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Surface-mounted permanent magnet (SPM) machines with skewed slots as vehicle drives are widely used. Due to skewed slots, electromagnetic characteristics are modulated by the skew effect. To analyze the skew effect, Maxwell’s equations-based 3-D analytical model is proposed. Based on differences in 3-D air-gap flux density distribution, the mechanism by which the skew effect modulates cogging torque, flux linkage, and back electromotive force (EMF) is investigated. The effectiveness of the theory about the skew effect is verified by both the finite element method (FEM) and the experimental result. [ABSTRACT FROM AUTHOR]

Due to the high power density, short axial size, and wide permanent magnet (PM) flux linkage regulation range, an axial-flux PM memory machine (AFPMMM) with hybrid Halbach array is investigated in this article. To solve the problem of magnetic density variation of Halbach array composed of different types of PMs in asymmetric bilateral air-gap structure, the analytical method for calculating the air-gap flux density of AFPMMM is presented through mathematical analysis, which uses cylindrical coordinate system instead of Cartesian coordinate system and is solved by equivalent method, separated variable method, and boundary conditions. The magnetic field generated by the Halbach array is divided into three directions: radial, circumferential, and axial. The analytical model is compared with the finite element method (FEM) simulation results to verify its effectiveness. In addition, an approximate piecewise linear hysteresis model with parallelogram return line is established based on the analytical expression of magnetic field. By applying different pulse currents to change the residual flux density of PM, the flux regulation characteristics of the motor are studied, and it is found that the air-gap flux density of the motor can be smoothly adjusted by continuously changing the pulse current, which plays a positive role in solving the problem of online magnetic regulation of the motor. [ABSTRACT FROM AUTHOR]

This article presents an accurate analytical model (AM) for synchronous reluctance machine (SynRM) that incorporates the effect of stator slots on the air gap flux density and torque waveforms. From the formulation of magnetic potential in the air gap for both the stator and rotor, the flux density is obtained, considering the first harmonic of the flux density and the electric loading, the average torque is calculated using the Lorentz’s force. The ripple torque is obtained from the energy stored in magnetic circuit. The method is developed for a rotor with one flux barrier per pole and then extended to a larger number of barriers. To validate the results obtained by the AM proposed finite element analysis have been carried out. Several comparisons have been derived considering different rotor positions as well as different harmonic orders, and the pros and cons of the method are highlighted. The model performs fast and can predict results with high accuracy, and can be adopted to speed up the preliminary design and optimizations of this type of motors, with respect to finite element. In addition, from the analytical expressions it is possible to obtain all the correlations between electrical, magnetic, and geometrical characteristics of the machine, with the advantage of enabling a faster machine design. [ABSTRACT FROM AUTHOR]

A new partitioned stator field modulation machine (PSFMM) with H-shape permanent magnet (HPM) excitation (HPM-PSFMM) is proposed, which is evolved from the conventional flux-switching machine (FSM) and flux-reversal machine (FRM). The proposed HPM-PSFMM combines the merits of high reliability and good heat dissipation characteristic. In addition, it exhibits high torque production with low torque ripple. Based on the theory of electrical machine operation, the FSM and FRM can be transformed into PSFMM with interior permanent magnet (IPM) and surface-mounted PM (SPM) excitation by changing the position of PM excitation, respectively. It benefits to improve space utilization and increase slot area for a large number of armature windings. For reducing the flux leakage and enhancing the flux density in air gaps, the IPM and SPM excitation are combined into HPM excitation. The iron-pole rotor between the inner and outer stators acts the role of modulator to modulate the magnetic field excited by HPM excitation to couple with the armature reaction for converting electromechanical energy. The evolution process, operating principle, and key design parameters of the proposed HPM-PSFMM are presented. Finally, using the finite element analysis (FEA), it can be proven that the proposed HPM-PSFMM has the merits of high torque production, low flux leakage, low total harmonic distortion (THD), and low torque ripple when compared to other stator-PM machines, which is a desirable choice for high stability applications. [ABSTRACT FROM AUTHOR]

The magnetic field distribution in the air gap is of great importance in the design of rotary machines. In this article, an efficient analytical method is presented, which is capable of plotting the air-gap flux density waveform of induction machines (IMs) less time-consuming than the finite element method (FEM) does. The proposed method, based on the product of the current linkage waveform and the permeance waveform, utilizes the calculations of the steady-state equivalent circuit to ensure the accuracy and an equivalent air-gap reluctance model to take into account both the slot opening effect and the rotor movement. The method is tested on a general IM with different load cases and different design parameters, and the results are compared to the FEM calculations. It can be concluded that the proposed analytical method is an efficient option in the motor design to investigate the influence of the parameters on the flux density distribution. [ABSTRACT FROM AUTHOR]

This article proposes a novel axial field switched flux memory machine (AF-SFMM) which is analyzed by a combined analytical method. Compared with conventional axial field (AF) permanent magnet (PM) machines having magnets in the rotor side, the AF-SFMM benefits from good heat dissipation, high rotor robustness, and improved power density. Meanwhile, because of the utilization of low coercive force PM materials, the proposed machine can flexibly regulate air-gap flux. This analytical method is characterized by the combination of a quasi-3-D (quasi-3D) finite element method, a magnetomotive force–permeance-based method, and a virtual linear hysteresis model of low coercive force PM. In addition, compared with conventional time-consuming 3-D finite element analysis (FEA), the proposed method can improve the computational efficiency significantly with satisfactory accuracy. This makes the proposed combined analytical method suitable for preliminary sizing determination of AF-SFMM. Meanwhile, the effectiveness of the proposed analytical method is validated by FEA results. [ABSTRACT FROM AUTHOR]

This study investigated an efficient procedure for developing an accurate behavioral model of a cage induction motor (IM) based on the multiport Cauer ladder network (CLN). The CLN method was applied to a cage IM with semi-closed rotor slots as a model order reduction (MOR) technique, and a method for selecting the appropriate space harmonics (SHs) included in the air-gap flux density, which is necessary for a multiport CLN method for induction machines, was discussed. Then, the developed approach was applied to the transient analysis of the cage IM coupled with a control system, and its effectiveness in terms of computational accuracy and cost was investigated. [ABSTRACT FROM AUTHOR]

A new type of hybrid magnet dual stator field modulation machine with different split ratios of stators (DSR-HMDSFMM) is proposed in this article, which has the merit of high torque density. The split teeth of stator sever as modulators to modulate air gap flux density based on the magnetic gearing effect for high torque production. The total split tooth number of inner stator is equal to that of outer stator because the pole pair numbers of armature reaction and permanent magnet (PM) excitation on rotor are equal. Furtherly, the inner and outer stators with different split ratios and same split tooth number are employed to increase torque production because armature windings with high winding factor and high turn number can be used. In addition, the employment of hybrid magnet excitation can increase space utilization and enhance the air gap flux density with low harmonic distortion. Therefore, the proposed DSR-HMDSFMM can achieve high torque production with the same volume and PM usage. In order to find the optimal split ratio match of stators, several DSR-HMDSFMMs with different combinations of split ratios are proposed and calculated. The configuration and operating principle are illustrated, together with electromagnetic performances of the proposed machines analyzed using finite element analysis (FEA). The FEA-predicted results show that the proposed HMDSFMM exhibits high air-gap flux density with low harmonic distortion and high torque density, which is promising for the direct-drive applications. [ABSTRACT FROM AUTHOR]

The consequent permanent magnet (CPM) pole rotor and harmonic utilization permanent magnet (HUPM) rotor are promising candidates for electric machines with less rare earth materials. Therefore, this article focuses on the analysis and comparison of these rotor types in terms of air-gap flux density characteristics, magnet utilization, and torque density. In the first part, an analytical approach is used to investigate the magneto motive force (MMF) distribution of the rotor and air-gap flux density characteristics. In the second part, finite-element methods (FEMs) are used to compare both rotor topologies with a conventional interior permanent magnet (PM) and spoke PM rotor. The results show that CPM and HUPM rotors can reduce the volume of PMs compared with the conventional configurations. However, with the HUPM rotor, a higher torque density and magnet utilization ratio can be achieved at the same time. [ABSTRACT FROM AUTHOR]

In this article, a novel spoke-type permanent magnet (PM) machine with two types of PM materials is proposed to reduce the cost. In order to improve torque density and reduce torque ripple, the multi-objective optimization combined finite element method (FEM) and genetic algorithm (GA) are used. In addition, the electromagnetic performances of the novel spoke-type PM machine, including no-load air-gap flux density, electromagnetic torque, torque ripple, efficiency, and cost are compared with the conventional spoke-type PM machine. It is demonstrated that the novel spoke-type PM machine obtains a 1.5% lower torque ripple and 36% lower cost, and the torque density is 4.3% lower than the conventional spoke-type PM machine. Meanwhile, the novel spoke-type PM machine has lower core loss and higher efficiency. Finally, a 40 kW spoke-type PM machine is manufactured to verify the analyzing method. Experimental results demonstrate that the proposed machine exhibits high torque density and low cost in the application of electric vehicles (EVs). [ABSTRACT FROM AUTHOR]

In order to solve the problems of poor capacity and unsatisfactory efficiency of flux-weakening control for the axial-flux permanent magnet (AFPM) machines with surface-mounted permanent magnet (PM) rotor structure, a new axial-flux hybrid-excitation machine (AFHEM) with double consequent-pole rotors is proposed, which combines the high torque density of the AFPM machine and the flexible flux regulation of the hybrid excitation machine. It meets the stringent requirements of the distributed in-wheel motor electric drive vehicle for high efficiency and high torque density. The topology, principle, and basic electromagnetic properties of the new axial-flux hybrid-excitation in-wheel motor are presented in this article. Based on the complex magnetic circuit of the AFHEM, a 3-D equivalent magnetic network (EMN) model is established. The air-gap flux density, flux linkage, back EMF, torque, and fault tolerance ability of the motor are solved through the EMN model and compared with the 3-D finite element analysis (FEA) to verify its validity and correctness. It is hoped to form a rapid design method for the new type of motor with the complex structure of 3-D magnetic flux path property. Finally, based on the EMN model, the influences of the magnetic saturation on the excitation regulation capability of the proposed AFHEM are analyzed, which provides a guideline for the optimization design of the new AFHE in-wheel motor. [ABSTRACT FROM AUTHOR]

The shaping of the air gap of a V-typed fractional slot concentrated windings interior permanent magnet synchronous machines (IPMSMs) is investigated for compressed-air system (CAS) applications in this article. The harmonics of no-load air gap density, average torque, torque ripple, and iron losses are studied by the finite element analysis (FEA). The results show that the air gap shaping of the V-typed IPMSM can be effectively used to reduce the torque ripple and stator core loss. It is because the low-order harmonics of the air gap flux density can be reduced with a little decrease in the average torque. The proposed air gap shaping methods have the advantages of simple design and simple manufacture. A V-typed IPMSM with air gap shaping is prototyped to verify the correctness of the analysis results. [ABSTRACT FROM AUTHOR]

In this article, a new method of enhancing the anti-demagnetization capability based on the modulation principle is proposed for a less-rare-earth permanent-magnet synchronous motor (PMSM). By means of analytical method, the relationship between the demagnetization effect and the air gap flux density, calculated by magnetic motive force (MMF) and magnetic permeance, is established. By implementing the design of the fundamental harmonic modulation, the anti-demagnetization capability of the less-rare-earth PMSM can be improved. Using the finite-element method, the electromagnetic performances of the initial and optimal motor are analyzed and compared in detail, including the demagnetization characteristics and torque characteristics. Finally, theoretical analysis and simulation results verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this article, a new magnetic equivalent circuit (MEC) model was presented to predict torque characteristics and reaction flux in slotted-type eddy-current couplings (SECs). The magnetomotive force and reaction field caused by eddy current in the conductor were innovatively introduced into the model; particularly, the modulations of the magnetic field and eddy current by iron teeth in conductor disk were taken into account by dividing magnetic flux paths in air gap into several branches. The expressions of magnetic flux and torque were obtained by combining Kirchhoff’s law and Ampere’s loop law. The torque was calculated using the method proposed and was compared with those obtained by the 3-D finite element method (FEM) and experiment, respectively. The results indicated that the method proposed is accurate and effective under conditions of low slip speeds and short air gap lengths. [ABSTRACT FROM AUTHOR]

In this article, two kinds of dual-layer segmented Halbach arrays have been proposed for permanent-magnet (PM) brushless machines. The analytical expressions of magnetic fields due to the inner-/outer-layer Halbach magnets have been separately obtained. For the maximal flux density in the air gap, the optimal magnet segment radian ratios or magnetization angles for each dual-layer Halbach array have been analytically determined separately. The induced back electromotive force and electromagnetic torque have been analytically obtained. The prediction results show that the optimized electromagnetic performances for each double-layer segmented Halbach array with different slot and pole combinations are better than those for the corresponding single-layer one. The proposed analytical model can also be applied for optimizing the multi-layer segmented Halbach array. The analytical prediction results of a PM machine with the double-layer segmented Halbach array have been compared with those obtained by a finite-element method. [ABSTRACT FROM AUTHOR]

This paper compares the performance of inner-only and inner–outer type of magnetizing fixture designs to achieve the radial magnetization profile in an isotropic-bonded neo magnet. In inner-only fixture, the magnetization coils are located on only one side of the magnet circumference, and inner–outer fixture uses magnetization coils on either side of the magnet circumference. For both fixtures, the finite-element analysis (FEA)-based performance is presented and compared with the experimental validation. The effect of misalignment between the inner and outer coils in an inner–outer fixture is discussed using the FEA as well as experimental results, and a limit on the misalignment angle resulting in negligible reduction in mid-air-gap flux density integral per pole is arrived at. [ABSTRACT FROM AUTHOR]

This paper proposes a dual-stator consequent-pole permanent magnet vernier machine comprised of two stators and a sandwiched rotor. The proposed topology has high torque density owing to its special working principle and low cost due to the consequent-pole structure. To verify the superiority of the proposed machine, it is compared with an existing dual-stator vernier machine in terms of important electromagnetic characteristics. The finite-element analysis comparison of the two machines shows that the proposed machine achieves a higher average torque and a higher torque-per-magnet volume in comparison with the existing machine. Moreover, the proposed machine uses less magnet volume; therefore, the cost of the machine is significantly reduced. Furthermore, the proposed machine is more efficient compared with the existing machine. [ABSTRACT FROM AUTHOR]

In this paper, an improved flux-barrier geometry configuration of transversally laminated rotor synchronous reluctance machine (TLR-SynRM) is proposed to suppress the torque ripple. The flux-barrier geometry configuration has two remarkable features. First, its flux barriers are step shaped and their shapes could be described by the parameter X. Second, the widths of multi-flux barriers in the middle regions are changing in a gradient style. The conformal mapping method is introduced to calculate the reluctances of the improved flux-barrier geometry configuration, and the corresponding magnetic equivalent circuit is established to analyze how the parameter X influences air-gap flux density distribution in order to obtain the minimum torque ripple. Based on the above analysis, the results are used to improve the flux-barrier geometry configuration. Last, the effectiveness of the improved flux-barrier geometry configuration is verified by finite-element analysis. [ABSTRACT FROM AUTHOR]

In this paper, an analytical method for predicting the rotor overhang (OH) effect is presented using two types of conformal mappings (CMs), which are the ${r}$ – ${\theta }$ and zr plane CMs. First, the no-load air-gap flux density (AFD) of a slotted air gap without OH is determined using the ${r} {\theta }$ plane CM. Second, the complex relative air-gap permeance (CRAP) in the zr plane is obtained by the zr plane CM. This helps in taking the OH effect into account. Finally, the no-load AFD of the slotted and OH air gaps in cylindrical coordinates is derived from the no-load AFD in the ${r} {\theta }$ plane with CRAP along the ${z}$ -axis. The accuracy of the presented method is verified by comparing the results of no-load analysis with those of 3-D finite-element analysis. [ABSTRACT FROM AUTHOR]

This paper adopts simple analytical modeling to investigate the contribution of air-gap field harmonics to the torque production in some three-phase, 12-slot/8-pole doubly salient synchronous reluctance machines (DSRMs) with both conventional and mutually coupled winding configurations. The air-gap flux density has been calculated based on the analytically obtained magnetomotive force and doubly salient air-gap permeance for both the double-layer and single-layer DSRMs with different winding configurations. Then, the contribution of different air-gap field harmonics to average torque and torque ripple can be investigated and validated by direct finite-element analyses. It has been found that in the DSRMs, the 10th-order harmonic in the double-layer conventional winding (DLC), the 4th-order harmonic in the double-layer mutually coupled winding (DLMC), the 7th-order harmonic in the single-layer conventional winding (SLC), and the 10th-order harmonic in the single-layer mutually coupled winding (SLMC) have the highest contribution to positive average torque and with positive influence on torque ripple reduction. However, the 2nd-order harmonic in the DLC, the 8th-order harmonic in the DLMC, the 5th-order harmonic in the SLC, and the 2nd-order harmonic in the SLMC machines mainly reduce the average torque. [ABSTRACT FROM AUTHOR]

This paper presents the simple analytical modeling for switched flux memory machine to provide in-depth insight into its working mechanism. The analytical approach is based on the slotless open-circuit air-gap flux density and the slotted air-gap relative permeance calculations for a doubly salient structure. In addition, due to low coercivity and highly nonlinear hysteresis curve at the second quadrant, the piecewise and virtual-linear hysteresis models of AlNiCo permanent magnet (PM) are presented to determine the PM working point. This combined analytical solution allows rapid calculation of several electromagnetic characteristics, e.g., air-gap flux density and back electromotive force. The effectiveness of the analytical method is validated by both finite-element results and measurements. [ABSTRACT FROM AUTHOR]

A nonlinear equivalent magnetic network (EMN) model is proposed for a linear permanent magnet vernier (LPMV) machine. The meshing method is employed to solve the problem of the modeling of complex flux paths in stator teeth tips. Especially, an end-region model based on the electromagnetic principle is developed to consider the longitudinal end effect of the LPMV machine. The key contribution of this paper is to present a faster and simpler approach to separate the detent force (end force component and cogging force component) than finite-element analysis (FEA). Besides, taking the iron saturation and air-gap flux leakage into account, the proposed model is used to predict the electromagnetic performances of the LPMV machine, such as air-gap flux density, back-electromotive force, cogging force, and thrust force. Finally, through comparisons among the FEA simulations, experimental measurements and EMN analyses, the accuracy and effectiveness of the proposed model are verified. [ABSTRACT FROM PUBLISHER]

In this paper, the air-gap flux density components in the eccentric surface-mounted phase modulation (SPM) machines are predicted analytically. In the provided model, the slotting effects of the armature are taken into account. In the modeling process, conformal transformations (CTs) are employed to obtain an equivalent concentric slotless machine for the eccentric slotted PM machine. To satisfy the condition of using CTs, i.e., having a Laplace equation, the PMs are replaced with an equivalent current sheet at the surface of the rotor. The approach of finding this current sheet is approved by the basis of the electromagnetic theory. One of the contributions of this paper is that the provided model is capable of modeling the eccentric SPM machines with any PM magnetization pattern by means of CTs. Substituting the predicted air-gap flux density components in the Maxwell stress tensor, the machine unbalanced magnetic force and its cogging torque are computed. Finally, the accuracy of the obtained results is evaluated by means of finite-element analysis. [ABSTRACT FROM PUBLISHER]

In this paper, the robust control method is proposed for air-gap positioning of magnetic levitation systems considering levitation disturbance forces caused by propulsion systems. Even though the disturbance effect occurs inevitably by propulsion systems, it is very difficult or impossible to be measured by sensors in real time. In order to maintain the constant air-gap position according to the reference command in the propulsion state of the vehicle, robust control for electromagnetic suspension against levitation disturbance force is highly required. The disturbance force caused by propulsion systems is predicted by the finite-element method analysis of the magnetic flux distribution. Based on the analyzed result, the robust and optimal levitation controller is designed by the convex optimization method for the proposed proportional integral derivative controller with the inner feedback compensator stabilizing the nonlinear plant. The proposed controller has the formulation of the conventional full-state feedback optimal controller based on state-output matching for the unmeasured state. The effectiveness of the proposed controller is verified by simulation and finite-element method analysis. [ABSTRACT FROM AUTHOR]

In this paper, a study was conducted using a unit equivalent magnetic circuit (EMC) in correlating the relationship between the magnet thickness, the modulating ring pole-piece thickness, and their circumferential pitch. A numerical optimization method is employed in selecting the optimum ratio of the magnet to pole-piece thickness. The study reveals the need to simultaneously consider these parameters during the design of a magnetic gear electric machine because of their strong mutual dependency. A finite element analysis (FEA) was conducted using the optimum ratios. The results correspond to those of the EMC. Also, the performance of the machine is analyzed and found to have a power factor of 0.78. To further verify the results of FEA, a prototype was built using the same configurations of the FEA model. Measurements taken from the prototype are on par with the simulated results. [ABSTRACT FROM AUTHOR]

The general flux weakening control method for permanent magnet synchronous motor (PMSM) is changing the angle between the current and the no-load back-electromotive force (EMF). This paper presents a novel structure of PMSM with a conical rotor (CR-PMSM) and studies its flux weakening performance in detail. The CR can be moved outside in axial direction, which decreases the air-gap flux density as well as the effective space between the stator and the rotor. This method is effective in increasing the maximum speed and the output power of PMSM, including the surface-type and interior-type. 3-D finite-element model is used to simulate the magnetic-field distribution, flux weakening, and driving performance in CR-PMSM according to rotor axial displacement. The motoring performance of CR-PMSM is compared with that of the general method. A prototype machine with a cone angle of 5.7 and a rated power of 140 W at a rated speed of 300 rpm is designed and built to validate the theory. [ABSTRACT FROM AUTHOR]

This paper introduces a mock-up with a solid iron cylinder rotating in a fixed excitation frame powered by dc current. A uniform field is created in the rotating cylinder, which is driven by an external motor. The braking torque is measured, allowing the study of iron losses generated by a uniform rotating field. The aim is to advance toward a vector iron loss model that takes into account different magnetization directions and their interdependency. The eddy current losses are the dominant loss source in the mock-up, rendering it easier to model. A standard eddy currents model is proposed. It models well the losses at low and medium magnetic flux density, but lower losses are measured near saturation levels. This could be due to the high thickness to radius ratio changing the eddy current paths near the edges of the rotor, which can be later analyzed by a full 3-D finite-element method analysis. A 2-D finite-element method simulation is performed, which estimates the magnetic flux heterogeneity in the rotor. Several lessons are drawn from this mock-up, which prepares a second version with a higher speed and a longer laminated stack rotor. A higher air gap will decrease the voltage fluctuation in the primary winding, a smaller angular opening of the excitation frame will improve the uniformity of the flux in the rotor. [ABSTRACT FROM AUTHOR]

Permanent-magnet vernier machines are becoming more and more attractive due to their high torque density and low-speed operating capabilities. This paper investigates the effects of the magnet thickness, magnet pole arc ratio, and slot open ratio on the torque capacity. An analytical model is first presented. It is validated by comparing the results with the finite-element analysis (FEA) under the same hypothesis. A mono-objective optimization is then conducted on the basis of the analytical model coupled to genetic algorithm to reach the optimal values yielding the highest value of the torque. Finally, the influence of nonlinear magnetic material behavior on the optimal design is investigated through nonlinear FEA. The results are presented and discussed. [ABSTRACT FROM AUTHOR]

In this paper, a hybrid-excited vernier permanent magnet (PM) machine is proposed. Two excitation sources, namely, the PM excitation and the electrical excitation are artfully combined together based on the homopolar topology, resulting in a parallel hybrid excitation. The flux regulation capability of the proposed machine is discussed and analyzed. Unlike other hybrid-excited machines, the flux regulation is realized based on the variation of the armature flux linkage rather than directly adjusting the air-gap flux. Performances of the bi-directional flux regulation are evaluated by the 3-D finite-element method. In order to verify the analytical results, the proposed machine is prototyped and tested as a generator. Both no-load and on-load performances are assessed. The experimental results agree well with the analytical ones. [ABSTRACT FROM AUTHOR]

This paper compares the performance of three different topologies of spoke-type permanent-magnet vernier machines (PMVM): 1) dual airgap dual stator winding (DSW); 2) dual airgap single stator winding (SSW); and 3) single airgap (SA). These topologies were compared in terms of torque/machine volume, cogging torque, and torque ripples. The 2-D finite element method was utilized to compare the performance of the three models. The dual airgap PMVM with a SSW showed similar performance with the same machine outer diameter and similar power in terms of torque/machine volume and torque ripples compared with the DSW model. The performance of the SSW model was better than that of the SA model for the same outer diameter and rotor. Furthermore, stator slot optimization was performed to improve torque/machine volume and reduce torque ripples in the SSW model. [ABSTRACT FROM AUTHOR]

Axial flux resolvers (AFRs) are used in motion control of electrical machines. In this paper, the effects of physical parameters on the accuracy of detected position are studied. The examined parameters are width of slot opening and slot width, number of poles, number of slots per pole and per phase, and skewing of rotor slots. An analytical model based on the winding function method is proposed for the first time in to estimate the error of position signal. The results of the analytical method are verified with 3-D time stepping finite-element method. Finally, the prototype of the studied AFR is constructed and tested. Good agreement between simulation and experimental results confirms the effectiveness of the proposed analytical model. [ABSTRACT FROM AUTHOR]

The finite-element calculations and experimental measurements are employed in this paper to detect faults in a two-pole synchronous generator. A special benchmark constructed for this study allows imposing short circuits in the rotor winding, and it is used to verify the numerical results. The air-gap magnetic field can be detected by means of sensors placed inside the machine, and it can be calculated by the finite-element method (FEM) as well. [ABSTRACT FROM AUTHOR]

The power balance in the numerical simulation of a cage induction machine with eccentric rotor has been studied. The asymmetrical air-gap flux density distribution caused by the non-uniform air gap due to eccentricity produced forces that play an important role in the rotor dynamic stability. These forces act both in the radial and the tangential directions. The tangential force together with the whirling motion produces additional power in the shaft. If the power balance of the simulation satisfies, the power due to the whirling can be calculated from the power balance. This could also give a new approach to compute the forces due to eccentricity or verify the existing force computation methods. The error in the power balance of an eccentric machine has been calculated and the sources of the errors have been illustrated and discussed. [ABSTRACT FROM AUTHOR]

This paper is aimed at an analytical approach to predict the no-load operation features of tubular-linear permanent magnet synchronous machines (T-LPMSMs). These are currently considered as viable candidates for wave energy conversion. The developed approach is based on the derivation of the air-gap flux density, considering both the first- and second-type modified Bessel functions of appropriate orders. Following its formulation, the air-gap flux density is applied for the prediction of the no-load operation features, with a focus on the cogging force, the phase flux linkages, and the back electromotive forces. A case study is treated considering three axial arrangements of a T-LPMSM, such as the case of an infinite length machine, the case of a finite length machine, and the case of a finite length machine enabling a quasi-cancellation of the end effect. A comparison between the analytically predicted features and those numerically computed by a 2-D finite-element analysis has led to good agreement. [ABSTRACT FROM PUBLISHER]

This paper presents a simple analytical model for two types of three-phase surface-mounted permanent magnet machines: modular and unequal tooth (UNET) width machines with different slot/pole number combinations. It is based on the slotless open-circuit air-gap flux density and the slotted air-gap relative permeance calculations. This model allows calculating the opencircuit air-gap flux density, phase flux linkage, back electromotive force, and average torque of both the modular and UNET machines. Its accuracy has been validated by the 2-D finite-element (FE) method. A flux focusing/defocusing factor has also been introduced to analyze the influence of flux gaps in alternate stator teeth of modular machines on the machine electromagnetic performances. It has been found that by properly choosing the slot/pole number combination and flux gap width, the open-circuit air-gap flux density, the winding factor, and the flux focusing effect can all be improved. As a result, the performance of the modular machine can be significantly boosted. The analytical and FE models have been validated by experiments. [ABSTRACT FROM AUTHOR]

This paper presents a field-modulated permanent magnet (FMPM) machine using spoke-magnet-array outer rotor for direct-drive applications. The operating principle with detailed theoretical derivation is analyzed to reveal the evidence for high torque capability of the proposed machine, just due to the utilization of effective harmonic flux adding to the contribution of air-gap fundamental flux for energy conversion. Using the finite element analysis, the performance characteristics of the proposed machine are assessed and compared with permanent magnet synchronous machine counterparts to verify the theoretical analysis. A prototype machine is also fabricated for experimental validation of the proposed machine. The analytical discussions also form an important foundation for research in various high-performance FMPM machines. [ABSTRACT FROM AUTHOR]

Synchronous reluctance (SynRel) machines are gaining more and more importance in various fields of application thanks to their known merits like rugged construction, high efficiency, absence of field windings, and no or reduced need for permanent magnets. Out of the possible design variants, in this paper, SynRel motors with uniform mechanical air gap and circularly shaped flux barriers are considered and a conformal-mapping approach to their analytical modeling and simulation is proposed. A suitable conformal transformation is introduced to compute the reluctance of each rotor circularly shaped flux barrier and the result is then used to analytically determine the air-gap flux density distribution and the electromagnetic torque of the machine in arbitrary operating conditions. The accuracy of the methodology proposed is assessed against finite element analysis. [ABSTRACT FROM AUTHOR]

Spoke-type interior permanent magnet (IPM) machines are an attractive topology for high-performance electric motors, especially designed for vehicle traction applications. In this paper, a special design for a spoke-type IPM motor is presented to enhance motor flux-weakening capability in the operation over a wide speed range. The proposed design consists of a simple and robust mechanical device that includes radially displaceable rotor yokes, connected to the shaft by means of springs. At high speed, the centrifugal force prevails over the elastic one due to springs, causing the mobile yokes to displace radially and establish a partial magnetic short circuit between PMs. This increases PM leakage flux and consequently reduces the air-gap field. As a result, a mechanical flux weakening effect is achieved at high speed, which helps significantly to reduce the demagnetizing \boldsymbol d -axis current to be injected by the inverter, along with the related copper losses and demagnetization issues. The proposed design is investigated in this paper using an analytical model whose parameters are computed by finite-element analysis. The effectiveness of the solution being set forth is successfully proven by some testing on a laboratory prototype. Experimental results are compared with analytical predictions showing a satisfactory accordance. [ABSTRACT FROM AUTHOR]

An overhang structure is used to enhance the air-gap flux density and increase the torque density of a motor. In the preliminary design stage, consideration of the overhang effect is important for a precise prediction of the performance of a motor with overhang and for the selection of the proper overhang length. The 3-D finite-element method (FEM) is essential when analyzing a motor with an overhang structure due to the asymmetry in the axial direction caused by overhang. However, it is computationally expensive and time-consuming, especially during the initial design stage. In this paper, we propose a magnetic equivalent circuit model, which considers the overhang structure of a surface-mounted permanent-magnet motor. With the proposed analytical method, the computational time is significantly reduced in the preliminary design stage. The proposed analytical model is verified with a 3-D FEM analysis. [ABSTRACT FROM PUBLISHER]

This paper presents a design and analysis method for a novel hybrid flux permanent-magnet (PM) machine for a high-power density. By combining radial and axial flux machines with integrated windings, the air-gap flux density is increased, and an overhang structure of the PM and additional magnetic cores are applied to increase the power density. For the analysis and design of the proposed motor, a time-consuming 3-D finite-element analysis (FEA) is required owing to its unique structure. To address this problem, a correct and rapid novel analysis method is proposed using an equivalent 2-D conversion method. The accuracy of the proposed analysis method and the usefulness of the proposed motor are confirmed via the 3-D FEA and experimental results. [ABSTRACT FROM PUBLISHER]

This paper investigates the air-gap magnetic field characteristics of homopolar inductor alternator (HIA), including theoretical analysis, numerical calculation, and experiment. First, the structure and magnetic circuit characteristics of HIA are analyzed. Second, a linear model of distributed magnetic circuit of HIA is established. An analytical formula for calculating the main air-gap magnetic field at different axial positions is deduced and obtained. Third, finite element method (FEM) is used to compute the magnetic field of HIA. The results from FEM are nearly consistent with those from analytical method. Finally, a prototype is constructed to verify the theoretical analysis and numerical computation. The research shows that the distribution of the main air-gap magnetic field of HIA is uneven along the axial direction. The proposed analytical formula contributes to calculate the main air-gap magnetic flux density of HIA. [ABSTRACT FROM PUBLISHER]

This paper analyzed thrust characteristics by considering the step-skew method and permanent magnet (PM) overhang in a linear synchronous motor. Although the PM overhang increases the thrust, it also influences the air-gap flux density distribution in the stacking direction, and thus, each step length should be adjusted according to the existence and length of the PM overhang. 3-D finite element analysis is used to calculate the magnetic field and the thrust characteristics are compared each other. The analysis results show that the stacking length of both ends of the step should be reduced to get lower detent force and thrust ripples, and higher generated thrust as the PM overhang is increased. [ABSTRACT FROM PUBLISHER]

This paper presents four types of three-phase permanent magnet (PM) machines, that is, modular and unequal teeth (UNET) machines either with or without tooth tips. Two-dimensional finite element (FE) modeling has been carried out to analyze the influences of flux gaps (in alternate stator teeth) and UNET widths. These influences are mainly on winding factors, air-gap flux density due to PMs, flux linkage, back-electromotive force, and electromagnetic torques. For UNET machines without tooth tips, it has been found that the UNET widths affect both winding factor and air-gap flux density due to PMs. However, for UNET machines with tooth tips, the UNET widths have no effect on machines’ electromagnetic performance. Nevertheless, for modular machines, the flux gaps influence three parameters: winding factor, air-gap flux density due to PMs, and flux focusing/defocusing. Meanwhile, for different slot/pole number combinations, the influences of flux gap and UNET widths are different. Several general rules concerning these influences have been established. These general rules can be extended to other single or dual three-phase modular or UNET machines with different slot/pole number combinations. Prototypes of modular machines have been built, and the predictions and conclusions have been validated. [ABSTRACT FROM PUBLISHER]

A combined analytical and FEM technique is proposed for predicting the air-gap magnetic field distribution of a PM embedded salient pole wind generator. The influence of slotting on both radial and circumferential components of air-gap flux density is taken into account. By employing the proposed combination technique, the magnetic field distributions when the stator and rotor are at different relative positions can be calculated much faster than that by FEM. Based on the magnetic field distributions, the cogging torques are predicted and verified by the FEM, while the relationship between cogging torque and design parameters are further investigated. The proposed combination technique provides an efficient and accurate prediction method for the air-gap magnetic field distribution of large electrical machines with a complex PM pole structure. [ABSTRACT FROM AUTHOR]

A simple magnetic circuit method (MCM) is developed for analytical calculation of the air-gap magnetic flux density waveform of a permanent magnet embedded salient pole wind generator (PMESPWG), which can consider the saturation in the side frame and the upper core of its pole shoe. In the MCM, the magnetic circuit is divided into a series of sub-circuits according to the flux paths to cope with different lengths of air-gap and different saturation levels of the pole shoe upper core. In order to evaluate the validity of the proposed method, air-gap flux densities of a 3.3 MW machine prototype are calculated and validated by the finite-element method (FEM) results. By utilizing the developed MCM, the air-gap flux distribution of the PMESPWG is optimized to obtain the maximum fundamental and minimum total harmonic distortion. [ABSTRACT FROM PUBLISHER]

This paper investigates a novel axial magnetic gear using ferrite magnets. In order to increase the air-gap flux density the ferrite magnets are arranged in flux focusing configuration. The simulation results presented in this paper indicate that a relatively high torque density can be achieved when using only ferrite magnets. [ABSTRACT FROM AUTHOR]

This paper deals with a new AC electric motor magnetic circuit structure made of shifted non-segmented grain oriented steel laminations. The aim of the paper is to understand with a finite element approach the local distribution of the magnetic flux density inside shifted laminations as well as in the air-gaps between them. It is shown that the air-gap flux distribution is not trivial at all and very difficult to appreciate. [ABSTRACT FROM AUTHOR]

This paper presents the design and analysis of a variable arc magnet array comprising two segments per pole for permanent magnet (PM) spherical motor. The harmonic model for radial air-gap flux density distribution is solved by magnetic scalar potential equation using spherical harmonic series and validated by finite-element method. After the influence of magnet array parameters on the fundamental harmonics amplitude and higher harmonic content of the air-gap flux density is analyzed, the optimization of four-pole magnet array is performed in which the higher harmonics of the radial air-gap flux density are minimized. The final design is compared with iron-cored classical array and air-cored equal arc Halbach array, and the result shows that for a given relative volume of magnetic material the proposed variable arc magnet array produces lower higher harmonic content than the other two arrays. [ABSTRACT FROM AUTHOR]

In this paper, an analytical method for the computation of the electromagnetic field in the airgap of an inset permanent magnet synchronous machine is proposed. The originality lies in the fact that both the stator and rotor saliencies have been taken into account in the analytical procedure. The purpose in to compute both quickly and accurately the magnetic fluxes and instantaneous torque of the machine, in order to minimize torque ripples in an optimal predesign process. It is shown that the instantaneous torque is in good agreement with finite element results, for a shorter computation time. The model presented here can be used when the 2-D approximation of the machine is valid, which is the case for most of machines' topologies. [ABSTRACT FROM AUTHOR]

The cogging torque in flux-switching permanent magnet machines (FSPMs) is high due to its unique structure and high air-gap flux density. The cogging torque principle in FSPM is different from that in traditional PM machines, which can not be correctly predicted by analytical consideration. The aim of paper is to present the investigation on cogging torque principle in FSPM by analyzing the flux density distribution and a simple cogging torque reduction technique, i.e., teeth notching. Various kinds of notching schemes and their influence on cogging torque are examined along with instantaneous torque and average output torque at different load conditions. Numerical optimization process combined with finite-element analysis, which gives more preciseness to calculations, is performed to minimize cogging torque. The results show that the cogging torque circle depends on the real flux density distribution in the machine rather than the number of stator/rotor poles and the presented method can greatly reduce the torque ripple at only slight cost of average output torque. [ABSTRACT FROM PUBLISHER]