Auxiliary Magnet Research Articles

Comparative analysis and optimization design of dual-side-permanent-magnet Halbach array vernier machine for high torque density

PurposeThe purpose of this paper is to introduce and analyze a dual-side-permanent-magnet Halbach array vernier (DSPMHV) machine and to propose methods for achieving high torque density.Design/methodology/approachFlux harmonics and torque characteristics are analyzed by using finite element analysis. First, a suitable pole-slot combination is selected by comparison. Second, field modulation processes of DSPMHV machine are analyzed to identify the reason for high torque density. And it is compared with dual-side-PM (DSPM) machine to analyze flux harmonic and verify the flux concentrating effect of the Halbach array.FindingsThe permanent magnet (PM) field of the DSPM machine is approximately equal to the superposition of stator-PM field and rotor-PM field, which is the reason for high torque density. And the Halbach array can reduce flux leakage and increase the amplitude of main flux harmonics, then further improves torque. Improvement of torque can be achieved by choosing right pole-slot combination, adopting DSPM machine structure, reducing flux leakage and adopting field modulation principle.Originality/valueThe DSPMHV machine with split-tooth is proposed in this paper by combining the Halbach array with DSPM structure. This paper analyzes the bidirectional field modulation process, the reason for high torque density of the DSPM machine is obtained. Comparison with the DSPM machine verifies the flux concentrating effect of Halbach array. To alleviate the magnetic saturation in part of stator teeth, this paper proposes an improved DSPMHV machine with shaped auxiliary magnet.

Magnetic Force Performance of Hybrid Multisurface HTS Maglev System With Auxiliary Onboard PMs

The vertical levitation force, guidance force, and magnetic stiffness values, and thus the loading capacity and movement stability of high-temperature superconducting (HTS) Maglev systems, are aimed to be increased in this study by using auxiliary permanent magnets (PMs) in the onboard unit together with the multisurface HTS-permanent magnetic guideway (PMG) arrangement (hybrid multisurface arrangement). First, the magnetic levitation force, guidance force, and stiffness performances of the hybrid multisurface arrangement were investigated at different field cooling heights (FCH). Then, to compensate for the negation of instability that results from the higher repulsive force between the onboard PMs and the PMG and to obtain an optimal magnetic field medium, we have changed the vertical position of the auxiliary onboard PMs (Z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PM</sub> ) to Z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PM</sub> = 0, 2, and 4 mm, at the cost of a bit of adecrement in the vertical levitation force. The bigger levitation force, together with the guidance force values for FCH = 25 mm and Z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PM</sub> = 0 mm, indicates that the hybrid multisurface HTS–PMG arrangements are beneficial to increasing the practical applicability of Maglev systems.

Investigation of the magnetic separation performance of a low-intensity magnetic separator embedded with auxiliary permanent magnets

Low-intensity magnetic separators (LIMSs) comprise one of the most widely employed magnetic separation equipment. It is worth studying how to reduce magnetic flux leakage and significantly improve magnetic induction. Typically, auxiliary permanent magnets (APMs) are embedded in the main permanent magnets (MPMs) to increase the magnetic induction. In this study, the effect of the matching relationship between the widths of the MPM and APM and the height of the APM on the magnetic field distribution and magnetic separation performance are investigated. The wider the width of the MPM is, the wider the area of the relatively high magnetic induction intensity. Therefore, increasing the width of the MPM can effectively capture farther magnetic particles, which can effectively improve the magnetic separation performance. In addition, when the size of the MPM is constant, although the height of the APM is increased, the magnetic induction is improved less significantly. The research findings indicate that the height of the APM is approximately two-thirds of that of the MPM, so a satisfactory magnetic field distribution and magnetic separation performance can be obtained. Furthermore, to verify whether APM-LIMSs have advantages, a conventional low-intensity magnetic separator (CON-LIMS) without MPMs was designed. The magnetic field distribution and the effect of important parameters (remnant flux density, drum/tank distance, feeding speed and particle size) on the separation recovery are systematically compared and investigated through detailed computational simulations corresponding to the operating conditions. All the comparison results indicate that embedding APMs in the gaps of MPMs significantly expands the area of relatively high magnetic induction, which can ensure that there is still a strong magnetic force in the area far from the surface of the drum, thereby significantly improving the separation performance. Therefore, APM-LIMSs can capture a wider range and finer particle size. Moreover, APM-LIMSs can select low-cost, ferrite, permanent magnets and set a higher feeding speed and a wider drum/tank distance, thereby significantly increasing the processing capacity while ensuring a high separation performance.

Study on the influence of auxiliary electrode and magnet on electrochemical machining of SS304 using NaCl and NaNO3

SS304 is a potential material for the use in defense, medical, aerospace, and automotive industries owing to its excellent mechanical and chemical properties. Machining of SS304 is a topic of great research interest and complex shapes can be produced effectively using Electrochemical machining (ECM). However stray corrosion is a problem in ECM that has a negative impact on the process. Moreover, acids are widely used as electrolytes in ECM. The use of eco-friendly electrolytes saves the operator and the environment from the threats associated with the use of acids as electrolytes. Hence in this study, eco-friendly electrolytes (NaCl and NaNO3) are used. This paper presents a study to reduce the adverse effect of stray corrosion using a magnet, an auxiliary electrode, and a combination of both on two eco-friendly electrolytes using SS304 as workpiece. The evaluation was done based on Taper angle, Radial overcut, MRR, Surface roughness, and Radial-Stray current affected zone. The magnet was placed below the workpiece using a 3D-printed fixture. From the experiments conducted it has been found that the use of Aluminum as an auxiliary electrode is effective when using NaCl as an electrolyte. Up to 37% decrease in taper angle and a 63% reduction in surface roughness was observed when machining was done under the influence of a magnet using NaCl, due to the formation of vortex flow in the machining zone.

Analysis and testing of a superconducting maglev submersible cryogenic liquid pump

This paper studies a superconducting maglev submersible cryogenic liquid pump (CLP) using superconducting magnetic bearing (SMB). A new structure is proposed for the self-stability of high-temperature superconducting magnetic levitation, and the compact structure of disk motor-pump. The rotor of the axial-flux disk motor is connected with a centrifugal impeller to form an impeller-rotor of the proposed superconducting CLP. Supported by a SMB system, the impeller-rotor rotates frictionlessly with self-stabilisation as a suspension rotor. The SMB system includes a radial-type SMB, an auxiliary permanent magnet bearing, and an electromagnetic bearing composed of the stator and the rotor of disk motor. Theoretical calculations and experimental measurements are performed to examine the axial and radial levitation force behaviours of the SMB system. Then, a kinetic model of the suspension rotor is established and analysed to assure force balance and stable levitation. Finally, a prototype pump is fabricated and an experimental setup for liquid nitrogen transmission is constructed for validation purposes. The experimental tests on the pump head and the flow rate are carried out, which demonstrate the effectiveness of the proposed superconducting maglev submersible CLP.

Optimization and Simulation of Auxiliary Magnetic Barrier Permanent Magnet Synchronous Machine for Wind Turbine

The auxiliary magnetic barrier permanent magnet synchronous motor(AMBPMSG) has not only the advantages of high power density and highefficiency of permanent magnet synchronous generator, but also the advan-tages of high temperature non-demagnetization and low cost of the reluctancemotor. It has a broad application prospect in the field of wind power gen-eration. Statement is presented in this paper, on the basis of structure andoperation principle of the motor, the magnetic barrier surrounding the shape,shape of magnetic bridge, magnetic barrier layer and a permanent magnet isoptimized, by means of two-dimensional finite element simulation softwareanalysis of air-gap magnetic field, the counter electromotive force, reduce no-load back electromotive force harmonic content, in order to obtain the optimalelectromagnetic performance, and develop the visual design and simulationplatform software. The research of this paper has a certain reference value forthe popularization and application of AMBPMSG.

Design and analysis of a novel claw‐shaped modular stator relieving‐DC‐saturation doubly salient machine with 3D complementary magnetic circuit

Here, a novel DC-excited doubly salient machine with a claw-shaped modular stator and three-dimensional (3D) complementary magnetic circuit is proposed for wind power generation application. The key is to artificially construct a 3D complementary structure to suppress torque ripple and employ auxiliary slot-opening PMs to relieve DC-saturation in the stator core and improve overload capability. The novel 3D complementary structure provides an alternative magnetic path for the main flux, so the flux leakages in the air gap at open-circuit position are effectively cancelled, and the flux in the yoke remains relatively constant. Hence, the output torque ripple is suppressed. Furthermore, the saturation issue in the stator is solved with auxiliary permanent magnets which have opposite magnetization direction to that of DC field excitation. Therefore, the torque capacity of the machine is improved. Here, the machine structure and operation principle are introduced, and a 2D equivalent model is also developed to replace the 3D model to improve the calculation efficiency. Multi-objective optimization algorithm is developed to improve the performance of this new machine. The validity of machine design is finally verified with 2D and 3D finite element analysis.

Modeling of the dynamics of a superconducting maglev in the mixed state

We studied the levitation of a YBa2Cu3O7 (YBCO) melt-textured superconducting specimen above a closed path of permanent magnets. The superconductor was magnetized with an auxiliary permanent magnet before brought to the path of magnets. This way, the superconducting levitation in the mixed state was achieved. The vertical and horizontal forces acting on the superconductor were calculated by means of two models. One model considers that the superconductor is in the Meissner state and assumes that it is possible to take into account the demagnetizing field by using a single average parameter. The second model considers that the superconductor with trapped field behaves as a permanent magnet with a uniform magnetization. The total force on the superconductor in the mixed state is result of the superposition of these two contributions. In order to validate the model, the height of levitation and the frequency of horizontal oscillations were measured. Both variables were then calculated with the model fed with experimental information. The calculated values were in agreement with the measured ones.

In-situ post-assembly magnetization of large rare-earth permanent-magnet machines

Auxiliary permanent magnet generator (PMG) represents an essential part of the large steam generator excitation system. It provides energy for main exciter (rated power 1600 kVA) which supplies excitation for steam generator (rated power 300 MW). While auxiliary PMG is out of service, its permanent magnets are demagnetized. In order to put auxiliary PMG into operation, magnetization of permanent magnet poles is needed. This paper presents a method for in-situ post-assembly magnetization (PAM) of rare-earth PMG by applying DC current to all three phases of its stator windings. Magnetization process is performed in the power plant, and all equipment used in experiment is readily accessible to plant maintenance personnel (transformer, rectifier, circuit breaker, cables, etc.). The main advantage of this technique is that magnetization is performed without demounting the PMG off the main rotor shaft, and as a result, generator overhaul duration is significantly reduced, and magnetization costs are decreased. Throughout the procedure, magnetizing currents, voltage on PMG stator terminals and magnetic induction (flux density) are measured. Prior to magnetization, DC currents, current pulse duration and rotor position are calculated. Based on the calculated values, the temperature rise in stator windings has to be checked. The technique is validated through case study in the real power plant at the PMG, rated power 35 kVA, which was successfully magnetized. Subsequently, the simulation is performed, in order to determine the unknown parameters of the equipment used.

Crack Protective Layered Architecture of Lead-Free Piezoelectric Energy Harvester in Bistable Configuration.

Kinetic piezoelectric energy harvesters are used to power up ultra-low power devices without batteries as an alternative and eco-friendly source of energy. This paper deals with a novel design of a lead-free multilayer energy harvester based on BaTiO3 ceramics. This material is very brittle and might be cracked in small amplitudes of oscillations. However, the main aim of our development is the design of a crack protective layered architecture that protects an energy harvesting device in very high amplitudes of oscillations. This architecture is described and optimized for chosen geometry and the resulted one degree of freedom coupled electromechanical model is derived. This model could be used in bistable configuration and the model is extended about the nonlinear stiffness produced by auxiliary magnets. The complex bistable vibration energy harvester is simulated to predict operation in a wide range of frequency excitation. It should demonstrate typical operation of designed beam and a stress intensity factor was calculated for layers. The whole system, without presence of cracks, was simulated with an excitation acceleration of amplitude up to 1g. The maximal obtained power was around 2 mW at the frequency around 40 Hz with a maximal tip displacement 7.5 mm. The maximal operating amplitude of this novel design was calculated around 10 mm which is 10-times higher than without protective layers.

Reconsidering Six-Degree-of-Freedom Magnetic Actuation Across Scales

Magnetic actuation, also known as magnetic manipulation, refers to the use of controlled magnetic fields, generated by electromagnets or permanent magnets, to impart forces and torques on a remote magnetic object. The magnetic object is typically modeled as a magnetic dipole, affording five-degree-of-freedom (5-DOF) actuation, comprising 3-DOF force and 2-DOF torque. A method was proposed that uses a three-magnet object in which one magnet is used for traditional 5-DOF actuation and two auxiliary magnets achieve the sixth (torque) DOF via a force couple, and this object can still be modeled and controlled as if it exists at a single point in space, as in traditional 5-DOF actuation. We reconsider this method of 6-DOF magnetic actuation. We perform a numerical study of torque that can be generated on a multi-magnet object of varying shape (but assuming that the individual magnetization vectors are coplanar), size, and orientation, using a variety of well conditioned magnetic manipulation systems. We find that, in the limit as the magnetic object is reduced in size, there is an optimal arrangement of the magnetic object, which is invariant to the manipulation system. We find that the sixth DOF comes at a cost to the original 5-DOF, reducing them by 61% when using the optimal magnetic arrangement; this value is also invariant to the manipulation system. Finally, we find that the sixth DOF scales poorly relative to the other five as the size of the object is reduced, but can be relatively large as we consider objects that are large relative to the distances over which they are being actuated.

Tunable microstructures and morphology of zirconium films via an assist of magnetic field in HiPIMS for improved mechanical properties

Although HiPIMS technology has been widely studied, its optimization still remains in the adjustment of the experimental parameters acting on the ions, such as impulse mode, due to the inherent complexity of partially magnetized plasma of HiPIMS. Herein, recapture and re-energy of electrons by the assistance of the A-type magnetic field configuration, constructed by field coupling of the cathode magnetron and the auxiliary magnets mounted behind the substrate holder, was proposed. The dynamic behavior of the ions is attempted to be guided by exploiting electron recapture. The studies on the plasma diagnosis by optical emission spectroscopy and magnetic field simulation revealed that when the cathodic discharge remains constant, the characteristics of the deposition plasma in front of the substrate can be altered. Zirconium films were prepared under the a-HiPIMS mode (operated with the A-type magnetic configuration) and the conventional HiPIMS mode. Results showed that the Zr films prepared in the a-HiPIMS mode exhibited smoother surface, denser morphology, finer grains, higher homogenous thickness distribution, higher hardness, enhanced elastic recovery and higher value of the ratios H/E⁎ and H3/E⁎2. The mechanism of microstructure evolution of Zr film was discussed. It demonstrated that the action of the A-type magnetic configuration can densify the Zr film, without the need for high energy ion bombardment. The A-type magnetic field configuration provided an alternative strategy for compensating for the shortcoming of substrate bias in HiPIMS, invalidity to electrical insulating substrates, in terms of the dense film.

Analysis of an on-line superconducting cryofan motor for indirect cooling by LH2

This work relates to the study of an electrically powered cryofan for circulating closed-loop cooling helium gas for superconducting applications with the following features:- Absence of any seal that can leak the pumped fluid or provide a path for heat transfer and require maintenance and/or is prone to failures.- The use of high temperature superconducting (HTS) stacks on the fan-rotor that, below critical temperature, can be magnetized contributing to the driving torque.The absence of electrically connected equipment as well as the lack of any seal, makes this arrangement especially suitable for reliable cryogenic helium gas circulation. Because HTS stacks cannot provide magnetic flux above Tc, during the initial stages of operation, in the presented study we analyse the torque that will be provided by the passive iron components of the machine (reluctance torque, due to the saliency of the rotor) and by auxiliary permanent magnets or alternatively magnetizing coils.

Lowering the potential barrier of a bistable energy harvester with mechanically rectified motion of an auxiliary magnet oscillator

In this study, we propose a bistable energy harvester with an auxiliary magnet oscillator (BEH-O), whose motion is mechanically rectified to enhance its broadband energy harvesting performance. The design of the proposed BEH-O system is based on local modification of the double-well potential. The auxiliary oscillator with the mechanical rectifier is designed in such a manner that its rectified half-sine motion tends to reduce the saddle barrier of restoring potential, leading to a possibility of an easier escape from the potential well, while keeping other parts of the potential, thereby maintaining high-energy orbital motion. Consequently, the lower bound of the operating frequency band of the BEH-O is reduced, when compared to its conventional counterpart, i.e., conventional bistable energy harvester (CBEH), while its upper bound remains unchanged. Such a broader frequency band of the BEH-O can be directly compared with that of the CBEH, as there is little difference in the high-energy orbital motion between the two. This beneficial effect of the BEH-O system is theoretically and experimentally supported by bifurcation analyses and frequency response analyses.

자기 포화 영역을 갖는 단상 6/6 SRM의 자기 구조 해석 및 개선

단상 SRM은 자기동이 어려운 관계로 다양한 방법으로 자기동을 실현시키려는 연구가 진행되고 있다. 보조자석을 사용하거나 보조극 등을 만들어 자기동을 실현시키는 방법들이 연구되고 있다. 최근에 회전자 형상에 변화를 주어 기동할 수 있는 방법이 제시되었다. 이는 회전자 형상에 변화를 주어 부분적으로 자기포화 정도를 다르게 하여 자기동을 실현하는 방식이다. 본 논문에서는 자기 포화 영역을 갖는 단상 6/6 SRM의 자기구조를 해석하고 기존의 자기구조를 개선하는 것을 목적으로 한다. 이 자기 해석을 위해 유한요소법 해석 프로그램인 FLUX2D를 사용하였다. Single-phase SRM is cost competitive because it can reduce the number of switches for small, low-cost applications. However, since the single-phase SRM is difficult to start itself, methods for realizing self-starting by using auxiliary magnet or auxiliary pole have been studied. Recently, a method of self-starting by changing the shape of the rotor with a saturable area has been proposed. The purpose of this paper is to analyze the magnetic structure of single phase 6/6 SRM with a saturable rotor and to improve the magnetic structure of rotor with a saturable area. For this magnetic analysis, FLUX2D, a finite element method analysis program, was used.

Lateral Position Effect of Auxiliary Permanent Magnets on the Magnetic Force Properties of Cylindrical YBCO

The magnetic levitation force (MLF) and the guidance force (GF) should be improved for loading capacity and stability of Maglev systems, respectively. Although there are some ways to increase these properties, using of auxiliary onboard permanent magnets (PMs) can be considered as the most efficient one. The auxiliary PMs increase the MLF significantly but, at the same time, decrease the GF. We have searched a solution to overcome this problem in this study. Firstly, we have determined the optimum vertical positions of the auxiliary PMs and then we have investigated the vertical levitation force and lateral guidance force of hybrid Maglev system depending on lateral position of auxiliary PMs in different cooling heights (CHs). A cylindrical YBCO superconductor, fabricated by a top seeding method with the diameter of 45 mm and the height of 15 mm, was used as a high-temperature superconductor (HTS). The maximum increment rate in MLF and the minimum decrement rate in GF were observed as 277 and 54 %, respectively. The increment in MLF was obtained five times more than the decrement in GF, and this reality points out that the results of this study can be useful for improving the loading capacity and thus enhancing the practical applicability of Maglev systems.

Novel Structure of Three-Axis Active-Control-Type Magnetic Bearing for Reducing Rotor Iron Loss

Magnetic bearings (MBs) are useful for suspending the rotor shaft of a high-speed, high-output motor because they can do so without mechanical contact. In [2] , we have proposed a three-axis active-control-type MB (3-axis AMB) with a cylindrical rotor whose diameter is equal to that of the rotor of a radial MB (RMB) or a motor. The proposed 3-axis AMB integrates an RMB and a thrust MB in one unit. However, the assembly of the conventional 3-axis AMB is complex, and the rotor iron loss is large. Thus, in order to simplify the assembly of the 3-axis AMB and to reduce rotor iron loss, this paper discusses a novel structure for the 3-axis AMB in which small auxiliary permanent magnets (PMs) are inserted in the radial winding slots. The suspension force and the rotor iron loss of the proposed device are evaluated by 3-D finite-element analysis in comparison with a 3-axis AMB without small auxiliary PMs.

Electrical detection of magnetization reversal without auxiliary magnets

First-generation magnetic random access memories based on anisotropic magnetoresistance required magnetic fields for both writing and reading. Modern all-electrical read/write memories use instead non-relativistic spin-transport connecting the storing magnetic layer with a reference ferromagnet. Recent studies have focused on electrical manipulation of magnetic moments by relativistic spin-torques requiring no reference ferromagnet. Here we report the observation of a counterpart magnetoresistance effect in such a relativistic system which allows us to electrically detect the sign of the magnetization without an auxiliary magnetic field or ferromagnet. We observe the effect in a geometry in which the magnetization of a uniaxial (Ga,Mn)As epilayer is set either parallel or antiparallel to a current-induced non-equilibrium spin polarization of carriers. In our structure, this linear-in-current magnetoresistance reaches 0.2\% at current density of $10^6$ A cm$^{-2}$.

Levitation and guidance force efficiencies of bulk YBCO for different permanent magnetic guideways

The development of superconductor Maglev systems depends on various disciplinary studies due to the inherent composition of available technologies. Because the fabrication cost is very effective on the Maglev, the requirement of the efficiency improvement focuses the researchers on the design considerations. In this study, the guidance force, the magnetic levitation force (MLF) and magnetic stiffness of different permanent magnetic guideway (PMG) arrangements were investigated in different cooling heights (CH) to enhance the efficiency of Maglev system. The single domain cylindrical bulk YBCO superconductors fabricated by top seeding method with the diameter of 45mm and the height of 15mm were used as HTS. Magnetic field distributions of the PMGs were calculated by finite element method to determine optimum HTS–PMG arrangements. We have used auxiliary onboard permanent magnets with YBCOs to improve the MLF of three pole Halbach PMG arrangements. It is seen that the efficiency of Maglev systems can be improved by using suitable HTS–PMG arrangements. In this study cost efficiency of the integrated levitation and guidance force ((Fz)max(Fx)max/(SPMG∗Cost)) was also determined. It is inferred from this study that the cooling height and PMG–HTS arrangement are key parameters for guidance force, levitation force, magnetic stiffness and efficiency of Maglev systems. It is believed that this study will supply useful references for practical application of HTS Maglev systems.

Optimization Methods of Torque Density for Developing the Neodymium Free SPOKE-Type BLDC Motor

In this paper, we propose a method for optimizing the torque density to develop a SPOKE-type brushless direct current (BLDC) motor that does not require the use of a neodymium permanent magnet. Recently, the price of neodymium magnets has increased significantly owing to the rising prices of rare-earth minerals. Therefore, here we developed a method to maximize the torque density by using ferrite magnets instead of neodymium magnets. The proposed model was inserted into the auxiliary magnets in the center of a rotor after changing the existing interior permanent magnet-type BLDC motor to a SPOKE-type motor, and the effective air-gap flux density ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Bg</i> ) was maximized. We also developed an optimization tool to determine the volume of a magnet that would generate the maximum torque at a SPOKE-type motor structure including an auxiliary magnet. We manufactured a SPOKE-type motor designed using these optimization tools. Finally, we compared and analyzed finite element method simulation results and experimental results.