PM Material Research Articles

The improvement of dry sliding tribological properties by designing nano-primary cementite in bainitic/martensitic matrix microstructure in hypereutectoid PM components

The production of nano-sized primary cementite in bainite/martensite matrix (NCBM) microstructure was designed to improve the dry sliding wear properties of high carbon PM parts. A different heat treatment cycle was carried out for the production of novel the NCBM microstructure. High purity iron powder 1.5 wt%. natural graphite powder was added and it was compacted in the form of a dry sliding wear test specimen in a mold and sintered at 1200 °C in a pure Ar gas atmosphere. The novel NCBM microstructure in the PM material was produced by quenching at 950 °C, then annealing at 600 °C for 12 min, then quickly cooling from 730 °C to 250 °C in a salt bath and keeping it isothermal for 100 s. The friction coefficient of materials with NCBM microstructure was less than other samples. It was found that while the wear coefficient were higher in the tempered martensitic microstructure sample having higher hardness, they were less than in the sample having bainitic/martensitic microstructure with similar hardness.

The Dual Detection of Uric Acid and Paracetamol in Biological Fluids with the Modified “Green” Sensor through the Electropolymerization

The PM material was effectively synthesized in this study via electropolymerization. The electrochemical characteristics of glassy carbon electrodes (GCE)@RGO were examined after the PM was polymerized onto its surface to create PM-RGO/GCE with the support of the CV technique. Furthermore, employing this modified electrode, URA and PCM were examined by applying CV and DPV electrochemical techniques. In comparison to employing the RGO/GCE, the modified PM-RGO/GCE electrode showed good responsiveness toward URA and PCM applying the DPV technique, with LOD values of 0.040 μM for URA, and 0.025 μM for PCM. The linear concentrations ranged from 0.06 to 1 μM. These factors like Na+, SO4 2−, Ca2+, Cl−, NH4 +, NO3 − ions, ascorbic acid, dopamine, hypoxanthine and xanthine, did not interfere during the modified electrode’s operation. Within this paper, it is worth emphasizing that these analytical processes for the URA and PCM in actual sample solutions are more dependable than the HPLC method.

Optimal design of hybrid consequent-pole permanent magnet motor to reduce torque ripple

Compared with the surface-mounted permanent magnet (SPM) motors, the consequent-pole permanent magnet (CPM) motors can obtain the approximate output torque on the basis of saving 30% PM material. However, due to the special arrangement of the CPM motor, its torque ripple is large, which will affect the smooth operation of this kind of motor. Therefore, this paper proposes a hybrid consequent-pole permanent magnet (HCPM) motor with an auxiliary PM on one side of the iron pole, which can reduce the torque ripple and ensure smooth operation effectively. In order to make the performances of proposed motor better, the Taguchi method is used to optimize the proposed HCPM motor. Furthermore, the influence rule and the relative importance of each optimization variable on the optimization goal are obtained by the average value analysis and the variance analysis, respectively. According to the above analysis results, the optimized hybrid consequent-pole permanent magnet (OHCPM) motor is obtained. Finally, the performances of SPM motor, CPM motor, and OHCPM motor are compared to verify the validity of the proposed structure.

A Review on Magnet Loss Analysis, Validation, Design Considerations, and Reduction Strategies in Permanent Magnet Synchronous Motors

Eddy current losses in magnets are a major consideration in the rotor design of permanent magnet synchronous motors (PMSMs). Stator design choices and the use of modern inverters with high switching frequency introduce harmonics that can contribute to significant losses in the magnets, causing the rotor to heat up. In typical PMSMs, the lack of rotor cooling can cause the magnet’s performance to degrade at high temperatures and eventually demagnetize. This review examines a large number of studies analyzing magnet eddy current losses using analytical methods and finite-element analysis. In some of these studies, magnet segmentation is carried out to reduce the losses; however, their loss-reduction effects depend highly on the type of PMSM and the mix of stator harmonics. Magnet segmentation without considering these effects can, in fact, increase the magnet losses, in addition to the extra manufacturing efforts. Multiple design analysis show the influence of rotor–stator geometric features on magnet losses. Although measuring magnet eddy current losses for these motor designs is a tedious task, authors have proposed calorimetric and loss segregation-based techniques to provide validation. This paper addresses magnet loss modeling techniques, PM material considerations, magnet segmentation effectiveness, motor and stator design effects, and experimental validation to inform motor designers about the costs and benefits of rotor designs that minimize rotor losses.

A Novel Slot-PM-Assisted Consequent-Pole-PM Machine With Hybrid Magnets of Ferrite PMs and Rare Earth PMs

In this article, slot-PM-assisted consequent-pole-PM machine (SPMA-CPMM) is proposed. The key is that the consequent-pole ferrite PMs are employed in the stator yoke to reduce the PM material cost largely, while a small amount of tangential magnetized rare-earth PMs is placed in the slot opening to improve the torque production. This proposed hybrid magnet design can greatly enhance the PM utilization ratio and reduce the PM cost while maintaining a relatively large torque density. In this article, the configurations of ferrite-PM machine (FPMM), consequent-pole ferrite-PM machine (CFPMM), and SPMA-CPMM are illustrated, while equivalent magnetic circuits (EMCs) of them are compared. Then, the electromagnetic performances of three machines are investigated and compared, which verifies the validity of the proposed machine.

A Modified Permanent Magnet-Assisted Synchronous Reluctance Motor Design for Torque Characteristics Improvement

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.

A comparison between conventional and flux‐intensifying interior permanent magnet synchronous machines

Flux intensifying interior permanent magnet synchronous machine (FI-IPMSM) was designed to improve the characteristic of conventional permanent magnet machines, especially, in constant power or field weakening region. Increasing a saliency ratio is the main method to achieve this target which leads to increasing reluctance torque than magnetic torque and so improving the machine performance. In this paper, the characteristics of FI-IPMSM are investigated. The effect of PM material, PM width, PM thickness, flux barriers width and iron bridge thickness on the machine parameters, output torque and no-load characteristic is studied. A comparison is carried out between the FI-IPMSM and conventional IPMSM to evaluate the improvement in machine performance. Two-dimension time-steeping finite element method (FEM) is employed in analysis of the FI-IPMSM and conventional IPMSM.

Design and Performance Investigation of 3-Slot/2-Pole High Speed Permanent Magnet Machine

High-speed rotating mechanical machinery is a developed, mature and reliable technology for many engineering applications. In high-speed permanent magnet machines, the rotor's permanent magnet PM is not strong enough to withstand the centrifugal force resulting from excessive rotational speed; thus, the PM material must be protected by a non-magnetic alloy sleeve. This paper presents a novel high-speed PM machine with solid rotor PM covered by a titanium retaining sleeve. The rotor stress condition is simplified as a plane stress problem according to the strength measurement of solid PM rotors in the high-speed PM motors. The analytical formulas for rotor stress are presented based on the polar coordinate displacement method. The proposed model is compared with a conventional model having auxiliary slots in stator teeth. Using a finite element analysis environment, the performance analysis shows that the proposed design has reduced magnet eddy current loss, cogging torque, and iron losses. The initial design is also optimized using a deterministic optimization algorithm that increases output torque by 26% compared to the initial design.

An Analytical Model and Optimization of a Novel Hybrid Rotor Machine for High Torque Density

This article proposes a novel hybrid rotor permanent magnet (HRPM) machine for the performance of torque and overload capability with the constraint of the rotor diameter. In order to optimize the electromagnetic performance, an analytical model (AM) is built by the magnetic equivalent circuit (MEC) of the rotor and stator considering the saturation and leakage flux effect. A good prediction accuracy is verified by the finite element method (FEM), even in high saturation condition. Based on the AM, the characteristics of the hybrid magnetic pole rotor are analyzed by the equivalent strategy that equivalent PM remanence and thickness of single pole in rotor. Furthermore, a response surface method (RSM) for multi-variate and multi-objective optimization is adapted to improve the electromagnetic performance because of the high torque density and PM material utilization. Finally, a comparison of the torque, PM eddy current loss and anti-demagnetization performance is investigated among surface-mount PM (SPM) machine, spoke-type PM (STPM) machine and HRPM machine. The comparison results show the hybrid PM rotor machine enhances higher torque density and overload capability. Finally, a 12 slot/10 pole HRPM machine is prototyped and tested to validate the analyses.

Parameter Design for a High-Speed Permanent Magnet Machine Under Multiphysics Constraints

Regarding high-speed permanent magnet machines (HSPMMs), there is a lack of complete and detailed design processes for main parameters under multiphysics constraints, which makes it difficult to obtain high-reliability designs for designers of HSPMMs. This paper presents a detailed and complete design process for the main parameters of an HSPMM under multiphysics constraints. Firstly, the initial sizes are obtained through electromagnetic and mechanical design theory. Then, the influence of design parameters on rotor stress is analyzed in detail, including PM material, rotor temperature, sleeve thickness, PM thickness and rotor diameter. Furthermore, the rotor dynamics have also been studied in detail, including the effects of bearing stiffness, impeller mass, rotor diameter, core length, and gyroscopic effect on critical speed. Afterwards, the comprehensive research on the electromagnetic filed and the loss characteristics is performed. The cooling system is designed and the thermal field is also studied in Ansys-Cfx. Besides, the coupled temperature-stress analysis is established considering the interaction between temperature and mechanical characteristics. Finally, a full-size HSPMM prototype has been fabricated and tested to validate the detailed multiphysics design process.

Analysis and Design of a New Type of Less-Rare-Earth Hybrid-Magnet Motor With Different Rotor Topologies

In this paper, a new type of less-rare-earth hybrid-magnet (LRE-HM) motors are design, analysis, where two types non-rare-earth ferrite-PM and rare-earth NdFeB-PM materials are involved. According to the proposed general design rules and requirements, three different rotor topologies, namely series, parallel and series-parallel mixed connections of magnetic circuit forms are evolved. And the design procedure of the new type of the LRE-HM motor is implemented in detail, where the series-parallel connection is acted as the design example motor. The corresponding electrometric performances of the three motors are investigated and compared. Both the theoretical analysis and electromagnetic performances demonstrate the effectiveness of the proposed design principle of excitation source equivalence and the LRE-HM motors. By incorporating both rear-earth PM and non-rear-earth ferrite PM materials in the rotor, the proposed LRE-HM motors can not only offer the comparable electromagnetic performances with the baseline motor, but also has the unique advantages of less consumption of rear-earth PM material and lower PM cost.

Analysis and design considerations of an axial‐flux dual‐rotor consequent‐pole Vernier‐PM machine for direct‐drive energy conversion systems

The Vernier permanent-magnet (VPM) machine is known as high-torque and low-speed drive solution suitable for direct-drive applications such as electric-vehicles and wind-turbines. This study presents a high-efficiency axial-flux VPM machine with dual-rotor of consequent-pole topology and one yoke-less concentrated-winding stator. The consequent-pole VPM machine is a special VPM structure that introduces high torque-density as the conventional-VPM machine incorporating a significantly lower volume of PM material. The proposed machine represents desirable features of higher efficiency, improved reliability and lower weight and axial-length compared to the traditional motor-gearbox approach. These advantages are achieved due to: dual-PM rotors for appropriate forming the magnetic flux lines and increasing torque-to-weight ratio, yokeless-stator for reducing flux path, concentrated winding with no overhang for reducing copper-loss, using rectangular-shaped copper conductors for increasing winding fill factor and selecting the core material from high-performance grain-oriented magnetic steel for reducing core-loss. After presenting the structure, the operating principles are discussed based on the magnetic flux behaviour and a quasi-3D magnetic-equivalent-circuit model is extracted. The accuracy of the analytical model is validated by comparing the results with the FE results. Finally, the effects of the design parameters on electro-magnetic performance are analytically investigated by studying a 10 kW machine.

Production of Porous Aluminium Using Sodium Chloride

Our workplace, Technical University of Liberec, is currently engaged in research and production of cellular metal systems. Basically, cellular metal systems are materials with lower density. It is a research in the field of mechanical engineering that is focused on the development of new materials. In general, many methods have been developed for the production of cellular metal systems, e.g. by BANHART [2] or ASHBY [4]. At their production, the direct gassing of molten metals (mostly aluminium ones) or gassing by the powder agents (e.g. specially formulated aluminium powders) are mostly used. Depending on the manufacturing method, a cellular system with open or closed cells can be obtained. The most commonly used metal is aluminium and its alloys. We are currently focusing on the production of porous aluminium by using sodium chloride. Sodium chloride occupies regular sites in the aluminium material and thus contributes to the aluminium porosity. After solidification of the aluminium, sodium chloride is dissolved in water. Sodium chloride is relatively inert to the aluminium and together with it, has a favourable density (2160 kgm-3) compared to the aluminium density (2700 kgm-3). The values of these physical quantities were observed on the produced aluminium test specimens having  60 x 10 mm: relative density of porous system REL; porosity of metal system P; amount of solid phase system volume fraction VPM; density of porous metal system PM and porous material Young's modulus of elasticity EPM.

A novel anti-air-leakage method and an organic polymer material for improving methane drainage performance

Coal mine methane (CMM) drainage is an important method to curb the occurrence of gas disasters and to reduce the amount of greenhouse gas emission, and to make full use of the methane resource. High-grade sealing boreholes is the key factor to achieve efficient drainage of methane. In order to improve the efficiency of CMM drainage as well as to seal in-seam horizontal boreholes and fractures around these boreholes effectively, a dynamic anti-air-leakage method called the dynamic fractures filling technology was presented, and an organic polymer material called the PM sealing material matching with this technology was developed in this paper. Firstly, the destruction of coal body around boreholes because of a roadway and a borehole excavation was analyzed from the view of stresses, and the range of fractures zone caused by roadway excavation was determined, then the sealing technology and sealing principle of the novel technology were analyzed systematically. Moreover, the development process of the PM sealing material was introduced, and the influence of preparation parameters on material properties was investigated. Besides, taking the coal seam in the 39,021 Transportation Lane in the Zhongmacun Mine(China) as the test site of this study, the attenuation law of the methane concentration in drainage boreholes under different sealing depths was investigated via adopting the conventional sealing technology. Finally, the methane-drainage effect of the novel sealing technology and the conventional technology were compared. The results indicate that: (1) Both a roadway excavation and a borehole excavation will cause the redistribution of stresses of the original coal mass, and the coal structure around a drainage borehole has been destroyed in different degrees due to stresses overlapping effect. Moreover, the dynamic developing fractures zone is the main channel of air-leakage during drainage process. (2) The novel technology uses the conventional sealing system and the dynamic sealing system to seal drainage boreholes and dynamic development of fractures around them. (3) When the water-to-material ratio is 7:1 and the treatment temperature is 180°C for 30min, the PM material has the best performance. (4) Comparing with the conventional sealing technology, the novel technology has the obvious characteristics of short sealing depth, long efficient continuous drainage time and high drainage amount of methane. and its advantages of methane-drainage effects and economic benefits are remarkable.

Elimination of Even-Order Harmonics and Unipolar Leakage Flux in Consequent-Pole PM Machines by Employing N-S-Iron–S-N-Iron Rotor

This paper presents a novel consequent-pole permanent magnet (CPM) machine featuring N-S-iron–S-N-iron sequences to eliminate the even-order harmonics of phase back electromotive force (EMF) and the unipolar leakage flux in the end region. The flux barrier is employed to improve the symmetry of the air-gap flux and reduce the saturation of the stator yoke, and hence the output torque can be improved. The proposed CPM machine, as well as its conventional counterpart with N-iron sequences, is optimized by finite-element analyses. Moreover, the electromagnetic performance of the proposed CPM machine, including the open-circuit air-gap flux density, back EMF, average torque, torque ripple, loss, efficiency, and unipolar leakage flux, is compared with the conventional CPM and surface-mounted PM (SPM) machines. Although both the proposed and conventional CPM machines have lower output torque than the SPM machine, the utilization ratio of PM material is increased by >33%. It is demonstrated that the proposed CPM machine has similar output torque and efficiency, but much lower torque ripple compared to the conventional one. Moreover, unipolar leakage flux does not exist in the end shaft of the proposed machine, and thus, the magnetization of the mechanical components can be effectively eliminated. Finally, the 9-slot/6-pole CPM machine is prototyped and measured to validate the analyses.

Multi-Objective Optimization Design and Multi-Physics Analysis a Double-Stator Permanent-Magnet Doubly Salient Machine

The double-stator permanent-magnet doubly salient (DS-PMDS) machine is an interesting candidate motor for electric vehicle (EV) applications because of its high torque output and flexible working modes. Due to the complexity of the motor structure, optimization of the DS-PMDS for EVs requires more research efforts to meet multiple specifications. Effective multi-objective optimization to increase torque output, reduce torque ripple, and improve PM material utilization and motor efficiency is implemented in this paper. In the design process, a multi-objective comprehensive function is established. By using parametric sensitivity analysis (PSA) and the sequential quadratic programming (NLPQL) method, the influence extent of each size parameter for different performance is effectively evaluated and optimal results are determined. By adopting the finite element method (FEM), the electromagnetic performances of the optimal DS-PMDS motor is investigated. Moreover, a multi-physical field analysis is included to describe stress, deformation of the rotor, and temperature distribution of the proposed motor. The theoretical analysis verified the rationality of the motor investigated and the effectiveness of the proposed optimization method.

Current Source Generator–Converter Topology for Direct-Drive Wind Turbines

Permanent magnet synchronous generator (PMG) based direct-drive wind turbines (DDWTs) have recently drawn the attention of the wind power market given their low operation and maintenance cost, reliability, and longer lifetime. In this paper, a zero dc-link impedance topology for DDWT-PMG systems is presented. The proposed topology eliminates the use of the failure-prone dc bus capacitor by replacing the grid-side converter with a phasor pulse-width modulation (PPWM) boost current source inverter (CSI), also referred to as indirect boost matrix converter. Furthermore, the novelty of the proposed topology lies in utilizing the synchronous inductance of the PMG as the dc-link inductor required by the boost-CSI, thus decreasing the overall system weight and size. In addition, the PPWM boost-CSI enables a high voltage-boosting ratio, which allows the design of a low-voltage PMG. As a result, the PMG size, weight, and high-cost PM material volume can be decreased. The feasibility of the low-voltage generator is investigated through finite-element computations using as a base for comparison an existing 1.5-MW DDWT-PMG. This comparison demonstrates a reduction in the generator volume, PM material, and the total weight of the generator. Finally, the proposed topology is validated through simulations and experiments.

Novel mechanisms for solid-state processing and grain growth with microstructure alignment in alnico-8 based permanent magnets

An estimated 750,000 new hybrid electric and plug-in battery vehicles, most with permanent magnet synchronous alternating current (PMAC) drive motors, took to the road in 2016 alone. Accompanied by 40% year over year growth in the EV market significant challenges exist in producing large quantities of permanent magnets (on the order of tens of millions) for reliable, low-cost traction motors [IE Agency, Energy Technology Perspectives (2017)]. Since the rare earth permanent magnet (REPM) market is essentially 100% net import reliant in the United States and has proven to have an unstable cost and supply structure in recent years, a replacement RE-free PM material must be designed or selected, fully developed, and implemented. Alnico, with its high saturation magnetization and excellent thermal stability, appears to be uniquely suited for this task. Further, while alnico typically has been considered a relatively low coercivity hard magnet, strides have been made to increase the coercivity to levels suitable for traction drive motors [W Tang, IEEE Trans. Magn., 51 (2015)]. If a simple non-cast approach for achieving near [001] easy axis grain aligned permanent magnets can be found, this would allow mass-produced final-shape anisotropic high energy product magnets suitable for usage in compact high RPM rotor designs. Therefore, a powder metallurgical approach is being explored that uses classic compression molding with “de-bind and sinter” methods, where a novel applied uniaxial loading, and an applied magnetic field may create final-shape magnets with highly textured resulting microstructures by two different mechanisms. Results indicate a positive correlation between applied uniaxial load and resulting texture (Fig. 1), along with benefits from using an applied magnetic field for improved texture, as well. The apparent mechanisms and resulting properties will be described using closed loop hysteresisgraph measurements, EBSD orientation mapping, and high-resolution SEM.

Quantitative comparison of partitioned-stator machines for hybrid electric vehicles

In this paper, three partitioned-stator (PS) machines, namely the PS flux-switching DC-field (PS-FSDC) machine, the PS-FS hybrid-excitation (PS-FSHE) machine, and the flux adjuster FS permanent-magnet (FA-FSPM) machine are proposed. With different flux-regulating mechanisms, all three proposed machines can offer satisfactory flux-weakening capabilities for wide-speed range operations. Unlike the traditional PS machine that installs the armature windings and the excitation sources in the outer-stator and inner-stator, respectively; the proposed machines purposely swap the installation arrangements. Upon the proposed structure, the FA-FSPM machine can fully utilize the stator core for PM material accommodations. As a result, excellent power and torque densities can be achieved. To verify the proposed concepts, these three PS machines are quantitatively compared based on the hybrid electric vehicle (HEV) specifications.

Optimization of Magnet Shape Based on Efficiency Map of IPMSM for EVs

A study on optimization exemplary for permanent magnet V straight shape of rotor in interior permanent magnet synchronous motor (IPMSM) is presented, aiming to achieve higher efficiency map in the operating duty cycle US06. The reduction of PM material is valuable as the cost of rare earth is increasing. The finite element analysis (FEA) is used to simulate d- and q-axis inductance, develop the efficiency map at the speed of 4500 and 9000 rpm, and analyze the energy loss. The optimal design process is introduced to reduce magnet material based on the efficiency map of IPMSM produced using FEA. This study has resulted in 20% reduction of magnet size, comparing with the original designs. The FEA result is confirmed by the tests of the prototype machine. As a result, the high-efficiency IPMSM optimizing process is concluded for electric vehicles as providing some reference in the future work.