145 research outputs found
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Nonlinear Control of a Flexible Rotor Magnetic Bearing System: Robustness and the Indefinate Model
Previously published control strategies for magnetic bearings primarily focus on linear optimal control techniques. While these methods afford many advantages, conspicuously absent from the literature are detailed attempts at nonlinear control. Here, we obtain the equations of motion of an overhung flexible rotor supported in magnetic bearings with two different levels of model sophistication. We derive a generic nonlinear controller in the manner of feedback linearization, and compare the eigenanalysis and transient response of the two rotor models under the action of this >perfect model> controller. We then proceed to obtain a robust nonlinear controller through the sliding mode technique and demonstrate that robustness by implementing it on an uncertain model.Center for Electromechanic
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Rotor Slot Permeance Harmonics under Distorted Air-Gap Flux Waveform for Cage Induction Motors
The air-gap flux waveform for a cage induction machine is not sinusoidal in shape and contains various harmonics, including the phase-belt harmonics, slot magnetomotive force (mmf) harmonics, slot permeance harmonics, and saturation harmonics. The slot mmf and permeance harmonics affect the stray losses considerably. Among the saturation harmonics, the third harmonic is usually the most significant one unless it is suppressed by allowing circulating current to flow. The magnitude and phase angle of the saturation harmonics compared to those of fundamental flux waveform depend on whether teeth or core (back iron) section is more saturated. The various amount of third harmonic air gap flux with different phase angle is intentionally injected into a cage induction motor to examine the effects of distorted flux waveform on rotor slot permeance harmonics. For the same air gap fundamental flux, the waveform which has the higher air gap peak flux also produce higher rotor slot permeance harmonics. The stator core losses, no-load rotor high frequency losses, no-load losses, and stray load losses under distorted air gap flux waveforms are presented and discussed.Center for Electromechanic
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Electromagnetic Launch Research at The University of Texas at Austin
The Center for Electromechanics at The University of Texas at Austin (CEM-UT) has been involved in the development of rotating electrical machines for pulsed power applications since 1973 and in the development of electromagnetic launch technology since 1979. The CEM-UT single shot laboratory gun, a 90 mm round-bore railgun 10 m long, is reviewed. The extensive operating experience with the ferromagnetic compulsator built at CEM-UT in the mid-1980's is reviewed and two new compulsator projects are described. Finally, future trends in the evolution of power supplies for electromagnetic railguns are surveyed.Center for Electromechanic
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Development of a simple nonlinear switched reluctance motor model using measured flux linkage data and curve fit
This paper presents the formulation and simulation of a simple nonlinear switched reluctance motor (SRM) model. The model formulation is developed by first measuring the motor's flux linkage. A suitable 3 dimension shape function is developed to curve fit this data. Multiple shape functions are added together to reduce the mean square error of the flux linkage equation. We call this equation the Chan Series. Motor parameters such as inductance and back electromotive force coefficient equations are obtained by differentiating the Chan Series. The coenergy and motor torque equations are derived from the Chan Series by mathematical manipulation. Nonlinear model analysis is then carried out. Ways to indicate the motor size that takes into consideration the effect of magnetic flux saturation are proposed. Two motor relations are presented. Computer simulation of the model for chop, singlechop, and single-pulse modes are performed and compared to those published in [19]. The comparisons show that the developed model can predict the SRM behavior.Center for Electromechanic
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Professional Responsibility: The Role of Engineering in Society
We argue that the practice of engineering does not exist outside the domain of societal interests. That is, the practice of engineering has an inherent (and unavoidable) impact on society. Engineering is based upon that relationship with society (inter alia). An engineer's conduct (as captured in professional codes of conduct) toward other engineers, toward employers, toward clients, and toward the public is an essential part of the life of a professional engineer, yet the education process and professional societies pay inadequate attention to the area. If one adopts Skooglund's definition of professional ethics (1) (how we agree to relate to one another), then the codes of professional conduct lay out a road map for professional relationships. As professionals, engineers need to internalize their codes and to realize that they have a personal stake in the application of codes as well as the process of developing the codes. Yet, most engineers view professional codes as static statements developed by >others> with little (or no) input from the individual engineer. Complicating the problem, questions of professionalism (such as ethics) are frequently viewed as topics outside the normal realm of engineering analysis and design. In reality, professional responsibility is an integral part of the engineering process.Center for Electromechanic
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Iron Core Compulsators for Railgun Power Supplies
Recent development efforts on compulsator based railgun power supplies have been focused on lightweight, composite, self-excited machines. However, operating experience with the Iron-core (ferromagnetic) compulsator at the Center for Electromechanics at The University of Texas at Austin (CEM-UT) has shown it to be extremely reliable and much more versatile than originally envisioned. Furthermore, recent experiments with high current solid state switches and studies or staged multiple compulsator discharges have made multiple compulsator installations attractive. For railgun installations where generator weight and volume are not primary concerns, multiple iron-core compulsators can provide a low cost, extremely versatile power supply. The design of such a system is presented, incorporating many or the most attractive features or advanced compulsator concepts. These Include: direct connection to mechanical prime power, Inherent power averaging, low jerk flat top current pulses producing high acceleration ratios, reclamation of the railgun magnetic energy with attendant elimination or muzzle arc, and rapid fire operation.Center for Electromechanic
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Hypervelocity Electromagnetic Gun Development at CEM-UT
Interest in railguns at the Center for Electromechanics at The University of Texas at Austin (CEM-UT) was the result of a visit to the railgun facility at the Australian National University (ANU) at Canberra in 1979. Soon after that visit the concept of a Distributed Energy Store (DES) railgun was invented and the first injected railgun was tested at CEM-UT. When railguns were introduced into the defense community in 1980, the technology started to grow in the United States. With the announcement of the Strategic Defense Initiative (SDI), electromagnetic launcher research took another quantum step. Today CEM -UT is actively testing state-of-the-art launchers on the pulsed power supplies developed at CEM- UT over the past twelve years. In addition, CEM-UT is preparing for the future with the installation of the Balcones Homopolar Generator Power Supply and by maintaining programs in state-of-the-art rep- rated power supply development and hypervelocity launch. A detailed description of the CEM- UT facility is presented in Appendix A at the end of the text.Center for Electromechanic
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Power Supplies for Airborne Laser Systems
This paper investigates the power supply options for an airborne laser system (solid state laser diodes). The application demands a power supply capable of a high repetition rate (1,428 pulses per engagement over 2 s) and delivering total energy of 20 MJ (i.e. 14 kJ per pulse). The high repetition rate precludes the use of capacitors. Hence rotating machines storing inertial energy appear to be the most viable option. In this paper the compensated pulsed alternator (compulsator) invented by the Center for Electromechanics at the University Of Texas (CEM-UT) at Austin is examined as a possible power supply option for the above application. The laser system is characterized as a 1.25 m (ohm) resistive load. In the past the compulsator has been examined essentially for inductive loads like the railgun aid hence the analysis presented here throws new light on the capabilities of the compulsator. Several configurations involving the compulsator are evaluated in this paper viz. two machines operating in parallel, a single machine storing all the energy and an external flywheel storing the required energy with compulsator serving as a energy conversion device. The paper explores the lower limits on the compulsator size and weight for the different configurations.Center for Electromechanic
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Using the Mixed Newton-Euler Formulation in the Orientation Control of Flexibly Mounted Bodies
Extended bodies whose own flexibility may conditionally be neglected can often be faithfully treated directly by any of several formulations based on classical dynamics. Here, the mixed approach employing the Newton-Euler equations for centroidal body-fixed frames will be used, where the absolute angular orientation will be computed via the associated kinematic differential equations relating the rotation matrix with the angular velocity vector. As an example of the practical (but restricted) use of simplified classical methods - and of the computationally attractive mixed Newton-Euler ODE formulation - the mathematical model of the U.S. Army's MLRS-ILMS mechanical launcher is described which is automatically controlled to simultaneously rotate about nonintersecting, nominally vertical and horizontal axes when commanded to target absolute angular orientation coordinates.Center for Electromechanic
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Development of Preloading and Precooling Systems for a Single-Turn Ignition Tokamak
A basic requisite of the Fusion Ignition Experiment (IGNITEX)1 is the production of a high (20 T) toroidal field (TF) by a single turn coil. The proposed high-field technology uses precooling and preloading systems. The Ignition Technology Demonstration (ITD) program, designed to produce 20 T on axis in a 0.06 scale prototype TF coil, utilizes a preloading structure and a precooling system. The preloading structure is a hydraulic press built around the TF coil, capable of a force of 1.1 Mlb (4.9 MN) and a stroke of 0.5 in. (1.3 cm). The precooling system is an open-top LN2 cryostat tub integrated into the preload press. The IGNITEX experiment is estimated to use a preload press with force capacity of approximately 150,000 tons (1.3 GN), and with a stroke on the order of 2 in. (5.1 cm). Design considerations include efficient use of material, design of large scale hydraulic actuators, shielding to reduce radiation from activated material, maintenance, cost, and reliability. The precooling system design involves considerations of feedthroughs, minimal cooling time between pulses, maintenance and reliability.Center for Electromechanic
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