This dissertation contains the results of research conducted on the design and control characterization of a Switched Reluctance Generator (SRG) for maximum output power. The SRG is an attractive solution to the increasing worldwide demand of electrical energy. It is low cost with a rugged structure, operates with high efficiency over a wide speed range, and is fault tolerant. In many applications, size and weight are the main criteria in selecting the generator. Hence, in design and control of the generator, system designers always strive for increasing power density, or in other words, maximizing the output power for a given size. Despite the extensive research on the motoring operation of the Switched Reluctance Machine, only a few publications have investigated the generating mode of operation of this machine. Results and algorithms from this research can be referenced for better utilizing the SRG in many applications. As the first stage to output power maximization, design parameters and control variables affecting the average output power of the SRG are identified through a systematic approach. The optimal values for maximizing the output power are found through an analytical approach and iterative simulations. The results are then verified experimentally. After finding the optimal values for control variables, a controller is designed. This controller is model dependent. If the model used for design is not accurate or the machine parameters are deviated from the designed values, the machine will not generate the maximum output power. Therefore, a self-tuning algorithm, based on a local search method, is proposed and experimentally tested. It works effectively and does not need extra hardware or rigorous calculations. The attempts to benefit from the SRG may look tantalizing, but it poses a challenge as well. Output power maximization can lead to an oversized SRG converter and its output filter, which will reduce the overall power density of the motor drive. The last piece of this dissertation analyzes the effect of a commutation algorithm on the output filter, reducing its size with active control of phase currents, and proposing a novel control algorithm that was investigated through experiments over all of the speed range.

This thesis explores the application of modem fault-detection methods to electric rail traction drives. Such drives consist of three main components, induction motors, power inverters and the control system. The power electronics are relatively simple so the scope for fault-tolerance is limited, whilst fault-detection techniques for induction motors are already well developed. There is however scope for work on the instrumentation. The thesis concentrates on the use of model-based techniques to produce a torque and flux estimator for an induction motor which is tolerant to intermittent sensor disconnections. The motors are controlled on torque and flux, these cannot be measured directly and are estimated from measurements of the applied voltages and the resulting currents. The existing estimator has poor steady-state performance at low speed and because of it's transient dynamics it is prone to sensor noise and disconnections. Induction motors have speed-dependent dynamics and the resulting state-space model has terms which are multiplied by speed, this model is strongly bilinear. Speed-dependent feedback is needed to give desirable dynamics to the state estimates. Starting from a state-space model for the induction motor, a closed-loop observer can be designed to estimate the motor states. A range of feedback methods for the observer have been considered, from gain scheduling to sliding mode techniques. These are evaluated in simulation, using a simplified model of the traction system. The simulation neglects many second order effects which would effect the real application. Using data from an induction motor test-rig the observers are shown to be able to track the motor torque during a change in operating condition. Only a limited set of data is available. The influence of parameter mis-match, noise and speed sensor errors are considered by deriving frequency domain expressions for the estimation error in the presence of uncertainty or disturbances. The effect of the observer's gain on its sensitivity to these are considered under conditions which occur in the real application. Using observer feedback to decouple sensors from the estimation a range of sensor fault-detection schemes are developed. In this way a bank of observers is designed which are independent of a different subset of sensors, this enables sensor faults to be isolated. These method are compared in simulation. A motor, inverter and instrumentation are set up, with a DSP to run an observer based sensor fault-detection scheme in real-time. This enables implementation aspects to be explored, such as discretisation, model mis-match and motor loading. These effect the detection by increasing fault-free residual or reducing the fault residual. For a each type of sensor the area of the motor operating range, where a fault is detectable is defined.

Internal combustion engines are the most commonly used engines in the automotive world. However, these engines lack an overheating prevention system against cooling system failures when they exceed their normal operating temperature. Less experienced drivers (users) usually do not notice overheating until the engine stops, generating economic expenses in engine repairs. As such, this paper describes the design and construction of an electromechanical device to prevent engine overheating. This device is installed in a vehicle and operates independently from the electronic control unit (ECU); it records the coolant temperature and controls air admission to the engine of the vehicle in which it is installed. In addition, a new Arduino-based card will receive signals from a temperature sensor as input and process them according to its programming. Then, it will send signal outputs to the actuators: A servomotor, monitor, LED display, and buzzer. To control the intake flow, a butterfly valve is used with the servomotor. This valve partially or totally restricts the engine airflow, based on the temperature programmed for the Arduino, thus protecting the engine from overheating.

Microscopy techniques have been developed and refined over multiple decades, but innovation around single photon modalities has slowed. The advancement of the utility of information acquired, and minimum resolution available is seemingly reaching an asymptote. The fusion of light microscopy and well-studied nonlinear processes has broken through this barrier and enabled the collection of vast amounts of additional information beyond the topographical information relayed by traditional microscopes. Through nonlinear imaging modalities, chemical information can also be extracted from tissue. Nonlinear microscopy also can beat the resolution limit caused by diffraction, and offers up three-dimensional capabilities. The power of nonlinear imaging has been demonstrated by countless research groups, solidifying it as a major player in biomedical imaging. The value of a nonlinear imaging system could be enhanced if a reduction in size would permit the insertion into bodily cavities, as has been demonstrated by linear imaging endoscopes. The miniaturization of single photon imaging devices has led to significant advancements in diagnostics and treatment in the medical field. Much more information can be extracted from a patient if the tissue can be imaged in vivo, a capability that traditional, bulky, table top microscopes cannot offer. The development of new technologies in optics has enabled the miniaturization of many critical components of standard microscopes. It is possible to combine nonlinear techniques with these miniaturized elements into a portable, hand held microscope that can be applied to various facets of the biomedical field. The research demonstrated in this thesis is based on the selection, testing and assembly of several miniaturized optical components for use as a nonlinear imaging device. This thesis is the first demonstration of a fibre delivered, microelectromechanical systems mirror with miniaturized optics housed in a portable, hand held package. Specifically, it is designed for coherent anti-Stokes Raman scattering, second harmonic generation, and two-photon excitation fluorescence imaging. Depending on the modality being exploited, different chemical information can be extracted from the sample being imaged. This miniaturized microscope can be applied to diagnostics and treatments of spinal cord diseases and injuries, atherosclerosis research, cancer tumour identification and a plethora of other biomedical applications. The device that will be revealed in the upcoming text is validated by demonstrating all designed-for nonlinear modalities, and later will be used to perform serialized imaging of myelin of a single specimen over time.

Microscopy techniques have been developed and refined over multiple decades, but innovation around single photon modalities has slowed. The advancement of the utility of information acquired, and minimum resolution available is seemingly reaching an asymptote. The fusion of light microscopy and well-studied nonlinear processes has broken through this barrier and enabled the collection of vast amounts of additional information beyond the topographical information relayed by traditional microscopes. Through nonlinear imaging modalities, chemical information can also be extracted from tissue. Nonlinear microscopy also can beat the resolution limit caused by diffraction, and offers up three-dimensional capabilities. The power of nonlinear imaging has been demonstrated by countless research groups, solidifying it as a major player in biomedical imaging. The value of a nonlinear imaging system could be enhanced if a reduction in size would permit the insertion into bodily cavities, as has been demonstrated by linear imaging endoscopes. The miniaturization of single photon imaging devices has led to significant advancements in diagnostics and treatment in the medical field. Much more information can be extracted from a patient if the tissue can be imaged in vivo, a capability that traditional, bulky, table top microscopes cannot offer. The development of new technologies in optics has enabled the miniaturization of many critical components of standard microscopes. It is possible to combine nonlinear techniques with these miniaturized elements into a portable, hand held microscope that can be applied to various facets of the biomedical field. The research demonstrated in this thesis is based on the selection, testing and assembly of several miniaturized optical components for use as a nonlinear imaging device. This thesis is the first demonstration of a fibre delivered, microelectromechanical systems mirror with miniaturized optics housed in a portable, hand held package. Specifically, it is designed for coherent anti-Stokes Raman scattering, second harmonic generation, and two-photon excitation fluorescence imaging. Depending on the modality being exploited, different chemical information can be extracted from the sample being imaged. This miniaturized microscope can be applied to diagnostics and treatments of spinal cord diseases and injuries, atherosclerosis research, cancer tumour identification and a plethora of other biomedical applications. The device that will be revealed in the upcoming text is validated by demonstrating all designed-for nonlinear modalities, and later will be used to perform serialized imaging of myelin of a single specimen over time.

M. Tech. (Department of Mechanical Engineering, Faculty of Engineering and Technology), Vaal University of Technology. / The subject of maintenance optimisation is not new, and many researchers have explored it. However, it is seen that one optimisation solution cannot be used in all industries. Each industry and equipment thereof are unique as the product streams differ, layouts and operation variables, to name a few. Though Turn-around management is the most used strategy in petrochemical industries. Equipment downtime remains the biggest challenge thus, the purpose of the study was to optimise the maintenance practices used on the critical electromechanical equipment in Sasol Synfuels Catalyst Preparation using both the Analytical Network and Analytical Hierarchy multi-decision approach. Data was collected from the SAP system database, of which the breakdown work orders was obtained from the period of January 2016 to June 2021. The data was collected for each 13 electromechanical equipment identified in the catalyst preparation unit. The applied maintenance strategies employed on the electromechanical equipment in the catalyst preparation unit was also analysed using the Meridium maintenance strategy software tool utilised in Sasol Synfuels. An analysis and identification of the critical equipment within the unit were obtained with the use of two different methods, namely the JADERI, (2019) and AFEFY, (2010) approaches. A theoretical distribution was drawn after that in order to assess the effectiveness of the current maintenance strategy compared to the identified key performance indicators. The theoretical distribution analysis was used to determine the plant utilisation, availability, and maintenance cost. The analytical network and hierarchy process application, and the super decision network model framework, were analysed to obtain the maintenance optimisation solution. Though the ANP and AHP approaches have different problem identification frameworks and cluster dependencies, it is seen that both methods portray more or less similar results. Both methods indicate that in order to achieve an optimised maintenance strategy within the catalyst preparation unit, condition-based maintenance strategy is the most weighed alternative node with 50% for optimal maintenance solution. The least most weighed alternative node is corrective maintenance, weighed at 7%. This is true as corrective maintenance is applied once a breakdown has occurred, of which the aim is to avoid unforeseen breakdowns. Fixed time maintenance is the second most weighed maintenance strategy with 30%, followed then by the operate to failure strategy at 13%. Considering that the operation to failure maintenance strategy is applied based on the consequence of failure and maintenance cost as well as mean time to repair, this is then concluded as practical as RCM priorities predictive and preventative strategies to be employed. It was drawn, for criteria nodes, that the ANP approach resulted in the environmental safety impact as the most important criteria to consider when applying the optimal maintenance strategy in the Sasol Synfuels Catalyst preparation unit. The environmental safety impact was rated at 0.33, followed by availability with a factor of 0.32. The least weighed criteria nodes are then the maintenance cost and MTTR, both with a factor of 0.17. This proves to true considering that the petrochemical industry is considered a high-risk industry as it processes and produces hazardous chemicals The AHP approach structure however, does not consider interdependencies through the criteria and alternative clusters thus the alternative weight could not be defined. The results obtained prove that the ANP approach is the most practical mutli criteria decision making method for maintenance optimisation compared to the AHP approach.

Les polymères ferroélectriques et plus récemment les matériaux électrostrictifs ont attiré l’attention de la communauté scientifique en raison de leur capacité de conversion d’une excitation électrique en une réponse mécanique et vice versa. La synergie entre les propriétés électro actives de ces polymères et leurs propriétés physico-chimiques intrinsèques (souplesse, légèreté, grande résistance mécanique, facilité de mise en œuvre etc.) en font des candidats de choix pour des applications de types capteurs et actionneurs souples. Cette thèse vise à déterminer de façon systématique le comportement électromécanique des terpolymères P (fluorure de vinylidène-trifluoréthylène-chlorotrifluoroéthylène) [P (VDF-TrFE-CTFE)] par des techniques de cristallisation et de technologies additives et entend étendre ces terpolymères à l'application des dispositifs de type capteur de force électromécanique. L'influence du traitement thermique sur la réponse électromécanique et la microstructure des terpolymères a d'abord été étudiée. Il a été mis en évidence que la déformation électrostrictive transversale S31 pour chaque terpolymère traité thermiquement suit une loi quadratique avec le champ électrique. Par ailleurs il a été démontré que la déflexion d’un actionneur unimorphe est maximisée pour une fraction de phase cristalline de 39,3%. La dynamique moléculaire des terpolymères cristallisés a également été étudiée par spectroscopie diélectrique à large bande. Une dynamique segmentaire contrainte a été observée dans le terpolymère contenant la fraction cristalline la plus élevée pour laquelle une distribution étroite du temps de relaxation a été mise en évidence. En outre, il a été démontré que l’ajout d’agent plastifiant permet d’augmenter de manière significative la réponse électromécanique des terpolymères fluorés, ouvrant la voie vers de nouveaux matériaux électrostrictifs hautes performances fonctionnant sous faible champ électrique. De plus, la réponse diélectrique et électromécanique accrue du terpolymère dopé a été étudiée par microscope à force atomique et spectroscopie diélectrique dynamique. Ces analyses ont permis de lier l’augmentation de la réponse électromécanique de ces mélanges à un effet de polarisation interfaciale intensifié lors de l’augmentation de mobilité moléculaire de la phase amorphe rigide de ces terpolymères fluorés. Enfin, des dispositifs électromécaniques basés sur le polymère ferroélectrique P (VDF-TrFE) et le terpolymère électrostrictif P (VDF-TrFE-CTFE) ont été élaborés. Un procédé de fabrication additive utilisant la technologie d'impression jet d'encre a permis de concevoir et valider la faisabilité de réalisation de capteurs de force dynamique. Il a alors été démontré que les propriétés pseudo-piézoélectriques du terpolymère électrostrictif sont équivalentes à celles du copolymère ferroélectrique pour un faible champ électrique de biais de 7,5 V /μ / Electromechanical coupling effect has been paid the increasing attention due to ability to realize conversion between electric excitation and mechanical response and vice versa. Thanks to their flexibility, light weight, relatively low mechanical strength, ease of processability into large-area films, and ability to be molded into desirable geometric dimensions, polymers materials which possess an electromechanical coupling effect have been emerging recently. This thesis aims to systematically determine the electromechanical behavior of the P(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) [P(VDF-TrFE-CTFE)] terpolymers via crystallization and additive technology approaches and intend to extend such terpolymers to the electromechanical force sensor devices application. The influence of the thermal processing on the electromechanical response and microstructure of the terpolymers were firstly investigated. Cantilever unimorph bending measurement found the tip displacement δ and transverse strain S_31 for each thermally treated terpolymer followed a quadratic correlation with the electric field. δ was maximized at a 39.3% crystal content, instead of S_31 peaking at lowest crystal content, showing an exponential decay against the crystal fraction increasing. The dynamics of crystallized terpolymers were additionally studied via broadband dielectric spectroscopy. Constrained segmental dynamics was observed in the terpolymer containing the highest crystal fraction for which a narrow relaxation time distribution was found. Moreover, the enhanced dielectric and electromechanical response of DEHP doped terpolymer were interpreted via morphology microstructure and molecular mobility analysis. Interfacial polarization shifted to the high frequency by one decade because of dopant DEHP. Finally, electromechanical devices based on ferroelectric P(VDF-TrFE) and electrostrictive P(VDF-TrFE-CTFE) towards the dynamic force sensor implementation were designed and fabricated via inkjet printing technology. The bias electric field for terpolymer sensor was much lower than the poling electric field for a copolymer sensor. And the piezoelectric properties equivalent to the corresponding copolymer sensor can be obtained for a bias as low as 7.5 V/μ

Control Designs for Low-Loss Active Magnetic Bearings: Theory and Implementation Brian C. D. Wilson 327 Pages Directed by Dr. Panagiotis Tsiotras and Dr. Bonnie Heck-Ferri Active Magnetic Bearings (AMB) have been proposed for use in Electromechanical Flywheel Batteries. In these devices, kinetic energy is stored in a magnetically levitated flywheel which spins in a vacuum. The AMB eliminates all mechanical losses, however, electrical loss, hich is proportional to the square of the magnetic flux, is still significant. For fficient operation, the flux bias, which is typically introduced into the electromagnets to improve the AMB stiffness, must be reduced, preferably to zero. This zero-bias (ZB) mode of operation cripples the classical control techniques which are customarily used and nonlinear control is required. As a compromise between AMB stiffness and efficiency, a new flux bias scheme is proposed called the generalized complementary flux condition(gcfc). A flux-bias dependent trade-off exists between AMB stiffness, power consumption, and power loss. This work theoretically develops and experimentally verifies new low-loss AMB control designs which employ the gcfc condition. Particular attention is paid to the removal of the singularity present in the standard nonlinear control techniques when operating in ZB. Experimental verification is conduced on a 6-DOF AMB reaction wheel. Practical aspects of the gcfc implementation such as flux measurement and flux-bias implementation with voltage mode amplifiers using IR compensation are investigated. Comparisons are made between the gcfc bias technique and the standard constant-flux-sum (cfs) bias method. Under typical operating circumstances, theoretical analysis and experimental data show that the new gcfc bias scheme is more efficient in producing the control flux required for rotor stabilization than the ordinary cfs bias strategy.

This thesis presents the design and analysis for development of a Capacitive Micromachined Ultrasonic Transducer (CMUT), a novel sensor and actuator, aimed at replacing the conventional piezoelectric transducers for air-coupled ultrasonic imaging applications. These CMUTs are fabricated using the silicon micromachining technology wherein all fabrication is done on the surface of a silicon wafer by means of thin-film depositions, patterning with photolithography and etching. The main emphasis of this study is on developing analytical models that serve as effective design tools for the development of these devices. A desirable goal of such study is to create reasonable mathematical models, obtain analytical solutions, wherever possible, for various measures of transducer performance and provide design aids. A logical start is the lumped parameter modeling wherein the explicit dependence of the physical parameters on the spatial extent of the device is ignored. The system lumped parameters, such as the equivalent stiffness, the equivalent mass, and the equivalent damping are extracted from reasonable analytical or numerical models and subsequently used in the static and dynamic analysis of the device. Useful predictions are made with regard to the key transducer parameters, such as, the pull-in voltage, the static deflection, the dynamic response and the acoustic field produced. The modeling work presented embodies two main objectives: (i) it serves to provide direction in the design phase, and, (ii) it serves to aid in the extraction of critical parameters which affect the device behavior. Comparison of the results with the more rigorous FEM simulations as well as with those present in the existing literature assure that the developed models are accurate enough to serve as useful design tools. The distributed parameter modeling is presented next. Analysis of MEMS devices which rely on electrostatic actuation is complicated due to the fact that the structural deformations alter the electrostatic forces, which redistribute and modify the applied loads. Hence, it becomes imperative to consider the electro-elastic coupling aspect in the design of these devices. An approximate analytical solution for the static deflection of a thin, clamped circular plate caused by electrostatic forces which are inherently nonlinear, is presented. The model is based on the Kirchhoff-Love assumptions that the plate is thin and the deflections and slopes are small. The classical thin-plate theory is adequate when the ratio of the diameter to thickness of the plate is very large, a situation commonly prevalent in many MEMS devices, especially the CMUTs. This theory is used to determine the static deflection of the CMUT membrane due to a DC bias voltage. The thin-plate electro-elastic equation is solved using the Galerkin weighted residual technique under the assumption that the deflections are small in comparison to the thickness of the plate. The results obtained are compared to those obtained from ANSYS simulations and an excellent agreement is observed between the two. The pull-in voltage predicted by our model is close to the value predicted by ANSYS simulations. A simple analytical formula, which gives fairly accurate results (to within 3% of the value predicted by ANSYS simulations) for determination of the pull-in voltage, is also presented. As stated, this formula accounts for the elastic deflection of the membrane due to the coupled interaction with the electrostatic field. The effect of vacuum sealing the backside cavity of a CMUT is investigated in some detail. The presence or absence of air inside the cavity has a marked effect upon the system parameters, such as the natural frequency and the pull-in voltage. The possibility of using sealed CMUT cavities with air inside at ambient pressure is explored. In order to estimate the transducer loss due to the presence of air in the sealed cavity, the squeeze film forces resulting from the compression of the trapped air film are evaluated. Towards this end, the linearized Reynolds equation is solved in conjunction with the appropriate boundary conditions, taking the flexure of the membrane into account. From this analysis, it is concluded that, for a sealed CMUT cavity, the presence of air does not cause any squeeze film damping even when the flexure of the membrane is taken into account (the case of a rigid plate is already known). Although the emphasis of the study undertaken here is not on the physical realization of a working CMUT, a single cell as well as a linear array based on the design presented here, were fabricated (in a foundry elsewhere) in order to verify some of the most fundamental device parameters from experimental measurements. The fabricated devices have been characterized for their resonant frequency, quality factor, and structural integrity. These tests were conducted using the laser Doppler vibrometer and the Focused Ion Beam milling. Having investigated thoroughly the behavior of a single cell, we proceed to demonstrate how these cells can be arranged optimally in the form of an array to provide a comprehensive ultrasonic imaging system. A thorough analysis of the requirements for the array architecture is undertaken to determine the optimal configuration. The design constraints that need to be taken into account for CMUT arrays, especially for NDE applications, are presented. The main issue of designing an array consisting of a large number of CMUT cells required for producing a pressure wave of sufficient strength which is detectable upon reflection from the desired location even after suffering severe attenuation resulting from propagation in various media is addressed. A scalable annular array architecture of CMUT cells is recommended based on the analysis carried out.

Micromachined biosensors are used in chemical and biological applications. A biosensor which uses mass based transduction is called a mass sensor. Mass sensors are used to detect extremely small mass of biomolecules such as proteins, viruses or even parts of DNA in the range of femtograms (10-15 gm) to zeptograms (10−21 gm). Highly effective and reliable microcantilevers are used for detecting the mass of biomolecules using either static deflection or dynamic resonant peak shifts. The main objective of our work is to investigate the effect of elasticity of the attached mass on the shift in the resonant frequency and examine the validity of the rigid mass assumption used in the literature. The natural frequencies of a resonator are either found by solving the governing differential equation or approximately using Rayleigh-Ritz method. The mass of a body, attached to a resonator beam is determined using resonant frequency shift method. In our study, we derive an analytical expression for ‘δm’ based on the shift in frequency ‘δf’ that accounts for the elasticity of the added mass and the location of the mass on the beam. We study the simplest model to incorporate these effects where the added mass is itself modeled as a single degree of freedom spring-mass system. The entire system is represented as a 2-DOF lumped model of cantilever and the attached elastic mass. The natural frequencies are obtained using eigenvalue analysis. We study the mass estimation of Escherichia Coli (E. Coli), a food borne pathogen, using experimental results reported in the literature. We treat E.Coli as an elastic mass and model it as a single degree of freedom system to account for its elasticity. We use the elastic model as well as the rigid mass model to check the results available in the literature and point out the difference that results in mass estimation using the two models. To demonstrate the effect of elasticity on mass sensing using the resonant peak shift technique, we conduct mesoscale experiments. Since the fundamental principle does not depend on any phenomenon exclusively dependent on micro scales, the mesoscale experiments are justified. For this purpose, an experimental set-up with metallic cantilevers and flexible rubber strands as attached masses are used. We also use our experimental set-up to study the effect of positional inaccuracy of the added mass (rigid) in the computation of its mass from the shift in the resonance frequency. The results obtained show that elasticity of the added mass as well as its position on the resonator affect the computed mass but this effect is dependent on the relative stiffness and mass of the resonator and the added mass. We also observe the limitations of the experiments in carrying out studies over the desired range of parameters. We also create a computational model of the system and carry out simulations to explore a larger range of parameter values. In particular, we create an FEM model of our system in ANSYS, and carry out modal analysis for the cantilever beam resonator with and without the added mass, varying the relative stiffness and mass of the two components (the cantilever beam and the added mass). We compare the results of shift in the resonant frequency with those obtained from the rigid mass model. The results show the effect of elasticity clearly in certain ranges of relative stiffness and mass.