Utilization Of Permanent Magnets Research Articles

Optimization Design of Surface-mounted Permanent Magnet Synchronous Motors Using Genetic Algorithms

The permanent magnet synchronous motor (PMSM) has gained widespread popularity in various industrial applications due to its simple structure, reliable performance, compact size, high efficiency, and adaptability to different shapes and sizes. Its exceptional characteristics have made it a focal point in industrial settings. The PMSM can be categorized into two primary types based on the arrangement of the permanent magnets (PM): interior permanent magnet (IPM) and surface-mounted permanent magnet (SPM). In the IPM, the magnets are embedded into the rotor, while in SPM, they are mounted on the rotor's surface. The utilization of PMs eliminates the need for excitation currents due to their high flux density and significant coercive force. This absence of excitation losses contributes to a notable increase in efficiency. In this study, a multi-objective optimal design approach is introduced for a surface mounted PMSM, aiming to achieve maximum efficiency while minimizing material costs. The optimization task is accomplished using a genetic algorithm. Furthermore, the motor designs are simulated using the finite element method (FEM) to assess and compare designs before and after the optimization process.

Investigation of a Flux-Switching Machine With U-V-Array Permanent Magnet Arrangement for Traction Applications

This paper investigates a flux-switching (FS) machine with U-V-array permanent magnet (PM) arrangement, termed UV-FSPM. The key design is to construct parallel magnetic circuit by adopting U-V-array PMs. Based on the parallel magnetic circuit, the operating principle of the UV-FSPM is illustrated. To provide a deeper insight into the torque enhancement mechanism, the analytical model of the UV-FSPM is built by using the general air-gap field modulation theory. It is found that the U-V-array PMs can significantly enhance the dominant working harmonic which effectively contributes to torque enhancement of the investigated UV-FSPM. To reveal the impact of key parameters on torque performances, the parametric optimization of the UV-FSPM is conducted. The electromagnetic performances of three FSPMs are comparatively studied by finite element analysis (FEA). It is proved that the investigated UV-FSPM exhibits the highest torque density and highest PM utilization ratio within the pool. Finally, a prototype of the UV-FSPM is fabricated and tested for verification of the investigated concepts.

Analysis of Torque Capability for Permanent Magnet Machines With Magnetic Gear Effect

Permanent magnet (PM) machines have been widely applied in industrial applications due to the advantages of high torque density, high reliability, and high efficiency. In this paper, the magnetic gear effect (MGE) in PM machines is investigated in depth. A comprehensive derivation of the torque-generating process is carried out and a quantitative analysis of the air-gap harmonics contributing to average torque under different configurational freedoms is studied. The improvement of torque capability for the PM machines with MGE is discussed. The electromagnetic properties of typical PM machines with MGE are analyzed based on the magnetic circuit analytical model, and the effectiveness of theoretical analysis is verified by finite element analysis and experimental prototype. It is shown that the PM machines with an independent modulation unit possess the characteristics of high torque density and large PM utilization rate. And the PM machines with tooth-pole modulation unit have strong overload capability.

Design and Evaluation of Reduced-Rare-Earth Interior Consequent-Pole Permanent Magnet Machines for Automotive Applications

This article investigates the feasibility of interior consequent-pole permanent magnet (ICPM) machines with reduced rare-earth magnet consumption for automotive applications. A new ICPM machine with a double-layer V-shaped permanent magnet (PM) arrangement is proposed and compared with a commercial Nissan Leaf interior PM (IPM) machine. Their basic electromagnetic performances and rotor mechanical strength are evaluated by finite-element (FE) simulation. It shows that the proposed ICPM machine exhibits comparable torque capability, similar high-efficiency region, and significantly improved PM utilization ratio compared with traditional Nissan Leaf IPM case. Besides, to verify the universality of ICPM designs with reduced-rare-earth consumption, two typical ICPM machines with different magnet configurations (single- and double-layer V-shaped) and power levels (80 kW and 2 kW) are, respectively, investigated and compared with their corresponding traditional IPM counterparts. Finally, some tested results on an ICPM machine prototype with V-shaped magnets are carried out to validate the FE analysis.

Design and Multiobjective Optimization of a New Flux-Concentrating Rotor Combining Halbach PM Array and Spoke-Type IPM Machine

In this article, a new spoke-type interior permanent magnet (PM) with a flux-concentrating rotor is proposed. Based on the flux-concentrating principle, the fitting parameters between PMs and magnetic cores on the rotor make a significant impact on the flux concentration and saliency effect, thus resulting in the output torque and power capacity. Therefore, taking the average torque, cogging torque, peak power, and PM utilization as the optimization objectives, first, the sensitivity analysis is carried out that includes the different geometric variables of the rotor. Afterward, the response surface model based on the Box–Behnken method is established by selecting the reasonable optimization variables. Then, the optimal solution of the design parameters is verified by solving the response surface model. Meanwhile, a set of Pareto solutions is generated by adopting a multiobjective genetic algorithm. By two-dimensional finite-element analysis, the electromagnetic performance of a 72-slot/16-pole topology with the optimized flux-concentrating rotor is analyzed and compared with that of the initial design model. The results are demonstrated based on the response surface model. The effectiveness of the multiobjective optimization design method and multiobjective genetic algorithm is confirmed for the flux-concentrating rotor. Finally, a 30-kW prototype is developed and experimented with to verify the finite-element analysis results as well as the effectiveness of multiobjective optimization.

A New Flux-Concentrating Rotor of Permanent Magnet Motor for Electric Vehicle Application

This article 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. With this rotor structure, the torque density and power density are improved obviously, while the rotor inner diameter can be maximized to reduce core material and increases internal space in the rotor. Accordingly, the electromagnetic performance of three motors consists of a unified stator but different rotors, namely flux-concentrating rotor, Halbach array permanent magnet (PM) rotor and spoke-type IPM rotor is compared by finite element analysis. Nevertheless, due to the segmented structure of flux-concentrating PM rotor without magnetic bridges, the mechanical challenges are analyzed in detail for electric vehicle application to hold the pole pieces validate 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.

Novel Flux-Switching Machine With Star-Array Permanent-Magnet Arrangement

This article presents a novel flux-switching (FS) machine adopting star-array permanent-magnets (PMs), termed as star-FSPM machine. In comparison with the conventional spoke-FSPM machine, the proposed one can achieve not only enhanced flux-concentration effect, but also enlarged stator-slot area, thus improving PM utilization ratio and torque density. The harmonic characteristics of both PM field and armature reaction field in the star-FSPM machine are investigated based on the field modulation theory. More importantly, the torque generation mechanism of the star-FSPM machine is also investigated and compared with that of the spoke-FSPM machine. The results show that the proposed machine can utilize the working harmonics more effectively for torque generation. Afterwards, the electromagnetic performance comparison of four PM machines is carried out by finite-element analysis. It is found that the proposed star-FSPM machine exhibits improved PM utilization ratio and enhanced torque density as compared to the spoke-FSPM machine. Finally, the theoretical analysis and FEA results are verified by experimental measurement.

Design and Analysis of a Novel Tubular High-PM-Utilization Transverse-Flux Linear Machine

Owing to the low permanent magnet (PM) utilization in conventional transverse-flux machines, a novel tubular high-PM-utilization transverse-flux linear machine (HPMU-TFLM) is proposed in this article. The PM utilization ratio of the proposed machine is nearly 100% in theory. Thus, this machine presents a higher power factor and thrust density. First, the basic structure and operation principle of HPMU-TFLM are introduced. The flux-concentrating teeth and multi-unit concentrated winding are designed to improve PM utilization and reduce magnetic flux leakage. Then, the electromagnetic performances of HPMU-TFLM are investigated by the 3-D equivalent magnetic circuit model (EMCM) and the finite element analysis (FEA) method. Finally, its key performances of thrust density, power factor, and efficiency are compared with other typical transverse-flux linear machines (TFLMs). The superiority and feasibility of the proposed machine are verified.

Design and Control of a New Compound Double-Rotor Electric Machine for Hybrid Propulsion System

In this article, a new compound consequent-pole double-rotor electric machine (CCPDRM) is proposed for hybrid propulsion system application. First, the operating principle and harmonic components in CCPDRMs are elucidated. The winding factor theory for conventional permanent magnet (PM) electric machines is further extended and applied in CCPDRMs. Then, this improved theory is adopted to investigate the structure and winding scheme requirement of the proposed CCPDRMs. In addition, the control strategy for the proposed CCPDRM is established. By utilizing a parameter sweep method, the variation trends of CCPDRMs’ torque density with respect to various geometrical parameters are revealed. Based on this, the structure of CCPDRMs is optimized to acquire a better electromagnetic performance. Next, the proposed CCPDRM is compared with a conventional compound bipolar double-rotor electric machine (CBDRM). It is found that the improved topology has a similar torque density but a much higher PM utilization factor and a lower PM demagnetization risk when compared with the CBDRM. Finally, a prototype is manufactured and tested in different operating modes. Furthermore, various mode-switching processes are performed to emulate the practical driving cycle of hybrid transportation. Both steady-state and dynamic mode-switching experimental results prove the effectiveness of CCPDRMs.

Performance Analysis of Permanent Magnet Vernier Motor with Surface and Halbach Magnets

Background: Surface permanent magnet motors (SPMVM) and dual permanent magnet motors (DPMVM) have broad prospects in direct drive systems, but some problems occur with large magnetic leakage, large torque ripple and large amount of permanent magnets (PMs). Objective: In order to reduce the torque ripple and magnetic flux leakage of SPMVM and DPMVM, and improve the torque density, a dual permanent magnet vernier machine with Halbach PM array (DHPMVM) is proposed. Method: By air gap permeance method, flux density analysis of three kinds of motors was analyzed, and the main harmonics of SPMVM and DHPMVM are investigated with structure parameters. Electromagnetic characteristics of three motors such as no-load back, electromotive force (EMF), torque, and inductance are compared and analyzed by finite element method (FEM). Results: The study found that under the same size, winding distribution, electrical load and speed conditions, DHPMVM uses Halbach PM array and consequent pole structures to reduce magnetic flux leakage and torque ripple, increase torque density, PM utilization and torque per unit PM volume. Compared with SPMVM and DPMVM, the DHPMVM proposed in this paper has better electromagnetic performance. Conclusion: The DHPMVM topology is the better choice in terms of torque density, torque ripple, and magnet usage among the investigated topologies.

Split Pole Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Opening and Consequent Pole Rotor

Due to simpler mechanical structure and magnetic gearing effects, Permanent Magnet Vernier Machines (PMVMs) attract researcher interest because of their higher torque density for direct drive applications. However, regular PMVMs utilize more rare earth Permanent Magnet (PM), which increases machine cost and weight. Moreover, the PMs are mounted on the rotor surface, which enhances flux leakage and flux circulation, which degrade electromagnetic performance that ultimately decreases average torque, torque density, power density and efficiency. A new Split Pole PMVM (SP-PMVM) with Halbach PM arrangement in the stator slot opening and consequent pole rotor is proposed to overcome the issues above. The proposed SP-PMVM enhanced flux modulation phenomena to improve electromagnetic performance. Comparing the proposed machine with the existing designs reveals that the proposed design reduces the PM utilization by 22.2% and improves the flux linkage by 41.3% due to suppression of leakage flux and flux circulation. Moreover, the average torque is boosted by 42.35%. Furthermore, torque and power densities are increased by 83.01% and 44.84%, respectively. In addition, in comparison with the existing conventional design, the efficiency of the proposed model is enhanced by 25.01% at the cost of 19.75% cogging torque.

Electromagnetic Performance Comparison of Doubly Salient PM Machines With Different Stator Iron Core Segments

This article compares the electromagnetic performances of doubly salient permanent magnet (DSPM) machines with different stator iron core segments. Since the permanent magnets (PMs) of the DSPM machines studied in this article exist in pairs, the feasible numbers of PMs in the 12/8-pole DSPM machine are 12, 6, 4, and 2, and thus, the corresponding stator tooth number between two adjacent PMs is 1, 2, 3, and 6, respectively. Therefore, the stator iron core segments of the four DSPM machines have different shapes. Furthermore, to improve the average torque, PMs are inserted into the slots, and flux focusing teeth are adopted. All four machines are designed to achieve larger average torque under the fixed copper loss and envelope size. The comparison shows that the DSPM machine with two stator teeth between adjacent PMs exhibits the largest average torque and the smallest torque ripple. Moreover, the DSPM machine with six stator teeth between two adjacent PMs has the optimal PM utilization. To verify the predicted results, a 12/8-pole DSPM prototype with two stator teeth between adjacent PMs is manufactured and tested.

Multi-Objective Optimization for a Dual-Flux-Modulator Coaxial Magnetic Gear With Double-Layer Permanent Magnet Inner Rotor

To improve the torque capability and permanent magnets (PMs) utilization efficiency of the dual-flux-modulator coaxial magnetic gear (DFM-CMG), a double-layer PMs (DLPM) layout on the inner rotor (IR) is proposed. In this article, the torque performance of the DFM-CMG is investigated by 3-D finite element analysis and validated by the corresponding experiment. According to the parametric analysis results, it is found that 6-D design parameters can significantly affect the stall torque (ST) and ST per PM volume (STPPV) of the DFM-CMG. To achieve multi-objective optimization (MOO) of the DFM-CMG given that the ST and STPPV normally conflict with each other, a metamodel-based MOO method is used under the premise of the constant active region volume. The optimized DFM-CMG with DLPM IR shows a 19.7% and 2.2% growth in the STPPV than the initial design and the optimized counterpart with single-layer PMs (SLPMs) IR under the same constraint of the ST. Furthermore, the optimized DFM-CMG with DLPM IR possesses excellent PMs utilization efficiency compared with other typical CMGs.

Design and Analysis of T-Shaped Consequent Pole Dual PM Vernier Machines With Differential Magnetic Network Method

This article has proposed a novel design of dual permanent magnet (PM) vernier machine (DPVM) with T-shaped consequent pole (TCP) rotor. The analytical model of T-shaped magnet rotor based on differential magnetic network method is first derived. Given the additional optimizing parameter, edge arc difference, TCP rotor has the potential to produce 6% higher fundamental airgap flux density or 30% higher PM utilization ratio than regular fan-shaped consequent pole (FCP) 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 TCP can produce higher torque than fan-shaped magnet in vernier machines. At last, a prototype of DPVM with TCP rotor is built and tested, which has achieved 28-N·m/L measured torque density.

Design Optimization of a Reluctance Lead Screw for Wave Energy Conversion

A reluctance lead screw (RLS) is proposed in this paper which consists of a rotor and a translator, forming a magnetic device that is able to transfer low-speed linear motion into high-speed rotational motion. Permanent magnets (PMs) are only installed in the rotor, making it more suitable for long-stroke applications. The design aspects are assessed by finite element analysis (FEA) and the performance is evaluated. In addition, the thrust force per magnet volume is presented for evaluating the utilization rate of the PMs. The simulation results show that RLS has an advantage in terms of the PM utilization rate. A new method for realizing spiral magnets has also been developed which can not only reduce the manufacturing difficulties, but also ease the installation work. Finally, based on the simulations and analyses, two RLS prototypes designed for wave energy converters (WECs) are presented to show the potential applications of this novel topology.

Flux-Weakening Capability Enhancement Design and Optimization of a Controllable Leakage Flux Multilayer Barrier PM Motor

In this article, a new controllable leakage flux multilayer barrier permanent magnet (PM) motor is proposed by adopting a new design concept of controllable leakage flux, where the PMs are uniquely placed in the d-axis magnetic circuit of the synchronous reluctance motor (SynRM). Compared to the conventional q-axis PM placement SynRM, the higher PM utilization and better flux-weakening capability can be obtained. For further comparison and verification, both of the controllable leakage flux multilayer barrier PM motor and the motor with traditional q-axis PM setting are designed. In addition, a multiobjective optimization method based on the correlation analysis method is proposed to obtain the optimized output torque and flux-weakening performances. Then, the performances of the two optimal motors are analyzed and compared in detail. Finally, two prototype motors are manufactured and tested. Both the theoretical and experimental analyses verify the effectiveness of the flux-weakening enhancement design and the proposed motor.

Magneto-Thermal Analysis of an Axial-Flux Permanent-Magnet-Assisted Eddy-Current Brake at High-Temperature Working Conditions

This article proposes an analytic coupled magneto-thermal analysis of an axial-flux (AF) permanent-magnet-assisted (PMA) eddy-current brake (ECB) at high-temperature working conditions. In the topology investigated, permanent magnets (PMs) are placed into stator slot openings to increase the braking torque production capability. This modification enables to control the magnet flux by altering the dc excitation current. However, the utilization of PMs will make the construction vulnerable at high operating temperatures simply because the magnet properties and the brake capability are strongly dependent on temperature. Such problems require complex coupled multiphysics finite-element analyses to obtain the actual brake performance. The proposed approach offers a simple and effective solution that consists of magnetic and thermal models, which are coupled to each other in the time domain. The nonlinear electrical, magnetic, and thermal properties are influenced by the temperature variation in time. An AF-PMA-ECB prototype is manufactured to validate the proposed coupled models and the experimental studies confirm that the proposed approach provides very practical results to determine the working conditions of the AF-PMA-ECB at high-temperature operations.

Open-Circuit Air-Gap Field Calculation of a New PM Machine Having a Combined SPM and Spoke-Type Magnets

This article presents the open-circuit analytical magnetic field distribution model for a new permanent magnets (PMs) rotor configuration designed to improve the utilization of rare earth magnets for flux density production. The air-gap flux density is determined with the superposition method according to the magnetomotive force (MMF) and the air-gap permeance model. Since the new rotor consists of two different rotor topologies, e.g., lateral and spoke magnets, their MMF functions are determined separately. The rotor flux barrier (FB) effect on the rotor MMF harmonics is included and studied closely. The investigations carried out on different rotor topologies show high positive impact of FBs on the third or the operating wave. Compared to the conventional rotor, the utilization of PMs for air-gap flux density production significantly is improved. To verify the analytic model, finite elements (FEs) are used and several simulation results are presented.

Pole Optimization and Thrust Ripple Suppression of New Halbach Consequent-Pole PMLSM for Ropeless Elevator Propulsion

Permanent magnet linear synchronous motors (PMLSM) has the advantages of high speed, high thrust density, high power density, high power factor and high reliability. In order to save permanent magnet (PM) materials and reduce magnetic leakage, a new type of PMLSM with Halbach consequent-pole (HCP) structure is presented, which has great potential for application to the ropeless elevator system. By using extensive finite element analysis (FEA), the electromagnetic properties of the proposed HCP-PMLSM, including magnetic field, back electromagnetic force (back-EMF), thrust force and cogging force are simulated and compared with the consequent pole PMLSM (CP-PMLSM) and surface-mounted pole PMLSM (SP-PMLSM). The comparison results show that the proposed HCP configuration can reduce substantial PM material and increase the air-gap magnetic field effectively. Then, the influence trend of HCP parameters such as pole thickness, pole width ratio, auxiliary PM width and magnetism angle, are studied and analyzed for evaluating the output performance in HCP-PMLSM. On this basis, Response surface method (RSM) is employed to optimize the HCP parameters with the target of maximum average thrust, minimum thrust ripple, and highest PM utilization. Furthermore, a double-sided pole shift method was proposed to significantly suppress the thrust fluctuation of HCP-PMLSM. Lastly, experimental results are provided to verify the investigation.

Analysis and modeling of tooth-tip leakage fluxes in a radial-flux dual-stator machine with diametrically magnetized cylindrical permanent magnets

Tooth-tip Leakage flux (TLF) has a major effect on the prediction of air-gap flux distribution and electromagnetic torque in the permanent magnet (PM) machines. Therefore, deriving a model for TLF is necessary for machine design and optimization. Accurate modeling of TLF can lead to fast and precise solutions, which ease the analysis of electromagnetic devices. It also provides the opportunity to increase torque density by more efficient utilization of PM's volume and prevent saturation in machine optimization. This paper presents a method for modeling and analyzing TLFs in a radial-flux dual-stator permanent magnet (DSPM) machine with diametrically magnetized cylindrical permanent magnets (DMCPM) in series and parallel magnetic circuit structures. In this model, some expressions in terms of machine dimensions are derived for the TLF analysis. Finite element method (FEM) is applied to validate the proposed model. Results indicate that the maximum error between the proposed model and FEM is insignificant (less than 6%). Finally, by a prototyped machine the validity of the proposed model was investigated with the experimental tests.