Three-dimensional Magnetic Field Analysis Research Articles

3-D nonlinear magnetic field analysis with a novel adaptive finite element method

In this paper, an adaptive degrees-of-freedom finite element method is extended to three-dimensional (3-D) nonlinear magnetic field analysis. The error distribution of the discrete solution changes along with the iterative process, and mesh coarsening or other operations with the same effect is needed to keep the scale of the problem small. In this proposed adaptive method, dispensable degrees of freedom (DoFs) are eliminated from the unknown list by constraining them with supplementary interpolation functions, which are formulated with master DoFs. Compared with mesh coarsening, the administration of DoFs and geometric data are no longer required, while the topology of the mesh is maintained. To extend to 3-D problems, a novel constraint, which produces accurate coefficients for an alterable number of master DoFs, is presented. The constraint is integrated into the element algebraic equation, followed by a conventional assembly. Other techniques for the adaptive algorithm are also included in this method. Several numerical examples are tested to showcase the effectiveness of this method in 3-D problems.

Torque Modelling and Validation for a Spherical Motor with Stepped Permanent Magnets

A spherical motor is an electromagnetic device with multi-degree-of-freedom motion. Three-dimensional (3-D) magnetic field analysis and torque analysis are needed for the design, optimization and control of the motor. Presently, these analyses are carried out by the finite-element method (FEM) with a large amount of calculation and time consumption. An analytical method (AM) can reduced the computational burden of the FEM without sacrifice of the accuracy. A stepped permanent magnet (PM) can obtain a large range of the magnetic field while effectively saving PM materials. However, its special structure causes difficulties in analytical modelling. This paper presents an AM for the 3-D magnetic field and torque of a permanent magnet spherical motor with stepped PMs. The analytical model of the 3-D magnetic field of the stepped PM is derived based on the loop current method, and the electromagnetic force of the stator coil is calculated based on the Lorentz force method. Thus the 3-D magnetic field and torque can be calculated efficiently with reasonable accuracy. The analytical model is verified by the FEM and experimental tests. The test results confirm the high accuracy of the developed model.

Research on High-Temperature Superconducting Machine With a Rotating-Pole Shoe

As a kind of high-power density machine, superconducting machines have important application prospects in the fields of aerospace, ship propulsion, and wind power generation. The existing semisuperconducting-type machines have great difficulties in design and application because of the need to use complicated structures such as brushes and rotating dewars. A rotating-pole-shoe-type high-temperature superconducting machine is proposed in this article. The machine separates the pole shoe from the magnetic pole and generates a magnetic field synchronized with the armature side by rotating the pole shoe. The excitation system of the machine consists of a rotating rotor and a stationary inner stator. The superconducting coil is placed on the inner stator, avoiding the use of complex structures such as brushes and rotary seals. Aiming at the special structure of the rotating-pole-shoe-type superconducting machine, a three-dimensional magnetic field analysis of the superconducting machine is performed to improve the machine structure. The output performance of the machine is calculated and compared with that of the semisuperconducting-type machine.

Comparative Studies of Three-Dimensional Analysis and Measurement for Establishing Pulse Electromagnet Design

A new horizontal shift bump electromagnet for the J-PARC 3-GeV RCS injection bump system was designed and fabricated. The bump magnet is a pulse magnet that repeatedly excites a trapezoidal waveform of about 1.5 ms duration at 25 Hz. And it is possible to change of the rising and falling time of the pulse waveform with the maximum current of 16 kA and the voltage of 12 kV between 150 and 500 microseconds according to the optimum beam generation condition. In order to design such magnets of such specifications, three-dimensional dynamic magnetic field analysis capable of evaluating eddy currents is required. Using one electromagnet model, comparison of static magnetic field analysis with dynamic magnetic field analysis, and two-dimensional calculations with three-dimensional ones were studied. In addition, we also confirmed the difference between the analysis and measurements as well as the difference of the magnetic field measurement method between the search coil and the Hall probe. We could then have established a pulse electromagnet design method.

A comparative study on 2D and 3D magnetic field analysis of permanent magnet synchronous motor using FEM simulations

ABSTRACTPermanent magnet synchronous motors (PMSMs) have recently gained increasing industrial and research interest. The PMSM design and especially its performance evaluation through two-dimensional (2D) and three-dimensional (3D) magnetic field analysis using finite element method (FEM) is not trivial, as it is a quite demanding and time consuming procedure. Furthermore, there has always been doubt on the accuracy of 2D analysis results and on which type of analysis is the most preferable one for the specific motor. This work aims to emphasize the difficulties and the advantages that arise from the 3D analysis. The aforementioned simulations were performed for the case of a four-pole PMSM. Several magnetic and electromechanical quantities have been determined. Additionally, various materials were utilized for the construction of stator and rotor cores and their effect on the motor’s behavior was investigated. Finally, the derived results are compared and useful conclusions regarding the solution accuracy are given.

Performance Enhancement of a Magnetic System in a Ultra Compact 5-DOF-Controlled Self-Bearing Motor for a Rotary Pediatric Ventricular-Assist Device to Diminish Energy Input

Research interests of compact magnetically levitated motors have been strongly increased in development of durable and biocompatible mechanical circulatory support (MCS) devices for pediatric heart disease patients. In this study, an ultra-compact axial gap type self-bearing motor with 5-degrees of freedom (DOF) active control for use in pediatric MCS devices has been developed. The motor consists of two identical motor stators and a centrifugal levitated rotor. This paper investigated a design improvement of the magnetic circuit for the self-bearing motor undergoing development in order to diminish energy input by enhancing magnetic suspension and rotation performances. Geometries of the motor were refined based on numerical calculation and three-dimensional (3D) magnetic field analysis. The modified motor can achieve higher suspension force and torque characteristics than that of a previously developed prototype motor. Oscillation of the levitated rotor was significantly suppressed by 5-DOF control over rotating speeds up to 7000 rpm with lower energy input, indicating efficacy of the design refinement of the motor.

Flux and Loss Distribution in Iron Cores With Hybrid T-Joint

Local high iron loss may occur due to the deviation of magnetic flux from the rolling direction of electrical steel in the T-joint area of the transformer core. In this paper, to reduce the iron core loss in the T-joint region, a hybrid iron core model using nonoriented and grain-oriented magnetic materials is proposed. Three-dimensional magnetic field analysis considering the nonlinearity and laminated structure of the original and proposed iron core models is carried out by using the finite element analysis. The flux and iron loss distributions of the original and the hybrid cores are compared. The results show that approximately 2% iron loss reduction can be achieved by using the proposed hybrid structure.

The 4 axes control magnetic bearing for a ventricular assist device

We propose simple homopolar magnetic bearings for a ventricular assist device. The bearings control radial position and inclination around radial axes of the outer rotor. In this paper, magnetic suspension characteristics of two types of the magnetic bearings which differ from each other in magnet arrangement or magnetization direction are compared using three-dimensional magnetic field analysis. The one is whose magnets are set on the outer rotor (Type A). The other is whose magnet is set on the stator (Type B). The radial control force and tilting control torque of Type A is 17% and 9.5% higher than that of Type B. The Type A magnetic bearing is made based on the analysis results and measured its magnetic flux density and axial restoring force. The bearing indicates the axial stiffness of about 2 N/mm.

Study on Consequent-Pole Type 5-DOF Self-Bearing Motor

Magnetic bearings can support rotating shafts without any contact and have been used in special conditions such as in cryogenic, vacuum, and clean environments. In this paper, consequent-pole type 5-DOF self-bearing motor is proposed. By using this motor structure, the rotor radial and tilt position control is easily possible because the forces and torques don’t depend on the rotational angle of the rotor. The three-dimensional magnetic field analysis using the finite element method is carried out. Based on these analysis results, the experimental setup was made and the motor performances are confirmed. Though the further improvement of the motor efficiency is necessary, the consequent-pole type 5-DOF self-bearing motor satisfies the target motor torque and shows the feasibility as an artificial heart pump.

504 コンシクエントポール型5軸制御セルフベアリングモータの基本特性解析(OS5-(1),OS5 オーガナイズドセッション≪ライフサポートにおける工学技術≫)

Magnetic bearings can support rotating shafts without any contact and have been used in harsh conditions such as in cryogenic and clean environments. In this paper, consequent-pole type self-bearing motor is proposed. It is possible to control the rotor radial positions without the rotational magnetic field of the rotor. Moreover, use of the thick permanent magnets in the consequent pole rotor slots can be avoidable for its demagnetization. The three-dimensional magnetic field analysis using the finite element method carried out. In the results of proposed model2, it is confirmed that the motor torques, radial control forces, and axial control forces accomplish the target value of an artificial heart pump.

High-Frequency Interbar Current Losses in Cage Induction Motors Under No-Load Condition

This paper describes a study of the interbar current losses in induction motors under no-load condition by comparing the measured and calculated results. The interbar resistances and losses are measured on the machine of the rotor with end rings removed. The increase in interbar resistances caused by the slot insulation treatment is ascertained to decrease the losses effectively. The losses are calculated with three-dimensional (3-D) magnetic field analysis on finite-element model reflecting the measured interbar resistance. The calculated losses agree well with the dependence of the measured losses on the interbar resistances. Moreover, it is confirmed that the core heating treatment caused the loss reduction and the increase of the high-frequency impedances form measurement results.

Three-Dimensional Magnetic Field Analysis for Local Induction Heating of Steel Sheet by Using Magnetic Flux Concentration Plate

In general, the magnetic properties of electrical steel sheets are strongly influenced by mechanical stress. We have reported the measurement results of vector magnetic properties of a non-oriented electrical steel sheet under stress conditions. From these results, it is possible to control the vector magnetic property by applying local mechanical stress. Therefore, we next focus on an induction heating technique that applies mechanical stress in a non-oriented electrical steel sheet. It is very important to control the eddy current distribution inside the non-oriented electrical steel sheet. This paper presents a magnetic flux concentration plate structure to control the eddy current in steel sheets by using an induction heating technique. The magnetic flux concentration plate structure is investigated in a three-dimensional magnetic field analysis by the finite element method.

Comparison of 3D Polycrtystal Magnetic Field Analysis and Distributed Magnetic Measurement

The three-dimensional polycrystal magnetic field analysis method is compared with the distributed magnetic measurement. In the three-dimensional polycrystal magnetic field analysis method, the local coordinates are fixed in each crystal grain and the global coordinates are defined in the polycrystal steel. It is assumed that each crystal grain has the same magnetic characteristics as those of a single crystal grain. When it is applied to the real grain oriented (GO) steel with two crystal grains and with 56 crystal grains in 80-mm × 80-mm, and with 0.35 mm thick, their results of the magnetic flux density distribution and the inclination angle are mainly explained by α angle distribution of the polyctristal steel and seem to be in good agreement.

Open-Type Magnetically Shielded Room Using Only Canceling Coil Without a Ferromagnetic Wall for Magnetic Resonance Imaging

In order to improve amenities for patients in hospitals, a new open type of magnetically shielded room (MSR) for magnetic resonance imaging (MRI), which uses only canceling coils without a ferromagnetic wall, has been developed. The device was designed by three-dimensional magnetic field analysis and experimentally investigated using an actual MRI of 1.5 T. First, a coil and ferromagnetic material were modeled on an actual MRI, so that the distribution of the leakage magnetic flux vectors was in agreement with that measured. Second, the optimal shaped canceling coil, a saddle-shaped coil which can reduce the leakage flux from the edge plane to the side plane of the room, was designed using the modeled MRI, and realized. The effectiveness of this coil for shielding and its influence on MRI imaging were confirmed experimentally using an actual MRI. In addition, an optimal U-shaped enclosure that can sufficiently shield the leakage flux generated by the coil itself was designed; its effectiveness was confirmed experimentally by using an actual canceling coil.

Open Type of Magnetically Shielded Room Combined With Cancelling Coil for Magnetic Resonance Imaging

In order to improve amenity for patients in hospitals, we have designed an open type of magnetically shielded room (MSR) for magnetic resonance imaging combined with cancelling coils, which enable transparent opening. First, an optimal arrangement of cancelling coils is investigated using three-dimensional magnetic field analysis. Secondly, the validity of the analysis method is verified and the realization of an open type of MSR designed both for keeping low leakage flux density and for maximizing the opening is confirmed by experiments using a small MSR model

Optimal Structure of Magnetic and Conductive Layers of a Magnetically Shielded Room

Although the method of optimal design of magnetically shielded rooms (MSRs) for dc magnetic noise seems to be well established, that for ac magnetic noise at a frequency range from 0.01 to 1 Hz is also required for measurements of extremely weak magnetic fields such as biomagnetic measurements. However, such a method cannot easily be established due to eddy current effects. In order to establish an optimal design method of an MSR for low frequency ac magnetic noise, we have investigated an optimal structure of the magnetic and conductive layers using three-dimensional (3-D) linear magnetic field analysis taking into account eddy currents. We show why a structure which sandwiches the conductive layer between double magnetic layers gives high shielding effect. Moreover, we found that the spacing between the layers does not affect the shielding effect for ac magnetic noise. This is useful knowledge from the standpoint of MSR production

3-D magnetic field analysis of permanent-magnet type of MRI taking account of minor loop

Authors have reported the behavior of residual magnetization in the permanent-magnet type of magnetic resonance imaging (MRI), but the analysis was limited to axi-symmetric finite-element method (FEM). In order to obtain a more accurate behavior, three-dimensional (3-D) magnetic field analysis taking account of the minor loop is indispensable. In this paper, the behavior of the minor loop and eddy current in a 3-D model, which was not clear until now, is examined. It is shown that the minor loop is considerably changed due to the eddy current

Analysis of Magnetic Properties on the Outer Rotor Type Hybrid Stepping Motors Using 3D Finite Element Method

The three-dimensional magnetic field analysis has clarified the effect of several structural and manufacturing factors on the properties of the outer rotor type stepping motors. (1) The number of rotor teeth, 128, can make a unit step angle under 0.5 degree and a cogging torque under 1mNm for the outer rotor type stepping motor with the outer diameter under 60mm and with the output torque above 0.4Nm. (2) The permanent magnet flux has an optimal value dependent on the thickness of the laminated core to maximize the motor torque. (3) The lamination stacking error of the small teeth of the rotor and stator has a large effect on the cogging torque of the stepping motor.

Calculation of sudden three-phase short-circuit current of turbine generators by 3D magnetic field analysis

Sudden three-phase short-circuit current of a turbine generator was calculated by a three-dimensional magnetic field analysis. That analysis takes into account the rotation, magnetic saturation, and eddy current at a rotor part. To compare test results and calculated results, a method was proposed for short-circuit phase estimation at sudden three-phase short-circuit test by line voltage waveform of the test results. The calculated results of short-circuit current waveform are in good agreement with the test results. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 153(1): 54–62, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20110

703 人工心臓用アキシャル型磁気浮上遠心ポンプの小型化(関東支部 茨城講演会)

The life time of a centrifugal pump for artificial heart is mainly determined by the durability of mechanical parts such as bearings and seals. The purpose of this study is to develop a durable centrifugal pump for artificial heart with magnetic suspension technique. Developed magnetically suspended motor consists of a top stator, a rotor, a bottom stator, and a permanent magnet bearing. The rotor is levitated between the top and the bottom stators. The tilt and axial position of the rotor is controlled with the top stator. The rotation of the rotor is controlled with the bottom stator. The top stator and the rotor were redesigned to miniaturize the motor by using the three-dimensional magnetic field analysis. As a result, the diameter of rotor was reduced from 60 to 54 [mm], and the motor height was reduced from 56 to 51 [mm] without deterioration of the suspension performance. The volume of the motor was reduced by 26.2 [%], and the weight of the motor was reduced by 21 [%].