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This paper proposes a high torque density dual-stator flux-reversal-machine with multiple poles Halbach excitation (MPHE-DSFRM), which uses two pole pairs' numbers (PPNs) of PM excitation on one outer stator tooth, and one PPN of PM excitation on one inner stator tooth. The introduction of different PPNs of PM excitation on the outer and the inner stators can optimize magnetic circuit and airgap flux density. A Halbach array is formed by inserting three pieces of circumferentially magnetized PMs into four pieces of radially magnetized permanent magnets (PMs) on the outer stator, which aims to further enhance torque density, and reduce torque ripple. Based on the flux modulation effect, the analytical modeling of the proposed MPHE-DSFRM is established, together with the evolution process, and the working principle is presented. Then, the key design parameters of MPHE-DSFRM are optimized to achieve high torque density and low torque ripple for high torque quality. Three representative DSFRMs and a conventional FRM are designed and analyzed, and they share the same design key parameters, including PM usage, outer radius of the outer stator, and active airgap length. The electromagnetic performances, including airgap flux density, back electromotive force (back-EMF), and torque characteristics, are analyzed and compared by finite element analysis (FEA). The calculated results show that the proposed MPHE-DSFRM can provide high torque density and high PM utilization. [ABSTRACT FROM AUTHOR]

Featured Application: The results of this work can be included in the design stage of interior permanent-magnet synchronous motors for aircraft drive applications. The torque performance of the interior permanent-magnet synchronous motor (IPMSM) must be further improved to satisfy the growing demand of aircraft drive application. To this end, this article focuses on the design optimization of the IPMSM structure in the aircraft drive systems to improve the torque density and reduce the torque ripple. A special fractional-slot winding and ∇-type magnetic-pole rotor topology are proposed as the optimized IPMSM structure compared with the structure of an existing motor. The simulations of the original and optimized structures at different current values reveal the variance of the torque in the average and ripple, mechanical and external characteristics, efficiency and steady-state temperature. The performance of an optimized prototype is analyzed by experimental testing, and the results show that an optimized motor has a higher torque density and lower torque ripple than the original one at the same speed and rated power, but it also has a higher temperature rise. However, the temperature rise value is acceptable in the experimental testing condition, so the validity of the design optimization method for the proposed structure is verified. [ABSTRACT FROM AUTHOR]

This paper proposes a high torque density dual-stator flux-reversal-machine with multiple poles Halbach excitation (MPHE-DSFRM), which uses two pole pairs’ numbers (PPNs) of PM excitation on one outer stator tooth, and one PPN of PM excitation on one inner stator tooth. The introduction of different PPNs of PM excitation on the outer and the inner stators can optimize magnetic circuit and airgap flux density. A Halbach array is formed by inserting three pieces of circumferentially magnetized PMs into four pieces of radially magnetized permanent magnets (PMs) on the outer stator, which aims to further enhance torque density, and reduce torque ripple. Based on the flux modulation effect, the analytical modeling of the proposed MPHE-DSFRM is established, together with the evolution process, and the working principle is presented. Then, the key design parameters of MPHE-DSFRM are optimized to achieve high torque density and low torque ripple for high torque quality. Three representative DSFRMs and a conventional FRM are designed and analyzed, and they share the same design key parameters, including PM usage, outer radius of the outer stator, and active airgap length. The electromagnetic performances, including airgap flux density, back electromotive force (back-EMF), and torque characteristics, are analyzed and compared by finite element analysis (FEA). The calculated results show that the proposed MPHE-DSFRM can provide high torque density and high PM utilization.

With the increasing demand for high torque density in motors, more and more new topologies emerge. Furthermore, the magnetic field modulation principle is widely concerned and has evolved into an effective analysis method for studying the new motor topology. This paper introduces the principle of magnetic field modulation. And the research on high torque density in recent years is reviewed from the perspective of magnetic field modulation, including permanent magnet vernier machine (PMVM), flux reverse machine (FRM), flux switching machine (FSM), dual permanent magnet (DPM) machine, and DC biased machine. The principle of magnetic field modulation makes it possible to propose higher torque density topologies in the future.

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This paper investigates the performance enhancements of permanent magnet Vernier machines (PMVMs) that can be achieved using a new structure of Halbach array permanent magnets (HAPMs) for a direct-drive motorcycle application. To start with, size and design specifications of the electric machine are determined based on the assumed acceleration and drive cycle performance of a motorcycle. Then, five-segment Halbach array permanent magnet Vernier machines (HAPMVMs) with two different slot/pole combinations (24 s/44 p and 12 s/20 p) are suggested and optimized to achieve a high torque density with an acceptable power factor while maintaining a low torque ripple. Two selected designs from optimizations are investigated in the full speed range considering power factor and efficiency maps. Consequently, in order to demonstrate the effectiveness of the proposed five-HAPM structure, the same optimization methods are repeated with three-segment HAPMs as well as with single-piece PMs. The comparisons show a great enhancement in torque and power factor achieved with the use of five HAPMs. For instance, for 22 s/44 p topology, generated torque doubles with the use of five-segment PMs compared to single-segment PMs. Finally, the harmonics of magnetic flux density in the airgap of PMVMs and HAPMVMs are compared and investigated to reveal the reasons behind the superiority of VMs with HAPMs. [ABSTRACT FROM AUTHOR]

Magnetic gear and magnetic-geared machine (MGM) are the potential solutions in electric vehicles (EVs) powertrains for inherent high efficiency and mechanical simplification. However, the torque density issue of the MGM greatly limits its industrial application. To enhance the torque performance of the MGM, a torque-enhanced magnetic-geared machine with dual-series-winding and its design approach are proposed. The key merits of the proposed design are to achieve a high space utilization with a dual-winding design, with no additional control topologies and power converters required. The auxiliary winding is supplemented and integrated with modulation rings. The relative position of the stator and armature winding are designed and rotated compared to the modulation rings with auxiliary winding, to ensure the auxiliary winding shares the excitation with the armature winding. Accordingly, simplifying the external control topologies. With the proposed design, the torque of the MGM can be significantly enhanced with a single three-phase driving. Theoretical analysis, parameters optimization and electromagnetic verification are given, demonstrating that the proposed machine can achieve an efficiency of 93.2%, generate a torque of 107.2 N·m, and reach a torque density of 10.81 N·m/kg. [ABSTRACT FROM AUTHOR]

The torque performance of the interior permanent-magnet synchronous motor (IPMSM) must be further improved to satisfy the growing demand of aircraft drive application. To this end, this article focuses on the design optimization of the IPMSM structure in the aircraft drive systems to improve the torque density and reduce the torque ripple. A special fractional-slot winding and ∇-type magnetic-pole rotor topology are proposed as the optimized IPMSM structure compared with the structure of an existing motor. The simulations of the original and optimized structures at different current values reveal the variance of the torque in the average and ripple, mechanical and external characteristics, efficiency and steady-state temperature. The performance of an optimized prototype is analyzed by experimental testing, and the results show that an optimized motor has a higher torque density and lower torque ripple than the original one at the same speed and rated power, but it also has a higher temperature rise. However, the temperature rise value is acceptable in the experimental testing condition, so the validity of the design optimization method for the proposed structure is verified.

The switched reluctance motor (SRM) benefits from its magnet-free nature, robust construction, low cost, flexible controls, and the ability to operate in harsh environments such as high temperatures and high pressure. It has received increasing attention for all-electric or multi-electric aircraft systems and electric vehicles (EVs) as compared with permanent magnet synchronous motors (PMSM) and other AC motors in some required high reliability and fault tolerance applications. However, the SRM is prone to considerable wind resistance due to the convex pole structure of the rotor during high-speed rotation, high torque ripple, and also vibration noise. Thus, it is currently a trending topic to develop special SRMs, tailored with high reliability and fault tolerance. Recent research demonstrates several promising feasible solutions to reduce torque ripples and enhance torque density and power factors, including changing topology of SRM, using advanced control methods, as well as different winding configurations. Among these options, the segmented switched reluctance motor (SSRM), as a deformation of the conventional topology, is shown to be capable of effectively optimizing the torque performance. Motivated by this advance, this paper aims to present a comprehensive literature review on the SSRM, first illustrating the development of the topology of the SRM, then providing a description as well as a classification according to the topology of the SSRM. In particular, we focus on the evolution of various kinds of segmental topology and improvement measures. Then, we discuss the performance, advantages, and disadvantages of various types of structures in terms of their electromagnetic aspects and their applications. Eventually, several promising future trends and application prospects of the SSRM are prospected, with the aim of shedding light on further research. In sum, the key contribution of this paper is to provide a valuable basis for detailed analyses of the structure and electromagnetic design of the SSRM that are expected to benefit future research. [ABSTRACT FROM AUTHOR]

With the rapid development of power electronic techniques and the increasing cost of permanent magnets (PMs) materials, switched reluctance motors (SRMs) have recently gained more attention. However, traditional SRMs have a relatively low torque density. For the sake of increasing the motor torque density, this paper proposes a novel segmental rotor type SRM. The proposed motor adopts hybrid stator poles and concentrated windings in the stator side and a segmental rotor structure in the rotor side, which is completely different from the structures of the traditional SRM. The special structure of the motor shortens the magnetic flux paths of the motor, separates the parts of the magnetic flux paths from one another, and eradicates the magnetic flux reversal in the motor stator in order to improve the electric utilization and output torque density of the motor. Meanwhile, the requirement of the magneto-motive force and the core loss of the motor is also decreased, thereby improving the efficiency of the motor. For the purpose of proving the proposed structure, the characteristics of the motor are analyzed using the finite element method and are compared to those of the traditional 12/8 SRM, which is designed for the same application. Moreover, the prototypes of the traditional 12/8 and proposed SRMs are manufactured, and experiments based on the prototypes are performed. Finally, the effectiveness of the structure of the proposed motor is further proven by the experimental results. [ABSTRACT FROM AUTHOR]

In order to achieve high-quality energy conversion operation in electric vehicles, the optimization design of drive motors has been considered as one of the most crucial research areas. For enhancing torque density without deteriorating power factor, a spoke-type flux modulated multi-winding permanent magnet machine is proposed and optimized, where the highly efficient utilization of harmonic flux is realized according to the contribution of windings with various pole pairs. Firstly, the operating principles and the initial design of topology are investigated. Then, the improved non-dominated sorting genetic algorithm is adopted for multi-objective optimization. To enhance the efficiency and accuracy of the optimization, the weight coefficients of the multi-objectives are established through a gray correlation strategy, while the design parameters are stratified based on a comprehensive sensitivity degree analysis. In addition, the comparative analysis of machines before and after optimization are carried out. Finally, the correctness of the theoretical analysis and the effectiveness of the proposed optimization are verified by a prototype machine. It shows that high torque density without deteriorating power factor is achieved on the proposed machines. • A new high-torque-density flux-modulated multi-winding PM machine (FMM-PMM) for EVs is proposed. • The multiple harmonic utilization can be achieved by the proposed FMM-PMM. • A comprehensive optimization method is established for further achieving high-quality energy conversion. • The gray correlation analysis, sensitivity analysis, and Latin hypercube sampling are carried out before the application of the NSGA-II algorithm. • The proposed optimization strategy and PM machine have been validated by experimental tests. [ABSTRACT FROM AUTHOR]

This paper proposes two structures of dual-stator permanent-magnet vernier machines (VMs) for high-torque low-speed applications. The proposed structures consist of dual-sided rotor which is sandwiched by inner and outer stators. These topologies include 22 and 46 consequent-pole magnets in the rotor and 24 and 48 stator slots for Design A and Design B, respectively. Design A is an improved structure of dual stator VM and Design B is a novel topology of a dual stator VM that can deliver considerably higher back-EMF and torque than Design A. The only drawback in Design B is lower power factor. The characteristics and performance parameters of the proposed VMs are evaluated using FEA. Sensitivity analysis is used to figure out the optimum dimensions of the magnets. In fact, two combinations of slot/pole number of the vernier machines are investigated as Design A and Design B. The capabilities of the proposed vernier machines are presented in a fair comparison with other VMs namely as consequent pole dual rotor VM (CPDRVM), consequent pole dual stator VM (CPDSVM) and dual stator spoke array VM (DSSAVM). In this regard, the key machine features considered for comparison are back-EMF, torque, torque per magnet volume (TPMV), power factor, loss, and efficiency profiles. The proposed structure (Design B) generates higher torque and TPMV compared to the other studied machines while Design A can achieve a higher power factor. [ABSTRACT FROM AUTHOR]

A novel 36-slot/14-pole dual three-phase permanent magnet synchronous machine (PMSM) is proposed to suppress non-working space harmonics in the synthesized magnetomotive force (MMF) and improve torque density simultaneously. The machine adopts unequal coil-turns winding and special stator core which includes two different types of slots, namely double-layer slots (DLSs) and single-layer slots (SLSs). The special structure of the machine improves the working space harmonic and eliminates lower non-working space harmonics in MMF, which leads to torque promotion and permanent magnet (PM) loss reduction. Harmonic content in MMF of the proposed machine is derived from theoretical analysis and verified by finite element (FE) calculation. Besides, the proposed machine is compared with existing machines, from aspects of MMF, back electromotive force (EMF), torque, losses, efficiency, unbalanced magnetic force (UMF), and torque-speed characteristic. The proposed machine has higher torque density, higher efficiency, and lower PM loss than existing machines. [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]

This paper presentsan investigation of a 3D-magnetic flux permanent magnet synchronous motor (3D-MF PMSM) used for electric vehicle applications. The investigated 3D-MF PMSM consists of an integrated radial-flux and axial-flux structure. It has two radial-flux air-gaps and two axial-flux air-gaps, as well as a toroidal winding wound stator. The integrated structure helps to concentrate all the flux within the motor to maximize torque production. Moreover, there are no end-windings in this motor and all the stator windings effectively are used in torque production. A comprehensive performance evaluation, in terms of the back-electromotive force, average output torque, cogging torque, torque ripple, flux-weakening capability, etc., of the investigated 3D-MF PMSM is conducted. An interior PMSM is purposely included as a benchmark for comparison. The results show that compared to the benchmark interior PMSM, the original 3D-MF PMSM exhibits significantly improved torque density, higher power factor, and higher efficiency, but suffers from serious cogging torque and torque ripple. Accordingly, a skewed arrangement is introduced to the 3D-MF PMSM. As a result, the cogging torque and torque ripple are significantly reduced. [ABSTRACT FROM AUTHOR]

This paper investigates the performance enhancements of permanent magnet Vernier machines (PMVMs) that can be achieved using a new structure of Halbach array permanent magnets (HAPMs) for a direct-drive motorcycle application. To start with, size and design specifications of the electric machine are determined based on the assumed acceleration and drive cycle performance of a motorcycle. Then, five-segment Halbach array permanent magnet Vernier machines (HAPMVMs) with two different slot/pole combinations (24 s/44 p and 12 s/20 p) are suggested and optimized to achieve a high torque density with an acceptable power factor while maintaining a low torque ripple. Two selected designs from optimizations are investigated in the full speed range considering power factor and efficiency maps. Consequently, in order to demonstrate the effectiveness of the proposed five-HAPM structure, the same optimization methods are repeated with three-segment HAPMs as well as with single-piece PMs. The comparisons show a great enhancement in torque and power factor achieved with the use of five HAPMs. For instance, for 22 s/44 p topology, generated torque doubles with the use of five-segment PMs compared to single-segment PMs. Finally, the harmonics of magnetic flux density in the airgap of PMVMs and HAPMVMs are compared and investigated to reveal the reasons behind the superiority of VMs with HAPMs.

This paper reveals the fundamental reason for the asymmetrical issue in magnetic-geared machines (MGMs) based on flux modulation theory. The analysis indicates that the magnetic circuits of three-phase windings in MGMs are inherently asymmetrical. This asymmetrical issue is even more severe in conventional consequent-pole MGMs (CP-MGMs) because of the more distorted magnetic field. Hence, to address the asymmetrical issue, a novel structure featuring enhanced harmonic elimination capability is proposed in this paper. Consequently, torque density can also be improved. In particular, the proposed CP-MGM employs modular structure and axially embedded permanent magnets (PMs) to achieve symmetrical back electromotive force (EMF) waveforms and improved torque capability, respectively. To further improve the electromagnetic performance of the proposed CP-MGM, the PM arc ratio and flux modulator width ratio are analytically designed, which provides a general design guideline for CP-MGMs. To illustrate the merits of the proposed CP-MGM, a few other MGMs are included for a fair comparison based on finite element analysis (FEA). Results show the proposed CP-MGM can achieve more symmetrical back EMF waveforms and lower torque ripple, as well as lower PM consumption and higher torque density, as compared with its MGM counterparts.

A novel dual-airgap permanent magnet Vernier machine (DADPMVM) is proposed and analyzed in this paper. The key of this design is combining the double-concentric-rotor structure, the dual permanent magnet structure along with the Vernier structure to improve the torque density while remaining the motor's volume unchanged. The maximized use of the winding length and the reduction of copper loss are also the main merits of this design. The machine structure and operating principle are discussed, and its transient performance is analyzed by using the finite element method (FEM). Two different configurations of pole pairs and two different structures are designed in the same peripheral dimension configuration and compared with the proposed machine by FEM. The results of the comparison are used to confirm the outstanding performance of the proposed machine. The torque density per machine volume can exceed 100 kNm/ m3 with the proper cooling method.

The switched reluctance motor (SRM) benefits from its magnet-free nature, robust construction, low cost, flexible controls, and the ability to operate in harsh environments such as high temperatures and high pressure. It has received increasing attention for all-electric or multi-electric aircraft systems and electric vehicles (EVs) as compared with permanent magnet synchronous motors (PMSM) and other AC motors in some required high reliability and fault tolerance applications. However, the SRM is prone to considerable wind resistance due to the convex pole structure of the rotor during high-speed rotation, high torque ripple, and also vibration noise. Thus, it is currently a trending topic to develop special SRMs, tailored with high reliability and fault tolerance. Recent research demonstrates several promising feasible solutions to reduce torque ripples and enhance torque density and power factors, including changing topology of SRM, using advanced control methods, as well as different winding configurations. Among these options, the segmented switched reluctance motor (SSRM), as a deformation of the conventional topology, is shown to be capable of effectively optimizing the torque performance. Motivated by this advance, this paper aims to present a comprehensive literature review on the SSRM, first illustrating the development of the topology of the SRM, then providing a description as well as a classification according to the topology of the SSRM. In particular, we focus on the evolution of various kinds of segmental topology and improvement measures. Then, we discuss the performance, advantages, and disadvantages of various types of structures in terms of their electromagnetic aspects and their applications. Eventually, several promising future trends and application prospects of the SSRM are prospected, with the aim of shedding light on further research. In sum, the key contribution of this paper is to provide a valuable basis for detailed analyses of the structure and electromagnetic design of the SSRM that are expected to benefit future research.

In this paper, a new multi-tooth switched reluctance motor (MT-SRM) is proposed and then based on the original topology, three novel multi-tooth hybrid reluctance motors (MT-HRMs) are introduced to improve the torque characteristics of the SRM. The proposed structures are an MT-HRM with permanent magnets (PMs) between the side teeth of the adjacent modules, an MT-HRM with PMs in the yoke, and finally an MT-HRM with dual-PM configuration. The operating principles of the MT-HRMs are illustrated and the flux adjusting effect and outstanding torque production ability of the PMs are demonstrated through the theoretical and simulation results. The flux distributions and static torque and flux linkage profiles of the motors are obtained and compared. The four proposed motors are compared in terms of the steady-state current and torque waveforms. All the simulation results indicate that the PM-assisted structures can achieve higher torque and power than their PMless counterpart with deploying only three/six small PMs. The four motors are prototyped and the experimental results are carried out. Both the experimental and simulation results prove the effectiveness of the proposed MT-HRMs. [ABSTRACT FROM AUTHOR]

With the rapid development of power electronic techniques and the increasing cost of permanent magnets (PMs) materials, switched reluctance motors (SRMs) have recently gained more attention. However, traditional SRMs have a relatively low torque density. For the sake of increasing the motor torque density, this paper proposes a novel segmental rotor type SRM. The proposed motor adopts hybrid stator poles and concentrated windings in the stator side and a segmental rotor structure in the rotor side, which is completely different from the structures of the traditional SRM. The special structure of the motor shortens the magnetic flux paths of the motor, separates the parts of the magnetic flux paths from one another, and eradicates the magnetic flux reversal in the motor stator in order to improve the electric utilization and output torque density of the motor. Meanwhile, the requirement of the magneto-motive force and the core loss of the motor is also decreased, thereby improving the efficiency of the motor. For the purpose of proving the proposed structure, the characteristics of the motor are analyzed using the finite element method and are compared to those of the traditional 12/8 SRM, which is designed for the same application. Moreover, the prototypes of the traditional 12/8 and proposed SRMs are manufactured, and experiments based on the prototypes are performed. Finally, the effectiveness of the structure of the proposed motor is further proven by the experimental results.

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]

Magnetic gears realize the characteristics such as low acoustic noise and low vibration, maintenance-free by contact-less power transformation. However, conventional magnetic gears are not suitable for high-speed motor drive systems because of their low mechanical strength, which results from the permanent magnets of the input rotor. This article proposes a novel flux-switching magnetic gear for high-speed motor drive systems. The input rotor of the flux-switching magnetic gear consists of an iron core. Therefore, the structure is highly robust and can be driven in the high-speed region. Moreover, the flux-switching magnetic gears offer a high torque density by utilizing stationary field magnets arranged between the pole pieces. Through simulations and the experiments, parameters such as the torque density, mechanical strength, losses, and efficiency of the proposed gear are evaluated. [ABSTRACT FROM AUTHOR]

This paper proposes a new rotary flux switching transverse flux machine with the ability of linear motion (FSTFMaLM), in which both the stator and the rotor cores are made by using soft magnetic composite (SMC) materials. With the special design pattern, for the rotary motion model, the proposed machine can combine both the advantages of the flux switching permanent magnet machine (FSPMM) and the transverse flux machine (TFM). It can output with relatively high torque density, and as there is no windings or the magnets on the rotor cores, the proposed machine can operate in the high speed region to improve the output power. With the adoption of the SMC materials, the manufacturing of this machine can be quite easy. By stacking the rotor core together and prolong it with the determined length in the axial direction, in addition with the special control algorithm, the proposed machine can have the ability of the linear motion. In this paper, the operation principle of this machine has been explained and the design methods are also presented. To seek the better performance, the main dimension of the machine is optimized, and for the performance evaluation, the finite element method (FEM) is adopted. The proposed machine can be used for the electric driving systems, robotic systems or other applications where the linear motion ability is required.

This paper reports the design of a magnetic-geared permanent magnet synchronous motor (MG-PMSM) for a 45 kW tram traction system based on high torque density. In the case of the existing tram driving system, due to mechanical reduction gear and induction motor, it causes power transmission loss, low efficiency, and difficulty in lightweight. To solve this problem, research on the MG-PMSM, which combines a contactless magnetic gear with a high-power-density PMSM, is being actively conducted. This motor has a double rotor structure, and the inner rotor, including permanent magnet, and the outer rotor composed of pole-pieces rotate at different mechanical speeds. However, it is hard to design a tram driving system with a high torque density within limited conditions, because only one rotor in MG-PMSM is used as an output. In addition, there is no study conducted from basic design to final design, including gear ratio and topology selection in MG-PMSM for tram. Therefore, this paper presents the design process of MG-PMSM with high torque density to be applied to the 45 kW–class tram driving system. After designing the magnetic gear part that increases torque and efficiency by selecting an appropriate topologies-and-gear ratio that meets the constraints, the final finite elements method (FEM) model and electromagnetic field analysis results were derived by considering the number of poles and the number of slots. Through this, we confirmed that it is superior in output characteristics compared to the existing induction motor + mechanical gear.

This article proposes a novel structure of consequent pole dual rotor permanent magnet vernier machine (CPDRVM). This structure consists of dual-sided stator in which windings are placed on the stator slots and magnets placed on the inner and outer rotor slots. Operation principles of the proposed VM carried out using flux modulation theory. The Finite Element analysis is utilized in order to evaluate the effect of magnet geometry on the produced torque and power factor. The motor characteristics and performance assessment are performed numerically. Furthermore, the parametric and sensitivity analysis are used to optimize the motor geometry. The proposed VM compared with PM machine and two conventional VMs. In this regard, performance indices such as flux, cogging torque, power factor, magnet volume, torque per magnet volume, Back-EMF, losses and efficiency profiles are calculated and compared. Results evidence better performance of the proposed structure. In fact, CPDRVM could produce higher torque density than conventional VMs. In addition, high power factor is reached for suggested topology. [ABSTRACT FROM AUTHOR]

This study proposes a hybrid excited (HE) doubly salient machine with permanent magnets (PMs) located on stator slot openings. The HE machine inherits the high torque density of PM machines as well as flexible magnetic field regulation of wound field machines. Since the PMs are located at stator slot opening, the PM flux is shunted in the stator without DC excitation, and the machine exhibits high fault‐tolerant capability at high‐speed operation. The proposed machine is optimised, together with a comparison with a conventional stator slot PM HE machine. It is revealed that the proposed HE machine exhibits a significantly higher torque density under the same copper loss and PM usage. Finally, a prototype is fabricated, and experiments have been conducted to verify the accuracy of finite element simulation on the proposed machine topology. [ABSTRACT FROM AUTHOR]

In this article, the implementation of a single-stator double-rotor fractional-slot concentrated-winding (FSCW) axial-flux permanent-magnet machine is presented to verify a simple and reliable structure design and oil-immersed cooling of the stator with modular soft magnetic composites (SMC) core. Due to the yokeless and segmented stator, the process of embedding the windings into the stator teeth will probably become simpler. By preforming rectangular copper wire, the shorter end-winding length and higher fill factor can be achieved. In order to eliminate eddy current losses and manufacturing costs, the fiberglass epoxy is used for the supporting components of the fixation for modular SMC stator and PMs, which is a nonmagnetic and nonconductive material. Hence, the robustness of stator and rotor are taken into account due to the stator modularity weakening effect on strength. Meanwhile, a fully sealed stator with oil-immersed cooling is proposed to enable the current density of 20 A/mm2 in the armature windings for stable operation. The electromagnetic properties, including in magnetic field distribution, torque capacity, and flux-weakening ability, are performed based on the three-dimensional finite-element analysis, as well as the mechanical performance. The coupled thermal and computational fluid dynamics model is built to predict the flow and temperature distribution inside stator with oil-immersed forced cooling. The construction and experimental verification of a full-scale 30-kW prototype are elaborated to verify the predicted performances in terms of torque density, structural strength, and cooling. [ABSTRACT FROM AUTHOR]

This article proposes an enhanced-torque switched reluctance motor with two sets of permanent magnets (PM-SRM) embedded inside the stator yoke and the end teeth of the neighboring modules. The PMs contribute to intensify the air-gap flux density and reduce the magnetic saturation in the stator poles. As a result, the output torque can be enhanced to a significant extent. The working principle of the proposed PM-SRM is clarified using its magnetic circuit model (MCM). The characteristics of the PM-SRM are obtained and compared with classical 12/8 and 6/5 SRMs and hybrid reluctance motors (HRMs) in terms of static and average torque and average torque per PMs volume. The steady-state performance of the PM-SRM in terms of current and torque waveforms is carried out, and the PM-SRM is compared with considered SRMs and HRMs in terms of output torque, power, and efficiency. All the comparisons demonstrate the out-performance of the proposed PM-SRM over other SRMs and HRMs. To validate the simulation results, a prototype of the PM-SRM is manufactured and the experimental results are obtained. Both the simulation and experimental results are indicative of the fact that the proposed PM-SRM can gain high torque and high PM utilization factor, simultaneously. [ABSTRACT FROM AUTHOR]

Flux switching machines (FSMs) encompass unique features of conventional direct current machine, permanent magnet (PM) synchronous machine and switch reluctance machine. Permanent magnet FSM (PMFSM) is capable of high torque density and applicable for high‐speed application, however conventional PMFSM exhibits demerits of high PM volume, high torque ripples and significant stator flux leakage. In this paper, a novel consequent pole E‐core stator PMFSM is proposed and compared with conventional topology utilising 2D finite‐element analysis (2D‐FEA). Finite‐element analysis revealed that proposed design enhanced flux modulation effects by introducing flux bridges and flux barriers as a result reduced cogging torque by reducing 46.53% of the total PM volume, reduce torque ripples by reducing PM slot effects and reduce flux leakage utilising flux bridges in the stator. Furthermore, analytical model for flux linkages, cogging torque, mechanical torque, no load and on‐load magnetic flux density (MFD) is developed for initial design of conventional and proposed model. 2D analytical methodologies resolve equivalent magnetic circuits for open‐circuit flux linkages, Fourier analysis for cogging torque, Laplace equations for MFD and Maxwell stress tensor for mechanical torque. Finally, results obtained from 2D‐FEA and analytical methodologies are validated and compared. [ABSTRACT FROM AUTHOR]

Outer‐rotor permanent‐magnet (OR‐PM) machines provide several distinct advantages such as high torque density and large rotor inertia due to the large outer diameter of effective air gap for power conversion. The purpose of this study is to replace flywheel with the outer rotor by adopting OR‐PM machines since this topology is well‐suited for integration with diesel engines. This study specifically investigates a 16‐pole–18‐slot ring‐shaped PM motor with rectangular shaped PM rotor for integrated power generation application. At first, the pole arc, rotor yoke thickness and PM slot height of the OR‐PM machine with rectangular shaped PM are optimised. In addition, the no‐load magnetic field, cogging torque and back‐electromotive force of the OR‐PM machine with rectangular shaped PM and have been analysed and compared based on two‐dimensional finite element analysis. Additional comparison including torque characteristics, field weakening, cost and efficiency are also highlighted. The results show that the OR‐PM machine with rectangular shaped PM has better electromagnetic performances. Finally, a 25 kW OR‐PM machine prototype with rectangular shaped PM is manufactured and experimented. The predicted electromagnetic performance is validated by experimental results. [ABSTRACT FROM AUTHOR]

Electric machines with high torque density are needed in many applications, such as electric vehicles, electric robotics, electric ships, electric aircraft, etc. and they can avoid planetary gears thus reducing manufacturing costs. This paper presents a novel axial-radial flux permanent magnet (ARFPM) machine with high torque density. The proposed ARFPM machine integrates both axial-flux and radial-flux machine topologies in a compact space, which effectively improves the copper utilization of the machine. First, the radial rotor can balance the large axial forces on axial rotors and prevent them from deforming due to the forces. On the other hand, the machine adopts Halbach-array permanent magnets (PMs) on the rotors to suppress air-gap flux density harmonics. Also, the Halbach-array PMs can reduce the total attracted force on axial rotors. The operational principle of the ARFPM machine was investigated and analyzed. Then, 3D finite-element analysis (FEA) was conducted to show the merits of the ARFPM machine. Demonstration results with different parameters are compared to obtain an optimal structure. These indicated that the proposed ARFPM machine with Halbach-array PMs can achieve a more sinusoidal back electromotive force (EMF). In addition, a comparative analysis was conducted for the proposed ARFPM machine. The machine was compared with a conventional axial-flux permanent magnet (AFPM) machine and a radial-flux permanent magnet (RFPM) machine based on the same dimensions. This showed that the proposed ARFPM machine had the highest torque density and relatively small torque ripple.

A novel structure of axial flux stator and rotor dual PMs Vernier machine is presented as an effective option for high torque-density direct-driven applications. The key is to locate PMs on both sides of rotor and stator. With dual PMs, this proposed machine with a novel structure generates an improved torque per armature current at low speed. It is very suitable for direct drive applications with limited space such as the in-wheel electric vehicle (EV) motors. The theory of the structure with PMs on both sides is analyzed theoretically. The structure and operation principle of machine are introduced and the steady and steady performance of machine is analyzed and verified with time-stepping finite element method (TS-FEM).

This study presents a comparative study of different modular brushless wound rotor synchronous machines (MB-WRSM) using non-overlapping fractional slot double-layer concentrated windings. The goal of the study is to highlight the structure which offers the best fault-tolerance capability and the highest output performance. The fundamental winding factor is calculated by using the method based on voltage phasors as a significant criterion to select the preferred numbers of phases, stator slots, and poles. With the limited number of poles for a small machine (3.67 kW/7000 rpm), 15 different machines for different phase/slot/pole combinations are analysed using two- dimensional (2D) finite element method and compared according to three criteria: torque density, torque ripple, and machine efficiency. The seven-phase/seven-slot/six-pole machine is chosen with the best compromise of high torque density, small torque ripple (3.89%), and high nominal efficiency (95%). This machine is then compared with a reference design surface-mounted permanent magnet synchronous machine (SM-PMSM). The simulation results are discussed and demonstrate that the MB-WRSM presents interesting performance features, such as extended field weakening range, with overall performance closely matching that of an equivalent SM-PMSM.

Permanent magnet synchronous motors are widely accepted in automotive applications. The high torque density, high rotational speed with maximum efficiency in electric vehicle applications is technically challenging for motor design. However, these machines are expensive and difficult to work at high-temperature harsh environment due to permanent magnets demagnetisation features. Alternatively, switched reluctance motors can provide similar output characteristics and a wider speed. Thus these are considered to be more fault tolerant and more reliable. This study proposes a 20 kW, three-phase switched reluctance motor and analyse its overall performance and harmonic contents. The study is conducted by optimising the slot filling factor, excitation voltage and switching sequence of an asymmetrical half bridge converter. A finite element model is used to predict the core and copper losses and other influencing parameters. Simulation results are presented and analysed the effectiveness of the proposed switched reluctance motor (SRM).

The TC48 drive is a low-cost, low-voltage integrated motor-drive solution suitable for mild hybrid electric vehicles, off-highway traction, and any application where a compact, highly torque-dense machine is required. Low-voltage solutions for electric vehicles are attractive to manufacturers due to lower insulation requirements, and hence lower cost. The package is based on a six-phase switched reluctance machine, which uses a novel stator topology and unique winding design to achieve high torque density. The power electronics converter hardware is integrated into the motor housing, giving a physically, electrically, and thermally optimised solution. The complete package has been designed to be suitable for manufacturing in high volumes. This study describes the electromagnetic design of the motor, the mechanical innovations used to physically realise this design, and the cooling system which makes the high power density possible. The integration of the power electronics and their control is also discussed. The project is the result of collaboration between Newcastle and Loughbosrough Universities, RDM Ltd., Productiv, Infineon, Tata Steel, and Libralato.

This study introduces the development of the straight pole four-phase double-stator switched reluctance machine (SRM) which is considered to provide high torque density and low copper loss. The basic concept behind this design is to combine the features of the mutually coupled SRM and the double-stator SRM. In this study, the analytical method alongside the 2D finite element method (FEM) verification would be presented to reveal the developing path. Moreover, to verify the proposed SRM concept, the prototype machine has been designed and built. The performance result from 2D FEM is presented.

In this paper, the optimization and characteristics analysis of a three-phase 12/8 switched reluctance motor (SRM) based on a Grey Wolf Optimizer (GWO) for electric vehicles (EVs) application is presented. This research aims to enhance the output torque density of the proposed SRM. Finite element method (FEM) was used to analyze the characteristics and optimization process of the proposed motor. The proposed metaheuristic GWO combines numerous objective functions and design constraints with different weight factors. Maximum flux density, current density, and motor volume are selected as the optimization constraints, which play a significant role in the optimization process. GWO performs optimization for each iteration and sends it to FEM software to analyze the performance before starting another iteration until the optimized value is found. Simulations are employed to understand the characteristics of the proposed motor. Finally, the optimized prototype motor is manufactured and performance is verified by experiment. It is shown that the torque can be increased by 120% for the same outer volume, by using the proposed method.

The TC48 drive is a low-cost, low-voltage integrated motor-drive solution suitable for mild hybrid electric vehicles, off-highway traction, and any application where a compact, highly torque-dense machine is required. Low-voltage solutions for electric vehicles are attractive to manufacturers due to lower insulation requirements, and hence lower cost. The package is based on a six-phase switched reluctance machine, which uses a novel stator topology and unique winding design to achieve high torque density. The power electronics converter hardware is integrated into the motor housing, giving a physically, electrically, and thermally optimised solution. The complete package has been designed to be suitable for manufacturing in high volumes. This study describes the electromagnetic design of the motor, the mechanical innovations used to physically realise this design, and the cooling system which makes the high power density possible. The integration of the power electronics and their control is also discussed. The project is the result of collaboration between Newcastle and Loughbosrough Universities, RDM Ltd., Productiv, Infineon, Tata Steel, and Libralato. [ABSTRACT FROM AUTHOR]

This study presents a comparative study of different modular brushless wound rotor synchronous machines (MB-WRSM) using non-overlapping fractional slot double-layer concentrated windings. The goal of the study is to highlight the structure which offers the best fault-tolerance capability and the highest output performance. The fundamental winding factor is calculated by using the method based on voltage phasors as a significant criterion to select the preferred numbers of phases, stator slots, and poles. With the limited number of poles for a small machine (3.67 kW/7000 rpm), 15 different machines for different phase/slot/pole combinations are analysed using two- dimensional (2D) finite element method and compared according to three criteria: torque density, torque ripple, and machine efficiency. The seven-phase/seven-slot/six-pole machine is chosen with the best compromise of high torque density, small torque ripple (3.89%), and high nominal efficiency (95%). This machine is then compared with a reference design surface-mounted permanent magnet synchronous machine (SM-PMSM). The simulation results are discussed and demonstrate that the MB-WRSM presents interesting performance features, such as extended field weakening range, with overall performance closely matching that of an equivalent SM-PMSM. [ABSTRACT FROM AUTHOR]

Permanent magnet synchronous motors are widely accepted in automotive applications. The high torque density, high rotational speed with maximum efficiency in electric vehicle applications is technically challenging for motor design. However, these machines are expensive and difficult to work at high-temperature harsh environment due to permanent magnets demagnetisation features. Alternatively, switched reluctance motors can provide similar output characteristics and a wider speed. Thus these are considered to be more fault tolerant and more reliable. This study proposes a 20 kW, three-phase switched reluctance motor and analyse its overall performance and harmonic contents. The study is conducted by optimising the slot filling factor, excitation voltage and switching sequence of an asymmetrical half bridge converter. A finite element model is used to predict the core and copper losses and other influencing parameters. Simulation results are presented and analysed the effectiveness of the proposed switched reluctance motor (SRM). [ABSTRACT FROM AUTHOR]

This study introduces the development of the straight pole four-phase double-stator switched reluctance machine (SRM) which is considered to provide high torque density and low copper loss. The basic concept behind this design is to combine the features of the mutually coupled SRM and the double-stator SRM. In this study, the analytical method alongside the 2D finite element method (FEM) verification would be presented to reveal the developing path. Moreover, to verify the proposed SRM concept, the prototype machine has been designed and built. The performance result from 2D FEM is presented. [ABSTRACT FROM AUTHOR]

This paper proposes dual-stator permanent magnet Vernier (DS-PMV) machines for direct-drive applications. Also, the quantitative comparison of DS-PMV machines is carried out in terms of no-load performance and output torque characteristic. First, the operation principle is elaborated. Then, the theoretical expressions of air-gap magnetic fields are derived through the magnetic circuit approach. Moreover, the basic machine performances with different pole–slot configurations are quantitatively compared. The corresponding demonstration results are given, which verify that the designs without auxiliary teeth tend to have lower amplitudes of back electromotive force (EMF) harmonics, higher rated average torque, and lower torque ripple. [ABSTRACT FROM AUTHOR]