The present paper proposes a refined nonlinear axial bearing model not too complex for real-time applications, which may potentially improve the estimator quality of modulation-based self-sensing. Measurements show that the AC component (ripple) of the bearing current is an underlinear function of the AC excitation voltage, which causes the bearing admittance amplitude ¦Y(jω, i_ac)¦ to considerably increase at low amplitudes of i_ac. The non-consideration of this effect might explain the poor dynamic performance observed in former implementations of modulation-based self-sensing. The model proposed in this paper includes a dynamic (rate dependent) hysteresis model of the Bertotti type, where the magnetic H field is a nonlinear function of the time derivative of flux density dB/dt. Eddy currents are modelled by a linear lumped RL ladder network (Cauer type). The proposed model gives encouraging results and is able to reproduce the observed phenomena.

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The purpose of this paper is to present a parameterized electromechanical model taking into account both the electromagnetic nature of the forces acting inside a magnetic bearing and the general rotating machinery aspects, as well as their interactions. This model specifically includes the effect of induced currents. These induced currents in the bearings are submitted to inductive and resistive effects, as well as skin effect, and the influence of these effects is considered. It is shown that the stability of a bearing may be analyzed, based on this model. The parameters of the model are identified from experimental results for an existing semi-passive magnetic bearing, and it is shown that the forces predicted by the model are close to experimental measurements.

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Magnetic bearing motors have advantages such as no friction loss, no abrasion, and lubrication-free operation. However, they are not widely used due to their high cost and large size. In order to solve these problems, a self-bearing motor having a simple structure with distributed windings is proposed. The rotor consists of a permanent magnet and an iron yoke, which rotates in a body. The stator consists of a six-phase distributed winding and is installed between the permanent magnet and the back yoke of the rotor. A Lorentz force, generated by interaction between stator current and permanent magnet field, is used to control the rotation speed and radial position of the rotor. In this study, the rotating torque and bearing force are analyzed theoretically, and methods for their control are discussed. A simple experiment confirms that the proposed self-bearing motor can be realized.

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Several processes in chemical, pharmaceutical, biotechnology and semiconductor industry require contactless levitation and rotation through a hermetically closed process chamber. A highly interesting topology for these applications is the “bearingless slice motor” concept, where already some research has been done in the past, especially focusing on topology and implementation issues. However, only little work has been done to evaluate the ideal number of motor phases. In this paper, a performance evaluation between 2-phase and 3-phase bearingless slice motor concepts is undertaken. It is shown, that 3-phase systems can supply almost the same power as state-of-the-art 2-phase systems and achieve nearly the same acceleration behavior, although they have significantly less power electronics effort.

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A novel 5-DOF actively controlled self-bearing motor that combines the functions of a motor, two radial AMBs, and an axial AMB has been developed to achieve smaller size and higher performance simultaneously. In this paper, magnetic suspension performance of the 5-DOF controlled self-bearing motor is reported. First, radial control performance of the developed self-bearing motor is evaluated by the radial experimental setup. Next, tilt control performance and 5-DOF active control performance are evaluated by the 5-DOF experimental setup. Finally, the frequency response in the 5-DOF is measured with the contact-free levitation. The 5-DOF controlled self-bearing motor produced sufficient radial force and tilt control torque to overcome the radial negative stiffness and to stabilize the rotor. The sufficient frequency bandwidth was observed in the frequency response and the self-bearing motor successfully suppressed vibration at the resonant frequencies.

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The goal of this paper is use the Luenberger observer to research a new capability of controlling the axial gap self bearing motor, in which an analytical and experimental evaluation of a sensorless speed vector control of a permanent magnet type axial gap self bearing motor is presented. Rotor speed and position are estimated by using a state observer, not by using any shaft mounted position sensor as encoder or resolver etc. The approach is based on the estimation of the motor back-EMF (or induced voltage) through a Luenberger observer with help of measured stator currents and reference voltages. In order to achieve an accurate estimation of the rotor speed and position in all operating range, adaptive gain of observer controller is proposed. Furthermore, due to the change of air gap at the practical experiment, a compensation procedure also assures the system working stably at any axial position of rotor. The experiment is implemented based on dSpace1104 with two three-phase inverters. Results confirm that axial force and rotating torque can be controlled independently and motor can get the good performance in steady state at the average and high speed range.

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A wide magnetic gap consequent-pole type bearingless motor has been developed. The wide magnetic gap makes it difficult to start up and suspend a shaft with reasonable suspension voltage and current. To provide high current, high voltage rating is demanded, although, high voltage causes bad influence on magnetic suspension. In this paper, the authors have investigated the start-up and rotational characteristics of a prototype bearingless machine driven by voltage source inverters having the rated voltage of 200V and 100V. When the rated voltage is not suitable, significant problems are occurred. The effectiveness of proper selection in the rated voltage is discussed. The result of this study shows that the 100V inverter is a better choice for the bearingless motor.

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In this paper, flexural rotor vibration in a two-pole cage induction machine equipped with a built-in force actuator is examined. The built-in force actuator is based on the self-bearing machine technology in which a supplementary winding is placed in the machine for force production. The built-in force actuator enables active vibration control, but also it enables excitation of the machine for purposes of condition monitoring, for instance. A low-order parametric model is derived for the actuator-rotor system. In the model, the arbitrary eccentric rotor motion is coupled with the voltage-flux equations for the supplementary winding and eccentric rotor cage. Furthermore, based on frequency-domain system identification, a control method is examined for compensating synchronous rotor vibration. Experimental results are given for a two-pole cage induction motor. The main contribution of the article is to couple eccentric rotor motion, the built-in force actuator and the mechanical rotor model to obtain a low-order parametric model of the actuator-rotor system which can be applied to control design for rotor vibration suppression.

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Hybrid magnetic bearing is recognized as an efficient one even with wide airgap and suitable for low loss and wide gap application. Previously sub-pole type IPM hybrid magnetic bearing has been proposed. However the sub-pole produces bias flux and cannot produce any control force. To overcome this problem, two new types of hybrid magnetic bearings are proposed which have permanent magnets within their stator cores. This paper introduces structure and principle of the proposed magnetic bearings. The geometric parameters of these new type magnetic bearings are optimized using FEM analysis. The experimental setups are made based on these analytical results. The fundamental characteristics are measured and compared with the estimated bearing performances. The results show stable levitation and good levitated rotation.

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This paper gives a new passivity based control of active magnetic bearing systems. First we give a new modeling in port-Hamiltonian form of flywheel systems. Second, we give a new passivity based control which does not have any canceling term for the gyroscopic effect unlike the conventional cross-feedback control, and also does not have any gains to make the closed-loop unstable unlike PID feedback control. In this paper, the linear control is especially studied from the viewpoint of comparisons. Finally we give some simulation and experimental results and confirm the validity of the control methodology in the presence of unbalance influence.

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This paper presents a new modeling method and a control system design procedure for a flexible rotor with many elastic modes by using active magnetic bearings. The purpose of our research is to rotate the rotor for passing through critical speeds caused by flexible modes. To achieve this, it is necessary to control motion and vibration of the flexible rotor simultaneously. The new modeling method named as Extended Reduced Order Physical Model is presented to express its motion and vibration uniformly. By using this model, a PID controller to levitate the rotor and a LQ controller to suppress its vibration are designed.

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The control of contactless magnetically levitated planar actuators with stationary coils, moving magnets and 6-DOF is very complicated. In contradiction to normal synchronous AC machines the forces and torques cannot be decoupled using a sinusoidal commutation scheme. Instead, a feedback linearization law has to be applied as commutation scheme that decouples the forces and torques and calculates the required currents to realize the desired forces and torques of the magnetic suspension.
This feedback linearization law is based on the coupling matrix that links the current in each coil to the force and torque vector on the actuator. The accurate calculation of this coupling matrix in real-time is critical for controlling the planar actuator. In this paper a look-up table based method is used to apply feedback linearization and the performance of the algorithm is verified with measurements.

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Rotor unbalance in an AMB-based gyroscopic sensor is studied in this paper. An AMB-based gyroscopic sensor has been proposed to realize a high-accuracy, low-cost and compact gyroscopic sensor. In this sensor, an active magnetic bearing (AMB) is applied as a rotating gyro, which is an instrument for measuring angular velocity. The relative position and attitude of the AMB rotor to the AMB stator are maintained using magnetic forces. Two-axis angular velocities of a measurement object are estimated from the control currents required to cancel the gyroscopic torque acting on the AMB rotor. However, the estimated signals of angular velocities include several undesirable frequency components. These components are caused by rotor unbalance and the induction motor used to spin the AMB rotor. A beat appears due to composition of these components. The beat component cannot be eliminated by filtering because it is in the measurement bandwidth of the AMB-based gyroscopic sensor. In this study, two unbalance compensation methods are applied to the AMB-based gyroscopic sensor to eliminate the beat component from the estimated measurements of angular velocities. The efficacy of each compensation method is examined experimentally.

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In this paper, the dynamics associated with rotor-stator touchdowns involving full circular rub are considered. The expected range of phase shifts occurring in various measurable signals are examined from a theoretical standpoint, with the aim of developing model-free control algorithms that can limit contact force magnitudes during touchdown with auxiliary bearings and ensure contact-free rotor levitation can be restored following persistent contact. Two different strategies are proposed according to whether touchdown planes can be considered collocated with the magnetic bearings or not. Requirements for successful operation, in terms of available sub-models and measurement information are explained and verified through experimental tests on a multi-mode flexible rotor test rig.

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A new research program was jointly set up between GE Oil&Gas and Southwest Research Institute (SwRI), to predict and test the dynamics of a vertical rotor drop on catcher bearings. A numerical tool able to account for flexible rotor and stator dynamics, catcher bearing stiffness and damping mechanism was developed. An experimental activity on a new vertical rotor test rig was carried out. A first analysis of numerical simulations and experimental analysis is presented in this paper.

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A framework for the development of a feedback controller for an active auxiliary bearing is presented. In a new approach, a dry bushing type auxiliary bearing is attached to the foundation via two unidirectional actuators. The control force is applied indirectly using the active auxiliary bearing only in case of rubbing. A simulation for the elastic rotor and the auxiliary bearing including the non-smooth nonlinear dynamics of the rubbing contact is used to develop the feedback controller. A robust two-phase control strategy has been developed which stabilizes the rotor system in case of rubbing and effectively avoids “backward whirling”. Experimental studies have been carried out at a rotor test rig. The experiments show the outstanding success of the strategy. In case of rubbing, the contact forces are reduced up to 85%.

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A new control system for electrostatic actuators was applied to electrostatic suspension. This control system was designed to use a variable capacitor connected with an electrostatic actuator in series. A high voltage was applied to this connection. The voltage applied to the actuator was controlled by varying the capacitance of the variable capacitor. An experimental apparatus was fabricated in order to study the controllability of electrostatic force using this control system. The experimental results show that electrostatic force can be controlled both statically and dynamically. Another experimental apparatus was fabricated for demonstrating the feasibility of electrostatic suspension. This apparatus was able to control the 3-DOF vertical motions of the suspended object. Non-contact suspension was achieved with the developed control system using variable capacitors.

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This paper proposes a zero power control method for a permanent magnetic suspension system consisting mainly of a permanent magnet, an actuator, sensors, a suspended iron ball and a spring. A system using this zero power control method will consume quasi-zero power when the levitated object is suspended in an equilibrium state. To realize zero power control, a spring is installed in the magnetic suspension device to counterbalance the gravitational force on the actuator in the equilibrium position. In addition, an integral feedback loop in the controller affords zero actuator current when the device is in a balanced state. In this study, a model was set up for feasibility analysis, a prototype was manufactured for experimental confirmation, numerical simulations of zero power control with nonlinear attractive force were carried out based on the model, and experiments were completed to confirm the practicality of the prototype. The simulations and experiments were performed under varied conditions, such as without springs and without zero power control, with springs and without zero power control, with springs and with zero power control, using different springs and integral feedback gains. Some results are shown and analyzed in this paper. All results indicate that this zero power control method is feasible and effective for use in this suspension system with a permanent magnet motion feedback loop.

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This paper presents the active magnetic bearing control system synthesis and practical rotor dynamic experiences with a supercritical 250 kW turbo compressor. First, the physical boundary conditions of passing the first bending critical speed and feasible bearing characteristics near the critical speed are considered. Then, the control system is synthesized and analyzed using complex formulation. A synchronous response controller is added in parallel with the position controller in order to achieve the preferred bearing characteristics. Finally, measured performance of the control system when passing the critical speed with a real life compressor is presented.

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Since few years ago, electrical energy storage had been attracted as an effective use of electricity and coping with the momentary voltage drop. Above all, the flywheel energy storages using superconductor have advantages of long life, high energy density, and high efficiency. Our experimental machine uses a superconducting magnetic bearing (SMB) together with the permanent magnet bearing (PMB) and plans to reduce the overall cost and cooling cost. The purpose in this paper is to show the improvement of PMB and the motor drive, and estimate the system at momentary voltage drop by making a discharge system.

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This paper describes a novel concept and configuration of Electric Vehicle powered by flywheel with Active Magnetic Bearing suspended by gimbal mechanism to the vehicle body. The entire system consists of AMB Flywheel Energy Storage including energy charger/discharger module, mechanical 2-DOF gimbal, steer-by-wire module, and autonomous driving module as the supervising controller.
This paper shows the results of outdoor field experiments such as the feasibility test of steer-by-wire system, the implementation of input shaping to reduce vibration and gyroscopic effects, simple adaptive control method for flywheel attitude control, and the efficiency measurement of the energy conversion system.

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The development of sophisticated advanced vibration isolation is important because even the minutest vibrations have disastrous effects on the performance of static and moving parts in high-precision machines. This paper concerns with the isolation of these vibrations for a large static body in an advanced micro-lithographic system, where a passive/active electromagnetic solution is presented. In these configurations passive permanent magnets (PM) provide the gravity compensation and active electromagnets the accurate positioning. This paper only considers the applicability of a passive magnetic solution for this high force gravity compensation application, or, more specifically, the influence of various PM array topologies on the force density. Further, fast-solving analytical models are presented and consequently are used to illustrate the feasibility of using passive permanent magnets for gravity compensation in this demanding high precision industrial application.

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A flywheel energy storage system using an active magnetic bearing (AMB) is an effective method for storing electric power and reducing energy consumption. The stabilization of a flywheel rotor system supported by magnetic bearings fixed on the ground has been done. Currently, an electrical vehicle with a flywheel energy storage system using a magnetic bearing and a two-degree-of freedom gimbal which means two-axis gimbal have been carrying out. In this paper, the mathematical model for both the flywheel and the gimbals has been derived. Also, a discussion of the gimbal design is presented. It was verified through experiments that the proposed model in this paper is very effective.

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