Gap Field Distribution Research Articles

Synthesis of Application-Optimized Air Gap Field Distributions in Synchronous Machines

This paper deals with the method of shaping the magnetic field distribution in the air gap of a synchronous machine. The main goal is to obtain a specific distribution of the magnetic field in the machine’s air gap to enable easier powering, to increase the torque and power density, or to limit the content of higher harmonics in the induced voltage and torque. This method can be applied for both the electrically excited machines and permanent magnets excited machines. The problem has been reduced to solving a modified system of algebraic equations obtained by the finite element method. The presented examples show the effectiveness of the proposed method both in shaping the contours of the air gap and the magnetization of permanent magnets placed on the rotor. The method can particularly be used in the design of the high-speed synchronous machines.

Analytical Modeling of Air Gap Magnetic Fields and Bearing Force of a Novel Hybrid Magnetic Thrust Bearing

In this article, an analytical method is presented for modeling the complex air gap field distribution and the magnetic force of a novel permanent magnet (PM) bias hybrid magnetic thrust bearing (HMTB). This bearing has a very compact structure and is proposed to replace the traditional magnetic thrust bearings (MTBs) for high-speed rotor systems. The proposed method introduces the notion of the complicated air gap field, calculated from the Schwarz–Christoffel transformation of the air gap geometry, to take into account the effect of slot fringing and leakage. As a result, accurate solutions of the flux distribution and the bearing force can be obtained, which shows good agreement with the results of the finite-element method (FEM). The prototype of the HMTB is designed, analyzed, and tested. The results of the analytical model are compared with experimental data.

Modeling and Optimization of Air-Core Monopole Linear Motor Based on Multiphysical Fields

The key technology of the air-core monopole linear motor (AMLM), a core component of precision motion systems, is the distribution of the electromagnetic structure and cooling structure. Thus, AMLM can achieve small thrust fluctuation, high thrust density, and low surface temperature rise. Consequently, the multiobjective optimal design of AMLM under the multiphysical fields has become the key technology of AMLM. Consideration of the strict requirements of AMLM model calculational accuracy will cause an excessively long computation time for the finite-element analysis (FEA) software three-dimensional (3-D) model, and it is not convenient for an optimal computation of the multiphysical fields model. Therefore, a surface magnetic charge model and an image method are proposed in the paper to establish an air gap magnetic field model of AMLM. The saturation characteristic of magnetic materials can be reflected through saturation coefficient of the model. In addition, the air gap field distribution status of AMLM can be better predicted. An AMLM thermal field model is established by adopting the thermal network method. In the model, the heat transfer coefficient of cooling water is calculated based on the current curve obtained from the FEA software. Parametric modeling was performed on the AMLM electromagnetic and cooling structure through definition of 7-D proportionality coefficients. Based on the aforementioned electromagnetic field and the thermal field model, genetic algorithm (GA) was adopted for AMLM optimization design by setting cooling capacity and size as constrain conditions as well as by setting thrust density, thrust fluctuation, mover's mass, and motor constants as optimization objects. The AMLM electromagnetic field, the accuracy of thermal field model, and the validity of the AMLM optimization method were verified through simulation and tests. The method proposed has significantly improved the efficiency of optimization calculation.

Discrete Dipole Approximation Simulation of Nearly Touching Plasmonic Au Dimers and Influence of Particle Shape Assembly on Optical Response.

The method Discrete Dipole Approximation (DDA) is used to calculate the extinction spectra and field distribution of three types of dimers. In the paper we provide a systematic analysis of the optical response of different nanoscopic dimer structures with relatively small gap distances. A description is given about how the energy and excitation cross sections of dimer plasmons depend on nanoparticle separation. Resonance peaks of dimers show red-shift compared with single nanoparticle. Dimers formed by different single particle display distinct optical response. Interaction junctions in dimers can serve as hot spots for field enhancement. Field distribution in gaps made of two flat planes is nearly continuous. Changing gaps between two particles in dimers can tune the resonance wavelength effectively as well as different particle ensembles. Existence of sharp corners can attract and change field distribution. It is not effective volume but the effective cross-section that dominates the extinction efficiency.

AC-Space-Charge Effects on Gap Coupling Coefficient of a Klystron Cavity

A novel model was developed to evaluate gap coupling coefficient considering ac-space-charge effects due to the bunching in the interaction gap. The formulation was derived based on Webster's debunching theory and the electron-stream oscillation equation with arbitrary gap field distribution on the gridless gap. The coupling coefficient with ac-space-charge effects was investigated through both analysis and particle-in-cell simulation. The calculation results are in reasonable agreement with the simulation results. With the ac-space-charge effects, the coupling coefficient is lower than that calculated by ballistic theory. It is found that the plasma gap transit angle is a key factor in the effects of ac space charge on the coupling coefficient. Large beam current or gap length and, hence, mean large plasma transit angle indicate strong ac-space-charge effects on the coupling coefficient.

A high torque density permanent magnet motor for oil pumping unit

A low speed, high torque density compound permanent magnet (PM) motor is developed for oil pumping unit to reduce energy consumption. It consists of dual axial-field PM motors and an outer rotor PM motor. In order to account for the influence of skew, a multislice two-dimensional finite element method is employed to analyze the air gap field distribution, back-emf, cogging torque, and electromagnetic torque. Predicted results are validated experimentally.

General Model of a Five-Phase Induction Machine Allowing for Harmonics in the Air Gap Field

This paper presents a general mathematical model of a five-phase induction machine including the effects of higher space and time harmonics in the air gap field. These harmonic waves play a decisive role in the behavior of machines with more than three phases. Mathematical expressions for the calculation of the self and mutual inductances are presented, and results are compared with values obtained by finite element analysis and measurements. Based on the air gap field distribution produced by the stator and rotor, all the field harmonics are included in a direct and simple way in the self-inductances. The mutual inductances are obtained from a Fourier series description of the air gap field, resulting in a different inductance for each harmonic field. The machine equations are then simplified using coordinate transformations, which result in equivalent d-q models and equivalent circuits for given harmonic groups. In their final form, the equations are appropriated for the simulation of the machine behavior and developing new control strategies including higher space and time harmonics. Finally, practical results of a prototype machine are compared with simulations demonstrating the accuracy of the model

Temporal development of the electric field within a stressed oil gap

Extensive high-resolution electrooptic Kerr field-mapping measurements have been taken with transformer oil near 20 degrees C using parallel plane electrodes and field strengths near 0.2 MV/m. Static field measurements have been extended to the transient period following the application of a step voltage. Significant space-charge effects resulting in electrode fields being enhanced by a factor of up to 2.5 over the average field are observed. This factor is dependent on the gap length. A simple model based on charge-carrier generation, mainly by dissociation of ion pairs in the liquid bulk, is used in the discussion of the observation. Evidence suggests that polarity-dependent asymmetries in the gap field distribution arise primarily from differences in the mobilities of the two polarities off charge carrier rather than from injection of carriers at the electrodes. >

CSEM-Steel Hybrid Wiggler/Undulator Magnetic Field Studies

Current design of permanent magnet wiggler/ undulators use either pure charge sheet equivalent material (CSEM) or the CSEM-Steel hybrid configuration. Hybrid configurations offer higher field strength at small gaps, field distributions dominated by the pole surfaces and pole tuning. Nominal performance of the hybrid is generally predicted using a 2-D magnetic design code neglecting transverse geometry. Magnetic measurements are presented showing transverse configuration influence on performance, from a combination of models using CSEMs, REC (Hc = 9.2 kOe) and NdFe (Hc = 10.7 kOe), different pole widths and end configurations. Results show peak field improvement using NdFe in place of REC in identical models, gap peak field decrease with pole width decrease (all results less than computed 2-D fields), transverse gap field distributions, and importance of CSEM material overhanging the poles in the transverse direction for highest gap fields.

Air Gap Field for Pm Electric Machines

ABSTRACT The air gap field distribution in permanent magnet electric machines differs from that in wound field ones. In order to analyse the influence of magnet and air gap geometry on the shape of the air gap field in PM machines, an analytical method, which is much more economic and efficient than the numerical ones, is proposed in this paper. By using the method of Fourier expansion, a great set of curves for the air gap field characteristic coefficients in PM machines can be obtained. These design curves are necessary in simplified performance calculations for both AC and DC PM machines.

High-resolution field measurements near ferrite and thin-film recording heads

The accuracy of high-resolution magnetic field measurements near ferrite heads was increased by using an improved interference method for determining the measurement height, by measuring a known field distribution to calibrate the system, and by using a more accurate theory to compare with the data. Measurements on three MnZn heads gave dead-layer thicknesses of 0,0, 0.01 and 0.07 μm, which are practically negligible. Measurements near thin-film heads gave a gap-field distribution in good agreement with the theory of Potter et al, and showed no degradation of resolution after head saturation. Poor resolution was observed at the track edge for thin-film heads when the top and bottom poles were of unequal width.