Showing papers in "IEEE Transactions on Magnetics in 2017"

A Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Opening

Abstract: Permanent-magnet vernier (PMV) machines are attracting more and more attention due to their high torque density and simple mechanical structure. In this paper, a novel PMV machine with an improved permanent-magnet circuit is proposed. Compared with the regular PMV machine, half of the permanent magnets (PMs) in the rotor are moved to the stator slot opening, and Halbach array PMs are employed in the stator while the consequent pole is employed in the rotor. The analysis of this machine indicates that the back electromotive-force amplitude of the proposed PMV machine could be two times that of the regular PMV machine with similar magnet usage, and for the same torque density, viz., 23.1 kNm/m 3 , the power factor of the proposed machine can reach 0.89, while this value is only 0.65 in the regular PMV machine.

Comprehensive Analysis of Magnet Defect Fault Monitoring Through Leakage Flux

Abstract: This paper presents a detailed magnet defect fault detection analysis through fluxgate sensors by monitoring the leakage flux around permanent magnet synchronous motors. The flux spectra of electric machines contain direct and most critical information to monitor and characterize magnet defect faults and their progressions. In the mainstream diagnosis techniques based on phase current and back-EMF analysis, the fault corresponding signature characteristics may vary and cause misleading results depending on motor topology, winding configuration, number and location of defective magnets, and controller parameters. In this paper, it is shown that leakage flux analysis provides some superior results for magnet defect diagnosis. For this purpose, the fault patterns in the leakage flux spectrum are exhaustively analyzed at different torque/speed profiles. Simulation and experimental results show that the deployment of a direction sensitive fluxgate sensor in magnet defect fault detection yields very promising results both in time and frequency domain analyses.

Estimation of Current and Sag in Overhead Power Transmission Lines With Optimized Magnetic Field Sensor Array Placement

Abstract: Power distribution mechanism in smart grid necessitates the development of an easy-to-install and contactless sensing system to monitor the operational state of overhead high-voltage transmission lines. Here, we propose a robust phase current and sag estimation method at support structures. Novelty in our work is the use of dual-axis magnetic field (MF) sensors equal to the number of phase conductors. This is realized by installing an array of sensors optimally placed in the same vertical plane as of conductors on the tower. The optimal position of sensor array was found while minimizing the condition number of governing linear system close to unity. For any circuit configuration, our method processes the sensed MF vector projections through a linear system, which is based on the Biot–Savart law. It considers the practical factors, such as sag, span length, and sensor-to-conductor distance. An algorithm is then designed to estimate the electric current and sag by iterative comparison between the measured and calculated MF. The method is first tested by numerical simulations for a typical one-circuit configuration, which involves three scenarios of symmetrical and unsymmetrical sag in conductors. The algorithm converges to a maximum error of $\le 1$ % within 300 iterations. We then experimentally verify our scheme on a scaled laboratory setup. Retrieved current and sag values were verified with the readings from ammeter and vernier caliper, respectively. The results prove the viability of our approach within $\le 2.6$ % deviation for current and $\le 1$ % for sag in all conductors.

Nonlinear Analytical Prediction of Magnetic Field and Electromagnetic Performances in Switched Reluctance Machines

Abstract: This paper deals with the nonlinear analytical harmonic modeling (HM) of three phases, and 6/4 conventional switched reluctance machine (SRM). The proposed model consists in computing magnetic field distribution and electromagnetic performances of an SRM with conventional winding. Because an SRM has inherently nonlinear characteristics, the analytical subdomain model that does not take into account the saturation has a limited accuracy. This is due to the assumption of infinite tooth permeability. The new analytical model (AM) based on the HM technique, which overcomes this limitation, is presented with the consideration of the local magnetic saturation on the stator and rotor teeth. The results obtained with the nonlinear AM have been compared with the linear AM based on the subdomain method (i.e., without the saturation effect) and nonlinear finite-element method solutions.

Design of a New Enhanced Torque In-Wheel Switched Reluctance Motor With Divided Teeth for Electric Vehicles

Abstract: This paper presents a new switched reluctance motor (SRM) with wide speed range for the application of electric vehicles. It has an in-wheel structure for direct drive and multiple teeth per stator pole to enhance output torque. Also, the number of rotor poles is more than that of stator teeth. A 6/16 three-phase in-wheel SRM with the concepts of multi-teeth per stator pole and more rotor poles than stator teeth has been proposed for analysis. The torque performance of the topology with multi-teeth per stator pole is proven by theoretical analysis. Moreover, a new design formula is introduced for a novel combination of stator and rotor poles. The parameters of the motor are optimized by genetic algorithm method for the maximum torque output. Then the torque performance is computed by finite-element method (FEM) and compared with its counterparts, including three-phase 6/8 and 6/10 SRMs. The FEM results exhibit higher torque density for the proposed topology.

Semi-Analytical Approach for Finite-Element Analysis of Multi-Turn Coil Considering Skin and Proximity Effects

Abstract: Native application of finite-element method (FEM) to the analysis of skin and proximity effects in multi-turn coils results in large equation systems, whose solution needs long computational time. This paper proposes a semi-analytical approach to overcome this problem. For the analysis of the proximity effect, the complex permeability of a round conducting wire immersed in uniform time-harmonic magnetic fields is represented in a closed form. Then, the homogenized complex permeability over the cross section of the multi-turn coil is analytically evaluated using the Ollendorff formula. The magnetoquasistatic problem is thus replaced by the magnetostatic one, in which the multi-turn coil is treated as a uniform material with the homogenized complex permeability. The skin effect is taken into consideration by introducing the corresponding impedance in the circuit equation. The proposed method is shown to give the impedance of multi-turn coils, which is in good agreement with that obtained by the conventional FEM as well as experiments.

Multi-Objective Optimization of Circular Magnetic Couplers for Wireless Power Transfer Applications

Abstract: Recent expansion of emerging wireless power transfer technology has not been followed by an adequate systematic approach to the magnetic couplers design. The relation between design parameters (mutual inductance, coupling coefficient, leakage field flux density, coil quality factor, and so on) and structural parameters (coils and ferrite shape, size, thickness, and so on) has not been thoroughly explored, and practical designs often depend on trial-and-error methods supported by the finite-element modeling simulation to verify a final design. In order to fill that gap, this paper describes the adoption of multi-objective hybrid particle swarm optimization (MOHPSO) and multi-objective real-numbered particle swarm optimization (MORPSO) algorithms for a circular coupler design to increase performances and automate the design process. Objectives of this paper are threefold: 1) apply MOHPSO and investigate if there are some unconventional structures of circular couplers capable of outperforming traditional designs; 2) identify a minimum set of key optimization parameters for a circular magnetic coupler; and 3) demonstrate the operation of an MORPSO algorithm to optimize a circular magnetic coupler. The Pareto front concept is applied to provide multi-objective optimization. Two different multi-objective function pairs are considered, the first pair being the coil coupling coefficient ( $ {k}$ ) and maximum leakage field magnetic flux density ( $ {B_{\max }}$ ); for the second pair, the product between quality factor ( $ {Q}$ ) and $ {k}$ is combined with ( $ {B_{\max }}$ ). To validate the optimization algorithm effectiveness and accuracy, a selected magnetic coupler is fabricated and tested. Due to superior execution time, and satisfactory optimization capabilities, the MORPSO algorithm is employed to generate a final optimum design. Collected measurements demonstrate a very good agreement between the experimental and simulation results.

Acceleration of Frequency Sweeping in Eddy-Current Computation

Abstract: In this paper, a novel method for accelerating frequency sweeping in eddy-current calculation using finite-element method is presented. Exploiting the fact that between adjacent frequencies, the eddy-current distributions are similar, an algorithm is proposed to accelerate the frequency sweeping computation. The solution of the field quantities under each frequency, which involves solving a system of linear equations using the conjugate gradients squared (CGS) method, is accelerated by using an optimized initial guess—the final solution from the previous frequency. Numerical tests show that this treatment could speed up the convergence of the CGS solving process, i.e., reduced number of iterations reaching the same relative residuals or reaching smaller residuals with the same iteration number.

Force Ripple Minimization of a Linear Vernier Permanent Magnet Machine for Direct-Drive Servo Applications

Abstract: Linear vernier permanent magnet machines (LVPMMs) for direct-drive servo applications are attracting more and more attentions due to its high force density, easy maintenance, rapid dynamic response, and so on. This paper proposes an LVPMM structure, which has a similar secondary as that of a regular linear PM machine, while its primary mover is composed of three modules, and the modules are separated by flux barriers. Since high-precision servo systems have rigorous demands on the force ripple of the drive motors, two methods are introduced to minimize the force ripple of the LVPMM. One is to choose an optimal length of flux barriers; the other is to change the three-phase winding connection. The effectiveness of both methods is verified by time-stepping finite element analysis. It is found that the force ripple can be reduced from 10.6% to 2.4% by the proposed two methods.

Surrogate-Based Multi-Objective Optimization of Electrical Machine Designs Facilitating Tolerance Analysis

Abstract: Multi-objective optimization algorithms are becoming ever more popular in the field of electrical machine design as they provide engineers with an automated way of efficiently exploring huge design spaces when searching for machines that are simultaneously highly competitive regarding several objectives, such as efficiency, material costs, torque ripple, and others. Apart from exhibiting these good target characteristics, a good design should also be robust, i.e., it should not be very sensitive to slight changes in its design parameters as this would either seriously impact production costs or make the physical machine behave differently than its (optimized) computer simulation model. This paper is focused on describing how global surrogate models (i.e., nonlinear regression models), that are created in order to reduce the dependence on finite-element (FE) simulations during the multi-objective optimization run, can be easily reused to perform very fast local and global tolerance/sensitivity analyses of generated designs. While obtained in a fraction of the time required by the complementary FE-based approach, the surrogate-based sensitivity estimates are able to provide accurate and valuable information regarding the robustness of electrical machine designs. Ultimately, by integrating robustness-related information with Pareto front projections, we aim to provide engineers with much clearer pictures of the specific problem-related tradeoffs discovered by the automated design optimization procedure.

A Novel Linear Permanent Magnet Vernier Machine With Consequent-Pole Permanent Magnets and Halbach Permanent Magnet Arrays

Abstract: The linear permanent magnet (PM) vernier machine (LPMVM) can reach a higher thrust density at low speed compared to the regular linear PM machines due to the utilization of the magnetic gear effect, which makes it a good solution for low-speed direct-drive applications. In order to further improve the machine thrust density, a novel LPMVM with consequent-pole and Halbach PM array is proposed and optimized in this paper. Then, in order to show the superior thrust performance of the proposed LPMVM, it is compared to two conventional LPMVMs in terms of back electric motive force (back EMF), thrust force, and power factor. It is found that machine no-load back EMF can be improved by 72.5% and its thrust density is 46% higher than that of the conventional LPMVM.

Winding Function Approach for Winding Analysis

Abstract: The winding factor is an operand in order to consider the effect of winding distribution and chording on the spatial distribution of the magnetic field in the air gap of synchronous and induction machines. The sinusoidal functions for winding factor calculation presented in literature are not defined and valid for every irregular winding, e.g., single-layer fractional-slot, combined star-delta, multilayer (greater than two), and asymmetrical windings. Although the summation of induced voltage phasors (star of slots) is the most accurate method, asymmetrical windings require to be decomposed in symmetrical components. In this paper, in addition to deriving the symmetrical components for asymmetrical multiphase windings, the analytical formulation is presented to relate the harmonic content of winding functions to winding factors. The harmonic leakage factor is accurately formulated from the winding function instead of the Gorges diagram without the need for summing up an infinite number of normalized winding factors quadratically. Without restriction of the number of layers and the distribution of the winding, including full-pitch, chorded and fractional-slot symmetrical and asymmetrical windings, the suggested analysis method is validated with the star of slots and sinusoidal functions of distribution and pitch factors, where applicable.

Contribution of Current Harmonics to Average Torque and Torque Ripple in Switched Reluctance Machines

Abstract: This paper investigates the contribution of current harmonics to average torque and torque ripple in switched reluctance machines. In order to account for the magnetic saturation under different current amplitudes and waveforms, the self-inductances are obtained by finite element calculation using frozen permeability method and subsequently used in the analytical derivation of an instantaneous torque equation based on the Fourier series analyses. Five different current waveforms are also considered in order to identify the contribution of current harmonics. It is found that the average torque is mainly contributed by the dc, first, and second current harmonics. Meanwhile, the fourth and fifth current harmonics have high influence on the torque ripple but much lower contribution to the average torque. In addition, the optimization of current waveforms in terms of the maximum average torque under a given RMS current is also discussed. All analytical analyses are validated by direct nonlinear finite element and experimental results.

Model-Based Calibration for Magnetic Manipulation

Abstract: Model-based calibration of a magnetic workspace not only provides a smooth representation of the field and its gradient matrix, but also uses physical constraints to smooth the calibration measurements. This paper presents the first model-based technique to calibrate a magnetic manipulation system by using nonlinear least squares to solve for a scalar potential for each source. The performance of the method is verified by comparison to numerical finite element simulation and a case study calibration of a real system, where it is able to achieve an $R^{2}$ value of 0.9997. Furthermore, the analytical representations for the first three spatial derivatives of a spherical multipole expansion are provided for convenience, which correspond to the torque, force, and force-spatial-rate-of-change on a magnetic dipole in the workspace.

A New Nine-Phase Permanent Magnet Synchronous Motor With Consequent Pole Rotor for High-Power Traction Applications

Abstract: Although three-phase permanent magnet (PM) motors are quite common in industry, multi-phase PM motors are used in special applications where high power and redundancy are required. Multi-phase PM motors offer higher torque/power density than conventional three-phase PM motors. In this paper, a novel multi-phase consequent pole PM (CPPM) synchronous motor is proposed. The constant power–speed range of the proposed motor is quite wide as opposed to conventional PM motors. The design and the detailed finite-element analysis of the proposed nine-phase CPPM motor and performance comparison with a nine-phase surface mounted PM motor are completed to illustrate the benefits of the proposed motor.

Soft Magnetic Properties of Magnetic Cores Assembled With a High B_{s} Fe-Based Nanocrystalline Alloy

Abstract: Soft magnetic properties of magnetic cores assembled with Fe 81.8 Cu 1.0 Mo 0.2 Si 4 B 14 nanocrystalline alloy ribbon are discussed. The nanocrystalline alloy ribbon was cast in an amorphous phase by a melt quenching method, and a nanocrystalline phase was obtained by high-heating rate annealing. A medium-size toroidal core assembled with this nanocrystalline alloy ribbon exhibits magnetic flux density B 800 at 800 A/m of 1.74 T, core loss P 16/50 at 50 Hz, and at 1.5 T of 0.29 W/kg. A racetrack-shaped core, which includes curved and straight sections in the same core, exhibits core losses at 1.0 T and at 400 Hz and 1 kHz of 1.5 and 5 W/kg, respectively. These core losses are as low as those of Fe-based amorphous alloys. A medium-size toroidal core assembled with this nanocrystalline alloy ribbon, secondarily annealed under a perpendicular magnetic field, exhibits core loss P 2/10k at 0.2 T and at 10 kHz of 2 W/kg. This value of core loss is one of the lowest values for the metallic magnetic cores, which have a saturation induction B s higher than 1.5 T. A core assembled with this material can be used in several applications from low to medium frequency ranges. Since this material exhibits a higher B s and one half of the saturation magnetostriction λ s of Fe-based amorphous alloys with comparable core losses, the most possible applications are in such applications as distribution transformers and inductors in power electronics.

Reduction of Torque Ripple in Inset Permanent Magnet Synchronous Motor by Magnets Shifting

Abstract: This paper proposes a method of reducing total torque ripple by magnets shifting. The key of this method is to consider the reluctance torque ripple, because the reluctance torque ripple is the main source of torque ripple in inset permanent magnet synchronous motor. This method is realized by appropriately choosing Repeating Unit, which indicates a group of poles producing torques with consistency in waveforms and phases. Meanwhile, the uniform analytical expressions of torques with magnets shifting are established, including cogging torque, reluctance torque, and total torque. Moreover, the total torque ripple can be reduced greatly, and the average total torque loss is acceptable when one pole-pair is chosen as one Repeating Unit and the shifting angles of Repeating Unit are 3.75 and 1.875 mechanical degrees. These theoretical analyses are verified by the finite-element method.

Electromagnetic and Thermal Analysis of a Surface-Mounted Permanent-Magnet Motor with Overhang Structure

Abstract: Recently, overhang structures are increasingly used for various applications requiring high torque and power densities in a limited space such as traction motors of electric vehicles and servo motors of robot arms. In the design stage, overhang effects should be taken into account to predict the performances and the temperature rise of a motor with overhang. However, little research has been conducted on the thermal characteristics and analysis methods for a surface-mounted permanent-magnet (SPM) motor with overhang. To address this problem, the electromagnetic and thermal characteristics of the SPM motors with and without overhang are invested in this paper. Specifically, 3-D finite-element method is used in electromagnetic analysis to accurately calculate electromagnetic losses which are heat sources in thermal analysis. Moreover, the lumped-parameter thermal network (LPTN) which can consider overhang effects rapidly and precisely is proposed as an analytical method. Through the proposed LPTN, the computation time for thermal analysis is reduced considerably in comparison with a computational fluid dynamics method, and the temperature rise of the motors are precisely predicted. The results calculated in electromagnetic and thermal analysis are verified experimentally with 0.3 Nm, 20-pole/24-slot SPM motors adopting natural cooling.

Analysis and Experimental Evaluation of Normal Force of Linear Induction Motor for Maglev Vehicle

Abstract: This paper presents the analysis and experimental of the effective normal force and power consumption in a maglev vehicle. A maglev vehicle employs the electromagnets as suspension and linear motors for propulsion. These components give the higher ride comfort but suffered from energy efficiency. Therefore, a vector control-based algorithm and various air gaps are employed to increase the propulsion efficiency and lower the system energy consumption. The effective levitation load according to the levitation gap and normal force of a linear induction motor is calculated by power consumption in a levitation system and compared with finite-element analysis results. The experiment is carried out with the full-scaled train in test line and the efficiency of a propulsion system is also presented.

Design Characteristics of IPMSM With Wide Constant Power Speed Range for EV Traction

Abstract: This paper presents study of design characteristics with wide constant power speed range (CPSR) for electric vehicle Propulsion. Through analysis of interior permanent magnet synchronous motor (IPMSM) control logic, design characteristic of extending CPSR is proposed. To achieve wide CPSR, center of voltage limit ellipse should be placed at cross point of current limit circle and d-axis. To analyze characteristic of voltage ellipse, four types of representative IPMSM rotor topologies are selected. Through rotor topology analysis, tendency of φ f and L ds parameters which decide center of voltage limit ellipse is analyzed. This paper also considers shifting of voltage limit ellipse center according to change in motor speed. Reflecting the result, this paper focuses on center of voltage limit ellipse position at maximum speed, because central coordinates of high-speed range determine characteristics of CPSR. Through the analysis result, this paper suggests direction of IPMSM design for wide CPSR.

Design of Permanent Magnet-Assisted Synchronous Reluctance Motor for Maximized Back-EMF and Torque Ripple Reduction

Abstract: This paper proposes the optimization of the shape and size of a ferrite magnet and the arrangements necessary to reduce torque ripple and maximize back electromotive force (B-EMF) in a permanent-magnet-assisted synchronous reluctance motor. First, four different models of general magnet arrangements were selected, and analysis using the finite-element method was performed under open circuit and load operations for each of the four models. Next, the relationship between the cogging torque and the torque ripple was analyzed, considering the segment saturation phenomenon. Then, based on the initial model, the design was optimized for maximum B-EMF and minimum torque ripple, and the total harmonic distortion was measured. Finally, the validity and superiority of the optimized design were confirmed by manufacturing a prototype motor and performing the experiment.

Comparison of Axial Flux Permanent Magnet Synchronous Machines With Electrical Steel Core and Soft Magnetic Composite Core

Abstract: This paper presents a comparison of axial flux permanent magnet machines (AFPMs) with an electrical steel core and that with a soft magnetic composite (SMC) core SMCs have several advantages such as low core loss and low eddy current loss However, compared with electrical steel, SMCs have poor magnetic properties such as low flux density saturation and unsaturated relative permeability The analysis of the electromagnetic characteristics in a wide frequency range revealed that for an AFPM using an electric steel core, the performance was excellent in a low-frequency range; however, for an AFPM using an SMC core, the performance improves with an increase in frequency Finally, the operation area of an AFPM using an SMC core is proposed

Design and Analysis of a Novel PM-Assisted Synchronous Reluctance Machine With Axially Integrated Magnets by the Finite-Element Method

Abstract: This paper presents the design and analysis of a novel permanent-magnet (PM)-assisted synchronous reluctance machine (PMA-SynRM) with axially integrated magnets for improving machine performance by using a finite-element method (FEM). The proposed PMA-SynRM features a simple structure with high performance by incorporating the advantages of a SynRM and a surface-mounted PM machine (SPMM). In particular, the rotor parts of the SynRM and SPMM are assembled to make the “q-axis” located 45° (elec.) from the d-axis. Thus, the magnetic torque and reluctance torque of the proposed PMA-SynRM reach the maximum values at the same current phase angle, for efficient production of the total torque. To highlight the advantages of the proposed PMA-SynRM, a conventional PMA-SynRM is adopted for comparison under the same operating conditions. The FEM analysis results finally demonstrate that the proposed PMA-SynRM has a higher total torque and power factor, as well as greatly reduced torque ripple, when compared to the conventional PMA-SynRM with the same magnet amounts. In addition, the Mises stress analysis indicates that the configuration of the proposed PMA-SynRM exhibits the advantage of avoiding stress deterioration in the rotor ribs.

Net Shape Processing of Alnico Magnets by Additive Manufacturing

Abstract: Alternatives to rare earth permanent magnets, such as alnico, will reduce supply instability, increase sustainability, and could decrease the cost of permanent magnets, especially for high-temperature applications, such as traction drive motors. Alnico magnets with moderate coercivity, high remanence, and relatively high-energy product are conventionally processed by directional solidification and (significant) final machining, contributing to increased costs and additional material waste. Additive manufacturing (AM) is developing as a cost effective method to build net-shape 3-D parts with minimal final machining and properties comparable to wrought parts. This paper describes initial studies of net-shape fabrication of alnico magnets by AM using a laser engineered net shaping (LENS) system. High-pressure gas atomized pre-alloyed powders of two different modified alnico “8” compositions, with high purity and sphericity, were built into cylinders using the LENS process, and followed by heat treatment. The magnetic properties showed improvement over their cast and sintered counterparts. The resulting alnico permanent magnets were characterized using scanning electron microscopy, energy dispersive spectroscopy, electron backscatter diffraction, and hysteresisgraph measurements. These results display the potential for net-shape processing of alnico permanent magnets for use in next generation traction-drive motors and other applications requiring high temperatures and/or complex engineered part geometries.

Detent Force Minimization of Permanent Magnet Linear Synchronous Machines Using Subdomain Analytical Method Considering Auxiliary Teeth Configuration

Abstract: This paper presents electromagnetic modeling and analysis of the detent force in a permanent magnet linear synchronous machine (PMLSM) according to auxiliary teeth configuration. Analytical solutions for magnetic fields generated by PMs are derived based on the Maxwell equation in terms of a 2-D Cartesian coordinate system. The magnetic vector potential of each subdomain (PM, air-gap, slot, and end region) is derived, and the field solution is obtained by applying the boundary and interface conditions between the subdomains. Based on the analytical solution, the magnetic force is derived by using the Maxwell stress tensor. All the analytical results were extensively validated using nonlinear finite-element analysis and experimental results. Using the proposed method, we investigated the influence of the machine parameters on the detent force. Therefore, the proposed method can be very useful in the initial design and optimization process of PMLSM for detent force analysis.

Estimation of Depth and Length of Defects From Magnetic Flux Leakage Measurements: Verification With Simulations, Experiments, and Pigging Data

Abstract: Magnetic flux leakage (MFL) method is the most widely used non-destructive testing techniques for detection and characterization of defects in product transmission pipelines. The maximum safe operating pressure is a crucial parameter in practice, which is predicted with respect to the length, width, and depth of defects. In a previous work, an algorithm is devised to detect and estimate the width of the defect based on MFL signals. In this paper, an efficient method based on axial MFL level contours is devised to estimate the length of the defect. This method uses the patterns of signal level contours in the region corresponding to the defect’s area. In addition, a Gaussian radial basis function neural network (NN) is trained to approximate the depth of the defect. The NN is fed with the estimated length, width, and signal peak-to-peak values, and the output of the network is the estimated depth. The proposed detection and estimation method is applied to MFL measurements to detect and determine the sizing of metal loss defects. The efficacy and accuracy of the proposed methods are examined through a rich set of sample defects that contains simulated defects, designed defects that are carved on a real pipe by milling, and actual pigging data validated by several dig up verifications. Obtained results confirm the effectiveness and accuracy of the proposed depth and length estimation method along with the previously devised detection and width estimation methods, in characterization of metal loss defects.

Performance Comparison of Surface and Spoke-Type Flux-Modulation Machines With Different Pole Ratios

Abstract: In this paper, performance comparison between surface and spoke-type flux modulation (FM) permanent magnet (PM) machines is presented. Generally, spoke-array magnet arrangement is capable of increasing the torque density of PM machines due to its flux-focusing effect. Nevertheless, a flux-barrier effect is found when this magnet topology is applied in FM machines, which may offset the advantage in torque capability when the pole ratio is high. By flux distribution comparison of these two-machine topologies, the flux-barrier effect is visually explained. Through numerical FEA, this effect is further investigated in spoke-type vernier PM machines with a series of pole ratios. Finally, compared with surface-type FM machines, considerable reduction in modulated magnetic field as well as output torque capability is verified in high pole ratio, spoke-type FM machines.

Analysis and Reduction of Unipolar Leakage Flux in Series Hybrid Permanent-Magnet Variable Flux Memory Machines

Abstract: A series hybrid variable flux memory (VFM) machine employing two kinds of permanent magnets (PMs) on alternate rotor poles is investigated This VFM machine features controllable PM flux and thus good flux-weakening capability, as well as improved torque density However, it is found that the unipolar end leakage flux occurs if the two kinds of PMs are not balanced According to the analyses of series connection between two PMs based on the fundamental magnetic circuit, the mechanism of the unbalanced rotor poles and the unipolar end leakage flux is revealed Further, the rule of obtaining balanced poles is identified and the effects of operating conditions are presented A series hybrid VFM machine prototype is fabricated and tested

A Novel Asymmetric and Unconventional Stator Winding Configuration and Placement for a Dual Three-Phase Surface PM Motor

Abstract: Multi-phase permanent magnet (PM) motors are becoming more popular because of their higher torque densities, enhanced efficiency, and fault-tolerant capabilities. In this paper, a novel six-phase PM synchronous motor with a new asymmetric stator ac winding scheme and placement is proposed. Two identical dual three-phase asymmetrical winding sets are placed in two separate half of the stator in 180 mechanical degrees. This approach reduces the phase resistance and thus copper losses. Torque quality of the proposed motor is also analyzed using 2-D finite element method in detail. It can be concluded that the proposed novel asymmetric stator has more advantages to offer than conventional six-phase PM motors.