Permanent Magnet Structure Research Articles

Design and Analysis of Rotor Shapes for IPM Motors in EV Power Traction Platforms

The recent increase in the use of permanent magnet rotor motors underlines the importance of designing a rotor with an interior permanent magnet (IPM) structure, high power, and high efficiency. This study analyzed the rotor shapes of IPM motors for electric vehicles. Five types of motor rotors for automobiles were analyzed, including two hybrid vehicles. In order to minimize the number of variables in the analysis, the size of the motor stators was fixed and only the rotor shapes were modified to compare torque, torque ripple, efficiency and back-electromotive voltage. When the motor properties were compared as a function of rotor shape, the rotor shape with the smallest magnet volume exhibited excellent results for torque, efficiency and torque ripple.

Experimental Investigation on the Performance of a Parallel Plate-Based Active Magnetic Regenerator

This paper describes a prototype of a linear reciprocating magnetic refrigerator using a gadolinium parallel plate. The new design of the regenerator, installation, and experiment is presented. The regenerator consists of a gadolinium plate and an inlet/outlet section. The thickness and length of the gadolinium plate are 1[Formula: see text]mm and 80[Formula: see text]mm, respectively. The gap between parallel plates is 0.1[Formula: see text]mm. Water is used as the heat transfer fluid. The permanent magnet structure used in the present study can generate a maximum magnetic field intensity of 0.94 T. The effects of surface roughness of the gadolinium parallel plate on the temperature span and cooling capacity are investigated. The results show that there is no significant effect of surface roughness on the magnetic refrigerator performance at a high utilization factor. The results from the present study are important for the design of magnetic refrigerators operating at room temperature.

Effect of proton irradiation on microstructure evolution of permanent magnet

Nd2Fe14B rare earth and Sm2Co17 type permanent magnets have been widely used in the third generation of synchronous radiation light source and free electron laser facility in undulators and other components of particle accelerators. In addition, the permanent magnets are used in the radiation treatment system for cancer as a beam line component. Compared with Sm2Co17 type permanent magnet, Nd2Fe14B rare earth permanent magnet has the characteristics of large magnet energy product, rich starting materials and low price. Although its Curie point and coercive force are lower than those of Sm2Co17 type of permanent magnet, Nd2Fe14B rare earth permanent magnet is still widely used. As an important part of the accelerator, the magnetic loss phenomenon appears when permanent magnet is used in long-term irradiation environments, which affects the stability and quality of the beam. Therefore, it is important to investigate the magnet demagnetization induced by photon irradiation. Recently, there have appeared many researches of the phenomena of demagnetization for the permanent magnets under the irradiation of various kinds of particles. By using different research methods and experimental conditions, single particle irradiation is performed and then the effect of irradiation on magnetic loss is investigated by comparing the macro magnetic properties (such as magnetic flux loss rate, saturation magnetization, etc.). However, there are not any available reports on the microstructure investigations of permanent magnets after irradiation. Microstructure affects macroscopic magnetic properties. In order to discuss the microscopic demagnetization mechanism, the transmission electron microscope is used to characterize and analyze the microstructure evolutions of Sm2Co17 type permanent magnet and Nd2Fe14B rare earth permanent magnet before and after proton irradiation. The evolution of the number density of nanocrystal and its size distribution induced by proton irradiation are calculated. Moreover, the effect of microstructure evolution on macroscopic magnetic loss is discussed. The results indicate that the microstructure of permanent magnet transforms from single crystal structure to polycrystalline structure with the increase of the proton irradiation damage level. Nanocrystal and the matrix of permanent magnet have the same crystal structure. With the irradiation damage level increasing, the nanocrystal density of Nd2Fe14B first increases and then decreases, while the particle size distribution first increases and then keeps constant; the number density of nanocrystal of Sm2Co17 type permanent magnet gradually decreases, while particle size gradually increases, and comparing with Sm2Co17 type permanent magnet, the crystal structure of Nd2Fe14B permanent magnet shows an obvious tendency to be amorphous in 2 dpa irradiation damage level.

Permeance Analysis and Calculation of the Double-Radial Rare-Earth Permanent Magnet Voltage-Stabilizing Generation Device

The structure and magnetic circuit of the modern permanent magnet (PM) generator are often very complicated, which makes the traditional finite element analysis of magnetic field highly difficult. This paper establishes an equivalent magnetic circuit model of a new double-radial PM generator using the traditional equivalent circuit method and data analysis, introduces the calculation formulas of permeance and leakage permeance (LP) in magnetic circuits in detail, analyzes the influence factors of the LP, and provides the solutions. These studies will have a certain guiding significance for the design and optimization of generator circuits. To obtain the best matching parameters, the main parameters of the generator are tested and analyzed, such as the thickness of PM steel in the magnetization direction, length of PM steel, number of pole pairs, and the thickness of spacer bush. Finally, a prototype is tested, and the results show that the output characteristics of the designed double-radial PM voltage-stabilizing generation device are very good.

Development and Evaluation of an Axial Gap Motor Using Neodymium Bonded Magnet

In general, radial gap motors employing neodymium sintered permanent magnet (Nd sintered PM) are used to achieve high torque density in many applications. However, the motors are not suited to a flat, disk-like shape because the dead space, such as the coil ends, occupies most of the motor volume. Therefore, axial gap motors are frequently used for flat shape instead of radial gap motors. Nd sintered PM is a well-known high-performance magnet that has high residual magnetic flux density, but eddy current loss easily occurs in the magnet because of its high conductivity. In axial gap motors for industrial applications, it is difficult to take measures against eddy current loss of Nd sintered PM in terms of cost. Therefore, general axial gap motors employing Nd sintered PM often have unsatisfactory characteristics, such as low efficiency, even though the motor produces high torque. On the other hand, radial gap motors can take measures to suppress eddy current in PMs easily if radial gap motors employ interior permanent magnet structure. Accordingly, this paper discusses an axial gap motor employing neodymium bonded permanent magnet (Nd bonded PM) for flat shape. Compared with Nd sintered PM, Nd bonded PM has lower residual magnetic flux density, but also lower cost. In addition, Nd bonded PM has extremely low eddy current loss due to its low conductivity. It is found from three-dimensional finite element analysis and experimental results that the axial gap motor employing Nd bonded PM can achieve higher torque and higher efficiency compared with the radial gap motor employing Nd sintered PM with the same PM weight and a flat shape.

Effect of inner diameter of hollow cylindrical permanent magnet on levitation force of single domain GdBCO bulk superconductor

The influence of inner diameter of hollow cylindrical permanent magnet on the levitation force of single domain GdBCO bulk superconductor is investigated by measuring the levitation force between the hollow cylindrical permanent magnet and the single domain GdBCO bulk superconductor. The results show that the levitation force is closely related to the inner diameter of the hollow cylindrical permanent magnet when the inner diameter (d) increases from 0 mm to 26 mm (minimum measuring gap distance Z=2 mm), and all the superconducting magnetic levitation force curve shows magnetic hysteresis phenomenon. With the increase of the inner diameter of the hollow cylindrical permanent magnet, the levitation force at a minimum distance decreases gradually from 14.8 N at d=0 mm to -0.1 N at d=26 mm. The levitation force at the minimum gap distance is negative when d ≥ 20 mm. When 0 mm ≤ dd ≥ 5 mm. The larger magnetic field strength of the superconductor can be obtained, and the levitation force can be effectively improved by the scientific and reasonable designing of the permanent magnet structure. The results have certain guiding significance for designing and optimizing the magnetic suspension bearing system, ring track and superconductor.

Development of omnidirectional A0 mode EMAT employing a concentric permanent magnet pairs with opposite polarity for plate inspection

This work presents an omnidirectional electromagnetic acoustic transducer (EMAT) for generating and receiving A0 mode of Lamb waves in plate structures. The proposed EMAT is composed of a spiral meander coil (SMC) and a new concentric permanent magnet pairs with opposite polarity (CPMP-OP) for enhancing the generation and detection of A0 mode. A finite element model was established to simulate the directions of the static magnetic field produced by the permanent magnets and the incentive process of guided waves. To verify the performance of the EMAT, several experiments were performed. Firstly, we experimentally verified that the developed EMAT could generate and receive a pure single A0 mode omnidirectionally. Then, the relationship between the frequency response characteristic of the developed EMAT and the interval l (the distance between the two adjacent annular wires of the SMC) were explored. Furthermore, the circumferential consistency of the transducer was well demonstrated. Finally, the sensing performance of the developed omnidirectional A0 mode EMAT employing a CPMP-OP was compared with that of EMAT with different structures of coils and permanent magnets. The experimental results indicated that the developed omnidirectional A0 mode EMAT employing a CPMP-OP could enhance the signals of the A0 mode.

Optimization for Airgap Flux Density Waveform of Flywheel Motor Using NSGA-2 and Kriging Model Based on MaxPro Design

The performance of flywheel motor is decided by the airgap flux density waveform. This paper establishes an efficient model to optimize the airgap flux density waveform and provides the Pareto optimal solutions, which give the design boundary of airgap flux density waveform for flywheel motor. The key elements of the structure of permanent magnet and the airgap are considered to optimize the sinusoidal distortion rate and the fundamental amplitude of the airgap flux density waveform. The brief optimization process is three steps: (1) sampling by maximum projection design; (2) building surrogate model by the Kriging method; and (3) multi-objective optimization by non-dominated sorting genetic algorithm with elitism approach (NSGA-2) based on the Kriging model. Then, the Pareto optimal solutions are obtained. The three cases optimized by different strategies are compared, and the optimization method is verified by finite-element method.

ИЗУЧЕНИЕ ТЕМПЕРАТУРНО-ВРЕМЕННЫХ РЕЖИМОВ СПЕКАНИЯ И ИХ ВЛИЯНИЯ НА СТРУКТУРУ МЕТАЛЛОКЕРАМИЧЕСКИХ ПОСТОЯННЫХ МАГНИТОВ

ИЗУЧЕНИЕ ТЕМПЕРАТУРНО-ВРЕМЕННЫХ РЕЖИМОВ СПЕКАНИЯ И ИХ ВЛИЯНИЯ НА СТРУКТУРУ МЕТАЛЛОКЕРАМИЧЕСКИХ ПОСТОЯННЫХ МАГНИТОВ

Modelling toolkit for simulation of maglev devices

A stand-alone App has been developed, focused on obtaining information about relevant engineering properties of magnetic levitation systems. Our modelling toolkit provides real time simulations of 2D magneto-mechanical quantities for superconductor (SC)/permanent magnet structures. The source code is open and may be customised for a variety of configurations. Ultimately, it relies on the variational statement of the critical state model for the superconducting component and has been verified against experimental data for YBaCuO/NdFeB assemblies. On a quantitative basis, the values of the arising forces, induced superconducting currents, as well as a plot of the magnetic field lines are displayed upon selection of an arbitrary trajectory of the magnet in the vicinity of the SC. The stability issues related to the cooling process, as well as the maximum attainable forces for a given material and geometry are immediately observed. Due to the complexity of the problem, a strategy based on cluster computing, database compression, and real-time post-processing on the device has been implemented.

Flux-Concentrated External-Rotor Switched Flux Memory Machines for Direct-Drive Applications

In this paper, an external-rotor switched flux hybrid magnet memory machine with a flux-concentration design is developed. Due to the external-rotor configuration, the stator design space is enlarged to alleviate the stator geometric conflictions existed in the internal rotor machine. Meanwhile, the spoke-type permanent magnet (PM) structure is designed to cope with the reduced armature slot area in its original “U”-shaped PM counterpart. In addition, the high-efficiency operation within a wide range of speeds and loads can be achieved. The topology, flux-adjusting principle and distinct features are introduced. Thereafter, the key design parameters including the stator/rotor pole combination, PM hybridizing ratio, and LCF PM thickness are optimized. Finally, the electromagnetic characteristics of the proposed machine are investigated and quantitatively compared with that of its“U”-shaped PM counterpart, which confirms the advantages of the proposed design.

Analysis of a PM Vernier Motor With Spoke Structure

In this paper, a vernier motor with a spoke permanent-magnet (PM) structure instead of a surface PM is proposed in order to obtain higher power factor (PF) and flux density. However, upon investigating this structure with a single gap, unique effects that virtually eliminate the vernier effect are analytically identified. To avoid these effects and improve the PF, a spoke PM vernier motor with a double gap is then proposed. Analytic equations for back electromotive force and the PF are then derived for this motor in terms of various geometric factors such as the numbers of magnets and winding poles, the magnet thickness, etc. For a case study, the practical achievable maximum power and PF are calculated and verified with accurate simulations.

ANALYSIS OF COGGING TORQUE REDUCTION TECHNIQUES IN AXIAL FIELD FLUX-SWITCHING PERMANENT MAGNET MACHINE

An axial-field flux-switching permanent-magnet machine (AFFSPMM) is suitable to be used in wind power generation and electric vehicles. However, the cogging torque (Tcog) is large. To obtain high-performance AFFSPMM, the reduction of Tcog in AFFSPMM is investigated. The theoretical Tcog expression is deduced. Based on a 3-D finite-element method, the influences of the design parameters on the Tcog and the reduction methods of Tcog, such as rotor tooth skewing (RTS), rotor tooth circumferential pairing (RTCP), and rotor tooth notching (RTN), are analyzed. The design parameters, except the axial length of rotor, have influences on Tcog, and optimizing the design parameters can decrease Tcog. Tcog can be greatly reduced by RTS for AFFSPMM with a parallel stator tooth and fan-shape permanent-magnet structure. However, RTS is not effective in reducing Tcog for AFFSPMM with a fan-shape stator tooth and parallel PM (FSST-PPM) structure. Tcog greatly decreases by RTN and RTCP for an FSST-PPM stator structure. Moreover, the reduction effect of Tcog with RTN is better than that with RTCP.

Electromagnetic Performance Analysis of Novel Flux-Regulatable Permanent Magnet Machines for Wide Constant-Power Speed Range Operation

Two novel structures of permanent magnet (PM) machine, namely a hybrid excitation flux modulation machine (HEFMM) and a variable flux memory machine (VFMM), which have excellent field-weakening capability, are presented in this paper. The HEFMM incorporates the advantages of parallel hybrid excitation structure and flux modulation structure, so as to increase the torque density as well as increase the constant-power speed range. Inspired by the HEFMM, aiming to further improve the efficiency of machine, the VFMM with aluminum-nickel-cobalt (AlNiCo) PMs in the inner stator which can be magnetized by the current pulse of the direct current (DC) windings is developed. With double-stator structure, flux modulation effect in both machines can be employed to realize the hybrid excitation and regulate the air-gap flux density readily. The operation principle is illustrated and the static and steady performances of the machines are analyzed and compared with time stepping finite element analysis, which validates the effectiveness of the proposed designs.

Optimization design of an interior permanent-magnet synchronous machine for a hybrid hydraulic excavator

A hybrid power transmission system (HPTS) is a promising way to save energy in a hydraulic excavator and the electric machine is one of the key components of the system. In this paper, a design process for permanent-magnet synchronous machines (PMSMs) in a hybrid hydraulic excavator (HHE) is presented based on the analysis of the working conditions and requirements of an HHE. A parameterized design approach, which combines the analytical model and the 2D finite element method (FEM), is applied to the electric machine to improve the design efficiency and accuracy. The analytical model is employed to optimize the electric machine efficiency and obtain the stator dimension and flux density distribution. The rotor is designed with the FEM to satisfy the flux requirements obtained in stator design. The rotor configuration of the PMSM employs an interior magnet structure, thus resulting in some inverse saliency, which allows for much higher values in magnetic flux density. To reduce the rotor leakage, a disconnected type silicon steel block structure is adopted. To improve the air gap flux density distribution, the trapezoid permanent magnet (PM) and centrifugal rotor structure are applied to PMSM. Demagnetization and armature reactions are also taken into consideration and calculated by the FEM. A prototype of the newly designed electric machine has been fabricated and tested on the experimental platform. The analytical design results are validated by measurements.

Simple method for the generation of multiple homogeneous field volumes inside the bore of superconducting magnets.

Standard Magnetic Resonance magnets produce a single homogeneous field volume, where the analysis is performed. Nonetheless, several modern applications could benefit from the generation of multiple homogeneous field volumes along the axis and inside the bore of the magnet. In this communication, we propose a straightforward method using a combination of ring structures of permanent magnets in order to cancel the gradient of the stray field in a series of distinct volumes. These concepts were demonstrated numerically on an experimentally measured magnetic field profile. We discuss advantages and limitations of our method and present the key steps required for an experimental validation.

A Double-Stator Switched Reluctance Motor for Direct-Drive Washing Machine Application

Abstract. Switched reluctance motors (SRMs) are known as an economical solution by several unique features such as: simple structure and low cost maintenance. Furthermore, due to the lack of permanent magnet, powerful and economical structure of these types of motors, they are proposed as a good choice for use in household appliances. In this paper, a high power flat-type double-stator SRM with low operating voltage in direct-drive system is introduced. Initially, proportional to the intended application, the acceptable attribute of SRM structure is selected, and was followed by the calculation of the motor design. Next, the magnetic characteristics are analyzed by finite element method (FEM) to determine the efficiency of the motor. Finally, the collection of experimental data is tested to confirm the calculated values and the simulation results and ensure the proper functioning of the obtained collection.

Micromachined Graphite Rotor Based on Diamagnetic Levitation

This letter reports the first micromachined rotor of highly oriented pyrolytic graphite (HOPG), a strong diamagnetic material. The HOPG rotor is levitated above a permanent magnet structure to allow for its friction-free rotation. The 600-μm-thick HOPG rotor is micropatterned to have four blades with 1-mm inner diameter disc and 2-mm outer diameter including the blades. The levitation height of 132 μm measured for the rotor matches well with a simulation result. The revolution of the rotor is demonstrated by applying gas flow, showing stable continuous actuation with the maximum rate of 500 r/min. These promising results suggest potential applications of the mechanism toward frictionless microsensors and microactuators.

Low-frequency driven energy harvester with multi-pole magnetic structure

This paper describes the vibration energy harvester using the electromagnetic energy conversion method. To operate at low-frequency with high efficiency, we have suggested a new spring mass system in addition to a thin flame-resistant (FR)-4 spring and multi-pole neodymium iron boron (NdFeB) permanent magnetic structure. FR-4 spring with spiral structure and multi-pole magnetic structure is a suitable design for low-frequency operation and power efficiency. ANSYS finite element method was used to explore the mechanical properties of the device. The experimental results showed that the proposed energy harvester can generate a maximum output power of 490 μW with a resonance frequency of 12 Hz and an acceleration of 0.2 g (g = 9.81 m/s2). In addition, it is attached to an automobile engine producing an output voltage of 231 mV, showing promising potential applications.

ИСПОЛЬЗОВАНИЕ СКАНИРУЮЩЕЙ ЗОНДОВОЙ МИКРОСКОПИИ ДЛЯ ИЗУЧЕНИЯ СТРУКТУРЫ И СВОЙСТВ ПОСТОЯННЫХ МАГНИТОВ

ИСПОЛЬЗОВАНИЕ СКАНИРУЮЩЕЙ ЗОНДОВОЙ МИКРОСКОПИИ ДЛЯ ИЗУЧЕНИЯ СТРУКТУРЫ И СВОЙСТВ ПОСТОЯННЫХ МАГНИТОВ