Air-gap Magnetic Field Research Articles

Analysis and Design of New Composite HTS Magnet With Active Magnetic Shield

The magnetic field modulated superconducting (SC) machines (FMSCMs) with advantages of stationary seal of coolant and brushless current transmission have become a research hotpot in the field of superconducting electrical machine. However, the complex airgap magnetic field in the FMSCM greatly affects the current-carrying capacity and AC losses of the HTS coils, further affecting the electromagnetic performance of the FMSCM. As a result, it is necessary to take measures to suppress the effect of the airgap magnetic field on the HTS coil. To overcome the problem faced by the FMSCM, a new composite HTS magnet with active magnetic shield is proposed and designed in this paper for a kind of distributed HTS armature winding permanent magnet machine (DHTSAW-PMM) belonging to FMSCM. In this paper, the topology of DHTSAW-PMM and the composite HTS magnet are illustrated in detail and their electromagnetic performances are comprehensively analyzed. The results show that the proposed composite HTS magnet can effectively suppress the effect of the complex airgap magnetic field on the HTS coil in the DHTSAW-PMM.

Investigation of surface-inset Halbach machines with trapezoidal mixed grade magnets

In order to increase the torque performance of the conventional surface-inset Halbach machines, a surface-inset Halbach machine with trapezoidal mixed grade magnets is proposed and investigated. Based on a layered and linear superposition method, the air-gap magnetic fields are analytically obtained from solution of matrix equations. In addition, the dimensions of mid-magnet and the remanences of Halbach magnets are analytically optimized. In order to show its advantages, the optimized performances of the proposed machine model are compared with those of the conventional Halbach and trapezoidal equal grade Halbach machines. The prediction shows that the proposed optimized machine model has the largest electromagnetic torque and the lowest torque ripple. The demagnetization performance is also investigated. Finally, the finite element analysis (FEA) results verify the analytical predictions.

Identification of Rotor Position of Permanent Magnet Spherical Motor Based on Compressed Sensing

The accurate identification of the rotor position of permanent magnet spherical motor (PMSM) is crucial to its closed-loop control. A novel method for rotor position identification of the PMSM based on compressive sensing is proposed, which can obtain accurate rotor position by a limited number of Hall sensors. Firstly, the paper designs a Hall sensor array based on the distribution characteristics of the rotor magnetic and the frequency domain characteristics of the air gap magnetic field, combined with the Fibonacci sequence. Then, an observation matrix construction method is proposed, used for compressed sensing of the radial magnetic field strength information in air gap. Finally, the position of the spherical rotor is identified according to the reconstructed information based on the sensor output value. The identification method is verified by experiments, which shows that the identification accuracy is about 1 degree.

Design and Performance Analysis of 25 kW Class HTS Induction/Synchronous Motor With Self-Organizing Method for Transportation Applications

We proposed a non-empirical self-organizing design method to obtain a unique stator structure for a high-temperature superconducting induction/synchronous machine. The method starts from a line current model with an approximately ideal sinusoidal distribution of the air-gap magnetic field. It keeps increasing the cross-sectional area of the windings under appropriate constraints to achieve a model with realistic current density. In this work, we applied this method to design a 25 kW-class high-temperature superconducting induction/synchronous motor. In the model, each slot has three-phase windings with different areas representing different numbers of turns. The width and height of the two slots are different for each pole and phase. The results demonstrated that the self-organizing design method significantly suppressed the torque ripple of the motor and reduced the high-order harmonics. The self-organizing windings are equivalent to a short-pitching configuration, which produce a more sinusoidal air-gap flux density than windings in general design. Reducing torque ripple to the lowest possible level facilitates the practical use of superconducting machines for transportation applications.

Performance Analysis of HTS Armature Axial Flux Magnetic Field Modulation Direct Drive Wind Generator

Axial flux electrical machine has higher power density than the radial flux electrical machine, showing a promising application in the field of offshore wind power generation. However, the conventional copper armature winding will suffer from severe joule loss when improving the electrical loading, resulting in that the further improvement of the power density of axial flux electrical machine is limited. In order to overcome the limitation of the electrical loading improvement of the copper armature winding, this paper uses the high-temperature superconducting (HTS) armature winding instead of the conventional copper armature winding, proposes an HTS armature axial flux magnetic field modulation direct-drive wind generator (HTSAAFFM-DDG). In this paper, the topology and operational principle of the proposed HTSAAFFM-DDG is clearly demonstrated. Meanwhile, the electromagnetic performances are carefully analyzed, including airgap magnetic field, basic electromagnetic characteristics, and AC loss analysis of the HTS armature winding. The research results show that the torque density of the proposed HTS armature axial flux machine can be 24% higher than that of the copper armature axial flux machine with the same size and topology. Besides, the superconducting (SC) shielding layer used in the proposed HTSAAFFM-DDG exhibits an excellent inhibition effect on the PM excited field, and can reduce the AC loss of the armature winding obviously.

Performance Comparison Between Permanent Magnet Synchronous Motor and Vernier Motor for In-Wheel Direct Drive

Nowadays, in-wheel drive mode is considered as one of the most promising modes for electric vehicles (EVs). The motor type plays a significant role to the vehicle performances. This paper focuses on performance between permanent magnet synchronous motor (PMSM) and vernier motor (PMVM) for in-wheel direct drive. Firstly, the required performances are determined by the vehicle requirements. The prototypes of PMVM and PMSM are manufactured after the comparison. Then, the expressions of air-gap magnetic field harmonic, electromagnetic torque, and power factor are theoretically derived, where the parameter torque ratio is introduced to evaluate the torque ratio between PMVM and PMSM. Based on experiment, the back-EMF harmonics, cogging torque, maximum torque per ampere capability, flux-weakening capability, torque, efficiency, power factor, are compared and analyzed. Subsequently, the discussions are carried out, where the strength and weakness of two-type motors for in-wheel drive are concluded and the future prospects are suggested. Finally, the conclusions of two-type in-wheel motors are then extracted. This paper aims at providing a reference for the exploration of alternating in-wheel motor types, which can promote the development of high-performance in-wheel drive system for EVs.

Evolution and optimization of a brushless doubly‐fed machine with an asymmetrical reluctance and magductance rotor

AbstractThe brushless doubly‐fed machine (BDFM) utilizes an asymmetric composite rotor featuring salient pole reluctance and magductance to effectively compensate for the phase shift in space, as well as enhance magnetic field modulation effects, and is therefore used as a modulator. This paper evaluates the modulation capability of the modulator from the perspective of the magnetic field conversion mechanism. The theoretical evolutions of the average magnetic field conversion factors and torque contributions of various airgap field harmonics are accomplished. Additionally, multi‐objective optimization is conducted for better performance, using stratified sensitivity analysis on typical 4/2 pole pair BDFMs featuring symmetrical and asymmetric composite rotors. As a result, further improved modulation of the air gap magnetic field is expected, the cross‐coupling efficiency of the rotor is improved, and a lower output torque ripple is also achieved compared to the conventional symmetrical counterpart. Theoretical investigation of the optimized BDFM, including its effectiveness in enhancing performance metrics such as coupling factor, airgap flux density, and phase shift mechanism, is verified through 2D finite element analysis. Furthermore, a proof‐of‐concept prototype for experimentation was manufactured, which achieved good agreement with the theoretical predictions.

A Novel Design of a Built-in V-Rotor Ultra-Efficient PMSM Based on Multiple Air Slots

According to indicators, the New V-Rotor Permanent Magnet Motor (NVRPM) for compressors with a rated power of 22 kW and a rated speed of 3000 rpm is optimally designed. Because of the large number of permanent magnets in the V-type PM motor, the magnetic leakage between rotor poles will increase, and its air gap magnetic field contains large harmonic components, which is easy to increase the loss and reduce the efficiency. The structure of the initial V-shaped rotor was optimized by adding multiple air slots and cosine non-uniform air gaps on the rotor surface. Through the finite element simulation of electromagnetic characteristics of NVRPM, it is proved that the improvement of the new motor structure can reduce the loss, weaken the cogging torque, and decrease the torque ripple, and the simulation efficiency is up to 96%, and its operation area is wide and efficient. Finally, the results show that the optimization design of the NVRPM structure is feasible.

Comparison of Two Analytical Methods for Calculating Cogging Torque Based on Homopolar Inductor Machines

Cogging torque can cause the torque ripple and noise of machines and reduce the machine control accuracy. The analytical calculation method of cogging torque has always been a hot research topic in the field of machine. Conventional energy method is usually adopted to compute the cogging torque. Recently, a novel energy method is proposed. To reveal the fundamental difference and respective merits of these two energy methods, this paper first derives the analytical models of cogging torque in homopolar inductor machines (HIMs) considering the leakage fluxes of the stator slots by the two energy methods. Based on the derived analytical models, the cogging torque production mechanisms expressed by the two energy methods are analyzed and compared from the viewpoint of air-gap field modulation principle. The cogging torque computed by the two energy methods is all produced by the interactions of the air-gap magnetic fields modulated by the harmonics of the air-gap magnetomotive force (MMF) and air-gap permeance. However, due to the difference in the approaches of solving the air-gap magnetic field energy density, the novel energy method takes into account more harmonics of the air-gap MMF and air-gap permeance. Furthermore, the computational accuracy and complexity of the two energy methods are analyzed and compared based on the analytical calculations and three-dimensional (3-D) finite element analysis (FEA) for the cogging torque in a 48-slot/4-pole (48S4P) permanent magnet (PM) HIM and a 45-slot/6-pole (45S6P) field winding HIM. Compared with the conventional energy method, the novel energy method has higher accuracy, but is more complex. Finally, a prototype of the 48S4P PM HIM is manufactured. The results of analytical calculation, 3-D FEA and comparison are verified by experiments.

Analytical Model for Electromagnetic Performance Prediction of IPM Motors Considering Different Rotor Topologies

Aiming at the problem of long computation time of finite element analysis (FEA) and poor calculation universality of existing analytical models, this paper proposes a general hybrid analytical model to predict the no-load and load performance of interior permanent magnet motors with any slot-pole combination, where the form of magnet can be V-shape, U-shape or flat-shape. The magnets are equivalent correspondingly according to the rotor structure in the modeling process and the motor can be divided into eight types of subdomains, the no-load and load magnetic field of the motors can be obtained by solving the equations established by boundary conditions, where the nonlinear of core is calculated by local MEC. The proposed model can be used to calculate the air-gap magnetic field, no-load back electromotive force, cogging torque and electromagnetic torque of IPM motors with different rotor topologies. The effectiveness of the proposed model is verified by both FEA and experiments. Compared with FEA, this model can consume less time with the acceptable accuracy, which brings convenience to the design and optimization of related types of motors.

Determination of the Magnetic Intermediate Permeability of Special Materials Based on FEM-Simulation and Hall-Sensor Measurement

This document presents the process flow and the experimental conditions for calculating the static magnetic intermediate permeability of a specimen with a dedicated geometrical contour and surface for simulation parameter of metal detection systems. In this case, intermediate is explained and defined as probes with a magnetic permeability between 10 and 1000. An analysis of recent and current measurement standards as well as similar simulation principles leads to the contribution value of this new hybrid process flow. To calculate the permeability value in a first step, an electromagnetic circuit was constructed and excited with a defined electrical DC current with a dedicated tolerance for generating a static approximated homogenic magnetic field in a defined air gap space sector. Additionally, to the H-field generation part double copper coil, two magnetic ferrite cylinders with known permeability were used. The electrical and magnetic circuit has been modeled by an Ansys FEM Electronic Desktop software; the solver is magnetic static. Specifically, the simulated magnetic field distribution of the airgap was evaluated by using different Hall sensor elements with different tolerances. Subsequently, the electromagnetic circuit was expanded by implementing different cylindrical and cube shaped probes on a defined position inside the air gap sector with homogenic magnetization. Moreover, based on the analysis of the air gap structure without the probes, a detailed 3D-FEM model of the air gap magnetic field with special probes was established, which provides the environmental field distribution of the probes. The simulation models were compared with the corresponding Hall sensor measurements, which proved the high accuracy experimental validity of the models established in this paper. Finally, some key features related to parameter variations in the electromagnetic circuit were extracted, which can significantly reflect the characteristics of the robustness of the measurement principle. The main findings reported in this paper will be beneficial for magnetic parameter settings in electromagnetic simulation.

Electromagnetic force ripple suppression strategy of the micro permanent magnet linear motor

In order to make the micro permanent magnet linear motor in this paper have an excellent position response in MEMS application scenarios, an electromagnetic force ripple suppression strategy based on harmonic current injection is proposed. Because of the simulation phenomenon of large force ripple under standard sinusoidal current driving, combined with the non-sinusoidal distribution model of the air-gap magnetic field, it is theoretically verified that the odd harmonic current injection can effectively suppress the force ripple. The electromagnetic force under the fundamental + 3rd/7th harmonic currents and only the fundamental current is compared by simulation. The force ripple coefficient is reduced from 31% to 1.3%, and the position response speed is increased by about 11% in the 4 mm position closed-loop response simulation. The experimental results show that under a current with 200 Hz frequency, the motor can achieve a displacement of 5 mm within 0.11 s, providing a peak velocity of 40 mm/s, which verifies the correctness of the design concept and control strategy of the micro linear permanent magnet motor.

High-integrated micro permanent magnet linear actuator positioning system

A tunnel magnetic resistance (TMR) sensor is a magnetic detection sensor with low power consumption and high sensitivity. The TMR sensor has promising applications in the position detection of micro permanent magnet linear actuators since the surrounding magnetic field of the micro actuator in this paper will be changed by its movement. Firstly, according to the air-gap magnetic field distribution characteristics of the micro permanent magnet linear actuator and the detection principle of the TMR sensor, the integrated installation parameters of TMR sensors were determined. Then, with the help of TMR technology, the backpropagation neural network (BPNN) algorithm and improved BPNN using particle swarm optimization (PSO) algorithm were used to study the position identification strategy of the slider, and the algorithm strategy with the minimum error was selected. Finally, the experimental results show that the slider position identification strategy based on the PSO-BPNN algorithm can achieve position tracking error within 0.1 mm under the given step position tracking and sinusoidal position tracking, and the movements can be repeated well.

Magnetic Field Analysis for the Permanent Magnet Spherical Motor With SMC Core

This paper presents a permanent magnet spherical motor (PMSM) with soft magnetic composite (SMC) core. The analytical model of the no-load air-gap magnetic field of the PMSM with SMC core is obtained based on the Laplace equation with the boundary conditions. When the SMC core is added to the stator teeth, a cogging effect occurs, which makes the three-dimensional magnetic circuit of the entire spherical surface uneven. When the spherical motor completes multi-degree-of-freedom motion, the air-gap magnetic field is severely distorted. In order to solve the above problems, this paper proposes for the first time the method of adding spherical shaped pole shoes to the stator teeth, which perfectly solves the problem of magnetic field distortion in this paper. The air-gap magnetic field distribution is improved by optimizing the structure of the stator tooth pole shoes. Finally, the static torque measurement platform was built to test the rotation energized output torque. The research results of this paper lay a theoretical foundation for the structural optimization design of the PMSM with SMC core.

A Linear Hybrid Model for Analytical Magnetic Field Analysis in Flux-Switching Permanent-Magnet Machine

A hybrid model for the flux-switching permanent-magnet (FSPM) machine is proposed in this paper. In this hybrid model, the air-gap magnetic field in FSPM machine is investigated from the perspective of the stator modulation effect and rotor modulation effect. The stator modulation is discussed from the perspective of equivalent air-gap in the stator slots and permanent-magnets (PMs). The rotor modulation effect is divided to two aspects, namely the effect on the magnetomotive force (MMF) and the effect on stator modulation effect. Different from the conventional model where the stator modulation effect and the rotor modulation are independent of each other, stator modulation effect in the proposed model is coupled with the rotor modulation effect by the minimal reluctance principle. Therefore, MMF and the stator modulation effect in FSPM machine become susceptible to rotor positions with the influence of the rotor modulation effect. Air-gap flux density in FSPM machine is calculated by this hybrid model and compared with those by conventional model and finite element analysis (FEA). Finally, the effectiveness of the proposed hybrid model is validated by comparison of the electromotive force with FEA and experimental results.

Impact of Rotor Flux-Barriers on Coupling Coefficient in a Brushless Doubly-Fed Reluctance Machine

A brushless doubly-fed reluctance machine offers several advantages over a single-port machine since it requires a partially-rated power converter, provides reduced maintenance, and operates without permanent magnets. The complexity of the air-gap magnetic fields due to differing winding-pole numbers interacting with a reluctance rotor have precluded the use of an analytical framework to optimize the rotor. Instead, researchers have relied upon time-consuming finite element analysis (FEA). This paper presents an analytical method to compute closed-form solutions for the mean torque, captured by the coupling coefficient, using a practical circular ducted rotor. The method also accounts for the potential drop across the flux-barriers, leading to a better estimation of mean torque. The model is validated using both FEA and experimental tests.

Quasi-Synchronous Operation Principle of a Variable Air-Gap Doubly Fed Linear Motor for High-Speed Maglev Application

Compared to a long-stator linear synchronous motor (LLSM), a long-stator doubly-fed linear motor (DFLM) exhibits two distinct advantages for high-speed maglev application: 1) It has two additional degrees of freedom with both the frequency and the phase angle of the mover to improve its control accuracy and dynamic responses; 2) It can use the slip power to feed the mover contactlessly and directly. In order to achieve the propulsion, the levitation, and the contactless power transfer through the common air-gap magnetic field, the “quasi-synchronous operation (QSO)” principle of the DFLM is proposed for high-speed maglev train. Based on the DFLM modeling and distinctive constraint analysis for high-speed maglev application, the performance evaluation of the DFLM is further investigated. To validate the feasibility of the DFLM application for high-speed maglev train, a unit DFLM prototype is designed and tested, and the corresponding simulation studies of the QSO control structure are provided with the comparison to the LLSM system.

Analytical Calculation of Air Gap Magnetic Field of SPMSM with Eccentrically Cut Poles Based on Magnetic Pole Division

In the design process of surface-mounted permanent magnet motor (SPMSM) for industrial robots and computer numerical control (CNC) machine tools, to pursue the sinusoidal nature of the back electromotive force, the magnetic poles in the form of eccentric pole cutting structure are often used. To analyze the no-load air gap magnetic field of the SPMSM with eccentrically cut poles simply and accurately, a subdomain model magnetic field analytical calculation method based on equal-area integral block processing of permanent magnets is proposed. The problem that the traditional subdomain analysis model cannot be directly applied to the SPMSM with eccentrically cut poles of unequal thickness is solved. The proposed method considers the influence of stator slotting and the actual permeability of permanent magnets, and directly obtains the fundamental wave and harmonic components of the no-load air gap flux density by solving the subdomain model. The finite element method (FEM) is used to directly calculate the air gap magnetic field for verification. The results of the analytical method and the no-load air gap magnetic density calculated by the FEM are consistent, which verifies the accuracy of the proposed analytical method and can quickly guide the design of the SPMSM with eccentrically cut poles.

A Novel Design of Permanent Magnets for the Air Gap Magnetic Field of Hollow-Cup Motor

Spacecraft motors are often driven with trapezoidal phase currents to achieve higher output torque. For hollow cup motors (HCM) driven by trapezoidal wave currents, parallel magnetised permanent magnet (PM) motors produce an air gap magnetic field (AMF) waveform which is significantly different from the trapezoidal wave, causing the motor to generate noise or vibration. The existing control optimisation method or structure improvement design method is difficult to directly apply to HCM due to its large gas gap. In this paper, according to the fundamental theory of a constant magnetic field, the AMF of HCM is analysed using the equivalent surface current method (ESCM) and its mathematical model is established. The analytical expression of the AMF is solved, and the influencing parameters of the AMF are clarified. The structural design of the HCM with eccentric PMs sintered with high-performance NdFeB is further improved. On this basis, a prototype motor is designed. Simulation results show that the structure can effectively increase the width of the flat section of the AMF and make the AMF close to an ideal trapezoidal wave (ITW). Experiments verify the correctness of the method.

Electromagnetic-mechanical coupling analysis and optimization method of electromagnetic vibroseis

Electromagnetic vibroseis is an important seismic wave excitation device. At present, the research of electromagnetic vibroseis mainly focuses on application and prototype design, lacking research on electromagnetic-mechanical coupling. Analyzing the electromagnetic-mechanical coupling and optimizing the air gap magnetic field is of great significance to improve the excitation quality of low-frequency seismic waves. In this paper, the electromagnetic-mechanical coupling is analyzed by studying the parameter force factor, and two novel optimal designs of the air gap magnetic field are proposed. Firstly, the finite element model of the air gap magnetic field is established, and the influence of the force factor distribution curve on the vibration signal is analyzed by using the Gaussian function and parameter spline difference method. Further, an asymmetrical axial dual-magnet design is proposed to enhance the radial magnetic induction intensity in the air gap. The design of adding a radial magnet to the outer yoke is proposed to compensate for the nonlinearity of the in the air gap. The simulation results show that the asymmetric axial dual-magnet structure increases the by 22.2% compared with the axial single-magnet structure. Adding a radial magnet to the outer yoke reduces the amplitude ratio of the third harmonic to the fundamental wave from 23.24% to 4.66%. It is necessary to consider the influence of the height of the driving coils on the maximum displacement, force factor distribution curve, and harmonic distortion.