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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.

Traditional multi-point hybrid maglev systems cannot realize the zero-power horizontal levitation state under eccentric load, which means the steady-state current is zero, and the air gap of each magnet is equal. This paper proposes a new maglev system with two rotary magnets to solve this problem. The two magnets can move on an annular guideway to counteract the moment caused by the eccentric load. At first, we established the linear parameter varying model of this maglev system. Then the control strategy is designed, which consists of a zero-power horizontal levitation controller and rotation controller. The levitation control is realized by introducing feedback of integral current and deviation of air gap in the proportional-derivative control system. The rotation controller employs a centroid observer and centroid Jacobian. It outputs the rotating angle at the demand of the zero-power and horizontal levitation. Experimental results demonstrate that the proposed maglev system has a better zero power and horizontal levitation performance than without rotary magnets. The direction of the air gap variation is opposite to that of the loading direction. The variation size of air gap length depends on the load weight, while rotation angle is related to the load weight and loading position.

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.

An increasing interest for permanent magnet synchronous machines with low torque ripple and low vibration is observed. The purpose of this paper is to investigate the topology of non-uniformly distributed teeth and its influence of on cogging torque, tooth ripple harmonics and torque ripple of permanent magnet synchronous machines. The topologies with different number of non-uniformly distributed teeth are investigated. Analytical procedure is developed to illustrate the impacts of non-uniformly distributed teeth on cogging torque and unbalanced magnetic pull (UMP), and then identify the appropriate non-uniformly distributed teeth. A commercial 10kW 8-pole 48-slot V-shaped IPM machine is taken as the reference base machine. The machines with 2- and 6 non-uniformly distributed teeth are chosen to make an overall comparison to that with the well-known skewing slots. The machine with 2 non-uniformly distributed teeth is finally chosen to be fabricated. Intensive experiments including cogging torque, back-EMF, load current, efficiency and instantaneous torque are done.

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.

This paper reveals the flux leakage design and modeling principle of a flux leakage controllable permanent magnet (FLC-PM) machine by considering driving cycles. The key is to obtain the relationship between flux leakage characteristics and multiple operating conditions. Based on the flux leakage controllable concept, an FLC-PM machine with an artfully designed flux leakage region is proposed. The design principle of the machine is investigated by analyzing the magnetic circuit of the machine in multiple operating conditions. The flux leakage factor is introduced to characterize the variable magnetic field in multiple operating conditions. On this basis, the mathematical model of the FLC-PM machine is deduced, and the driving characteristics of the machine are studied in detail. In order to evaluate the presented principle of the FLC-PM machine, a prototype is manufactured for experiments. Through the theoretical analysis and experimental testing, it is verified that the proposed principle is feasible and effective.

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.

In this work, a reverse saliency (RS) spoke-type permanent magnet (PM) synchronous motor (PMSM) besides its hybrid adaptive notch filter (HANF) based self-sensing for driving a solar photovoltaic water pump system (WPS) is presented. The conventional spoke-PMSM driven WPS experiences two types of problems. Firstly, the motor is operated with a flux-weakening current to produce positive reluctance torque, thereby increasing the PM demagnetization risk. Secondly, an encoder is used to sense the rotor angle, which in turn affects the cost and reliability. To solve the first problem, the RS-PMSM is presented, which operates with a flux-intensifying current to produce positive reluctance torque. While second issue is resolved by using the HANF based rotor angle estimation. Although conventional methods give an estimate of rotor angle, they do not eliminate both the DC-offset and dominant harmonics. The superiority of both the RS-PMSM and HANF over existing solutions, is shown respectively by using finite-element methods and MATLAB/ Simulink based performances. Besides, a prototype motor is also manufactured. The performance of RS-PMSM prototype along with its HANF based self-sensing is obtained in the laboratory and various test results are reported. Meanwhile, a comparison of the HANF with available self-sensing techniques, is also performed.

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.

A generalized fault-tolerant control (FTC) strategy for the field-oriented control (FOC) and direct torque control (DTC) of five-phase fault-tolerant permanent magnet (FPFTPM) motors under various open-circuit faults is presented in this paper. Most previous studies regarding FTC target a specific primary control algorithm and involve different reduced-order transformation matrices and additional current controllers, which increase the complexity of the entire drive system. In this study, a solution to the aforementioned problems is devised by developing optimal fault-tolerant voltages, which are derived from fault-tolerant mechanism analysis and steady-healthy design. Because the coordinate transformation need not be changed and additional voltage compensation is not required, a minimal control drive system reconfiguration under various open-circuit faults can be achieved to avoid accommodating the change of the primary control algorithm. The proposed control strategy not only improves the torque performance and dynamic response under healthy and fault conditions but also adapts to both FOC and DTC. Experimental results for a 2 kW FPFTPM motor prototype are provided to evaluate the proposed strategy.

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 study presents a computationally efficient model predictive torque control (MPTC) method for permanent magnet synchronous machines (PMSMs). The existing MPTC methods require solving complex optimization problems in iterations; this approach is computationally demanding. In contrast, the proposed MPTC transforms the optimization problem into two subproblems and derives the corresponding solutions explicitly using numerical techniques, which entail linearization of the torque function and current constraint; the proposed approach can significantly reduce the computational burden. Additionally, the proposed MPTC does not involve any control gains and weighting factors; hence, gain tuning is not required for the proposed MPTC. These features are advantageous when implementing torque control. Using a 4-kW PMSM drive, the effectiveness of the proposed MPTC is demonstrated both numerically and experimentally in terms of dynamic performance and computational efficiency. This is realized by comparing the proposed method with the existing methods.

A novel cage-secondary permanent magnet linear eddy current brake (ECB) with wide speed range and its analytical model are presented in this paper. Differ from the existed permanent magnet ECB, the proposed ECB owns the variable parameters cage-secondary structure. This unique secondary structure can keep braking force at a large constant value from high speed to low speed by changing the secondary parameters in different speed ranges. First, both the structure and working principle of the proposed ECB are given. Then, a new analytical model combined with multilayer theory is proposed, where the saturation of secondary iron teeth and the end effect are considered. Based on the magnetic field distribution result, the characteristics of proposed eddy current brake are analyzed. Third, the accuracy and validity of the analysis results are verified by the finite element method and prototype experiments. Moreover, based on the genetic algorithm, the optimal secondary parameters are obtained with the objective of maximum braking force at each speed.

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.

this paper proposes a ferrofluid soft capsule robot (FSCR) with magnetic actuation for diagnostic and therapeutic medical applications inside the human stomach. A composite shell consisted of ferrofluid, permanent magnet rings and soft elastomer is developed for the FSCR, which is actuated remotely by an external permanent magnet. The proposed FSCR presents two novel characteristics. First, the composite shell not only has soft outer surface that reduces damage to contact tissue, but also an improved magnetic circuit with a combination of the ferrofluid and permanent magnet rings makes the locomotion of the device more controllable and security. Second, the FSCR is equipped with a specific oscillation module that enables advanced functions such as drug releasing. Detailed structure design and fabrication of the FSCR are presented in this study. The surface rolling locomotion of the FSCR is modeled and evaluated by numerical simulations, as well as the drug releasing function. In order to verify the simulation result, a FSCR prototype is manufactured to perform experimental validation. The analysis result demonstrates the feasibility and efficiency of the proposed FSCR for drug releasing inside a printed human stomach model.

It is known that permanent magnet vernier machine has multiple flux field harmonics which can produce stable torque. However, some flux field harmonics would create torque that undermines the torque output. Such as the 6slots26poles split-tooth PMVM here, of which modulated flux field outputs torque while fundamental flux field undermines torque output. In this paper, a 26poles PMVM with coding-shaped tooth is proposed. The coding-shaped tooth can introduce permeance harmonics with specific phase and amplitude, thus modulating flux fields that all output torque. Air-gap permeance harmonics of the proposed and the regular split-tooth PMVM are obtained via FEA. Based on MMF-permeance model, flux fields of two machines and their contributions to average torque are investigated, proving that the proposed machine has multiple flux fields that all output torque. By optimizing geometry of coding-shaped tooth, the proposed machine obtains largest average torque and smallest torque ripple simultaneously. Electromagnetic performances of the optimized machines are studied in semi-analytical way and FEA. It is proved that with same overall size, PM usage and copper loss, the proposed machine achieves 30% larger torque density, 86% smaller cogging torque and 62% lower torque ripple than its counterpart. Finally, a 16Nm (rated)prototype is built and tested.

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.

In this article, the fault-tolerant control (FTC) strategy based on current redistribution is compared for three types of triple redundant 3×3-phase motor: surface-mounted permanent magnet synchronous motor (SPMSM), synchronous reluctance motor (SynRM), and permanent magnet assisted synchronous reluctance motor (PMa-SynRM), under a single-phase open-circuit fault. The output torque of SPMSM and SynRM is produced by permanent magnet (PM) torque and reluctance torque, respectively. Nevertheless, for PMa-SynRM, it is necessary to determine the distribution ratio of PM torque and reluctance torque in the proposed FTC strategy. By comparing the FTC performance of motors, the conclusions are as follows: (1) Torque ripple of the SPMSM can be completely suppressed. (2) Torque ripple minimization for the SynRM and PMa-SynRM can be realized. (3) Optimal solution obtained in SynRM can also be applied to the PMa-SynRM when the load is heavy. In addition, to reduce the complexity and improve the reliability of the control system, a mono-inverter driven triple paralleled control system is constructed in healthy and postfault operations. The comparison results of the FTC strategy for three types of motor are obtained by simulation. And the experimental results based on a 3×3-phase PMa-SynRM are accomplished to verify the feasibility of the theory.

This paper investigates the air-gap field distribution of the permanent-magnet vernier machine (PMVM) using nonlinear exact conformal model (NECM) to account for slotting effect, flux modulation effect and iron nonlinearity. The exact conformal model based on the region of one-slot and one-flux-modulation-pole (OSECM) are introduced to show the effectiveness of linear analytical model for PMVM. It can keep high calculation accuracy and significantly reduce the computational burden. Then, the NECM is developed from OSECM by introducing the equivalent saturation current into the air region and coil region. The lumped parameter magnetic circuit model (LPMCM) model is used to obtain the magnetic potential of iron region and therefore calculate the equivalent saturation current. The NECM which combines LPMCM and OSECM can essentially improve the accuracy of linear analytical model. The harmonic analysis of air-gap field is performed to theoretically explain the component of electromagnetic torque. Both finite element model (FEM) simulation and test results are presented to validate the NECM.

A fault-tolerant hybrid current control is proposed for dual 3-phase permanent magnet synchronous machines (PMSMs) with one phase open in this paper. The maximum torque control, minimum copper loss control, and single 3-phase mode control are unified in the proposed method, which is a combination of single 3-phase mode control and maximum torque control with different percentages. When the percentage of single 3-phase mode control (k) varies from 0% to 100%, the hybrid current control transitions from maximum torque control (k=0%), to minimum copper loss control (k=50%), and then to single 3-phase mode (k=100%). Therefore, the hybrid current control can be switched among the aforementioned three control methods easily and smoothly. Meanwhile, it can be a mixed-mode with a tradeoff between the maximum torque control and minimum copper loss control, such as the minimum copper loss control for a given torque within the full torque range, which can be achieved by changing k. The smoothness of transition among the maximum torque control, minimum copper loss control, and single 3-phase mode control is verified by experimental results on a prototype machine.

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.

in order to enhance motor torque performance of existing two-phase 8/10 E-Core SRM, an improved modular permanent magnet (PM)-assisted Switched Reluctance Motor (SRM) structure is presented. Firstly, basic structure and operation principle of the proposed structure are introduced. To further evaluate performance improvement, effects of various parameters on the design such as inductance, flux-linkage, average torque and cogging torque are compressively investigated by finite element method (FEM) software subsequently. In the meantime, comparisons with other two-phase SRM structures are also performed including average torque, torque/PM volume, torque/ motor volume, torque/current, etc. Finally, a prototype is fabricated, and simulation and experimental results verify that the proposed design has high torque performance.

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).

A passive field conversion-amplification scheme, is proposed and demonstrated for the first time, by integrating a magnetic cantilever with a TMR (Tunnel magnetoresistance) for current monitoring. In the scheme, a magnetic structure with a strong field, is driven and vibrated by the interaction with a weak field. The passive movement of magnetic structure physically results in a movement of strong field. The weak field, is converted by the movement and further passively amplified into a strong one. The degree of amplification is determined by the structure geometry, the position of magnetic structure, as well as the weak field. A TMR cantilever current sensor, mainly composed of two units, is developed to demonstrate the proposed scheme. One is a cantilever with a permanent magnet fixed at its free end as a sensing unit and the other is the TMR as a detecting unit. Experimental measurements demonstrate that a higher detection sensitivity can be achieved, compared to that with only TMR detection. The gain of the sensitivity reaches more than an order of magnitude. If an energy harvesting unit is integrated into the current sensor, a self-powered sensing node can be accomplished for potential wireless sensor network (WSN) applications.

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.

In this paper, a parallel-series magnetic circuit multi-permanent magnet motor is designed and optimized considering magnet characteristic variation effects, where two kinds of PMs are utilized as co-magnetic. Based on the equivalent magnetic circuit method, the detailed design method for the multi-permanent magnet motor is illustrated. And considering the various operation conditions in potential EV applications, the B-H curves of two PMs of different typical operation conditions are obtained. Then, a multi-objective optimization method is newly proposed which not only focuses on the magnet characteristics variation effect, but also considers output torque, toque ripple as well as anti-demagnetization capability under three typical operation conditions. And the performance of the initial motor and optimal motor are compared under typical operation conditions. Finally, a prototype machine is built and tested. Both theoretical analysis and experimental results verify the validity of the motor and the proposed design optimization method.

High-speed Permanent Magnet Linear Synchronous Motor (PMLSM) is desired by high performance electromagnetic propulsion system. A novel frequency modulation (FM) secondary proposed here to overcome the issues resulting from a big pole pitch of high-speed PMLSM, as well as avoid a damage to the thrust characteristics. Firstly, the topology structure of FM secondary is designed, modeling of the main magnetic field excited by permanent magnets (PMs) is accomplished. And the impacts of FM secondary on the main magnetic field and PM eddy-current loss are presented based on the analytical method and finite element method (FEM). The electromagnetic thrust of PMLSM with FM secondary is calculated, and the influences of FM secondary on thrust characteristics are studied by FEM simulations. Finally, a prototype of PMLSM with FM secondary is manufactured, the experiments are provided to validate the analytical results and simulation results of FM secondary.

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.

The magnetic gear integrated permanent magnet brushless machine (MG-IPMBM) is a kind of compact structure with high torque density and complex electromagnetic energy transfer. In order to analyze the transient characteristics of the machine, an analysis method of field circuit coupling is proposed. Both magnetic gear and permanent magnet motor are magnetized by Halbach array. Combining the analytical model of the magnetic gear magnetic field with MATLAB motor simulation module, a joint simulation model of field circuit coupling double closed-loop control system based on the Simulink-analytical method is established. The electromechanical transient response characteristics of machine under load starting, load mutation and overload self-protection are analyzed. The simulation results show that the output speed and torque of machine can accurately follow the given value, and its unique overload self-protection ability greatly improves the safety of machine operation. In addition, a prototype is made and an experimental platform is built. The experimental results show that the output torque follows quickly, the torque ripple is small, and transient performance of the machine is good.

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.

Harmonic suppression plays a key role in the current control of dual-three-phase (DTP) permanent magnet synchronous machines (PMSMs). Existing current control schemes are scarcely verified by designed DTP motor prototypes or consider the impact of inherent electromotive force (EMF) harmonics quantitatively. Also, few studies discuss the low-reactance case which requires additional concerns for current prediction and modulation. Therefore, this article conceives and presents an improved deadbeat-based active current harmonic control scheme particularly for low-reactance PMSMs. From the aspect of motor design and finite element analysis, the quantitative effect of EMF harmonics on control behaviors is analyzed. Based on the non-ideal mathematical model (MMM) of designed slotless PMSM with analyzed EMF harmonics, the proposed scheme is firstly introduced theoretically and verified by simulation. Subsequently, the slotless PMSM prototype fabrication and control experiments validate the proposed scheme and recognize the necessity of active harmonic suppression.

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.