Axial Magnetic Bearing Research Articles

Analytical modeling and experimental validation of the six pole axial active magnetic bearing

The article presents a novel design of the axial active magnetic bearing with six poles. An analytical magnetic bearing model was developed to provide the axial magnetic induction distribution in 3D. The model utilizes magnetic vector potential formulation and Schwarz-Christoffel mapping. The paper covers in-depth deliberations on the end effect influence and the conjugate complex permeance function. Numerical model and simulations were provided in 3D mode with support of COMSOL Multiphysics software. The six pole axial active magnetic bearing was manufactured and investigated experimentally. Identification of the magnetic field distribution was carried out with a single axis magnetic induction sensor using custom automatic field scanner. High convergence of the modeling results and experimental research was demonstrated. The main advantage of the proposed analytical method is significantly shorter computation time compared to the numerical one that is useful from the modeling and controller study point of view. The configuration, modeling, simulation and experimental investigation results are well illustrated for the better overview.

Exploring the Physical Limits of Axial Magnetic Bearings Featuring Extremely Large Vertical Levitation Distances

This work provides an analytical method, based on the Ampèrian model of permanent magnets (PM), for a fast calculation of the magnetic flux density in three-dimensional space applying Biot–Savart law, and the calculation of the forces using Lorentz's law. The applied approach enables the characterization regarding forces, torques, and stiffnesses of the levitating PM for any arbitrary position in space. Furthermore, it permits the extension of the investigation to any shape and configuration of ironless magnetic bearings (MB). In order to demonstrate the simple use of the analytical model, in this article, the dimensions of an ironless axial MB employing PMs are optimized with a multiobjective Pareto analysis, which reveals the physical limits concerning maximum achievable levitation height with respect to given constraints on, e.g., the required force and tilting stiffnesses, and the MB robustness defined by the maximum allowable payload on the levitating magnet. Moreover, the optimized axial MB and a corresponding test bench are realized to validate the proposed model with experimental results. For the sake of completeness, it should be mentioned that in a later stage, the optimized MB can also be scaled with simple scaling laws if the demanded specifications, e.g., concerning desired maximum levitation height or payload capability, would have changed.

Voltage Sensorless Control of Split Capacitor for Three-Phase Four-Wire Motor System With Zero-Sequence Suspension Winding

This article aimed to simplify magnetically levitated motor system by implementing the voltage sensorless control of the split capacitor potential for a three-phase four-wire motor system with a zero-sequence suspension winding. In the system, the suspension winding for magnetic suspension is connected between the neutral point of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Y</i> -connected three-phase motor winding and the midpoint of two capacitors of direct-current (dc) link, thereby enabling simultaneous control of a three-phase interior permanent magnet synchronous motor and an axial magnetic bearing (iron-ball magnetic suspension, in this article), with only six power switches. However, the split capacitor potential is unbalanced by the dc component of the zero-sequence current, owing to the offset detection error of the current sensor and the bias current of the magnetic suspension. For suppressing the imbalance, we propose a voltage sensorless control. In the proposed method, the split capacitor potential is controlled without voltage detection by utilizing the zero-sequence voltage reference in the controller. The experimental results demonstrated that the split capacitor potential was successfully balanced while the iron-ball magnetic suspension and motor drive were performed. For further improvement of voltage sensorless control, a simplified control system was configurated with a filter controller based on an equivalent block diagram. The results indicated that the use of the filter controller improved the positioning accuracy of the magnetic suspension for the sensorless control system.

Modeling of a 30 000 Rpm Bearingless SPM Drive With Loss and Thermal Analyses for a 0.5 MW High-Temperature Heat Pump

The article addresses coupled loss and thermal analyses of a bearingless drive with an operating speed range of 17 000–32 000 rpm. The drive is a part of a high-temperature heat pump system integrated in a high-speed compressor. This drive system comprises two bearingless motor units and an axial active magnetic bearing. The drive can be positioned horizontally or vertically. The positioning is directly related to the force necessary to raise and suspend the rotor. Furthermore, the amplitude of the suspension current has a significant effect on the motor winding and iron losses. The iron losses, eddy current losses in the magnets, and losses in the bandage are investigated by three-dimensional (3-D) and 2-D finite-element analysis. The influence of segmentation of the magnets on losses is analyzed. Friction losses of the coolant are calculated analytically, and all the losses obtained from the electromagnetic analysis are represented as distributed heat sources and coupled with the 3-D thermal field analysis. The temperature fields are modeled under different motoring and suspension current conditions and evaluated for horizontal and vertical positions of the motor. As a precaution, demagnetization of the magnets is also considered.

New Three-Pole Combined Radial–Axial Magnetic Bearing for Industrial Bearingless Motor Systems

This article investigates combined radial–axial magneticbearing (CRAMB) technology as an enabling component for shafted bearingless motor systems. The unique requirements of high-speed bearingless motors designed for significant power levels are used to guide a literature review on CRAMB designs. Fundamental bearing topology aspects are identified and compared. Based on the outcome of this review, a new CRAMB topology is proposed and developed to meet the needs of a bearingless motor. Key features of the proposed design include a three-pole radial force stage (driven by a three-phase motor drive) and utilization of an optimal bias flux that improves radial force density by approximately 15% (improved rotor dynamics). A full design procedure for the new bearing topology is developed and it is shown that compared to a conventional four-pole side-by-side CRAMB, this topology decreases the bearing shaft length and requires two fewer power electronic switches (6 instead of 8). The new bearing is validated via finite-element analysis and experimental test results.

Structural optimization and dynamic characteristics of the new type 3-degrees of freedom axial and radial hybrid magnetic bearing

A new type of three degrees of freedom axial-radial hybrid magnetic bearing (3-DOF ARHMB) with compact structure, shorter axial length and smaller volume is proposed for the flywheel energy storage system. The axial direction adopts the permanent magnet biased thrust bearing (PMB) made of soft magnetic composite materials (SMCs). In the radial direction, the laminated structure is used to reduce the eddy current, and the Halbach array is introduced to strengthen the magnetic density of the radial air gap. Firstly, the dynamic magnetic flux distribution of the 3-DOF ARHMB is analyzed by the finite element method (FEM). Based on the equivalent magnetic circuit method, the equivalent reluctance model with comprehensive consideration of eddy current effect and magnetic leakage effect is established, and then the frequency responses are analyzed. Secondly, a constraint model coupled with structural parameters, equivalent reluctance and magnetic leakage coefficient is established, and an adaptive particle swarm optimization algorithm (APSO) is used to optimize the bearing parameters. Finally, based on the equivalent reluctance model, the axial and radial force-current factor and force-displacement factor are derived, and the dynamic characteristics of bearings with different structures and materials are compared and analyzed. The results show that the new 3-DOF ARHMB made of SMCs can provide much larger and more stable magnetic force and larger bandwidth than that made of carbon steel materials, and has better dynamic characteristics under higher-frequency conditions, which can meet the industrial requirements of flywheel energy storage system.

Bearingless PM-synchronous machine with axial active magnetic bearing fed by zero-sequence current

A novel inverter supply for bearingless PM-synchronous motors with magnetic suspension allows the reduction of the number of power electronic switches. Hence, all six motional degrees of freedom of bearingless AC machines may be controlled via 3-phase inverter topologies. In this paper, instead of a bearingless motor consisting of two half motors, one bearingless motor with an additional radial active magnetic bearing is treated. Bearingless machines with cylindrical rotors in contrast to double cone rotors generate – apart from the electromagnetic torque – only radial magnetic forces. Hence, an axial magnetic bearing is used.For this bearing, there is no need for a feeding converter bridge as the bearing coil is fed by the zero-sequence current of the feeding 3-phase inverters. The bearing coil is placed between the two star points of the motor winding. The zero-sequence current amplitude is adjusted by the 3-phase inverters via pulse width modulation. The feasibility of this kind of axial position control is proven by simulation as well as with an experiment with a 1 kW prototype motor up to 60000 min−1.

An axial passive magnetic bearing using three PM rings

An axial passive magnetic bearing using three PM rings

Dynamic Stiffness Analysis and Experimental Verification of Axial Magnetic Bearing Based on Air Gap Flux Variation in Magnetically Suspended Molecular Pump

Current and displacement stiffness are important parameters of axial magnetic bearing (AMB) and are usually considered as constants for the control system. However, in actual dynamic work situations, time-varying force leads to time-varying currents and air gap with a specific frequency, which makes the stiffness of appear decrease and even worsens control performance for the whole system. In this paper, an AMB dynamic stiffness model considering the flux variation across the air gap due to frequency is established to obtain the accurate dynamic stiffness. The dynamic stiffness characteristics are analyzed by means of the dynamic equivalent magnetic circuit method. The analytical results show that the amplitude of current and displacement stiffness decreases with frequency increasing. Moreover, compared with the stiffness model without considering the variation of flux density across the air gap, the improved dynamic stiffness results are closer to the actual results. Through the dynamic stiffness measurement method of AMB, experiments of AMB in magnetically suspended molecular pump (MSMP) are carried out and the experimental results are consistent with theoretical analysis results. This paper proposes the dynamic stiffness model of axial magnetic bearing considering the variation of flux density across the air gap, which improves the accuracy of the AMB stiffness analysis.

ANSYS Based Simulation of Single and Double Coil Axial Active Magnetic Bearing using Finite Element Method

For the successful design of an AMB system, proper material selection and actuator design is a must. The strength of the magnetic force depends upon the current density of the winding, actuator dimension and the gap between the actuator and the rotor. This paper presents the design of a U-O type single-actuator and a double-actuator Active Magnetic Bearing (AMB) utilizing ANSYS Maxwell 17.1 software. In double actuator AMB the actuators are placed at 180 degrees apart. In this study, Finite Element Method (FEM) based simulation has been performed for two different structures and their magnetic properties for instance- flux pattern, force, flux density and inductance are obtained for various air-gaps. Analysis has also been done with the change in current density by varying in the coil turns. The comparative results of single and double coil AMB are illustrated in 2-D and 3-D plots.

Design and Modeling of an Integrated Flywheel Magnetic Suspension for Kinetic Energy Storage Systems

The paper presents a novel configuration of an axial hybrid magnetic bearing (AHMB) for the suspension of steel flywheels applied in power-intensive energy storage systems. The combination of a permanent magnet (PM) with excited coil enables one to reduce the power consumption, to limit the system volume, and to apply an effective control in the presence of several types of disturbances. The electromagnetic design of the AHMB parts is carried out by parametric finite element analyses with the purpose to optimize the force performances as well as the winding inductance affecting the electrical supply rating and control capability. Such investigation considers both the temperature dependence of the PM properties and the magnetic saturation effects. The electrical parameters and the force characteristics are then implemented in a control scheme, reproducing the electromechanical behavior of the AHMB-flywheel system. The parameter tuning of the controllers is executed by a Matlab/Simulink code, examining the instantaneous profiles of both the air-gap length and the winding ampere-turns. The results of different dynamic tests are presented, evidencing the smooth air-gap changes and the optimized coil utilization, which are desirable features for a safe and efficient flywheel energy storage.

Measurement System of a Magnetic Suspension System for a Jet Engine Rotor.

This paper presents laboratory results on the measurement system of a magnetic suspension bearing system for a jet engine rotor of an unmanned aerial vehicle (UAV). Magnetic suspension technology enables continuous diagnostics of a rotary machine and eliminates of the negative properties of classical bearings. This rotor-bearing system consists of two radial magnetic bearings and one axial (thrust) magnetic bearing. The concept of the bearing system with a magnetically suspended rotor for UAV is presented in this paper. Rotor geometric and inertial characteristics were assumed according to the parameters of a TS-21 jet engine. Preliminary studies of the measurement system of rotor engines were made on a laboratory stand with homopolar active magnetic bearings. The measurement system consisted of strain gauges, accelerometers, and contactless proximity sensors. During the research, strains were registered with the use of a wireless data acquisition (DAQ) system. Measurements were performed for different operational parameters of rotational rotor speed, control system parameters, and with the presence of disturbance signals from the control system. In this paper, obtained operational characteristics are presented and discussed.

The effect of permanent magnet position on axial and radial load capability in axial hybrid magnetic bearing

The axial and radial load capacity of axial hybrid magnetic bearing (HMB) is critical for the magnetic levitation system. In this paper, the effect of permanent magnet (PM) position on axial and radial magnetic force and stiffness in axial HMB is investigated. Six different configurations are considered and the equivalent magnetic circuits of HMBs for each configuration is built and studied based on the distribution of magnetic field and magnetic leakage. The dependence of axial and radial magnetic force and stiffness on the axial displacement, radial displacement and control current is calculated and investigated for different configurations. To validate the calculated results, the axial and radial magnetic forces for each configuration are simulated by finite element method. A good agreement between the calculated and simulated results validated the proposed magnetic circuit models.

Active Surge Control for Magnetically Suspended Centrifugal Compressors Using a Variable Equilibrium Point Approach

Surge is one of the main rotor dynamic instabilities limiting the operation of centrifugal compressors. This paper proposes an active surge control scheme for magnetically suspended centrifugal compressors using a variable equilibrium point approach. Multiple uncertainties caused by magnetic air gap adjustment are considered for the active magnetic bearing (AMB) control systems. By using the combination of an analytical model and a finite-element method, the perturbation of bearing force parameters, including the force-current factor and the force-displacement factor, is analyzed. The model uncertainties caused by the perturbation of the power amplifier parameters are identified through the online frequency sweep excitation. Based on the uncertainty analysis of the AMB control system, a μ-synthesis-based controller is designed for the axial magnetic bearing system to suppress the vibration caused by surge. The experiments demonstrate that the proposed method can suppress surge and improve the reliability of the system by using automatic magnetic air gap adjustment of the AMB-rotor system.

A Type of Electromagnetic Biased Axial Magnetic Bearing with Low Target OD

A type of electromagnetic biased axial magnetic bearing is proposed. Compared with traditional axial magnetic bearings, it has low target OD, which is helpful to improve the critical speed of the rotor in theory. By using the equivalent magnetic circuit method, a magnetic circuit analysis is carried out. The expressions of magnetic flux density of each part are obtained, and the structural parameters are obtained and the finite element model (FEM) is established. The magnetic flux leakage coefficient and magnetic reculance are calculated by using simulation data, and the rationality of the parameter design is verified. The results show that the parameter design and electromagnetic field simulation of this type of the electromagnetic bias axial magnetic bearing are in accordance with the rationality of the design. It can be used as a reference for the design of magnetic bearing.

Parameter design and electromagnetic field analysis of electromagnetic biased axial magnetic bearing

A type of electromagnetic biased axial magnetic bearing is studied. Compared with traditional axial magnetic bearings, it has a smaller external diameter of the thrust plate, which is helpful to improve the critical speed of the rotor in theory. The structural parameters are obtained and finite element model(FEM) is established. The magnetic flux leakage coefficients and the magnetic resistances are calculated. The rationality of parameter design is verified. The results show that the parameter design and the electromagnetic field simulation are in accordance with rationality of the design. Therefore, the magnetic biased axial magnetic bearing is not only simple in structure, but also reasonable in design, which is of great significance to the design of magnetic bearing.

Emulation and experimental analysis of an axial superconductor magnetic bearing

Today the high-speed and high-performance systems are each more important for many areas like industry and transport system. The magnetic levitation system can be used to improve the performance. For superconducting levitation, it is important to know the behavior of levitation force. However, its behavior is not completely known and studies about it are necessary. This work presented a description of the test bench and a brief introduction to the new software developed to the magnetic levitation measurement system (SCML-02). The system tested is compound by a superconducting bulk and permanent magnet. This system makes data acquisitions using the load cells and the data processing is built by the new software developed in the LabVIEW. The results are verified and compared by simulations which were done in the software of finite elements and measurement data of the magnetic levitation done at Federal University of Rio de Janeiro - UFRJ. The measurements of the new system show compatible results with the simulations and the measurement data done at UFRJ. Therefore, with this new software, the users can easily to do magnetic levitation measurements through an interface easy to understand.

Integral definition method to solve magnetic force of axial permanent magnetic bearing

In the design process of the permanent magnetic bearing, the calculation of the magnetic force between the magnetic rings is an important element. Transforming complicated physical problems into mathematical problems by establishing the mathematical model of the magnetic ring is a common method when calculating the magnetic force. In this paper, the equivalent magnetic charge model of a permanent magnet bearing is established by the former’s magnetic charge viewpoint, and the quadratic integral based on this model is solved by the integral definition method. This paper compares the results of integral definition method with those obtained by Monte Carlo method and ANSYS in order to verify the correctness.

Analysis and design method of a combined radial–axial magnetic bearing based on asymmetric factor

Combined radial–axial magnetic bearings (MBs) use a common bias magnetic circuit to provide radial and axial bias magnetic flux. Different from separate MBs, there is a constraint relation between the radial and axial bias flux. Meanwhile, there is also a constraint relationship between the radial and axial maximum bearing capacity. Therefore, the design method for separated MB is not suitable for a combined radial-axial MB (CRAMB). In this study, a design method of the CRAMB based on an asymmetric factor was proposed. The definition of the asymmetric factor was proposed. In order to avoid the radial and axial magnetic flux into the weak magnetic field and saturation region, the optimum range of the asymmetric factor is analysed. The influence of the asymmetry factor on stiffness is analysed; the prototype designed by this method can run stably. The validity and accuracy of the design method are verified by experimental results.

Bearingless PM synchronous machine with zero-sequence current driven star point-connected active magnetic thrust bearing

Common cylindrical bearingless drives require a separate thrust bearing, which is fed by a DC supply. Here, a technique is presented, which enables the feeding of the thrust bearing by an artificially generated zero-sequence current between the two star points of the two parallel windings in the bearingless PM synchronous machine. This way, no additional DC supply for an axial active magnetic bearing is needed. It is replaced by two three-phase inverters as stator winding supply, which are needed in any case to generate torque and lateral rotor force in the motor. This examination explains the technique of adapting the electric potential of the star points in two three-phase windings of the motor. The focus is on the determination of the operating area (maximum zero-sequence current and band width). It is constrained by the bearingless motor due to torque and lateral force ripple as well as additional eddy current losses. On the other hand, the DC link voltage and the modulation degree of the inverter for simultaneous motor operation as well as the bearing inductance limit the system dynamic. It is shown that the proposed technique is applicable for a modulation degree &lt; 0.866, taking into account that other constraints by the bearingless machine and the inverter are mainly noncritical.