Passive Magnetic Bearings Research Articles

Optimal design of a compact passive magnetic bearing based on dynamic modelling

Passive magnetic bearings offer significant advantages relative to common active magnetic bearings, such as simple, robust, and efficient structure. Permanent magnet (PM) passive magnetic bearings are composed of opposing magnet rings on rotor and stator. Although their stiffness has been improved using alternating or Halbach magnetisations in many previous studies, they still suffer from lack of damping force. In this study, the optimal design is focused on a combination of PM bearing and eddy current damper by adding a conductive layer along the magnets of the stator or rotor. This will moderate the magnetic material consumptions; thereby, the cost and overall size of the bearing are reduced. A complete analytical method is performed to calculate the stiffness and axial, radial, and rotating damping coefficients. The accuracy of the analytical model is estimated quantitatively using 3D finite element method simulations. Moreover, all of the parameters are normalised and optimised for maximum stiffness and damping.

Augmentation of passive magnetic bearing performance by using air or iron intervals

PurposeThis paper aims to suggest the use of air or iron intervals between axially magnetized rings to increase the forces and stiffness of permanent magnet passive magnetic bearings (PMBs). The paper calculates the stiffness of such bearings through an analytical method and optimizes the dimensions of the magnets for achieving maximum stiffness.Design/methodology/approachFor determining the magnetic fields distribution, forces and stiffness of the bearings, a 2D analytical method is used, based on the subdomain method. For the sake of generalization, all of the parameters are normalized and optimized for maximum normalized stiffness per magnet volume ratio.FindingsThe optimum sizes of the magnets as well as the optimum dimensions of the air or iron intervals are calculated in this paper. The optimum sizes of the magnets are around the air gap length and it is very difficult to realize them. Using iron intervals can improve the stiffness to the extremely high values in practical dimensions of the magnets.Originality/valueThis paper presents a novel configuration for improving the performance of PMBs with alternately axially magnetized rings.

Novel repulsive magnetic bearing flywheel system with composite adaptive control

Here, a novel flywheel structure is proposed with passive permanent magnet (PM) bearings in the radial and axial directions and an active magnetic bearing (AMB) in the axial direction. In the proposed structure, passive magnetic bearings do not provide a stable magnetic levitation in all directions, but it is possible to maintain the dynamic stability of the flywheel by using AMB in the axial direction. In the proposed bearing structure, radial repulsive magnetic bearings (RMBs) reduce the power consumption with less complexity in the bearing structure but impose disturbance forces that deteriorate the stability of the actively controlled flywheel system. A complete model of the flywheel system is derived and transformed for a control design. A Lyapunov-based composite adaptive feedback control is designed for maintaining the stability under disturbances and a close convergence to the desired trajectory with fast parameter estimation. The performance of the composite adaptive control was experimentally verified for different cases using the RMB flywheel system. Additionally, a PID control was experimentally verified to demonstrate the usefulness of parameter estimation.

Design and Implementation of a Novel Passive Magnetically Levitated Nutation Blood Pump for the Ventricular-Assist Device

Considering the wear in mechanical bearings and the requirement for sensors or electrical power in active magnetic bearings, a novel nutation blood pump using a passive magnetic spherical bearing was developed in this paper. A mathematical model was derived to calculate the magnetic forces of the bearing between two pairs of magnetic sleeves in the nutation process. The calculation results demonstrate that the fluctuations of magnetic forces enlarge with the increase in the nutation angle; the magnetic forces obviously increase with the decrease in the air gap, especially along the z-axis. The dynamic magnetic finite element simulation was carried out to validate the mathematical model. The simulation and calculation results of the magnetic forces show consistent trends and provide a theoretical basis for the parameter design. To validate the performance of the pump, computational fluid dynamics (CFD) analyses and in vitro experiments were conducted. The predicted values of the flow velocity vector through the pump, and the wall shear stress, demonstrate that the pump has an antithrombotic property and would not cause serious blood damage. The hydraulic experiment shows that a pressure rise can be achieved in the range of 60–140 mmHg, at a rotational speed of 600–1600 rpm and a flow rate of 0.4–6.7 L/min. The normalized index of hemolysis (NIH) of the nutation pump was 0.0043 ± 0.0008 g/100L. The in vitro tests indicate the feasibility of a magnetically levitated ventricular-assist nutation blood pump for further suspension stability and animal trials.

Design methodology for monolithic layer radial passive magnetic bearing

Passive magnetic bearings (PMBs) are considered to be one of the economical and effective methods for levitating two surfaces in relative motion. This obviates the use of lubrication, provides zero wear, and negligible friction, thereby making the operation maintenance free. Due to these advantages, the modeling and design of the PMBs were given substantial importance in many studies. However, a well-defined designing procedure to achieve desired load carrying capacity for the given space constraints for the intended PMB application is yet to be established. Prior studies were performed on PMBs for achieving maximum load carrying capacity, but no design methodology was proposed that could facilitate easier design of a PMB in lesser computational time. In the present work, a very effective and a straightforward method is proposed to design a PMB for its paramount output. For this, dimensions of PMBs from the literature are considered for analysis and a set of equations are proposed for the determination of mean radius, axial length, and clearance for a given inner and outer radii of single layer PMBs. Finally, an equation is provided for estimating the load carrying capacity for the determined dimensions of PMB from the proposed design procedure. The effectiveness of the proposed methodology is demonstrated by considering the dimensions of PMBs from 10 literature.

Magnetically suspended flywheel in gimbal mount – Nonlinear modelling and simulation

Flywheel energy storage systems (FESSs) with active and passive magnetic bearings are generating interest due to their increasing energy-storing potential caused by advances in motor, bearing and fibre-composite technology. Magnetically suspended FESS are used commercially on static foundations while vehicle applications pose challenges due to manoeuvring, impacts, and other outer perturbations and have thus only seen successful experimental application in a few research projects where the FESS has been mounted in a passive gimbal to avoid gyroscopic forces. Although experimentally implemented, a mathematical model is still missing that determines motions and forces when the FESS is suspended in magnetic bearings, gimbal-mounted, and subject to outer perturbations. This work thoroughly describes how to set up a mathematical model that couples the multi-body dynamics of a flywheel rotor, housing, and gimbal-mount with the magnetic forces of the bearings. The model is used to simulate the behaviour of a FESS with and without gimbal and subject to various perturbations. The results demonstrate how the gimbal mount effectively removes gyroscopic forces but introduces other potential challenges such as large rotor and housing displacements due to dynamical interactions between the rotor, active magnetic bearings, housing, and gimbal.

Investigation of the Axial Gap Clearance in a Hydrodynamic-Passive Magnetically Levitated Rotary Blood Pump Using X-Ray Radiography.

The HeartWare HVAD is a radial rotary blood pump with a combination of passive magnetic and hydrodynamic bearings to levitate the impeller. The axial gap size between impeller and housing in this bearing and its sensitivity to speed, flow, and pressure difference is difficult to assess. Shear stresses are exceptionally high in this tiny gap making it important for blood damage and related adverse events. Therefore, the aim of this study was to measure the axial gap clearance in the HVAD at different operating conditions employing radiography. To quantify the gap size in the HVAD, the pump was positioned 30 mm in front of the X-ray source employing a microfocus X-ray tube with an acceleration voltage up to 300 kV. Beams were detected on a flat panel detector (Perkin Elmer XRD 1611-CP3). The pump was connected to a tubing circuit with a throttle to adjust flow (0, 5, 10 L/min) and a water glycerol mixture to set the desired viscosity (1, 4, 8 mPas). Rotational speed was varied between 1800 and 3600 rpm. In this study, for clinically relevant conditions at 5 L/min and 2700 rpm, the axial gap was 22 µm. The gap size increased with rotational speeds dependent on the viscosity (2.8, 6.9, and 9.4 µm/1000 rpm for 1, 4, and 8 mPas, respectively), but was independent from the volume flow and the pressure head at constant speeds. In summary, using X-ray radiographic imaging small gaps in a rotary blood pump during operation can be measured in a nondestructive contact-free way. The axial hydrodynamic bearing gap in the HVAD pump was determined to be in the range of about three times the diameter of a red blood cell. Its dependence on operating volume flow and generated pressure head across the pump is not pronounced.

Modelling and Development of Passive Permanent Magnetic Bearing for a Small Cross Flow Vertical Axis Wind Turbine

Mechanical frictional resistance offered by the conventional ball bearings prevent the self starting ability of vertical axis wind turbine at low wind speed regimes. This is overcome with use of passive permanent magnetic bearings. The present study focuses on analysing different arrangements of stacked rings of passive permanent magnetic bearings for a small cross flow vertical axis wind turbine using COMSOL Multiphysics software. Configuration 1 shows the highest value of stiffness and maximum axial force exerted by the outer ring magnet on the inner magnet. Therefore, configuration 1 is chosen for fabrication and implementation in a cross flow VAWT. Rotational speed tests are carried out. The rotational speeds of cross flow VAWT with passive permanent magnetic bearings increased by around 2.36 to 3.28 times the speed of the VAWT with ball bearings. The test results showed that the use of permanent magnetic bearings would lead to a significant improvement in the performance of cross flow VAWT.

Axial Gap Self-Bearing Motor with Permanent Magnet Attractive Type Passive Magnetic Bearings

Axial Gap Self-Bearing Motor with Permanent Magnet Attractive Type Passive Magnetic Bearings

Comprehensive comparison of different structures of passive permanent magnet bearings

Here, different feasible configurations of passive permanent magnet bearings (PMBs) are presented and compared with each other. In these configurations, stiffness is improved by adding iron cores and air intervals between magnets. Bearings with opposite magnetisation stacking (standard) and rotating magnetisation stacking (Halbach) are studied here. A two-dimensional planner model is used to calculate the magnetic field and stiffness. The optimisation will be performed for obtaining maximum stiffness per magnet volume ratio. The results show that standard stacking with radially magnetised PMs and having back iron and air intervals between magnets is the most optimum structure. For larger dimensions of magnets, other structures will be useful too.

A Pragmatic Optimization of Axial Stack-Radial Passive Magnetic Bearings

Passive magnetic bearing's (PMB) adaptability for both lower and higher speed applications demands detailed and critical analysis of design, performance optimization, and manufacturability. Optimization techniques for stacked PMB published in recent past are less accurate with respect to complete optimum solution. In this context, the present work deals with a pragmatic optimization of axially stacked PMBs for the maximum radial load using three-dimensional (3D) equations. Optimization for three different PMB configurations, monolithic, conventional, and rotational magnetized direction (RMD), is presented based on the constraints, constants, and bounds of the dimensions obtained from published literature. Further, to assist the designers, equations to estimate the mean radius and clearance being crucial parameters are provided for the given axial length and outer radius of the stator with the objective of achieving maximum load-carrying capacity. A comparison of the load-carrying capacity of conventional stacked PMB using the proposed equation with the equation provided in literature is compared. Finally, effectiveness of the proposed pragmatic optimization technique is demonstrated by analyzing three examples with reference to available literature.

Multi-objective optimization of stacked radial passive magnetic bearing

Modeling, design, and optimization for performances of passive magnetic bearings (PMBs) are indispensable, as they deliver lubrication free, friction less, zero wear, and maintenance-free operations. However, single-layer PMBs has lower load-carrying capacity and stiffness necessitating development of stacked structure PMBs for maximum load and stiffness. Present work is focused on multi-objective optimization of radial PMBs to achieve maximum load-carrying capacity and stiffness in a given volume. Three-dimensional Coulombian equations are utilized for estimating load and stiffness of stacked radial PMBs. Constraints, constants, and bounds for the optimization are extracted from the available literature. Optimization is performed for force and stiffness maximization in the obtained bounds with three PMB configurations, namely (i) mono-layer, (ii) conventional (back to back), and (iii) rotational magnetized direction. The optimum dimensions required for achieving maximum load without compromising stiffness for all three configurations is investigated. For designers ease, equations to estimate the optimized values of load, stiffness, and stacked PMB variables in terms of single-layer PMB are proposed. Finally, the effectiveness of the proposed method is demonstrated by considering the PMB dimensions from the available literature.

Design and Analysis of a Permanent Magnetic Bearing for Vertical Axis Small Wind Turbine

An interest toward zero frictional losses for small wind turbine is gaining popularity because of a considerable portion of the energy is lost due to friction in the ball bearing. The concept of levitation caused by repulsion of opposite pole in the permanent magnet reduced the friction between the stator and wind turbine rotor, so that the net power output of the turbine increases. The problem associated with usage of this kind of Passive magnetic bearing is its low load carrying capacity and low stiffness. To improve the load carrying capacity and stiffness, numerical simulation has been done for four different configurations. It is found that the stiffness is improved by stacking the magnet in the special combination of different radial cum axial direction of magnetization. The best configuration based on this analysis is fabricated and tested in the vertical axis wind turbine.

Influence of unbalance levels on nonlinear dynamics of a rotor-backup rolling bearing system

Rotor drops in magnetic bearing and unbalance in rotors have been objective of study for many years. The combination of these two well-known phenomena led to an interesting chaotic response, when the rotor touches the inner race of the back-up bearing. The present work explores the nonlinear rotor backup bearing dynamics both theoretically and experimentally using a fully instrumented test rig, where the position of shaft, its angular velocity and the contact forces between the shaft and the backup bearing are sampled at 25kHz. The test rig is built by a removable passive magnetic bearing, which allows for simulation of magnetic bearing failure (loss of carrying capacity and rotor fall). The rotor is studied numerically as well as experimentally. A theoretical approach is given beforehand and supplies the basis of the study. Finally the presented results are commented on the point of view of nonlinear dynamics applied to the practical use. The theoretical and numerical analyses are shown through orbit plots, phase plans, Poincaré maps, force response in time and double sided spectrum. The latter is important to characterize the condition at different levels of unbalance between forward and backward whirl. Our preliminary results indicate that for smaller amount of unbalance the rotor swings at the bottom of the bearing, the more the unbalance increases, other dynamical behavior occur and some can be extremely harmful, since the rotor can be lifted from the contact state and return, starting to impact innumerable times without reaching a steady state.

Eddy currents in a passive magnetic axial thrust bearing for a flywheel energy storage system

Two types of passive magnetic lift bearings were evaluated in terms of thrust force and eddy current losses. The first type of bearings were based on two sets of segmented Halbach arrays mounted in ...

Magnetic Suspension with Motorization to Measure the Speed of Gravity

This work aims to design a magnetic suspension for an experiment to measure gravitys velocity. Such device must rotate two objects symmetrically with the greatest mass and largest radius as possible, at the speed of [Formula: see text], which means this device falls into the high-speed machines category. The guidelines and solutions proposed in this paper constitute a contribution to this class of engineering problems and were based on an extensive literature search, contacts with experts, the tutors and author’s experience, as well as on experimental results. The main solution proposed is a hybrid bearing that combines a radial passive magnetic bearing with an axial sliding bearing, here called MPS (Magnetic Passive and Sliding) bearing.

全置換型磁気浮上人工心臓のための反発型磁気軸受の検討

全置換型磁気浮上人工心臓のための反発型磁気軸受の検討

Design, Modeling and Control of Magnetic Bearings for a Ring-Type Flywheel Energy Storage System

This study is concerned with the magnetic force models of magnetic bearing in a flywheel energy storage system (FESS). The magnetic bearing is of hybrid type, with axial passive magnetic bearing (PMB) and radial hybrid magnetic bearing (HMB). For the PMB, a pair of ring-type Halbach arrays of permanent magnets are arranged vertically to support the rotor weight. For the HMB, a set of ring-type Halbach array is placed on the rotor side, which corresponds to coil sets on the stator side. The HMB can produce both attraction and repulsion forces on the radial direction, depending on the direction of the coil currents. It is found that the ring-type configuration and the differential winding scheme for coil sets can yield linear magnetic force models for both PMB and HMB. Based on the obtained magnetic force model, an integral sliding mode controller is designed for the stable rotor levitation in the radial direction. The experimental results show that the rotor can be stabilized to the bearing center, verifying the accuracy of the magnetic force models and effectiveness of the levitation controller.

Resonance mode detuning in rotor systems employing active and passive magnetic bearings with controlled stiffness

In the paper, the investigator offered a method of reducing the amplitude of vibrations of turbo machinery rotors with passive and active magnetic bearings in resonances and resonance zones corresponding to one of the critical speeds ranging from zero to operating rotational ones. The method was based on the ability to vary the nonlinear force characteristic and the damping properties of active magnetic bearings and passive magnetic bearings of a novel design by changing the electric parameters of electromagnet circuits. The offered design of a passive magnetic bearing with permanent ring magnets and a control winding enabled a short-time change of rotor bearing stiffness. Such rotor bearings can realise the method of detuning from critical speeds during rotor speed-up and run-down. Earlier, this method was feasible only when active magnetic bearings were used. However, a complete magnetic suspension of a rotor with the employment of two radial passive bearings and one axial active magnetic bearing was advantageous as compared to three active magnetic bearings. The feasibility of the detuning method had been substantiated by study results. The study presented the results of numerical analysis, which simulated the process of transition through resonances of the initial system with a significant reduction of vibration amplitudes. The nonlinear system of differential magnetic-mechanical equations was solved using the 5th-order Runge-Kutta method with a validation for the duality of solutions. The results were shown as 3-dimensional spectra of displacement of bearing points and amplitude-frequency responses. These results had been confirmed by experimental data obtained for a laboratory setup that implemented a combined passive-active magnetic suspension of a rotor. The overall total relative error of measurements was maintained at less than 0.5%. The discrepancy between the experimental and design data for amplitudes was within 2-3%, and for resonance frequencies, it was less than 0.2%. Hence, these studies substantiated the feasibility of passive magnetic bearings with controlled stiffness. They also confirmed the possibility of using passive-active magnetic suspensions for lightweight rotors (e.g., expanders and compressors) with the implementation of the suggested method of detuning from resonance modes.

Magnetic Levitation Systems for Cost-Sensitive Applications—Some Design Aspects

Alongside technical performance features, low system costs are the highest priority in the field of low-power electric drives. This makes adoption of magnetic bearing technologies difficult in applications with higher production volumes. Since published literature on cost-saving measures in this field is scarce, we present in this paper some ideas and stimuli using three selected examples: 1) a highly integrated hybrid bearing that provides active stabilization in 3 degrees of freedom (DOF); 2) a brushless permanent magnet motor with additional axial bearing capability; and 3) a bearingless flux-switching motor. We describe their particular designs and operational features, and compare the additional mechanical and electrical costs of these and similar systems with those of standard motor technologies. This paper concludes with a stability analysis of example 2), since it features passive permanent magnetic bearings, which are inherently only weakly attenuated.