Hybrid Magnetic Bearing Research Articles

Internal model control for reduction of bias and harmonic currents in hybrid magnetic bearing

Abstract Bias and harmonic currents, which are caused by rotor gravity, mass imbalance and sensor runout, are the dominant disturbances of the hybrid magnetic bearing (HMB) systems. To reject these disturbances and realize the low power control, a novel internal model control method based on positive current feedback and repetitive control is proposed. The positive current feedback can tune the levitation position of the rotor adaptively so that the rotor gravity can be supported precisely by the force resulting from the permanent magnet in the HMB. To suppress the harmonic currents caused by the mass imbalance and sensor runout, a novel plug-in repetitive controller is proposed. Compared to the conventional repetitive controller, the low-pass filter is removed from the internal time lag loop outside so as to improve the system stability and reduce the elimination error of the high-order current harmonics. The absolute stability of the whole closed-loop system is analyzed by using the Nyquist criterion to the time-delay system with the help of the regeneration spectrum method. Upon the phase-frequency characteristic, phase compensators in low, middle, and high frequencies are designed, respectively. Both simulations and experiments are carried out to demonstrate the validity of the proposed control method.

Soft Sensing Modeling of Magnetic Suspension Rotor Displacements Based on Continuous Hidden Markov Model

Aiming at the problem that rotor displacements in magnetic bearing system are difficult to be accurately detected, a soft sensing method based on continuous hidden Markov model (CHMM) is proposed. First, the structure and operation principle of a 3-degree-of-freedom hybrid magnetic bearing (3-DOF-HMB) is described, and its nonlinear mathematical model is derived by using equivalent magnetic circuit method. Then, combining the well prediction ability of CHMM, a position prediction model is built by collecting representative current-displacement data. The accuracy of established model is promised by comparing the predicted results with the rest collected data. Finally, a 3-DOF-HMB system based on the CHMM is established for the simulation, and the mean squared error is taken as model evaluation index to compare predictive ability of the proposed model and other self-sensing models, showing that the proposed model has higher accuracy. The experiment results verify the well performance of anti-interference.

Analysis of spatial thermal field in a magnetic bearing

AbstractThis paper presents two mathematical models for temperature field analysis in a new hybrid magnetic bearing. Temperature distributions have been calculated using a three dimensional simulation and a two dimensional one. A physical model for temperature testing in the magnetic bearing has been developed. Some results obtained from computer simulations were compared with measurements.

Magnetic circuit designing and structural optimisation for a three degree‐of‐freedom hybrid magnetic bearing

The three degree-of-freedom (3-DOF) hybrid magnetic bearing (HMB) sets radial, axial at one entirety, which can effectively save the bearing installation space. Here, a 3-DOF HMB is designed, optimised, and tested for a 30 kW 60,000 r/min high-speed motor system. The radial and axial bearing capacity is analysed by equivalent magnetic circuit method and three dimensional finite element model (FEM) of initial model of 3-DOF HMB is established. Then, the radial bearing capacity, axial bearing capacity, current-stiffness, and displacement-stiffness are selected as the optimised design target by using chaos particle swarm optimisation algorithm. Meanwhile, the axial length, eddy-current loss, and air-gap flux density are selected as constraints of optimization. The optimal results showed that the axial length is decreased, the eddy-current loss is reduced, and the harmonics in the air gap is lower while the bearing capacity is improved. Furthermore, a 30 kW 60,000 r/min high-speed motor with proposed 3-DOF HMB is manufactured, and the experiments of the radial/axial static bearing capacity test, dynamic performance of high-speed motor with no load in 60,000 r/min and with load in 55,000 r/min are carried out. Experiment results show that the optimised 3-DOF HMB has good force performance and dynamic performance.

Design and Adaptive Sliding-Mode Control of Hybrid Magnetic Bearings

In this paper, a hybrid magnetic bearing (HMB) prototype system is designed and analyzed. Two compact bearings are used to suspend the rotor in five degrees of freedom. Electromagnets are used for axial suspension of the rotor, while permanent magnets are used for the passive radial stability. A brushless DC motor is designed in order to rotate the shaft around its axis. The 3-D finite-element model of the HMB system is established and distribution of magnetic fields in the air gaps and magnetic forces on the rotor under various control currents and displacements is calculated. A nonlinear adaptive sliding-mode controller is designed for the position control of the rotor in axial direction. Since the control characteristics of the active magnetic bearing system are highly nonlinear and time varying with external interference, a radial basis function compensator is designed first, and then, a sliding-mode control law is used to generate the control input. The stability analysis for the designed controller is given based on the Lyapunov theorem. Experimental setup is built to guide the design process. The performance of the HMB system based on the designed control algorithm is evaluated under different operating conditions.

Modeling and Analysis of Hybrid Permanent Magnet Type Bearingless Motor

The traditional bearingless permanent magnet synchronous motor has complex decoupling control problems. To overcome the drawbacks above, a novel hybrid permanent magnet type bearingless motor (HPMTBM) is proposed in this paper, which has integrated the merits of hybrid excitation permanent magnet motor and magnetic bearings. The main advantages of this HPMTBM are the simple control mechanism and the low power consumption. First, the principle and theoretical background of this motor are introduced. Then, the mathematical models of radial suspension force and torque are established using Maxwell stress tensor method, and air-gap magnetic fields, radial suspension forces are calculated by finite-element analysis. Finally, the prototype motor is designed and constructed. The radial suspension forces and rotor radial displacements are tested. The simulation and experimental results show the feasibility of the proposed HPMTBM.

Design Optimization of a Novel Heteropolar Radial Hybrid Magnetic Bearing Using Magnetic Circuit Model

In this paper, one novel heteropolar radial hybrid magnetic bearing (HRHMB) with low-power loss is proposed for flywheel energy storage system. First, its structure and equivalent magnetic circuit (EMC) are introduced in detail. Then, some main design parameters are analyzed based on EMC, including air-gap bias flux density, magnetic pole area, permanent magnet (PM) dimensions, and control current. Furthermore, to improve the performances of the novel HRHMB, the optimizations are implemented both on its structure and some key size parameters, such as the second air-gap length, PM height, and width. Finally, the optimal scheme is verified by the 3-D finite-element analysis, which indicates the maximum control current can be reduced to only 40% that of initial design by the optimizations.

Model-free adaptive control for three-degree-of-freedom hybrid magnetic bearings

Mathematical models are disappointing due to uneven distribution of the air gap magnetic field and significant unmodeled dynamics in magnetic bearing systems. The effectiveness of control deteriorates based on an inaccurate mathematical model, creating slow response speed and high jitter. To solve these problems, a model-free adaptive control (MFAC) scheme is proposed for a three-degree-of-freedom hybrid magnetic bearing (3-DoF HMB) control system. The scheme for 3-DoF HMB depends only on the control current and the objective balanced position, and it does not involve any model information. The design process of a parameter estimation algorithm is model-free, based directly on pseudo-partial-derivative (PPD) derived online from the input and output data information. The rotor start-of-suspension position of the HMB is regulated by auxiliary bearings with different inner diameters, and two kinds of operation situations (linear and nonlinear areas) are present to analyze the validity of MFAC in detail. Both simulations and experiments demonstrate that the proposed MFAC scheme handles the 3-DoF HMB control system with start-of-suspension response speed, smaller steady state error, and higher stability.

Novel Heteropolar Radial Hybrid Magnetic Bearing With Low Rotor Core Loss

In this paper, one novel heteropolar radial hybrid magnetic bearing (HRHMB) is proposed for flywheel energy storage system. First, its structure and working principle are introduced in detail. Then, its fundamental equations are derived based on magnetic circuit model, such as displacement stiffness, current stiffness, and load capacity. Furthermore, its suspension performance and magnetic coupling are analyzed based on the 2-D finite-element analysis. Finally, the comparison of main performance indexes between the proposed HRHMB and conventional one under the same constraints is made. It indicates that the displacement stiffness can be reduced by the novel structure. In addition, the rotor core loss of the novel HRHMB is just 22.53 W, which is only 41.6% of the conventional eight-pole HRHMB with the same load capacity.

300 마력급 터보 압축기용 자기베어링의 설계 및 평가

Recently, the international community is making steady efforts to reduce energy consumption to counter climate change and reduce CO₂ emissions. In view of this trend, there is a high interest in oil-free turbo compressors that are highly efficient in replacing conventional screw compressors and do not generate waste oil in the compressor field. In accordance with this trend, in the field of compressors, there is a high interest in oil-free turbo compressors which can replace existing screw compressors, have high efficiency and do not generate waste oil. In the case of an oil-free turbo compressor, magnetic bearings tend to be applied in a large amount, which has a high rotational stability at high speed and a load capacity capable of coping with a large axial thrust. In this study, magnetic bearings were designed to apply to a compressor of 300-HP and 50,000 rpm, and a rotor in the compressor were designed by direct drive method by applying a permanent magnet synchronous motor. After fabricating a 300-HP compressor with magnetic bearings, the motoring test under the no-load condition without impellers was performed up to 51,000 rpm to evaluate the structural stability against the centrifugal force of the rotating shaft. In addition, the rotational stability was evaluated by motoring test up to 50,000 rpm under the load condition with impellers. Based on the experimental results, it is presented that the hybrid magnetic bearings are suitable oil-free bearings capable of stably supporting turbo compressors.

A Novel 4-DOF Hybrid Magnetic Bearing for DGMSCMG

In this paper, a novel structure of four degrees of freedom (4-DOF) hybrid magnetic bearing is proposed for double gimbal magnetically suspended control momentum gyro (DGMSCMG). It includes two active parts and one passive part, and every active part has eight stator magnetic poles around the circumference in X and Y directions, which are divided into upper and lower layers. The passive part has two whole magnetic rings, which is located in the middle of this 4-DOF hybrid magnetic bearing. The radial active force is analyzed by equivalent magnetic circuit method (EMCM) and the axial resilience force is analyzed by the infinitesimal method based on the end magnetic flux. Meanwhile, three-dimensional finite-element model of the 4-DOF hybrid magnetic bearing is established with ANSYS software, and the radial displacement versus radial force, the current versus radial force, and the axial displacement versus axial resilience force characteristics are analyzed compared with the EMCM. Furthermore, the 10 Nms DGMSCMG prototype with the proposed 4-DOF hybrid magnetic bearing is manufactured, and the experiments of the radial active force test and the axial resilience force test are carried out. Experimental results show that the presented 4-DOF hybrid magnetic bearing has good force performance and verify the correctness of the theoretical analysis.

Magnetic flux leakage modelling and optimisation of a CRAHMB for DC motor

In this study, a combined radial–axial hybrid magnetic bearing (CRAHMB) with four poles is designed for high-speed brushless DC motor. Owing to the small distance of radial and axial unit of CRAHMB, the magnetic flux leakage (MFL) in both radial and axial directions is complex and serious. This study focuses on effective analytical model and optimisation of CRAHMB including flux leakage of permanent magnet circuit and control electromagnetic circuit. MFL analytical model was built based on equivalent magnetic circuit method. Under the condition of satisfying the maximum bearing capacity, the MFL coefficients were optimised with sequence quadratic programming method. A set of optimum parameters were suggested. MFL before and after optimisation are compared by finite element method. Finally, current stiffness calculated with optimised analytical model was verified on a DC motor experiment. The result shows the accuracies of both the axial and radial current stiffness are enhanced.

Experimental Analysis and Full Prediction Model of a 5-DOF Motorized Spindle

The cost and power consumption of DC power amplifiers are much greater than that of AC power converters. Compared to a motorized spindle supported with DC magnetic bearings, a motorized spindle supported with AC magnetic bearings is inexpensive and more efficient. This paper studies a five-degrees-of-freedom (5-DOF) motorized spindle supported with AC hybrid magnetic bearings (HMBs). Most models of suspension forces, except a “switching model”, are quite accurate, but only in a particular operating area and not in regional coverage. If a “switching model” is applied to a 5-DOF motorized spindle, the real-time performance of the control system can be significantly decreased due to the large amount of data processing for both displacement and current. In order to solve this defect, experiments based on the “switching model” are performed, and the resulting data are analyzed. Using the data analysis results, a “full prediction model” based on the operating state is proposed to improve real-time performance and precision. Finally, comparative, verification and stiffness tests are conducted to verify the improvement of the proposed model. Results of the tests indicate that the rotor has excellent characteristics, such as good real-time performance, superior anti-interference performance with load and the accuracy of the model in full zone. The satisfactory experimental results demonstrate the effectiveness of the “full prediction model” applied to the control system under different operating stages. Therefore, the results of the experimental analysis and the proposed full prediction model can provide a control system of a 5-DOF motorized spindle with the most suitable mathematical models of the suspension force.

On the Question of the Hybrid Magnetic Bearings Design

On the Question of the Hybrid Magnetic Bearings Design

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.

Designing and Experimental Verification of the Axial Hybrid Magnetic Bearing to Stabilization of a Magnetically Suspended Inertially Stabilized Platform

To decrease the mass and power loss of axial hybrid magnetic bearings (HMBs) in the application of inertially stabilized platform (ISP) with a large axial diameter, this paper investigates the effects of the layout of axial HMBs and the degree of asymmetry (DOA). An asymmetry axial HMB is proposed for ISP based on DOA. Each single axial HMB is modeled and analyzed using the reluctance network method. And the relationship between current and force, as well as the displacement and force, are studied. Additionally, the optimization design method of the axial HMB is presented based on DOA. According to the principle of the design, the layout of the complete asymmetry axial HMB is designed with eight single axial HMBs in the upper end and four single axial HMBs in the lower end of ISP. Furthermore, the relationship among displacement, current, and displacement stiffness and the relationship among displacement, current, and current stiffness are analyzed as the DOA varies. A prototype is manufactured based on the above design and analysis, and experiments are carried out. Experimental results illustrate that the mass and power loss will be decreased dramatically compared with the symmetry layout of axial HMBs.

Basic Characteristics and Design of a Novel Hybrid Magnetic Bearing for Wind Turbines

This paper proposes a five-degree-of-freedom (5-DOF) hybrid magnetic bearing (HMB) for direct-drive wind turbines, which can realize suspension in the 4-DOF radial and 1-DOF axial directions. Only two sets of radial control windings are employed in the proposed HMB because only one set of radial control windings can achieve the 2-DOF suspension in the radial direction. Unlike the traditional active thrust magnetic bearings, this paper uses a cylindrical rotor core without a large thrust disc in the novel HMB. The numbers of the controller, power amplifier and system volume can be reduced in the magnetic suspension system. This paper also presents the structure and basic characteristics of the proposed magnetic bearing. A precision equivalent magnetic circuit analysis of the permanent magnet ring and control magnetic field is conducted in this study, in consideration of the non-uniform distribution of magnetic density. Accordingly, the mathematical models, including the suspension force expression, are derived based on the accurate equivalent magnetic circuit. The basic principle of the structure parameter design is presented, based on the given key parameters. The accuracy of the analytical method is further validated by 3D finite element analysis.

Mathematical model of the hybrid system of magnetic levitation energy production equipment autonomous power 97 supply systems

Introduction. Typically, when developing mathematical models magnetocavitation systems (magnetic bearings, electrostatic bearings, hybrid magnetic bearings (GMP, etc.) is considered just the very bearing as a separate, isolated Electromechanical system. This approach allows us to accurately explore the process magnetocavitation systems, but practically does not allow to evaluate the processes occurring in the system of magnetic bearing-object position. To solve this problem, the author proposes a different approach to the analysis of the processes in magnetocavitation systems in General and GPC in particular considering the magnetic bearing-object position, as a single complex. Goal. The work aimed the creation of a generalized analytical model of high-speed, AMPE with coercivity permanent magnet (VPM) on an elastic bearing supports, taking into account the mutual influence of processes in AMPA and bearing supports. This task is new and relevant and is essential to modern engineering. To solve this problem this paper developed a generalized mathematical model of the rotor system on a hybrid magnetic suspension. Evaluate the impact of hybrid magnetic bearings on the overall behavior of the rotor system. Performed analysis of processes in Electromechanical energy converters and mechanical processes occurring in the rotary system. Method and methodology. The research methodology is based on the joint solution of Maxwell equations and equations describing the mechanical processes of a rotor system with five degrees of freedom. Conclusion. The generalized mathematical model of high-speed, AMPE with VPM on a non-contact bearing supports and conducted her research. Based on research of the developed mathematical model, the authors developed an original control algorithm for the rotor position in a hybrid magnetic bearings, which allows for the design of high-speed, AMPE with VPM to abandon the position sensors of the rotor. In addition, on the basis of the results of calculations, a method was developed for diagnostics of eccentricity of rotor are high-speed, AMPE with VPM, as well as new methods of calculation of high-speed, AMPE with VPM, past experimental verification.

Radial Force-Current Characteristics Analysis of Three-Pole Radial-Axial Hybrid Magnetic Bearings and Their Structure Improvement

The radial stator of three-pole radial-axial hybrid magnetic bearings (HMB) has three magnetic poles and the three magnetic poles are driven by a three-phase converter, so the three-pole radial-axial HMB has the advantages of compact structure, low cost, low power consumption and so on. However, as the sum of three-phase current is zero and the three radial magnetic poles are asymmetric, the relationship between the radial suspension force and the control current is nonlinear. In this paper, firstly a mathematical model of three-pole radial-axial HMB is built based on the equivalent magnetic circuit method. The radial force-current characteristics are then analyzed based on the non-linearized model. The calculation, finite element method (FEM) and experimental results show that the suspension force on the x-axis is a quadratic function of the control current, but the suspension force on the y-axis is linear with control current. Besides, the suspension forces on the two radial axes are coupled with each other. Then, in order to decrease the nonlinearity and coupling of radial force-current characteristics, the six-pole radial-axial HMB is proposed based on the above analyses. The radial force-current characteristics of the six-pole radial-axial HMB are also analyzed based on the non-linearitzed model and are validated by 3-D FEM analysis. The calculation and FEM results have shown that the radial force-current relationship of a six-pole radial-axial HMB is linear and there is no coupling between the two radial axes.

Research on Operation Principle and Control of Novel Hybrid Excitation Bearingless Permanent Magnet Generator

Under the condition of load changing, the magnetic field of traditional permanent magnet generators (PMG) is hard to be adjusted, and the mechanical bearings are significantly worn. To overcome the drawbacks above, a novel hybrid excitation bearingless permanent magnet generator (HEBPMG) is proposed in this paper, which has integrated the merits of hybrid excitation permanent magnet generators and magnetic bearings. Firstly, the structure and winding configuration of the HEBPMG are introduced, and then the principles of radial suspension and power generation are presented. The suspension principle as well as power generation principle is analyzed in this paper. Then, the flux linkage and induced voltage equations are derived, and the accurate mathematical model of radial suspension force is built based on the Maxwell tensor method. Subsequently, by means of the finite element analysis software-ANSYS Maxwell, the corresponding electromagnetic characteristics are analyzed to verify the correctness of the mentioned models. In addition, a compensation control strategy based on flux-linkage observation is proposed to solve the problems of unstable suspension force and generating voltage under variable load condition in this paper. Meanwhile, the corresponding control system is constructed and its feasibility is validated by simulation results. Finally, an experimental prototype of a 2.2 kW HEBPMG is tested. Experimental researches show that the HEBPMG can operate steadily under variable load condition and possess good suspension performance and power generation quality.