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This paper proposes a method to reduce the torque pulsation of the three-phase fractional-slot concentrated-winding (FSCW) interior permanent magnet (IPM) motor by lowering sub-harmonics. The key principle of this method is the selection of an optimized six-layer winding with different numbers of conductors. Firstly, the interaction of stator-rotor magnetomotive force (MMF) which contributes to the torque pulsation is analyzed. Additionally, the relationship between sub-harmonics (1st sub-harmonic and 2nd sub-harmonic) and torque pulsation orders is revealed. Then, different numbers of conductors are adopted in coils to eliminate the 2nd sub-harmonic. Nevertheless, the 1st sub-harmonic increases in the two-layer and four-layer windings. Therefore, the optimized six-layer winding is employed to suppress the 1st sub-harmonic and ensure that the 2nd sub-harmonic is zero. Besides, there are almost no other harmonics except the main harmonic and slot harmonics in the proposed IPM motor. Hence, the torque pulsation can be greatly reduced even under different current angles. Furthermore, the principle for torque pulsation reduction by lowering sub-harmonics is revealed. The effectiveness of the proposed method is verified through the comparisons with finite element analysis and experimental test. [ABSTRACT FROM AUTHOR]

In this paper, on the basis of a conventional 12-stator-coils/17-rotor-teeth (12/17) flux-switching permanent magnet (PM) (FSPM) machine and a 6/17 V-shaped FSPM machine, a novel 6/17 multi-tooth FSPM machine with a pair of magnets located in the upper apex of stator tooth is proposed. Then, four multi-tooth topologies sharing the same 6-stator-coils but with different rotor teeth combinations, namely, 6/17, 6/10, 6/11, and 6/13, are compared by the 2-D finite element analysis (2-D-FEA). The FEA-predicted results reveal the optimal combinations of stator coils and rotor teeth should be 6/17 for high-performance multi-tooth machines. Thereafter, an optimal design criterion of multi-tooth FSPM machines for the combinations of stator coils and rotor teeth is proposed. Afterward, electromagnetic performance evaluation between the 6/17 V-shaped and 6/17 multi-tooth machines is conducted, in terms of back electromotive force (back EMF), electromagnetic torque, cogging torque, phase inductance, unbalanced magnetic force (UMF), torque/magnet ratio, and efficiency. The comparative results indicate that the proposed 6/17 multi-tooth machine is superior to the V-shaped one, since it exhibits much higher torque/magnet ratio, larger torque, lower inductance, and much lower UMF, though the cogging torque and total harmonic distribution of phase back EMF are unfavorably larger. [ABSTRACT FROM AUTHOR]

This paper proposes a novel hybrid excitation vernier permanent magnet machine (HE-VPM). The characteristics of the proposed machine are: 1) the PMs are embedded in the stator teeth, which is helpful for the heat dissipation; 2) the rotor is salient structure without PMs and windings, which ensures the reliability of high-speed operation; 3) the nonoverlapping concentrated winding shortens the end-connection, and improves the torque density, 4) only half of the stator teeth possess PMs, and the total amount of PMs are decreased; and 5) the dc current are injected to the armature coils, therefore, the exciting field can be adjusted flexibly. In this paper, the electromagnetic performance, including back electromotive force, torque, etc. are analyzed with finite element analysis. The results show that the proposed machine exhibits flexible field adjustment capability, which may be suitable for applications requiring wide speed range operation. Besides, it is found that, compared with the existing pure sinusoidal phase current, higher torque density can be obtained with dc-biased phase current under constant stator copper loss. [ABSTRACT FROM AUTHOR]

This paper deals with the design and testing of an interior permanent-magnet (IPM) machine that exhibits advanced features. It adopts fractional-slot (FS) nonoverlapped coil windings that reduces the end winding length, i.e., the Joule losses and machine cost. As a consequence, higher rated current can be supplied so that higher torque density and higher efficiency in a wide operating region can be reached. The rotor saliency increases the performance in flux-weakening operating region and the fault-tolerance capability. In order to decrease the torque ripple, it is important to minimize the interaction between the magnetomotive force (MMF) harmonics due to the stator currents and the rotor anisotropy. To do that, the winding has been optimized so as to minimize the MMF harmonics, taking advantage from the higher degree of freedom of the four-layer winding. However, the so-called slot-harmonics cannot be minimized by rearranging the winding coils. Hence, the rotor geometry has been designed so as to minimize the impact of such slot-harmonics. A 12-slot 10-pole IPM FS machine has been designed and manufactured. The experimental tests confirm the expectations. [ABSTRACT FROM AUTHOR]

In order to increase the torque density of the five-phase machines, the third harmonic is commonly employed. In this paper, the optimal and critical ratios for the third harmonic current injection are analytically derived and validated by finite element (FE) analyses. It is found that the optimal and critical injection ratios along with the torque improvement are dependent on the ratio of the third harmonic back electromotive force to the fundamental one. In order to improve the electromagnetic torque contributed by the third harmonic component, this paper employs unequal tooth to increase both the fundamental and third harmonic winding factors. Meanwhile, the optimal unequal tooth width combination is deduced and demonstrated by the FE method. When the third harmonic current is injected under the same amplitude constraint, the output torque can be improved. When the third harmonic current is injected under the same RMS value constraint, for the ten-slot/eight-pole equal tooth machine, the output torque can barely be increased, whilst for the unequal tooth machine, the output torque can be increased by 2.1%. Finally, the ten-slot/eight-pole machine with unequal teeth is prototyped and tested to prove the analyses. [ABSTRACT FROM PUBLISHER]

This paper aims to analyze the characteristics of a surface permanent-magnet Vernier motor (SPMVM) according to the pole ratio among the rotor magnet pole pairs, stator teeth, and winding pole number. The SPMVM has the same operational principle as a magnetic gear, and it is operated using the space harmonics of the air-gap flux density due to the magnetomotive force and air-gap permeance. In this paper, first, the design parameters of the SPMVM are specified based on an analytical calculation of the air-gap magnetic flux density. Moreover, various combinations of the rotor magnet pole pairs and stator teeth number are made and compared according to the operational principle of a Vernier motor using a 2-D finite-element method. [ABSTRACT FROM AUTHOR]

This paper studies the vibration and noise analysis of flux-modulation double-stator electrical-excitation synchronous machine (FM-DSEESM) in both no-load mode and on-load mode by using the mode superposition method. First, the theoretical excitations of vibration and noise, namely the radial electromagnetic force harmonics, are deduced and classified by their sources. Second, the finite element analyses (FEA) of these radial electromagnetic force harmonics are analyzed via Fourier decomposition and compared to their theoretical results for validation. Third, to perform the vibration and noise analysis, the modal test is conducted, and the modal FEA model is established based on the tested modal results. Also, the radial electromagnetic forces are coupled with the modal FEA model to conduct the vibration and noise analysis, and the responses of sound power levels in A-weighting are calculated. By using the modal participating factors, the main contributing modes are determined in the vibration and noise responses. [ABSTRACT FROM AUTHOR]

Partial demagnetization is a condition that may occur in Permanent Magnet machines due to overloading or thermal stress. Whenthis happens, the magnetic field locally weakens leading to an asymmetry of the air-gap field. This asymmetry will cause harmonics, which will be expressed as extra losses and mechanical oscillations. Moreover, since the field becomes weaker, more current is required to serve the load leading to less efficiency, increased losses and consequently increase of the temperature, which will cause further progression of the demagnetization severity until a total machine breakdown. Several methods have been proposed in the literature for the online detection of the demagnetization, however they have not related the fault to the manufacturing characteristics of the machine, which play an important role on the expected harmonic index and the associated fault signatures. This paper presents for the first time a detailed analytical investigation of the expected harmonics in the stator current spectrum in case of demagnetization, as a function of the stator winding and number of poles. The analytical results are verified by extensive simulations via the finite element method and experimental testing. [ABSTRACT FROM AUTHOR]

In this paper, the ringed-pole surface-mounted permanent-magnet machine is investigated from the point of view of the ring losses. The rings around the poles create a high-frequency anisotropy that is useful to detect the rotor position by means of a high-frequency signal injection. However, the presence of the rings causes additional rotor losses. The causes of ring losses are investigated in the paper. The first cause is the high-frequency signal injection itself. The harmonics in the airgap magnetomotive force, which are not synchronous with the rotor and hence induce currents in the rings, are the second source of losses. The third source is the airgap flux fluctuation due to stator slotting. Machines of different sizes and winding types are investigated. A finite-element analysis and an analytical model are used to estimate the ring losses, comparing the results. The influence of the ring cross-sectional area on the ring losses is analyzed, showing that the ring losses can be reduced in certain configurations. [ABSTRACT FROM PUBLISHER]

The brushless doubly fed induction machine (DFIM) is a special machine type that is of interest as a generator in wind turbine drive trains. The brushless DFIM has a significant space-harmonic content compared with conventional machine types, due to its construction. This results in additional harmonic distortions, such as torque-ripple and time harmonics. This paper studies the causes and origins of harmonic distortions in the brushless DFIM. Using time- and space-harmonic analysis, an analytical evaluation method is derived to predict the torque ripple frequencies and time-harmonic frequencies in stator and rotor voltages and currents. The evaluation method is applied to a prototype brushless DFIM to demonstrate the severity of harmonic related distortions that can be present in the brushless DFIMs. The evaluation is validated by additional finite-element analysis and measurements. Furthermore, measures are proposed to reduce harmonic distortions. The insight into harmonic distortions in the brushless DFIM and the ability to predict and prevent them must lead to the improved brushless DFIM designs in the future. [ABSTRACT FROM PUBLISHER]

In previous studies, the field winding of the brushless pulsed alternator (BPA) is embedded in the stator slots, which is supplied by dc power or variable frequency power. The advantage is that the field current can be independently adjusted. It means that the BPA system needs a standalone excitation system, which will increase the volume and cost of the system. If we substitute electric excitation for permanent magnet excitation, not only the volume and cost of the BPA system can be decreased but the efficiency and flexibility can be enhanced. In this paper, the design schemes for electric excitation and permanent magnet excitation BPA are presented. For comparison, the stator and rotor dimensions of the two kinds of BPA are both the same. The characteristics of electric excitation and permanent magnet excitation BPA are analyzed by the finite-element method and field-circuit coupling method. Finally, the BPA systems with a resistive load are established, the performances of both the two excitation modes are compared. According to the simulation results, we conclude their advantages and disadvantages. [ABSTRACT FROM AUTHOR]

This paper presents a novel consequent-pole hybrid brushless wound-rotor synchronous machine (CPH-BL-WRSM). The proposed machine employs permanent magnets (PMs) on the alternate poles of the salient pole rotor, which has considerably less magnet usage compared to the regular (PM) assisted synchronous machine. The proposed CPH-BL-WRSM offered the advantages of high starting torque, high torque density, and better performance under full-load conditions. The BL operation for the proposed machine is achieved by generating a composite magneto motive force (MMF) with a fundamental component and sub-harmonic component. The sub-harmonic component of the stator MMF is used for BL excitation of the rotor. The finite-element method was used to analyze the performance of the CPH-BL-WRSM in comparison with the performance of the existing BL-WRSM and regular PM-assisted BL-WRSM. Finally, a prototype of the CPH-BL-WRSM was manufactured and the experiment was conducted to demonstrate the performance of the proposed CPH-BL-WRSM. [ABSTRACT FROM AUTHOR]

This paper presents a fast method to compute wound rotor induction machines in steady state. Coupled time-harmonic finite-element (FE) circuit equation is used under a first space harmonic approximation for the air-gap magnetic field. It is shown that only four magnetostatic FE computations are necessary to determine the machine performances for any slip value. The performance comparison with a conventional complex magnetodynamic and time-stepping FE analyses show the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

Consequent-pole (CP) permanent magnet (PM) configuration suffers asymmetric electromagnetic characteristics although it saves PM usage. The CP-based stator-PM synchronous machines are investigated in this paper, with particular reference to symmetrical issues. The electromagnetic performances of the CP-based stator-PM synchronous machines are firstly evaluated. Afterwards, the rule of even order harmonics cancellation is presented for different slot/pole number combinations and winding layouts, based on which symmetrical phase flux-linkages can be obtained although the unbalanced magnetic flux naturally occurs. Moreover, based on the three-dimensional finite element analysis, the unipolar end leakage-flux caused by the asymmetric magnetic field is identified, and the risk of the shaft magnetization is revealed. Finally, a pair of prototype machines are fabricated and measured to validate the analyses. [ABSTRACT FROM AUTHOR]

This paper proposes a high temperature superconducting (HTS) double stator machine (HTS-DSM), based on the magnetic field modulation principle. In the proposed HTS-DSM, the HTS field winding and the copper armature winding are separately located on the two stators, so that it overcomes the drawbacks caused by the coupling device for cryogenic transfer, the torque tube, the carbon brushes, and slip rings in the conventional HTS synchronous machines with the rotating field winding, bringing the merits of high reliability and low maintenance cost. Moreover, a method of amounting a ferromagnetic ring outside the HTS field winding is also proposed to reduce the negative effects of the armature reaction field on the HTS field winding, since the alternating current (AC) losses induced by the armature reaction field easily cause the quench of the HTS field winding. Totally four different topologies are proposed, and the operation principle of the HTS-DSMs is analyzed based on the magnetic field modulation principle. Then the design and optimization of the HTS-DSM is discussed in detail to present the main design parameters of the four topologies. Finally, the performance of the four different topologies are compared by the finite element analysis, the results reveal that the HTS-DSM with modular dewar and iron-teeth inner stator exhibits the merits of higher power density. [ABSTRACT FROM AUTHOR]

This paper aims to identify the optimal number of flux modulation pole (FMP) in Vernier permanent magnet synchronous machines (VPMSMs) with concentrated tooth-coil windings. First, the influence of number of FMP on machine performance is revealed based on the unified permanent magnet magnetomotive force permeance analytical model. It is found that for a fixed stator slot number, there always exists an optimal number of FMP to maximize the torque, thanks to the enhanced contribution by the fundamental permeance harmonic. Then, the influence of critical dimensional parameters, including the machine diameter, the permanent magnet thickness, and the width of FMP, on the electromagnetic performance of VPMSMs with different numbers of FMP are parametrically analyzed by both analytical and finite element analyses. Results show that the VPMSMs with the optimal number of FMP always have advantages of a higher torque density together with a reduced PM volume, particularly for those with a relatively large diameter. Finally, two VPMSM prototypes with different numbers of FMP are manufactured and tested to validate the analyses. [ABSTRACT FROM AUTHOR]

The design rules of winding configurations and stator-pole/rotor-tooth (SP/RT) number combinations of doubly-fed flux-switching permanent magnet (DF-FSPM) machines are investigated in this paper based on coil electromotive force (EMF) vectors. The relationships between the components of stator and rotor coil-EMF vector diagrams are unveiled at first, including the numbers of stator and rotor phases, and the numbers of stator and rotor spokes. Then, the SP/RT number combinations are derived considering feasible stator/rotor phase number combinations and different winding configurations. The SP/RT number combinations are optimized considering the winding factors, magnetic field harmonics, unbalanced magnetic forces and machine diameter. It is shown that both of the stator and rotor pitch factors increase when the SP and RT numbers get closer. Furthermore, the influence of winding configurations and SP/RT number combinations on electromagnetic performances of DF-FSPM machines are analyzed by finite-element method. Finally, the analysis results are validated by experiment. [ABSTRACT FROM AUTHOR]

This paper proposes a novel dual-stator brushless doubly-fed machine (DSBDFM) with cage-barrier rotor structure for torque density improvement in application of wind power generation. The torque density of electrical machine mainly relates to machine main dimensions and rotor coupling capability (CC). Therefore, optimizing the DSBDFM, especially the machine power distribution and rotor, affects machine torque density and rotor CC. At first, several rotor topologies are proposed and analyzed to strengthen rotor CC. Then, design principles and methods in deciding the main dimensions and power distribution for the developed DSBDFM are analyzed and illustrated in detail. Based on the machine structure and design methods, a 50-kW DSBDFM is designed, with outer and inner unit electrical machine power distribution, rotor CC, slot-pole combinations, and non-magnetic ring considered. The design example with detailed design procedure in this study provides designers a practical method in initial estimation of the dimensions and parameters for the designed DSBDFM. Meanwhile, a finite-element method is used to analyze performances of DSBDFM with winding series connection, which are verified by the experimental test. Through the results analysis, it is found that the designed DSBDFM satisfies the requirements with desirable performances, indicating the validity and rationality of design methods. [ABSTRACT FROM AUTHOR]

This paper aims to comprehensively analyze the influence of number of permanent magnet (PM) pieces on electromagnetic performance of flux reversal permanent magnet (FRPM) machines. First, the unified analytical model of FRPM machines having different numbers of PM pieces is established, from which the optimal number of PM pieces and the corresponding rotor pole number can be identified. It shows that by employing the optimal number of PM pieces instead of the conventional two on each stator tooth, additional back-EMF component can be generated which is beneficial to boost the machine performance. Then, the influence of critical design parameters including stator slot opening ratio, split ratio, and stator slot number is investigated, providing a guidance to the design of FRPM machines aiming at maximum output torque. In addition, both finite element analyses and experimental tests are conducted to verify the analytical analyses. For 6-slot-stator FRPM machines, experimental results show that more than 40% higher output torque can be achieved in the machine with optimal number of PM pieces when compared to the conventional one. [ABSTRACT FROM AUTHOR]

The main purposes of this paper consist of two parts. First, the geometric topology of novel modular spoke-type permanent-magnet (MSTPM) machines with two different magnetization modes is introduced. Second, based on the magnetic field modulation (MFM) analysis and finite-element (FE) method, the influence of magnetization mode on MSTPM machines is investigated with respect to the field harmonic, combination of stator slots and rotor poles, back electromotive force, and eletromagnetic torque. A prototype machine is manufactured and tested to verify the MFM and FE predicted results. [ABSTRACT FROM AUTHOR]

The recent novel dc-biased sinusoidal current reluctance machines (dc-biased VRMs) adopt a doubly salient structure and concentrated windings, which is similar to that of switched reluctance machines (SRMs). The special point is that the phase current is in the form of an ac component superimposed with a dc component. Some literary works show that these machines would have better performance than the existing SRMs and variable flux reluctance machines. In this paper, the slot/pole combinations and winding configurations of the dc-biased VRMs are deeply investigated. First, relationships among slots/poles are given based on the operation principles. Then, several feasible slot combinations are obtained, and the electromagnetic performances including magnetizing inductance, virtual back electromotive force, torque quality, and losses are compared by the finite element analysis. Finally, the correctness of the proposed analysis is validated by the experiment on two 12/10 prototypes. [ABSTRACT FROM AUTHOR]

This paper proposes a new method to estimate the electrical parameters of five-phase induction motors based on the response to a step voltage applied to the stator with the rotor at standstill. The first part of the method consists of the identification of the parameters of the dynamic model expressed in terms of transfer functions including the fundamental and third-harmonic components of the airgap induction. The second part consists of an open-phase test proposed to estimate the stator leakage inductances of each circuit separately. Further, the impact of iron saturation on the parameters is discussed through Finite Element Analysis of a case study. The accuracy of the proposed method is experimentally assessed through the analysis of the behavior of a 4.5-kW motor running in a closed loop under Rotor Field-Oriented Control. The theoretical and practical results suggest that the method can also be applied to self-commissioned drives, given that the estimation proceeds under null torque and speed. The prominent advantages of the proposed method are (i) the possibility of tracking the saturation effects on the parameters, (ii) the tests are easy to execute, and (iii) few sensors are required. [ABSTRACT FROM AUTHOR]

This paper proposes several slot-pole combinations of flux-reversal machines (FRMs) with fractional-slot windings (FSWs) to achieve a larger torque density and a lower pulsating torque. First, the general rules for the determinations of the winding pole pair and slot per pole per phase (SPP) are introduced, and then the feasible slot–pole combinations of three-phase FRMs with FSWs are given. Second, the analytical expressions for the back electromotive force (EMF) and torque of fractional-slot FRMs are derived and expressed in terms of machine dimensions. Based on the analytical equations, the effects of rotor pole number, split ratio, slot opening ratio, permanent magnet (PM) thickness, and rotor pole arc on back EMF are investigated and analyzed, which gives a prediction for maximal achievable back EMF and power density of the FRM with FSWs. Third, the proposed 12-slot/14-pole FRM is compared to a conventional 12-slot/16-pole FRM in terms of cogging torque, flux linkage, back EMF, average torque, torque ripple, and efficiency. It is found that the cogging torque and torque ripple of the proposed FRM are 55% and 48% lower than that of the conventional one, respectively. Moreover, the rated torque of the former is also 4% higher than the latter. Finally, the analysis results are verified by the experiments on a 12-slot/14-pole FRM prototype with FSWs. [ABSTRACT FROM PUBLISHER]

Direct-drive permanent magnet (PM) synchronous generators (DDPMSGs) are gaining more and more attention and application for wind power. This paper presents a comprehensive performance comparison of an external rotor surface-mounted PM synchronous generator equipped with three commonly used winding types, i.e., integral-slot distributed winding (ISDW), fractional-slot concentrated winding (FSCW), and fractional-slot distributed winding. The tradeoff between torque and the power factor, loss distribution, current, torque, and PM demagnetization characteristics under a short-circuit fault and the steady temperature rise are investigated and compared using finite-element analyses. It is found that, generally, FSCW PM generators exhibit high rotor losses compared with ISDWs, which will lead to an overly high temperature rise. Measures such as segment PMs and the adoption of lamination steel in the rotor can reduce the rotor loss and greatly improve the machine efficiency. However, the temperature rise of FSCW machines is still higher than that of ISDW machines. The conclusion is intended to help choose the proper winding types. [ABSTRACT FROM AUTHOR]

In this paper, a linear permanent-magnet vernier machine is proposed, in which both magnets and armature windings are placed in the short mover, while the long stator consists of an iron core only. Hence, it is suitable for long-stroke applications such as urban rail transit. The proposed machine integrates two magnetization directions of magnets together, which can reduce leakage flux and enhance flux density. Meanwhile, since different topologies and different slot/pole number combinations have an effect on the winding factor, several general rules are established. It is revealed that the thrust force ripple of the proposed machine is lower than its cogging force ripple, which is explained by a built analytical model. Both the analytical model and the finite-element results are validated by experiments based on a prototype machine. [ABSTRACT FROM AUTHOR]

Removing some sections of the stator yoke in a permanent-magnet brushless machine can be beneficial for reducing punching waste and simplifying motor manufacture. However, in some cases, restricting the possible flux paths, in this way, will have a detrimental impact on the torque and air-gap harmonics. This paper discusses the potential implications of modular stator core arrangements and presents the air-gap flux density harmonics and winding factors for potential slot/pole combinations. Finite-element analysis (FEA) simulations are presented to support the analytical calculations. The analysis indicates that the performance reduction from using a modular stator is minimal when the number of slots and poles are similar but drops off substantially when this is not the case. A modular core stator will increase the MMF subharmonics due to the magnet field but can reduce the subharmonics due to the armature if a single-layer winding is used. The effect of slotting is very similar for a modular and conventional core machine, and FEA results match previously published analytical analyses. [ABSTRACT FROM PUBLISHER]

DC-biased sinusoidal current vernier reluctance machines (dc-biased VRMs) have a doubly salient structure, and their phase currents contain an alternating current (ac) component and a direct current (dc) component. Hence, their main features are one set of concentrated windings compared with variable flux reluctance machines, low vibration and noise due to smooth current, compared with switched reluctance machines, and robust rotor structure. Besides, its achievable high slot fill factor can improve the torque density further. In this paper, based on the flux modulation principles, the torque production mechanism of dc-biased VRMs is analyzed, and two slot combinations of 12/8 and 12/10 are proposed. First, the machine topology and inverter main circuit are illustrated. Second, the torque production mechanism is explained. Furthermore, the inductance characteristic, optimal current configuration for maximum torque and lowest torque ripple are analyzed theoretically and by the finite-element analysis. Finally, one prototype was designed and built, and the proposed analysis is validated by the experimental results. [ABSTRACT FROM AUTHOR]

This paper investigates the rotor design optimization of synchronous reluctance machines (SynRMs) by using electromagnetic and structural finite-element simulations. Three conflicting objectives, i.e., average torque, torque ripple, and sound pressure level, were considered using a surrogate-based multi-objective approach. While the stator is fixed, the rotor flux barriers of a 33-slot 8-pole SynRM were geometrically varied to extract optimal design regions. These regions or constraints help decrease the computational time during the sampling procedure of a multiple-barrier design. Different numbers of flux barriers were studied and related to each other. Adding the sound pressure level was observed to affect previous results by spreading the Pareto front solutions across the design space. [ABSTRACT FROM AUTHOR]

The noise of electrical machines has drawn more attention in recent years due to their harm to people and the environment. Normal skewed slot has proven to be an effective method to reduce vibration and noise of squirrel-cage induction motor. Double skewed slot is superior to normal skewed slot on reducing vibration and noise. However, it is still difficult to meet the requirements of noise standards in some occasions. In this paper, based on double skewed slot, a new skewed slot type is proposed, which can offer a better effect on reducing vibration and noise. 2-D fast Fourier transform and 3-D finite-element method are adopted to analyze and compare the performance of the three types of skewed slots. [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]

This paper proposes a new parallel-hybrid-excited permanent-magnet machine (PHEM) with harmonic-differential (HD) effect, termed HD-PHEM. The key is to place the DC-field windings in the DC pole sandwiched by the two adjacent permanent-magnet (PM) poles, thereby realizing the parallel flux paths of PM flux and DC-field flux. Moreover, the HD effect is created so that the DC-field harmonics can differentiate the effective and ineffective harmonics in the air gap to weaken the resultant effective magnetic field. Consequently, attractive flux-weakening ability and extended speed-operating range can be achieved for electric vehicle propulsion. The machine configuration, operation principle, torque-sizing equation and drive system are introduced first. Then, the harmonic analysis is conducted to elaborate on the HD effect, followed by the finite-element verification. Besides, both the electromagnetic and structural performances of the proposed machine are comprehensively evaluated by finite element analysis. Further, a comparative study is performed between the proposed design and other existing topologies in terms of electromagnetic performances. Finally, an experimental prototype is constructed and tested for verification. [ABSTRACT FROM AUTHOR]

In this paper, a harmonic field current injection method is proposed for torque ripple reduction in 6-stator/4-rotor-pole (6s/4r) variable flux reluctance machines (VFRMs). Initially, the torque production of VFRM is analyzed based on an analytical torque model and harmonic analysis. The torque ripple of 6s/4r VFRM is found to have multiples of third harmonics. Then, one finite-element analysis (FEA)-based and one analytical equation-based method are developed to calculate the magnitude of the injected harmonic current. Both methods are proved to be effective in torque ripple reduction. Finally, the influence of the inductance mismatch on the proposed method is investigated. It shows that the torque ripple reduction performance is not affected much unless the fundamental component of nominal inductance is underestimated. The feasibility and effectiveness of the proposed methods are validated by both 2-D FEA and experimental test. [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]

This paper proposes a new winding layout for high-power medium-voltage nine-phase induction machines (IMs) based on a single-layer concentrated winding layout having a unity winding factor. The machine is fundamentally an asymmetrical nine-phase IM, where phases are connected in such a way as to provide six terminals that are fed from two three-phase inverters. Compared to a conventional asymmetrical six-phase IM with the same stator and copper volumes, it provides improved torque density, a higher torque/current ratio, and a simpler winding layout. Finite-element simulation is used to compare the proposed winding layout with a conventional split-phase six-phase IM to assess the claimed merits. A 1.5-hp prototype IM is also used for experimental verification. The experimental results are given under both healthy and fault conditions, where the faulty converter is completely disabled. The achievable derating factors under this case are then given and compared with those of conventional six-phase IMs. [ABSTRACT FROM PUBLISHER]

This paper proposes a design technique for electric ship traction machines to achieve high torque density and low torque ripple by adopting dual m-phase windings with an appropriate phase shift. Firstly, the general relationship between the slot number and the phase number for dual m-phase windings is investigated. Secondly, the uniform analytical expressions of torque with different phase shifts are derived. Also, the optimal phase shift angle is summarized from the perspective of improving torque performance. Then, the 48-slot and 22-pole permanent-magnet machines for electric ship with different windings configurations are designed. The finite-element method is used to calculate their electromagnetic performances, such as back electromotive force, torque capability, stator magnetic motive force and radial force. Finally, some experiments on the prototype machine for electric ship are carried out for validation. [ABSTRACT FROM AUTHOR]

Owing to bidirectional field modulation effect, dual-permanent-magnet-excited (DPME) machine could offer improved torque capability, which has attracted increasing attention in recent years. However, conventional DPME machine only utilizes a small amount of abundant field harmonics to yield torque, which leads to limited torque enhancement. To solve this issue, a novel DPME machine with enriched working harmonics is proposed in this paper. The key of the proposed DPME machine is to design some non-uniformly distributed permanent-magnets and flux modulation poles on the stator. Thus, increased field harmonics are produced to produce effective torque, offering the potential to enhance torque. Firstly, the topology and feature of the machine are introduced. Moreover, operating principle is analyzed by using air gap field modulation theory. Then, the operating principle and torque enhancement are verified and evaluated by using finite-element method. At last, a corresponding principle machine is fabricated, and some experiments are performed for validation. [ABSTRACT FROM AUTHOR]

Owing to a group of permanent magnets (PMs) with the same magnetization direction are replaced by salient iron core, the consequent-pole (CP) PM machines generally suffer from asymmetry flux density. This will leads to the even-order back-EMF harmonics, which have negative influence on the electromagnetic performance. It is widely known that the even-order back-EMF harmonics cannot be eliminated for the machines with odd back-EMF phasor belongs to one phase in one machine periodicity, i.e., ${\boldsymbol{N}_0}$ is odd (${\boldsymbol{N}_0} = {\boldsymbol{N}_{\boldsymbol S}}/\boldsymbol{mt}$ , where ${\boldsymbol{N}_{\boldsymbol S}}$ is the number of slot for one machine, t is the unit sub-machine periodicity, m is the number of phase). Hence, this paper proposes a general modularization method solving this problem. The elimination principle of even-order back-EMF harmonics in the modular stator (MS) is explained by the star of slots. Further, the MS with auxiliary winding (AW) and auxiliary teeth (AT) are proposed to improve the electromagnetic performance of the MS CP (MSCP) PM machine. Then, the electromagnetic characteristics, including open circuit field distribution and back-EMFs, torque characteristics, unbalanced magnetic force (UMF), loss distribution characteristics as well as efficiency contours are comprehensively compared. Finally, the MSCP PM machine with auxiliary winding (MSCP-AW) is fabricated and tested to verify the theoretical analysis as well as the finite element (FE) results. [ABSTRACT FROM AUTHOR]

Multi-turn resolvers are employed in the applications that high reliability; high accuracy and absolute position measurement are required, simultaneously. They are basically consisted of two individual resolvers in a common frame. In this paper a novel sinusoidal air-gap length multi-turn resolver is proposed. The rotor shape and the winding configuration are designed to achieve single-speed and multi-speed operations using a single rotor and a single stator core. Furthermore, some constraints are laid down and discussed in such a way that the performance of two resolvers has no interference with each other. All the mathematical calculations are validated using time stepping finite element analysis. Finally, a prototype of the sensor is built and tested. Experimental measurements are used to verify the analytical and finite element discussions. [ABSTRACT FROM AUTHOR]

This paper analyzes the electromechanical characteristics of a novel shell-like spherical induction machine with multiple degrees-of-freedom (DOF), formed by a shell stator and a spherical hollow rotor. The shell-like induction machine is evaluated using n-harmonic analytical models for its electromechanical characteristics. The electromechanical model includes the distribution of the copper windings in the stator slots, incorporating the currents harmonic content to describe its spatial distribution. The distribution of the magnetic potential vector and the components of the magnetic flux density are computed using the real source-current distribution. A small prototype was built to validate the analytical model. To do so, experimental tests were done to the magnetic flux density and the torque. The shell-like induction motor is concretized as traction motor in an electric wheel-chair. Its results are compared with a finite-element analysis tool. [ABSTRACT FROM PUBLISHER]

This paper proposes a six-phase surface-mounted permanent-magnet machine with a 24-slot/10-pole fractional slot winding, which not only eliminates the air-gap flux subharmonics, but also minimizes the effect of slot harmonics, which highly affect both the core and magnet losses. The six-phase winding design also offers an improved drive train availability for electric vehicle applications due to its inherent high fault-tolerant capability. When compared with a three-phase design, the proposed winding offers approximately 3.5% improvement in torque density, a significant reduction in both the core and magnet losses, and an improved overall efficiency. The proposed winding is deduced based on the stator shifting concept of two 12-slot/10-pole stators with single tooth windings. The coil span of the resulting machine will be two slots, which stands as a compromise between single tooth and distributed windings. The concept of stator shifting is first presented, and then, a prototype machine is designed and simulated using the 2-D finite-element analysis to validate the proposed concept. A comparative study is also carried out to compare six-phase and three-phase designs with the same slot/pole combination and also with the 18-slot/10-pole combination, which was recently shown to be a competitive alternative. [ABSTRACT FROM AUTHOR]

In this paper, the magnetic gearing principle is extended to the flux-switching permanent magnet (FSPM) motor for its armature winding configuration design. First, the no-load flux density in motor air gap is qualitatively analytically calculated using the equivalent magnetic circuit method, so that the predominant space harmonic components (PSHCs) can be separated. Then, the slot vector graph can be drawn according to the pole-pair numbers and rotation directions of these PSHCs. Consequently, the armature winding configuration of a 12/10-pole FSPM motor is designed based on the slot vector graph using the conventional motor design method. In addition, two new 12/7-pole FSPM motors with the conventional non-overlapping concentrated and distributed winding are proposed, and the electromagnetic performances of the three motors are analyzed and compared. Finally, the analytical results are verified by the finite-element analysis and experimentation. [ABSTRACT FROM AUTHOR]

This paper proposes a novel linear permanent-magnet (PM) vernier machine, which offers high force density, high efficiency, simple structure, and low cost. The novelty of the proposed machine is substantiated by integrating appropriate magnetization directions of PMs in the armature core. First, the structure and the operation principle of the proposed machine are descried. The machine is subsequently designed for a given set of specifications and its electromagnetic performances are analyzed by time-stepped transient finite-element method. An analytical equation is derived for evaluation of the thrust force ripple. Finally, experiments on a prototype of the proposed machine are carried out for validation. [ABSTRACT FROM AUTHOR]

This paper proposes a novel cogging torque mitigation method for modular permanent magnet (PM) machines with flux gaps in alternate stator teeth. The slot openings (SOs) of the modular PM machines are divided into two groups in a special way. By shifting the SOs of two groups in opposite directions with the same angle, the machine cogging torque can be significantly reduced. An analytical formula of the desired shift angle is derived, and can be applicable to other modular machines with different slot/pole number combinations. Meanwhile, the influence of the proposed method on phase back electromotive force (EMF) is investigated, and the three-phaseback EMF waveforms remain balanced for all slot/pole number combinations after slot shifting. Experiments based on the existing prototypes are carried out to validate the finite-element modeling. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel magnetic-geared tubular linear machine for tidal and wave energy conversion. The key of the proposed machine is to embed the armature windings into slots adjacent to the modulating segments of a linear magnetic gear (LMG). The compact component designed can serve simultaneously as the modulating poles in the LMG and the armature stator in the generator. When compared with its existing counterparts, the proposed machine has an improved force density and a simpler mechanical structure by virtue of its gearing effect. Moreover, Halbach permanent-magnet (PM) array is used to build up the PM arrays in both the inner mover and outer mover of the LMG, resulting in increase in thrust force density, reduction in cogging force, and high machine efficiency. The working principle of the proposed machine is introduced, and the electromagnetic performance is investigated quantitatively using the time-stepping finite-element method. [ABSTRACT FROM AUTHOR]

This paper proposes a new topology of a variable-flux pole-changing permanent magnet (PM) memory machine. The fractional-slot concentrated windings are employed in the stator side, which can increase the utilization ratio of winding under different pole modes. The neodymium–iron–boron PM poles and aluminum–nickel–cobalt (AlNiCo) PM poles are hybridized in the rotor side. The proposed machine features the capability of its pole number to switch back and forth between six poles and two poles through changing the magnetization directions of AlNiCo PMs via the stator winding. Besides, the air gap flux can be flexibly adjusted by varying the amplitudes of magnetization current pulses. The topology and design principle of the machine are described in detail, and the electromagnetic characteristics, including magnetic field distributions, air-gap flux density, as well as back electromotive force (EMF), in different operation modes are computed using a finite-element method. Due to the existence of the fifth harmonic component of back EMF, the torque quality is improved through injecting the fifth harmonic current under different magnetized levels of AlNiCo PMs. Besides, the field regulation capabilities in both the pole modes are analyzed. [ABSTRACT FROM AUTHOR]

This paper presents the design characterization, optimization, and experimental validation of a multilayer ac winding that provides a high quality rotating MMF with reduced end-turn length. Harmonics in the airgap MMF have been characterized with standard winding functions and verified using finite element analysis (FEA). The multilayer winding design is optimized for a commercial premium efficiency/IE3 benchmark machine using grid multiobjective genetic algorithm (GMGA) and a prototype has been built. Performance of the designed motor has been verified with both FEA and experiments. Evaluation under IEEE 112 test standard demonstrates that by only updating its stator winding design, the designed motor can achieve IE4 class efficiency under the same frame size and cooling type as its IE3 class benchmark. [ABSTRACT FROM AUTHOR]

This paper presents for the first time the analysis and experimental validation of a six-slot four-pole synchronous reluctance motor with nonoverlapping fractional slot-concentrated windings. The machine exhibits high torque density and efficiency due to its high fill factor coils with very short end windings, facilitated by a segmented stator and bobbin winding of the coils. These advantages are coupled with its inherent robustness and low cost. The topology is presented as a logical step forward in advancing synchronous reluctance machines that have been universally wound with a sinusoidally distributed winding. The paper presents the motor design, performance evaluation through finite element studies and validation of the electromagnetic model, and thermal specification through empirical testing. It is shown that high performance synchronous reluctance motors can be constructed with single tooth wound coils, but considerations must be given regarding torque quality and the d-q axis inductances. [ABSTRACT FROM AUTHOR]

One of the main drawbacks of nonoverlapped coils in fractional slot concentrated winding permanent magnet (PM) machines are the high eddy current losses in both rotor core and permanent magnets induced by the asynchronous harmonics of the armature reaction field. It has been shown in the literature that the reduction of low space harmonics can effectively reduce the rotor eddy current losses. This paper shows that employing a combined star-delta winding to a three-phase PM machine with fractional slot windings and with a number of slots equal to 12, or its multiples, yields a complete cancellation to the fundamental magneto-motive force (MMF) component, which significantly reduces the induced rotor eddy current. Besides, it offers a slight increase in machine torque density. A case study on the well-known 12-slot/10-pole PM machine is conducted to explore the proposed approach. With the same concept, the general $n$ -phase PM machine occupying $4n$ slots and with a dual $n$ -phase winding is then proposed. This configuration offers a complete cancelation of all harmonics below the torque producing MMF component. Hence, the induced eddy currents in both rotor core and magnets are significantly reduced. The winding connection and the required number of turns for both winding groups are also given. The concept is applied to a 20-slot/18-pole stator with a dual five-phase winding, where the stator winding is connected as a combined star/pentagon connection. The proposed concept is assessed through a simulation study based on 2-D finite element analysis. [ABSTRACT FROM AUTHOR]

A model of permanent-magnet synchronous machine (PMSM), including the electromagnetically originated torque ripple, is presented in this paper. This unique representation of such equivalent circuit is highly critical to understand the torque ripple content and to develop an appropriate mitigation scheme for low torque ripple applications requiring four quadrant operations. This research proposes a method to quantify the various sources of torque ripple and modifies the existing dq-model to enhance the modeling capabilities for both surface-mount and interior PMSMs. Finite-element (FE) analysis is used for modeling various PMSMs to verify the lumped circuit model proposed in this research. The theoretical results obtained from analytical and FE analysis are validated using experimental test. [ABSTRACT FROM AUTHOR]

Fractional-slot concentrated-winding (FSCW) permanent magnet (PM) machines have been widely studied in recent years. This is mainly due to the several advantages, including high power density, high efficiency, short end turns, high fill factor, low cogging torque, good flux-weakening and fault-tolerant performance. However, the key challenges of utilizing FSCW-PM machines are the abundant stator magnetomotive force (MMF) harmonics. In this paper, the multiphase star–delta hybrid connection (SDHC) windings configuration that can eliminate some stator MMF harmonics is systematically studied. First, the general relationship between the number of slots and phases which are appropriate for the SDHC windings configuration is derived. In addition, the particular principle of the MMF harmonics elimination by the SDHC windings configuration is researched. In order to verify the analysis results, four three-phase SDHC FSCW-PM machines with different slot–pole combinations are built and calculated by the finite-element method. Finally, experiments on a prototype three-phase 12-slot ten-pole FSCW-PM machine are carried out for validation. [ABSTRACT FROM AUTHOR]