Permanent Magnet Volume Research Articles

Design and Optimization of a Large-Scale Permanent Magnet Synchronous Generator

Direct drive permanent magnet synchronous generators have numerous advantages such as improved reliability, low maintenance, long life, and developed performance characteristics. Focus of this paper is on the development of a step-by-step method for the design of a permanent magnet synchronous generator. Then the winding function method is used to model the generator and to analytically calculate its output characteristics. The analytical results of the designed generator are evaluated with the finite element analysis (FEA) results and it is demonstrated that the achieved results from both methods are well matched with the experimental measurements of the Northern Power direct-drive generator. The sensitivity analysis and the optimization based on the genetic algorithm are used to achieve an optimum generator. The optimization goal is obtaining higher efficiency and power factor with lower required permanent magnet (PM) volume and voltage regulation for the optimum machine compared to the initial design. In addition, the calculation of the voltage total harmonic distortion (THD) is presented and the optimum skew angle for the optimum generator is computed to reduce the voltage THD.

Torque Enhancement for a Novel Flux Intensifying PMa-SynRM Using Surface-Inset Permanent Magnet

This paper proposes a flux-intensifying permanent magnet-assisted synchronous reluctance motor (FI-PMa-SynRM) using surface-inset permanent magnet (PM) instead of embedded PM in the rotor. The proposed FI-PMa-SynRM employs a small amount of PM that is inset on the rotor surface facing $d$ -axis instead of facing $q$ -axis as in common PMa-SynRMs. It also differs from conventional flux-intensifying interior PM motor, where the PM is embedded inside the rotor. The proposed motor enables making use of the arrangements of two types of flux barriers (FBs): the cutoff FB and the magnet FB, collectively referred to the outer FBs, to enhance the torque output and reduce the torque ripple. The first objective in this paper is to explain the principles of the proposed FI-PMa-SynRM, and the second is to analyze the proposed technique for enhancement of the torque output with small PM volume while keeping the lowest possible torque ripple. The finite-element analysis is employed to validate the proposed motor and analyses, and the results demonstrate their advantages and effectiveness.

Design Aspects of a Reluctance-Based Magnetic Lead Screw

This paper introduces a new type of reluctance-based magnetic lead screw (RBMLS) that is attractive for many potential applications. The proposed topology presents the implementation of discretized permanent magnets (PMs) and ferromagnetic semi-rings. The proposed RBMLS has PMs in only one of its movable parts, making it suitable for long-stroke applications. The proposed RBMLS is analyzed through the 2-D and 3-D finite-element method in order to test its topology and obtain the force produced per PM volume. Detailed design features are presented for the realization of a prototype.

Multiobjective Optimization of a Tubular Coreless LPMSM Based on Adaptive Multiobjective Black Hole Algorithm

In most multiobjective optimization problems of electrical machines, the weighted function method is used to convert them into single-objective optimization problems. This paper applies a kind of new multiobjective evolutionary algorithms (MOEAs), called adaptive multiobjective black hole (AMOBH) algorithms, to achieve effective multiobjective optimization of a tubular coreless linear permanent magnet synchronous motor (LPMSM). To reduce the computation cost of the MOEAs, a one-layer analytical model (AM) is presented for the tubular coreless LPMSM in this paper. The accuracy of the simplified one-layer AM is verified by comparisons with multilayer AM and finite element analysis (FEA) under different structure parameters. It is found that the simplified AM has good accuracy and can decrease the computation cost significantly. AMOBH algorithm is subsequently introduced. The optimal Pareto front with regard to thrust, copper loss, and permanent magnet volume are analyzed, and more diversified optimization results are provided. The final Pareto solution can be selected directly by practical physical values according to the application requirements. Finally, a prototype is fabricated for the selected design; its experimental results are provided and compared with those of the FEA results.

Dual‐stator consequent‐pole Vernier PM motor with improved power factor

The Vernier permanent-magnet (VPM) machines are recently attracting more attention for utilisation in low-speed, high-torque applications including renewable energy conversion systems, electric vehicles and elevators. Although, the VPM machines present interesting advantages, they suffer from lower power factor (PF) in comparison to the conventional permanent-magnet (PM) drives. In this study, a novel structure of the VPM machine with dual-stator and consequent-pole (CP) rotor topology is proposed with enhanced PF. The objectives in this new structure are achieving higher torque density per PM volume, higher efficiency, simpler and more robust installation of PM pieces, lower cogging torque and simpler rotor core laminations compared to the previously proposed VPM structures with reasonably improved PF. The low PF issue of VPM machines is analysed in details and the novel CP-VPM geometry is designed to diminish this drawback. Then analytical relations are derived based on the magnetic-equivalent-circuit for evaluating the flux density distribution, induced back electromotive force, magnetising reactance and PF. The effectiveness of the novel structure in enhancing the operating features is validated using analytical and 2D-FE simulation results. Finally, it is concluded that the performance of the optimally designed structure can be enhanced reasonably so that to consider it as a good choice for direct-drive applications.

Comparison of the Electromagnetic Characteristics of Single-Phase Linear Oscillating Machines according to Magnetic Flux Flow

Linear oscillating machines are typically classified according to flux flow, as longitudinal and transverse flux type devices. In longitudinal flux linear oscillating machines, the direction of the current flow is perpendicular to the direction of the moving part, while the direction of the current flow in transverse flux linear oscillating machines is parallel to the direction of the moving part. Since the direction of the magnetic flux and the current are different in the two models, their electromagnetic characteristics can also be expected to be different. In this paper, we compare the electromagnetic characteristics of these two types of linear oscillating machines. For a fair evaluation of these characteristics, both models are designed to have the same stator outer diameter, permanent magnet volume, and no-load back electromotive force. In characterizing the devices, we analyze air gap flux density, flux linkage, and inductance, as well as the electromagnetic loss.

Torque Improvement and Cost Reduction of Permanent Magnet Machines With a Dovetailed Consequent-Pole Rotor

This paper presents a consequent-pole permanent-magnet (CPM) machine to reduce the volume of permanent magnets (PM) and the cost of retaining sleeve, and meanwhile the average torque and efficiency can be improved due to the reduced airgap reluctance. The proposed configuration uses dovetail consequent-pole to protect quasi-trapezoidal PMs with lower total rotor loss than a conventional surface-mounted PM (SPM) machine due to the half number of PMs and the removed sleeve loss. In addition, the stress and deformation of the rotor are investigated. The electromagnetic performance including back EMF, average torque, torque ripple, loss, efficiency, unbalanced magnetic force, demagnetization withstand capability of the proposed CPM machine is investigated by finite element analyses. It is demonstrated that the output torque of the CPM machine can be enhanced by 3%, while the PM volume is reduced approximately 20% compared to that of the conventional SPM machine. Simultaneously, the CPM machine can have lower total harmonic distortions of phase back EMF, lower torque ripple, higher efficiency, and stronger demagnetization withstand than the SPM machine. Finally, the 12-slot/10-pole CPM machine is prototyped to validate the analyses.

Design and Performances of Multi-Tooth Stator Permanent Magnet Flux Switching Machine for Light Weight Applications

Permanent magnet flux switching machines (PMFSMs) in which their torque performance produced by interaction between armature coils and permanent magnet (PM) have been widely designed for various applications. In this regard, single-phase 8Slots-12Poles PMFSM with single tooth stator is considered the most suitable candidate for light weight applications because of their advantages of lower copper loss, high efficiency and robust rotor. However, issues of low torque performance due to weak flux linkage, high of PM volume, and high distortion in back-emf that need to be improved. In this paper, a new design of single-phase PMFSM using multi-tooth stator is proposed. Both PMFSMs have been designed using JMAG Designer version 15 and analysed through 2D-FEA. Parameters of stator outer radius, rotor outer radius, air gap, and stack length are set to 37.5mm, 22mm, 0.25mm, and 20.3mm, respectively. Based on the 2D-FEA, PM flux linkage and torque performances of the PMFSM using multi-tooth are 5 times and 38% higher than PMFSM using single-tooth. As a conclusion, single-phase 4Slot-12Poles PMFSM using multi-tooth stator considered as the best candidate for light weight applications due to the less PM volume, and good performances of toque, power and based speed of 1.44Nm, 219W, 1,062rpm, respectively.

Quantitative Evaluation of the Topologies and Electromagnetic Performances of Dual-Three-Phase Flux-Switching Machines

Hybrid-excited flux-switching machines based on permanent magnet (PM) flux-switching machines were proposed to achieve improved torque–speed characteristics. However, due to the reduction of PM volume, decreases in torque density and efficiency are usually inevitable. Thus, it is necessary to make a comprehensive comparison between the dual-three-phase hybrid-excited flux-switching machines and their PM flux-switching counterparts. To obtain a full understanding of flux-switching machines, PM flux-switching machines with U-shaped stator cores and alternate-pole magnets or C-shaped stator cores are considered. From the perspective of the frequency domain, this paper not only gives a comprehensive evaluation and comparison of the above-mentioned six flux-switching machines, but also reveals the theoretical mechanism that results in their different electromagnetic behavior in a unified way by the general field modulation theory, which is the main contribution of this paper.

A Novel Double-Rotor Planetary Magnetic Gear

This paper presents a novel topology of a planetary magnetic gear having only two rotating parts. The proposed gear is a planetary mechanism with two internal engagements that is typically characterized by high torque density. The operational principle and basic design considerations are discussed. The proposed topology offers a simple rotational motion of input and output shafts that does not require additional mechanical converters. The simulation study is carried out with the gear having the gear ratio of −14 with the 2-D finite-element method. The modeling gave promising results in comparison with other high-performance topologies of magnetic gears. The proposed magnetic gear demonstrates torque density of $187~\text {kN}\cdot \text {m}/\text{m}^{3}$ and maximum torque per volume of permanent magnets of $825~\text {kN}\cdot \text {m}/\text{m}^{3}$ . Finally, a 3-D sketch is developed showing principal mechanical design peculiarities of the proposed magnetic gear.

Analytical Determination of Optimal PM-Arc Ratio of Consequent-Pole Permanent Magnet Machines

This paper analytically derives the optimal permanent magnet (PM) arc ratio of the consequent-pole PM (CPM) machines to improve the utilization of rare earth PM material and maximize the output torque. The relationship between the output torque and the PM-arc ratio is established. Moreover, the optimal PM-arc ratio is analytically derived and confirmed by finite element (FE) analysis. It is found that the optimal PM-arc ratio is determined by the ratio of the airgap length to the PM thickness, and its influence on the optimal PM-arc ratio is investigated as well. The electromagnetic performances of the CPM machine with the optimal PM-arc ratio, including the open-circuit airgap flux density, the back EMFs, the average torque, and the torque ripple, are compared with those of the conventional surface-mounted PM (SPM) machine. It is demonstrated that the CPM machine with optimal PM-arc ratio features 33% reduction of PM volume and its torque ripple is almost unchanged compared with the conventional SPM machine. Although the output torque is decreased by 8%, the torque per PM volume is improved by 38%. Finally, a 12-slot/10-pole CPM machine is prototyped and tested to validate the analyses.

Design and Optimization of a Novel Wound Field Synchronous Machine for Torque Performance Enhancement

This paper presents the design and optimization of a novel wound field synchronous machine topology, in which permanent magnets (PMs) are introduced into the rotor slot opening with segment configuration for high quality output torque performance. The rotor shape of the proposed PM-assisted wound field synchronous machine with segment configuration is optimized for maximizing the average output torque and decreasing torque ripple under constant PM volume and motor size. The segment configuration can be benefit to improve the reluctance torque. In addition, it is further clarified that the assisted-PM can help to increase the field torque by enlarging the magnetizing synchronous reactance (Xf), as well as increasing airgap flux density. An optimal method combining Kriging method and genetic algorithm is applied for rotor shape optimization of proposed PM-assisted wound field synchronous machine (PMa-WFSM). Then, the 2-D finite-element analysis results, with the aid of JMAG-Designer, are used to confirm the validity. It is determined that the average output torque is improved by 31.66%, and keeps lower torque ripple without decreasing efficiency, increasing PM volume and motor size compared with those of the basic model. Finally, irreversible demagnetization and mises stress analysis verifies the reliability of the novel topology.

Multi-Objective Optimization of Moving-magnet Linear Oscillatory Motor Using Response Surface Methodology with Quantum-Behaved PSO Operator

To reduce the difficulty of manufacturing and increase the magnetic thrust density, a moving-magnet linear oscillatory motor (MMLOM) without inner-stators was Proposed. To get the optimal design of maximum electromagnetic thrust with minimal permanent magnetic material, firstly, the 3D finite element analysis (FEA) model of the MMLOM was built and verified by comparison with prototype experiment result. Then the influence of design parameters of permanent magnet (PM) on the electromagnetic thrust was systematically analyzed by the 3D FEA to get the design parameters. Secondly, response surface methodology (RSM) was employed to build the response surface model of the new MMLOM, which can obtain an analytical model of the PM volume and thrust. Then a multi-objective optimization methods for design parameters of PM, using response surface methodology (RSM) with a quantum-behaved PSO (QPSO) operator, was proposed. Then the way to choose the best design parameters of PM among the multi-objective optimization solution sets was proposed. Then the 3D FEA of the optimal design candidates was compared. The comparison results showed that the proposed method can obtain the best combination of the geometric parameters of reducing the PM volume and increasing the thrust.

Design improvement of permanent magnet flux switching motor with dual rotor structure

This paper presents design enhancement to reduce permanent magnet (PM) volume for 7S-6P-7S dual rotor permanent magnet flux-switching machines (DRPMFSM) for electric vehicle application. In recent years, Permanent magnet flux switching (PMFS) motor and a new member of brushless permanent magnet machine are prominently used for the electric vehicle. Though, more volume of Rare-Earth Permanent Magnet (REPM) is used to increase the cost and weight of these motors. Thus, to overcome the issue, new configuration of 7S-6P- 7S dual rotor permanent magnet flux-switching machine (DRPMFSM) has been proposed and investigated in this paper. Initially proposed 7S-6P-7S DRPMFSM has been optimized using “deterministic optimization” to reduce the volume of PM and to attain optimum performances. In addition, the performances of initial and optimized DRPMFSM have been compared such that back-emf, cogging torque, average torque, torque and power vs speed performances, losses and efficiency have been analysed by 2D-finite element analysis (FEA) using the JMAG- Designer software ver. 14.1. Consequently, the final design 7S-6P-7S DRPMFSM has achieved the efficiency of 83.91% at reduced PM volume than initial design to confirm the better efficient motor for HEVs applications.

Design and Analysis of a Novel Bearingless Flux-Switching Permanent Magnet Motor

Conventional bearingless permanent magnet motors have magnets on their rotor, and their maximum electric loading performance may be restricted by thermal instability and lack of mechanical integrity. To overcome such drawbacks, a novel bearingless motor with magnets, suspension force windings, and torque windings in the stator is proposed; the proposed motor is called bearingless flux-switching permanent magnet motor. First, the structure and winding configuration of the bearingless flux-switching permanent magnet motor are designed and introduced. Second, the operation principle of radial suspension force is illustrated based on the principle of reverse direction magnetization for symmetrical rotor teeth. Third, the corresponding electromagnetic characteristics, including flux field distributions, torque, and controllability of radial suspension forces, are investigated. Finally, the decoupling characteristics between suspension force windings and torque windings are discussed and analyzed comprehensively. High power per permanent magnet volume, good controllability of radial suspension forces, and excellent decoupling characteristics are achieved with the proposed bearingless flux-switching permanent magnet motor. Analytical results are validated through finite-element analysis and experimentation.

A Novel Modular-Stator Outer-Rotor Flux-Switching Permanent-Magnet Motor

A novel modular-stator outer-rotor flux-switching permanent-magnet (MSOR-FSPM) motor is proposed and studied in this paper. Structure, operation and design principles of the MSOR-FSPM motor are introduced and analyzed. Considering that the combination of different pole number and slot number has a great influence on the motor performance, the optimum rotor pole number for the 12-stator-slot MSOR-FSPM motor is researched to obtain good performance and make full use of the space in the MSOR-FSPM motor. The influences of rotor pole number on cogging torque, torque ripple and electromagnetic torque are analyzed and a 12-slot/10-pole MSOR-FSPM motor was chosen for further study. Then, several main parameters of the 12-slot/10-pole MSOR-FSPM motor were optimized to reduce the torque ripple. Finally, the utilization of permanent magnet (PM) in the MSOR-FSPM motor and a conventional outer-rotor flux-switching permanent-magnet (COR-FSPM) motor are compared and analyzed from the point of view of magnetic flux path, and verified by the finite element method (FEM). The FEM results show that the PM volume of MSOR-FSPM motor is only 54.04% of that in a COR-FSPM motor, but its average electromagnetic torque can reach more than 75% of the torque of COR-FSPM motor.

Numerical Simulation and Experimental Validation of the Critical Pressure Value in Ferromagnetic Fluid Seals

Ferrofluids have various engineering applications, and one of them is magnetic fluid seals. Development for this design is a complex process, which requires knowledge about ferrofluid physical properties and magnetic field distribution inside the sealing gap. One of the most important parameters of ferromagnetic fluid seals is a critical pressure value. It is a pressure at which rapid leakage will occur. This publication presents the results of critical pressure value obtained from experimental studies and calculations based on numerical simulations. Shape of sealing stage, volume of ferrofluid, and volume of permanent magnet used in seal construction were taken into account. Experiments and calculations were performed for four ferrofluids differ in saturation magnetization, density, and zero magnetic field viscosity.

A Novel Design Method of Permanent Magnet Synchronous Generator From Perspective of Permanent Magnet Material Saving

This paper puts forward a novel design method of permanent magnet synchronous generator (PMSG). The most significant advantage of this method is that the output power of PMSG can be prominently improved without increasing any material costs. The main difference from the traditional design scheme is that the volume of permanent magnet (PM) remains unchanged during the entire design procedure. And the maximum output power scheme is found out just by optimizing the PM's shapes with the change of mechanical pole-arc coefficient. In other words, this method aims to obtain the maximum PM utilization design scheme that can produce more “effective” magnet field so that it can generate the larger output power. The dimension parameters of PMs with different shapes are calculated by the equivalent analytic geometry method. To verify its availability, this novel method is performed on four common types of PMSGs with different rotor structures, and their satisfactory performance results are obtained. The comparison with the traditional machine design scheme is also presented to illustrate the innovation and priority. The finite-element analysis method based on Ansoft/Maxwell is applied for the electromagnetic models’ building and simulation.

Optimal Sizing and Comparison of Permanent Magnet Thrust Bearings

The aim of this paper is to study different permanent magnet (PM) bearings geometries based on PM rings with a minimum volume of PM for a given load. Simple and general scaling laws (SCLs) are proposed for each bearing geometry to predict its behavior. These SCLs allow a fast sizing of those geometries, as a function of the number of PM rings, the load reference, the air gap, and the remanent flux density. Those SCLs are derived for optimized topologies without any constraint on the geometrical parameters, as well as for optimized geometries with a constraint on the PM dimensions. For both cases, SCLs for the thrust-bearing stiffness are also proposed.

Failure Diagnosis for Demagnetization in Interior Permanent Magnet Synchronous Motors

Since a high degree of reliability is necessary for permanent magnet synchronous motors, the detection of a precursor for the demagnetization of permanent magnets is very important. This paper investigates the diagnosis of very slight PM demagnetization. The permanent magnet volume is altered so as to mimic the effect of demagnetization. This paper investigates the influence of demagnetization by using several methods: the 3D finite element analysis (FEA) of the motor, the measurement of high-frequency impedance, and the measurement and FEA of the stator voltage and current under vector control. We have obtained the following results. The back-EMF is proportional to permanent magnet volume, and there is no difference in the demagnetization in the radial direction and in the axial direction. Even harmonics and subharmonics of flux density at the teeth tip could be useful for diagnosis if a search coil is installed there. The relatively low frequency resistance at the d-axis position is useful for diagnosis. Under vector control, the stator voltage is useful except in an intermediate torque range, and the intermediate torque is expressed by a simple equation.