Radial Magnet Research Articles

Авиационные генераторы с постоянными магнитами

The capacity of aircraft generators reaches several hundred kV×A. For decreasing their specific mass, the generators are designed for limiting rotation frequencies in terms of strength considerations. With increasing the capacity of aircraft generators, their excitation system on the basis of high-energy permanent magnets can be regarded as an alternative to the electromagnetic excitation system. This is because the volume of magnets is several times smaller than that of ferromagnetic poles with windings. Therefore, permanent-magnet generators can be made with a rotor having a smaller mass and a shaft diameter several times larger than in a generator with electromagnetic excitation, due to which it becomes possible to increase their critical frequency and limit power capacity. In addition a rotor with permanent magnets has a higher strength and can be designed for higher rotation frequencies and for a larger number of poles than in case of using electromagnetic excitation. Permanent-magnet generators have higher efficiency values and higher overloading ratios. Rotors fitted with tangential magnets produce higher magnetic induction values in the air gap than the rotors fitted with radial magnets, due to which it becomes possible to make a high-frequency generator with a shorter length while keeping its mass almost unchanged. On the other hand, generators fitted with radial magnets have a stronger rotor and can be designed for higher capacities and rotation frequencies than generators with tangential magnets. Among many design arrangements of rotors, those with nonmagnetic yokes are the simplest ones, whereas arrangements with yokes made of gradient material are the most efficient ones. The most rational application of multipole permanent-magnet generators is in DC systems involving electronic converters.

A COMPARATIVE STUDY OF QUASI-FEA TECHNIQUE ON IRON LOSSES PREDICTION FOR PERMANENT MAGNET SYNCHRONOUS MACHINES

The paper presents an advanced quasi-FEA technique on the iron losses prediction using Bertotti’s iron loss separation models, in which a curve fitting is taken into account for coefficients calculation of each model. Moreover, the skin effect and saturation consideration are applied in order to check the accuracy through the relative error distribution in the frequency domain of each model from low up to high frequencies 50 to 700 (Hz). Additionally, this comparative study presents a torque-speed-flux density computation that is discussed and presented. The iron loss characteristics of a radial flux permanent magnet synchronous machine (PMSM) with closed-slots and outer rotor topology are also discussed. The quasi-finite-element (FE) analysis was performed using a 2-D and 3-D FEA, where the employed quasi-2-D FEA is proposed and compared with 3-D FEA, and along with experimental verifications. Finally, all the iron-loss models under realistic and non-ideal magnetization conditions are verified experimentally on a surface-mounted PMSG for wind generation application.

Analytical Model-Based Multiphysics Optimization of a Nanopositioning Electromagnetic Actuator

This paper presents the multiphysics optimization of a new class of nanopositioning actuators, termed as flexure-based electromagnetic linear actuator (FELA). The optimization is carried out analytically based on the derived closed-form magnetic field, force, and thermal models, while its objectives include the maximizing of force generation and minimizing of thermal generation, which are both crucial for the nanopositioning actuators. The optimization results show that the new version of FELA achieved 67.3% improvement in force generation for certain current and 46.2% thermal reduction for certain output force, compared to the previous version of FELA with the same size, which was optimized using the numerical methods. The optimization results are also validated by the experiments of the new version FELA prototype, where 56.2% improvement in current–force sensitivity and 43% above reduction in thermal power are demonstrated experimentally. Furthermore, by utilizing the established modeling framework, several fundamental questions on the design of FELA are answered theoretically in this paper, such as the effect about the uniform and radial magnetization of the permanent magnet and the performance tradeoff between the different number of magnet segments.

Permanent Magnet Tubular Generator with Quasi-Halbach Array for Free-Piston Generator System

In this paper, the performance of a free-piston generator system with tubular single-phase stator winding is investigated for three different configurations of permanent magnet arrays on the mover: radial, rectangular quasi-Halbach and trapezoidal quasi-Halbach arrays. The optimal shape of the rectangular quasi-Halbach magnetization is obtained by employing an optimization technique called Imperialist Competitive Algorithm (ICA), and the results are compared with the previously developed permanent magnet linear generator (PMLG) with magnets of radial magnetization. Then, the resultant design of rectangular quasi-Halbach array, is changed to trapezoidal quasi-Halbach array and its performance is compared with other types of magnet arrays. The employed ICA is based on the analytical model of the magnetic flux distribution in air-gap, and is further verified by a nonlinear transient finite element (FE) model. The FE model has been developed to study the performance of the reciprocating PMLG. The accuracy of the proposed FE model is exemplified by comparing the calculated results with the experimental ones regarding the PMLG with radial magnetization.

Analytical Prediction and Optimization of Cogging Torque in Surface-Mounted Permanent Magnet Machines With Modified Particle Swarm Optimization

An analytical method is proposed to predict and optimize cogging torque accurately. It is derived by the exact subdomain model, equivalent current sheet of magnet, and modified particle swarm optimization (PSO), in surface-mounted permanent magnet machines (SPMs) accounting for the effect of stator slotting and tooth-tips. The analysis works for internal/external rotor motor topologies, radial/parallel magnetization, as well as for any combinations of pole and slot numbers. Then, four important design parameters, viz. magnet thickness, air-gap length, slot-opening to slot pitch ratio, and pole-arc to pole-pitch ratio, are adopted as optimal variables, and the peak of fundamental order of the radial component of the air-gap flux density is constrained to optimize cogging torque by modified PSO based on forgoing model. Finally, the cogging torque of two prototype machines with both radial and parallel magnetizations is optimized notably. The paper validates the results of analytical prediction by finite-element analysis.

A new optimal design of surface mounted permanent magnet synchronous motors with integral slot per pole

PurposeThe purpose of this paper is to present a new optimal design for integral slot permanent magnet synchronous motors (PMSMs) to shape the air-gap magnetic field in sinusoidal and to reduce the cogging torque, simultaneously.Design/methodology/approachFor obtaining this new optimal design, the influence of different magnetizations of permanent magnets (PMs), including radial, parallel and halbach magnetization is investigated on the performance of one typical PMSM by using the conformal mapping (CM) method. To reduce the cogging torque even more, the technique of slot opening shift is also implemented on the stator slots of analyzed PMSM without reduction in the main performance, including the air-gap magnetic field, the average torque and back-electromotive force (back-EMF).FindingsFinally, an optimal configuration including the Hat-type magnet poles with halbach magnetization on the rotor and shifted slot openings on the stator is obtained through the CM method, which shows the main reduction in cogging torque and the harmonic content of air-gap magnetic field.Practical implicationsThe obtained optimal design is completely practical and is validated by comparing with the corresponding results obtained through finite element method.Originality/valueThis paper presents a new optimal design for integral slot PMSMs, which can include different design considerations, such as the reduction of cogging torque and the total harmonic distortion of air-gap magnetic field by using the CM method.

Fourier decomposition of segmented magnets with radial magnetization in surface-mounted PM machines

Abstract This paper presents a generic field model of radial magnetization (RM) pattern produced by multiple segmented magnets per rotor pole in surface-mounted permanent magnet (PM) machines. The magnetization vectors from either odd- or even-number of magnet blocks per pole are described. Fourier decomposition is first employed to derive the field model, and later integrated with the exact 2D analytical subdomain method to predict the magnetic field distributions and other motor global quantities. For the assessment purpose, a 12-slot/8-pole surface-mounted PM motor with two segmented magnets per pole is investigated by using the proposed field model. The electromagnetic performances of the PM machines are intensively predicted by the proposed magnet field model which include the magnetic field distributions, airgap flux density, phase back-EMF, cogging torque, and output torque during either open-circuit or on-load operating conditions. The analytical results are evaluated and compared with those obtained from both 2D and 3D finite element analyses (FEA) where an excellent agreement has been achieved.

Cogging Torque Cancellation by Magnet Shaping in Surface-Mounted Permanent-Magnet Motors

This paper presents a new method for cancellation cogging torque by magnet shaping. First, the conditions to be met by the induction space wave for the total cancellation of cogging torque are analytically established. These results are then used to determine the shape of the magnets. The approach followed is inverse to that used by traditional methods, whereby, based on a predetermined shape of the magnets, the cogging torque is calculated. As a result, the proposed method enables optimum results to be obtained directly and it is generalizable to any motor configuration. The methodology has been first validated by means of finite elements and then tested experimentally on a dc motor and on an ac motor for both radial and parallel magnetization.

EMF waveform optimization using the permanent magnet volume-integration method

The emf expression can be derived with the PM volume-integration method, allowing easier optimization and prediction of the emf harmonic content. An analytical expression is developed for predicting the electromotive force (emf) waveforms and flux linkage resulting from the motion of permanent magnets (PM) in the case of two cylinders, where the outer cylinder carries a surface-mounted winding and the inner cylinder carries the PMs. The expressions are based on the PM Volume-Integration Method, which uses a volume integral calculated over the magnet volume, rather than the usual surface integral over the coil surface. The specific case of surface-mounted arc PM with radial magnetization is analyzed. An outer cylinder with infinitely thin winding distribution on its inner surface is considered. The chording factor, slot factor and spread factor are included in the analytical expression. The emf waveform and related harmonics are predicted analytically and validated by comparing with a finite element analysis and with experiment.

Axial flux PM BLDC motor design methodology and comparison with a radial flux PM BLDC motor

The aim of this paper is to develop a methodology to design an axial flux permanent magnet brushless direct current (AFPM) motor for a washing machine and compare the results with a conventional radial flux permanent magnet brushless direct current (RFPM) motor with the same power ratings. The AFPM motor is designed based on the maximum power density for an optimum inner-to-outer diameter ratio by using the reference RFPM motor constraints, such as the same rated torque at the rated speed. Both motors use the same materials in terms of lamination, permanent magnet, and conductor. They both use ferrite magnets; however, the AFPM motor has a surface-mounted structure and the RFPM motor has a buried one. The algorithm is used to determine the motor dimensions such as motor diameters, lengths, and the number of turns. The optimum number of poles considered for the design is chosen. Both motors are analyzed by finite element method (FEM) to verify the analytical approach and are compared in terms of power density, torque density, total weight and volume, torque ripple, and efficiency.

Dual rotor flux switching permanent magnet machines with phase-group concentrated-coil windings for high performance

This paper proposes a novel dual rotor radial field flux switching permanent magnet machine (FSPMM) with phase- group concentrated-coil (PGCC) windings and two misaligned rotors to obtain high performance, including high torque density and low cogging torque, as well as low torque ripple. The proposed FSPMM features a new combination of stator slots and rotor poles, which is determined by the winding configurations. The PGCC windings are adopted to obtain a unity displacement winding factor, and enhance the flux focusing effects together with the use of spoke-type PM constructions. The unaligned arrangement of two rotors will help to not only achieve further flux magnification by an alternate operating principle for PM flux concentration, but also suppress the cogging torque. To highlight the advantages of the proposed FSPMM, two conventional FSPMMs with typical machine configurations having concentrated windings are adopted for performance comparison based on a finite element method (FEM) using JMAG-Designer.

Study on Torque Calculation for Hybrid Magnetic Coupling and Influencing Factor Analysis

Specific to a problem that the present transmission of magnetic coupling torque was subjected to restrictions of its own structure, a hybrid magnetic coupling was proposed. Then, finite element method was adopted to carry out numerical calculations for its three-dimensional magnetic field to obtain three-dimensional magnetic field distribution of radial and axial configurations. Major influencing factors of its torque, such as lengths of axial and radial air gaps, thicknesses of axial and radial permanent magnets, the number of slots in axial copper rotor, thickness of axial and radial copper rotor, etc., were analyzed. The relevant results indicated that in certain conditions of shapes, ten magnetic poles of the axial permanent magnet rotor, nine of the radial permanent magnet rotor and nine slots from the axial copper rotor were used. Correspondingly, the axial copper rotor had a thickness of 20 mm and it was 5 mm for the radial copper rotor. Moreover, the maximum torque could reach 190 N.m approximately. If lengths of axial and radial air gaps increased, the torque may go down otherwise. Within a certain scope, the torque rose in the first place and then fell with increases in the permanent magnet thickness of axial permanent magnetic rotor, the number of axial and radial magnetic poles, the number of slots in axial copper rotor, and the thickness of axial copper rotor. Additionally, the number of slots in the axial copper rotor could not be equivalent to that of magnetic poles in axial permanent magnetic rotor. However, as the permanent magnet thickness of radial permanent magnetic rotor rose, the torque went up as well.

Magnet loss analysis for a high-speed PM machine with segmented PM and modified tooth-tips shape

Abstract This paper presents the loss-oriented performance analysis of a radial highspeed permanent magnet (PM) machine with concentrated windings for automotive application. The PM synchronous machine was designed for an operating frequency up to 800 Hz. The main aim of this paper is to analyse the selected methods for magnet eddycurrent loss reduction. The first approach to rotor modification regards magnet segmentation in circumferential and axial directions. The second approach is based on changes in tooth-tips shape of the stator. The best variants of tooth-tip shapes are determined for further investigation, and adopted with a rotor having magnet segmentation. It is found that the machine with a segmented magnet leads to magnet loss reduction by 81%. Further loss reduction by 45% can be realized with the proposed tooth-tip shape. Additionally, owing to the stator and rotor modifications, the main machine parameters are investigated, such as back-EMF, electromagnetic torque, torque ripple and cogging torque. The 2-D and 3-D finite element analysis (FEA) is used for electromagnetic analysis. An experimental approach based on a partially wound stator is employed to verify the 3-D FEA.

Alterations in brain white matter contributing to age-related slowing of task switching performance: The role of radial diffusivity and magnetization transfer ratio.

Successfully switching between tasks is critical in many daily activities. Age-related slowing of this switching behavior has been documented extensively, but the underlying neural mechanisms remain unclear. Here, we investigated the contribution of brain white matter changes associated with myelin alterations to age-related slowing of switching performance. Diffusion tensor imaging derived radial diffusivity (RD) and magnetization transfer imaging derived magnetization transfer ratio (MTR) were selected as myelin sensitive measures. These metrics were studied in relation to mixing cost (i.e., the increase in reaction time during task blocks that require task switching) on a local-global switching task in young (n = 24) and older (n = 22) adults. Results showed that higher age was associated with widespread increases in RD and decreases in MTR, indicative of white matter deterioration, possibly due to demyelination. Older adults also showed a higher mixing cost, implying slowing of switching performance. Finally, mediation analyses demonstrated that decreases in MTR of the bilateral superior corona radiata contributed to the observed slowing of switching performance with increasing age. These findings provide evidence for a role of cortico-subcortical white matter changes in task switching performance deterioration with healthy aging. Hum Brain Mapp 37:4084-4098, 2016. © 2016 Wiley Periodicals, Inc.

Explicit Torque and Back EMF Expressions for Slotless Surface Permanent Magnet Machines With Different Magnetization Patterns

Slotless permanent magnet machines are attractive in some modern drive and power generation fields, where the cogging torque and additional losses need to be minimized or removed. The stator slotless design can be combined with different surface permanent magnet (SPM) rotor topologies. In this paper, explicit analytical expressions are derived to analytically compute the slotless machine torque and no-load back Electro-Motive Force in the case of segmented SPM rotor with parallel, radial, or Halbach-array magnetization patterns. The expressions are found by solving the magnetic field due to the slotless stator winding and to the permanent magnet blocks; the latter modeled through equivalent surface current densities. The accuracy of the method is successfully assessed by comparison with the finite-element analysis (FEA). The proposed formulas are an effective alternative to the FEA to quickly compare different design solutions as well as to optimize them. Application examples are provided in which the presented method is adopted to define the machine cross section that maximizes the torque density.

Optimization study on a 0.6 kW PMSG for VAWTs and determination of open and short circuit performances by using external circuit method

As is known, machine design is a time-consuming and complicated process. And consequently, the verification of the designs and machine performances with known optimization methods prior fabrication are becoming more complex and expensive. Relating to this issue, many studies have been achieved to realize optimization and analyze dynamic performance of the designed machines. In this paper, optimization and short/open circuit fault analysis along with transient performance of a designed 0.6 kW radial flux permanent magnet synchronous generator (RFPMSG) for a stand alone wind turbine was studied. The main feature of this study is to use RMxprt dynamic generator model which is linked with the ANSYS Simplorer external circuit simulator. The co-simulation method has been used to analyze the performance of the generator considered for feeding an ohmic load. This method also yields the waveforms of load voltages and load currents for different load and wind speed conditions along with experimental studies.

Novel switched flux machine with radial and circumferential permanent magnets

Purpose– The paper purposes a novel SFPM machine topology with radial and circumferential permanent magnets (PMs). The paper aims to discuss this issue.Design/methodology/approach– In order to reduce the flux leakage in the stator-outer region and consequently achieve higher magnetic material utilization in switched flux permanent magnet (SFPM) machine, a novel topology with radial and circumferential PMs is proposed. This topology (SFRCPM) has the same structure as conventional SFPM (CSFPM) machine except of the additional set of radially magnetized PMs located around the back iron and surrounded by a laminated ring frame. Using finite element analysis (FEA) the influence of the design parameters on the performance is investigated in order to obtain an effective optimization procedure. Internal and external rotor SFRCPM machines with either NdFeB or ferrite magnets are investigated, optimized and compared with the CSFPM machine having the same size, copper loss and stator/rotor pole combination.Findings– It is concluded that comparing SFRCPM with its CSFPM machine counterpart, internal rotor SFRCPM machine can achieve high PM flux-linkage per magnet volume, however reduced slot area leads to low output torque, whereas external rotor SFRCPM machine can produce higher torque and torque per magnet volume.Originality/value– This paper proposes a novel SFPM machine topology.

Preliminary studies of a new permanent magnet generator (PMG) with the axial and radial flux morphology

In this work, a new axial and radial flux permanent magnet generator (PMG) is introduced. The machine has multiple cores in its stator, which has double sides, coils in these sides. It operates in 3 phases and uses disc type magnets in two rotors at each side. PMG has 24 circular coils and 12 laminated cores. Each rotor has 16 magnets and the stator is stable at the middle of the rotors. The simulations include magnetostatics and magnetodynamics analyzes via finite element method (FEM). After the determination of optimal physical, electrical and magnetic parameters, a prototype machine is constructed for the experiments. The rated values of the machine are measured experimentally for different rotor speeds and different ohmic loads. According to the experimental and theoretical analyzes, the rated power is found as 250 W with the efficiency ratio of 92% for the testing values of airgap 5 mm.

ANALYTICAL MODEL ON REAL GEOMETRIES OF MAGNET BARS OF SURFACE PERMANENT MAGNET SLOTLESS MACHINE

We present in this paper an analytical model for the calculation of the electromagnetic field in a slotless surface mounted permanent magnet machines. This model takes into account the two essential directions of magnetization of the magnets, namely tangential magnetization and radial magnetization. It especially accounts for the parallel form of the magnetization direction. The model uses equivalent currents on the surfaces of the magnets, and in an original way, it uses currents in all volume of the magnet. The model is validated by numerical results obtained with a free software of calculation of the electromagnetic fields (FEMM: Finite Element Method Magnetics) which uses the finite elements method and by an existing experimental structure. The model is extended to the magnets segmented in bars and separated. It is then extended to the shape of magnets close to parallepiped forms which are really used in large machines.

VIBRATION INDUCED FAILURE ANALYSIS OF A HIGH SPEED ROTOR SUPPORTED BY ACTIVE MAGNETIC BEARINGS

Active Magnetic Bearings (AMBs) are increasingly used in various industries and a quick re-levitation of AMBs supported high speed flexible rotor is necessary in case of vibration induced failure. A robust fault diagnosis algorithm is presented to detect suspected saturation type of nonlinearity associated with a power amplifier. A five degree-of-freedom AMB system consisting of four opposing pair of radial magnets and a pair of axial magnets is considered. In this paper failure of an industrial grade AMB system is investigated using Sinusoidal Input Describing Function (SIDF) method. SIDF predicts the gain and frequency at which failure occurs. It is demonstrated that the predicted frequency is in agreement with the frequency at which failure occurs.