Air-gap Field Research Articles

Measurement of Air Field in Air Gap around Simulated Human Body

Measurement of Air Field in Air Gap around Simulated Human Body

Использование метода конформных преобразований для расчета магнитного поля в воздушном зазоре синхронного двигателя с модулированным магнитным потоком

Использование метода конформных преобразований для расчета магнитного поля в воздушном зазоре синхронного двигателя с модулированным магнитным потоком

Analysis of Torque Production in Variable Flux Reluctance Machines

In this paper, the torque production mechanism of variable flux reluctance machines (VFRMs) is investigated. Initially, based on an analytical instantaneous torque model developed from the Lorentz force law and airgap field harmonic analysis, the magnetic gearing effect is revealed in the torque production of VFRMs. Then, by using a 6-stator-pole/4-rotor pole (6s/4r) VFRM as an example, all its torque components, including synchronous torque, reluctance torque, and cogging torque, are analyzed separately under linear condition. Their average torque and torque ripple characteristics are comprehensively illustrated. Finally, the influence of saturation effect is also accounted for with the help of finite element and frozen permeability methods. The analysis results are verified experimentally.

Design Optimization and Comparative Study of Novel Dual-PM Excited Machines

This paper systematically studies a new kind of PM machines with both stator and rotor PM excitations, namely, dual-PM excited machines. The key is to rely on the PM-iron structure in the machine to provide both PM excitation and flux modulation. Besides the fundamental field component in the air-gap, some other predominant harmonics introduced by the flux modulating effect can also contribute to the electromagnetic torque production. Therefore, this kind of machines can be designed with high torque density. Four dual-PM excited machine concepts with the same rotor configuration but different stator structures are comparatively studied, which include double-stator PM machine, stator multitooth-PM machine, stator slot-PM machine, and stator tooth-PM machine (STPM). Based on the flux modulating effect, the general design principle of the dual-PM machines is proposed in this paper. Through analytically investigating the air-gap field harmonics, the physical insight of the dual-PM machines is brought forward. All the four machines are optimized using an improved Tabu search coupled with finite element method, and their electromagnetic performances are comprehensively studied and compared. A prototype of STPM is manufactured. Experimental tests are conducted and the results well verify the electromagnetic design.

Magnetic Field Analysis of Multi-Flux-Barrier Interior Permanent-Magnet Motors Through Conformal Mapping

An extended analytical method for predicting the open-circuit air-gap field distribution in interior permanent magnet (IPM) machines equipped with multilayer Permanent Magnets (PMs) is proposed in this paper. This presented method is based on the conformal mapping technique. The mapping is used to calculate the relative permeances, which consider the effect of stator slots and rotor saliency on the magnetic field distribution. The open-circuit air-gap field distribution in a multi-flux-barrier IPM can be predicted through the superposition principle. The analytical solution is implemented on: an eight-pole, 50 kW IPM motor used in 2004 Toyota Prius hybrid electric vehicle and four IPMs with two, three, four, and five flux barriers per pole. To verify this extended method, the results are compared with those obtained from the finite-element analysis.

Design and analysis of a novel rotor-segmented axial-field switched reluctance machine

As excitation strategy is influenced by the parity of phase number, and serious end effect is caused by full pitch windings adopted by the conventional rotor-segmented switched reluctance machine (RS-SRM), a novel rotor-segmented axial-field switched reluctance machine (RS-AFSRM), which adopts concentrated windings, is proposed in this paper, whose control strategy is independent of the parity of phase number. The stator of the proposed RS-AFSRM consists of inner and outer flux-conductive ring, excitation poles, and stator yoke, while the rotor consists of fan-shape cylinder-type segments. The structure and principle of the proposed machine is introduced through the magnetic circuit model of the machine. The fringing effect on air-gap field is considered. The simplified magnetic circuit considering the fringing effect is presented and the fringing effect coefficient is introduced. The design procedure considering the fringing effect through iterative modification is presented in this paper and is validated through 3D finite-element method (3D-FEM). Results show that both magnetic field distribution and operation are reasonable and satisfy the requirements.

MADES Tool for the Analysis and Design of Electrical Machines

In this paper, a numerical tool is presented in the field of the computation of electrical unknown of an electrical machine, very suitable to solve non-symmetrical condition too by means of a very friendly computer evaluation. This software tool, written in MATLAB language, bases itself on a formulation of air-gap field distribution by means of the linear combinations of the most elementary components of m.m.f (in case of windings) or of flux density (in case of permanent magnets) called Window functions. Differently from the standard methods, that allow appreciable results only after laborious calculations and complicate mathematical approaches that consent to formulate the problem in convenient domain, the proposed technique approaches and solves any problem directly in the time domain. The other most important feature of this procedure is its easy implementation into a proper tool that allows a friendly utilisation both by non expert people and by specialists in design phase activity or during the computation of performances in transient operations or in test conditions. In the paper, this tool is proposed in order to solve three cases of electrical machines simulations: the results demonstrate the interesting performance of the proposed tool.

Magnetic conduction of a magnetic reducer modulator

The through magnetic conductivities of a modulator have been considered in the magnetic fluxes produced by the stator winding and rotor magnets at observation points that are located on the outer surface of magnets and bore surface of a stator, respectively. The numerical calculations have shown that these conductivities, which substantially differ from each other, are formed by the fundamental harmonics. The contribution of higher harmonics in these conductivities is negligible. The analytical calculations of the through magnetic conductivity of a modulator (based on the classical approaches to electrical machines for calculations of magnetic fields in air gaps with single-sided serration) lead to a significant error. The effect of magnetic saturation of the modulator cores made of laminated electric steel sheets on the through magnetic conductivities has been estimated.

Improved method for field analysis of surface permanent magnet machines using Schwarz–Christoffel transformation

Air gap field solution for an outer rotor permanent magnet (PM) machine is derived based on numerical Schwarz–Christoffel (SC) transformation of a single slot geometry and analytical solution of a point wire field in the rectangular canonical domain. This approach takes into account geometrical distortions of PM edges and field evaluation points located along the air gap centre, which occur due to conformal mapping of the slotted air gap into a slotless domain and impair the accuracy of the existing analytical field solutions using SC transformation and complex relative air gap permeance. The increased accuracy of the improved solution is confirmed by comparing the air gap flux density waveforms produced by the PMs and armature winding, cogging torque, and total torque with the results of time-stepping transient finite element simulation.

Unbalanced magnetic force prediction in permanent magnet machines with rotor eccentricity by improved superposition method

An improved superposition method accounting for both permanent magnet (PM) and armature field is proposed to predict the unbalanced magnetic force (UMF) of PM machines having static/dynamic eccentricity. It virtually divides the original eccentric machine into a number of sections along the circumferential direction. Then, a series of concentric machine models are established with equivalent air-gap lengths corresponding to those air-gap sections. From the electromagnetic field of each concentric machine predicted by subdomain method, the air-gap field of the original eccentric machine can be synthesised. Finally, the UMF can be easily obtained by the integral of force density along the air-gap circumference. The effectiveness of the proposed method is validated on both rotating asymmetric and symmetrical PM machines by direct finite-element analysis and experiment, with particular emphasis of rotor eccentricity influence on the UMF of later one.

Analysis and Comparison Between No-Insulation and Metallic Insulation REBCO Magnet for the Engineering Design of a 1-MW DC Induction Heater

A 1-MW industrial-scale high-temperature superconductor (HTS) dc induction heater is being designed and manufactured in Shanghai Jiao Tong University, China. This paper is to present the design and engineering analysis of a HTS magnet with iron yoke for this heater. This magnet is to generate a 0.5-T dc magnetic field in the iron's air gap, where the billet is rotated. To enhance the thermal stability, the no-insulation (NI) coil and metallic insulation (MI) coil (co-wind with stainless steel strips) is introduced to the magnet. The influence of the NI&MI technique on the magnet's ramping process is analyzed. A significant ramping delay occurs on both the NI and MI magnet. Joules losses are generated by the current “bypassing” through turn-to-turn contacts, which may lead to significant temperature rise on the coils. Higher ramping rate often means faster ramping process and higher temperature rise induced by ramping loss. The MI magnet shows a much shorter ramping time and lower ramping loss than its NI counterpart, due to higher turn-to-turn resistivity. The MI coil is more suitable than the NI coil for this large-scale magnet.

A Novel Hybrid-Excited Dual-PM Machine With Bidirectional Flux Modulation

This paper presents a novel hybrid-excited dual permanent magnet (PM) brushless machine with bidirectional flux-modulating effect. Two sets of windings are housed in the stator slots, in which the armature windings are used to produce the rotating magnetic field, and dc field windings are used to generate the excitation field. The air-gap flux can be regulated effectively by controlling the direction and magnitude of the dc currents, and hence the constant power operating region can be expanded efficiently. Meanwhile, both the rotor and the stator have PM excitations, and dual field modulating effect is artfully incorporated into the machine design to ensure an effective magnetic coupling among the magnetic fields excited by the armature windings, dc field windings and the two sets of PMs. The torque capability of the proposed machine can be improved. Through analytically studying the air-gap field harmonics, the working principle of the proposed machine is discussed. The electromagnetic performances are investigated using finite element method and verified by experimental results.

An improved conformal mapping method for magnetic field analysis in surface mounted permanent magnet motors

PurposeThe purpose of this paper is to present an improved conformal mapping (ICM) method that simultaneously considers the influence of relative recoil permeability of PMs, the armature reaction, the stator slotting, and the magnetic saturation on determination of the PM operating point in its different parts.Design/methodology/approachThe ICM method is a time-effective method that considers the magnetic saturation by suitable increments in air-gap length under each tooth and also the width of slot openings. In this paper, the analytical and numerical conformal mappings such as the Schwarz-Christoffel (SC) mapping are used for magnetic field analysis due to the permanent magnets and the armature reaction in one slotted air gap. The field solution in the slotted air gap is obtained through the modulation of field solution in one slotless air-gap using the complex air-gap permeance.FindingsThe ICM method can consider the magnetic saturation in different electric loadings, and also the variation of PM operating points in its different parts.Practical implicationsThe ICM method is applied to one surface mounted permanent magnet (SMPM) motor and is verified by comparing with the corresponding results obtained through finite element method (FEM), and frozen permeability finite element method (FP-FEM).Originality/valueThis paper presents an ICM method with a new technique for saturation effect modeling, which can be used to separate and calculate the on-load components of air-gap field and torque.

Performance investigation of odd primary pole linear switched-flux PM machine with mechanical flux adjuster

Linear switched-flux permanent-magnet machines (LSFPMMs) exhibit high thrust force density and low cost, which is especially suitable for long stroke application. They have big normal force so that the assembly becomes difficult. The mechanical flux adjuster is a suitable method to lower the big no rmal force. This paper investigates the performances of two kind odd primary pole LSFPMMs with mechanical flux adjuster based on FEA, including E- and C-core structure. The analysis results show this method can effectively lower the magnetic field in air gap. The structure parameters of mechanical flux adjuster are also optimized, and the operating curves are calculated with or without mechanical flux adjuster. With this method, not only does the assembly become easier, but also the operating range extends at small load.

Eddy current losses in permanent magnets of surface mounted permanent magnet synchronous machines\u2014Analytical calculation and high order finite element analyses

Permanent magnet exited synchronous machines always show three significant portions of their losses: Iron losses within the magnetic circuit, power losses within the stator winding and finally eddy current losses within the permanent magnets. In particular, surface mounted magnets are directly exposed to asynchronous components of the air-gap field caused by either higher harmonic waves or higher time harmonics. Analytical calculation of the eddy current losses within the permanent magnets for both linear as well as cylindrical arrangements describe fundamental characteristics in dependence on only few significant parameters. These results serve as reference results for detailed numerical calculations using the finite element method, too. The finite element analyses with various formulations of the shape functions show the significant influence of the higher order elements on the accuracy of the eddy current losses. Additionally, the effects of a various pole coverage can be obtained from the results of the numerical calculations. Therefore, a clear summary of the significant parameters influencing the eddy current losses within the permanent magnets for both linear as well as cylindrical arrangements will be established.

A hybrid analytical model for open-circuit field calculation of multilayer interior permanent magnet machines

Due to the complicated rotor structure and nonlinear saturation of rotor bridges, it is difficult to build a fast and accurate analytical field calculation model for multilayer interior permanent magnet (IPM) machines. In this paper, a hybrid analytical model suitable for the open-circuit field calculation of multilayer IPM machines is proposed by coupling the magnetic equivalent circuit (MEC) method and the subdomain technique. In the proposed analytical model, the rotor magnetic field is calculated by the MEC method based on the Kirchhoff’s law, while the field in the stator slot, slot opening and air-gap is calculated by subdomain technique based on the Maxwell’s equation. To solve the whole field distribution of the multilayer IPM machines, the coupled boundary conditions on the rotor surface are deduced for the coupling of the rotor MEC and the analytical field distribution of the stator slot, slot opening and air-gap. The hybrid analytical model can be used to calculate the open-circuit air-gap field distribution, back electromotive force (EMF) and cogging torque of multilayer IPM machines. Compared with finite element analysis (FEA), it has the advantages of faster modeling, less computation source occupying and shorter time consuming, and meanwhile achieves the approximate accuracy. The analytical model is helpful and applicable for the open-circuit field calculation of multilayer IPM machines with any size and pole/slot number combination.

Calculation of the influence of slot geometry on the magnetic flux density of the air gap

The objective of this work is to investigate the influence of slotted air gap constructive parameters on magnetic flux density of rotating machines. For this purpose, different approaches were used to solve the air gap field diagram using finite element method and the magnetic field distribution uniformity was evaluated by Carter's factor calculation on two-dimensional and three-dimensional models. Sensitivity analysis of slot constructive parameters was performed and results show that slot geometry modifies the magnetic flux on air gap and shifts the air gap magnetic equipotential midline of double slotted machines. Finally, minimization of Carter’s factor on two-dimensional model presents an optimized slot geometry with a near uniform magnetic flux density distribution.

Unbalanced Magnetic Force Analysis in Eccentric Surface Permanent-Magnet Motors Using an Improved Conformal Mapping Method

This paper introduces an improved conformal mapping (ICM) method for the calculation and analysis of unbalanced magnetic force (UMF) in eccentric surface-mounted permanent-magnet (SMPM) motors considering the static, dynamic, and mixed rotor eccentricities. Having the on-load air gap field components obtained through ICM, and by using the Maxwell Stress Tensor method, the ICM method accurately predicts the on-load components of magnetic local traction and UMF due to PMs, the armature reaction, and the mutual interaction between both fields under the rotor eccentricity. The other purpose of this paper is to illustrate the difference between the influences of static, dynamic, and mixed rotor eccentricities on the UMF using the ICM method. The influence of initial eccentricity angle and the magnitude of eccentricity on the UMF are also investigated under the static, dynamic, and mixed rotor eccentricities. The predicted results obtained through ICM are verified by comparing with the corresponding results obtained through finite element method and the frozen permeability method. The ICM method is also validated by the experiment.

A Coaxial Magnetic Gear With Consequent-Pole Rotors

In this paper, a novel coaxial magnetic gear (MG) is proposed, in which both permanent magnet and consequent poles are employed on the inner and outer rotors. The MG is expected with improved torque transmission capability by increasing the effective magnetic flux and offering additional reluctance torque. Air-gap field distribution and torque–angle characteristic of this MG are analyzed and compared with the conventional MG, which adopts dual surface-mounted permanent magnet rotors. To maximize the torque density, several key design parameters are investigated using finite-element method. Analysis results indicate that the proposed MG with ferrite magnets can largely improve the pull-out torque. In addition, end effect and power losses with different rotor structures are analyzed. Performance of two optimized MGs is then validated with test. Also, the MG cost effectiveness with different magnet materials is presented.

Influence of Skewed Squirrel Cage Rotor with Intermediate Ring on Magnetic Field of Air Gap in Induction Machine

The article compares the flux density spectrum in air gap of squirrel-cage induction machine with different rotor geometries. The skewed squirrel cage with an intermediate ring and ordinary skewed squirrel cage are compared to the straight bars rotor using the finite element method. The novelty lies in a deep investigation in issues relating to rotor cage with an intermediate ring.DOI: http://dx.doi.org/10.5755/j01.eie.23.1.17580