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Millimeter wave components, such as circulators and isolators, frequently use magnetic fields to break symmetry of the signal propagation and provide unidirectional signal transmission. While effective, these components have not seen the level of miniaturization of other millimeter wave components, primarily due to the discrete nature of the magnets used in the components. Using circulators in the 40-50 GHz range as a motivating application, requirements arise for the deposited films, namely immunity to eddy currents, sufficient magnetization to act as self-biasing magnets, and out-of-plane orientation of the self-biasing field. Based on these required properties, hexaferrite materials are selected for their strong magnetocrystalline anisotropy (MCA) and low conductance. The difficulty of integrating these components monolithically with monolithic microwave integrated circuits (MMIC) originates from the incompatibility of crystal structure with standard semiconductor materials and process conditions. Additive manufacturing using a composite of strontium hexaferrite (SrFe12O19) particles and photoresist has been chosen as a method to overcome the difficulties of integrating hexaferrite material to semiconductor substrates. Due to their large internal anisotropy field, the particles of strontium hexaferrite tend to rotate to the field direction instead of changing magnetization direction under application of an external magnetic field (less than the anisotropy field). We have developed a method for 3D printing composites of high strontium hexaferrite concentration (up to 20% by volume) in a liquid photoresist, SU8. Rotation of hexaferrite particles in polymer matrix and thus magnetic anisotropy has been demonstrated in the composite, which is subsequently cured to hold the physical position and orientation of the particles. The anisotropy of the self-biasing field provided by the films has been experimentally characterized, and a ferromagnetic resonance (FMR) frequency ~43 GHz has been observed. We have also characterized the viscosity of the particle-laden polymer at different particle concentrations. 3D printing of this composite with poling will make it possible to directly print magnetic components that require out-of-plane anisotropic magnetization.

In this paper a novel Radial-Axial (RA) Flux Switching Permanent Magnet Generator (FSPMG) is introduced. In contrast to other RA flux machines, a major advantage of this generator is its implementation only by the use of conventional Non-Oriented Electrical Steel Sheets (NOESSs), even though the flux linkage of the novel RA-FSPMG has a three-dimensional (3D) path. Besides that, it benefits from the flux concentration strategy and a passive rotor. A concrete foundation of the novel RA-FSPMG is provided, in which, the 3D-Flux path is described, working principles are discussed, and power-sizing equation is derived. No-load (NL) characteristics and the Full Load (FL) performance of an optimized RA-FSPMG are investigated in contrast to an optimized Double Stator Radial (DSR) FSPMG and an optimized Double Stator Axial (DSA) FSPMG with similar volume, number of Permanent Magnets (PMs), and electrical loading. The results show the competitiveness of the novel RA-FSPMG, in particular, in the output power and the required copper mass. Furthermore, the PM demagnetization possibility and the rotor axial pull force of the optimized RA-FSPMG are investigated, in detail. All discussions are supported by the 3D Finite Element Analysis (3D-FEA) and experimental results.

This paper presents a new interior permanent magnet (IPM) rotor structure/ assembly which inherits from the Halbach magnet configuration and spoke-type IPM rotor to achieve a high saliency ratio and high torque/power density. A higher air-gap flux density and a higher saliency ratio are expected to improve torque density, while the rotor inner diameter can be maximized as much as possible to reduce core material consumption and increase internal space of the rotor. Accordingly, the electromagnetic performance of three motors consists of a unified stator but three different rotors, namely flux-concentrating rotor, Halbach array PM rotor and spoke-type IPM rotor is compared by finite element analysis (FEA). Due to the segmented structure of flux-concentrating PM rotor without magnetic bridges, the mechanical challenges are analyzed in detail for electric vehicle application. The stress analysis on the prototype design with fixing pins to hold the pole pieces validates the structural feasibility at 7200 r/min. Finally, a 72-slot/ 16-pole fractional-slot PM motor with new flux-concentrating rotor is manufactured and tested to verify its performance and feasibility. It can be concluded that the new rotor is superior to the spoke-type IPM and Halbach array PM rotor in terms of torque density and PM utilization.

This paper presents design studies on a rotor for the high-speed homopolar type permanent magnet motor that can be applied to super chargers for automobiles, cordless stick vacuum cleaners and so forth. A stator consists of a core and a permanent magnet. The rotor is composed of only a core, thus allowing removal of a retaining ring on the surface. In order to realize the maximum torque and power required from a target application under a constraint of core stack length, design studies based on three-dimensional finite element analysis are conducted. The design validation is confirmed through experimental tests using a prototype.

This paper presents and evaluates a dual rotor axial flux permanent magnet motor for electric aircraft applications. Several features, including grain oriented electrical steel (GOES), magnet segmentation, and wires with rectangular cross-sections, are used to improve torque density and efficiency. Rather than simply optimizing the motor by itself, this paper evaluates the tradeoffs between motor performance and its interfaces with the drive, thermal management system (TMS), and mechanical structure. This information can be used along with similar analyses of the drive, TMS, and structure to select a design that achieves the system-level optimal performance. The paper uses finite element simulations to characterize tradeoffs between active mass, efficiency, fundamental frequency, power factor, axial forces on the rotors, and cooling surface area. Several designs exceed 95% efficiency at takeoff with less than 8 kg of active mass. While high pole counts, a large outer radius, and short stator teeth tend to optimize the magnetic performance at takeoff, this can reduce cruise efficiency, reduce the surface area through which the TMS can extract heat, increase the fundamental frequency the drive must supply, and increase the structural mass required to support the rotors. Additionally, designs with 20 °C cooler magnets were simulated to evaluate the impact of a more effective TMS, but the improvements in magnetic performance were relatively small.

Magnetic positioning approach (MPA) is a reliable solution for automated guided vehicles (AGVs) under relatively fixed route conditions. Ferrite magnets are usually buried in the ground and employed as magnetic nails (MNs) for the parking and steering of AGVs. Our previous studies implemented a novel MPA based on super-strong NdFeB magnets and the minimize iterations between magnetometer data and predicted values via the magnetic dipole model, with the advantage of more exceptional positioning performance than traditional MPAs. Nevertheless, the iterative optimization algorithms depend on the initial guess setting; besides, the complicated calculation based on multiple magnetometer data makes it difficult to be executed on a microcontroller in real-time. In this article, we propose a simplified MPA based on the analytical method. The analytical expression for calculating the two-dimensional position of an MN is derived from the magnetic dipole model. Even a single tri-axis magnetometer can localize the MN, whereas multiple magnetometers tend to achieve higher positioning performance. Thus, positioning results of multiple magnetometers are fused based on the confidence criterion. Comparing with the MPA based on the Levenberg–Marquardt algorithm, the proposed MPA could achieve comparable positioning accuracy but with far lower computational complexity and greater robustness. Thereby, this article introduces a new concept of high-precision MPA for AGV applications without the complicated visual perception.

Permanent magnet synchronous motors (PMSMs) with non-concentric magnetic poles (NCMP) structure are widely used as high-precision servo motors. The current subdomain method mainly equates the NCMP to a rectangular magnet to make each subdomain boundaries of magnet parallel when calculating the magnet eddy current loss (ECL), which results in a lower accuracy of the calculation. This paper divides the NCMP into non-concentric region and concentric region along the radial direction. The non-concentric region is further divided along the circumferential direction, and each divided region has a single thickness. Based on the subdomain method, a novel analytical method of magnet ECL in PMSMs with NCMPs is proposed. Moreover, the 3-D distribution coefficient of ECL in the NCMP is derived by the equivalent impedance method. The effects of eddy current reaction and stator slotting are taken into account to improve the calculation accuracy. Then, through theoretical derivation, the relationship between the minimum magnet loss and the pole parameters is obtained, which provides a reference for the design of NCMPs. Finally, the loss separation experiment is performed on four prototypes with NCMPs. The experimental results, finite element method results and analytical results are compared to verify the correctness of the model.

The hollow-cup Permanent Magnet (PM) motors have the characteristics of low power consumption, and are widely used in the aerospace field. At present, the tile-shaped PMs used by hollow-cup PM motors have poor sinusoidal characteristics of the air gap magnetic flux density waveform, which will cause torque ripple. The existing method for improving the air gap magnetic flux density waveform is not very effective when applied to hollow cup, a special motor with no stator core and large air gap. A bow-shaped PMs structure is designed for the hollow-cup motor in this paper. First, the equivalent surface current method is used to calculate the analytical formula of the static magnetic field of the model. Then, the Finite Element (FE) method is used to calculate the static air gap flux density waveform of conventional tile-shaped PMs and bow-shaped PMs with different bow heights, and the corresponding harmonics and sine distortion are obtained by Fourier decomposition. The simulation results show that the bow-shaped PMs can effectively improve the sinusoidal characteristics of the static air gap flux density waveform. And the suitable bow height is determined. Finally, a prototype is made based on the suitable bow height for experiments, and compared with the analytical result and the FE result, and the accuracy and effectiveness of the bow-shaped PMs with the suitable bow height are verified.

In this paper, a method of simultaneous sensorless rotor position and torque estimation is proposed for interior permanent magnet synchronous machines at standstill and low speed. The proposed method estimates the torque using high frequency inductances identified from the current variations due to high frequency square wave voltage injections in the estimated dq-axeswhich are simultaneously used for sensorless rotor position estimation. The proposed method is not dependent on the fundamental model and has taken the cross-coupling effect into consideration, allowing for low cost and fast torque estimation at standstill and low speed. Both simulations and experiments are carried out to verify the effectiveness of the proposed method.

This paper has proposed a novel design of dual PM vernier machine with T-shape consequent pole rotor. The analytical model of T-shape magnet rotor based on differential magnetic network method are firstly derived. Given the additional optimizing parameter, edge arc difference, T-shape consequent pole (TCP) rotor has the potential to produce 6% higher fundamental airgap flux density or 30% higher PM utilization ratio than regular fan-shape consequent pole rotor. The influence of magnet size parameters including magnet thickness, pole pitch ratio and arc difference angle on airgap flux density of TCP rotor is then analyzed. The torque performance of TCP in regular consequent pole and dual PM consequent pole vernier machines are also studied. The comparison shows that T-shape consequent pole can produce higher torque than fan-shape magnet in vernier machines. At last, a prototype of dual-PM vernier machine with TCP rotor is built and tested, which has achieved 28 Nm/L measured torque density.

Homopolar inductor machine (HIM) has caught much attention in the field of flywheel energy storage system (FESS) due to its merits of robust rotor, brushless exciting, high reliability, etc. Compared with permanent magnet HIM (HIM-PM), the HIM with field winding (HIM-FW) can effectively eliminate the idling loss caused by the no-load magnetic field by cutting off the excitation current, while the charge/discharge efficiency of HIM would be decreased due to the copper loss of field winding. To address this contradiction, a novel PM HIM with mechanical flux modulator (HIM-MFM) is proposed to achieve low idling loss and high charge/discharge efficiency. Firstly, the special structure and operation principle of the HIM-MFM are investigated. Afterwards, the characteristic of equivalent magnetic circuit of the HIM-MFM is analyzed and several key structure parameters of it are optimized. Moreover, the electromagnetic performance indexes of the HIM-MFM, including back-EMF, flux weakening ability, losses, etc. are fully analyzed. Finally, a prototype of the HIM-MFM is designed, manufactured, and tested. Experiment results confirm those obtained by simulations. Results show that the proposed HIM-MFM inherits the merits of high charge/discharge efficiency of HIM-PM and almost no idling electromagnetic loss of HIM-FW.

This paper investigates the eddy current loss mechanism of a dual permanent-magnet-excited machines (DPMM). Based on the flux modulation effect, abundant harmonics are induced in the air gap of DPMM. The harmonics of air-gap flux density due to rotor PMs, stator PMs, and armature reaction are investigated qualitatively and separately. Then, the orders, frequency, and rotation speed of the harmonics are deduced theoretically. The harmonics that contribute to the eddy current losses are deduced accordingly. Finally, the loss distribution of the proposed DPMM is estimated through simulation and the thermal field of the proposed motor is analyzed. A prototype is fabricated to validate the analysis. Temperature rise of both stator and rotor PMs under rated load condition is measured through experiment.

This paper presents the design and control of a new Halbach-array-based two-phase motor (HTM) with a 3-D printed coil mount and magnet housing for precision motion control applications. The motor is based on a 2-pole Halbach cylinder that generates a uniform magnetic field within its inner diameter. Each pole has 10 magnet segments. This uniform field simplifies the Lorentz force calculation based on the volume integration. In addition, it allows for the real-time measurement of the rotor position based on Hall-effect sensors. Compared with conventional stepper motors and iron-core DC motors, this motor design can produce a continuous torque and precise positioning at any angular position without a cogging torque. In this paper the design of the motor together with its dynamics and control are presented. The design uses only one type of square-cross-section magnets that are readily available, making it easy to scale the design to a variety of sizes and torque capabilities. The 3-D printed stator and rotor housings allow for the motor to be constructed at a low cost in a short time. With a total magnet volume of only 30.7 cm3, a total effective coil volume of only 10.4 cm3, and a maximum current of 4 A, the maximum torque generated is 0.044 Nm. Experimental results with closed-loop control on a simple empirically-identified plant model are provided to validate the magnetic design of the motor. The feedback signals are from two Hall-effect sensors connected to a microcontroller, offering a theoretical angular resolution of 0.16. A minimum step size of 0.32 is demonstrated in positioning with closed-loop control. The motor has the capacity to track the commanded motion and speed with an error less than 0.64.

A modified configuration for Permanent Magnet Assisted Synchronous Reluctance Motors (PMaSyRM) is studied in this paper. Conventionally, the PM materials are inserted in the flux barriers region of the rotor. Consequently, the PMs sizing parameters will be restricted to the available space that may limit the efficient use of PMs benefits. In this study, a portion of the rotor structure is replaced with an Interior PM (IPM) rotor so that an axially segmented integration of IPM and SyRM is obtained. Thus, the PMs design is performed specifically in the IPM segment independent of the SyRM scheme, while the SyRM segment remains PM-less. The main motivation of this concept is to improve the contribution of the PM material in the total torque as well as utilizing the special property of the proposed rotor configuration for pulsating torque reduction. A computationally cost-effective algorithm is proposed for the optimal design of IPM-SyRM motor by which a low-power design is carried out for a lightweight electric vehicle. The results for torque profile characteristics, PM volume, power-factor, and efficiency are compared with a conventional PMaSyRM that has been optimally designed as the reference case. Finally, a prototype is constructed to verify the theoretical analysis.

This paper proposes an improved analytical model for fractional-slot concentrated-winding (FSCW) spoke-type permanent magnet (STPM) machines, where the impact of slotting on magnetomotive force (MMF) is elaborately considered. Firstly, the deficiency of the existing MMF-permeance model using Carters coefficient is discussed. It is found that adopting Carters coefficient will cause considerable prediction errors in flux density, especially for machines with a small equivalent airgap and considerable PM-MMF fluctuation. Secondly, an improved analytical model is proposed based on the relative permeance function and a simplified magnetic circuit model (MCM). The proposed model enables to predict common electromagnetic performance, such as PM flux density and back electromotive force (EMF) with more accuracy. Moreover, the radial forces exerted on the stator teeth can be predicted precisely as well, which is conducive to further vibration analysis. Both the experimental and finite element analysis (FEA) results indicate that the proposed model can enhance the characterization capability of slotting effect and improve performance prediction accuracy.

This paper proposes a novel approach to the modelling of HTS transformer-rectifier flux pumps that can charge HTS magnet-ic loads without the need for bulky current leads or expensive cryogenic requirements. The model was built in MATLAB/Simulink for a flux pump with 2 HTS switches, an HTS transformer with a primary inductance of 15 mH, second-ary inductance of 50 H and an HTS magnetic load with an in-ductance of 2 mH. With a 5 A pk-pk triangular current wave-form at 2 Hz the system can load the HTS load to 34.63 A in 5 s. This incremental addition of flux to the load demonstrates the advantage of flux pumps as they can charge high-field magnets without the need for large power sources. The speed of flux pumping is improved by increasing the system frequency, the magnitude of the dynamic voltage developed in the HTS switches and by increasing the primary inductance of the trans-former. This has widespread industrial applicability in fields such as the charging of high-field magnets for MRI systems.

The three-dimensional (3-D) finite element (FE) analysis is an extremely time-consuming task in the design and optimization of axial flux permanent magnet (AFPM) machines. The aim of this paper is to present a fast and accurate design model of slotless AFPM machines. Thanks to the separation of active- and end-winding parts, the overhang structure, which has widely been used in the air gap winding, can be handled by the proposed method. The winding eddy current loss, a primary source of losses in the air core structure, is incorporated into the analytical model. In addition to the high accuracy, this approach makes it possible to evaluate machine performances only once without needing to rotate the rotor position. As a result, the proposed analytical model can significantly reduce the computational time, preferred in applying an optimization algorithm. Finally, the accuracy of the proposed method is verified by both FE and experimental results.

This paper presents a novel magnetic-geared direct-drive machine (MGDM) with V-shaped permanent magnets (PMs) installed on its rotor. By extending the inner rotor shaft and connecting it to a prime motor, the torque and power density of the proposed MGDM is boosted. Additionally, compared with the conventional MGDM with surface-mounted PMs, the proposed MGDM with V-shaped PMs has a more robust rotor structure to cope with extreme operating conditions. The operating principle and structure requirement of this MGDM are first derived. Then, the geometrical parameters are optimized via a three-stage multi-objective optimization method to maximize output torque and efficiency and minimize torque ripple via the genetic algorithm and finite element analysis (FEA) combined optimization strategy. Furthermore, the proposed MGDM is artfully integrated into hybrid electric ships (HESs) to construct an onboard integrated power system (OB-IPS). Since the proposed system possesses various operating modes to cope with practical operating conditions, it enjoys a high systematic efficiency and good dynamic performance. Finally, a prototype is fabricated and tested with various operating modes by referring to the practical navigation cycle of a HES. The experimental results validate the feasibility of the proposed MGDM for being applied in HESs.

As a new type of flux modulation machine, line-start permanent magnet vernier machine (LSPMVM) has drawn more and more attention. Thanks to the rotor starting winding, the self-starting capability of which can be acquired without applying the inverters. As a result, the system reliability has been improved and cost can be decreased, which is promising for industrial applications, such as pumps and fans. In order to extend the family of LSPMVMs and select the preferable topologies meeting the different requirements, four LSPMVMs, including V-shaped LSPMVM, consequent-pole U-shaped LSPMVM, dual-stator spoke LSPMVM and consequent-pole surface-mounted permanent magnet (SPM) LSPMVM, have been proposed in this paper. And the steady state performance, starting and synchronization capability are comprehensively analyzed and compared, where the regular commercial line-start permanent magnet synchronous machine (LSPMSM) is used as a counterpart. It is found that all the proposed LSPMVMs can acquire the higher torque density. Especially, the V-shaped LSPMVM and consequent-pole U-shaped LSPMVM have the highest torque density, while the consequent-pole SPM LSPMVM can be a better candidate where the low cost is desirable. Finally, the prototype of V-shaped LSPMVM has been manufactured, where experimental results match well with finite element analysis (FEA).

The paper presents research on the development of a line-start synchronous reluctance motor (LSSynRM) and line-start permanent magnet synchronous motor (LSPMSM) based on components of a mass-produced three-phase low-power squirrel cage induction motor (IM). The aim of the research was to modify the squirrel cage rotor structure for which the best functional parameters characterizing the steady state of the LSSynRM and LSPMSM were obtained, while meeting the additional requirements for asynchronous start-up. Field-circuit models of the LSSynRM and LSPMSM have been developed in the professional finite element method (FEM) package, MagNet, and applied in the design and optimization calculations of the considered machines. Experimental testing on the designed LSSynRM and LSPMSM prototypes were carried out. The obtained results were compared with the performance of the reference IM. The conclusions resulting from the comparative analysis of these three motors are given and proposals for further work are discussed.

The influence of rotor position error generated by resolver on electromagnetic noise of permanent magnet synchronous motors (PMSMs) is analyzed in this paper. The motor noise is mainly caused by the electromagnetic force acting on the surface of stator teeth or permanent magnets. Firstly, the influence of rotor position error on current harmonics is deduced theoretically. The spatial and temporal characteristics of the electromagnetic force are then analyzed. The results show that the rotor position error will introduce extra sideband frequency harmonics to the current and electromagnetic force. This will lead to more abundant noise harmonics. The field-oriented control (FOC) model and the electromagnetic finite element model (FEM) are then established to simulate the influence of rotor position error on current harmonics and electromagnetic force. Finally, a test is carried out to capture the phase current and noise spectrum. Both the simulation and test results are consistent with the theoretical analysis results. This study can give a reference to the source identification and optimization of acoustic performance for PMSMs in electric vehicles.

Consequent pole (CP) permanent magnet (PM) machines offer scope to reduce the quantity of PM material and hence cost compared to more conventional PM machine topologies of the same rating. In this type of machine, the rotor pole arc is usually optimized to realize the largest output torque with pole shaping methods used to reduce torque ripple. However, such approaches tend to be limited by constraints imposed on the pole shapes. It is common practice to adopt similar PM and iron pole shapes, an approach which does not fully account for the different characteristics of PM and iron poles in CPPM machines, often leading to large even order harmonics in the airgap flux density. This paper proposes a shaping method with a variable rotor profile and pole arc span being established by means of optimization by a Genetic Algorithm. It is demonstrated that for a fixed quantity of PM material, different PM and iron pole shapes in combination with optimal PM and iron pole arc spans are essential for ensuring both maximum output torque and lower torque ripple when due account is taken of flux leakage. It also demonstrates that since the flux density in the region under a PM pole is governed by the magnetic potential produced by magnets while it is governed by magnetic reluctance under iron pole, different PM pole and iron pole shapes are necessary to reduce the even order harmonics in a CPPM machine and consequently to reduce torque ripple. The performances of optimized and more conventional CP machines are compared by finite element method on 12-slot/8-pole prototype motors.

This paper aims to analyze and design a fault-tolerant permanent magnet vernier (FTPMV) machine with improved power factor. Different from the existing FTPMV machine with uniform distributed split-teeth stator, hybrid stator and multiple working harmonics designs are adopted in this proposed machine. With these designs, the proposed machine can obtain not only improved power factor but also higher torque and good fault-tolerant performance. Firstly, the topologies, fault-tolerant design and working principle of the proposed machine are introduced. Then, accurate permeance and equivalent magnetic circuit analytical models are established for investigating the mechanism of power factor improvement. And the influences of some key design parameters on power factor and torque of the proposed machine are analyzed by finite element analysis. Lastly, a FTPMV prototype is manufactured and tested to validate the designs and analyses.

This paper investigates the short-circuit (SC) fault-tolerant control (FTC) method for a five-phase permanent-magnet synchronous machine (PMSM) with surface-mounted permanent magnets (PMs). By relieving constraint of zero d-axis armature magnetomotive force (MMF) and restraining backward-rotating MMF components to be zero, round rotating armature MMF with maximum q-axis armature MMF is achieved, which enables five-phase PMSM to output maximum smooth torque with lower losses and higher efficiency under SC fault condition. To ensure smooth post-fault operation in full speed range, the influence of winding resistance on SC current is further considered, which improves low speed operation performance. The proposed FTC method features sinusoidal currents with equal amplitude, which ensures better control simplicity and post-fault thermal uniformity between phases. Finite element analysis and experiments are carried out to verify the proposed method.

This paper proposes some effective approaches to address the inherent issues of consequent-pole (CP) permanent magnet (PM) machines, such as saturation of the salient rotor core and unipolar PM leakage flux of the end region caused by asymmetric field. The effect of CP Halbach PM array with different magnetization direction and parameters that affect the saturation have been investigated for the CP PM machine with short pole pitch. By employing the CP Halbach array, the saturation issue can be solved and superior performance can be obtained without reducing the PM pole arc. In addition, unequal and multistep staggered rotors with magnetic barriers have been proposed to reduce the unipolar leakage flux in the end region. Compared with regular staggered rotors, not only better electromagnetic performance can be achieved, but also the end unipolar leakage flux can be reduced. Finally, a prototype is manufactured and the predictions have been validated by measurements.

This study deals with a consequent-pole (CP) vernier motor with low cost ferrite magnets. To investigate the magnetic behavior of the CP permanent magnet vernier motor (CP-PMVM) quantitatively, two magnetic equivalent models are newly proposed which are applied to estimate the main and the modulation flux densities in air-gap, respectively. Using the proposed models, it is revealed that the CP structure substantially reduces the effective air-gap length, and thus a CP-PMVM with half number of magnets has much higher modulation flux density than that of a regular surface PM vernier motor (SPMVM). Consequently, the CP-PMVM is expected to able to keep the vernier effect high even with thick ferrite magnets, producing higher back EMF than the SPMVM does. Moreover, large variation of air-gap length due to thick magnet thickness leads to a considerable advantage of reluctance torque. For a proto-designed CP-ferrite PMVM, the electromagnetic characteristics such as main and modulation flux densities, back EMF, d-q inductances and torque have been investigated by using proposed method as well as finite element (FE) method. In addition, through the demagnetization analysis, it is proven that the proposed CP-PMVM has certainly enough anti-demagnetization capability while a SPMVM with ferrite magnets loses its magnetism. From the analysis results, it is confirmed that the proposed machine with less magnet volume and low-cost ferrite magnets has higher torque as compared to its SPM vernier counterpart. Finally, to validate the analytical and numerical analysis experimental results are provided.

This article presents a novel permanent magnet assisted flux-controllable machine, namely the hybrid-excited biased-flux machine (HEBFM). The proposed machine can implement flexible flux regulations (i.e., either field weakening or strengthening) by integrating the field current winding with the half consequence permanent magnet (PM) poles in the stator. The topology of the HEBFM can be explored to multi-pole cases, which contributes to improved flexibility for the flux control and winding regulation. Compared to the conventional flux-controllable machines, the proposed machine gains the merits of owning (i) extended flux control range via the modulation of winding factor (i.e., winding factor modulation), (ii) stable and compact structure and (iii) reduced demagnetization risk of permanent magnetics (PMs), (iv) capability of topology exploration. In this paper, operation principle and electromagnetic performance of the proposed machine is analyzed using the finite element method (FEM). Besides, the torque and torque ripple are optimized based on the multi-objective differential evolution (DE) coupled with FEM. Finally, a prototype is manufactured and tested to validate the effectiveness and feasibility of the proposed machine designs.

One of the main issues in manufacturing rotors for integer slot surface mounted permanent magnet (PM) synchronous motors is the rotor skew. Motor manufacturers typically prefer to avoid skewing due to the added complexity and the difficulty in controlling the accuracy of the skewing and achieving the required outcome. This paper proposes a design that minimizes torque ripple without using any kind of skewing in the rotor by using asymmetric AC windings with unconventional stator slot-pole combinations. First, feasible slot and pole combinations are reviewed for PM synchronous motors. Theory behind unconventional asymmetric and unbalanced AC winding PM motors is presented. A lumped-parameter magnetic equivalent circuit for such unconventional stator is provided for a 1.7kW PM motor. Detailed 2D Finite Element Analysis (FEA) is performed and compared with the lumped parameter model. A prototype motor is manufactured, and open-circuit as well as full-load tests are performed. Good agreement between the analytical, FEA and test results is obtained.

Permanent magnets vernier (PMV) machine is gaining more and more attention due to its high torque density contributed by multi-orders working harmonics, especially low-pole-pair numbers harmonics. Spoke array PM machine seems to be a good way to increase the machine working harmonics. But the flux barrier effect is revealed and it explains why the advantages of the spoke array PM vernier machine are not fully used. Thus, its low-pole-pair numbers harmonics could be further enhanced. In this paper, a novel structure—claw pole permanent-magnet vernier (CPPMV) machine is firstly proposed and its working principle is investigated. Then, the CPPMV machine is compared with the surface mounted PM vernier machine, the spoke array PM vernier machine and the spoke array PM vernier machine with alternate flux bridges in terms of their electromagnetic performances using equivalent circuit analysis and FEM. The result shows that claw pole structure can enhance the magnetic flux modulation effects, which increases the machine torque density. At last, a CPPMV machine prototype is manufactured and tested. Experimental results indicate that it reaches torque density of 30.5kNm/m3 and power factor of 0.84 under rated condition.

This paper focuses on the electromagnetic vibration source and its reduction design in fractional-slot concentrated-windings (FSCW) permanent magnet (PM) machines. Firstly, the electromagnetic force and vibration characteristics of a 12-slot/10-pole FSCW PM machine are investigated. Then, four electromagnetic vibration sources are investigated and compared, in which the machine operates state is considered. The result shows that the electromagnetic force modulation and stator MMF harmonics are the two sources that contribute most to the vibration under rated and heavy load condition, respectively. Afterwards, two new designs to reduce the vibration caused by the electromagnetic force modulation and stator MMF harmonics are proposed, and the reduction principles are described in detail. Finally, the prototypes of the existing and proposed 12-slot/10-pole FSCW PM machines are manufactured. The tests are conducted to validate the theoretical analysis and proposed vibration reduction design.

A novel concept of fractional pole-pair linear permanent magnet machine (FP-LPM) has been proposed recently. It is found that using fractional pole-pair number in linear permanent magnet machine(LPM) could effectively reduce slot cogging force as well as back EMF unbalance. Thus thrust ripple is curtailed which improves its thrust quality and enhances its application potential. However, some issues of FP-LPM still remain unsolved, such as phase split, current phase adjustment, plus structure optimization is different from the traditional topology due to extra auxiliary tooth, etc. This paper contributes to giving a detailed designing methodology including winding arrangement, regulations of choosing slot/pole combination and effective end optimization method of FP-LPM. Thus, this paper can give helpful guidance in designing FP-LPM to satisfy different application demands. Finally, an 18slots/29poles fractional pole-pair linear permanent magnet vernier machine (FP-LPMVM) is designed and constructed using the proposed method and the test results verifies the research conclusions.

This paper aims to investigate and reveal the torque enhancement mechanism in several emerging switched flux permanent magnet (SFPM) machines by employing a unified torque equation with an improved winding factor function. Based on a hybrid finite-element (FE)/analytical method, the torque contributions of the major air-gap field harmonics in the conventional, C-core and E-core, and consequent-pole (CP) SFPM machines are identified and quantified by taking a conventional 12-stator-slot/13-rotor-tooth (12s13r) SFPM machine as a benchmark, which shows that the dominant torque proportions are contributed by the low-order field harmonics due to the amplification effect of the gear ratio. Besides, a low-order field harmonic impeding effect is observed in the conventional and C-core SFPM structures, resulting in a compromised torque capability. Whereas, since the auxiliary teeth and stator iron bridge designs provide relatively lower magnetic reluctances for low-order harmonics, the E-core and CP structures can produce improved the low-order harmonics and higher torques than the conventional one. Finally, some experiments on a CP-SFPM machine are conducted to validate the theoretical and FE analyses.

This paper presents the design and analysis of a novel topology for a Permanent Magnet Assisted Synchronous Reluctance Motor (PM-assisted-SynRM). The proposed topology presents a simple structure that incorporates the assistance of an internally inserted V-shape permanent magnet (IVPM) machine and also a Synchronous Reluctance Machine (SynRM). The main novelty in this paper is that, the permanent magnets in the rotor are diverted so that the reluctance component of the torque and the magnetic component of the torque reach their maximum values at the same load angle that can eventually leads to a higher output torque in the same volume. To further highlight the advantages of the proposed topology to the conventional topologies, its characteristics including, air gap flux density, electromagnetic torque, and back electromotive force (Back-EMF), are compared to a conventional PM-assisted-SynRM. The key improvement of the proposed topology is that, it features a higher torque density while consuming fewer amounts of permanent magnets which is very beneficial in mass productions. Finally, by using the finite-element-analysis (FEA), the Von Mises stress for the proposed topology in different rotational speeds shows its capability in handling mechanical stresses and the experimental results validate the characteristics of the proposed topology.

Internal model control gets wide attentions in electric drives for its distinct robustness. Underdamped oscillations however, al-ways can be seen in the synchronous d- and q- axis components of the stator currents if without extra damping elements included, especially in the occasions of low sampling to fundamental fre-quency ratios. The reasons for these oscillations are unveiled through analysis in the discrete-time domain. Following that, a distinctive active damping matrix is proposed for the current closed- loop control of interior permanent magnet synchronous machines (IPMSMs). As a result, the disturbance rejection capa-bility is enhanced, allowing the disgusting oscillations suppressed very well. Compared with other damping methods, the typical PI structure is still retained, which is beneficial to engineering prac-tices. At last, the analysis as well as the damping effects are vali-dated through experiments.

Accurate calculation of iron losses in electric machines are essential for optimal machine design. This is especially important for axial flux permanent magnet motors with solid stator and rotor cores. This paper investigates iron losses in axial flux motor with soft magnetic composite material for the stator and the rotor. First, an analytical model is proposed to estimate iron losses under different operating conditions. The model is based on combining the Quasi 3-D computation approach and the magnetic equivalent circuit. The proposed model can be modified to account for different motor topologies and different stator and magnet designs. Then, The effect of torque ripple, on iron losses, is studied by comparing two motors: an optimized motor, with dummy pocket added to the stator tooth, and a non-optimized motor. Finally, the effect of the motor control scheme and the inverter switching frequency is studied by implementing two controllers: the field oriented control and the trapezoidal control. Simulations using 3-D finite element analysis and experimental tests are conducted, under different operating conditions, on two 12V, 6 slots, 8 poles single stator single rotor fractional horsepower axial flux permanent magnet synchronous motor prototypes.

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

Dual-winding bearingless flux-switching permanent magnet motor (BFSPMM) is composed of power winding and suspension winding. The permanent magnet and the power winding provide a biased air gap magnetic field, and the suspension winding generates an air gap modulation magnetic field. The structure of stator and rotor are double salient poles. This paper proposes a subdomain model for on-load field prediction in the Dual-winding BFSPMM. In the developed model, the field domain is divided into seven types of subdomains, viz.rotor slot, internal air gap, stator slot, permanent magnet slot upper layer, permanent magnet slot lower layer, permanent magnet, and external air gap. The electromagnetic parameters of the motor are analyzed, including air gap flux density, flux linkage, back-EMF, suspension force, and electromagnetic torque. Based on the principle of conservation of magnetomotive force, a distributed equivalent magnetic circuit model is proposed to compensate for the magnetic saturation. Finally, the analytical predictions are verified by finite-element analysis and prototype experiments.

Thermal management is often considered a bottleneck in the pursuit of the next generation electrical machines for electrified transportation with a step change in power density. Slot-channel cooling is considered to be an effective cooling technique, either as an independent method or as a secondary heat transfer path which compliments traditional cooling systems. The slot-channel specific geometry and position effects on the thermal benefits are not thoroughly investigated in literature, while previous work focuses on passing fluid through the un-used space left in between coils forming concentrated windings. In this paper, slot-channel cooling is implemented within an oil-flooded cooling system for a high power density motor used as a pump. A flexible and detailed lumped parameter thermal network (LPTN) is proposed for the cooling system, with the LPTN used to optimize the slot-channel dimensions and location for obtaining maximum thermal benefits. Finally, a surface-mount permanent magnet (SPM) machine with the optimized slot channel geometry is built and tested to validate the thermal model, experimentally achieving an armature continuous current density in excess of 30A/mm2.

The low-order lumped parameter thermal models (LPTMs) are one of the most competitive online approaches to estimate the critical temperatures in electrical machines. Firstly, this paper explores the correlation between the conventional high-order and low-order LPTMs and then presents some critical modelling guidelines of low-order LPTM together with an improved four-order LPTM. Secondly, a simple dynamic quasi-linear model (DQM) is proposed to define convection thermal resistances, which can be used in both conventional high-order and low-order LPTMs. The application of DQM can improve the estimation accuracy by indirectly introducing more degrees of freedom, which is especially beneficial for the magnet temperature estimation in the low-order LPTM due to its highly abstract rotor thermal modelling. Finally, a prototype permanent magnet synchronous machine is used for experimental validation under different operation profiles.

This paper describes a novel analytical methodology for modelling winding copper losses as a result of circulating currents (CC) in permanent magnet synchronous machines (PMSM). Nowadays mainly FEM method is used for precise calculation of circulating currents. However, it suffers on significant computational time required for building models and simulation of circulating current effect that makes it inapplicable for optimization purpose. The paper demonstrates the computationally efficient methodology through comparison with FEM based models for high power density PMSM with concentrated winding and validation against experimental results for a stator section at the fundamental frequency from 500 Hz to 2000 Hz. The methodology allows simulation of CC and AC Ohmic losses when machine supplied by any current waveforms, for arbitrary size and location of the conductors in the slots. A key novelty of the proposed method is the utilization of subdomain (SDM) approach in conjunction with solution of a system of ordinary differential equations (ODE) for an equivalent electrical circuit of machine windings. This approach is precise and fast but has never been used before for circulating current loss evaluation in windings of electrical machines

This article proposes a torque ripple minimization strategy based on minimizing interactive space harmonics of fractional slot permanent magnet (PM) machines using a space-shifted wye-delta stator winding. A radial force analysis has also been carried out which showed a substantial reduction in the second order mode for these space-shifted wye-delta wound machines; this will improve the noise and vibration performance. The effectiveness of the proposed method is shown by analyzing the performances of a low power surface-mounted permanent magnet (SPM) machine for the electric power steering (EPS) applications, and a high power interior permanent magnet (IPM) machines for the hybrid electric vehicle (HEV) applications on the 12-slot/10-pole (12S/10P) configuration. The proposed winding doubles the stator slot number of the base model, and as a result, the base 12S/10P configuration becomes 24-slot/10-pole (24S/10P) combination. Compared with the existing ripple minimization techniques of magnet shaping or rotor skewing, the proposed stator winding based strategy achieves better torque ripple performance and magnet utilization leading to an improvement in average torque while reducing the amplitude of the low order radial force. A 10-pole SPM machine has been built and tested for experimental validation of both the concept and the finite element analysis (FEA) simulation results.

This paper deals with the finite element analysis of Hybrid Excitation Permanent Magnet Synchronous Motors, that is, synchronous motors characterised by a rotor including both permanent magnets and an excitation winding. Such a winding is adopted to modulate the rotor flux so that the motor exploits the maximum torque for any operating speed. The higher benefit is obtained at speeds higher than the nominal speed, i.e. during the flux weakening operations. Thus the focus is to determine the flux weakening performance of different topologies of hybrid excitation PM synchronous motors, considering different topologies. In addition, the performance parameters are compared to those achieved with a standard interior PM synchronous motors. The possibility to vary the rotor flux in the hybrid excitation PM motors allows to design the motor with a high no-load flux linkage, necessary to get high torque at low speeds, and to get high torque in a wide speed range.

Based on the back-EMF generation principle in Part I of the series papers, the electromagnetic torque generation mechanism of flux-switching permanent magnet (FSPM) machines is rethought in this paper as Part II from the perspective of air-gap modulation magnetic field. By magnetic field modulation theory (MFMT), the air-gap armature magnetic field due to winding currents is modeled. Considering the unipolarity of the stator core, a novel concept of fictitious modulation reluctance (FMR) rotor for FSPM machines is proposed. Then, by combining with the air-gap PM field and the FMR rotor, generation mechanisms of harmonic PM torque and reluctance torque are investigated. The requirements for FSPM machines to produce a stable electromagnetic torque are determined, i.e., |mPwvPr|=Ppm, mrvMfm0, and e=Prr. Besides, the harmonics operation states and harmonic torque characteristics of FSPM machines are analyzed and calculated based on the Maxwell stress tensor method. Further, the average torque versus current density predicted by finite element (FE) is validated by testing on an exampled 12s/10p FSPM one.

The electromagnetic suspension system (EMSS) plays a critical role in providing attractive force for middle-low-speed maglev trains, which contains two critical components– an electromagnet and a steel track. However, with the acceleration of trains, the eddy current generated by the relative motion between the electromagnet and the track becomes intensified, which may directly weaken the attractive force. To maintain the suspension airgap between the iron yoke and the track stable, more current needs to be inserted into the winding of the electromagnet. The local thermal surge existing in the winding may appear due to the overloaded input current for long term, which may cause the insulation aging or even damage of the winding. If the short circuit accident occurs between the neighboring turns of the winding due to the inter-turn insulating damage of the winding, the loss of suspension force tends to be deteriorated undoubtedly. In this paper, a novel hybrid suspension system mixed electromagnetic and permanent magnetic modes is proposed for enhancing suspension force with economical power consumption. But, when applying permanent magnets for assisting electromagnets, the firm absorption (FA) phenomenon needs to be considered. Two suspension schemes with unequal-width and unequal-height iron yokes are launched for reducing FA risk. The corresponding FEM models have been built and verified by experimental results. The comparison of different suspension schemes under dynamic condition with different relative velocity between the suspension module and the track has been undertaken in the end.

In this paper, a coreless stator axial-flux permanent magnet (CSAFPM) indirect drive (ID) in-wheel motor is proposed and researched with consideration of the multi-physics constraints, including electromagnetic performance and mechanical strength for unmanned ground vehicle (UGV). At first, two 12-slot-14-pole CSAFPM motors with different rotor structures are designed to meet the vehicle rim space and driving system demand. In addition, the rotor parameters are optimized to obtain higher torque density based on the response surface method (RSM) and finite element model (FEM). Meanwhile, the electromagnetic performance of optimized motors with different rotors are compared, including back electromotive force (EMF), output torque capability and efficiency characteristics. The results indicate that the Halbach-array PM rotor has higher torque and efficiency than the spoke-type PM rotor. On that basis, the thermal stress and deformation of the stator support are analyzed and optimized considering material property and temperature distribution. In addition, the stress of PM rotor, annular gear and gear reducer are analyzed and optimized to achieve higher torque density. Finally, a 35kW prototype is manufactured and tested to verify the performance of the design.

This article investigates rotor losses in permanent magnet Vernier machines. By analyzing air-gap field, the harmonic distribution and frequency of modulated open-circuit flux density and armature reaction flux density are obtained. Then, rotor losses production principle is revealed and the influence of each harmonic on the loss is analyzed. Meanwhile, the influence of each harmonic on torque is also studied. It is found that some harmonics have no contribution to torque but produce additional losses. On this basis, a new rotor structure is proposed to suppress the rotor losses. Comparison results indicate that by suppressing nonworking harmonics, the rotor losses can be reduced effectively without affecting the effective torque. Finally, the theoretical and finite-element analysis results are verified by prototype tests.

This work investigates the effect of design parameters of permanent magnet (PM) and flux barriers (FBs) in the rotor on the anti-demagnetization ability (ADA) of fractional slot concentrated windings interior permanent magnet (IPM) motors for electric scooters. A 2.5 kW IPM motor (12 slots and 8 poles) is designed for a wide speed range, and its ADA associated with different PM and FB arrangements is studied under high temperature and high current density operations. The analysis shows the relationship between the ADA and characteristic current (Ich, defined as the ratio of PM flux linkage to d-axis inductance). It is also found that proper designs of flux barriers can significantly improve the ADA of the IPM motor without much affecting Ich. Thus, the motor ADA and performance can be simultaneously improved. Finite element analysis is used for evaluation, and experiments are conducted to validate the analysis.

In this paper, two novel dual stator machines with different biased permanent magnet (PM) configurations are developed and comparatively studied. For the proposed machines, the PMs are only located in the inner stator, but with different configurations, i.e., surface-mounted PM (SPM) and interior PM (IPM), respectively. The machine topologies and operating principle are introduced first. Then, the electromagnetic characteristics, including open-circuit performance, torque characteristics, field weakening capability, loss and efficiency are comprehensively analyzed and compared by finite element method (FEM). The experimental validation are conducted to verify the FEM analyses.