Ferrite Permanent Magnet Research Articles

Demagnetization investigation of a partitioned rotor flux switching machine with hybrid permanent magnet

In this paper, the partitioned rotor flux switching permanent magnet machine with ferrite permanent magnet is proposed. By the adoption of the partitioned rotor configuration, the stator flux leakage is eliminated and the permanent magnet utilization is improved. The ferrite permanent magnet machine often suffers from irreversible demagnetization due to the inherent relatively low coercivity of ferrite permanent magnet. To mitigate the machine irreversible demagnetization risk, an improved partitioned rotor flux switching permanent magnet machine with hybrid permanent magnet topology is also proposed. Two little pieces of rare-earth permanent magnet are installed at the corners of ferrite permanent magnet, thus forming the hybrid permanent magnet topology. And the demagnetization mechanisms of both machines are clarified by the magnetic equivalent circuit method, which prove that the rare-earth permanent magnet offer magnetic protection function for the ferrite permanent magnet. Furthermore, by the 2-D finite element analysis, the demagnetization characteristics and the electromagnetic performances of the two machines are quantitively assessed, revealing that the demagnetization risk is reduced significantly. Both theoretical analysis and simulation results verify that the improved machine can not only maintain low-cost design, but also possess enhanced demagnetization withstand capability and competitive electromagnetic performances as expected.

Design of a Brushless PM Starter Generator for Low-Cost Manufacture and a High-Aspect-Ratio Mechanical Space Envelope

This paper presents the results of a brushless permanent magnet (PM) starter-generator design, which caters for low-cost manufacture and a highly constrained mechanical space envelope. The starter-generator design addresses the low-cost requirement through the use of aluminium winding conductors and ferrite PM. This presents several challenges which include, but are not limited to, the selection of an appropriate machine topology to realise a high specific output with the lower performance materials, minimizing the power losses associated with the higher resistivity of aluminium, and the enhancement of thermal performance. The problem is further exacerbated by the demanding space envelope, operating requirements, and the necessity of “design for manufacture.” The selection of an appropriate machine topology is paramount in the present application as the limited mechanical space-envelope results in a “pancake” like geometry in which the aspect ratio of the stator outer diameter to the machine active length is high. To provide a solution satisfying all these challenging design requirements, an approach combining the theoretical electromagnetic and thermal analyses together with tests on machine subassemblies has been employed here. Such a method allows for a more informed design process, where the manufacture and assembly nuances affecting the starter-generator's performance are identified and accounted for prior to prototyping of the complete machine assembly. This paper discusses the employed design methodology in detail. A number of machine designs with alternative winding constructions have been considered providing an insight into challenges and limitations for the cost-effective winding construction utilizing aluminium conductors. The results from analysis of the starter generator suggest that the proposed machine design is capable of achieving the design requirements for both continuous and transient operating modes.

페라이트 영구자석을 갖는 고속 매입형 영구자석 전동기의 특성해석 및 설계

We propose an interior permanent magnet syhchronous motor (IPMSM) with arc-shape ferrite permanent magnets (PMs) as a substitute for the rare-earth permanent magnet, and determine its optimal design through parametric study. First, we use 2D finite element analysis to analyze 4-poles and 6-slots initial model according to performance requirements and design parameters. The current angle of the maximum average torque considered in the analysis is different compared with the current angle of the minimum torque ripple. Thus, the parametric study for optimal rotor design is performed by varying the thickness and the offset radius of the PMs according to current angle. In particular, a narrow bridge is required in conventional IPMSM for reducing flux leakage; however, the increase in cogging torque in the analysis model saturates the narrow bridge (large offset radius). Therefore, we suggest an appropriate shape considering limiting conditions such as DC link voltage, average torque, torque ripple, and cogging torque taking into account performance requirements.

A Novel Proposal to Improve Reliability of Spoke-Type BLDC Motor Using Ferrite Permanent Magnet

This paper proposes a novel proposal to improve reliability of a spoke-type brushless direct current (BLDC) motor using ferrite permanent magnets (Fe-PMs) through a new design. First, the design process for a neodymium permanent magnet (Nd-PM) free spoke-type BLDC motor without assistant permanent magnets (PMs) is presented. The proposed motor is designed by taking into account the demagnetization phenomenon. Second, the effect of the armature reaction on the PMs is analyzed by using the finite element method (FEM) in order to evaluate the robustness of the proposed motor with Fe-PM. In addition, another proposal to avoid the demagnetization phenomenon is suggested. Finally, a prototype motor is manufactured based on the proposed motor. The output characteristics of prototype motor and the demagnetization phenomenon are verified through an experiment.

Recent technical trends in permanent magnet synchronous motors

This paper presents an overview of the recent technical trends in permanent magnet synchronous motors (PMSMs), especially the rare earth (RE)‐less PMSMs that have been developed in Japan. The RE‐less PMSMs, along with PMSMs with reduced RE permanent magnets (PMs), PM‐assisted synchronous reluctance motors (PMASynRM) with ferrite PMs, spoke‐type interior PMSMs (IPMSMs) with ferrite PMs, and axial‐gap PMSMs with ferrite PMs, are reviewed. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Sensorless Control of a Ferrite PM Assisted-Synchronous Reluctance Machines by Using Sliding Mode Observer and High Frequency Signal Injection

This paper presents sensorless control of ferrite permanent magnet-assisted synchronous reluctance machines (FPMA-SynRM) over wide speed range by using sliding mode observer (SMO) and high frequency signal injection. The basic equation of sliding mode observer will be derived based on dynamic model of PMSynRM. In the study, the equivalent of EMF-based SMO is proposed to estimate rotor position at medium and high speed range. The principles of high frequency signal injection, digital signal processing and rotor polarity identification is also analysed. Finally, the theoretical analysis have been verified with the experiments and the results obtained show that the resolution of estimated position signal can meet requirements of some industrial drive applications.DOI: http://dx.doi.org/10.5755/j01.eie.22.4.15906

Variable-speed PM synchronous motors with ferrite excitation

The standard motor for variable-speed main drives is the induction motor (IM). In comparison to synchronous machines (SYM), induction motors show the disadvantage of additional ohmic losses in the rotor. Therefore, especially low-power induction motors are not able to reach energy efficiency levels as high as IE4. The transition of motor technology from induction motors to synchronous motors with ferrite excitation provides the opportunity to increase motor efficiency without using expensive rare-earth magnets. Therefore, this paper deals with the steady-state modeling, simulation and design of PM synchronous motors with ferrite excitation in respect of reaching the highest possible motor efficiency. Due to the comparatively poor magnetic parameters of the ferrite magnet, a motor design using the flux concentration effect has to be used. An analytical approach based on a magnetic network is developed to describe the steady-state operating behavior of the ferrite excited PM synchronous motor. The non-linear network equations are solved by applying the Newton-Raphson Method. Due to short calculation times and a high flexibility in respect of the design of a whole product series, the analytical approach is preferred to a numerical approach. To validate the simulation results, a prototype is designed based on a fundamental induction motor. Finally, the test of the prototype in laboratory allows a comparison between simulation and measurement as well as between ferrite excited PM synchronous motor and induction motor.

Determining demagnetisation risk for two PM wind power generators with different PM material and identical stators

Ways to utilise ferrite permanent magnets (PMs), in a better way has been in focus the last couple of years since the use of neodymium-iron-boron (NdFeB) PMs has been debated. While ferrite PMs offer a low-cost alternative to rare-earth PMs, it is a trade-off for lower energy density. Depending on the type of PM and if the PMs are surface mounted or buried, the risk of demagnetisation during a fault condition can vary significantly between machines. In this study, the demagnetisation risk of two electrically similar generators with identical stators has been studied during several short-circuit faults at different temperatures. The study is simulation-based, and the results show that the generator with the ferrite rotor will suffer from a small but not significant amount of demagnetisation in the worst, three-phase-neutral, short-circuit case at a temperature of 5°C, whereas the NdFeB PMs will suffer from partial demagnetisation if a fault occurs at 120°C. For operational temperatures between 20 and 60°C both generators will sustain a short-circuit event.

A 32 000 r/min Axial Flux Permanent Magnet Machine for Energy Storage With Mechanical Stress Analysis

This paper focuses on the design and analysis of a high-speed axial flux permanent magnet (PM) machine for an aerospace flywheel energy storage system. The design target is to experimentally verify the sinusoidal back electromotive force (EMF) considering the mechanical stress limitation of the machine at a speed of 32 000 r/min. Two machine models based on ferrite and SmCo PMs have been proposed. First, the back EMF analysis using a 3-D finite-element method is performed to determine the performance of the two models. Second, the mechanical stress analysis is performed to check the durability of the rotor strength. Finally, the selected model utilizing the ferrite PMs has been manufactured and tested at 32 000 r/min to validate its effectiveness at high-speed operation.

Comparative Study of Electromagnetic Performance of High-Speed Synchronous Motors With Rare-Earth and Ferrite Permanent Magnets

The rare-earth permanent magnet (PM) is commonly used to improve the performance of high-speed electrical machines to compensate for their high production costs, while it is very likely that the demand for high-speed machines will increase in the near future as markets for new technologies continue to grow. However, a high-speed machine is required to have high performance and low manufacturing cost, because mass production is needed for these applications. Therefore, in this paper, a high-speed machine using a ferrite PM was designed to significantly decrease the manufacturing costs. To examine the performance of the high-speed machine suggested in this paper, the performance of a high-speed model using a ferrite PM is compared with that of a SmCo PM model. A high-speed machine with a specification of 3 kW and 30 000 r/min is designed and manufactured. The designed model is analyzed using the finite-element method. Finally, the no-load back electromotive force in each model is examined through a back-to-back experiment.

Analysis and Design of a Double-Stator Flux-Switching Permanent Magnet Machine Using Ferrite Magnet in Hybrid Electric Vehicles

A double-stator flux-switching permanent magnet (DS-FSPM) machine using ferrite is proposed to replace an interior permanent magnet synchronous motor (IPMSM) on hybrid electric vehicles. A conventional FSPM machine is designed, and its torque characteristic is analyzed by a frozen permeability method. It is verified that magnetic saturation causes the reduction of flux linkage generated by PM and leads to the deterioration of electromagnetic torque. A DS-FSPM machine is effective for magnetic saturation because of its unique structure and makes the improvement of efficiency and power density. The proposed DS-FSPM machine achieves distinct performance enhancement compared with an IPMSM, even by utilizing ferrite PM.

Site-dependent cobalt electronic state in La–Co co-substituted magnetoplumbite-type ferrite: 59Co nuclear magnetic resonance study

The nuclear magnetic resonance of 59Co was measured over a wide frequency range in a powder sample crushed from a well-characterized single crystal of La–Co co-substituted magnetoplumbite-type strontium ferrite (SrFe12O19), a familiar base material for the ferrite permanent magnet. The simultaneous observation of both high- and low-frequency resonances suggests the coexistence of both high- and low-spin states of the substituted Co or the presence of Co orbital moment at a particular site. The possible presence of trivalent Co was also investigated. The results suggest that the Co atoms are distributed across different crystallographic sites with different local environments, and that the electronic state of Co is much more subtle than the conventional understanding.

An Analytical Approach to Design the PM in PMAREL Motors Robust Toward the Demagnetization

In the permanent magnet (PM)-assisted reluctance motors, low-energy PM, such as Ferrite PM, is used to get a cheap rotor. As far as the design choices are concerned, the PM width has to be selected so as to achieve the desired air-gap flux density at no-load condition and the PM thickness has to be selected to avoid the demagnetization of the PM under full-load conditions. This paper presents a practical analytical approach to compute PM width and thickness according to a given air-gap flux density and stress on the PM itself. Two approaches based on a complete model and a simplified model are considered and compared. As an example, a 36-slot 4-pole machine is designed. Finite element analysis confirms the results achieved by means of both analytical analyses.

Low‐torque ripple design of a ferrite‐assisted synchronous reluctance motor

This study illustrates the design of a low-torque ripple ferrite-assisted synchronous reluctance machine. The design strategy initially adopts a simplified analytical model in order to select the optimal values for the flux barrier angles that mainly affects the torque ripple. Then, synchronous reluctance rotor geometries selected on the basis of analytical results are analysed by finite elements (FEs) simulations. The simulated geometries are provided by ferrite permanent magnets (PMs) to enhance machine performance. The optimisation steps are properly coordinated in order to realise the maximum reduction of the torque ripple, taking into account the PM quantity and the flux barrier shape as well as the demagnetisation risk. Two optimal rotor geometries are presented and compared in terms of torque ripple by FEs simulations. Then, the comparison have been extended to other machine characteristics (as high-frequency saliency and demagnetisation tolerance) to the aim of selecting the more promising one. Available measurements on prototypes are reported to confirm the simulation results and the design approach.

Irreversible Demagnetization of Permanent Magnet in a Surface-Mounted Permanent Magnet Motor With Overhang Structure

The overhang structure is an effective solution to increase the performance of a surface-mounted permanent magnet (SPM) motor using a ferrite PM. If a ferrite PM, which can be demagnetized through a large armature reaction, is used for an SPM motor controlled by the field-weakening method, the ferrite PM can suffer from irreversible demagnetization. Moreover, if an SPM from the overhang structure is directly exposed to the armature reaction by the winding of the stator, a ferrite PM of an SPM motor could be partially demagnetized. Because of this, when the field-weakening method is used for the control of the SPM motor with the overhang structure, PMs are disadvantageous to the irreversible demagnetization. To solve these problems, a novel structure is proposed, which can increase the motor performance through the overhang structure without irreversible demagnetization in the overhang part.

Estimation of Rotor Type Using Ferrite Magnet Considering the Magnetization Process

This paper deals with the post-assembly magnetization process of motors using ferrite permanent magnets (PMs). In order to meet the needs of mass production, most motors are magnetized post assembly. However, increasing complex shapes are required to maximize the flux of PMs. As a result, certain locations in the magnet are not fully magnetized by the magnetizing fixture due to insufficient magnetomotive force. Therefore, an analysis concerning the post-assembly magnetization is needed. In this paper, the concentrated flux spoke-type synchronous motor is analyzed with regard to the magnetization process. Owing to more flux, this motor is designed as a V-shape PM. Therefore, it is not fully magnetized according to magnet shape. By identifying the effect of the magnet shape, the magnetization level is compared by the amount of flux linkage between post assembly and at full magnetization. Finally, the back electromotive force is estimated by the post-assembly magnetization method according to the magnet shape.

Rotor Unbalanced Magnetic Force in Flux-switching Permanent Magnet Machines Due to Static and Dynamic Eccentricity

This article investigates the rotor unbalanced magnetic force characteristics of a 12-stator-slot 10-rotor-pole flux-switching permanent magnet machine due to both static and dynamic eccentricity. The equations for radial and tangential components of the unbalanced magnetic force on the rotor are formulated. The 2D finite-element analysis results for a baseline 10-kW 15,000-rpm ferrite flux-switching permanent magnet machine show that both static and dynamic eccentricity will result in a significant amount of unbalanced magnetic force in the flux-switching permanent magnet machine even under the no-load condition. This article also shows that the direction of rotor unbalanced magnetic force due to static eccentricity is fixed, while the direction of rotor unbalanced magnetic force due to dynamic eccentricity is rotating. This research clearly reveals the influence of eccentricity on the performance of flux-switching permanent magnet machine, and facilitates further research on the vibration and acoustic noise analyses of flux-switching permanent magnet machines.

Structure, Magnetic Properties, and Coercivity Mechanism of Rapidly Quenched Mn<sub><italic>x</italic></sub>Ga Ribbons

Recently, due to the short supply of rare earth element, there is a great demand in developing the rare-earth-free permanent magnets with giant magnetic anisotropy. Among the rare-earth-free permanent magnetic materials of current interest, Mn x Ga alloys are potential candidates as permanent magnets [1]. In the Mn x Ga alloys, the ferromagnetic L1 0 -MnGa phase and ferrimagnetic D0 22 -Mn- 3 Ga phase are theoretically expected to have maximum energy product comparable with the commercial AlNiCo and ferrite permanent magnets. The two phases also show high spin polarization and low damping constant for application in spintronic devices and have been investigated intensively in the past decades. In our recent studies, the annealing time of the rapidly quenched Mn x Ga ribbons was reduced to 1 hour [2]. In this study, the coercivity mechanism and exchange interaction in Mn x Ga alloy has been investigated.

Influence of damping coefficient from permanent magnets on chatter formation during end milling of titanium alloy (Ti-6Al-4V)

In machining operations, chatter is undesirable due to its adverse effects on the product quality, operation cost, machining accuracy and machine tool life. It is also responsible for reducing output. Chatter is a self-excitation phenomenon occurring in machine tools, in which the cutting process tends to lower the damping capacity of the machine structural components ending in an unstable behavior of the system. Chatter arises due to resonance when the vibrations of the instability of chip formation and the natural vibration modes of the machine-system components coincide. This paper focuses on the influence of damping coefficient from permanent magnets on chip serration frequency as an approach of minimizing chatter in end milling of Titanium alloy (Ti6Al4V). The method consists of two ferrite permanent magnet bars (dimensions: 1" × 6" × 3"), mounted 5mm from the cutting tool using a specially designed fixture which provided a uniform magnetic field of 2500-2700 Gausses. A titanium alloy Ti6Al4V block was then end milled using uncoated WC-Co inserts. A sequence of 15 experimental runs was conducted based on a small Central Composite Design (CCD) model in Response Surface Methodology (RSM). The primary (independent) parameters were: cutting speed, feed, and depth of cut. The data acquisition system comprised a vibration sensor (accelerometer) and a signal conditioning unit was used to measure the vibration data. The resultant vibrations were then analyzed using the DASYLab 5.6 software. Machining tests were conducted for two different conditions - with and without the application of magnets. Scanning Electron Microscope (SEM) was used to measure the chip segmentations. The SEM analysis of chip serrations demonstrated that the chip serration frequency were more stable while cutting under the presence of permanent magnets due to lower intensity of chatter.

Manganese-based Permanent Magnets

There is a significant gap between the energy product, BH, where B is the magnetic flux density and H is the magnetic field strength, of both the traditional ferrite and AlNiCo permanent magnets of less than 10 MGOe and that of the rare earth magnets of greater than 30 MGOe. This is a gap that Mn-based magnets could potentially, inexpensively, fill. This Special Issue presents work on the development of both types of manganese permanent magnets. Some of the challenges involved in the development of these magnets include improving the compounds’ energy product, increasing the thermal stability of these metastable compounds, and producing them in quantity as a bulk material.[...]