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In this paper, an improved magnetic equivalent circuit (MEC) model of a coreless axial-flux permanent-magnet synchronous machine (AFPMSM) with printed circuit board (PCB) winding is presented, which considers the curvature effect, fringing effect, leakage flux, and rotor yoke's magnetic saturation. The axial air-gap flux density distribution, no-load back electromotive force, winding inductances, and electromagnetic torque are predicted by the proposed MEC model. The steady-state performances of the machine under heavy load, as well as the dynamic response of the machine with a connected voltage source and mechanical load, are calculated. All the results obtained from the proposed model are in good agreement with those issued from the 3D finite element method (FEM). The computation time of the proposed model is greatly reduced compared to 3D FEM. Finally, a coreless AFPMSM prototype with a PCB stator is manufactured, and experiments are carried out to verify the predicted results. [ABSTRACT FROM AUTHOR]

This article presents a successful design of a three-phase large capacity line-start permanent magnet synchro nous motor (LSPMSM) developed for industrial applications. A hybrid rotor containing both slotted solid steels and cage bars is included in the designed LSPMSM to enhance the motor starting and synchronizing abilities. A salient rotor periphery making air-gap length, which maximizes at the quadrature axis and minimizes at the direct axis, is employed to reduce the harmonics of air-gap flux density and motor losses. The implementation of a genetic algorithm coupled with a neural network optimizes the rotor-periphery saliency ratio and other crucial dimensions for further performance improvement. Finite-element analyses highlight the advantages of the designed LSPMSM by comparing its performance indexes with those of a conventional cage-rotor LSPMSM. The effectiveness of the designed motor is validated by a series of prototype tests. [ABSTRACT FROM AUTHOR]

Homopolar inductor machine (HIM) has been applied in the field of flywheel energy storage system (FESS) due to its merits of simple structure, high reliability, and low idling losses. However, the HIM features unipolar air-gap flux density, which makes its power density lower than that of the electrical machine with bipolar air-gap flux density. Addressing this issue, a novel outer rotor homopolar inductor machine (OR-HIM) is proposed in this article. First, the special structure and operation principle of the OR-HIM are illustrated. Then, the unit motors of the OR-HIM are obtained and investigated based on the magnetic equivalent circuit method to facilitate the design. Moreover, the performance indexes, including power density, output characteristics, losses, and rotor stress of the OR-HIM, are fully analyzed. Finally, a 13-kW prototype is designed, manufactured, and tested. The back electromotive force, load voltage, output torque, and efficiency are measured and compared with those obtained by the finite element analysis. The results indicate that the proposed OR-HIM is a promising candidate for the application of FESS. [ABSTRACT FROM AUTHOR]

In this article, a variable flux reluctance machine (VFRM) with dc field excitation and modular structure is proposed and it exhibits controllable flux, simplified manufacture, better fault tolerant capability, and potentially reduced material consumption. Its operational theory is illustrated by using flux modulation principles, and the working harmonics considering the modular structure are analyzed. Besides, the winding factors of modular VFRM are derived considering the flux gap width. The parameters are optimized by two-dimensional finite element method to maximize the back electromotive force (back-EMF) and the ratio of phase self-inductance to mutual inductance. Moreover, the electromagnetic performance including open circuit air-gap flux distributions, open circuit air-gap flux densities, flux linkage, back-EMF, inductance of armature windings, output characteristics, loss, power factor, and efficiency-map are compared for 12s10r and 12s14r nonmodular and modular VFRM. Additionally, the fault including short circuit and open circuit fault are analyzed. Finally, a modular 12s14r VFRM prototype is manufactured and tested to validate the theoretical and finite-element analyses. [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]

High-speed permanent magnet machine (HSPMM) design is considered with particular attention paid to machine electromagnetic, thermal, and mechanical analyses. In this article, a 140-kW, 15 000 r/min HSPMM is designed with its power losses evaluated at first. Afterward, the machine temperature distribution is obtained based on computational fluid dynamics modeling. HSPMM is prototyped with experimental tests conducted to verify the calculation results. Mechanical strength analysis is performed for the HSPMM rotor structure with pole filler by finite-element method for the rotor at three operational conditions, while the influences from sleeve parameters on rotor strength are comprehensively studied for the HSPMM rotor at the most challenging condition. In this article, stator auxiliary slotting is extensively researched to reduce the rotor eddy current loss with little effects on machine output torque. The air gap flux density for HSPMM with auxiliary slotting is analytically predicted, while the working mechanism is illustrated in-depth. The effects from auxiliary slot dimensions, numbers and positions, on machine performances are further proposed and investigated. The experimental tests also validate the reduction of HSPMM rotor eddy current loss by the application of auxiliary slotting. [ABSTRACT FROM AUTHOR]

In this article, a fast circuit-field coupling method is proposed for the analysis of the skewed induction motor. Based on the multislice model, the equivalent circuit of the skewed induction motor is established. The distributed magnetic field method is used to calculate air-gap flux density and deal with the core saturation at each axial slice. Based on the coupling analysis of the equivalent circuit and magnetic field, a two-layer iterative process is used to calculate the magnetic field distribution and performance indexes of the skewed induction motor. By comparing with finite element analysis and experiment results, the proposed method is proved to be correct and effective. The proposed method is characterized by fast computation speed and good accuracy, so it is an ideal approach to analyze the skewed induction motor. [ABSTRACT FROM AUTHOR]

Large medium-voltage electric machine stators are usually equipped with form wound coils made of flat conductors (strands) and embedded in open (rectangular) slots. Air-gap magnetic flux lines can enter the slot and, sweeping the strands placed nearest the slot opening, induce eddy currents in them. Such eddy currents cause additional losses which can be much higher than usual skin-effect and proximity losses. In order to avoid dangerous overheating and hot spots, the additional losses in question need to be carefully predicted in the design stage. Time-stepping finite-element analysis (TSFEA) can be used for the purpose, which however implies a large computational burden and requires the machine geometry to be modeled in detail. This article proposes alternative methods based on time-harmonic finite-element analysis (THFEA) simulations performed on highly simplified machine models and with no need to take rotor motion into account. The proposed methods are shown to produce very accurate results, compared to TSFEA, but with very significant time and computational savings. [ABSTRACT FROM AUTHOR]

Permanent magnet adjustable speed drive (PMASD) has been widely applied to regulate the speeds of large pumps and fans for energy-saving. For improving the torque density and simplifying the actuator of traditional PMASD, a novel squirrel-cage rotor (SCR-) PMASD with a non-rotary mechanical flux adjuster (MFA) is proposed in this paper. An analytical model considering the slot effect and the MFA shifting is established to analyze the magnetic field and the output torque efficiently for the initial design of the proposed drive. The air-gap flux density distributions obtained by the analytical model are verified by two-dimensional (2D-) finite element analysis (FEA). During the speed regulation process, the torque characteristics, power, loss, and efficiency of the drive under different MFA shifting distances are compared with the 2D-FEA and experimental results. The analysis and measured results show that the proposed drive can achieve a wide speed regulation range. [ABSTRACT FROM AUTHOR]

Since the linear induction motor commonly work with a laterally asymmetric secondary as it is applied to pull rail vehicles, this paper presents a complete equivalent circuit model considering the asymmetry to predict thrust, vertical and transversal forces. First, six correction factors are presented to quantify the variations in the air-gap magnetic flux and secondary induced current as the linear induction motor operating with a laterally asymmetric secondary. Second, it develops a circuit model based on the existing T-model for the rotary induction motor and two correction factors for the magnetizing branch, which is used to indicate the electromagnetic variations in the air-gap flux and secondary plate due to the asymmetry. Third, the mathematical expressions for the thrust, vertical and transversal forces are derived by applying the equivalent circuit model. Then, the six correction factors are calculated with a prototype motor, and the results of them are comprehensively analyzed. Finally, the characteristics in the prototype motor are calculated with the mathematical expressions in a range of rated speed, and validated by the experimental measurements carried out on a test rig and line for linear motors. [ABSTRACT FROM AUTHOR]

It is known that the slot frequency vibration is the one of the main components in electromagnetic vibration spectrum of permanent magnet DC motors (PMDCM). After finding that the vibration reduction scheme of the piecewise varying pole width (PVPW) is only effective for the odd order harmonic of slot frequency vibrations by analytical method, the PM pole with sawtooth edge is put forward to reduce all harmonic components of slot frequency vibrations of PMDCM. In this article, after the air gap flux density and radial force density are analyzed, the two vibration sources, radial force and bending moment, are derived for the motor with sawtooth edge poles (SEP). Then the optimized pole shape is obtained to reduce all harmonic components of both the radial force and bending moment at the same time. Three dimensional finite element method of electromagnetic field and structure are used to calculate the magnetic flux density, radial force and vibration for the motors of PVPW and SEP. Three permanent magnet motors with fixed pole width (FPW), PVPW and SEP are manufactured and tested. The comparison and verification show that SEP is better than the other two schemes in general. [ABSTRACT FROM AUTHOR]

This paper proposes a novel high-temperature superconducting stator-excited axial-flux magnetic gear (HTS-SEAFMG) for the high-torque transmitting system. The proposed magnetic gear combines the merits of both HTS-excitation and stator-excitation. By using the HTS-excitation, a high air-gap flux density can be easily obtained, thus achieving the high torque density. The HTS-excitation windings are placed on the stator with a static seal of cooling Dewar which greatly reduces the manufacturing difficulty and the cost of refrigeration system compared with the dynamic seal. Thanks to the stator-excitation pattern, both the high-speed rotor and the low-speed rotor comprise only iron, thus contributing to the high mechanical reliability. The axially sandwich structure can also simplify its assembly in the high torque transmission applications. The dimensional parameter optimization and the electromagnetic performance evaluation are conducted by using the finite element method, respectively. The results show that the torque density of the proposed HTS-SEAFMG can reach 123 kNm/m3. Theoretical analysis and results are both given to verify the feasibility of the proposed HTS magnetic gear design. [ABSTRACT FROM AUTHOR]

In this paper, a novel mechanical flux-adjusting interior permanent magnet (MFA-IPM) motor is proposed. The key is to employ an additional mechanical flux-adjusting (MFA) device attached to one side of the rotor, which can achieve flexible adjustment of the air-gap flux and obtain a wide speed range. This system with appropriate gears uses centrifugal force to set the cylindrical PMs in a required position. The topology and working principle of the MFA-IPM motor are introduced. Then, the dynamic performance prediction between the deformation length of spring and the rotation angles of PMs is obtained by the dynamic simulation. Moreover, the electromagnetic characteristics of the proposed MFA-IPM motor and a conventional IPM motor are analysed and compared based on finite element analysis, including no-load performances, inductances, electromagnetic torque, flux-weakening ability and speed range, as well as demagnetization evaluation. Finally, a prototype MFA-IPM motor is fabricated and tested. Both the simulation and experimental results indicate the validity and feasibility of the MFA-IPM motor. [ABSTRACT FROM AUTHOR]

The open phase fault is much specified in three--phase squirrel cage induction motors. However, this defect develops an unsymmetrical magnetism generates noise and vibration in the motor. Finite Element Method (FEM) is the most accurate technique to analyze the induction motor, because it can include all actual characteristics of both healthy and faulty conditions. In this paper, an FEM to analyze a 2.2 (kW) three--phase squirrel cage induction motor with the open phase fault is proposed. An experimental investigation to display the stator current waveforms with healthy and faulty conditions are obtained and compared under different load operations. The currents obtained are introduced into FEM analysis, which is used for magnetic field calculation and the magnetic flux density in the air-gap, stator teeth and in the stator yoke for both healthy and faulty operations. [ABSTRACT FROM AUTHOR]

Summary: In this paper, an interior permanent magnet synchronous motor with a D‐type rotor configuration is presented. The performance of the proposed motor is compared with that of the widely used V‐type interior permanent magnet synchronous motor. For a fair comparison, all the motor parameters are identical. With the advent of different rotor topologies, multilayered and multisegmented permanent magnets are extensively used; however, an analytical modeling of D‐type interior permanent magnet synchronous motor has not yet been conducted. Furthermore, its analysis using the finite element method is considerably time‐consuming. To resolve this problem, an analytical method based on a magnetic equivalent circuit is proposed for the slotless D‐type interior permanent magnet synchronous motor. It is then compared with the finite element method at different pole arc–pole pitch ratios to demonstrate the effectiveness of the proposed method. Additionally, Schwarz‐Christoffel mapping is employed to maintain the slot shape and include the effect of adjacent slots by considering the slotting effect in the slotless air‐gap flux density. Finally, the presented motors are optimized based on the pole arc–pole pitch ratio to maximize the fundamental air‐gap flux density and minimize the total harmonic distortion. [ABSTRACT FROM AUTHOR]

In order to improve the air-gap flux density of the permanent magnet synchronous motor and reduce the cogging torque, a novel structure with asymmetric magnetic poles for automobile was proposed. Based on the characteristics of the parallel magnetic circuit, the magnetic flux path diagram is established. And the equivalent magnetic circuit model is established by the equivalent magnetic circuit method. The Taguchi method is used to be a multiobjective optimization algorithm. The total harmonic distortion of the air-gap flux density is the first optimization goal. The second and third optimization goals are the cogging torque and the average of output torque, respectively. And the torque ripple is a constraint condition. The optimized parameter combination is obtained by the Taguchi method. Finite element simulation analysis and prototype test are carried out for the optimized motor structure. The results show that the total harmonic distortion of air-gap flux density is reduced by 36.7% comparing with the initial structure. The cogging torque is reduced by 26.0%. And the average output torque is increased by 4.8%. [ABSTRACT FROM AUTHOR]

This article presents a quasi-3-D analytical model for double-sided axial-flux permanent magnet machines (AFPMMs) with coreless structures. A simple, fast, and accurate technique is developed to calculate flux densities in different parts of the AFPMM combining the solution of Maxwell’s equations and the magnetic equivalent circuit (MEC). In this technique, Maxwell’s equations are used to generate flux sources that are used in the reluctance network of the MEC. After calculating all the reluctances and flux sources, the magnetic flux densities are obtained. This method takes into account the effects of permanent magnet (PM) reluctance, leakage flux between PM-to-PM, PM-to-rotor leakage flux at different PM edges, and the fringing flux effect. By considering these leakage fluxes as a factor called variation function in the design procedure of the machine, the analysis time is dramatically reduced compared to numerical methods while maintained high reliability. It should be noted that since considering saturation phenomenon effects in coreless AFPMM analysis does not give rise to significantly different performances, they are not included in the proposed model. Furthermore, the machine’s main features, such as the axial and tangential components of the no-load flux density in the air-gap and stator areas, as well as the back electromotive force (EMF), are derived by using magnetic field solutions and simple equivalent circuits. Finally, to validate the accuracy of the proposed method, the analytical results are compared to the case that no leakage fluxes are included in the analytical model and to the 3-D finite-element analysis (FEA) in terms of computation time and accuracy. [ABSTRACT FROM AUTHOR]

A portable flux probe is proposed and investigated in this article to detect turn-to-turn fault in the rotor poles of the high rated salient pole synchronous machines. The rotor circuit is fed by a low amplitude sinusoidal voltage source with a fixed voltage amplitude which has a frequency more than a few hundred Hz to achieve the higher reaction of the shorted turns on the faulty pole, which results in a significant reduction of the magnetic flux in the air-gap. Numerous simulations and experimental tests are carried out to investigate the proposed probe and the related technique performance to specify the faulty pole versus the number of shorted turns, applied frequency and probable eccentricity in the rotor position. The obtained test results show that all stable turn to turn faults (weak or heavy ones) can be specified easily by applying a portable sinusoidal voltage source with the frequency in the range of more than a few hundred Hz. The experimental test results validate that the flux density can be reduced to about zero in the faulty pole face, even in the case of one shorted turn in the sample machine. [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 process for reducing the electromagnetic vibration and noise by changing the shape of the stator is presented. Although the fundamental wave of the air gap magnetic flux density contributes to the average torque of the motor, other spatial harmonics which were except the fundamental wave of that cause vibration and enfeeble the output of the motor. Therefore, it is important to reduce the spatial harmonics for performance of the motor. Through the proposed process, it is possible to obtain an objective function to reduce the specific harmonics by assigning weights to each spatial harmonic. The reduction in the fundamental wave is minimized and it is possible to reduce the spatial harmonics that have an adverse impact on vibration. After the process, a model can be found that maintains the electromagnetic performance as much as possible while optimally reducing the vibration. To verify the process, the electromagnetic vibrations by a radial force of the proposed and conventional models were compared, and it was confirmed that the electromagnetic vibration of the proposed model was reduced. The validity of the analysis was proved through finite-element analysis. [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]

The interior permanent magnet synchronous motor uses a barrier structure to block the magnetic flux circulating inside the rotor and to send the magnetic flux into the air gap. Although the airgap magnetic flux density can be increased through the barrier, there is the disadvantage of increased torque ripple. Thus, this study is conducted to determine whether the torque ripple could be reduced by changing the barrier shape. The problem here is that the torque inevitably decreases when the torque ripple is decreased. Therefore, in this study, a novel shape of the bridge is proposed in a model in which the torque ripple is reduced but the torque is not. The notch structure is applied to the bridge and is analyzed through finite-element method analysis. To intuitively express the relationship between the torque and the torque ripple, a torque efficiency factor is devised, and as a result, the torque is maintained but the torque ripple is reduced. [ABSTRACT FROM AUTHOR]

In this article, to improve the adjustment ability of air gap flux, a new interior permanent magnet (IPM) synchronous machine with permeability modulation characteristics is proposed for electric vehicles’ (EVs) potential applications. The main trait of the machine structure is that a bridge between the rotor poles is intentionally established, which can produce a smooth magnetic path for the leakage flux. Thus, the flux leakage state can be adjusted by controlling the magnetic saturation of the bridge according to the machine load current. To clarify this feature, the machine performances are investigated by theoretical analysis and finite-element method. Finally, the designed machine is manufactured and its performances are verified by experiments. Both the simulation and experimental results prove that the torque of the proposed machine under loaded conditions can be flexibly adjusted by the magnetic permeability modulation without any complex control strategy. [ABSTRACT FROM AUTHOR]

An extremely fast magnetostatic magnetic field modeling method is developed that includes nonlinear relative permeabilities (or “magnetic saturation”) of soft magnetic materials with nonuniform magnetization. The model assumes regions of linearity within the material in order to apply analytic equations and superposition. This article presents the general theory and method for 3-D geometries, along with a 2-D axisymmetric example case study that is of interest for tubular linear actuator (or motor) design. The case study maximizes the average air-gap flux of an axially magnetized pole piece and shows a close correlation of the internal and external magnetic flux densities with a finite element analysis. This demonstrates the method as suitable for large parametric searches of topologies, toward the optimization of electrical machines, linear actuators, transformers, or more general 3-D electromagnetic problems. [ABSTRACT FROM AUTHOR]

In this article, a new low-cost small-scale three-phase brushless motor topology is proposed. This is a new topology for self-excitation of brushless wound rotor synchronous motor investigated initially for rated speed. For brushless excitation, the stator is designed to contain two windings, namely, three-phase armature winding and exciter winding. The rotor consists of two windings, that is, harmonic winding and field winding, and a diode rectifier. An inverter feeds the three-phase armature winding which is connected in series through an uncontrolled three-phase rectifier to a single exciter winding. When the current is supplied from the inverter, both the armature and exciter windings are energized eventually producing a flux in the air gap. Since the flux produced by the exciter winding is not synchronized with the field winding, it produces a harmonic to be intercepted by the harmonic winding on the rotor. Eventually, the voltage produced in the harmonic winding is used to feed dc current to the field winding for brushless operation. The results obtained by 2-D finite-element analysis (FEA) validate the brushless operation of the motor. The proposed motor is analyzed basically for topology verification with the FEA results. Since the topology can be verified, further effort can be put to investigate such low-cost topologies for brushless wound rotor synchronous motor. It can be an alternative to a costly permanent magnet synchronous motor for specific applications. [ABSTRACT FROM AUTHOR]

This article presents two novel double-layer permanent-magnet flux reversal (PMFR) machines to improve the torque capability, namely Machine A and Machine B. Both the Machine A and Machine B are designed as the consequent-pole PMFR machines. The rotors of two machines are identical, which adopt Halbach array permanent-magnet (PM) in the rotor slot to guide the flux into the rotor teeth to reduce the leakage flux. However, the PM relative positions of two PMFR machines on the adjacent stator teeth are different, which result in different pole numbers of air-gap flux density. The operation principles and performances of two machines are introduced and compared in this article. In addition, the air gap fields of two machines by PM magnetomotive force (MMF) are analyzed and the contribution of the dominant air-gap flux density harmonics to torque is revealed. [ABSTRACT FROM AUTHOR]

In order to improve the driving performance of electric vehicles (EV), a permanent magnet synchronous motor with double V-shaped magnet structure (DVMPMSM) and its driving system are studied in this paper. A 150 kW DVMPMSM for EV is designed firstly, and the design parameters of the motor are determined. In order to overcome the drawbacks of the finite element analysis (FEA), especially the issue on calculating time, a dynamic equivalent magnetic network (EMN) model of the DVMPMSM is constructed, by which the air gap flux density, back electromotive force, electromagnetic torque and winding inductance parameters of the motor can be solved. Compared with the FEA, the dynamic EMN model constructed in this paper greatly increases the calculation speed while the calculation accuracy is maintained well. This paper also introduces the stator winding switching method to replace the field-weakening control method. Then, a vector control method of DVMPMSM based on dynamic EMN model and stator winding switching is proposed. The demands brought forward by EV for high torque output under low speed and high upper limit of speed can be well satisfied. Finally, the accuracy of the dynamic EMN model and the effectiveness of the proposed control method is validated through prototype experiments. [ABSTRACT FROM AUTHOR]

The linear induction motors, due to their unique features, utilize in various applications. The most crucial drawback of the linear induction motors is the large air gap between secondary and primary. This problem deteriorates the performance of linear induction motor, increases power loss, and causes to low efficiency. In this paper, a novel structure of single-sided linear induction motor is proposed to reduce the magnetic air gap. This structure consists of ladder-slit sheets and salient back iron for secondary of single-sided linear induction motor. The salient parts of back iron fill the slits of sheet, and therefore, the effective magnetic air gap can be decreased owing to partial form. Also, the electromagnetic aspects of the proposed secondary such as z-component of air gap flux density, y-component of aluminum eddy current density, and three components of Lorentz force are analyzed. Also, the finite element method and the analytical method is used for the 3 D analysis of the edge effects as well as the end effects. To show the advantages of the proposed structure, the results are compared with other secondary structures. The results show that the thrust and efficiency of the salient single-sided linear induction motor increased in comparison with other ones. [ABSTRACT FROM AUTHOR]

A novel magnetic properties tester is designed to accurately and conveniently change the air gap of the core, which can fix cores of various types. The dynamic magnetic characteristics of the amorphous core under sinusoidal excitation within 20 kHz is measured with different air gap lengths and magnetic flux density. It is found that in the case of the small air gap, the total loss decreases as the air gap increases. When the frequency is 20 kHz and the flux density is 0.1 T, the loss can even be reduced by 7%. This paper analyzes the experimental data and summarizes the influence of the air gap and magnetic flux density about the core loss. Besides, the influence of air gap on magnetic flux density distribution is illustrated and analyzed by the means of FEM (Finite Element Method). It is valuable for the design of high frequency transformer and inductor. [ABSTRACT FROM AUTHOR]

This article presents a novel power-angle control method of the doubly fed induction generator dc system based on regulating the air gap flux vector. The relationship between the angle of air gap electromotive force (EMF) vector and the stator output power is revealed in this article, which can be used for controlling the output power directly. Since the stator frequency is determined by the rotating speed of air gap flux vector and the output power is determined by the angle of air gap EMF vector, the stator frequency can be generated by the power control loop that can avoid the classical voltage model or current model and reduce the parameter dependence. The stator frequency can be regulated through the d-axis rotor current since the product of the stator frequency and the d-axis rotor current is constant. Furthermore, the improved direct resonant control for torque ripple and harmonic current mitigation can still be applied in this novel control method because air gap flux orientation is achieved through controlling the q-axis air gap flux to be zero. Finally, the experimental results are presented to validate the proposed control method. [ABSTRACT FROM AUTHOR]

The proposed technique focuses on the nonsinusoidal power supply control strategy aiming to obtain the optimal air gap flux density distribution. The electrical constraints for the alignment between rotated fundamental and harmonic air gap flux are illustrated in detail. The supporting simulation is performed to analyze the misaligned angles between fundamental and harmonic air gap flux for the traditional methods. Different from traditional flux-oriented methods, the improved algorithm for harmonic currents injection is designed based on rotor flux orientated control in fundamental plane and air gap flux orientated control in harmonic planes. The synchronous and aligned control of the fundamental and harmonic air gap flux is achieved regardless of load condition. The experimental verification is implemented based on a multiphase driving platform using a seven-phase induction machine as prototype. Various scenarios are provided for the proposed control strategy comparing with the traditional ones in terms of induced electromotive force waveforms, harmonic currents, and advance angles of air gap flux. The simulated and experimental results validate the theoretical assumption and the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Summary: The structure of the rotor magnetic circuit has an obvious effect on the eddy current loss of the rotor of the high voltage line start permanent magnet synchronous motor. In this paper, a 10 kV to 1000 kW high voltage line start permanent magnet synchronous motor is taken as an example. The two‐dimensional electromagnetic field model of the motor with V‐shaped permanent magnet arrangement is established by using the finite element method. The no‐load back EMF and armature current of the motor are calculated, and the correctness of the model is verified. On this basis, this paper proposes a sector permanent magnet structure, compares the difference between the air gap flux density and the rotor eddy current loss of the two magnetic circuit structures, analyzes the advantages and disadvantages of the above magnetic circuit structure on the harmonic effect of the air gap flux density of the motor. The mechanism of the influence of different magnetic circuit structures on the eddy current loss of the rotor is revealed, which provides a reference for the design of a high voltage line start permanent magnet motor. [ABSTRACT FROM AUTHOR]

High-speed surface-mounted permanent magnet synchronous machine is often used in micro gas turbine generation system due to its high rotor strength and high efficiency. The electrical machine in this kind of generation system needs to integrate two functions of starter and generator. Therefore, its comprehensive performance, including starting performance and generating performance, has become a comprehensive standard to measure machine performance. In this paper, a 40 kW, 20,000 r/min high-speed machine is taken as an example, the influence of magnets magnetization direction on the machine comprehensive performance is studied. The machine models with different magnets magnetization directions are established by using finite element method and the correctness of the models is verified by comparing the experimental data with the finite element calculation data. On this basis, the influence of different magnetization directions on the performance of the machine, such as generation loss, torque ripple, output voltage, start-up time and maximum starting ability, is analyzed. Furthermore, based on the Fourier decomposition of air gap flux density and the decoupling analysis of starting torque, the influence mechanism of magnetization direction on the performance of the machine is revealed. The presented results provide a reference for the selection of a suitable magnetization direction for high-speed surface-mounted permanent magnet machines. [ABSTRACT FROM AUTHOR]

This paper proposes an analytical model for analyzing the electromagnetic performance of axial flux permanent magnet machines (AFPMMs) with the coexistence of static rotor radial deviation and angular eccentricity. Firstly, a quasi-3-D analytical model for the healthy AFPMMs is established using the scalar potential. Then, the analytical model of AFPMMs with the mixed eccentricity is derived by the coordinate transformation and air gap length function. The end effect under the mixed eccentricity is considered by an end coefficient, which improves the accuracy of back EMF by 1.3%. Based on the analytical model, the air gap flux density distribution, back EMF and cogging torque of AFPMMs with different rotor radial distances and angular eccentricities are calculated and compared with the corresponding results obtained by finite element analysis (FEA). The proposed model has higher analysis speed and less computer performance requirement than FEA with the similar accuracy. According to the results, the back EMF reduces obviously as the rotor radial deviation distance increases, and the back EMF almost unchanged as the angular eccentricity becomes serious. [ABSTRACT FROM AUTHOR]

This article proposes a novel analytical model which combines subdomain method and magnet equivalent circuit (MEC) method to predict the cogging torque of surface-mounted permanent magnet (SPM) motors with rotor eccentricity and magnet defects in any slot-pole combination cases. Firstly, the general solution of open-circuit magnetic field distribution in a slotless SPM motor with magnet defects is derived. Then, the motor is divided into several subdomains along the air-gap circumferential direction to consider the non-uniform air-gap caused by rotor eccentricity, where the air-gap lengths of each subdomain are considered to be uniform. Finally, the methods of conformal mapping and MEC combined with equivalent current is used to consider the effect of slotting and saturation, which is beneficial to improve the calculation precision. The magnetic field distributions and cogging torque calculated by the proposed model are consistent with the results of finite element analysis (FEA). Compared with the FEA, the proposed model can perform fast calculations of air-gap flux density and cogging torque under rotor eccentricity and magnet defects for SPM motors, which can be utilized for optimizing the motor towards fault tolerance. [ABSTRACT FROM AUTHOR]

The fault-tolerant capability is a prerequisite for electrical safety-critical applications. In this regard, multi-phase induction motors are well-known actuators used to provide this feature. Compared to conventional three-phase machines with distributed windings, induction machines having concentrated windings could be more fault-tolerant because of increasing the number of phases. In addition, concentrated windings have shorter end-winding and less required copper weight which makes it a lower cost solution compared to distributed windings. However, concentrated windings adversely increase the distortion of the air gap flux density which affects motor performances. In this paper, a pseudo-concentrated winding layout has been proposed for six-phase squirrel-cage induction motors to improve performances compared to conventional concentrated windings. Winding function and equivalent circuit methods are used to analytically calculate performances. Finally, time-stepping finite element method and experimental measurements have been presented to confirm obtained analytical results. [ABSTRACT FROM AUTHOR]

Vernier permanent magnet (VPM) machines have been widely used in the last two decades due to their high torque density resulting from their magnetic gearing effect. In this paper, we present a new design of VPM machine with higher efficiency and power/weight ratio than their conventional counterparts. The proposed design is a combination of discrete-pole and hybrid-pole VPM machines, which incorporates the attractive characteristics of both types to improve the distribution of air-gap flux density and reduce construction costs. The arrangement of the magnets in the stator is spoke type, and their magnetization is peripheral. In order to determine the performance characteristics of the proposed machine, an analytical model based on the subdomain method is presented. The proposed method employs a quasi-Cartesian coordinates system to express the Laplace's and Poisson's equations, as well as to determine the solution for each region. Then, the solution of the equations is written in the form of hyperbolic functions and the mathematical expression of the coefficients of the equations will be simpler. To validate the proposed analytical model, a Vernier machine is designed and fabricated and the results of the experimental experiments are compared with numerical (machine simulation in finite element analysis software) and analytical results. The comparison of these results shows that the proposed model is highly accurate. [ABSTRACT FROM AUTHOR]

In permanent magnet synchronous machine design, a limited number of stator and rotor slots distorts the air-gap flux distribution and its effective length. It causes machine parameters to vary with the rotor position. The rotor flux linkage harmonics introduce nonsinusoidal back-EMF, which causes current harmonics when conventional PI current controller is adopted. Those machines suffer from high-frequency torque ripple due to air-gap flux harmonics in low-speed region. However, in high-speed region, where the torque ripple is filtered out by the mechanical system, the torque ripple may be disregarded. In this case, torque-ripple suppression methods and the associated harmonic current components generate losses. Therefore, a sinusoidal current control is required to reduce the undesired harmonic losses. In this manner, this article focuses on the sinusoidal current control strategy based on harmonic voltage injection, which requires knowledge of rotor magnet flux linkage harmonics. This article also proposes both off- and on-line schemes for the identification of rotor magnet flux linkage harmonics. These methods do not require any proprietary machine design details such as the shape of stator or rotor for finite element analysis. Commonly used PI plus resonant controller is also designed and its disadvantages in terms of speed-dependent gain and stability, in comparison to the proposed scheme, are highlighted. Finally, experimental results are presented to compare the proposed scheme with the conventional method at different operating conditions. [ABSTRACT FROM AUTHOR]

This article investigates magnetic design aspects of the trans-rotary magnetic gear (TROMAG) that using a quasi-Halbach array. TROMAG is a magnetic gear that converts high-force, low-speed linear motion to low-torque, high-speed rotational motion and vice versa. It is shown that quasi-Halbach magnetization significantly improves the force capability of the device compared to that of radial magnetization. Finite element analysis is used to study several design aspects of the quasi-Halbach TROMAG, including optimization of magnet dimensions and core thickness, effect of air gap length, effect of magnet remanent flux density, and distribution of flux density in the air gap. Moreover, the possibility of demagnetization is studied, and it is shown that if the quasi-Halbach TROMAG becomes overloaded repeatedly, demagnetization of magnets can degrade its force performance down to that of a similar TROMAG with radial magnetization. A quasi-Halbach TROMAG is prototyped, and static force and flux measurements verify the theoretical results. [ABSTRACT FROM AUTHOR]

Permanent magnets together with yokes to concentrate the magnetic flux into a cylindrical air gap are widely employed in Kibble balances. These experiments require a uniform magnetic flux density along a vertical path, typically a substantial fraction of the length of the air gap. Fringe fields that are present at both ends of the air gap limit the region where the flux density does not change more than a certain relative fraction (here, $5\times 10^{-4}$) of the flux density in the center of the magnet system. By simply adding an iron ring with a rectangular cross section to the inner yoke at each end of the air gap, the effects of the fringe fields can be counteracted, and hence, the length of the region, where the flux density remains within a given tolerance band, is increased. Compared with the alternative, employing a taller magnet, the proposed method yields a magnet system with an extended region of a uniform field without significantly increasing the mass of the magnet system. Potential applications include compact and tabletop Kibble balances. We investigate possible adverse effects on the performance of the magnet system caused by the additional rings: magnetic field strength, coil-current effect, and a dependence of the radial field on the radial position in the field. No substantial disadvantage was found. Instead, the method presented here outperformed previously suggested methods to improve the radial dependence of the radial field, e.g., shorter outer yoke. In summary, adding rings to the inner yoke improves the uniformity of the field without a detrimental effect to function, cost, and form factor of the magnet system. [ABSTRACT FROM AUTHOR]

This paper examines the influence of pole and slot combinations on the electromagnetic performance of the flux-switching permanent magnet (FSPMs) machine. For this purpose, first the production of air gap flux density in machine analytically discussed. Next, five different pole and slot combination are selected by using the knowledge of air-gap flux density expression. The performances of the different combinations are analyzed and compared using the finite element analysis (FEA), and optimal pole and slot combination is suggested. It is found that the pole and slot combination has a dominant effect on machine performance and needs to be considered during the design stage. [ABSTRACT FROM AUTHOR]

This paper presents a new rotor shape design with optimum reverse 3rd harmonic for wound field synchronous machines to effectively enhance the saliency ratio and reduce the torque ripple in a micro electric vehicle traction system. Due to the enhanced saliency ratio, the reluctance torque is expected to be improved. The air gap flux density distribution is reshaped by the new rotor shape method, which benefits the low torque ripple. By contrast, the reverse 3rd harmonic injection is much more suitable than the general 3rd harmonic injection for increasing the effective air gap length along the q-axis for a high saliency ratio. Subsequently, three amplitudes of the reverse 3rd harmonic are studied and it is found that the optimum reverse 3rd harmonic is 1/6 of the fundamental one. To verify the effectivity of the proposed design, the original model and the ICS model are compared. Finally, all the motor characteristics, such as back electromotive force, cogging torque, and electromagnetic torque, are predicted using a 2-D finite-element method with the aid of JMAG-Designer. [ABSTRACT FROM AUTHOR]

There is only slot frequency electromagnetic vibration and no pole frequency vibration in rotating armature permanent magnet motor (RAPMM), which is the advantage of this motor. The open of slot makes the air-gap magnetic field distorted and causes the harmonic of electromagnetic excitation force. In order to reduce the slot frequency vibration of the RAPMM, the method of placing magnetic slot wedge (MSW) at the slot opening is put forward accordingly. Through the finite-element simulation, it is finally shown that the MSW is capable of weakening the harmonic of the air-gap flux density, as well as decreasing the high-frequency component of the electromagnetic excitation force. Therefore, it is acknowledged that MSW can suppress the cogging torque and the vibration of corresponding frequency on the stator significantly. Finally, it is confirmed by the experiments that the built-in MSW is an effective measure for reducing the vibration of the RAPMM. [ABSTRACT FROM AUTHOR]

In this article, we present a new configuration of bearingless slice motor that levitates and rotates a ring-shaped solid steel reluctance rotor. The rotor is 50 mm in diameter and has salient features on the outer surface. Symmetric sets of Halbach magnet arrays, mounted on the tips of stator teeth, establish a homopolar bias flux around the rotor. The bias flux passively stabilizes the rotor in the out-of-plane tilts and axial translation, whereas the rotor's radial translations are actively stabilized by feedback control. The rotor saliencies spatially modulate the air-gap bias flux such that the resulting torque-current relationship is similar to that of permanent-magnet synchronous machines. We have designed, built, and tested a prototype bearingless motor and control system. The prototype system achieves a torque constant of 14.9 mNm/A, maximum speed of 5500 r/min, and suspension bandwidth of 84 Hz with a phase margin of 11.3 $^{\circ }$. The rated torque and speed are 26.8 mNm and 3486 r/min, respectively, and the axial and tilting passive stiffnesses are 15.3 N/mm and 34.4 mNm/ $^{\circ }$ , respectively. [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, a novel hybrid analysis method for spoke-type permanent magnet (PM) machines (STPMMs) is presented, which considers axial flux leakage using the machine’s lumped magnetic circuit. The STPMM can increase its air-gap flux density due to its effective flux concentration, but high flux leakage occurs in the axial end of its PMs. This results in a discrepancy between conventional 2-D finite-element analysis results and experimental data. To correct the discrepancy resulting from the unwanted axial flux leakage, a virtual residual flux density of the PM is proposed through equivalent circuits and a finite analysis model. The modified residual flux density is applied to 2-D numerical analyses, and the accuracy and usefulness of the proposed method are confirmed through 3-D numerical analyses. [ABSTRACT FROM AUTHOR]

In this paper, a permanent magnet assisted synchronous reluctance machine (PMASRM) with optimized permanent magnet width and asymmetric rotor structure is proposed. A typical PMASRM is selected as the reference motor (Pre-optimized PMASRM). In order to reduce the large torque ripple of conventional PMASRM, an optimization method to design the permanent magnet width is investigated and the Optimized Magnet-width PMASRM is proposed. On this basis, an asymmetric flux barriers structure is proposed to further reduce the torque ripple. Some electromagnetic characteristics including air-gap flux density, no-load back EMF and motor efficiency are examined by Finite Element Analysis (FEA). The simulation results show that the proposed PMASRM can not only decrease the harmonic component of no-load back EMF obviously, but also reduce the torque ripple in steady-state operation, which proves the rationality of the motor structure. [ABSTRACT FROM AUTHOR]

In a squirrel-cage induction motor, because the rotor windings are assembled from conductor bars short-circuited by end rings, the number of poles is not an intrinsic characteristic of the windings, as it occurs in the case of wound rotor windings, but it is a consequence of the distribution of the currents induced in the bars. However, since the motor works, the number of stator and rotor poles must necessarily be the same, and the explanation of why this occurs is usually left to physical considerations. The paper proposes the analytical proof that in a squirrel-cage induction motor, the number of rotor poles is the same as that of the stator. The proposed demonstration is based on the determination of the air gap flux density distribution generated by any set of currents circulating in the rotor bars, without any hypothesis about their waveform. The distribution is expressed as sum of infinite space harmonics, for each of which a current space vector can be defined. First, the special case of sinusoidal stator currents is addressed, and then the general one of stator currents having any waveform. In this way, it is possible to show that the only nonzero rotor current space vector is the one corresponding to the space harmonic having a number of poles as that of the stator. [ABSTRACT FROM AUTHOR]