On Sandwiched Magnetic Bearing Design

Magnetic bearings are systems capable of supporting rotors in absence of mechanical contact. Among many advantages with respect to ball and roller bearings are the possibilities of operating at extremely high rotational speeds and free of maintenance. Nevertheless, classical active magnetic bearings (AMB) are costly systems and may suffer from reliability problems. The most common types of passive magnetic bearings (PMB) based on the use of permanent magnet and reluctance forces are robust and relatively cheap but are affected by an intrinsic stability problem related to negative stiffness. The alternative of superconducting bearings has to deal with the difficulties for guaranteeing low temperatures for the superconducting materials to work; this represents a barrier for this technology. In the last decades an alternative for obtaining stable passive magnetic levitation has been searched, leading to the development of electrodynamic bearings. These systems, capable of realizing electrodynamic suspension for rotors using regular materials at room temperature, may be an alternative for the suspension of high rotational speed machines in the near future. The technological solutions proposed are still unable of devising a system capable of demonstrating the feasibility of this concept. Introduced in this context, this doctoral dissertation aims at developing models and design procedures to bring electrodynamic levitation of rotors closer to industrial applications. To this end, a large portion of the work is devoted to develop a unified model for representing the electromechanical interaction between rotor and stator generated by electrodynamic bearings of different types, namely homopolar and heteropolar configurations. The electromechanical model is developed taking advantage of the complex coordinate representation, typical in rotordynamics, in order to enable easy integration of the bearing's model with different rotordynamic models. An experimental validation of the model is carried out for homopolar configurations. The study of the dynamics of rotors on electrodynamic bearings is probably one of the most important aspects that must be dealt with before the bearings can reach the technological development needed to become industrially available. Bearing this in mind, the dynamics of a Jeffcott rotor and that of a four degree of freedom rotor are studied devoting special attention to the study of stability demonstrating the presence of unstable cylindrical and conical modes. The unbalance and frequency responses of the rotor on electrodynamic bearings are used to evidence the advantages and drawbacks between homopolar and heteropolar configurations. The studies are conduced using the state space formalism to obtain easy to manipulate system models. The modelling of the suspension evidences the strong coupling between the subsystems, showing that the influence of each subsystem on the rotordynamic stability is not obvious, thus complicating the design of the whole suspension. Considering an iterative design approach, the design of a test rig is presented. It is designed to test the validity of the models and the feasibility of radial electrodynamic suspension. A the mechanical layout of the test rig is developed to deal with the stability aspects introduced by the use of electrodynamic bearings.

This thesis is motivated by one of the largest markets: aviation. This market, in which competition and investments are extraordinary, requires constant technical improvements in order to increase its competitiveness. Jet engines have an important influence on fuel consumption and servicing of airplanes, thus on the transportation cost. The present work was supported by the European Community [9]. This thesis investigates the use of active magnetic bearings for jet engines. It is expected that magnetic bearings could considerably reduce losses and service intervals in jet engines. The present work concentrates on the design and characterization an active magnetic bearing for applications at high temperature. The report begins with an introduction locating the accomplished work into the current economic and technical context. The advantages of such system are given, as well as the scientific contribution of the research which has been undertaken. An introduction to magnetic bearings is given, so that the key elements of the dimensioning of such a system are comprehensible for readers of all horizons. The maximum force produced by magnetic bearings is mainly limited by the heating related to the losses in the coils. A thermal model for high temperature magnetic bearings has been implemented. An experimental part allowed the validation of this model for a wide temperature range. The construction of a magnetic bearing requires various types of materials; soft magnetic materials, electrical conductors, electrical insulators as well as several fixation materials. Tests have been carried out and a catalogue lists the materials available for high temperature magnetic bearings. Position sensors are usually used in magnetic bearings. Eddy current position sensors have been developed. They were realized with coils printed on a ceramics substrate by using thick-film technology. Measurements done at high temperature show the great characteristics of these sensors. Problems of silver migration between the wires welding have been encountered during tests carried out at high temperature. Various solutions have been tested with the aim of avoiding the silver migration. The materials exposed at high temperature have unfortunately sometimes a limited lifespan. Studies of failures related to an exposure at high temperature have been done. Some failures are detectable by the magnetic bearing. An example of detection of possible short-circuits in the actuator coils is presented. Finally a prototype of an active magnetic bearing system with five degrees of freedom has been built. A furnace especially developed, makes it possible to create environments at high temperature. The characteristics of the active magnetic bearing have been measured during levitation at ambient temperatures from 25°C up to 550°C.

The blower with Active Magnetic Bearing (AMB) has the advantage of high speed, high reliability, small size, good adaptability. Power amplifier is an important part of the magnetic bearing system, directly determines the magnetic bearing system performance. The three-level PWM signal generation algorithm is analyses in this paper, and the IR2113 gate driven circuits with a negative bias is designed, and build a three-level magnetic bearing power amplifier. The gate driven signal of circuit is test, and entire power amplifier tracking step signal and sinusoidal signal also be test, the test results indicate that the three-level power amplifier meet the design requirements. At last, the power amplifier application on the blowers with AMB successful. Introduction Active Magnetic Bearings (AMB) using electromagnetic force to suspend rotor, with no friction loss, no lubrication, high-speed, non-polluting characteristics.The blower with AMB has the advantage of high speed, high reliability, small size, good adaptability Power amplifier is an important part of the overall magnetic bearing system, directly determines the magnetic bearing system performance . Depending on the realization of the principle, magnetic bearings power amplifier divided into linear power amplifier and switching power amplifier. With respect to the linear power amplifier, switching power amplifier has the advantage of low power consumption and high conversion efficiency; occupy a dominant position in large power amplifiers. Switching power amplifier can be divided into two-level amplifier switching amplifier and three-level switching amplifier depending on the switching signal. In two-level switching amplifier, the magnitude of current ripple is related to the DC voltage. Increases the DC voltage to improve the dynamic characteristics of the system, it will increase the electromagnetic coil current ripple at the same time. The current ripple of three-level switching power amplifier is not only smaller than the two-level power amplifier, but also nothing affected by the DC voltage , and therefore more suitable for high-power active magnetic bearings. In this paper, using FPGA chip to generate three-level switching signals, half-bridge circuit using IGBT modules and IGBT gate drive circuit is designed based on the drive requirements. The Three-level PWM Signal Generation Algorithm: D2 L Drive circuit FPGA Current sensor feedback AD circuit A D1 Vref S1 S2 I Reference signal Q1

A new type of flywheel energy storage system uses a magnetic suspension where the axial load is provided solely by permanent magnets, whereas active magnetic bearings are only used for radial stabilization. This means that the permanent magnet bearing must provide all the axial damping. Furthermore, it must have as low a negative radial stiffness as possible to reduce the workload on the radial active magnetic bearings. Many different mathematical models for determining force, stiffness, and damping of permanent magnet bearings are available in the literature. This work will further develop the most applicable analytical and numerical methods in order to make them directly implementable for designing permanent magnet thrust bearings for flywheel energy storage systems. The outcome is a fast and efficient method for determining force, stiffness, and damping when the bearing setup contains magnetic materials with relative permeability higher than one as well as when it does not. The developed method is validated against numerical and experimental results with good agreement.

A magnetic bearing is an industrial device that supports a rotating shaft with a magnetic field. Magnetic bearings have advantages such as high efficiency, low maintenance, and no lubrication. Active magnetic bearings (AMBs) use electromagnets with actively controlled coil currents based on rotor position monitored by sensors integral to the AMB. AMBs are apt to the Internet of Things (IoT) due to their inherent sensors and actuators. The IoT is the interconnection of physical devices that enables them to send and receive data over the Internet. IoT technology has recently rapidly increased and is being applied to industrial devices. This study developed a method for the condition monitoring of AMB systems online using off-the-shelf IoT technology. Because off-the-shelf IoT solutions were utilized, the developed method is cost-effective and can be implemented on existing AMB systems. In this study, a MBC500 AMB test rig was outfitted with a Raspberry Pi single board computer. The Raspberry Pi monitors the AMB’s position sensors and current sensors via an analog-to-digital converter. Several loading cases were imposed on the experimental test rig and diagnosed remotely using virtual network computing. It was found that remote AMB condition monitoring is feasible for less than USD 100.

For an attitude control and energy storage flywheel (ACESF), not only does the speed of the rotor must be high but also the position of the rotor must be controlled accurately. To research the relationship between superconducting magnetic bearings (SMBs) and active magnetic bearings (AMBs) in this presented superconducting ACESF, the rotor model is established, the force of SMBs and AMBs is simplified by linearization, and the radial translation and tilting movement of the rotor suspended by only SMBs, SMBs with equivalent permanent-magnet bearings, and SMBs and AMBs with proportional–derivative-type control are researched, respectively. For the disklike rigid rotor with large inertia and high speed, simulation and experimental results proved that the gyroscopic effect of the rotor is prominent, the rotor model including gyroscopic couples can describe its behaviors, and the linearization of force for SMBs and AMBs are reasonable. The AMB can suppress the nutation and precession of the rotor effectively by a cross-feedback control method or other modern control methods; the SMB, together with the AMB, can make the rotor in ACESF be stable and the amplitude of the vibration of rotor be small.

Magnetic-bearings, which support shafts with magnetic levitation rather than mechanical contact, have been in industrial use for decades. Recent technological developments, especially in digital processing and control, have made magnetic bearings a more-robust and cost-effective design solution than ever. The dynamic characteristic of electromagnetic bearing depends upon adopted controller; the active control can makes the electromagnetic bearings to realize complex control and special control. With the development of signal processing technology and modern control theory, the main parts of the control system are the digital signal-processing (DSP) electronics, a power supply, and amplifiers. An Active Magnetic Bearing (AMB) controller is mainly discussed in the paper, which is to be solved to realize this flexible control by hardware design based on DSP using TMS320C32 processor. It is proved by experiment that this kind of controller can optimize for this system, improve its stability and also have a very important referential value on the further study of AMB system.

Aiming at the magnetic seal in an aero-engine accessory, the range of magnetic force required for the normal operation of the magnetic seal is analyzed. The finite element analysis method based on the Maxwell stress tensor method is used to calculate the magnetic force between the dynamic ring and the magnetic static ring in the magnetic sealing system. The magnetic force under different magnetization modes and gaps is tested by the magnetic measuring test bench, which verifies the correctness of the magnetic calculation method. The effects of permanent magnet material, permanent magnet magnetization direction, magnetic seal structural parameters, and working conditions on the magnetic force between the dynamic ring/magnetic static ring in the magnetic seal are analyzed. Under the same structure, the magnetic force of NeFeB35, SmCo28, Alnico5, and Ferrite as magnetic static rings is compared. The results show that NdFeB35 has the largest magnetic force, SmCo28 is second, Alnico5 and Ferrite are relatively small, and their magnetic forces are about 1/4 to 1/5 of the first two materials. When the rotor or the casing is moving axially, NeFeB35 and SmCo28 materials with large magnetic force should be selected to meet the normal working requirements. Under the same material, the magnetic forces of axial, radial, and radiative magnetization modes are compared. the ratio of magnetic force under axial, radiative, and radial magnetization is about 2.3:1.1:1. If NeFeB35 and SmCo28 materials are axially magnetized, their magnetic forces will exceed the allowable range, which will increase the seal wear. The increase in the inner diameter of the dynamic ring and the gap between the dynamic ring and the magnetic static ring causes a decrease in the magnetic force. The increase in temperature affects the magnetic properties of permanent magnetic material, which leads to the decline of magnetic force between the dynamic ring and the magnetic static ring. The increase in rotor speed leads to the acceleration of the fluctuation frequency of the magnetic force. Still, the maximum and minimum values of the magnetic force under different speeds remain unchanged, and the maximum fluctuation rate is less than 3%. According to the analysis results, the fitting formula of magnetic force calculation is presented by the orthogonal test and the least squares method.

Field analysis was applied to the simulation of magnetic field distribution and calculation of its integral parameters in an active magnetic bearing (AMB). 3D Finite Element Method (FEM) was employed for the computations. The magnetic force which act on the moving shift and stiffness parameters of AMB were calculated under the steady state conditions. The measurement results confirm rightness of the field modeling. The inductances of the stator winding coils were computed, as well. They have been used for the analysis of the AMB dynamics, which is not presented here.

The distribution of the magnetic coupling between the poles in active magnetic bearings is examined. The study is based on an analysis of the electromagnetic characteristics of four main configurations of magnetic poles: NNSS, NSNS, NNNN, and SSSS. The electromagnetic forces generated by the NNSS and NSNS configurations were calculated and comparatively analyzed, which makes it possible to evaluate their power capabilities and efficiency. To study the phenomenon of magnetic coupling and its effect on the distribution of magnetic induction, equivalent magnetic circuits were simulated, and the results obtained were verified by the finite element method. Optimal pole configurations have been found using the criterion of minimal mutual influence of magnetic circuits.

With the advancement in science and technology, a wall-climbing robot attached to the ship's outer surface is increasingly replacing humans in the rust removal. The magnetic force is not just the adsorption force but also the moving resistance force, which is currently the technological bottleneck in wall-climbing robotics based on magnetic adsorption. This paper proposes a novel wall-climbing robot based on electrically controlled permanent magnet technology to solve this problem. An electrically controlled permanent magnetic wall-climbing robot is proposed to realize the function of magnetization and demagnetization by changing the pulse current. The results of the experiments reveal that the magnetizing force is adequately adsorbed on the ship's outer surface. The magnetic attraction force is close to 0 N during demagnetization, meaning that the system is fully unloaded, as predicted by the theoretical analysis.

An active magnetic bearing (AMB) is a bearing used to suspend a rotor by magnetic forces without any contact. Feedback control is indispensable for a magnetic bearing, because it is essentially an unstable system. To design a feedback control system, a linear mathematical model of the plant is convenient; however, the force of the electromagnet is highly nonlinear. Thus, usually a linear approximation around the operating point is employed, but the obtained linearized model cannot express the exact behavior of the system at any other operating points. In this paper, we discuss the wide area stabilization of magnetic bearings using the exact linearization approach. First, we derive a nonlinear mathematical model for a magnetic bearing, then we show that this nonlinear system belongs to a class of exactly linearizable nonlinear systems. Next, by using the exact linearization method, we transfer the nonlinear model of a magnetic bearing to a linear time-invariant state model in spite of change of the operating point and the rotational speed of the rotor. Then we construct the state feedback control system by the conventional LQ method. Finally, we evaluate the validity of our proposed method by experiments. © 1999 Scripta Technica, Electr Eng Jpn, 128(2): 53–62, 1999

A constant stiffness magnetic bearing

The most common component of mechanical systems today is rotating machines. In these systems, vibration is caused by rotating components. As a result, to decrease the amplitude of vibrations created by rotating equipment, it’s required to understand the behavior of the system. In this work, the problem of vibrations in conventional bearing systems and the effect of adding active magnetic bearings to rotating machines to reduce the amplitude of vibrations are discussed. In this paper, the vibrations in the rotary bearing system were studied theoretically and analytically by using simulation programs to calculate the natural frequencies and parameters affecting the performance. In the theoretical part, the shaft of the rotating bearing was analyzed by the Jeffcott method depending on several parameters changed with the frequency value to observe the amplitude of the vibrations in the shaft. In an analytical aspect by simulation, a representative model of active magnetic bearings was built using the COMSOL 2020 program, and the effect of adding these bearings on capacitance, vibration reduction, and frequency behavior was examined. SolidWorks 2018 software was used to analyze the magnetic field and its distribution in the magnetic bearing coil. The results indicate that when magnetic active bearings were introduced to the rotating bearing shafts, the vibration amplitude was reduced by approximately 60%. From this work, it can be concluded that the system becomes more stable when the active magnetic bearing is added to the rotating bearing shaft, giving it a more stable and firm nature.

This paper introduces the applied AMB(Active Magnetic Bearing) System supported by magnetic bearing which is controlled. The system needs component design technique for develop AMB System. Magnetic field analysis, PID control and 3D rotordynamic analysis of AMB is performed. The required performance of motor is a 220 kW, 30 krpm high speed motor. The 3D rotordynamic analysis considering magnetic bearings are simulated to find the critical speed of rotor by Cambpell diagram. The analysis shows that the critical speed of the rotor is higher than operating speed with sufficient separation margin. All the performances of the AMB high speed motor prototype are verified successfully