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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]

Incipient stator winding fault in permanent magnet synchronous wind generators (PMSWGs) is very difficult to be detected as the fault generated variations in terminal electrical parameters are very weak and chaotic. This paper simulates the incipient stator winding faults at different degree of insulation degradation of one turn in the winding of a PMSWG. Cosimulation method by combining finite element model and external circuits is used. Hilbert–Huang transformation is applied to detect the very early stage fault in interturn insulation by analyzing the stator current. Detection results show that the minimum detectable severity degree of interturn fault in this paper is 0.1488%, which is much better than the best record in the literature. [ABSTRACT FROM AUTHOR]

A new type of three-phase stator hybrid excited machine with permanent magnets (PMs) located at the slot openings of field winding slots is presented in this paper. It has the advantage of good flux regulation capability due to the field excitation. The machines with different stator/rotor pole combinations, i.e., 6-stator pole and 7-/8-/10-/11-/13-/14-rotor poles, have been comparatively investigated in terms of the open-circuit and on-load characteristics, as well as the influence of dc current and the unbalanced magnetic forces. The 2-D finite element analysis (FEA) has been employed for analysis and optimization of the machines together with experimental validation. [ABSTRACT FROM AUTHOR]

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]

Double-Sided Linear Flux-Switching Permanent Magnet (DSLFSPM) motor has the merits of high efficiency, high power factor and low-cost stator structure. But the speed range of DSLFSPM is limited due to its adoption of permanent magnets. Double-Sided High Temperature Superconducting Linear Flux-Switching Motor (DSHTS-LFSM) adopts HTS coils to replace the permanent magnets, thus obtaining better power density and wider speed range. However, when the magnetic field gets much stronger, the iron core is easily saturated and flux leakage gets serious, which threatens the reliability of HTS coils and lowers the utilization of iron core. To solve this problem, a novel Double-Sided High Temperature Superconducting Linear Modular Flux-Switching Motor (DSHTS-LMFSM) is proposed. The armature windings are designed different from existing DSHTS-LFSMs to reduce flux leakage. Furthermore, by sealing the HTS coils together in a Dewar away from armature windings, the reliability is improved. In this paper, the structure and working principle of the proposed DSHTS-LMFSM is explained. The electromagnetic performance of it is calculated using Finite Element Method (FEM). As evaluation, its performance is compared against a traditional DSHTS-LFSM. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of stator/rotor pole number combinations and permanent magnet (PM) numbers on electromagnetic performance of consequent-pole hybrid excited flux reversal machines (CP-HEFRMs), which have different numbers of PM poles and iron poles and concentrated AC and DC windings on the stator and a salient pole rotor. PMs in the slots of one stator pole are magnetized radially in the same direction, while opposite on adjacent stator poles. Magnetic field paths of DC, PM, and hybrid excitations are investigated. The phenomenon of flux cancellation, i.e., PM and DC MMFs in CP-HEFRMs are of opposite polarities in the flux-enhancing operating mode, is revealed and verified, for the first time, as the key feature that makes CP-HEFRMs different from other hybrid excited machines. Consequently, the saturation in stator pole and yoke can be mitigated and hence the overload capability of DC excitation is enhanced, which is verified by finite element analysis (FEA). Global optimizations are utilized to obtain the optimal rotor and stator pole number combinations and PM numbers for each stator pole. Torque, torque ripple, inductance, unbalanced magnetic force, and flux regulation capability are compared for different PM numbers and rotor pole numbers. Comparisons are made on consequent-pole and non-consequent-pole topologies in terms of torque capacity, flux regulation capability, and PM consumption to further illustrate the advantages of consequent-pole topology. A prototype machine is built and tested to validate the analyses. [ABSTRACT FROM AUTHOR]

Linear permanent magnet Vernier machines (LPMVMs) is an attractive solution for stroke and direct-drive applications. Several LPMVM topologies have been presented for different applications that operate based on magnetic flux modulation. LPMVMs have some advantages including high force, and torque density at low speeds. This paper introduces a double-excited linear Vernier machine for wave energy conversion. To model the machine, finite element analysis and nonlinear equivalent network model are used. To improve the accuracy of the model and compact the network, a new meshing method is proposed. For better continuity in the output waveforms of the machine, special positioning is utilized. The end-effect is modeled using two separate networks. Finally, the modeling and simulation results are compared with each other and validated experimentally. [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 presents a novel modular stator hybrid-excited synchronous machine with stator slot permanent magnets (PMs). By regulating the field current, the magnetic field, and consequently the back electromotive force, as well as the average torque can be controlled. The existence of stator slot PMs alleviates the magnetic saturation and improves the flux regulation ratio. The frozen permeability method is employed to investigate the torque contributions by different magnetic sources. Possible stator and rotor pole combinations are illustrated, and the corresponding electromagnetic performances are evaluated with the finite-element method. It is revealed that 12-stator pole machines with 11- and 13-rotor poles exhibit superior average torque and lower torque ripple due to even-order harmonics elimination. Finally, a prototype with modular stator segments is manufactured to validate the analyses and simulations. [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 transverse flux permanent-magnet (PM) linear machine has attracted much attention in high-performance direct-drive applications because of its high torque density and efficiency. However, due to its inherent large open-circuit flux leakage, the prominent cogging force makes it difficult to obtain a high accuracy in position and speed control, which restricts its potential for precision industrial processing applications. To overcome this problem, a novel transverse flux linear machine is proposed in this paper. The key is by creatively combining a consequent-pole mover design and a stator-segment-interlacing configuration in such a way that a parallel and complementary transverse magnetic circuit is realized for the moving PMs, which can effectively minimize the open-circuit leakage flux and cogging effect. In this paper, the machine structure, operation principle, and theoretical modeling are introduced, with its electromagnetic performance evaluated by using the finite-element method. A prototype is also built for the experimental verification, and relevant test results agree well with the finite-element predications. [ABSTRACT FROM AUTHOR]

Permanent-magnet vernier machine has an excellent potential for electric vehicles due to its desirable features of a simple mechanical structure and high torque density, whereas the poor power factor is its main drawback. In this paper, a spoke-type permanent-magnet vernier machine is designed and optimized for torque density and power factor improvement. First, the machine structure, operation principle, and sizing equation are introduced. Then, the machine is optimized by a multi-objective genetic algorithm. To enhance the optimization efficiency and accuracy, multi-level, sensitivity analysis, and approximate model technologies are employed in the optimization. It is shown that the improved torque density and power factor are achieved in the optimized machine as compared to the initial one. Finally, a prototype machine is built, and the experiments on the prototype machine are carried out to verify the design optimization. [ABSTRACT FROM AUTHOR]

Compared with rotary electrical machines in linear drive applications, linear machines without rotary–linear motion conversion equipment can have higher force density and efficiency. Linear superconductivity machines (LSMs), consisting of high-performance superconducting magnets instead of permanent magnets, can offer very high force density and efficiency compared with other linear machines, such as linear induction machine, linear permanent magnet machine, and so on. In this paper, LSMs with different stators and winding configurations are investigated, specifically LSMs with concentrated or distributed windings, and unilateral or bilateral side stators. The electromagnetic parameters and performance of these LSMs are calculated and compared by using the finite element method, and then, the main difference between various design methods in LSM has been presented. [ABSTRACT FROM AUTHOR]

A novel dual-stator bidirectional-flux modulated permanent magnet (PM) machine is presented in this paper. The key of the design is to locate consequent PM poles in both stator and rotor sides and the merit is that the magnetic flux produced by either the rotating or stationary PMs and dual-stator windings can be modulated by the stator teeth and rotor iron segments. It is shown that with this flux modulation effect and improved reluctance torque effect, the torque density of the machine can be increased. The bidirectional flux modulation theory and operation principle of the machine are explained and analyzed using time-stepping finite element method. [ABSTRACT FROM AUTHOR]

This paper proposes and analyzes a novel radial partitioned stator HTS-excitation flux-switching (RPS-HTSFS) machine. The key is that the single ring-shaped HTS-excitation coil is independently placed in the coaxial claw-pole outer stator while the armature windings are wound around the U-shaped iron core on the inner flux-switching armature stator without permanent magnets. This solution has been explored to realize the physical isolation of armature winding and excitation winding, relieving the influence of armature field on the HTS-excitation coil. Moreover, only a single ring-shaped HTS-excitation coil is employed, therefore, reducing the HTS wires and the bending strain of the HTS-excitation coil. Also, the special refrigeration system can realize stationary seals of the double-layer ring-shaped cooling Dewar pattern, improving the cooling performance. By using the three-dimensional finite element analysis (3D-FEA), the machine performances are investigated and the validity of the proposed machine is verified. [ABSTRACT FROM AUTHOR]

In this paper, three partitioned-stator (PS) machines, namely the PS flux-switching permanent-magnet (PS-FSPM) machine, the PS-FS hybrid-excitation machine, and the flux adjuster PS-FSPM (FA-PS-FSPM) machine are proposed for the hybrid electric vehicles (HEVs). Owing to the installation of additional inner-stators, all three proposed machines can offer satisfactory power and torque densities. In particular, the FA-PS-FSPM machine artfully utilizes its inner space to accommodate the mechanical FAs, such that outstanding flux-weakening capability for wide-speed range operation can be achieved. To verify the proposed concept, the established machines are purposely compared with the profound Prius HEV machine based on finite-element method. [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]

A dual-stator hybrid-excited switched-flux (DS-HESF) machine, which is based on the conventional SF permanent magnet machine but employs a secondary stator to accommodate the field windings, is proposed in this paper. The DS-HESF machine inherits the robust rotor and benefits from a better space utilization. The topology and operating principle of the proposed machine are introduced in detail. Based on the 2-D finite-element analysis, the comparison between the DS-HESF machines having different rotor pole numbers is carried out, accompanied with a conventional HESF machine as a baseline. The results reveal that the DS-HESF machines exhibit not only higher torque density but also a better flux regulation capability. The prototype is manufactured and tested to validate the predictions. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel flux reversal linear-rotary permanent magnet actuator (FR-LRPMA) with permanent magnets (PMs) mounted on the stator surface. The proposed FR-LRPMA uses only 50% of the PM materials when compared with that of the topology with four-PM poles in a conventional stator pole actuator. The FR-LRPMA provides a pathway for the magnetic field, which is generated by currents in the armature winding, resulting in substantial reduction in the possibility of irreversible demagnetization of the PMs to increase its torque density. According to the physics of PM demagnetization, a simplified fitting analytical expression, which considers the angular velocity, current, temperature, and PM thickness, is derived to determine the least work point of the PM. The torque prediction using the proposed algorithm at different currents agrees well with the values calculated using a finite-element method. It also confirms that the novel topology has a larger torque density. [ABSTRACT FROM PUBLISHER]

This paper investigates the appropriate permanent magnet (PM) arrangement of novel flux-modulating synchronous machines (FMSMs) in which PMs are embedded in the stator back iron. Using finite element analysis (FEA), three types of FMSMs with different PM arrangements are designed, and their performance characteristics are compared. As a result of the investigation, it was found that the FMSM with a V-shaped PM arrangement has a higher torque capability than do other FMSMs. The accuracy of the FEA simulations was confirmed through experiments on a prototype machine. [ABSTRACT FROM AUTHOR]

In this paper, a new stator-permanent magnet (PM) bearingless machine (SPMBM) is proposed. Its suspending windings, armature windings, and PMs are in the stator, while no PMs or windings are in the rotor. However, it is the focus in establishing an accurate mathematical model of radial suspension force to levitate the rotor stably by directly and effectively controlling the rotor eccentric displacement. First, operating principle and air-gap flux density distributions of the SPMBM are analyzed in detail. Then, an accurate mathematical model of radial suspension force is deduced by the Maxwell stress tensor method, and it is verified by the 2-D finite-element method (FEM). Results are consistent both by the radial suspension force mathematical models of the SPMBM and FEM. [ABSTRACT FROM AUTHOR]

An analytical model is proposed for the prediction of electromagnetic quantities of slotted flux-reversal permanent magnet (FRPM) machines. Equivalent current theory is used to model the effects of permanent magnets (PMs), stator slots and rotor grooves. First, the stator slots and rotor grooves are nullified and the Poisson equation is solved in a slotless stator and cylindrical rotor machine. The effects of the stator slots and rotor grooves are then considered by injecting equivalent magnetization currents (EMCs) respectively on the stator slots wall and on the rotor groove edges. The PMs are also replaced by EMCs. Finally, the results of the proposed analytical model are verified by means of the finite element analysis. [ABSTRACT FROM AUTHOR]

This article proposes an analytical model of modular spoke-type permanent magnet (MSTPM) machines based on air-gap field modulation (AFM) theory. Firstly, a fundamental AFM model of open-circuit MSTPM machines is introduced. The open-circuit air-gap field of MSTPM machines is determined by three fundamental elements including the primitive magnetizing magnetomotive force (MMF) produced by permanent magnet (PM), and two modulators which consist of stator and rotor permeance. The analytical MMF excited by PM (PM-MMF) can be calculated by using magnetic circuit method, while the stator and rotor permeance models are developed based on relative permeance (RP) method. Thereafter, a general model is proposed to calculate the open-circuit back electromotive force (EMF) of MSTPM machines. Further, the winding inductance model is established on the basis of equivalent magnetic circuit method and RP model. Finally, the machine performance is predicted by the analytical model, and verified by both finite element analysis (FEA) and experimental results. [ABSTRACT FROM AUTHOR]

In this article, an axial-flux permanent-magnet (PM) Vernier machine with the triple-stator, spoke-type PM rotor, and toroidal winding wound on the innerstator is proposed. Benefited from the flux focusing spoke-type PM rotor and short end length toroidal winding, the proposed machine has a high torque density and the improved power factor. Based on the air-gap permeance function, the analytical expression of the proposed machine is derived to qualitatively analyze the machine's performance. The quasi-three-dimensional (3-D) finite element analysis (FEA) is adopted to optimize the design parameters, such as innerstator diameter, PM thickness, and slot opening width. The quasi-3-D FEA results match well with the 3-D FEA. The 3-D FEA results show the torque densities of the proposed machine reach 49.4 Nm/L and 11.4 Nm/kg, respectively, under the 232 A/cm average electrical loading. The performances, such as overload capacity, PM demagnetization, and PM and core losses, are also analyzed by 3-D FEA. The comparison with the other axial-flux PM Vernier machine is conducted, and the results reveal that the proposed machine has the great advantages of the torque density and power factor. Since the prototype is not built, in this article, the assembly scheme and thermal behavior of the proposed machine are discussed. [ABSTRACT FROM AUTHOR]

This article presents a new type of surface-mounted three-phase permanent magnet synchronous motor with the same number of poles and slots which has obvious advantages in cogging torque. Since the same-pole and same-slot three-phase permanent magnet motor has three or more slot types and the slots are not evenly distributed on the circumference, this article adopts an accurate subdomain model that considers the position and slot width of each slot separately to perform an analytical calculation of the magnetic field. The motor is divided into three subdomains and modeled by Maxwell’s equations, and the magnetic scalar vector equation satisfied by each subdomain is solved by the method of separation of variables. A 24-pole 24-slot three-phase permanent magnet motor consisting of 13-pole 12-slot and 11-pole 12-slot is used to verify the correctness of the proposed analytical computational model. Compared with the finite element analysis, the proposed analytical model shows high accuracy in the calculations of the magnetic flux density of the three subdomains. [ABSTRACT FROM AUTHOR]

In this article, two double flux modulation permanent-magnet machines (DFMPMs) with PMs on both stator and rotor are introduced. The two DFMPMs share a similar operation principle. However, due to the different stator-PM arrangements, the two DFMPMs show different performances. In order to analyze their performance characteristics, their analytical models are built and verified by finite element analysis (FEA). Moreover, to quantitatively compare their electromagnetic performances more accurately, the two DFMPM topologies are optimized, respectively, and compared in terms of back-EMF, cogging torque,rated torque, torque ripple, power factor, and efficiency. Finally, the DFMPM topology with relatively better performances is built and tested. The experimental results match well with the FEA simulations. [ABSTRACT FROM AUTHOR]

This article investigates the total demagnetization fault in Axial Flux Permanent Magnet (AFPM) synchronous generator, suitable for wind power applications, using the three-dimensional Finite Element Method (3D-FEM). The machine, in which the demagnetization diagnosis has been investigated, consists of one coreless stator with concentrating winding, embed in resin and two rotors. In the current study, faulty cases of different number and relative position of total demagnetized magnets are studied. Finally, simulation results are compared to experimental results for validation. The stator current spectrum is studied as fault identification mean and it is shown that the fault signatures depend on the number of total demagnetized magnets, the relative position of the magnets on the rotor and the stator winding topology. In addition, there is an investigation of the partial demagnetization fault for comparison purposes. Moreover, analytical expressions for the magnetic flux density in the healthy case and in every faulty case are exported. These novel expressions, related to every demagnetized case, are presented for the first time in the literature. [ABSTRACT FROM AUTHOR]

This article presents a comprehensive design methodology to improve the field weakening (FW) operation of low inductance slotless permanent magnet synchronous machines (PMSMs). The proposed concept of using a stator embedded inductor integrated with the torque producing machine windings helps achieve a wide constant power speed range (CPSR) and a desired torque/speed characteristics. Key performance parameters including system efficiency and PWM induced current ripple are summarized for scenarios with and without the embedded inductor in the entire operating range using 2-D finite element analysis. The concept helps to achieve the desirable extended torque/speed range. It also helps to improve the efficiency beyond the base speed operation for a high speed, high power machine. In addition to achieving desired CPSR, this method also helps to reduce the PWM induced current ripple, short circuit current, and current ripple induced core losses. A slotless machine with the integrated embedded inductor has been designed following the proposed design guidelines to extend the CPSR, and a prototype motor has been built to validate the simulation results with the experimental results. [ABSTRACT FROM AUTHOR]

Transverse flux permanent magnet (TFPM) machine possesses the characteristic feature of decoupled electric load and magnetic load to obtain high power density. A novel TFPM generator (TFPMG) with double C-hoop stator and flux-concentrated rotor is proposed for low-speed applications, such as direct-drive power generation, which has larger torque capability and more poles than traditional double-side TFPMGs. The structure and operation principles of the generator are described in detail. The 3-D finite-element method (3-D FEM) is employed to compute the no-load magnetic field distributions. The analytical results, including flux density waveform, electromotive force (EMF) waveform, and inductance waveform of the armature winding, are obtained to verify the principle and feasibility of the proposed generator. The cogging torque is also analyzed and optimized by the 3-D FEM. A prototype is fabricated, and some experiments are conducted. The experimental results of back EMF and waveforms of current and voltage with different loads verify the FEM analysis previews well. [ABSTRACT FROM AUTHOR]