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This paper investigates the use of fractional-slot concentrated windings (FSCWs) in large-scale (MW level) offshore wind generators. It focuses specifically on a power rating of 3 MW and uses an existing direct-drive synchronous PM machine (DD-SPM) with 480s/160p and dual three-phase integer-slot winding (ISW) as a baseline. A multiple of the common 12s/10p FSCW machine is used that matches the electrical frequency of the ISW machine, yielding a 192s/160p dual three-phase machine. The hybrid star–delta connection has grown increasingly popular owing to its unique harmonic cancellation properties, which can help reduce rotor and PM eddy current losses in FSCW machines. In this paper, two dual three-phase star–delta-wound machines are scaled to 3 MW and included in the investigation. Specifically, a 384s/160p dual three-phase and dual star–delta winding machine, which is a multiplication of the 24s/10p machine, and a 192s/176p dual three-phase and dual star–delta winding machine, which is a multiplication of the 24s/22p machine, are used. These machines are investigated using finite element analysis (FEA) and compared on the basis of their air-gap flux density harmonics, open-circuit electro-motive force (EMF), torque performance, and losses and power. It is found that the proposed 384s/160p dual star–delta winding machine has the best electromagnetic performance of all, with a stator power that is 1.2% greater than that of the baseline ISW machine. However, this machine has a coil pitch of 2 and so loses the manufacturing and fault-tolerant advantage of having concentrated windings. If concentrated windings are desired, then the proposed 192s/176p dual star–delta winding machine is the best choice, with the stator power only 2.6% less than that of the baseline ISW machine, but unfortunately still has significant rotor and PM eddy current losses. [ABSTRACT FROM AUTHOR]

Axial flux permanent magnet (AFPM) machines are being increasingly used in several applications owing to their outstanding features. Most importantly, they are characterized by a high power-to-weight ratio, compactness, and high efficiency. Designers of AFPM generators seek to achieve the required performance and ensure the proper operation of the machine for the targeted application. Among many other parameters, the performance of the machine is highly dependent on the air gap magnetic flux density and no-load induced voltage. Accurate computation of such parameters helps minimize the overall design process. Therefore, the estimation of flux density plays a vital role in determining many other dependent parameters in AFPM machines. This manuscript provides a robust Correlated Analytical Method (CAM) for calculating the air gap magnetic flux density and no-load induced voltage of Coreless Axial Flux Permanent Magnet Generators (CAFPMG). CAM is an extended version of the Simplified Analytical Method (SAM) that is adjusted using correlated coefficients derived from an experimentally validated Three-Dimensional (3D) Finite Element Model (FEM). A complete procedure for the calculations is provided. The results showed the integrity of the CAM compared to the results obtained from the validated FEM. Such a technique will help designers of CAFPM machines perform parametric analysis and optimization in a fast and reliable manner. [ABSTRACT FROM AUTHOR]

This paper introduces a novel index for static eccentricity (SE) fault diagnosis in synchronous reluctance motors (SynRMs). Although SynRMs with rotor barriers under SE have been modeled in a few papers, any indices for the fault detection have not yet been reported. The proposed index is a specific frequency pattern in the motor current, which can also determine the fault severity. A novel analytical magnetic field investigation is applied to ascertain the proposed index. An accurate nonlinear numerical method is proposed for the motor inductances calculation. The model considers the rotor flux barriers, magnetic saturation, and the stator slots effect. The air gap flux density and the motor current are then achieved. The fast Fourier transform is exploited as a signal-processing tool to calculate motor current spectra. Then, a two-dimension time-stepping finite element method is used to attest of the proposed numerical model. Effectiveness of the proposed index is verified by simulation and experimental tests. [ABSTRACT FROM AUTHOR]

Cogging torque can affect the performance of permanent magnet (PM) homopolar inductor machines (HIMs). In order to find the reduction methods of the PM HIM cogging torque, it is necessary to investigate its production mechanism and analytical model. In this paper, the production mechanism of the PM HIM cogging torque is revealed from the perspective of air‐gap field modulation principle. It is found that the air‐gap permeance of PM HIMs can modulate their air‐gap magneto‐motive force (MMF) and then a large number of modulated air‐gap magnetic fields are generated. These magnetic fields with identical production condition but different rotation speeds or rotation directions can interact with each other, hence the production of the PM HIM cogging torque. By the combination of energy method and air‐gap field modulation principle, the cogging torque analytical model of PM HIMs is derived. Based on the obtained analytical model, the methods for reducing the PM HIM cogging torque are further analyzed. Finally, a 48‐slot/4‐pole (48S4P) PM HIM is designed and exampled. The air‐gap flux density of the 48S4P PM HIM is simulated by three‐dimensional (3‐D) finite element analysis (FEA). Based on the harmonic analysis for the simulated results, the correctness of the proposed cogging torque production mechanism is validated. In addition, a prototype of the 48S4P PM HIM is manufactured. The cogging torque in the prototype is obtained by the analytical model, 3‐D FEA and experiments, respectively. The simulation and measurement results verify the correctness of the cogging torque analytical model. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

The effect of winding chording on five-phase synchronous reluctance motor (SRM) modelled in phase variables is presented. The stator winding configuration is shifted a pole pitch from a fullpitch configuration to a 54 degrees over-full-pitched configuration incorporating the effect of 3rd harmonic of the air-gap magneto-motive force in the inductance equations. The models are monitored on starting, synchronism, loading, faults and loss of synchronism. These are considered simultaneously with vector potential, rotor speed, air-gap flux linkage and winding current. The phase variable (analytical) models have been simulated by using MATLAB/Simulink software while ANSYS Maxwell software has been used to simulate the finite element model (FEM) of the motor for corresponding chording ranges for comparison on direct online starting (DOL). Under all conditions considered in the work, the detailed results are presented and very close similarity is observed between the analytical and the nearly ideal FEM model for all chording ranges and the similarity is enhanced with increase in chording angle. [ABSTRACT FROM AUTHOR]

A transverse flux linear motor is a special type of linear motor with a high thrust force density, and it has broad application prospects in the field of linear direct-drive systems. In the process of oil production, the vibration of the linear motor poses a significant amount of harm to the system due to its special slender structure. This paper focuses on the electromagnetic vibration of a transverse flux permanent magnet linear submersible motor (TFPMLSM). Firstly, the no-load air gap flux density is calculated based on the field modulation principle. Secondly, the radial electromagnetic force (REF) of the TFPMLSM is calculated, and the finite element method (FEM) is used to analyze the time-space and spectral characteristics of the REF. Then, the influence of secondary eccentricity on the frequency spectrum of the REF is further concluded. Finally, the natural frequencies of each vibration mode are calculated using the modal superposition method and the influence of the REF on the motor vibration is obtained through magnetic-structural coupling analysis. The research results found that the motor does not cause resonance at low speeds, and the fundamental frequency of REF has the greatest impact on electromagnetic vibration. [ABSTRACT FROM AUTHOR]

In this study, a generalized torque estimation method is proposed for synchronous motors, including surface permanent magnet synchronous motors (SPMSMs), synchronous reluctance motors (SynRMs), and interior permanent magnet synchronous motors (IPMSMs) for building the analytical motor model. The average motor torque is estimated using the Lorentz force by the generated flux density in the air gap to determine the relationships among torque, flux density, and injected current. In the proposed method, the generated flux density is derived step by step by considering the effects of magnetic flux saturation, the stator slot, the rotor barrier, and permanent magnets (PMs) to ensure that the generated average torque complies with the operating condition of the motor. To verify the proposed method, the output torque of finite element analysis (FEA), Maxwell 2D, is compared to the proposed method in a SPMSM. Moreover, a phasor diagram is plotted to determine the mechanism through which torque is generated in SynRMs and IPMSMs. A SynRM and an IPMSM with ferrites PMs are analyzed using the proposed method, FEA, and the experimental results of this study indicate the effectiveness. [ABSTRACT FROM AUTHOR]

The aim of this article is to develop a rotor reconstruction method for the V‐shaped interior permanent magnet (IPM) machine so that the subdomain method to analytically calculate the air‐gap flux density can be applied. With the proposed method, the V‐shaped IPM rotor with rectangular magnets, magnetic barriers, and saturated iron bridges can be transformed into a U‐shaped equivalent analytical model. The geometry and material parameters of the magnets in the equivalent U‐shaped model can be determined according to the flux equivalence in the air‐gap of the motor. Then using the subdomain method on the U‐shaped equivalent rotor, the static magnetic field problem can be solved and the flux density distribution in the air‐gap be obtained. The validity of this method and accuracy of the solution is verified by the finite element method with case studies. Compared with existing methods, the improved subdomain method has higher accuracy in calculating flux density including radial and tangential components. The presented rotor reconstruction method is not only limited to single‐layer V‐shaped rotor, it can also be applied to other IPM rotors with more complex structures. It is valuable in the design, optimisation of IPM motors, and even development of new rotor topology. [ABSTRACT FROM AUTHOR]

Recently, the interest in consequent-pole flux-switching permanent magnet (CP-FSPM) machines has been increasing because of the flux-focusing PM arrangements and the removal of the flux-barrier effect. A simple and rigid outer-rotor salient pole rotor structure can be adopted in CP-FSPM machines, making them applicable for in-wheel direct-drive applications. In this study, three CP-FSPM machines with II-shaped (II-PM), V-shaped (V-PM), and straight U-shaped PM (SU-PM) arrays are analyzed and compared. Moreover, a CP-FSPM machine with inclined U-shaped PM (IU-PM) arrays is proposed to improve the flux-focusing effect and stator slot utilization. The working principles of CP-FSPM machines are analyzed by adopting a semi-analytical model. Combining the finite element analysis (FEA) results of air gap flux density and the analytical model of phase back electromotive force (EMF), the contributions of multiple working harmonics to the back EMF are quantitatively analyzed. Additionally, 6/16 and 6/17 CP-FSPM machines with different PM arrangements are globally optimized. Both the no-load and on-load performance of the optimized machines are included in the performance comparison. The results illustrate that the 6/16 and 6/17 machines exhibit their respective merits, and the IU-PM machine shows the best torque production ability in these CP-FSPM machines with the same design criteria. [ABSTRACT FROM AUTHOR]

Based on the magnetic gear effect, the field-modulated permanent-magnet machine (FMPMM) can realize the unequal pole design of the rotor PM field and the stator armature magnetic field. With the advantages of high torque density and high efficiency, the FMPMM has been widely studied in low-speed direct-drive applications. As a kind of machine excited by PMs, the performance of the FMPMM was affected by the demagnetization state. However, the method for establishing the FMPMM demagnetization model based on a finite element analysis (FEA) presented some problems, including tedious repeated modeling work and long calculation time-consuming under fine subdivision. Therefore, in this paper, a six-phase surface-mounted FMPMM was taken as an example, and an equivalent magnetic network (EMN) model was proposed for evaluating the machine performance under demagnetization. In order to realize the rapid establishing EMN models under diverse demagnetization types, the variable coercivity of PM was introduced. Furthermore, for the purpose of improving the calculation accuracy and shortening the calculation time, the least square method was used in fitting and analyzing the discrete results. Then, in order to verify the validity of the proposed EMN model, a prototype was fabricated and a testing platform was built. The air-gap flux density and the no-load back EMF obtained by the FEA, the proposed EMN model, and the experimental testing were compared. The results showed that the proposed EMN model can realize the rapid modeling and accurate analysis of the six-phase surface-mounted FMPMM under diverse demagnetization types. [ABSTRACT FROM AUTHOR]

In the design process of surface-mounted permanent magnet motor (SPMSM) for industrial robots and computer numerical control (CNC) machine tools, to pursue the sinusoidal nature of the back electromotive force, the magnetic poles in the form of eccentric pole cutting structure are often used. To analyze the no-load air gap magnetic field of the SPMSM with eccentrically cut poles simply and accurately, a subdomain model magnetic field analytical calculation method based on equal-area integral block processing of permanent magnets is proposed. The problem that the traditional subdomain analysis model cannot be directly applied to the SPMSM with eccentrically cut poles of unequal thickness is solved. The proposed method considers the influence of stator slotting and the actual permeability of permanent magnets, and directly obtains the fundamental wave and harmonic components of the no-load air gap flux density by solving the subdomain model. The finite element method (FEM) is used to directly calculate the air gap magnetic field for verification. The results of the analytical method and the no-load air gap magnetic density calculated by the FEM are consistent, which verifies the accuracy of the proposed analytical method and can quickly guide the design of the SPMSM with eccentrically cut poles. [ABSTRACT FROM AUTHOR]

To improve the performance of low-speed large-torque direct drive systems in limited space, an axial field flux-switching composite machine (AFFSCM) is proposed in this paper. The AFFSCM is composed of an axial field flux-switching permanent magnet machine (AFFSPMM) and magnetic gear. Therefore, it has the advantages of a compact structure, a large power/torque density, and a wide speed regulation range. First, the topology and magnetic modulation mechanism of the AFFSCM are investigated in detail. Then, the harmonic components of the inner/outer air-gap flux density are analyzed before and after the regulation of the rotary magnetic modulation ring. Based on this, the coupling conditions of the inner/outer air-gap magnetic field are deduced. Then the AFFSCM is initially designed, a three-dimensional finite-element model of the AFFSCM is built, and the electromagnetic performances are analyzed by the finite-element method, including the flux density of the inner/outer air-gap, the speed, the static torque, etc. Next, the cogging torque of the AFFSPMM is analyzed and optimized based on the magnetic modulation mechanism to suppress the torque ripple of the AFFSCM. Finally, an 800 W prototype is constructed and related experiments are done to validate the AFFSCM. [ABSTRACT FROM AUTHOR]

This study elaborates upon a new modular split‐tooth permanent magnet‐assisted switched reluctance motor (MSTPM‐SRM). In the proposed topology, the stator comprises six modular E‐cores in which the middle poles are split into two teeth. Two permanent magnets (PMs) are placed between each module's middle and side poles. Primarily, the proposed topology is introduced. Next, the principle of operation of the proposed topology are elucidated, and the magnetic equivalent circuit analysis is adopted in order to validate the operational basics. It is proved that the embedded PMs significantly increase the air‐gap's flux density and adjusts the poles' flux density. The flux density distributions, static, and steady‐state characteristics of the proposed MSTPM‐SRM motor and its PMless counterpart are extracted by utilising 2‐D finite element analysis. It is illustrated that the average torque of the proposed MSTPM‐SRM is dramatically increased compared to its PMless counterpart, especially at high excitation currents. Furthermore, the cogging torque analysis is done and it is shown that the proposed structure has approximately zero cogging torque. Finally, a prototyping version of the proposed motor is fabricated, and the experimental results are elicited. It is shown that the experimental results endorse the simulation results. [ABSTRACT FROM AUTHOR]

This paper deals with the design and analysis of a surface-mounted outer rotor in-wheel motor (IWM) with the aim of reducing cogging torque and torque ripple for electric vehicles. The proposed IWM is equipped with axial sinusoidal surface-mounted permanent magnets (PMs), with the purpose of producing sinusoidal air gap flux density distribution, thus to realize sinusoidal back electromotive force (EMF) and smooth electromagnetic torque. To highlight the advantage of the proposed IWM, the conventional IWM with tile-shaped PMs and the IWM with stepwise-shaped PMs are also studied for comparison. The finite element method in the commercial software package is utilized to analyze the performance of the three motors, including the radial flux density of air gap, back EMF, cogging torque, and electromagnetic torque. Through the quantitative comparison, it is found that the proposed IWM greatly reduces the cogging torque, highly improves the sinusoidality of back EMF, and nearly eliminates the torque ripple. [ABSTRACT FROM AUTHOR]

This paper investigates the torque generating capabilities and performance comparison of induction machines (IM) and interior-permanent magnet (IPM) machines for electric vehicle (EV) traction applications. Electromagnetic performance characteristics, such as torque, torque ripple, air-gap flux density, etc. are quantitatively compared by changing the level of electric loading. Other performance metrics such as saturation factor, power losses, efficiency, and so on, as well as the flux-weakening capability and efficiency map have also been compared. For calculations of the electromagnetic performance characteristics, 2D time-stepping finite element analysis (FEA) has been employed. It has been revealed that due to the reduction in torque components of IPM machine as a consequence of magnet demagnetization, it cannot generate toque as high as IM under overloading operating conditions. A thorough review of the literature on comparative studies on the electrical machines used in EV or Hybrid EV (HEV) applications is also included. [ABSTRACT FROM AUTHOR]

Multiple factors and consequences may lead to a stator winding fault in an external rotor permanent magnet synchronous motor that can unleash a complete system shutdown and impair performance and motor reliability. This type of fault causes disturbances in operation if it is not recognized and detected in time, since it might lead to catastrophic consequences. In particular, an external rotor permanent magnet synchronous motor has disadvantages in terms of fault tolerance. Consequently, the distribution of the air-gap flux density will no longer be uniform, producing fault harmonics. However, a crucial step of diagnosis and controlling the system condition is to develop an accurate model of the machine with a lack of turns in the stator winding. This paper presents an analytical model of the stator winding unbalance fault represented by lack of turns. Here, mathematical approaches are used by introducing a stator winding parameter for the analytical modeling of the faulty machine. This model can be employed to determine the various quantities of the machine under different fault levels, including the magnetomotive force, the flux density in the air-gap, the flux generated by the stator winding, the stator inductances, and the electromagnetic torque. On this basis, a corresponding link between the fault level and its signature is established. The feasibility and efficiency of the analytical approach are validated by finite element analysis and experimental implementation. [ABSTRACT FROM AUTHOR]

This document deals with the design of a Permanent Magnet Synchronous Motor (PMSM) to peripherally drive a counter-rotating pump inducer. The motor/pump is associated using a rim-driven principle where the motor's active parts are located at the periphery of the inducer blades. It proposes using a Halbach array of permanent magnets for the active rotor of the motor. This solution allows the generation of a Sinusoidal Electromotive Force (EMF). Therefore, a more stable electromagnetic torque is reached. An optimum geometry suitable for the inducer specifications while respecting operational constraints is determined. The obtained geometry is then simulated using the Finite Element Method. The results are satisfactory in terms of average torque and EMF waveform. Use of the Halbach array allows a significant improvement of the flux density in the air gap compared to a designed surface-mounted machine. The experimental validation will be performed once the prototype is realized in the Laboratory of Fluid Engineering and Energy systems (LISFE). [ABSTRACT FROM AUTHOR]

In this paper, power-sizing equations of rotor-permanent-magnet flux-switching (RPM-FS) machines are proposed and implemented, where the main decisive factors of the electromagnetic torque, namely electric loading and magnetic loading, are deduced, respectively. Although the topologies of RPM-FS machines are evolved from traditional stator-PM flux-switching machines, there are still seriously flux leakages between poles, and it is hard to derive the peak value of the air-gap flux density directly. Hence, a local simplified magnetic equivalent circuit is utilized to calculate the magnetic loading, which is crucial for the power-sizing equation. The influences of the pole-to-pole flux-leakages and harmonics in back-EMF are considered to improve the calculated accuracy of the power-sizing equation. Consequently, the electromagnetic torque can be predicted with acceptable accuracy. The feasibility of the power-sizing equation is verified by the finite element analysis and experimental results. [ABSTRACT FROM AUTHOR]

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]

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]

The double‐sided permanent magnet linear synchronous motor (DS‐PMLSM) is widely used in the industrial field with high precision and long strokes due to simple construction, high instantaneous thrust and high controllability. However, parasitic issues, such as unavoidable manufacturing tolerances, might cause the symmetrical position deviation of primary or secondary components, which results in an asymmetrical air‐gap between components, affecting the motor's electromagnetic characteristics further. In this paper, it is taken into account secondary torsional or offset conditions (the secondary component is displaced sideways from a symmetrical position), and investigates the variations of electromagnetic characteristics on the 12‐solt 14‐pole short‐primary DS‐PMLSM. Based on the finite element method (FEM), the effects of secondary torsion or offset on the air‐gap flux density, the back‐EMF, the detent force, the thrust force, and the normal force are investigated and compared respectively. In addition, the analytical results of the back‐EMF considering lower secondary torsion are verified on a lower secondary torsional prototype. From the analytical results of electromagnetic characteristics, it is revealed that with the torsional angle or offset distance rising, the normal force and detent force in the Y‐axis gradually increase, while the thrust force and the back‐EMF decrease. These theoretical researches can play an important role in the operation and assembly process of the DS‐PMLSM. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [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]

This paper presents a new topology of an axial flux-switching memory machine with series-type permanent magnets (SPMs) to improve the flux regulation capability. The key idea was to combine low coercive force (LCF) PMs, which can be magnetized and demagnetized readily, with high coercive force (HCF) PMs in series to provide a variable air-gap magnetic flux. The flux regulating principle and the forward magnetization effect of HCF PMs on LCF PMs are presented and discussed. Based on 3D finite element analysis (FEA), the magnetization variation of LCF PMs and the electromagnetic performances of the machine under different magnetization states were investigated. Simulation results showed that the air-gap magnetic flux could be weakened by up to 45% by using a magnetization current impulse, significantly extending the PM motor's flux-weakening speed range. Finally, a prototype machine was built, and experiments were performed to validate the predictions. The basic experimental validation shows that the measured back-EMF and the flux regulating characteristic matched the 3D FEA results well. [ABSTRACT FROM AUTHOR]

Factors such as insufficient heat dissipation and excessively high temperature can easily lead to demagnetization of the PMs in permanent-magnet (PM) motors. As a result, the magnetic field distribution of the motor will not be uniform, producing fault harmonics and lowering the operational performance of the motor. An essential stage in the diagnosis of faults and the monitoring of motor condition is the establishment of an accurate model of motors with demagnetization faults. In this paper, demagnetization faults are modeled by changing the Fourier coefficients in the Fourier expansion of the magnetization of PMs. This model can be used to determine the motor performance under various types of demagnetization, including radial air gap flux density, back electromotive force (EMF), and torque. On this basis, the corresponding relationship between the demagnetization degree and the fault signature is established, to provide a theoretical foundation for the subsequent demagnetization fault diagnosis. The finite element analysis (FEA) verifies the effectiveness and superiority of the proposed analytical model. The modeling method proposed in this paper can be applied to PM motors with PMs having different magnetization directions and shapes because it is based on the demagnetization region of PMs. [ABSTRACT FROM AUTHOR]

An analytical subdomain model is employed in this paper for predicting the magnetic field distributions in a three-phase double-stator permanent magnet synchronous machine (DSPMSM) during open-circuit and onload conditions. Due to the stator cores are located in the outer and inner parts of the motor, the DS-PMSM construction is quite complex. The rotor magnets are positioned between these two stators. The stator inner radius, stator outer radius, slot opening, magnet arc, magnet thickness, inner and outer air-gap thickness and number of windings turns will directly influence the motor performance in DS-PMSM. The analytical subdomain model employed in this paper has a significant advantage as a rapid design tool since it is capable of precisely predicting the performance of DS-PMSM while requiring less computational effort. The analytical model was initially created using the separation of variables technique in four subdomains based on the Poisson’s and Laplace’s equations: inner air-gap, inner magnet, outer magnet and outer air-gap. Applying the appropriate boundary and interface conditions yields the field solutions in each subdomain. Besides, the fractional DSPMSM with different number of slots between outer and inner stators to rotor poles can result in low cogging torque and non-overlapping winding configuration. The analytical results are validated by Finite Element Analysis (FEA). The slotted air-gap flux density, back-emf, and output torque have all been evaluated as electromagnetic performances. The results demonstrate that the suggested analytical model is capable of accurately predicting the DSPMSM performance. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNT), CNT–aluminum (CNT–Al), and CNT–copper (CNT–Cu) composite wires have shown remarkable electrical and mechanical properties for developing windings of single-phase induction motor. A quest has been made that if these advanced carbon nanomaterials can outclass commonly used electrical wire metals to significantly leverage electrical machines. However, these advanced materials are still in laboratory stage and most material properties are not yet experimentally reaching to their expectations. Therefore, there is need to understand the potential of these nanomaterials for electrical machines and the numerical analysis of the performance of electrical machines with various advanced novel carbon nanomaterials is still a challenge. This paper presents a comprehensive study to compare the performance of a single induction motor with its stator and rotor made with different winding materials. In doing so, the traditional copper and aluminum rotor and stator coils have been replaced by windings made of pure CNT yarn, CNT–Al, and CNT–Cu wires. A 2-D induction machine model was developed for the simulation study conducted in COMSOL Multiphysics finite element-based software. General-purpose sizing and power equations were utilized during the computation. The simulated results of flux distribution, air-gap flux density, torque, and corresponding output power were used as criteria to determine the highest quality solution. The simulation results revealed that using CNT–Cu and CNT–Al wires as machine winding can achieve 25.9% and 16.8% higher efficiency, respectively, than using CNT wires. The motor torque from the proposed finite element model was validated against the experimental results under identical speed and input voltage, and an error of 5.9% suggests that the model can be used to predict the motor performance with reasonable accuracy. [ABSTRACT FROM AUTHOR]

In this study, the influence of slot opening on the leakage reactance, power factors, winding current, and air gap flux density, as well as other parameters of the surface-mounted permanent magnet synchronous motor driven by an inverter is analyzed using the two-dimensional time-step finite element method. Thus, the law of permanent magnet power loss caused by slot opening under PWM qa obtained. The results show that the leakage reactance of the motor increased when the slot opening decreased from 7 mm to 2 mm. Then, the armature ripple current caused by the inverter was found to be suppressed well, and the high harmonic current was filtered well. This reduced the amplitude of the high-order harmonic of the air gap flux density, and the permanent magnet power loss was reduced by nearly 75%. Finally, two prototypes with different slot openings were tested for permanent magnet temperature rise, which verified the analysis method and calculation results proven in this paper. [ABSTRACT FROM AUTHOR]

This article proposes a hybrid evaluation method of electromagnetic force and vibration for electrical machines considering high-frequency current harmonics caused by the inverter. First, the permeance and armature magnetomotive force (MMF) is calculated based on the virtual MMF and the slot matrix. Then, the air-gap flux density and electromagnetic force construction process under arbitrary current is thoroughly studied. The vibration transfer function is obtained by utilizing the modal analysis and the modal test. Finally, the vibration can be calculated according to the modal superposition method. By applying this method to an interior permanent magnet machine, it can significantly reduce the computation efforts compared with the multiphysics procedure due to the extensive use of the finite-element method. In addition, the accuracy of this method is validated by conducting an experimental study. [ABSTRACT FROM AUTHOR]

The use of a magnetic adjustable speed drive is a popular choice in industrial settings due to its efficient operation, vibration isolation, low maintenance, and overload protection. Most conventional magnetic adjustable speed drives use various forms of the permanent magnets (PMs). Due to the PMs, this type of machine has continuous free-wheeling losses in the form of hysteresis and induced eddy currents. In recent years, the homopolar-type rotor has been widely used in high-speed machines, superconducting machines, and in the application of flywheel energy storage. This study proposes a new application of the homopolar-type rotor. A novel adjustable speed drive with a homopolar-type rotor (HTR-ASD), which has obvious advantages (no brush, no permanent magnet, and no mechanical flux regulation device), is designed and analyzed in this study. Its speed and torque can be adjusted only by adjusting the excitation current. Firstly, in this study, the structure, operation principles, and flux-modulated mechanism of the HTR-ASD are studied. The homopolar-type rotor has a special three-dimensional magnetic circuit structure with the same pole. The 3D-FEM is usually used to calculate its parameters, which is time consuming. In this study, an analytical method is developed to solve this issue. To analytically calculate the torque characteristics, the air gap magnetic flux density, and the winding inductance parameter, the equivalent circuit and the air gap permeance are researched to simplify the analysis. Then, the key parameters of the HTR-ASD are calculated. Finally, the performance of the HTR-ASD is comparatively studied using the analytical method and finite element method, and a comparison of the results is carried out. The comparison indicates that the analytical method is in good agreement with simulation results, and that it is very helpful for designing homopolar-type rotor machines. According to the analysis, the proposed adjustable speed drive displays a great performance in relation to the operating characteristics of a flexible mechanical speed drive. [ABSTRACT FROM AUTHOR]

As one of the key components, low-speed direct-drive in-wheel machines with high compact volume and high torque density are important for the traction system of electric vehicles (EVs). This paper introduces four different types of outer-rotor permanent magnet motors for EVs, including one five-phase SPM machine, one three-phase IPM machine with V-shaped PMs, one seven-phase axial flux machine (AFM) of sandwich structure and finally one hybrid flux (radial and axial) machine with a third rotor with V-shaped PMs added to the AFM. Firstly, the design criteria and basic operation principle are compared and discussed. Then, the key properties are analyzed using the Finite Element Method (FEM). The electromagnetic properties of the four fractional slot tooth concentrated winding in-wheel motors with similar dimensions are quantitatively compared, including air-gap flux density, electromotive force, field weakening capability, torque density, losses, and fault tolerant capability. The results show that the multi-phase motors have high torque density and high fault tolerance and are suitable for direct drive applications in EVs. [ABSTRACT FROM AUTHOR]

Due to the high power density, short axial size, and wide permanent magnet (PM) flux linkage regulation range, an axial-flux PM memory machine (AFPMMM) with hybrid Halbach array is investigated in this article. To solve the problem of magnetic density variation of Halbach array composed of different types of PMs in asymmetric bilateral air-gap structure, the analytical method for calculating the air-gap flux density of AFPMMM is presented through mathematical analysis, which uses cylindrical coordinate system instead of Cartesian coordinate system and is solved by equivalent method, separated variable method, and boundary conditions. The magnetic field generated by the Halbach array is divided into three directions: radial, circumferential, and axial. The analytical model is compared with the finite element method (FEM) simulation results to verify its effectiveness. In addition, an approximate piecewise linear hysteresis model with parallelogram return line is established based on the analytical expression of magnetic field. By applying different pulse currents to change the residual flux density of PM, the flux regulation characteristics of the motor are studied, and it is found that the air-gap flux density of the motor can be smoothly adjusted by continuously changing the pulse current, which plays a positive role in solving the problem of online magnetic regulation of the motor. [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]

In this paper, the boundary discretization method is used to improve the traditional subdomain model. The improved model can be used to calculate the magnetic field distribution in the region containing non-orthogonal boundary, avoiding the influence of the simplified stator slot or permanent magnet shape on the results in calculating the motor magnetic field using the traditional subdomain model. In addition, the improved subdomain model can also be used to calculate the air-gap flux density when the rotor is eccentric, instead of segmenting the air-gap to an equivalent state without eccentricity. The calculation object of this paper is a surface-mount permanent magnet motor with a rectangular stator slot. The air-gap flux density under no-load and load conditions is calculated, respectively. Since the improved subdomain model does not need to simplify the stator slot shape, the magnetic potential in the stator slot is also calculated. Finally, the air-gap flux density under rotor eccentricity is calculated, and the influence of the calculating parameters on the results of the improved subdomain model is discussed. All the calculated results are compared with those obtained by the finite element method, which verifies the accuracy of the improved calculation model. [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]

The magnetic field distribution in the air gap is of great importance in the design of rotary machines. In this article, an efficient analytical method is presented, which is capable of plotting the air-gap flux density waveform of induction machines (IMs) less time-consuming than the finite element method (FEM) does. The proposed method, based on the product of the current linkage waveform and the permeance waveform, utilizes the calculations of the steady-state equivalent circuit to ensure the accuracy and an equivalent air-gap reluctance model to take into account both the slot opening effect and the rotor movement. The method is tested on a general IM with different load cases and different design parameters, and the results are compared to the FEM calculations. It can be concluded that the proposed analytical method is an efficient option in the motor design to investigate the influence of the parameters on the flux density distribution. [ABSTRACT FROM AUTHOR]

This article proposes a novel axial field switched flux memory machine (AF-SFMM) which is analyzed by a combined analytical method. Compared with conventional axial field (AF) permanent magnet (PM) machines having magnets in the rotor side, the AF-SFMM benefits from good heat dissipation, high rotor robustness, and improved power density. Meanwhile, because of the utilization of low coercive force PM materials, the proposed machine can flexibly regulate air-gap flux. This analytical method is characterized by the combination of a quasi-3-D (quasi-3D) finite element method, a magnetomotive force–permeance-based method, and a virtual linear hysteresis model of low coercive force PM. In addition, compared with conventional time-consuming 3-D finite element analysis (FEA), the proposed method can improve the computational efficiency significantly with satisfactory accuracy. This makes the proposed combined analytical method suitable for preliminary sizing determination of AF-SFMM. Meanwhile, the effectiveness of the proposed analytical method is validated by FEA results. [ABSTRACT FROM AUTHOR]

This study investigated an efficient procedure for developing an accurate behavioral model of a cage induction motor (IM) based on the multiport Cauer ladder network (CLN). The CLN method was applied to a cage IM with semi-closed rotor slots as a model order reduction (MOR) technique, and a method for selecting the appropriate space harmonics (SHs) included in the air-gap flux density, which is necessary for a multiport CLN method for induction machines, was discussed. Then, the developed approach was applied to the transient analysis of the cage IM coupled with a control system, and its effectiveness in terms of computational accuracy and cost was investigated. [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 this paper, a type of novel composite structure coil applied in the coreless stator is proposed and studied to improve the output performance and efficiency of the axial flux permanent magnet (AFPM) machine. In which the effective conductor is changed to be wedge-shaped by the rolling technology so that the turns of coils and filling factor can be further increased, and the ends are kept in the cylinder with a larger diameter to reduce the DC copper loss. Meanwhile, the air region between the double rotors of the machine is also modified to be wedge-shaped, which fully matches the proposed coils and shortens the air gap length. The advantages of performance can be verified by the three-dimensional (3D) finite element analysis (FEA) and analytical method so that the output characteristics of no-load and load can be improved, and the DC copper loss and eddy current loss of coils can be reduced. The coreless AFPM machine finally performs a high efficiency of 95.34% according to these valuable optimizations. [ABSTRACT FROM AUTHOR]

Compared with the single‐stator permanent magnet synchronous motor(SS‐PMSM), the double‐stator permanent magnet synchronous motor(DS‐PMSM) can make full use of the space in the motor cavity to make it have higher torque density, so it is more suitable for direct‐drive occasions with low‐speed and high‐torque. This paper aims to design and compare the parameters and performances of DS‐PMSMs with four different rotor structures: 1)Series magnetic circuit of radial magnetised single‐layer permanent magnet(type Ⅰ), 2)Series magnetic circuit of radial magnetised double‐layer permanent magnet(type Ⅱ), 3)Parallel magnetic circuit of radial magnetised double‐layer permanent magnet(type Ⅲ), 4)Parallel magnetic circuit of tangential magnetised permanent magnet(type Ⅳ). Firstly, the equivalent magnetic circuit method is used to analyse the magnetic circuits of the four DS‐PMSMs. Next, the finite element analysis tool is used to compare the performances of the four DS‐PMSMs with the same volume. Their air‐gap flux density, no‐load back‐EMF, cogging torque, torque characteristics, moment of inertia, rotor loss and efficiency are quantitatively analysed and compared. Finally, this paper provides guidance and suggestions for the selection of the rotor structure of DS‐PMSM. [ABSTRACT FROM AUTHOR]

This paper presents an analytical approach to determine the air-gap magnetic field and the winding inductance in the brushless doubly-fed reluctance machine (BDFRM) with flux barriers. By dividing one flux guide layer into several segments, a calculus method based on magnetic circuit analysis is developed and specific analytical expression of the air-gap flux density is rigorously derived. Then, the included angle between fundamental components with the same pole pairs is also discussed. Based on the air-gap flux density distribution, the inductance expressions between different windings are also presented. Three kinds of finite element analysis models are established and studied. As a result, the accuracy of the analytical model can be verified by simulations and experimental data from an existing BDFRM prototype. [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]

Variable speed, permanent magnet synchronous machines with hybrid excitation have attracted much attention due to their flux-control potential. In this paper, a design of permanent magnet axial flux machines with iron poles in the rotor and an additional electrically controlled source of excitation fixed on the stator is presented. This paper shows results pertaining to air-gap flux control, electromagnetic losses, electromagnetic torque, back emf and efficiency maps obtained through field-strengthening and weakening operations and investigated by 3D finite element analysis. Moreover, the temperature distribution of the machine was analyzed according to the fluid–thermal coupling method. The presented machine was prototyped and experimentally tested to validate the effectiveness of numerical models and achieved results. [ABSTRACT FROM AUTHOR]

Axial flux permanent magnet (AFPM) motors are widely applied in many applications due to their performance advantages. A novel AFPM which owns a special winding form (120-degree phase belt toroidal windings) and a distinct rotor structure (sinusoidal rotor segments) is proposed in this paper to further improve the torque density of this kind of machine. First, the structure and working principle of the 120-degree phase belt toroidal windings sinusoidal rotor segments AFPM interior synchronous motor (120D-TWSRSAFPMISM) are clarified. Then, the design formula and crucial parameters of the motor are presented. Subsequently, the cogging torque is optimized by dividing the magnet grouping. Finally, the characteristics of the 120DTWSRSAFPMISM are analyzed and compared with those of the traditional toroidal windings sinusoidal rotor segments AFPMISM (T-TWSRSAFPMISM) and another T-TW motor without the sinusoidal rotor segments (T-TWAFPMISM) by finite element method (FEM). The results show that the 120D-TW can significantly increase the back electromotive force (EMF) compared with the T-TW, and the sinusoidal rotor segments can increase the air-gap flux density compared with the traditional interior rotor. Therefore, the 120D-TW and sinusoidal rotor segments are combined in the AFPM motor. This combination can further increase the torque density compared with the contrast motors. [ABSTRACT FROM AUTHOR]

To reduce the manufacturing cost, the cogging torque and the torque ripple of the traditional V‐shaped permanent magnet motor (TPMM), an asymmetrical less‐rare‐earth permanent magnet motor (ALREPMM) is proposed. An equivalent air‐gap flux density model is established, the model is employed to calculate the analytical expression of the no‐load back‐EMF, and the multiple objectives optimisation are carried out for the motor parameters based on the Taguchi algorithm. Electromagnetic performance of the TPMM structure and the ALREPMM structure is compared by finite element method‐based simulation. It is shown that the ALREPMM structure can reduce the amount of rare‐earth materials by 19%, and the cogging torque and the THD values of no‐load back‐EMF are reduced by 77.3% and 26.8%, respectively. Finally, a prototype is manufactured, thus verifying the rationality of the design of the ALREPMM structure through experiments. [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]

The consequent permanent magnet (CPM) pole rotor and harmonic utilization permanent magnet (HUPM) rotor are promising candidates for electric machines with less rare earth materials. Therefore, this article focuses on the analysis and comparison of these rotor types in terms of air-gap flux density characteristics, magnet utilization, and torque density. In the first part, an analytical approach is used to investigate the magneto motive force (MMF) distribution of the rotor and air-gap flux density characteristics. In the second part, finite-element methods (FEMs) are used to compare both rotor topologies with a conventional interior permanent magnet (PM) and spoke PM rotor. The results show that CPM and HUPM rotors can reduce the volume of PMs compared with the conventional configurations. However, with the HUPM rotor, a higher torque density and magnet utilization ratio can be achieved at the same time. [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]