Axial Magnetic Bearing Research Articles

Research on magnetic fluid precise localized lubrication thrust cylindrical roller bearing with low-friction micro-vibration and high load-bearing capacity

Abstract As the magnetic field that is difficult to be distributed in the existing magnetic fluid thrust cylindrical roller bearing structure, it is more difficult for the magnetic fluid to be evenly distributed inside the bearing raceway with the axial localized lubrication, which seriously affects the engineering application of the magnetic fluid bearing. To solve the magnetic field control problem that the magnetic fluid is uneasy to be accurately localized and adsorbed, a new type of magnetic fluid thrust cylindrical roller bearing is designed in this study, which shows good characteristics of low-friction, micro-vibration and high load-bearing capacity. The seat-ring is set as an annular raceway that can be used for magnetic fluid storage and matching with the roller lubrication system, and an annular permanent magnet is designed as an external magnetic field source to be placed below the annular raceway to adsorb the magnetic fluid on the friction surface. The structure design of the axial magnetic fluid localized lubrication bearing is reasonable, which is especially suitable for precision instruments with strict operating-conditions and precision-lubrication.

Design and Analysis of an Axial Hybrid Magnetic Bearing With the Slice Stator for the Magnetically Suspended Centrifugal Compressor

Design and Analysis of an Axial Hybrid Magnetic Bearing With the Slice Stator for the Magnetically Suspended Centrifugal Compressor

Real-time application of a dynamic disturbance suppression control approach for an axial active magnetic bearing system

Active Magnetic Bearings (AMBs) use magnetic forces to suspend the rotor, allowing contactless operation and the ability to adjust stiffness and damping. However, compared to mechanical bearings, magnetic bearings are much weaker in terms of rigidity. A large external force can lead to rotor/stator collision. This study proposes a Dynamic Stiffness Controller (DSC) for AMBs. The DSC dynamically adjusts the AMB stiffness to counter external disturbance forces in real-time. Experimental results show the effective change of AMB stiffness by DSC based on the magnitude of the external load. Furthermore, not only the AMB stiffness can be real-time adjusted to counterbalance disturbances but the steady-state energy consumption is improved as there is little disturbances applied to the system. The AMB-DSC system exhibiting only 33% energy consumption compared to AMBs with constant stiffness. DSC for AMB systems offers benefits like lower risk of rotor-stator collisions, preventing coil burnouts, and improved energy efficiency.

Two-DoFs active deflection control of MSW based on fractional-order integral SMC method

The active deflection of the rotor shaft in the magnetically suspended wheel (MSW) could generate three-dimensional torques to realize the attitude control of spacecraft, but the torsional torque and nonlinear torque could affect the control precision of active deflection. Therefore, a fractional-order integral sliding mode control (SMC) method is designed to improve the control precision and robustness of active deflection. Firstly, the electromagnetic (EM) torques generated by the three degrees of freedom (DoFs) axial magnetic bearing (MB) are analyzed, and the torsional torques of two-DoFs MB are developed during the active deflection process of the flywheel rotor. Results show that the active deflection is affected by the nonlinear EM torques and torsional torques. Furthermore, the fractional-order integral SMC law is designed to improve the control performance of active deflection, and the closed-loop stability of active deflection with the fractional-order integral SMC method. Finally, the simulations and experiments are conducted to verify the control performances of the proposed method, and experiment results indicate that the angle obviation of active deflection is reduced by 50% compared to the general PID control with the cross-feedback model.

Numerical model of the axial magnetic bearing with six cylindrical poles

Numerical model of the axial magnetic bearing with six cylindrical poles

Analysis of a Segmented Axial Active Magnetic Bearing for Multi-MW Compressor Applications

In high-speed compressor and turbine applications, active magnetic bearings are employed to increase reliability, reduce maintenance, and provide contact-free and oil-free operation. Evidently, the dynamic performance of active magnetic bearings must correspond to application-specific events like compressor surge or thrust disturbances. This article presents a segmented stator as one of the solutions to increase the bandwidth of axial active magnetic bearings (AMBs) and further improve the stability of the shaft system. We analyze the effects and discuss the tradeoffs of axial active magnetic bearing stator segmentation and slitting to alleviate bandwidth limitations. Finite element method design optimization and control plant modeling methods, open- and closed-loop tests, and identification of the overall thrust AMB–rotor control plant are studied.

5-axes Levitation of a Rotor by Active Magnetic Bearings Employing Direct Output Feedback Control

In recent years the application of active magnetic bearings (AMB), as supporting element as well as vibration controller for rotors, has attracted considerable attention from researchers. In this work an attempt has been made for the complete levitation of a rotor weighing 4 kg, supported on two radial active magnetic bearings and two axial passive magnetic bearings (PMB) resulting in 5-axes levitation. The active bearings working in the mode of attraction make the system inherently unstable. Herein, a direct output feedback control scheme based on proportional and derivative of position signal has been employed to achieve stability. The active magnetic bearings consist of electromagnetic actuators, proximity probes for position measurement, feedback controller and current feedback type power amplifier. The passive bearings consisting of axially magnetized circular permanent magnets work in the mode of repulsion. The design of the electromagnetic actuator has been carried out considering load carrying capacity of the AMB, core loss and the resistive loss in the coil, so that the temperature rise in the core as well as in the coil is within allowable limit. Design of the feedback controller is based on direct output feedback control scheme, which makes the controller design easier and implementation of the controller hardware becomes simpler. The feedback controller parameters have been selected appropriately to generate required stiffness and damping in the AMBs for stable levitation of the rotor. The rotor has been driven up to a speed of 2000 rpm.

Analysis and Compensation of Hysteresis Effect on Electromagnetic Force in Axial Magnetic Bearings

Magnetic bearings (MBs) enable the rotor to run at high speed without lubrication due to no mechanical contact. However, the inherent hysteresis of ferromagnetic materials affects the support characteristics, reducing the design performance and stability margin of MBs, especially for axial MBs using materials with high coercive force. To analyze and compensate for the hysteresis effect on the electromagnetic force in axial MBs, an efficient method is proposed in this paper. Firstly, the hysteresis properties of the ferromagnetic materials are simulated by the Preisach model, and the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> - <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> relationships under any external magnetic field can be determined. Taking into account the non-ideal factors such as hysteresis and saturation effects, the nonlinear magnetic circuit model of the axial MBs is established. The magnetic flux density working point under different control currents and eccentric displacements can be determined through iterative calculation, and then the air gap flux density distribution and electromagnetic force of the axial MBs are calculated. On this basis, the adverse effects of hysteresis on the bearing capacity and system stability of axial MBs are analyzed. A compensation algorithm is designed based on the inverse model to reduce the hysteresis effect. The inverse model is approximated modeled by the Lissajous curve. Finally, the proposed analysis and control methods are verified by the finite element method (FEM) or experiments. The results show that the proposed analysis method is capable of accomplishing good accuracy and requires less computation time than FEM, it can be applied to arbitrary current variation processes. In addition, the phase lag of the system is effectively improved with the compensation algorithm.

Interdisciplinary identification of the six-pole axial active magnetic bearing prototype

Interdisciplinary identification of the six-pole axial active magnetic bearing prototype

Development of an experimental plant and a numerical model of an axial magnetic rotor suspension

This article presents the results of the work on the creation of an experimental plant, its testing, as well as the development of a computational model of a rotor magnetic suspension with the use of axial electromagnets. The main purpose of producing the plant was to test the results of the developed numerical finite element model. An automatic control system was developed for the experimental installation. The electrical circuit was assembled on the basis of a ESP32 microcontroller with a clock frequency of 240 MHz and a PWM with a capacity of 10 bits. A PID-regulator program was developed. The coefficients kP, kD, kI used in the code of the electronic control system program (PID-controller) were selected. An experimental study of the bearing capacity of the axial active magnetic bearing under the influence of an external axial force was conducted. The required power of the axial active magnetic bearing was determined. The maximum load-bearing capacity of the installation for the selected coefficients of the PID-controller was determined. An axisymmetric finite-element model of the axial active magnetic bearing was created in the open-source program FEMM 4.2. The load-bearing capacity of the installation for a given current intensity value was calculated. The results of the numerical modelling were compared with the experimental data obtained. The basic principles of creation and operation of the experimental plant and its numerical model are outlined.

Research on Electromagnetic System of Large Capacity Energy Storage Flywheel

A large capacity and high power flywheel energy storage system (FESS) is developed and applied to wind farms, focusing on the high efficiency design of the important electromagnetic components of the FESS, such as motor/generator, radial magnetic bearing (RMB) and axial magnetic bearing (AMB). Firstly, a axial flux permanent magnet synchronous machine (AFPMSM) based on soft magnetic composite material (SMC) is designed. Then, considering the structure of FESS and machine, a permanent magnet biased radial magnetic bearing (PMRMB) and a HALBACH axial passive magnetic bearing (PMB) is proposed which have the advantages of low power consumption and large bearing capacity, then the analyses are carried out according to the load capacity requirements. Finally, the flywheel prototype is fabricated and tested. The experimental results verify the relevant theoretical analysis, and finally can achieve stable and reliable operation.

Electromagnetic Characteristics and Capacity Analysis of a Radial–Axial Hybrid Magnetic Bearing with Two Different Radial Stators

Compared with the widely used four-pole magnetic bearings, three-pole magnetic bearings are driven by a three-phase power inverter and have advantages pertaining to their small volume, low costs, and low power losses. However, the asymmetric structure of the three-pole bearings presents disadvantages in terms of their strong nonlinearity and couplings among the suspension forces of the control currents and displacements. The radial–axial hybrid magnetic bearing (RAHMB) with six-pole bearings is proposed to solve this problem. Firstly, the structure and working principle of the RAHMB are introduced. Secondly, the mathematical models of the RAHMB are established, and in order to obtain the radial capacity, the maximum suspension forces of the three-pole and six-pole RAHMBs are theoretically analyzed. Thirdly, the nonlinearity and couplings of the suspension forces with the control currents and displacements are analyzed. The radial capacity of the three-pole and six-pole RAHMB is 74.6 N and 83.6 N, respectively, which is an increase of 12.0%. Finally, the experiment results prove that the nonlinearity and couplings of the six-pole RAHMB are smaller than the nonlinearity and couplings of the three-pole RAHMB, and the maximum radial capacity of the three-pole and six-pole RAHMB is 84.1 N and 94.8 N, respectively, which is an increase of 12.7%. The simulation results are basically consistent with the experimental results, indicating the correctness of the theoretical analysis.

The Influence of Magnetic Field of AMB on Eddy-Current Sensor Operation.

This paper presents laboratory results on the influence of the magnetic field of an active magnetic bearing (AMB) on the eddy-current sensor operation. The magnetic suspension technology enables continuous diagnostics and monitoring of a rotary machine and eliminates drawbacks of classical bearing properties. The magnetic bearing system usually consists of two radial and one axial magnetic bearing. It is combined with a control unit, amplifiers and sensors for measuring the instantaneous position of the shaft. For this purpose, eddy-current sensors are frequently used. They operate in close proximity to the electromechanical actuators; therefore, the question arises whether the actuators do not interfere with the correct operation of these sensors. In the paper, the test rig and research plan prepared for that investigation are delivered. Measurement signals were registered from four control channels for different configurations of power supplies for system elements, e.g., with sensors and AMBs turned off, with sensors turn on and at normal work. Recorded time courses are presented and discussed in the paper. For the prepared test rig and AMB/eddy-current sensor configuration, no significant influence of the generated magnetic field from the support is found for the eddy-current sensor output.

Design and Optimization Method with Independent Radial and Axial Capacity for 3-DOF Magnetic Bearings in Flywheel

The six-pole radial–axial hybrid magnetic bearing (RAHMB) has the advantages of small space and low power consumption, making it suitable for flywheel batteries. The bearing capacity and the volume are the main specifications of magnetic bearings that should be considered comprehensively. In this work, the six-pole RAHMB was used in a horizontal flywheel battery. As the axial bearing capacity is relatively smaller than the radial bearing capacity, a design method with independent radial and axial bearing capacity is proposed, and the parameters are optimized to minimize the volume. The mathematical model of six-pole RAHMB was derived from the equivalent magnetic circuit method. The relationships between bearing capacity, biased flux density, saturation flux density and the section area of magnetic poles were analyzed. The basic principle of the design method with independent radial and axial bearing capacity is to determine which five of the variables are preferred. According to the design method, one radial or axial biased flux density should be optimized to minimize the volume, and the genetic algorithm (GA) was adopted to search for the optimal value. The structural parameters were designed based on the optimized value of biased flux density. The total volume of the six-pole RAHMB was reduced by 24%. A 3D finite element (FE) model was built. The analysis results and experimental results show that the proposed design and the optimization method are feasible and valid.

Разработка экспериментальной установки для исследования несущей способности одностепенного магнитного подвеса ротора

An installation for studying the dynamics and carrying capacity of a single-stage magnetic rotor suspension has been created. The evaluation of the proposed installation with regard to its potential use was carried out. The possibility of creating a rotor suspension based on hybrid active magnetic bearings was investigated with the help of the setup. If hybrid active magnetic bearings are used, the magnetic rotor suspension will allow to replace the existing classical active magnetic bearings used in vacuum, cryogenic and pumping equipment, reducing the energy costs without changing the geometric parameters of the existing units' housings. Experimental research of characteristics of axial active electromagnet is conducted (minimum power required to keep the rotor in vertical position is obtained). A finite-element model of the axial active magnetic bearing is created. The calculation results of the model are compared with the experimental data and the inductive transducer is calibrated. Experimental installation of a single-step rotor magnetic suspension is designed and manufactured. An electrical circuit for controlling the experimental setup is assembled. The program for PID-controller is given and its principle of operation is described with respect to the specified installation

Magnetic field analytical calculation method for radial unite of a combined magnetic bearing

AbstractCombined magnetic bearing with radial and axial unites is an important supporting element for high speed and high energy density motor. Accurate calculation of the magnetic field is a key to design and optimise a Combined Radial and Axial Magnetic Bearing (CRAMB). This study focuses on magnetic field analytical calculation method for radial Unite of CRAMB. The analytical calculation model of magnetic field is based on subdomain method. The Laplace's equations in the air‐gap subdomain are solved by the variable separation method. The magnetic field of magnetic bearing with large diameter rotor is analysed and calculated in Cartesian coordinate system. Considering the influence of curvature the magnetic field distribution of magnetic bearing with small diameter rotor is deduced and calculated analytically in polar coordinate system. The effectiveness of the analytical method is verified by finite element and experimental results.

Modeling and Control Strategies of a Novel Axial Hybrid Magnetic Bearing for Flywheel Energy Storage System

This article presents modeling and control strategies of a novel axial hybrid magnetic bearing (AHMB) for household flywheel energy storage system (FESS). The AHMB combines a passive permanent magnet (PM) magnetic bearing (MB) and an axial active MB in one unit, thus can offer benefits such as compactness of the structure, high load capacity, and low power consumption. A coupled magnetic field-circuit method is proposed for modeling this bearing. Compared with the regular equivalent magnetic-circuit (EMC) method, it introduces special concerns of the complex air-gap field, calculated from the conformal transformation of the air-gap geometry, to take into account the effect of flux fringing and leakage. A low-cost Hall sensor is used to replace the expensive Eddy-current position sensor to measure the changes in air gap flux density caused by the rotor axial displacement. Therefore, a novel flux density feedback control is adopted instead of the traditional position feedback control to directly stabilize the magnetically suspended flywheel. A prototype of this bearing is designed and fabricated, which is tested in a small-scale FESS. The simulation results and the experimental results demonstrate that the proposed model provides better accuracy than the traditional EMC and the flux-density feedback control strategy based on a low-cost Hall sensor can achieve a consistent performance with the traditional position feedback control strategy.

Experimental analysis of a large range of the load capacity for the axial AMB in the HTR-PM

An axial active magnetic bearing (AMB) is equipped to provide axial support of the vertical rotor of the helium circulator in the High Temperature Gas-cooled Reactor Pebble Bed Module (HTR-PM). The axial AMB is required to support the rotor and the aerodynamic load. High-strength alloy steel is selected as the material of the thrust disk. Maximum load capacity of the axial AMB in the HTR-PM helium circulator is analyzed with the consideration of the rotating velocity and the material strength. Also, experiments are conducted based on a 1:1 prototype to reveal a large range of the load capacity for the axial AMB. The dynamic electromagnetic force corresponding to the allowable stress, the rotational velocity, and other parameters of the axial AMB, such as B-R Curve, resistance and inductance, are revealed. Effect of the heat treatment to the load capacity is also discussed. The results will provide some theoretical and engineering reference to the design and the type selection of the axial AMB in the rotor system of the HTGR (High Temperature Gas-cooled Reactor) energy conversion system.

A modified active disturbance rejection control strategy based on cascade structure with enhanced robustness

Active disturbance rejection control (ADRC) is considered to be a common control method in the presence of external disturbances and uncertainties. This work proposes a modified ADRC control strategy to further enhance robustness to uncertainties. First, the cascade structure of modified ADRC composed by two control loops is introduced. Two extended state observers that can be tuned independently are arranged in a cascade structure. The outer loop observer provides system state estimation to build the feedback controller, and the inner loop observer deals with the generalized disturbance. Then, the enhanced robustness is verified by the improved sensitivity in the intermediate frequency range. Finally, for the axial magnetic bearing system with unstable system dynamics, the variation trend in maximum sensitivity with different control parameters is explained in the simulation. The experiments are conducted under varying disturbances and parameter uncertainty to verify the enhanced control performance.

Structural optimization design and mechanical performance analysis of laminated six-ring redundant axial magnetic bearings

Targeting at the axial magnetic bearing, a structure of laminated six-ring redundant axial magnetic bearing, which is featured in both high redundancy and low heat, was designed in this paper. Meanwhile, the design criteria of the laminated redundant axial magnetic bearing was proposed, and the theoretical research, numerical simulation and empirical research on the redundancy and electromagnetic force of the laminated redundant axial magnetic bearing were conducted as well in this study.