Active control constitutes the state of the art in vibration management in rotating machines. However, existing designs are impractical and costly, and hence not yet widely applied. The goal of the research reported here was to develop a design which would allow the implementation of active technology in a wider range of rotating machine applications. Thus, this study focuses on a novel active rotor topology, consisting of a hollow rotor with internally mounted sensors and actuators. This layout provides greater freedom to select the sensor and actuator positions along the rotor, and naturally protects the devices from harsh working environments. The research was structured according to four themes. Firstly, the concept feasibility was explored by constructing a fully functioning prototype. MEMS accelerometers and mass balancer actuators were mounted in an assembled rotor, together with a microcontroller and radio unit to enable wireless transmission of data. Secondly, the behaviour of MEMS accelerometers in a rotating frame of reference was studied. An output model was derived and applied to the study of whirl orbits and transient vibration. Further, techniques were developed to extract mean displacement and angular velocity information from the sensor signals. An analysis of potential sources of measurement error was conducted, and methods for their mitigation devised. The third theme focused on developing active vibration control techniques suitable for use with active rotors. The core of this work is the development and successful implementation of a non a priori method, Algorithmic Direct Search Control. This technique enables vibration to be minimised without knowledge of the system characteristics, by applying a direct search optimisation technique as a control law. Finally, the combination of active rotors and Active Magnetic Bearings was considered to tackle the problem of sensor/actuator non-collocation. The challenge of levitating a rotor on AMBs using only internal accelerometers was approached via integration-based displacement information extraction, to exploit existing PID controllers. This method proved unfeasible in practice, but valuable lessons were derived from the study. The key finding of this work is that active rotor technology is versatile, cost-effective, powerful and feasible. As such, it offers great potential as a route to achieving a more practical and generalised implementation of active control technology in rotating machinery.

An objective in the design of high performance machinery is to minimize weight so magnetic bearings are often designed to operate slightly lower than the magnetic material saturation. Further weight reduction in the bearings requires operation in the nonlinear portion of the B-H curve. This necessitates a more sophisticated analysis at the bearing and rotordynamic system levels during the design stage. This dissertation addresses this problem in a unique manner by developing a fully nonlinear homopolar magnetic bearing model. The nonlinear dynamics of permanent magnet-biased homopolar magnetic bearing (PMB HoMB) system with 2-dof rigid and 4-dof flexible rotor is analyzed. The dynamic behavior of the rotor-bearing system is examined in the feedback control loop that includes low pass filter effects. An analytical magnetization curve model is proposed to predict the nonlinear magnetic force under the influence of the magnetic flux saturation more accurately. The modified Langmuir method with the novel correction terms for the weak flux region is used to curve-fit the experimental magnetization data of Hiperco 50. A new curve fit model of the B-H curve is shown to have significantly better agreement with the measured counterpart than conventional piecewise linear and other models. PMB HoMB characteristics with flux saturation, such as forces depending on the rotor position and bearing stiffness, are compared with these other models. Frequency response curve, bifurcation diagram, Poincare plot, and orbit plot are utilized to demonstrate the effects of the nonlinearities included in the 2-dof rotorbearing system. Due to heavy static loads applied to the rotor, it operates within the magnetic flux saturation region at the bearing clearance. The voltage saturation in the power amplifier of the magnetic bearing introduces lag in the control loop and the response of the heavily loaded 4-dof rotor-bearing system shows that limit cycle stability can be achieved due to the magnetic flux saturation or current saturation in the amplifier; otherwise the system would experience a destructive instability. These simulation results provide the first explanation of this commonly observed limit cycle which is referred to as ‘virtual catcher bearings’.

The Electron Energy Corporation (EEC) along with National Aeronautics and Space Administration (NASA) in collaboration with Vibration Control and Electro mechanics Lab (VCEL), Texas A & M University, College Station, TX are researching on high temperature permanent magnet based magnetic bearings. The magnetic bearings are made of high temperature resistant permanent magnets (up to 1000 degrees F). A test rig has been developed to test these magnetic bearings. The test rig mainly consists of two radial bearings, one axial thrust bearing and two catcher bearings. The test rig that the catcher bearing is inserted in is the first ultra-high temperature rig with permanent magnet biased magnetic bearings and motor. The magnetic bearings are permanent magnet based which is a novel concept. The Graphalloy bearings represent a new approach for ultra-high temperature backup bearing applications. One of the main objectives of this research is to insure the mechanical and electrical integrity for all components of the test rig. Some assemblies and accessories required for the whole assembly need to be designed. The assembly methods need to be designed. The preliminary tests for coefficient of friction, Young's modulus and thermal expansion characteristics for catcher bearing material need to be done. A dynamic model needs to be designed for studying and simulating the rotor drop of the shaft onto the catcher bearing using a finite element approach in MATLAB. The assembly of the test rig was completed successfully by developing assembly fixtures and assembly methods. The components of the test rig were tested before assembly. Other necessary systems like Sensor holder system, Graphalloy press fit system were designed, fabricated and tested. The catcher bearing material (Graphalloy) was tested for coefficient of friction and Young's modulus at room and high temperatures. The rotor drop was simulated by deriving a dynamic model, to study the effect of system parameters like clearance, coefficient of friction, negative stiffness, initial spin speed on system behavior. Increasing the friction increases the backward whirl and decreases the rotor stoppage time. Increasing the clearance reduces the stoppage time and increases the peak bearing force. Increasing the initial spin speed increases the rotor stoppage time. The maximum stress encountered for as built conditions is more than allowable limits.

Thesis (Ph. D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2004. / Habetler, Thomas, Committee Member ; Sadegh Nader, Committee Member ; Taylor David, Committee Member ; Tsiotras Panagiotis, Committee Co-Chair ; Heck-Ferri Bonnie, Committee Co-Chair. Vita. Includes bibliographical references (leaves 319-326).

The McTronX Research group at the Potchefstroom campus of the North-West University, aims to establish a knowledge base on active magnetic bearing (AMB) systems. Up to date, the group has established a firm knowledge base on various topics related to AMB systems. A recent focus was the design and development of a high speed AMB supported rotor system called the rotor delevitation system (RDS) to analyse rotor drops. During the testing phase of the RDS, the machine exhibited vibrations, of which the origins were unknown. The research presented in this dissertation sets out to characterize the vibrations of the RDS, which is the group’s first attempt to fulfil the need for characterizing vibrations in an AMB supported rotor. Emphasis is placed on characterizing the natural response of the RDS rotor, stator and integrated system. The research project is defined in terms of four main objectives: rotor and stator characterization, modelling, system characterization and rotor dynamic diagnostics. A comprehensive literature study introduces the fundamental concepts regarding vibrations of single and multiple degree of freedom systems. These concepts include; natural frequencies, damping, machine vibrations, rotor dynamics and modelling techniques. These modelling techniques are introduced to verify the experimental methodology used to determine the natural frequencies. A critical overview of the literature contextualises the theory with the research investigation. For the RDS rotor and stator characterization, a modal analysis process also known as the “bump test” is implemented in order to validate the bending natural frequencies of the rotor and stator. A simulation model of the RDS is constructed in the finite element (FE) package DyRoBeS®. The model is verified with a numerical and an analytical model and validated with the measured bending natural frequencies of the RDS rotor. For the system characterization, a number of modal analysis processes are implemented, which validates the rigid body natural frequencies of the RDS. These frequencies are also used to validate the FE simulation. The origins of the synchronous vibration harmonics are verified by formulating and evaluating hypotheses according to different modal analysis processes. From the RDS rotor modal analysis it was identified that a bending natural frequency of the rotor is situated at approximately 443.33 Hz. This was verified using the FE simulation model. During the system modal analyses, it was identified that only one rigid body natural frequency, situated at approximately 62 Hz, is excited. This frequency increases with the differential gain control parameter of the system up to approximately 140 Hz. After evaluating two hypotheses regarding the origins of the synchronous vibrations harmonics, it was verified that non-circularity of the rotor at the measuring positions is the cause. Overall the objectives of the study were addressed by characterizing the natural frequencies of the rotor, stator and RDS system. This include the mode forms of the rigid body and bending natural frequencies of the system. The results of the verification and validation methods correlated, which imply these methods are reliable to identify the origins of vibrations in rotor-bearing systems. The differential gain control parameter of the AMBs control the equivalent damping in the RDS. An increase in this parameter should lead to a decrease in amplitude and frequency of the maximum vibration, and vice versa. However, it was noted that an increase in this parameter caused a linear increase in the rigid body natural frequency. The literature indicates that this effect can only be caused by an increase in system stiffness. It is therefore recommended to evaluate the stiffness of the system as a function of the differential gain control parameter. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2012.

The McTronX Research group at the Potchefstroom campus of the North-West University, aims to establish a knowledge base on active magnetic bearing (AMB) systems. Up to date, the group has established a firm knowledge base on various topics related to AMB systems. A recent focus was the design and development of a high speed AMB supported rotor system called the rotor delevitation system (RDS) to analyse rotor drops. During the testing phase of the RDS, the machine exhibited vibrations, of which the origins were unknown. The research presented in this dissertation sets out to characterize the vibrations of the RDS, which is the group’s first attempt to fulfil the need for characterizing vibrations in an AMB supported rotor. Emphasis is placed on characterizing the natural response of the RDS rotor, stator and integrated system. The research project is defined in terms of four main objectives: rotor and stator characterization, modelling, system characterization and rotor dynamic diagnostics. A comprehensive literature study introduces the fundamental concepts regarding vibrations of single and multiple degree of freedom systems. These concepts include; natural frequencies, damping, machine vibrations, rotor dynamics and modelling techniques. These modelling techniques are introduced to verify the experimental methodology used to determine the natural frequencies. A critical overview of the literature contextualises the theory with the research investigation. For the RDS rotor and stator characterization, a modal analysis process also known as the “bump test” is implemented in order to validate the bending natural frequencies of the rotor and stator. A simulation model of the RDS is constructed in the finite element (FE) package DyRoBeS®. The model is verified with a numerical and an analytical model and validated with the measured bending natural frequencies of the RDS rotor. For the system characterization, a number of modal analysis processes are implemented, which validates the rigid body natural frequencies of the RDS. These frequencies are also used to validate the FE simulation. The origins of the synchronous vibration harmonics are verified by formulating and evaluating hypotheses according to different modal analysis processes. From the RDS rotor modal analysis it was identified that a bending natural frequency of the rotor is situated at approximately 443.33 Hz. This was verified using the FE simulation model. During the system modal analyses, it was identified that only one rigid body natural frequency, situated at approximately 62 Hz, is excited. This frequency increases with the differential gain control parameter of the system up to approximately 140 Hz. After evaluating two hypotheses regarding the origins of the synchronous vibrations harmonics, it was verified that non-circularity of the rotor at the measuring positions is the cause. Overall the objectives of the study were addressed by characterizing the natural frequencies of the rotor, stator and RDS system. This include the mode forms of the rigid body and bending natural frequencies of the system. The results of the verification and validation methods correlated, which imply these methods are reliable to identify the origins of vibrations in rotor-bearing systems. The differential gain control parameter of the AMBs control the equivalent damping in the RDS. An increase in this parameter should lead to a decrease in amplitude and frequency of the maximum vibration, and vice versa. However, it was noted that an increase in this parameter caused a linear increase in the rigid body natural frequency. The literature indicates that this effect can only be caused by an increase in system stiffness. It is therefore recommended to evaluate the stiffness of the system as a function of the differential gain control parameter. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2012.

This document presents a novel active magnetic levitation system. In the pursued of this endeavour different topics related with wave energy were explore. Climate change and energy security are the main motivation to pursued new options for non-fossil fuels energy generation. An overview of renewable energy and specifically of wave energy was presented. The potential for wave energy in The United Kingdom turn out to be 75 TWh/year from wave energy, 3 times more of what wind energy has produced in 2013. This means a massive impact on the energy market and emission reduction. In order to achieve this, improvements on wave energy devices have to be done. An overview of wave energy converters was covered selecting the C-Gen as the generator topology this document will base its studies. Linear generator bearings are desired to have long lifespan with long maintenance intervals. The objective is to come with an active magnetic levitation design that can replace traditional bearings augmenting the reliability of the system. Therefore magnetic bearings option have been reviewed and simulation experimentations has resulted in a novel active magnetic levitation system using an air-cored coils Halbach array acting over a levitation track. The configuration would generate bi directional repulsion forces with respect of the levitating body. Different software were used to analyse the magnetic field and forces generation. Additionally a prototype was built and tested to corroborate the results. As part of the modelling a mathematical model was explored and robust control implementation was also realised. Finally a scalability study of the device as well as a reliability analysis was done. Although the reliability studies shows an increase of ten times of the mean time to failure, the concept is not able to endure the loads acting on the generator unless the magnetic bearings became bigger than the generator and therefore economically unfeasible.

Existing thrust measurement systems (TMSs) at NASA Stennis Space Center use strain gauges and flux plates to measure forces produced by a test article. Alignment and calibration can take two weeks or more every time a piece of hardware or test article is changed. Cross axis loading is also problematic because it is impossible to perfectly align the flex plates and strain gauges in the thrust direction. In response to these problems, a magnetically levitated thrust measurement system has been proposed and a 300lb capacity demonstrator has been designed and built. In this design, the magnetic bearings work concurrently as support bearings and force measurement devices. The demonstrator consists of a floating frame that is completely levitated within a fixed frame by four support bearings carrying loads in the x- and y-direction and seven thrust bearings carrying loads in the z- or thrust direction. Joe Imlach of Imlach Consulting Engineering designed the demonstrator and magnetic bearing components, while Virginia Tech's role has been the application of the multipoint calibration technique including code development, the implementation of a 128-channel data acquisition system, and the overall test verification of the TMS demonstrator.A turnbuckle assembly and magnetostrictive actuator are used in series with a conventional load cell for static and dynamic testing, respectively. Both current based and flux based force equations were used to measure the reaction forces at the bearings. The static results using the current based equations including the current based fringing equations resulted in accuracies of 93% of full load, while the static results using the flux based equations including the flux based fringing equations resulted in accuracies of 99.5% of full load. These accuracies can be compared to accuracies of 83-90% seen in previous work using magnetic bearings to measure forces by monitoring currents and to accuracies of about 99% in previous work using magnetic bearings to measure forces by monitoring fluxes. All of the improved accuracies were made possible through the implementation of a calibration technique known as the multipoint method and the implementation of a gap dependent fringing correction factor developed by Joe Imlach. The demonstrator was not outfitted with accelerometers so the inertia of the floating frame could not be accounted for, limiting the scope of dynamic testing. However, the tests confirmed the ability of the demonstrator to measure dynamic loads in general. / Master of Science

Active magnetic bearings have several potential applications in spacecraft design. Based on the gyrostat model, we develop equations that describe the internal torques and forces that occur between the body and one of the attached wheels. We evaluate the transverse torques for the torque--free gyrostat and a gyrostat undergoing attitude maneuvers using momentum wheels and external torques. We then apply these internal forces to a model of an active magnetic bearing system and discuss their effects on the force limit, the actuator slew rate and the equivalent stiffness and damping parameters. As a basis for this study we use the Distributed Spacecraft Attitude Control System Simulator (DSACSS) with a Revolve MBRotor active magnetic bearing system. The results of several numerical simulations show that the magnitude and frequency of the internal torques remain small over the estimated range of motion of the DSACSS--MBRotor gyrostat. As such, the transverse torques caused by the rotational motion remain less than the discussed performance limits. We show that the magnitude of the internal torques can also be minimized by reducing the axial moment of inertia of the wheel. Furthermore, we discuss the equivalent Jeffcott model. By applying a standard Proportional--Integral--Derivative controller to the active magnetic bearing both the equivalent stiffness and damping parameters remain constant. / Master of Science

The electric car is a technically efficient driveline, although it is demanding in terms of the primary energy source. Most trips are below 50 km and the mean power required for maintaining speed is quite low, but the system has to be able to both provide long range and high maximum power for acceleration. By separating power and energy handling in a hybrid driveline, the primary energy source, e.g. a battery can be optimised for specific energy (decreasing costs and material usage). Kinetic energy storage in the form of flywheels can handle the short, high power bursts of acceleration and decceleration with high efficiency. This thesis focuses on the design and construction of flywheels in which an electric machine and a low-loss magnetic suspension are considered an integral part of the composite shell, in an effort to increase specific energy. A method of numerically optimising shrink-fitted composite shells was developed and implemented in software, based on a plane stress assumption, with a grid search optimiser. A composite shell was designed, analysed numerically and constructed, with an integrated permanent magnet synchronous machine. Passive axial lift bearings were optimised, analysed numerically for losses and lift force, and verified with experiments. Active radial electromagnets optimised for high stiffness per ohmic loss were built and analysed in terms of force and stiffness, both numerically and experimentally. Electronics and a high-speed measurement system were designed to drive the magnetic bearings and the electric machine. The control of these systems were implemented in an FPGA, and a notch-filter was designed to suppress eigenfrequencies to achieve levitation of the rotor. The spin-down losses of the flywheel in vacuum were found to be 1.7 W/Wh, evaluated at 1000 rpm. A novel switched reluctance machine concept was developed for hollow cylinder flywheels. This class of flywheels are shaft-less, in an effort to avoid the shaft-to-rim connection. A small-scale prototype was built and verified to correspond well to analytical and numerical models, by indirect measurement of the inductance through a system identification method.