Active Magnetic Bearings for Energy Storage Systems for Combat Vehicles

Advanced energy storage systems for electric guns and other pulsed weapons on combat vehicles present significant challenges for rotor bearing design, Active magnetic bearings (AMBs) present one emerging bearing option with major advantages in terms of lifetime and rotational speed, and also favorably integrate into high-speed flywheel systems. The Department of Defense Combat Hybrid Power Systems (CHPS) program serves as a case study for magnetic bearing applications on combat vehicles. The University of Texas at Austin Center for Electromechanics (UT-CEM) has designed active magnetic bearing actuators for use in a 5 MW flywheel alternator with a 318 kg (700 lb), 20000 rpm rotor. To minimize CHPS flywheel size and mass, a topology was chosen in which the rotating portion of the flywheel is located outside the stationary components. Accordingly, magnetic bearing actuators are required which share this configuration. Because of inherent low loss and nearly linear force characteristics, UT-CEM has designed and analyzed permanent magnet bias bearing actuators for this application. To verify actuator performance, a nonrotating bearing test fixture was designed and built which permits measurement of static and dynamic force. An AMB control system was designed to provide robust, efficient magnetic levitation of the CHPS rotor over a wide range of operating speeds and disturbance inputs, while minimizing the occurrence of backup bearing touchdowns. This paper discusses bearing system requirements, actuator and controller design, and predicted performance; it also compares theoretical vs. measured actuator characteristicsCenter for Electromechanic

Advanced control of active magnetic bearings with learning control schemes

Master'sMASTER OF ENGINEERIN

Feasibility assessment of a Kalman filter approach to fault detection and fault-tolerance in a highly unstable system: The RIT heart pump

The purpose of this project is to assess the feasibility of a Kalman Filter approach for fault detection in a highly unstable system, specifically the heart pump currently under development at RIT. Simulations and experimental work were completed to determine the effects of possible position sensor fault conditions on the system; that information was then used in conjunction with a pair of Kalman filters to create a method of detecting faults and providing fault-tolerant operation. The heart pump system was modeled using Simulink and then the fault diagnosis and tolerance system was added to the model and tested via simulation in SIMULINK TM. The simulations showed the filters were able to calculate and remove bias caused by any type of position sensor error, provided the estimated plant model is nearly identical to the actual plant model. Sensitivity analysis showed that the fault detection/fault-tolerance method is extremely sensitive to discrepancies between the estimated plant model and actual pump behavior. Because of this, it is considered unfeasible for implementation on a real system. Experimental results confirmed these findings, demonstrating the drawbacks of model-based fault detection and tolerance methods

Design and Implementation of Modern Controls for Drive and Suspension of a High Speed Double Conical Bearingless Motor on a Real-Time System

In this work, modern control approaches for drive and suspension of a high speed double conical bearingless motor are designed. Firstly, the air gap flux density and the forces acting on the rotor are analytically calculated. Subsequently, an elaborate model of the magnetically levitated rotor is developed, which considers the non-collocation of position sensors and levitation windings as well as the presence of angular motion. Three different control approaches are designed and simulated. The first approach comprises a state controller augmented with integral action, with which the closed loop dynamics are freely defined after pole placement. The other two approaches concern Linear Quadratic Gaussian and Model Predictive control. The pole placement control approach is tested successfully on the test bench with the real motor. Sinusoidal disturbance forces, with the rotational frequency, can cause large rotor orbits and may drive the inverters to their limits. For this reason, two synchronous filtering control strategies are developed. Using Imbalance Force Compensation, the rotor can be driven with low orbits at relatively low speed and using Imbalance Force Rejection, the rotor can be driven with low levitation currents at high speed. The control performance is evaluated by measurements and the measured frequency response of the closed loop system is presented

Stabilization of electrodynamic bearings with active magnetic dampers

Electrodynamic Bearings (EDBs) are a kind of passive magnetic bearings that exploits the interaction between the induced eddy currents in a conductor and a magnetic field to provide re-storing forces. They have been regarded as an appealing alternative to Active Magnetic Bearings (AMBs), having the ability to provide positive stiffness passively without introducing negative stiff-ness in any direction. Compared to AMBs, EDBs present advantages such as lower cost and higher reliability due to simplicity of configurations. One of the most interesting features of EDBs is the possibility to obtain stable levitation using standard conductive materials at room temperature, requiring no control systems, power electronics or sensors. Thus EDBs could be suitable solutions for highâspeed rotating machinery such as flywheels, small size compressors, centrifuges and vac-cum pumps. Despite these promising characteristics of EDBs, applications are still limited because of instability issues. The main problem is that the effect of the rotating damping force in EDBs causes unstable behavior of the rotor. In existing solutions, stabilization is achieved mainly by introducing non-rotating damping to the rotor with passive ways. Although stable levitation is possible, the effectiveness of the existing methods is still limited. A hybrid solution has been proposed in this thesis, where EDBs are combined with active magnetic dampers (AMDs). Using similar magnetic actuators as those used in classical active magnetic bearings (AMBs), nonârotating damping forces are applied on the rotor supported by EDBs to obtain stable operation. This system is designed to exploit the high reliability of EDBs, overcoming the stability problem by means of controllable AMDs. It results in increased global system reliability. In case of AMBs failure, the EDBs are able to guarantee a stable levitation down to a certain speed considered safe for touchâdown. During the operation speed range, the AMDs provide nonârotating damping to stabilize the rotor. This nonârotating damping can be easily tuned during rotor operation phase. At low speeds when the EDB forces are not sufficient to support the rotor, the active magnetic actuators work as AMBs to guarantee stable levitation of the rotor in a wide speed range. Besides, the EDBâAMD configuration also allows characterizeing in dynamic condition, which opens the possibility to establish damping strategy that can in perspective be implemented by totally passive means, such as eddy currents, elastomeric mounts. The combination of EDB and AMD forces are studied both analytically and experimentally. An analytical model of the system, as well as a test rig, has been built. Simulations and experi-mental tests validate the model and characterize the system. The effectiveness of the proposed solution is confirmed. The control strategy of AMDs and stabilizing alternatives of EDBs are dis-cussed consequently. The combination of EDB and AMD can be exploited to investigate easily dif-ferent damping strategies

IDENTIFICATION OF SEALS IN ROTATING MACHINES

Kvantifikace dynamických silových koeficientů labyrintových ucpávek používaných v parních turbínách není v současné době jednoznačně vyřešena. Výpočetní numerické nástroje umožňují výpočet koeficientů při návrhu turbosoustrojí, avšak nedostatek experimentálních dat neumožňuje porovnání a validaci výsledků. Proto je nezbytné provádět experimentální měření a identifikaci koeficientů ucpávek. Tato disertační práce se zaměřuje na identifikaci koeficientů ucpávek s využitím magnetických ložisek. Je popsána konstrukce nového experimentálního zařízení s magnetickými ložisky a jeho uvádění do provozu. Dále jsou prezentovány výsledky identifikačních experimentů labyrintové ucpávky. Motivací bylo porovnání výsledků s výpočetním numerickým nástrojem používaným ve společnosti Doosan Škoda Power, která se také účastnila projektu. Úvodní část této práce se zaměřuje na poskytnutí uceleného pohledu na význam silových koeficientů ucpávek a na způsoby jejich identifikace s využitím aktivních magnetických ložisek. Je vysvětlen vliv koeficientů na stabilitu rotoru a jsou popsány identifikační metody v časové a frekvenční oblasti. Dále se práce věnuje popisu nového experimentálního zařízení a jeho uvádění do provozu. Zařízení se skládá z jednoho axiálního a dvou radiálních magnetických ložisek, která podpírají rotor a řízeně budí jeho vibrace. Dále jsou součástí zařízení motor, stator s ucpávkami a měřící ústředna s elektronikou. Je popsán návrh zpětnovazebního řízení magnetických ložisek, které umožnuje vybudit požadované vibrace rotoru během identifikačního experimentu ucpávky. Dále jsou měřeny magnetické síly radiálních ložisek pomocí snímačů instalovaných pod ložiskovými domečky. Je popsán postup jejich kalibrace pomocí hmotnosti rotoru a měření jeho výchylky. V závěru práce jsou představeny výsledky identifikačního experimentu labyrintové ucpávky. Z měření tlaku v kavitách labyrintové ucpávky a výchylky rotoru jsou určeny síly působící na rotor vlivem proudění média v ucpávce a jsou identifikovány koeficienty ucpávky. Pro okrajové podmínky odpovídající experimentu byly napočítány ve výpočetním nástroji odpovídající koeficienty ucpávky. Vypočtené a identifikované koeficienty vykazují určitou shodu, nicméně bude zapotřebí pokračovat v práci a provést další experimenty pro ověření a zpřesnění výsledků. Změřené magnetické sily ložisek byly použity pro určení sil působících na rotor vlivem ucpávky. Další práce bude spočívat v analýze a upřesnění získaných sil tak, aby mohl být tento způsob měření sil použit pro identifikaci koeficientů ucpávek.ObhájenoThe quantification of the dynamic force coefficients of labyrinth seals used in steam turbines is currently not clearly resolved. Numerical tools offer the calculation of seal coefficients in the design of the turbomachinery; however, a lack of experimental data makes comparison and verification impossible. Therefore, it is necessary to carry out experimental measurements and identification of seal coefficients. This dissertation focusses on identification of seal coefficients with use of magnetic bearings. The design and commissioning of a new test device with active magnetic bearings is documented. Furthermore, preliminary experiments were performed, and the results are presented. The motivation was to compare the results with the numerical tool used at Doosan Škoda Power, which is the manufacturer of steam turbines and a participant of this project. The introductory part of this work is focused on providing a comprehensive review of the meaning of the seal dynamic force coefficients and methods of their identification, especially when using magnetic bearings. The effect of coefficients on rotor stability is explained and the identification methods in time domain and frequency domain are introduced. Furthermore, the work describes a new experimental device and its commissioning. The test device consists of one axial and two radial magnetic bearings that support a rotor and excite the rotor vibration. The test device also includes a drive unit, stator with seals and the control and measurement system. The design of feedback control system of magnetic bearings is described. The control system enables to excite the required rotor vibration during the experiment. The measurement of the magnetic force of radial bearings is carried out using sensors mounted under the bearing housing. A calibration procedure using known rotor mass and measured vibration is described. Finally, the results of the identification experiments are presented. The seal fluid induced forces acting on the rotor were determined based on seal pressure and rotor vibration measurement and the seal coefficients were identified. The seal coefficients were calculated using the numerical tool for the boundary conditions corresponding to the experiment. The calculated and identified coefficients show a certain agreement. However, it will be necessary to carry out further experiments and future work for verification and refinement. The measured magnetic forces were used to determine the fluid-induced forces. Further analysis and refinement of the acquired forces is required

Commande par mode glissant de paliers magnétiques actifs économes en énergie : une approche sans modèle

Abstract : Over the past three decades, various fields have witnessed a successful application of active magnetic bearing (AMB) systems. Their favorable features include supporting high-speed rotation, low power consumption, and rotor dynamics control. Although their losses are much lower than roller bearings, these losses could limit the operation in some applications such as flywheel energy storage systems and vacuum applications. Many researchers focused their efforts on boosting magnetic bearings energy efficiency via minimizing currents supplied to electromagnetic coils either by a software solution or a hardware solution. According to a previous study, we adopt the hardware solution in this thesis. More specifically, we investigate developing an efficient and yet simple control scheme for regulating a permanent magnet-biased active magnetic bearing system. The control objective here is to suppress the rotor vibrations and reduce the corresponding control currents as possible throughout a wide operating range. Although adopting the hardware approach could achieve an energy-efficient AMB, employing an advanced control scheme could achieve a further reduction in power consumption. Many advanced control techniques have been proposed in the literature to achieve a satisfactory performance. However, the complexity of the majority of control schemes and the potential requirement of powerful platform could discourage their application in practice. The motivation behind this work is to improve the closed-loop performance without the need to do model identification and following the conventional procedure for developing a model-based controller. Here, we propose applying the hybridization concept to exploit the classical PID control and some nonlinear control tools such as first- and second-order sliding mode control, high gain observer, backstepping, and adaptive techniques to develop efficient and practical control schemes. All developed control schemes in this thesis are digitally implemented and validated on the eZdsp F2812 control board. Therefore, the applicability of the proposed model-free techniques for practical application is demonstrated. Furthermore, some of the proposed control schemes successfully achieve a good compromise between the objectives of rotor vibration attenuation and control currents minimization over a wide operating range.Résumé: Au cours des trois dernières décennies, divers domaines ont connu une application réussie des systèmes de paliers magnétiques actifs (PMA). Leurs caractéristiques favorables comprennent une capacité de rotation à grande vitesse, une faible consommation d'énergie, et le contrôle de la dynamique du rotor. Bien que leurs pertes soient beaucoup plus basses que les roulements à rouleaux, ces pertes pourraient limiter l'opération dans certaines applications telles que les systèmes de stockage d'énergie à volant d'inertie et les applications sous vide. De nombreux chercheurs ont concentré leurs efforts sur le renforcement de l'efficacité énergétique des paliers magnétiques par la minimisation des courants fournis aux bobines électromagnétiques soit par une solution logicielle, soit par une solution matérielle. Selon une étude précédente, nous adoptons la solution matérielle dans cette thèse. Plus précisément, nous étudions le développement d'un système de contrôle efficace et simple pour réguler un système de palier magnétique actif à aimant permanent polarisé. L'objectif de contrôle ici est de supprimer les vibrations du rotor et de réduire les courants de commande correspondants autant que possible tout au long d'une large plage de fonctionnement. Bien que l'adoption de l'approche matérielle pourrait atteindre un PMA économe en énergie, un système de contrôle avancé pourrait parvenir à une réduction supplémentaire de la consommation d'énergie. De nombreuses techniques de contrôle avancées ont été proposées dans la littérature pour obtenir une performance satisfaisante. Cependant, la complexité de la majorité des systèmes de contrôle et l'exigence potentielle d’une plate-forme puissante pourrait décourager leur application dans la pratique. La motivation derrière ce travail est d'améliorer les performances en boucle fermée, sans la nécessité de procéder à l'identification du modèle et en suivant la procédure classique pour développer un contrôleur basé sur un modèle. Ici, nous proposons l'application du concept d'hybridation pour exploiter le contrôle PID classique et certains outils de contrôle non linéaires tels que contrôle par mode glissement du premier et du second ordre, observateur à grand gain, backstepping et techniques adaptatives pour développer des systèmes de contrôle efficaces et pratiques. Tous les systèmes de contrôle développés dans cette thèse sont numériquement mis en oeuvre et évaluées sur la carte de contrôle eZdsp F2812. Par conséquent, l'applicabilité des techniques de modèle libre proposé pour l'application pratique est démontrée. En outre, certains des régimes de contrôle proposés ont réalisé avec succès un bon compromis entre les objectifs au rotor d’atténuation des vibrations et la minimisation des courants de commande sur une grande plage de fonctionnement

Continuous time state-space model identification with application to magnetic bearing systems

This thesis presents the identification of continuous time linear multi-variable systems using state-space models. A data-driven approach in realization by the subspace methods is carried out in developing the models. In this thesis, the approach by subspace methods is considered for both open-loop and closed-loop continuous time system identification. The Laguerre filter network, the instrumental variables and the frequency sampling filters are adopted in the framework of subspace model identification. More specifically, the Laguerre filters play a role in avoiding problems with differentiation in the Laplace operator, which leads to a simple algebraic relation. It also has the ability to cope with noise at high frequency region due to its orthogonality functions. The instrumental variables help to eliminate the process and measurement noise that may occur in the systems. The frequency sampling filters are used to compress the raw data, eliminate measurement noise so to obtain a set of clean and unbiased step response data. The combination of these techniques allows for the estimation of high quality models, in which, it leads to successful performance of the continuous time system identification overall. The application based on a magnetic bearing system apparatus is used to demonstrate the efficacy of the proposed techniques

Applications of axial and radial compressor dynamic system modeling

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, February 2001.Includes bibliographical references (p. 255-262).The presented work is a compilation of four different projects related to axial and centrifugal compression systems. The projects are related by the underlying dynamic system modeling approach that is common in all of them. Two types of models are introduced, suitable for modeling the dynamic behavior of axial and centrifugal compression systems: a compact single semi-actuator disk model, Model I, and a new modular multi semi-actuator disk model, Model II. The first project analyzes aerodynamically induced whirling forces in axial-flow compressors and a new unsteady low order model is introduced to predict the destabilizing whirling forces. The model consists of two parts: compressor Model I with the effect of tip-clearance induced distortion, and an aerodynamically induced force model. The modeling results are compared to experimental data obtained from the GE Aircraft Engines test program on compressor whirl. Previously outstanding whirl-instability issues are resolved, including prediction of the direction and magnitude of rotor whirl-inducing forces; such issues are important in the design of modern axial-flow compressors.(cont.) Additional insight is gained from the model on the effects of forced rotor whirl. In particular, a non-dimensional parameter is deduced that determines the direction of rotor whirl tendency in both compressors and turbines due to tangential blade loading forces. The second project is a first-of-a-kind feasibility study of an active stall control experiment with a mag- netic bearing servo-actuator in the NASA Glenn high-speed single-stage compressor test facility. Together with CFD and experimental data the tip-clearance sensitive compressor Model I was used in a stochastic estimation and control analysis to determine the required magnetic bearing performance for compressor stall control. A magnetic bearing servo-actuator was designed that fulfilled the performance specifications, setting a milestone in magnetic bearing development for aero-engine applications. Control laws were then developed to stabilize the compressor shaft. In a second control loop, a constant gain controller was imple- mented to stabilize rotating stall. A detailed closed loop simulation at 100% corrected design speed resulted in a 2.3% reduction of stalling mass flow which is comparable to results obtained in the same compressor using unsteady air injection.(cont.) The third project is the investigation of unsteady impeller-diffuser interaction effects on compressor stability. First, the unsteady blade-row interaction in axial compressors is analyzed using Model II. The results reveal a new signature of pre-stall waves that travel backward, altering the system dynamics when rotor and stator are moderately coupled. The physical mechanism for this behavior is explained from first principles and a coupling criterion is presented. The theory is then applied to centrifugal compressors and in particular to the NASA CC3 high-speed centrifugal compressor, in which experiments are conducted to verify the model predictions. The measurements show the predicted behavior and confirm the existence of backward traveling stall pre-cursors. The fourth project is an experimental demonstration of stability enhancement in the NASA CC3 high-speed centrifugal compressor with air injection. Based ...by Zoltán Spakovszky.Ph.D