken. Six different linear motors were constructed with output powers ranging from one to fifty kWatts. In addition, inverters, dynamometers, flux measurement apparatus, speed measurement, thrust measurement and friction measurement apparatus were designed and constructed. The effects on performance of slot harmonics, winding connections, the end effect and the edge effect were measured. Several contributions to the field of electrical machine theory are presented. The first is a new annular disc motor resistivity correction factor. Second, is the analysis of the effects of poles in parallel versus in series in linear induction motors. Third, is the experimental comparison between odd and even pole designs. The fourth is a second optimum goodness consideration for LIMs, which had not previously been considered. The fifth is the analysis of the rotor/stator attractive force for magnetic rotor double sided motors and a description of the flux (crenelated flux) which causes the force. Finally, a criterion for when the re-entry effect may occur is presented.
Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate

To stay competitive in the steel industry, steelmakers are utilizing different production methods to reduce production cost without compromising on the quality of their products. In steelmaking, the production process plays a significant role on the steel cleanliness. Recent increasing demands on the cleanliness level therefore require optimization of production process to meet the requirement. Often, the types and distribution of non-metallic inclusions in steel determines the steel cleanliness. In order to optimize the production process, complete assessment of the non-metallic inclusions in the steel is necessary, leading to implementation of measures to control and/or remove non-metallic inclusions in the steel. The present study was performed to investigate the cleanliness level of steel bars produced from a high frequency induction furnace (HF) route at Uddeholms AB. Experimental studies were carried out and characteristics such as number, composition, size distribution and morphology of non-metallic inclusions were investigated. Total oxygen and total nitrogen content were also measured for indirect assessment. Further, the production operations at the HF were observed and evaluated to determine their influence on the inclusion characteristics. The characteristics obtained were compared with characteristics of inclusions in steel bars produced from an electric arc furnace production (EAF) route at Uddeholms AB and a competitor producer sample. The results showed that the level of cleanliness varies from different production routes and is hence dependent on the process at each production route. The number, maximum and mean size of inclusions were found to be higher in the HF route compared to the other routes. More so, there were differences in the types of oxide inclusions observed from each process route. However, sulphide inclusions exhibit similar characteristics from the different process routes. Further, the compositions of oxide inclusions observed from the HF route were found to be closely related to the steel chemistry. More importantly, the types of inclusions formed in the HF route were found to be sensitively affected by the extent of aluminium and calcium contents in the steel. Thus, the oxide inclusion types in the HF samples could be traced to the extent of different additions and operations such as deoxidation and calcium treatment that were carried out during the steelmaking process.

Recently induction cookers, which are based on induction heating principle, have become quite popular due to their advantages such as high energy efficiency, safety, cleanliness, and compact size. However, it is widely known that with current technology, induction cookers require the cookware to be made of magnetic materials such as iron and stainless steel. This is why a lot of cookware is labeled â Induction Readyâ on the bottom. The limited choice of â Induction Readyâ cookware causes inconvenience to customers and limits the growing popularity of the induction cooker. Therefore, a novel induction cooker, which can work for non-magnetic material cookware such as aluminum and copper, can be very competitive in the market. This thesis studies the induction cooking application; briefly introduces its fundamental principle, research background and the motivation of the development of a non-magnetic material induction cooker. Followed by the research motivation, three commonly used inverter topologies, series resonant inverter, parallel resonant inverter, and single-ended resonant inverter, are introduced. A comparative study is made among these three topologies, and the comparative study leads to a conclusion that the series resonant inverter is more suitable for non-magnetic material induction cooking application. The thesis also presents several major issues about non-magnetic material induction cooking and how to deal with these issues through induction coil design, higher operating frequency and novel control strategy. Because of non-magnetic materialâ s low resistivity and permeability characteristics, it is difficult to be heated and to achieve soft-switching while the coupling between the induction coil and the cooking pan can be easily changed. Later in this thesis, these issues will be discussed in detail and some potential solutions to these issues such as self-sustained oscillating control, optimized induction coil design, proper selection of power semiconductor device, etc. A 1.5 kW high frequency series resonant inverter with self-sustained oscillating control is prototyped. Experimental results demonstrated successful operation of the resonant inverter under up to 1.5 kW, and the inverterâ s capability to maintain zero-voltage turn-on during wide operating condition is confirmed. At the end, a summary is given about the research work done in the thesis and future research work is discussed.
Master of Science

The McTronX research group at the North–West University designs and develops Active Magnetic Bearings (AMBs). The group’s focus shifted to the design and development of AMB supported drive systems. This includes the electromagnetic and mechanical design of the electric machine, AMBs, auxiliary bearings as well as the development of the control system. The research group is currently developing an AMB supported high speed Induction Machine (IM) drive system that will facilitate tests in order to verify the design capability of the group. The research presented in this thesis describes the mechanical design and manufacturing of a high speed IM rotor section. The design includes; selecting the IM rotor topology, material selection, detail stress analysis and selecting appropriate manufacturing and assembly procedures. A comprehensive literature study identifies six main design considerations during the mechanical design of a high speed IM rotor section. These considerations include; magnetic core selection, rotor cage design, shaft design, shaft/magnetic core connection, stress due to operation at elevated temperatures and design for manufacture and assemble (DFMA). A critical overview of the literature leads to some design decisions being made and is used as a starting point for the detail design. The design choices include using a laminated cage rotor with a shrink fit for the shaft/magnetic core connection. Throughout the detail design an iterative process was followed incorporating both electromagnetic and mechanical considerations to deliver a good design solution. The first step of the iterative design process was, roughly calculating the material strengths required for first iteration material selection followed by more detailed interference fit calculations. From the detail stress analysis it became apparent that the stress in the IM rotor section cannot be calculated accurately using analytical methods. Consequently, a systematically verified and validated Finite Element Analysis (FEA) model was used to calculate the interferences required for each component. The detail stress analysis of the assembly also determined the allowable manufacturing dimensional tolerances. From the detail stress analysis it was found that the available lamination and squirrel cage material strengths were inadequate for the design speed specification of 27,000 r/min. The analysis showed that a maximum operating speed of 19,000 r/min can be achieved while complying with the minimum factor of safety (FOS) of 2. Each component was manufactured to the prescribed dimensional tolerances and the IM rotor section was assembled. With the failure of the first assembly process, machine experts were consulted and a revised process was implemented. The revised process entailed manufacturing five small lamination stacks and assembling the stack and squirrel cage afterwards. The end ring/conductive bar connection utilises interference fits due to the fact that the materials could not be welded. The process was successful and the IM rotor section was shrink fitted onto the shaft. However, after final machining of the rotor’s outer diameter (OD), inspections revealed axial displacement of the end rings and a revised FEA was implemented to simulate the effect. The results indicated a minimum FOS 0.6 at very small sections and with further analytical investigation it was shown that the minimum FOS was reduced to only 1.34. Although the calculations indicated the FOS was below the minimum prescribed FOS ? 2, the rotor spin tests were scheduled to continue as planned. The main reasons being that the lowest FOS is at very small areas and is located at non critical structural positions. The fact that the rotor speed was incrementally increased and multiple parameters were monitored, which could detect early signs of failure, further supported the decision. In testing the rotor was successfully spun up to 19,000 r/min and 27 rotor delevitation test were conducted at speeds of up to 10,000 r/min. After continuous testing a secondary rotor inspection was conducted and no visible changes could be detected. The lessons learnt leads to mechanical design and manufacturing recommendations and the research required to realise a 27,000 r/min rotor design.
Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2011.

Induction machine drives with various configurations are getting a lot of attention in several industrial applications. Due to this increasing demand in industrial applications, the significance of developing effective control approaches for obtaining a high dynamic performance from the induction machine drives became essential. Up to the present time, the control of induction machine drives using power converters has been based on the principle of mean value, using pulse width modulation with linear controllers in a cascaded structure. Recent research works have demonstrated that it is possible to use Predictive Control to control induction machine drives with the use of power converters, without using modulators and linear controllers. This new approach will have a strong impact on control in power electronics in coming decades. The advantages of Predictive Control are noticed through the ability to consider a multi-objective case within the model, easy inclusion of non-linearities within the model, simple treatment of system constraints, easy of digital implementation, and flexibility of including modifications and extension of control horizons according to the required applications. Upon this, the research presented in this thesis concerns with developing different control topologies for various configurations of induction machine drives based on finite control set model predictive control (FCS-MPC) principle, which actuates directly the switch states of the voltage source inverter (VSI). In addition, for enhancing the robustness of the induction machine drives, different sensorless approaches are utilized and tested for validations. The first topology of induction machine drives that has been studied is the induction motor (IM) drive. An effective model predictive direct torque control (MP DTC) approach is used to control the torque and stator flux of the motor through the utilization of an effective cost function, through which the understanding and comparing implementation variants and studying convergence and stability issues can be easily investigated. The speed sample effect on the control variants and overall performance of the proposed MP DTC is analyzed, which enables the understanding of the real base principle of DTC, as well as why and when it works well. Two different sensorless procedures for estimating the speed and rotor position are used by the proposed MP DTC approach; the first utilizes a model reference adaptive system (MRAS) observer, while the other exploits the prediction step during the implementation of proposed MP DTC to get the speed information through performing a linear extrapolation of the speed values starting from the last two estimated samples. Extensive simulation and experimental tests have been carried out to validate the effectiveness of both sensorless approaches in achieving precise tracking of speed commands for a wide range of variations. For enhancing the robustness of proposed MP DTC, the stator flux as a control variable is replaced with controlling the flow of the reactive power through the induction motor drive. As the reactive power is a measured quantity compared with the estimated value of stator flux, thus, the sensitivity of the control against parameters variation is limited, and this confirmed through the obtained results from both simulation and experimental tests. In addition, an effective alternative approach to the MP DTC is presented, which based on controlling the instantaneous values of the active and reactive powers of the IM drive based on model predictive principle, instead of controlling the torque and flux as in MP DTC. This technique has the advantage that all controlled variables are became measured quantities (active and reactive powers), thus the estimation problems that commonly present in classic DTC schemes are effectively limited. For the last two control approaches (MP DTC reactive power control, and MP IPCactive and reactive power control), the sensorless that utilizes the predictive feature is also adopted. Obtained results via simulation and experiments confirm the feasibility of the two alternatives control procedures in obtaining a robust dynamic response of IM drive. To limit the accompanied ripple contents in the controlled values of electromagnetic torque and stator flux of induction motor, an effective ripple reduction technique has been presented. The technique is based on the derivation of the optimal value for the weighting factor (w_f) used in the cost function. A detailed mathematical derivation of the optimal value of w_f is introduced based on the analysis of torque and flux ripples behaviors. The proposed ripple reduction technique has been validated via simulation utilizing Matlab/Simulink software, and experimentally tested using a fast control prototyping dSpace 1104 board. In addition, the prediction step based sensorless approach is adopted during implementation. The performance of the IM drive using the proposed approach is compared with the results obtained from MP DTC approach that uses an arbitrary value of w_f. The comparison confirms the validity of the proposed ripple reduction procedure in reducing the ripple contents in the controlled variables while preserving the permissible computation burdens during the implementation. The FCS-MPC principle is also utilized to control the current of induction motor as an alternative to classic field oriented control (FOC), the proposed model predictive current control (MPCC) approach belongs to the class of the hysteresis predictive control (for limiting the switching frequency) as the MPCC is triggered by the exceeding of the error of a given threshold. In addition, a sensorless drive is achieved by including an effective Luenberger observer (LO) for precise estimation of rotor flux vector together with stator current, speed and load torque. The stator currents are estimated to eliminate the accompanied noise in their values when they are directly measured, thus the currents noise during prediction is limited. An effective pole placement procedure for the selection of observer gains has been adopted. The procedure is based on shifting the poles of the observer to the left of the motor poles in the complex (s-plane) with low imaginary part, so that the stability of the observer is enhanced for wide speed range. The feasibility of the sensorless MPCC for IM drive is confirmed through the obtained simulation and experimental results. The second topology of induction machine drives that has been studied is the doubly fed induction motor (DFIM) drive. An effective model predictive direct torque control (MP DTC) algorithm is developed for controlling the torque and rotor flux of DFIM drive. In addition, an effective sensorless approach is presented, which estimates the speed and rotor position in an explicit way without the need for involving the flux in the estimation process, thus the effect of parameters variation on the overall performance of the sensorless observer is effectively limited, this has been approved through the obtained results that are performed for a wide speed range from sub-synchronous to super-synchronous speed operation. During the operation, the stator resistance and magnetizing inductance values are changed from their original values to study the variation effect on the observer performance. Matlab/Simulink software and a prototyping dSpace 1104 control board are used to validate the effectiveness of proposed sensorless MP DTC approach through simulation and experiments, respectively. The results proof the robustness of the proposed sensorless approach and its ability to achieve precise estimation of the speed and rotor position. The third topology of induction machine drives that has been studied is the doubly fed induction generator (DFIG). A detailed analytical derivation for the proposed model predictive direct power control (MP DPC) approach for DFIG is presented, which as a sequence considered as a transposed control approach from the MP DTC used before for doubly fed induction motor (DFIM). A sensorless approach based on model reference adaptive system (MRAS) observer is adopted for estimating the speed and rotor position. Both simulation using Matlab/Simulink software and experimental test using a prototyping dSpace 1104 control board have tested the dynamic performance of the drive. Obtained results affirm the feasibility of the proposed MP DPC approach in achieving a decoupled control of active and reactive powers for DFIG. In summary, it can be said that the proposed model predictive control approaches have proved their ability in achieving high dynamic performance for different topologies of induction machine drives. In addition, the proposed sensorless techniques have confirmed their effectiveness for a wide range of speed variations. All of this are approved and validated through extensive simulation and experimental tests.
Gli azionamenti con machine ad induzione (macchine asincrone nelle loro varie configurazioni), stanno riacquistando molta attenzione in diverse applicazioni industriali. A causa di questo crescente interesse applicativo, è diventato di essenziale importanza lo sviluppo di efficaci tecniche di controllo per ottenere dagli azionamenti in questione elevate prestazioni dinamiche. Fino ad oggi, il controllo degli azionamenti con macchina a induzione alimentati da convertitori di potenza è basato sul “principio del valore medio” delle grandezze in commutazione, utilizzando la modulazione di larghezza di impulsi con controllori lineari in una struttura a cascata. Recenti ricerche hanno dimostrato che è possibile utilizzare il Controllo Predittivo per controllare gli azionamenti con macchina a induzione, con l'utilizzo di convertitori di potenza senza utilizzare modulatori e controllori lineari. Questo nuovo approccio avrà un forte impatto sul controllo dell'elettronica di potenza nei prossimi decenni. I vantaggi del Controllo Predittivo derivano dalla possibilità di perseguire problemi multi-obiettivo, di includere facile le non linearità all'interno del modello, di trattare in modo semplice i vincoli di sistema, nonché dalla facilità di implementazione digitale e dalla flessibilità di includere modifiche ed estensioni al controllo secondo le applicazioni richieste. Inlinea con tutto ciò, la ricerca presentata in questa tesi riguarda lo sviluppo di diverse topologie di controllo per varie configurazioni di azionamenti con macchine a induzione, basate sul principio di Controllo Predittivo a modello con insieme finito degli stati di controllo (Finite Control Set Model Predictive Control - FCS-MPC), che definisce direttamente l’assetto dell'inverter di tensione (VSI). Inoltre, per aumentare la robustezza degli azionamenti, vengono proposti e sperimentati diversi approcci senza sensori elettromeccanici (sensorless). La prima topologia studiata di azionamenti con macchina a induzione (IM) è l'azionamento con motore a gabbia. Il controllo diretto di coppia (DTC) è aggiornato in termini di controllo predittivo a modello (MP DTC) e usato per controllare la coppia e il flusso statorico attraverso l'utilizzo di una efficace funzione di costo attraverso la quale è anche possibile facilmente comprendere e confrontare le varianti di implementazione e studiare i problemi di convergenza e di stabilità. Viene analizzato l'effetto della velocità sulle diverse versioni di controllo e sulle prestazioni complessive del MP DTC proposto; ciò consente di comprendere appieno il principio del DTC, nonché perché e quando esso funzioni bene. Vengono utilizzate due diverse procedure di stima della posizione e della velocità del rotore nel MP DTC proposto; il primo utilizza uno stimatore adattivo con modello di riferimento (MRAS), mentre l'altro sfrutta la stessa fase di predizione del MP DTC proposto per ottenere le informazioni sulla velocità effettuando infine un'estrapolazione lineare dei valori di velocità a partire dagli ultimi due campioni stimati. Sono state eseguite numerose prove in simulazione e sperimentali per convalidare l'efficacia di entrambi gli approcci sensorless nell’ottenere un preciso inseguimento del comando di velocità per una vasta gamma di situazioni. Per migliorare la robustezza del MP DTC proposto rispetto alle variazioni parametriche, il controllo del flusso dello statore viene sostituito con quello della potenza reattiva assorbita dal motore ad induzione; di conseguenza la sensibilità del controllo alle variazioni dei parametri è limitata e ciò è confermato attraverso i risultati ottenuti sia dalla simulazione che dalle prove sperimentali. Inoltre, viene presentato un ulteriore efficace approccio alternativo per il MP DTC, basato sul principio del controllo predittivo a modello dei valori istantanei delle potenze attive e reattive dell'azionamento, invece di controllare la coppia e il flusso come nell’usuale MP DTC. Questa variante ha il vantaggio che tutte le variabili controllate sono divenute quantità misurate (potenze attive e reattive) e quindi i problemi di stima comunemente presenti nei classici schemi DTC sono efficacemente limitati. Per gli ultimi due approcci di controllo (controllo di coppia e di potenza reattiva e controllo di potenza attiva e reattiva) viene anche adottato la stima della velocità rotorica che sfrutta la funzione predittiva del controllo. I risultati ottenuti attraverso la simulazione e la sperimentazione confermano la fattibilità delle due procedure alternative di controllo per ottenere una risposta dinamica robusta dell’azionamento con IM. Per limitare il ripple che accompagna gli andamenti controllati della coppia e del flusso statorico del motore, è stata presentata una tecnica efficace di riduzione della sua ampiezza. La tecnica è basata sull’impiego di un valore ottimale per il fattore di ponderazione w_f utilizzato nella funzione di costo per sommare i due contributi che la definiscono. Viene introdotta una derivazione matematica dettagliata del valore ottimale di w_f attraverso l'analisi dei comportamenti dell’ondulazione di coppia e del flusso. La tecnica di riduzione del ripple proposta è stata verificata tramite la simulazione usando il software Matlab/Simulink e sperimentalmente utilizzando la scheda di rapida prototipazione del controllo dSpace 1104. Ancora, l'implementazione adotta l'approccio sensorless basato sulla fase di predizione. Le prestazioni dell’azionamento con IM utilizzando quest’ultimo approccio proposto sono confrontate con i risultati ottenuti con l'approccio MP DTC che utilizza invece un valore arbitrario di w_f. Il confronto conferma la validità della procedura di riduzione del ripple nelle variabili controllate mantenendo nel contempo gli oneri di calcolo entro i limiti consentiti per l'implementazione. Il principio FCS-MPC è anche utilizzato per controllare la corrente del motore di induzione come alternativa al controllo classico ad orientamento di campo (Field Oriented Control -FOC). L'approccio proposto di controllo di corrente di tipo predittivo (Model Predictive Current Control - MPCC) appartiene alla classe del controllo predittivo ad isteresi (per limitare il frequenza di commutazione) in quanto il MPCC viene attivato dal raggiungimento dell’errore di corrente di una determinata soglia. In questo caso, la caratteristica sensorless dell’azionamento è ottenuta includendo un efficace osservatore Luenberger (LO) per una precisa stima del vettore del flusso del rotore insieme alla coppia di carico e alla velocità. È stata adottata una efficace procedura di allocazione dei poli per la selezione dei guadagni dell'osservatore; la procedura si basa sul posizionamento dei poli dell'osservatore a sinistra di quelli del motore nel complesso (piano di s) con una ridotta parte immaginaria, in modo che la stabilità dell'osservatore sia migliorata in un'ampia gamma di velocità. La fattibilità dell'azionamento sensorless con MPCC è ancora confermata attraverso la simulazione e i risultati sperimentali. La seconda topologia degli azionamenti con macchina a induzione che è stata studiata è l'azionamento con motore ad anelli con rotore alimentato da invertitore e statore da rete (Doubly Fed Induction Motor DFIM). È stato sviluppato un efficace algoritmo predittivo a modello (MP DTC) per il controllo dinamico della coppia e del flusso di rotore dell'azionamento DFIM. Inoltre, viene presentato un approccio efficace di soluzione sensorless che valuta la velocità e la posizione del rotore in modo esplicito senza la necessità di coinvolgere la stima del flusso nel processo di predizione; di conseguenza l'effetto delle variazioni dei parametri sulle prestazioni complessive dell'osservatore di posizione e velocità è sensibilmente limitato. Questo è stato provato attraverso i risultati ottenuti con test eseguiti in un'ampia gamma di velocità, dal sub-sincronismo a velocità super-sincrona. Durante l'operazione, la resistenza dello statore e i valori di induttanza di magnetizzazione sono stati modificati rispetto ai valori reali per studiare l'effetto di variazioni parametriche sulle prestazioni dell'osservatore. Anche in questo caso, il software Matlab/Simulink e una scheda di controllo dSpace 1104 sono stati utilizzati per convalidare l'efficacia dell'approccio sensorless del MP DTC per l’azionamento. I risultati dimostrano la robustezza del controllo sensorless proposto e la sua capacità di ottenere una precisa stima della posizione e della velocità del rotore. La terza topologia di azionamenti con macchina a induzione che è stata studiata è quella del generatore ad induzione con rotore avvolto (DFIG) e invertitore sul rotore. Viene presentata una derivazione analitica dettagliata del controllo predittivo diretto di potenza (MP DPC) per DFIG, che trasferisce ed estende l’approccio di controllo del MP DTC citato prima per il motore a induzione a doppia alimentazione (DFIM). Una soluzione sensorless ancora basata sull'osservatore adattivo a modello di riferimento (MRAS) è adottato per stimare la velocità e la posizione del rotore. Sia le simulazioni usando il software Matlab/Simulink che i test sperimentali utilizzando la scheda dSpace 1104 hanno mostrato le elevate prestazioni dinamiche dell'azionamento. I risultati ottenuti confermano la fattibilità del metodo MP DPC proposto per ottenere un controllo disaccoppiato di potenze attive e reattive per DFIG. In sintesi, si può dire che l'utilizzo proposto del controllo predittivo a modello ha dimostrato la sua capacità di ottenere elevate prestazioni dinamiche per le diverse topologie degli azionamenti con macchina ad induzione considerati. Inoltre, le tecniche sensorless proposte hanno confermato la loro efficacia per una vasta gamma di velocità. Tutto questo è stato verificato e validato attraverso una vasta attività analisi simulativa e di sperimentazione in laboratorio.

Recycling has proven not only to address today’s economical, environmental and social issues, but also to be imperative for the sustainability of human technology. The current thesis has investigated the feasibility of a new philosophy for Recycling (Alloying-Recycling) using steel 1020 and aluminum 6061T6. The study was limited to the metallurgical aspects only and has highlighted the potential of recycled alloys made of recycled aluminum and steel to exhibit substantially increased wear resistance and strength-to-weight ratio as compared to initial primary materials. Three alloy-mixtures are considered: TN3 (5wt% 1020 +95wt% 6061T6); TN5 (0.7wt% 1020 + 99.3wt% 6061T6); and TN4 (10wt% 6061T6 + 90wt% 1020). A Tucker induction power supply system (3kW; 135-400 kHz) is used to melt the alloy mixtures for casting in graphite crucibles. Heat treatment of the cast samples is done using a radiation box furnace. Microscopy, Vickers hardness and pin-on-disc abrasive wear tests are performed. Casting destroyed the initial microstructures of the alloys leading to a hardness reduction in the as-cast and solution heat-treated aluminum rich samples to 60 Hv from 140 Hv. Ageing slightly increased the hardness of the cast samples and provided a wear resistance two times higher than that of the initial 6061T6 material. On the steel rich side, the hardness of the as-cast TN4 was 480 Hv, which is more than twice as high as the initial hardness of steel 1020 of 202 Hv; this hints to strong internal and residual stress, probably martensite formation during fast cooling following casting. Solution heat treatment lowered the hardness to the original value of steel 1020, but provided about ten (10) times higher wear resistance; this suggests higher ductility and toughness of normalised TN4 as compared to 1020. In addition, TN4 exhibits about 25% weight reduction as compared to 1020. The actual recycling process and the effect of non-metallic impurities shall be investigated in future works. Also, the casting and heat treatment processes need to be improved.

Although there are several achievements made by the Namibian government after independence, there are still many constraints and challenges facing the education system, particularly with regard to novice teachers&rsquo
support and professional development. Most novice teachers are coming into the teaching profession and receive little or no assistance. Nevertheless, novice teachers are expected to perform the full teaching responsibilities despite their inexperience. Novice teachers are expected to formulate their own coping strategies and to grapple with the challenges they encounter during their first year of teaching on their own. This study aims at investigating the coping mechanisms used by novice teachers to achieve their teaching goals during their first year of teaching. The study recommends that the teacher training institutions, the Ministry of Education and schools have an important role to play in facilitating the use of effective coping mechanisms and in assisting novice teachers in alleviating these challenges. Teacher training should ensure that a balance is maintained between theory and practice. In addition the Ministry needs to provide favourable working conditions and put up support systems for novice teachers. Schools should also provide orientation to all novice teachers and most especially render support to all novice teachers until they are fully integrated into the school and teaching culture.

碩士
國立虎尾科技大學
電機工程研究所
102
In this thesis, a novel high performance parallel resonant high frequency induction heater is proposed. The induction heater consists of three-phase AC/DC buck-boost converter, single-phase DC/AC inverter and RLC parallel resonant circuit. Compare to the traditional two-stage resonant induction heater, the proposed induction heater has several advantages such as one-stage structure, unity power factor, pure sinusoidal input current and simple control circuit etc.. The three-phase AC/DC buck-boost converter is operated at discontinuous current mode. In order to produce maximum power output, three inductor currents are converted to single phase high frequency current source to supply RLC parallel resonant circuit. Make the switches of converter and inverter synchronous switching with Altera MAXR II Micro Kit EPM2210F324C3 and Quartus II 9.0 software for controlling signal. Finally, some experimental results are presented to verify the feasibility of the proposed induction heater.

碩士
國立成功大學
電機工程學系碩博士班
91
The purpose of this thesis focuses on both efficiency improvement and characteristic analyses of conventional induction machines. The primary drawback of a conventional induction machine is its lower efficiency as compared to a synchronous machine of the same ratings and size. This thesis employs both equivalent-circuit method and finite-element method to analyze transient and steady-state performance of an induction machine in order to promote efficiency by modifying its size, the employed core material, and difference design scheme, etc. The performance of two three-phase, 220 V(Δ)/380 V(Y), 4 poles, 1 HP induction machines of conventional and high-efficiency are employed to investigate and compared. Three operating modes of an induction machine, i.e., induction motor, isolated self-excited induction generator and grid-connected induction generator, are respectively utilized. Both steady-state and transient characteristics as well as both experimental and simulated results of the two studied induction machines are performed and compared in order to validate the important features of the high-efficiency induction machines.

博士
國立成功大學
電機工程學系
88
This dissertation proposes an induction motor drive with current and torque control. The current control based on the current error with the current controller yields the control signal of current controller. The torque control based on the torque error with the torque controller yields a control signal of torque controller. According to the output signal of current controller and torque controller, the appropriate voltage vector is selected by using a look-up table to control the induction motor drive to obtain a rapid speed response. The torque controller, current controller, and stationary reference frame transform are constructed by the hardware which reduce the running time of the microcomputer to obtain a high performance drive. Meanwhile, employing the advantages of the added zero voltage vector to reduce the inverter switching frequency greatly increasing the efficiency of the inverter. This dissertation also presents a control scheme for an induction motor drive which consists of a compensator, neural network identification (NNI) and neural network load torque estimator (NNLTE) based on the conventional proportional-integral (PI) controller. The NNI is a two-layer neural network which uses a projection algorithm to estimate the parameters of the induction motor and to regulate the gain of the compensator such that the response of the induction motor follows that of the nominal plant. The NNLTE is a two-layer neural network which uses the steepest descent algorithm to estimate the load disturbance and forward feed resulting in equivalent control such that the speed response of the induction motor is robust against the load disturbance. Computer simulations and experiment results demonstrate that the proposed method can obtain a high performance induction motor drive.

Thesis (M.S.)--University of Wisconsin--Madison, 1991.
Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 197-201).

碩士
國立中山大學
電機工程學系研究所
91
Saturated reluctance identification of induction motor can be implemented by additional sensor, finite-element method, spectrum analysis, or step voltage test in the research accounts. But it is not easy to implement in the field evaluation when we need to build up the power system model, because of the factory parameter absent, expansive cost, extra sensor installation, or variable voltage and frequency. To be concerned with practicality, it is always inconvenient to build up simulation for the end user. The linear model of motor can’t provide the simulation answer accurately when models run into saturated during power system transient. Accordingly, this thesis discuss two paragraphs as following: First, This thesis introduces a simple and practical method base on the manufacturer instruction manual to estimate the saturated reluctance of high / medium voltage induction motor in modeling. And we can analyze the motor dynamic characteristic by using the induction motor d-q-0 model directly, in place of traditional mathematical power equations. Moreover, we can evaluate the motor-generation reaction because of the rotor inertia due to loss of voltage. To identify the discrepancy between numeral situations what the line capacitor existed or not. Besides, we can explain the existing voltage after power system break down by comparing the simulation result with recorder chart.