Search

In this paper, a novel dual-rotor axial-gap flux-switching permanent-magnet machine with dc excitation winding is proposed. First, the topology and operation principles of the proposed topology are clarified. Basic design equations and parameters are provided, and the electromagnetic analyses of the proposed flux-switching machine with 3-D FEA are performed. Parametric optimizations using 3-D FEA are completed for different dc excitations. A prototype machine is manufactured, tested, and validated. It is shown that the air-gap flux of the proposed axial-gap machine can be controlled in a wide range compared to conventional surface magnet machines. [ABSTRACT FROM AUTHOR]

This paper presents an optimal design for a surface-mounted permanent magnet (SPM) motor to suppress torque pulsations and save the magnet cost, by using multi-grade permanent magnets. Based on a conventional SPM motor with single-grade bonded NdFeB magnets, the proposed SPM motor is designed with two-grade bonded NdFeB and one-grade ferrite magnets, and then optimized by combining the Kriging method with a genetic algorithm, for further minimizing torque pulsations and saving the magnet cost by maintaining the high average torque. As a result, the cogging torque, torque ripple, and magnet cost of the optimized SPM motor are highly reduced compared to those of the conventional SPM motor. Furthermore, the optimized SPM motor is verified to have superior endurance against the magnet’s irreversible demagnetization within three times of the rated current excitation. All motor characteristics, including airgap flux density, cogging torque, electromagnetic torque, and demagnetization ratio are first predicted with the aid of a finite-element method. Finally, the optimal design and analysis results are validated by the experimental results. [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]

This paper presents the detail analysis of the radial force and bending moment responsible for vibration in the stator permanent magnet synchronous motors (PMSMs). The vibration characteristics, especially vibration mode, of stator PMSM are studied. First, the air-gap flux density distribution and radial force density distribution are derived in detail. Then, two types of vibration modes, called pulsating and bending modes, and their reasons as pulsating force and bending moment are analyzed and elaborated which are not analyzed and verified before. In addition, the relationships between these two vibration shapes and pole width, pole number, and slot number are analyzed. To confirm the analysis and theory, the multi-probe mode-included test method of vibration acceleration is used to obtain the vibration mode information of motors, and the experimental results on a 6-pole/36-slot stator PMSM match well with the simulation results. [ABSTRACT FROM AUTHOR]

Electromagnetic performance of three multi-layered interior permanent magnet (IPM) machines are investigated and compared for electric vehicle applications in this paper. The rotor structure, air-gap field distribution, torque density, torque ripple, core loss, magnet eddy-current loss, and output power are studied with finite-element analysis. It is demonstrated that the two-layered rotor structure with magnets buried deeply has the lower torque density and magnet eddy-current loss due to the utilization of magnets and the block effects of the armature-reaction flux is lower. The three-layered IPM machine has the lower torque ripple and core loss than two-layered IPM machines because the harmonics of air-gap density are reduce by the increase of magnet layers. Finally, an IPM machine with three-layered magnets rotor is prototyped to verify the analysis. [ABSTRACT FROM AUTHOR]

This paper presents a new method by sticking a copper ring on the permanent magnet pole of the permanent magnet brush dc (PMBDC) motor to reduce the electromagnetic vibration. First, the air-gap flux density distribution and radial force density distribution are derived and the principle of the electromagnetic vibration reducing technique by the copper ring is analyzed in detail. Then, finite-element method is used to calculate the Maxwell force and the vibration spectrum of a 2-pole 24-slot PMBDC motor and a modified motor. Finally, experimental results are given to validate the proposed technique, by testing the vibration spectrum of the two prototype PMBDC motors. It is shown that the acceleration of the motor with copper ring can reduce the vibration effectively compared with the origin motor, and the reduced ratio can be up to 40%. [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]

In this paper, the torque production mechanisms of flux-reversal permanent magnet (FRPM) machine and Vernier permanent magnet (PM) machine are analyzed and compared based on air-gap field modulation. Working harmonics of PM magnetomotive force (MMF) and air-gap permeance in two machines are analytically identified and compared, indicating that the fundamental PM MMF together with all permeance harmonics contribute to the torque production of Vernier machine whereas all PM MMF harmonics but only fundamental permeance in FRPM machine produces the torque. Thanks to the utilized large dc component of air-gap permeance, the torque density of Vernier machine is revealed to be better. Influence of critical parameters on machine performance, such as PM thickness and slot width ratio of the modulation pole, is also investigated. It shows that FRPM machine is more sensitive to the design parameters. Both finite-element analysis and experimental validation are conducted to verify the conclusion. [ABSTRACT FROM AUTHOR]

The homopolar inductor machine (HIM) is of particular interest in the field of flywheel energy storage system, where it has the potential to significantly reduce self-discharge associated with magnetic losses. However, the conventional HIM suffers from low power and torque density due to its unipolar air-gap flux density. Besides, the air-gap flux density of HIM is limited by the cross section of rotor, and the rotor diameter is limited by the maximum tip speed of the rotor. Thus, the maximum effective length and diameter of rotor should be within a certain range, which constrains the output power and stored energy of the HIM. To solve these problems, a novel multi-unit out-rotor HIM (MO-HIM) with bipolar air-gap flux density is proposed in this paper. First, the structure and operating principle of MO-HIM is illustrated. Then, the characteristics of the proposed machine are analyzed, indicating that MO-HIM can be regarded as a superposition of multiple unit machines. Finally, to verify the superior performances of the proposed MO-HIM, it is compared with a unipolar out-rotor HIM with multi-segment stator cores in terms of air-gap flux density, back electromotive force, and output torque. Results show that the proposed MO-HIM has larger fundamental air-gap flux density, higher power, and torque density. [ABSTRACT FROM AUTHOR]

Halbach array-based permanent magnet (PM) brushless machines exhibit attractive features when compared with conventional PM brushless machines with normal segmented magnets, including the flux-concentration effect, essentially sinusoidal air-gap flux density due to PMs, and negligible cogging torque. However, as for a motor/generator used in flywheel, an external rotor composed of Halbach array and rotor back-iron is necessary to increase the inertia of flywheel system, which is different from the conventional external-rotor machines. In this paper, a Halbach array PM motor is studied compared with the radial magnet array. The relationship between the air-gap field distribution and the magnet array is discussed. Finally, the eddy current loss in PMs of the external-rotor ironless brushless dc motor is analyzed between the Halbach PM motor and the conventional PM motor. [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]

The traditional bearingless permanent magnet synchronous motor has complex decoupling control problems. To overcome the drawbacks above, a novel hybrid permanent magnet type bearingless motor (HPMTBM) is proposed in this paper, which has integrated the merits of hybrid excitation permanent magnet motor and magnetic bearings. The main advantages of this HPMTBM are the simple control mechanism and the low power consumption. First, the principle and theoretical background of this motor are introduced. Then, the mathematical models of radial suspension force and torque are established using Maxwell stress tensor method, and air-gap magnetic fields, radial suspension forces are calculated by finite-element analysis. Finally, the prototype motor is designed and constructed. The radial suspension forces and rotor radial displacements are tested. The simulation and experimental results show the feasibility of the proposed HPMTBM. [ABSTRACT FROM AUTHOR]

The high stability of the dual-excited synchronous generator (DESG) can enhance the reliability of power supply for critical users. Based on the traditional synchronous generator (TSG), a DESG with two sets of symmetrical field windings on the rotor is presented in this paper. The rotor slots are spaced equally over the whole rotor surface of DESG, which is different from the structure of TSG. Such structures of DESG are expected to enhance the reliability and give the electromagnetic performances, such as air-gap flux density and electromotive force (emf) that are close to those of TSG. For this purpose the relationship between the excitation magnetomotive forces (mmf) of the single- and dual-axis excited DESG is investigated. The mmf with a different rotor pitch is calculated by the finite-element simulation, and the simulation results agree with those by the theoretical derivation. The excitation air-gap flux density, emf, and the magnetic saturation in stator and rotor cores are calculated under different excitation modes, and the results are compared with those of TSG. In order to validate the simulation results, the emf of 10 kW DESG model machine is measured under different excitation modes. This paper provides the theoretical basis for the design and manufacture of large DESGs. [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]

Air gaps are often used in a design of power inductors. Different arrangements of air gap in a magnetic circuit influence the parameters of an inductor. Understanding this dependence allows a design of more efficient inductors. In this paper, the influence of different air-gap arrangements on the distribution of the magnetic flux density, the value of saturation current, and the power losses is presented. The 3-D finite-element analyses and laboratory measurements were realized for the exemplary inductor made of grain-oriented steel and copper foil. Additionally, the main rules of the design of inductors with distributed air-gap arrangement are also given. [ABSTRACT FROM AUTHOR]

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]

This paper discusses a motor that was designed to satisfy the size constraints of system by using ferrite magnet and has the same performance as rare-earth magnet motor. In general, the size of the motor is increased in order to meet the same performance of motor using a ferrite magnet, because of its very low energy density compared to the rare-earth magnet. In order to compensate for these drawbacks, spoke structures capable of generating maximum magnetic flux at the same rotor size have been frequently studied. However, the spoke type motor structure has a drawback that demagnetization occurs in a magnet-specific portion. However, because it affects harmonics of the airgap flux density by demagnetization, it affects mechanical torque ripple and vibration. Therefore, in this paper, the changed air-gap flux density due to the demagnetization phenomenon and the changed mechanical vibration are analyzed by the finite-element method. In addition, we proposed an optimal rotor structure that can reduce the demagnetization phenomenon of magnets in spoke interior permanent magnet synchronous motor. Experiments were performed to evaluate the reliability of the optimized design. [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 presents a new method for calculating the braking force of a drum-type eddy current brake with a two-layer structure. The drum-type eddy current brake should have a structure that improves the braking force by applying a material with high conductivity inside the drum because the eddy current loss generated from the drum is used as the braking force. In addition, because the eddy current brake operates at various speeds while braking the vehicle, it is necessary to grasp the braking force according to the speed. Furthermore, because the material of the drum is composed of non-laminated iron having conductivity, the skin effect and the armature reaction phenomenon appear, and the skin depth and the air-gap flux density are different depending on the braking speed. In this paper, the value of the eddy current loss of the eddy current brake with a copper coating inside the drum is newly presented and compared with the finite-element analysis results. In addition, the change in the speed–torque curve according to the conductivity value of the drum and inner coating material are shown. Finally, an experiment was conducted to compare and verify the characteristic curve of the eddy current brake obtained from the newly derived equations. [ABSTRACT FROM AUTHOR]

The results of the 3-D finite-element method electromagnetic analysis of the constant speed variable output permanent magnet synchronous motor including the rotor retaining plate structure confirmed that the eddy current flow was induced in the rotor part. Eddy current flows from the permanent magnet to the rotor retaining plate, and it was found that there is induced voltage that generates eddy currents in the retaining plate from the aspect of eddy-current distribution. The eddy current flow from the permanent magnet to the retaining plate is related to the change in magnetic resistance during rotation and is also related to the effect of slot harmonics on the air-gap magnetic flux density. In this paper, the characteristics of the eddy current flow in the rotor assembly were investigated when the retaining plate is included for various slot combinations. The eddy-current generation according to the slot combination is analyzed and the cause of such tendency was investigated. Furthermore, from the pattern of eddy-current formation, it was noted that the aperiodic pole–slot combination models may have a larger eddy-current loss increase when combined with the retaining plate. [ABSTRACT FROM AUTHOR]

This paper develops a novel magnetomotive forces (mmfs) distribution model along the transverse direction for the 3-D analysis of linear induction motor, and it investigates the influence of a laterally asymmetric cap-secondary on the thrust, vertical force, lateral force, and efficiency in a prototype single-sided linear induction motor for linear metro. First, the mmf distribution model and its working conditions are defined, and the model is transferred into a mathematical model. Second, the air-gap flux and secondary eddy current in a prototype linear motor with a cap-secondary are obtained by a 3-D space harmonic analytical method. Third, the thrust, vertical force, lateral force, and efficiency of the test motor are analyzed with various lateral deflection, and the power factor in secondary is also presented. Finally, these results are experimentally verified by measurements on the test rig of the linear motor, and the comprehensive effect on the operating performance can be accurately calculated by the mmf model. [ABSTRACT FROM PUBLISHER]

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]

This paper investigates the characteristics of the radial force density according to the shapes of the flux modulation poles (FMP) in a surface-mounted vernier machine (SPMVM). The air-gap flux density harmonics obtained from the finite-element analysis method are analyzed using the analytical equations derived from the magnetomotive force and the air-gap permeance distributions. Then, in order to find the radial force density harmonics that generate the exciting force on the stator, the spatial orders and the angular frequencies of the radial force density harmonics are calculated by using the Maxwell stress tensor method. The analysis results show that the permeance harmonics generate the radial force density harmonics, but the resulting harmonics of the radial force density are time-invariant in the spatial domain. Consequently, the variation of the FMP shape can improve the torque characteristics of the SPMVM without the increase of the exciting force on the stator core. [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 flux of the embedded magnets in the rotor of an interior permanent magnet (IPM) synchronous machine causes a non-homogeneously saturated rotor iron. This alters the reluctance of the stator flux path due to the nonlinear $B$ – $H$ curve of the rotor iron and should be considered in the analytical field calculations; however, it is often neglected in the prior-art methods leading to inaccurate results. Moreover, the effect of a fractional-slot concentrated-wound (FSCW) stator on the analytical field calculations is not addressed in the existing literature. The magnetic field characteristics of IPM synchronous machines are commonly formulated using an equivalent air-gap function. In order to account for the aforementioned shortcomings in the existing methods for the analytical field calculations, an equivalent air-gap function is proposed in this paper that considers the particular properties of an IPM rotor and an FSCW stator. To this aim, based on the rotor geometry and the nonlinear $B$ – $H$ curve of the iron core, a method is first proposed to model the saturation level and the relative permeability at different regions of the rotor iron. This model is then used in the proposed equivalent air-gap function to compute the armature reaction air-gap flux density. The proposed theory is validated through finite element analysis and experimental results on a prototype FSCW IPM machine in the laboratory. [ABSTRACT FROM AUTHOR]

This paper deals with accuracy improvement of a traditional magnetic model for saliency switched reluctance machines. The machine is with high power density for traction application. The calculation is featured by taking conductor layout and slotting effect. Fundamental characteristics, such as flux linkage and air-gap flux density, are analyzed, based on magneto-motive force (MMF) as well as magnetic permeance. Specifically in the MMF model, the winding function is featured by conductor distribution of coils in stator slots, and relation between air-gap flux harmonics and conductor layout is discussed, which helps to reduce harmonics. In the magnetic permeance model, emphases are made on the air-gap permeance fitting using a fourth-order polynomial, followed by a fitting method of magnetic saturation especially with high excitation. A finite-element method is used as a reference. [ABSTRACT FROM PUBLISHER]

Axial flux permanent magnet (AFPM) motors are frequently used in many applications. Axial gap coreless motors with surface-mounted magnets are the most noteworthy ones due to their potentially higher efficiency and smaller axial length. In this paper, a new spoke-type AFPM coreless disk motor with dual rotor and single stator is proposed with sinusoidal rotor segments. This new disk-type motor is an interior PM (IPM) motor with spoke-type rotor and variable air gap to obtain sinusoidal back Electro-Motive Force waveform. It is shown that it is possible to increase the air-gap flux density in the proposed new coreless AF-IPM motor and increase the torque output compared with the conventional surface-mounted AFPM motors. [ABSTRACT FROM PUBLISHER]

Permanent magnet brushless (PMBL) motors have been widely applied in electric vehicles, since they inherently offer high efficiency, high power density, and free maintenance. However, because of the existing problem of uncontrollable flux, their constant-power speed range is relatively narrow. In order to gain a wide speed range, by employing the new concept of the flux-intensifying effect, a new flux-intensifying PMBL (FI-PMBL) motor is proposed in this paper. The proposed motor is innovatively designed, where the topology of two-layer segmented PMs and non-uniform air gap are adopted to make the corresponding d -axis inductance L_{d} become greater than the q$ -axis inductance L_{q} , which is far different from the conventional interior PM motor. By using the finite-element methods, the electromagnetic performances of the proposed motor are evaluated in detail. Simulation results show that the proposed motor possesses preferable flux-weakening capability and wide speed range. In addition, the experimental results of the FI-PMBL prototype are given to verify the performances of the motor. [ABSTRACT FROM PUBLISHER]

This paper concerns a coupled analysis of the stray magnetic field and the external housing vibration of a synchronous machine to detect rotor short-circuit faults. Indeed, in addition to the possibility to measure these parameters with non-invasive equipment, these two measures depend on the air-gap flux density that is directly impacted by the short circuits of any nature. Hence, correlating these two quantities, it is achievable to confirm or discard an eventual motor fault. This method allows both to develop an analysis of non-invasive manner and to establish the magnetic state of a synchronous generator in normal operation. The experimental survey of stray magnetic field and housing vibration spectrum is shown as a promising alternative at low cost and easy to implement and to determine, for instance, rotor turn-to-turn winding faults. Faulty and healthy signatures are drawn from the measured spectra to determine a degree of healthy state of the synchronous machine. [ABSTRACT FROM PUBLISHER]

In this paper, a novel magnetic equivalent circuit (MEC) is proposed to calculate magnetic flux of saturated electrical machines. The machine features double salient poles with high saturation. Emphases are made on modeling of air-gap permeance and magnetic saturation using a fitting method. The analyses are applied based on a 4-phase 8/6 switched reluctance machine (SRM) with high power density, which was designed for traction application. The air-gap reluctance in MEC that connects a tooth pair is studied, followed by distribution of magnetic saturation on teeth. The magnetic reluctance of circuit loop can be fitted as well as saturation quantity if the electrical steel is known. The proposed network offers a fast and accurate way of estimating flux characteristics of especially highly saturated machines with double slotting effect. [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 proposes an analytical method that combines the superposition and the subdomain methods to predict the air-gap field distribution in permanent magnet (PM) machines with rotor eccentricity. The original machine with rotor eccentricity is divided into a number of air-gap sections along the circumferential direction. For each air-gap section, a concentric model is employed by adopting an equivalent air-gap length to predict the air-gap field using the subdomain method. The air-gap field distribution of the original model can then be synthesized from these concentric models. Consequently, the electromagnetic performance can be predicted accordingly, such as flux-linkage, back EMF, and so on. Finally, the direct finite element analysis is used to validate the efficacy of the proposed method. The proposed analytical method can be extended to other machines with different slot/pole number combinations and is particularly useful for analyzing the machines with large slot and pole numbers. [ABSTRACT FROM AUTHOR]

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 proposes a novel tubular double-stator vernier permanent-magnet (TDS-VPM) motor for artificial hearts. The key of the proposed motor is double-stator and vernier structures. Due to its vernier structure, more PMs can be adopted in the proposed TDS-VPM motor and the useful harmonics of the air-gap flux density are increased, thus improving thrust density. Furthermore, double stator, namely inner stator and outer stator, has an appropriate 90° (electrical degree) angle difference. Since the inner stator is located inside the mover, the motor space is fully used. Hence, the thrust density is enhanced and the axial direction length is reduced. Meanwhile, the angle difference between the inner and the outer stator can reduce the cogging force of this TDS-VPM motor. The electromagnetic characteristics of the proposed motor are analyzed using the time-stepping finite-element method, confirming the validity of the theoretical analysis. [ABSTRACT FROM PUBLISHER]

This paper presents an effective permanent-magnet vernier (PMV) machine for direct-drive applications, in which the low-speed outer rotor employs a spoke-magnet arrangement with flux focusing to improve air-gap flux density, and the stator adopts an open-slot structure to enable the stator teeth to achieve field modulation. Using the finite element analysis, the performance characteristics of the proposed machine are investigated and compared with the split-slot surface PMV machine. A prototype is also built for experimentation to verify the validity. Both simulation and experimental results show that the proposed machine can offer the advantages of improved torque capability and low voltage regulation. [ABSTRACT FROM PUBLISHER]

This paper analyzes Maxwell tensor tangential and radial magnetic forces in permanent magnet synchronous machines in the no-load case. Using matrix notation in the complex domain, a simple expression of the Fourier harmonics of both radial and tangential forces is derived, including all space and time harmonics. These expressions prove that both the frequency content of cogging torque and zeroth-order radial forces are linked to the least common multiple between the stator slot number and the rotor poles number, and that the optimal pole arc to pole pitch ratio to reduce cogging torque is also optimal for the reduction of average radial magnetic forces. It is also shown that both the smallest non-zero spatial order of tangential and radial force harmonics are given by the greatest common divider of the number of slots and the number of poles. These results can be used during the design stage when choosing the pole and slot numbers combination. These analytical results are then compared with calculations using MANATEE vibroacoustic and electromagnetic simulation software. Finally, some variable speed acoustic noise simulations are carried out on three different designs to analyze the efficiency of different vibroacoustic design rules on the slot and pole numbers combination. An attempt to formulate a new vibroacoustic design rule choice is detailed. It is concluded that no simple analytical design rule can be used to evaluate noise and vibrations induced by magnetic forces, and that numerical simulation is necessary. [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]

In this paper, an analytical model is developed for surface mounted permanent magnet (SMPM) machines with skewed slots via the subdomain technique and the multislice method. It takes the nonuniform distribution of flux density along the axial direction caused by slot skewing into account and can be used to obtain air-gap flux density distribution in the 3-D space. The cogging torque, flux linkage, back electromotive force (EMF), and output torque are calculated with the obtained air-gap flux density. The results calculated by the analytical model are validated by the 3-D finite element analysis. The convergence and computation time of the analytical model are investigated, and good convergence and fast calculation speed can be achieved. Based on the developed analytical model, the effects of slot skewing angle and pole arc on back EMF and output torque are researched. The analytical model can be applied to the fast optimal design and performance analysis of SMPM machines with skewed slots. [ABSTRACT FROM AUTHOR]

The clamping of the power transformer magnetic circuit allows maintaining the sheet stack and provides an additional mechanical rigidity. It has consequences on the acoustic noise of transformers as the magnetic cores of power transformers vibrate because of the magnetostriction and, if the corners are considered, Maxwell’s forces. The indirect impact of a lack of clamping on the core losses is studied, especially on the interlaminar air gaps in the corners. In this paper, it is shown numerically with finite element modeling and experimentally with a specific testbench that induced vibrations can change the flux distribution and thus the losses. [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]

An analytical model for prediction of air gap flux density and cogging torque in slotted surface-mounted permanent magnet (SPM) machines is presented in this paper. The proposed method is based on superposition theorem, the concept of equivalent magnetization currents (EMCs), and analytically solving of Poisson’s equation. To solve Poisson’s equation easily, the air gap flux density of the slotted SPM machine is stated as superposition of the air gap flux density functions of two slotless machines. The first slotless machine is excited by PMs, while the second one is excited by surface EMCs. Therefore, the concept of EMC is used in an iterative algorithm which converges quickly with a negligible computation time. Using the obtained analytical model and Maxwell’s stress tensor, cogging torque of the slotted SPM machine is predicted. This analytical model provides a quick tool to study the effect of leading design parameters on the machine cogging torque. Finally, the validity of the proposed model and the obtained results are verified with finite element analysis. [ABSTRACT FROM AUTHOR]