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Due to the enhanced air gap flux density and eddy currents in the favorable path, eddy current brakes with slotted conductors have attracted more attention in recent years. However, due to the increased difficulty in analytical modeling, there is currently no suitable analytical model available for the optimization design of eddy current brakes with slotted conductor. To solve this problem, an improved analytical model is provided based on the subdomain model and the least squares method in this article. The proposed analytical model considers slotted conductor disk, magnetic saturation of primary core and actual path of eddy currents in the conductor disk. The accuracy of the proposed analytical model is verified by finite-element method (FEM) and experimental measurement. The results show that the improved analytical model has good accuracy in the entire speed range. As the analytical model takes less computational time than three-dimensional FEM, it can be used as an effective tool for the optimization design. [ABSTRACT FROM AUTHOR]

Compared with the conventional permanent magnet (PM) machines, the flux-switching permanent magnet (FSPM) machine exhibits higher torque ripple due to its special doubly salient structure and high air-gap flux density, leading to the deterioration of smooth operation. In this article, the output torque ripple suppression methods of FSPM machines from both rotor and stator sides are proposed with the aid of general air-gap field modulation theory. According to harmonic modulation mechanism, air-gap PM field can be modified by revising harmonic content of rotor and stator modulation functions and, consequently, three concepts, including cos-shaped edge rotor (CSER), cos-shaped edge stator, and double cos-shaped edge, are proposed and implemented to suppress the output torque ripple due to the cogging torque and electromagnetic torque ripple of FSPM machines. Finally, finite-element analysis and experiments are conducted to verify the proposed approaches. The results reveal that the CSER method exhibits the most effective suppression effect. [ABSTRACT FROM AUTHOR]

Permanent magnet Vernier motors (PMVMs) possess the advantage of high torque density for high-performance applications. However, the low power factor challenge makes it unacceptable for direct-drive applications. A lack of accurate modeling method based on the motor sizing law, i.e., air-gap flux density, linear current density, and motor geometry parameters, raises difficulties for machine designers to further conduct research on the performance metrics. This article presents a deep investigation into the analytical modeling technique for surface PMVMs (SPMVMs). It can identify an accurate approach to obtain the performance metrics, including electromagnetic torque and power factor. The modeling technique is developed based on the conformal mapping method. By using this, both radial and tangential permeability functions can be calculated to obtain the motor magnetic loading accurately, considering the leakage flux. The slotting effect on both air-gap flux density and armature-winding function is analyzed to achieve a precise formula for torque and power factor computations. The new modeling technique is applied to integral-slot SPMVMs with different slot/pole combinations, gear ratios, slot openings, and magnet thickness to evaluate the impacts of motor parameters on high-power-factor and high-torque-density designs. Finally, an SPMVM with the characteristics of high torque density and power factor is fabricated to verify the analytical model at the power rating of 0.8 kW and the speed of 500 r/min. The experimental results show that the prototype exhibits a high power factor of 0.9 and high torque density 22.5 Nm/L. [ABSTRACT FROM AUTHOR]

Variable reluctance resolvers (VRRs) have been widely used for rotor position detection in harsh working conditions. However, conventional installation of VRRs inevitably occupies the axial space of machine systems, and may weaken the reliability of rotor position detection encountering shock and vibration. In this article, a novel VRR structure with inner stator is investigated, which is radially integrated inside a permanent magnet synchronous machine (PMSM) to construct compact machine topology. The hybrid machine topology is first discussed, and detailed electromagnetic design is carried out. Improved analytical analysis on air gap flux density distribution and inductance evaluation of the integrated VRR is derived based on modified winding function approach, and testified by finite element analysis. A prototype is manufactured from an existing 2.2 kW PMSM, and experiments are conducted to validate the effectiveness of proposed machine topology. [ABSTRACT FROM AUTHOR]

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

The mechanism of torque ripple generation by time and space harmonic magnetic fields in permanent magnet synchronous motors is investigated to obtain advanced motor designs. The general expression between the torque ripples and harmonic air-gap flux densities in the motor is derived by using Maxwell stress tensor. Both the numerical and experimental verifications of this expression are carried out. By using this expression, the difference of the torque ripple generation between the surface and interior permanent magnet synchronous motors are discussed. Based on these investigations, the shape of the rotor surface of an interior permanent magnet motor is optimized. It is clarified that specific harmonic components of thetorque ripples in interior permanent magnet synchronous motors can be reduced to be nearly zero by optimizing the rotor surface shape. [ABSTRACT FROM AUTHOR]

To address the contradiction between dynamic performance and robustness of the enhanced linear active disturbance rejection control (ELADRC) method, a fuzzy-ELADRC method for a bearingless induction motor (BIM) is proposed. First, based on the air-gap flux oriented control, the first-order and second-order ELADRC are designed for the torque system and the suspension system of the BIM, respectively. Second, a fuzzy controller is introduced to adjust the controller bandwidth and observer bandwidth of ELADRC online. The fuzzy rules are established by analyzing the influence of ELADRC with different bandwidths on the BIM system, and adaptive initial bandwidth is adopted to improve the variable speed performance of the BIM. Finally, the simulation and experimental comparisons of the PID control method, the ELADRC method, and the fuzzy-ELADRC method are carried out. The results show that the proposed method not only realizes the rapid and stable suspension of the rotor, but also effectively improves the starting performance, variable speed performance, and antidisturbance performance of the BIM system. [ABSTRACT FROM AUTHOR]

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

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

This article proposes a new hybrid-excited partitioned stator flux modulated machine with a dual-permanent magnet (HE-PSFMDPMM). The HE-PSFMDPMM employs consequent-pole (CP) permanent magnets (PMs) on the inner stator and Halbach array CP PMs on the rotor, which can yield abundant air-gap flux density working harmonics to increase the torque capability. Meanwhile, the field windings are housed in the inner stator to achieve flux weakening. The topology, working principle, and design optimization of HE-PSFMDPMM are investigated, respectively. The electromagnetic performances of HE-PSFMDPMM are analyzed and compared with that of a contrast model with conventional CP PMs on the rotor. The results indicate that by using dual-PM excitation, HE-PSFMDPMM can provide large flux linkage, high torque production with low torque ripple, and high efficiency. Meanwhile, a good flux weakening capability is obtained with the aid of direct current (dc) excitation. Moreover, compared with the contrast model, the proposed HE-PSFMDPMM with Halbach array CP PMs on the rotor can offer the merits of lower cogging torque and torque ripple, higher power factor, and better flux weakening capability. [ABSTRACT FROM AUTHOR]

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

In recent years, Vernier permanent magnet machines (VPMs) have gained much interest in academia. However, due to the large leakage flux, the power factor of Vernier machines is too low to be applied in real industry. In this article, a novel split-tooth, concentrated-winding Vernier machine using ferrite magnets is proposed for high-torque, low-speed direct-drive applications in home appliance industry. It uses consequent-pole magnets in the rotor, as well as additional assisted magnets in the stator teeth, in order to reduce the leakage flux and boost the torque density. A systematic way of reducing the torque ripple from 40% to 4% is proposed by carefully choosing the right combination of stator/rotor pole-pair numbers. A comprehensive design optimization is conducted to achieve the optimal performance. Finally, the ac loading is carefully reduced to meet the torque, saturation, power factor and space requirements. The test results of a prototyped machine show that the proposed design can achieve 34% more torque and 20% less loss with a reasonable power factor of 0.63, compared with an optimized PM synchronous machine under the same volume. It is found that the significant torque boost is attributed to the multiple working harmonics of the air-gap flux density. [ABSTRACT FROM AUTHOR]

Spoke structure can increase the torque density of coaxial magnetic gear (CMG). However, the outer rotor can produce a large number of magnetic leakages. To improve the utility of PMs, a novel magnetic gear was proposed in this paper. The structure of the auxiliary flux modulator is a slotted iron yoke, and the slot angle is same as the stationary ring. Among, the permanent magnets (PMs) of inner rotor are adopted uneven block structure to improve air gap flux density. At the same time, the stationary ring adopts high-temperature superconducting (HTS) bulks, replacing the epoxy resin. In addition, Genetic algorithm (GA) is applied to calculate the optimal parameters of the proposed CMG. Finally, the air gap flux density and output torque of the magnetic gear a compared by the finite element method. The results show that the output torque of the proposed magnetic gear is effectively improved. [ABSTRACT FROM AUTHOR]

Asynchronous operation of a turbo generator after the loss of field caused by the excitation fault can avoid large-scale blackout and, therefore, improve the reliability of the power systems. In order to consume the magnetic energy stored in the field winding as soon as possible, a field discharge resistor (FDR) is often connected to the field winding after the excitation fault, but it may affect the asynchronous operating ability of the turbo generator and result in the overvoltage of the field winding. In order to study the influence of the FDR on the asynchronous operating ability of turbo generator, a field-circuit coupled time-stepping finite-element model is established, and the experimental validation is performed on a model machine. For a 300-MW turbo generator, the electromagnetic characteristics, such as torque pulsation, air-gap radial flux density, and flux density distribution, are calculated and compared under different FDRs. The variation of the asynchronous operating ability along with the increase of the value of the FDR is revealed. Under the consideration of the withstanding voltage of field winding, the suitable value of the FDR that can improve the asynchronous operating ability is obtained. The results could provide a theoretical basis for improving the asynchronous operating ability of the turbo generator. [ABSTRACT FROM AUTHOR]

This article proposes a swirling actuator that uses the electromagnetic radial force and mechanical gears to generate rotational torque. The proposed actuator generates a rotating radial force between an inner stator and a swirler. The gears on the swirler and outer rotor convert the circular motion of the swirler to low-speed rotor rotation. Thus, the proposed actuator is aimed at low-speed high-torque applications. In this study, the air-gap radial flux density and electromagnetic radial force are investigated analytically and verified through finite-element analysis. The static radial force and output torque are measured in a prototype of the actuator. The system efficiency and the gear efficiency are evaluated. A peak torque density of 27 Nm/L with a small volume of 0.16 L is realized in the prototype. [ABSTRACT FROM AUTHOR]

Torque ripple reduction for permanent magnet assisted reluctance (PMAREL) machine has always been concerned by designers. In order to seek the internal factors of torque ripple for PMAREL, this article proposes an effective torque calculation model considering air-gap field time-space harmonics using finite element method (FEM) combined with two-dimensional fast Fourier transform (2D-FFT). It can be used to investigate the contribution of air-gap field time-space harmonics to average torque and torque ripple, and precisely extract the characteristic components of the air-gap field time-space harmonics that contribute to the torque. Besides, the details of time-space harmonic order, movement form, magnitude and initial phase will be obtained from the characteristic components. Hence, the time-space harmonics of air-gap field that mainly contribute to the torque ripple can be found through this model and suppressed by adjusting the angles of the flux-barrier ends for making torque smooth. According to the optimized design, a 36-slot 4-pole PMAREL is manufactured and tested. Both finite element analysis and experimental results confirm the effectiveness of the proposed model. [ABSTRACT FROM AUTHOR]

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

Electromagnetic performance of high-speed permanent magnet synchronous machines (PMSMs) is studied for electro-hydrostatic actuator (EHA) applications in this article. The electromotive force (EMF) of different magnet pole-arc to pole-pitch ratios is studied. The no-load air-gap density, cogging torque, average torque, torque ripple, core loss, and rotor eddy current losses are investigated by closed slots design. The rotor eddy current losses of different magnetic retaining sleeve materials such as stainless steel, titanium alloy, and carbon fiber are calculated by finite-element analysis (FEA). The results show that, compared with the opening slot structure, the torque ripple and the rotor eddy current losses of closed slot structure are extremely reduced due to the fact that the 11th and 13th harmonics of air-gap flux density are significantly reduced and the slotting effect are effectively weakened. Increase the closed slot height not only reduce the average torque and increase the core loss but also the torque ripple and the rotor eddy current losses reduction effect is slight. A high-speed PMSM with closed slots design is prototyped to verify the analysis. [ABSTRACT FROM AUTHOR]

In this article, based on a 6-stator coil/17 rotor-tooth (6/17) conventional concentrated-winding multitooth flux-switching permanent magnet (C-MFSPM) machine, a novel full-pitch multitooth flux-switching permanent magnet (FP-MFSPM) machine is proposed by changing winding configurations. Then the electromagnetic performance of six FP-MFSPM topologies sharing the same 6-stator coil but with different rotor teeth combinations, namely, 6/13, 6/15, 6/17, 6/19, 6/21, and 6/23, is compared by using finite-element analysis (FEA). The results show that 6/17 and 6/19 are the optimal stator coil/rotor tooth combinations for FP-MFSPM machines, which exhibit better electromagnetic performance such as more enormous torque and smaller torque ripple. Thereafter, the existing C-MFSPM and the proposed FP-MFSPM machines with 6/17 and 6/19 structures are quantitatively compared in terms of no-load back electromotive force (back EMF), air-gap flux density, cogging torque, electromagnetic torque, torque ripple, and so on. The FEA-predicted results validate that the proposed FP-MFSPM machines have more sinusoidal back EMF, larger torque output, and smaller torque ripple, which are superior to the C-MFSPM topologies. [ABSTRACT FROM AUTHOR]

This article proposes a new maximum torque per ampere (MTPA) control strategy for an induction motor (IM) controlled by the scalar (v/f) method. In scalar control, constant air-gap flux control is generally adopted for IM drives to provide the same torque capability in all operating ranges. However, this control method results in poor motor efficiency due to excessive stator current at light loads. This work proposes a new MTPA control method to minimize the stator current amplitude based on reactive power without measuring the rotor mechanical speed, resulting in improved system efficiency at light loads. In addition, this method proposes an online machine parameter compensation method. Thus, this proposed method is robust to parameter variations. Simulation and experimental results are provided to verify the performance of this MTPA control strategy. [ABSTRACT FROM AUTHOR]

In this paper, superposition methods including the superposition of a single stator tooth and the superposition of a single rotor tooth, are proposed to predict the open-circuit performances of flux-reversal permanent magnet (FRPM) machines. By the proposed superposition methods, the electromagnetic performances, such as air-gap flux density, electromotive force, cogging torque, and unbalanced magnetic pull (UMP) are investigated and verified by 2D finite element analysis (FEA). Further, according to the superposition methods, cogging torque reduction techniques can be acquired from both stator side and rotor side. In addition, the influence of stator-slot/rotor-pole-pairs (slot/pole) combination on UMP is also studied, and consequently, a reasonable slot/pole combination rule is suggested to avoid UMP. Then, an improved configuration for UMP reduction is also investigated and verified by FEA. Finally, the prototype machines are manufactured and tested to further verify the theoretical analysis and FEA predictions. [ABSTRACT FROM AUTHOR]

This article investigates the influence of stator slot number on electromagnetic performance of two-pole high speed permanent magnet (HSPM) slotted motors with toroidal (TO) windings. Four two-pole slotted motors with different slot numbers, i.e., 3, 6, 9, and 12, are globally optimised for maximum torque, and their electromagnetic performance are compared, including winding factor, air-gap flux density, back electromotive force, cogging torque, electromagnetic torque, winding inductances, unbalanced magnetic force (UMF), and various loss components. It shows that the six-slot/two-pole HSPM motor with TO windings is eminently suitable for high speed application due to no UMF and easy to realise a modular structure. In addition, TO and tooth-coil windings are compared in the three-slot/two-pole motors, and the results confirm that TO windings are not suitable for use in the three-slot/two-pole HSPM slotted motor due to large airgap field harmonics. Finally, a six-slot/two-pole prototype motor is manufactured and tested to validate the finite element predictions. [ABSTRACT FROM AUTHOR]

In this article, three 6-slot/2-pole high-speed permanent magnet motors with 1, 2, and 3 coil-pitch windings are optimized by the finite element method taking into account stator copper loss and iron loss. Their electromagnetic performances are analyzed and compared, including air-gap flux density, back electromagnetic force, electromagnetic torque, winding inductances, and various loss components. For high-speed application, compared with 1 and 3 coil-pitch windings, the proposed 2 coil-pitch windings have a good tradeoff between winding factor and end-winding axial length which are attractive for improved torque density. Finally, the experimental results are given to validate some of the finite element predicted results. [ABSTRACT FROM AUTHOR]

In this article, we present a bearingless motor with a novel segmented dipole interior permanent magnet (IPM) slice rotor. The segmented dipole IPM rotor contains a unique pattern of interior permanent magnets arranged to generate a dipole air gap flux pattern. The magnets are encapsulated within an electrical steel rotor structure. The stator contains a three-phase, four-pole winding for suspension and a three-phase, two-pole winding for rotation. We present analyses of several candidate rotor designs. The analyses indicate that the segmented dipole IPM rotor achieves a reduced tradeoff between force and torque capacity and relatively symmetric force dynamics as compared to prior art designs and alternate topologies. Symmetric and decoupled force dynamics allow a simple force decoupling algorithm to be used. We designed, constructed, and tested a prototype system. We experimentally demonstrate that the prototype system can achieve stable levitation and open-loop rotation. [ABSTRACT FROM AUTHOR]

In this article, an optimization design method of power factor is proposed for vernier permanent magnet (VPM) machine, in which the key is to analyze and investigate the power factor from the perspective of air-gap flux harmonic modulation. To improve the design efficiency, air-gap harmonics are analyzed and serve as the crucial bridge between power factor and machine geometry. It is noted that, during the operation of the VPM machine, more attention is required for the power factor of low-speed operation area. Based on the popular new European driving cycle of the electric vehicles, three low-speed driving conditions are chosen for the optimization design. For the systematic investigation, a V-shape VPM machine is selected as an optimization example. In order to evaluate conveniently, the comprehensive power factor is defined and sensitive air-gap flux harmonics of different conditions are selected as the optimization objectives, for improving the power factor characteristics in low-speed conditions. In addition, power factor and machine performances are evaluated to validate the proposed method. Finally, the prototype machine is built and tested. Both the simulation and experimental results reveal the feasibility and effectiveness of the proposed method and investigated VPM machine. [ABSTRACT FROM AUTHOR]

Flux-modulation machines operate based on the so-called magnetic-gear effect. The modulator of the flux-modulation machine is one of the key elements. In this paper, a design method to obtain the distribution of modulators on split-pole flux-modulation machine is proposed to improve output performance. First, the operation principle of the flux-modulation machine is briefly discussed. Then, taking surface-mounted flux-modulation machines as examples, the air-gap flux density model is established by taking the distribution of the modulator into account. Besides, the formula of back-electromotive force of the flux-modulation machine is derived for both concentrated and distributed windings to determine the modulator distribution. Then, according to extreme equation, the optimal pole arc coefficient and distribution of the modulators can be obtained. Finally, the correctness of the proposed method is verified by both simulated and experimental results on a prototype machine. [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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

This article presents a new field-modulation double-stator electrical-excitation synchronous machine (FM-DSEESM) and analyzes its harmonic components of double-layer air gap magnetic field. The key is that both the types and sources of various harmonic-components of air gap magnetic field are derived by taking into account the permeance components of both inner and outer stator teeth and modulation-ring rotor. The selection criteria of main working harmonic components of excitation field is clarified to achieve the armature-winding configuration. Then, the working harmonic components of air gap magnetic field, which have the same pole pairs, rotating direction, and rotating speed, respectively, can be figured out by comparing the mathematical derivation and finite-element analysis results from the excitation field and armature reaction magnetic field. By analyzing the contributions of the air gap flux density components to the electromagnetic torque, it is found that the electromagnetic torque of the proposed FM-DSEESM mainly consists of two parts, namely the reluctance torque components generated by the stationary working harmonic components and the armature reaction torque components provided by the rotating working harmonic components. A low-speed direct-drive FM-DSEESM prototype is fabricated to verify the validity of the proposed analysis approach. [ABSTRACT FROM AUTHOR]

Dual stator winding induction machines (DSWIMs), which have two sets of three-phase windings with unequal pole pairs in their stator and a standard squirrel cage rotor, have overcame the narrow speed operation region and circulating current problems exists in other types of dual winding machines. These advantages are resulted from the independent operation of their winding sets. The independent operation of winding sets will be guaranteed if the flux saturation is avoided. This letter proposes a novel reference frame angle determination technique that not only guarantees the flux saturation avoidance but also results in flux optimization in DSWIMs. Despite pervious methods, the proposed method does not require position or speed sensor and it is easily applicable in various control schemes and in different reference frames. This method is implemented in a flux and torque vector control system for driving a 3.3 kW DSWIM. The experimental results confirm the effectiveness of the proposed method. Moreover, by implementing the proposed method, the torque sharing between the two winding sets is properly done according to the power rating of each of them. [ABSTRACT FROM AUTHOR]

This article focuses on a Transverse Flux Permanent Magnet generator which benefits from Halbach-array permanent magnets. In this topology, a sinusoidal air-gap flux is achieved and thus, lower THD content and cogging torque is resulted. The Transverse flux generators can be a proper choice for direct drive, low speed, and high torque density applications such as wind turbines. Regarding the available small scale turbines in the market, an operating point is chosen for the proposed machine. The problem of a high torque density generator is thermal stresses which should be taken into consideration in the design and modeling process. Precise thermal modeling at the design stage can take the risk of the increase in machine temperature. Using an active component meshed model by considering the localized losses along with a lumped parameter circuit for the unmeshed parts is proposed for the understudy machine. A 3 kW, 320 rpm generator is designed and analyzed by considering the electromagnetic and thermal properties. It is shown that the magnetic-thermal modeling of the proposed machine is highly consistent with the experimental results. [ABSTRACT FROM AUTHOR]

For the five-phase permanent magnet (PM) machines with conventional Halbach array rotor, although the third harmonic current is injected into the phase current, the torque density hardly increases due to the absence of the third harmonic air gap flux density. Hence, a Halbach array considering third harmonic air gap flux density is proposed in this paper, and the topology is described and compared with the conventional Halbach array. The magnetizing angle of the proposed Halbach array and the stator teeth width are optimized based on the nonlinear programing method. The electromagnetic performances of the five-phase PM machines with the proposed Halbach array, including open-circuit flux density, back electromotive force, flux density under the rated load, cogging torque, average torque, torque ripple, loss, and efficiency, are compared with the PM machine with conventional Halbach array by finite-element method. It is demonstrated that the torque density and efficiency of the PM machine with the proposed Halbach array are higher than that of the PM machine with conventional Halbach array. Finally, the five-phase 10-slot/8-pole PM machines with proposed Halbach array is manufactured and tested to verify the analysis. [ABSTRACT FROM AUTHOR]

This article focuses on a novel design of rotor topology for an interior permanent magnet superconductive radial flux magnetic gear to achieve sinusoidal air-gap flux density and lower cogging torque. The method is based on optimization of buried magnet's pole shape in a radial flux structure, modified by using a pulsewidth modulation technique and variable air-gap length applying the supershape formula on the iron core of the inner rotor. The unsatisfied harmonic contents of the air-gap flux density can be reduced with this technique while the main harmonic component and average torque can be maintained or enhanced. The key idea is to set the distribution of the air-gap flux density by segmenting the pole shoe into several elementary blocks and predetermined grooves based on a special curve. Superconductor bulks are placed between pole pieces of modulator ring to improve the flux-modulation effect and decrease cogging torque percentage. The computation of the block sizes and effects of variation of supershape formula parameters are performed by solving a constrained optimization problem. Results show that the radial air-gap flux density harmonics are eliminated, leading to almost sinusoidal air-gap flux density and lower level of cogging torque. [ABSTRACT FROM AUTHOR]

Braking torque is the most important performance parameter for a permanent magnet retarder used in heavy vehicles. This paper proposes a model of the permanent magnet retarder for braking torque at different speeds considering the skin effect, the magnetic leakage, and the actual path of the eddy currents. Based on the magnetic equivalent circuit and the piecewise function method, the static and the transient air-gap flux density models are established, and their accuracy is verified by comparison to the finite element method (FEM). The permeability distribution curve of the retarder stator is obtained by a simple permeability-measuring instrument, considering the skin effect on the permeability of the stator. Thus, the effective permeability function of the stator is obtained at different rotational speeds, and the transient air-gap flux density model is optimized using the effective permeability function. The simulation results showed that the optimized transient air-gap flux density of the calculation model was in good agreement with the FEM. Finally, the calculation model of the eddy current braking torque was verified by the bench test. [ABSTRACT FROM AUTHOR]

A novel hybrid excited asymmetric stator pole doubly salient machine (HEASPDSM) is proposed in this paper. The new topologies and operational principle are first investigated by using a simplified equivalent magnetic circuit model. The harmonic components of air-gap flux density are then analyzed. The influence of key structural parameters of the proposed machine on the flux regulation ability and torque is studied. A full comparison on main electromagnetic performance indexes of the proposed 12/7 (stator/rotor poles) HEASPDSPM and several traditional doubly salient machines is presented. A prototype is fabricated and tested to validate the theoretical analysis. The results well demonstrate that the HEASPDSPM possesses various merits, such as strong flux regulation capability, high torque density, low cogging torque, and low torque ripple. [ABSTRACT FROM AUTHOR]

In this paper, two flux-switching permanent-magnet (FSPM) wind power generators with 9- and 12-phase windings are designed and comparatively analyzed. Both two generators are designed under the rated specifications of 10 kW output power and 220 V phase voltage at 500 r/min. The static characteristics and power generating performances including output voltage, power, and efficiency at rated and variable load/speed conditions are predicted by finite-element analysis and validated by experimental tests based on the two FSPM prototypes. It shows that the 12-phase 24-stator-slot/22-rotor-pole FSPM generator exhibits a higher air-gap flux density, a higher torque/power density, and a lower voltage regulation factor. Besides, it has a better overload capability than its 9-phase 36-stator-slot/34-rotor-pole counterpart when the load and wind speed exceed the rated levels. The comparative study reveals the benefits of the lower leakage flux and permeance from the larger stator-slot opening and longer magnetic circuit. [ABSTRACT FROM AUTHOR]

In this paper, the design of the concentrated flux-type synchronous motor (CFSM) using ferrite permanent magnets to improve torque is proposed for an automotive chassis actuator. The thin pancake type CFSM of this paper has considerable axial magnetic leakage flux due to structural reasons. It is, therefore, necessary to improve the torque. In order to meet the required specifications in a constrained installation space, this paper proposes two methods for torque improvement. The first method is the alternate-stacking core as this structure removes the magnetic leakage flux path. The second method is the rotor overhang that increases the air-gap flux density. Furthermore, the structures require a three-dimensional (3-D) finite element method (FEM) analysis for accuracy. However, to analyze the characteristics easily and quickly, the 3-D structure is made into the equivalent 2-D FEM through an analytical method using an equivalent magnetic circuit. Finally, in this paper, the validity of the design process and the effectiveness for torque improvement is verified through experiments. [ABSTRACT FROM AUTHOR]

The performance of a brushless permanent magnet machine topology equipped with axially and circumferentially magnetized ferrite permanent magnets is presented. Simulation studies show that for smaller ratios of axial length to active length, air-gap flux densities in excess of 1 T can be achieved, resulting in significant improvements in torque production and efficiency. A prototype machine is manufactured, and test results confirm the predictions of the EMF and the static torque. [ABSTRACT FROM AUTHOR]

In this paper, a novel switched reluctance motor with two magnetically dependent stator and rotor sets (TMDSRM) is proposed and tested. The novelty of the TMDSRM is that there is an assistant exciting winding (short for exciting winding), which is placed between the two-stator sets and can be energized by controllable dc current to boost the air-gap flux density and to improve the output torque and torque density. What deserves to be mentioned the most is that the air-gap flux density is compensated when armature winding is in commutation because of the exciting winding carrying dc current and being permanently energized, and thus, the torque ripple is reduced. This paper describes the magnetic structure and the principle of the proposed motor in detail. Moreover, finite-element analysis has been carried out to investigate the influence of exciting field on electromagnetic torque of the motor. A prototype TMDSRM is manufactured, and the experimental results are presented. [ABSTRACT FROM AUTHOR]

In this paper, the partitioned stator (PS) structure is extended to variable-flux memory machines, forming two newly emerged PS switched-flux memory machines (PS-SFMMs) with series and parallel hybrid magnet configurations. From the perspective of geometry, both two PS-SFMMs share identical outer stator and rotor segments, while two different types of permanent magnet (PM) arrangements are employed in the inner stationary part. Thus, the developed machines can inherent the geometric separation of the armature winding and PM excitations from the PS design, thus achieving acceptable torque capability, and excellent air-gap flux control. A comparative study between PS-SFMMs with series and parallel structures is established. First, the topologies and operating principle are introduced, respectively. In addition, the design tradeoffs and PM sizing of the two PS machines are revealed and optimized with a simplified magnetic circuit model. Then, the electromagnetic characteristics of PS-SFMMs with different magnetic circuits are investigated and compared with the finite-element (FE) method. The FE results are validated by the experiments on a parallel prototype. [ABSTRACT FROM AUTHOR]

By developing a simple permeance-magnetomotive force (MMF) model of switched-flux permanent magnet (SFPM) machines, the air-gap flux density produced by both PMs and armature current can be derived, in which harmonics with the same order and rotational speed are called an effective harmonic pair (EHP). By investigating the influences of armature current angle $\delta $ on both the phase and amplitude of each EHP, it is found that the amplitudes of both PM and armature reaction flux-density harmonics maintain fixed, whereas the space phase shift between them changes accordingly with armature current angle. Specifically, the PM and armature reaction flux-density harmonics are orthogonal in space if zero ${d}$ -axis current is fed. Therefore, the maximal torque is realized for each EHP. As the total torque of SFPM machines is the superposition of the contributions by each EHP, the zero ${d}$ -axis current control method turns out to be the optimum for maximal torque per ampere, thus verifying analytically that the ${d}$ - and ${q}$ -axes inductances are equal according to the general torque equation for the investigated machine topology. In addition, the torque adjustment mechanism of each EHP in SFPM machines has also been analytically demonstrated to be resemble that of the surface-mounted PM synchronous machine (PMSM). Finally, the finite-element analysis (FEA) has been performed to validate the previous analytical predictions. [ABSTRACT FROM AUTHOR]