Permanent Magnet Array Research Articles

Harmonic Analysis of Magnetic Field Measurement of Maglev Plane Motor

With the rapid development of production scale and technology level in the field of precision engineering technology, plane motor is a new type of motor which can directly output plane motion and has the characteristics of simple structure, high precision and fast response speed. In this paper, the magnetic levitation plane motor (MLPM) as the research object, it is a hot research and development in recent years, MLPM has a good application prospect in driving advanced manufacturing equipment used under high vacuum conditions. In this paper, the harmonic characteristics of magnetic levitation plane motor are analyzed by establishing the analytical model of each odd harmonic. The actual magnetic field of the permanent magnet array is measured on the measuring platform of Tesla meter, and the measurement results are analyzed. And then the analytical data are compared with the actual field data. Further calculation shows that the maximum relative error between the simulated and measured results decreases gradually with the increase of the odd harmonic order of the magnetic field.

Influences of PM Number and Shape of Spoke Array PM Flux Reversal Machines

Spoke array permanent magnet (PM) flux reversal machines (SAFRPMMs), which are suitable for low speed and high torque applications, are able to enhance torque density due to the flux focusing effect. In this paper, what influence both the number of PM per slot and the PM shape have on their electromagnetic performance are investigated. The results show that both the PM number and the PM shape have significant effects on the performance of SAFRPMMs, and proper selections are critical in designing high performance machines. When the PM number per slot is 2, the SAFRPMM exhibits the best electromagnetic performances, i.e., the highest torque, power, efficiency, and power factor. Meanwhile, by properly designing the PM shape, the torque can be further improved by around 11%. A prototype is made and tested to validate the analyses.

Computationally Efficient PM Power Loss Mapping for PWM Drive Surface-Mounted Permanent Magnet Synchronous Machines

This paper proposes a computationally efficient approach for mapping permanent magnet (PM) power loss in permanent magnet synchronous machines (PMSMs). The PM loss mapping method here uses time-step finite element analysis (FEA) to determine the function parameters representing the loss variation with speed (frequency), amplitude modulation ratio, carrier ratio, and stator current and is suitable for rapid evaluation of machine performance over the entire torque–speed envelope. The PM loss can be accurately mapped across the full operational envelope, including the field-weakened mode. The loss mapping procedure takes into account the equivalent resistivity of axial segmentation of the PM array calculated by three-dimensional (3-D) FEA. The effect of temperature on the PM loss is also considered. The proposed methodology is validated on two surface-mounted PMSM designs. The results of the loss mapping procedure are consistent with those from direct 3-D finite element prediction and experimental results of PM power loss at each operating point of the machine.

Design of a New 1D Halbach Magnet Array with Good Sinusoidal Magnetic Field by Analyzing the Curved Surface.

In the linear and planar motors, the 1D Halbach magnet array is extensively used. The sinusoidal property of the magnetic field deteriorates by analyzing the magnetic field at a small air gap. Therefore, a new 1D Halbach magnet array is proposed, in which the permanent magnet with a curved surface is applied. Based on the superposition of principle and Fourier series, the magnetic flux density distribution is derived. The optimized curved surface is obtained and fitted by a polynomial. The sinusoidal magnetic field is verified by comparing it with the magnetic flux density of the finite element model. Through the analysis of different dimensions of the permanent magnet array, the optimization result has good applicability. The force ripple can be significantly reduced by the new magnet array. The effect on the mass and air gap is investigated compared with a conventional magnet array with rectangular permanent magnets. In conclusion, the new magnet array design has the scalability to be extended to various sizes of motor and is especially suitable for small air gap applications.

Partitioned Stator Hybrid Excitation Doubly Salient Machine With Slot Halbach PM Arrays

A new partitioned stator (PS) hybrid excitation (HE) machine with slot Halbach permanent magnet (PM) arrays is proposed in this paper. Due to the adoption of PS structure, its armature winding (AW) is located in the outer stator, and the PMs and the field winding (FW) are housed in the inner stator, thus the space utilization is significantly enhanced. The key difference of proposed machine is that Halbach PM arrays are employed in the inner stator slot openings, so that the parallel magnetic circuit between PM field and wound field is performed and the ratio of PM field short-circuited in the inner stator is effectively reduced. Thus a wider speed regulation region and a higher torque/power density can be achieved. Firstly, the configuration of proposed machine is described, based on which its operating principle is discussed. Then the electromagnetic performances are calculated and compared based on 2-dimensional finite element analysis (FEA). The results show that the torque can be improved by 76% with a similar magnetic field regulation ratio compared with an existing PS-HE machine with slot PMs. Finally, a prototype machine is built and tested to verify the analysis and FEA results.

Nonlinear Feedback Control of the Inductrack System Based on a Transient Model

Abstract As a new strategy for magnetic levitation envisioned in the 1990s, the Inductrack system with Halbach arrays of permanent magnets has been intensively researched. The previous investigations discovered that an uncontrolled Inductrack system may be unstable even if the vehicle travels well below its operating speed and that instability can be persistent near and beyond the operating speed. It is therefore necessary to stabilize the system for safety and reliability. With strong nonlinearities and complicated electromagneto-mechanical coupling, however, the transient response of such a dynamic system is difficult to predict with fidelity. Because of this, model-based feedback control of Inductrack systems has not been well addressed. In this paper, by taking advantage of a recently available two degrees-of-freedom transient model, a new feedback control method for Inductrack systems is proposed. In the control system development, active Halbach arrays are used as an actuator, and a feedback control law, which combines a properly tuned proportional-integral-derivative controller and a nonlinear force-current mapping function, is created. The proposed control law is validated in numerical examples, where the transient motion of an Inductrack vehicle traveling at constant speeds is considered. As shown in the simulation, the control law efficiently stabilizes the Inductrack system in a wide range of operating speed, and in the meantime, it renders a smooth system output (real-time levitation gap) with fast convergence to any prescribed reference step input (desired levitation gap).

Model of Magnetic Particle Capture Under Physiological Flow Rates for Cytokine Removal During Cardiopulmonary Bypass.

The objective of this study is to design a physical model of a magnetic filtration system which can separate magnetic nanoparticle (MNP)-tagged cytokines from fluid at physiologically relevant flow rates employed during cardiopulmonary bypass (CPB) procedures. The Navier-Stokes equations for the pressure driven flow in the chamber and the quasistatic stray magnetic field produced by an array of permanent magnets were solved using finite element analysis in COMSOL Multiphysics for 2D and 3D representations of the flow chamber. Parameters affecting the drag and magnetic forces including flow chamber dimensions, high gradient magnet array configurations, and particle properties, were changed and evaluated for their effect on MNP capture. Flow chamber dimensions which achieve appropriate flow conditions for CPB were identified, and magnetic force within the chamber decreased with increased chamber height. A magnetic "block" array produced the highest magnetic force within the chamber. Polymeric microparticles loaded with MNPs were shown to have increased particle capture with increased hydrodynamic diameter. The model achieved a predicted efficiency up to 100% capture in a single-pass of fluid flowing at 1.75 L/min. This work is an important step in designing a magnetic flow chamber that can remove the magnetically tagged cytokines under high flow employed during CPB. Cytokines have been shown to stimulate the systemic inflammatory response (SIR) associated with CPB and are an established therapeutic target to mitigate the SIR. In the long term, this work aims to guide researchers in the more accurate design of magnetic separation systems.

Development of an Omnidirectional SH0 Mode Electromagnetic Acoustic Transducer Employing a Circumferential Periodic Permanent Magnet Array

This work presents a new omnidirectional electromagnetic acoustic transducer (EMAT) employing a circumferential periodic permanent magnet array, which was proposed for generating and receiving shear-horizontal (SH) guided waves in an aluminum plate. The novel transducer consisted of 12 axially polarized sector magnets arranged in a circle, and the magnetic field directions of adjacent magnets were opposite. A spiral coil was arranged under the magnet array. A vertical magnetic field generated by the magnets and the circumferential eddy current generated by the spiral coil formed a Lorentz force in a plate acting in the radial direction of this new omnidirectional EMAT. By controlling the sizes of the sector magnets, the omnidirectional SH0 mode (fundamental SH guided wave mode) was generated. To maximize the output of the EMAT at the given excitation frequency, it was proposed to add acrylic spacers between the sector magnets and determine the size of the magnet based on the frequency bandwidth of the excitation signal while also optimizing the omnidirectional sound field. A three-dimensional (3D) finite element model of the EMAT was established using COMSOL Multiphysics to perform numerical simulations, and the effectiveness of the optimization method was verified. The effectiveness was verified by experiments. The simulations and experiments showed that the proposed EMAT could generate omnidirectional SH0 mode guided waves in an aluminum plate.

Design Study of a High Loading Superconducting Magnetically Levitated Planar Motor

Magnetically levitated planar motor (MLPM) with moving-magnet has the advantages of no electric cable interference and no cooling for moving part. In this paper a novel superconducting magnetic levitation planar motor (SMLPM) whose stator uses high-temperature superconducting coils is proposed. Based on the traditional design, the cooling system and thermal shield are added. The copper coil used in the traditional magnetic levitation planar motor cannot provide large current density and have very low force-to-mass ratio. As superconducting technology has the advantages of low energy consumption and high current density, SMLPM could provide greater driving force and torque. Based on the new system, an analytical model was used to calculate the electromagnetic force/torque acting on the Halbach permanent magnet array. The heat load to the cryogenic system is calculated. The finite element method (FEM) for full model has been used to benchmark the magnetic field and force of the theoretical result.

Magnetic levitation planar motor and its adaptive contraction backstepping control for logistics system

Magnetic levitation planar motor has the characteristics of no friction loss, fast dynamic response, and real-time change of transportation track according to the demand. Therefore, a kind of magnetic levitation planar motor based on logistics transportation system is designed, which can meet the transportation needs of the logistics system through any combination of unit modules. Firstly, based on the mechanical model of magnetic levitation float in Halbach permanent magnet array magnetic field, establishing the thrust and torque model of maglev float. Secondly, according to the force/current relationship, considering the influence of uncertain parameters and load disturbance on the system, the decoupling control model of six degree of freedom motion system of magnetic levitation planar motor is established. Thirdly the adaptive contraction backstepping (ACB) controller is derived that can eliminate the uncertain disturbance of the nonlinear model and realize the real-time control of the system. The simulation and experimental results demonstrate that the method has expected response speed, strong robustness, and good dynamic tracking performance. Applying it to the logistics transportation system described in this article and has a good control effect.

Dynamic analysis of Halbach coaxial magnetic gears based on magnetic equivalent circuit modelling

Halbach permanent magnet arrays (HPMAs) are an attractive configuration that can be applied in PM electric machines such as magnetic gears. These arrays have some merits, namely near-sinusoidal distribution of flux density along air gap, low torque ripple and iron losses. This article proposes a two-dimensional magnetic equivalent circuit method to determine the magnetic field distribution of HPMA based on coaxial magnetic gears (HCMG). Furthermore, regarding the proposed model, distribution of radial and tangential components of flux densities is extracted within outer and inner rotors. Moreover, the dynamic model of HCMG is extracted and its pull-out torque and output speed are calculated using it. Finally, in order to validate the effectiveness of the proposed model, the obtained results for a sample HCMG are compared with finite element analysis method results.

Reduction of Saturation and Unipolar Leakage Flux in Consequent-Pole PMV Machine

This article proposes some effective approaches to address the inherent issues of consequent-pole (CP) permanent magnet (PM) machines, such as saturation of the salient rotor core and unipolar PM leakage flux of the end region caused by asymmetric field. The effect of CP-Halbach PM array with different magnetization directions and parameters that affect the saturation has been investigated for the CP PM machine with short pole pitch. By employing the CP-Halbach array, the saturation issue can be solved and superior performance can be obtained without reducing the PM pole arc. In addition, unequal and multistep staggered rotors with magnetic barriers have been proposed to reduce the unipolar leakage flux in the end region. Compared with regular staggered rotors, not only better electromagnetic performance can be achieved, but also the end unipolar leakage flux can be reduced. Finally, a prototype is manufactured and the predictions have been validated by measurements.

Research on torque of based hydraulic rotary hole cleaning tool on Halbach permanent magnet array

The hydraulic rotary hole cleaning tool does not require a drill string to provide torque, so it is compatible with downhole motors in the sliding phase of directional drilling. It facilitates efficient cutting cleaning, especially in the directional interval and horizontal interval. The magnet array structure must be optimized to enhance the magnetic torque transmission capacity and thus increase the output power of this tool. Magnetic field analysis was conducted in this study using Laplace and Poisson equations. A mathematical model was established to calculate the magnetic torque transmitted by the hydraulic rotary hole cleaning tool. The effects of various magnetic field and tool design parameters on the magnetic torque transmission capacity were compared among different permanent magnet array structures. The negative-positive Halbach magnet array structure shows enhanced magnetic torque transmission capacity compared to the traditional radial magnet array structure; it achieves a better excitation magnetic field direction of the permanent magnets on the magnetic shafts and an increased magnetic flux density within the tool housing. The suggested tool housing thickness under the field operation safety requirement is 9–10 mm. The optimum tool design features include a negative-positive Halbach magnet array structure, 100% magnet field coverage within the tool housing and a permanent magnet thickness range of 9.5–10.5 mm. The maximum magnet torque transmission capacity can be obtained within these parameters. The proposed magnetic torque transmission capacity model was compared against laboratory experiment data to prove that it is reliable and precise enough to optimize existing hydraulic rotary hole cleaning tools with the negative-positive Halbach magnet array structures.

2-D and 3-D Analytical Calculation of the Magnetic Field and Levitation Force Between Two Halbach Permanent Magnet Arrays

As we know, the analytical calculation of magnetic field and magnetic force has important guiding significance for the optimal design of the size and structure of a magnet. At present, the magnetic field and magnetic force between two permanent magnet (PM) monomers have been described by effective analytical models. However, the magnetic field strength and magnetic force generated by two PM monomers are limited and cannot meet the requirements of a PM levitation system with high magnetic field strength and large levitation force. To this end, this article establishes analytical calculation models of magnetic field and levitation force between two Halbach PM arrays. First, on the basis of Ampere molecular circulation hypothesis, the 2-D analytical model of magnetic field was established based on the surface current method; on the basis of magnetic charge theory, the 3-D analytical model of magnetic field was established based on the magnetic charge method. Second, based on the analytical models of magnetic field, the 2-D and 3-D analytic models of levitation force were derived by virtual work method, respectively. Numerically, the results of two analytical models of magnetic field and two analytical models of levitation force have been compared to verify the accuracy of the models. At the same time, the 2-D and 3-D finite element simulation models of magnetic field and levitation force were established, respectively, and the accuracy of the analytical models were verified again. The results show that the analytical models established in this article is effective and can be used to guide the design and optimization of the magnet composed of two Halbach arrays.

Design of coaxial magnetic gear utilising a novel permanent magnet Halbach array structure

Mechanical gears are constrained due to wear and tear and call for lubrication. A magnetic gear, utilising permanent magnet (PM) arrays, facilitates the mechanical gear roles. It can withstand high-speeds and large loads with zero friction. The magnetic gear is more efficacious on account of the least noise, performance, overload protection, and physical isolation between parts than conventional mechanical gears. The quantity of PMs in magnetic structures plays a principal role in its total price, which necessitates optimal arrangements for PMs. Halbach array provides a bigger torque density according to its one-sided flux. In this research, proposing a novel Halbach array structure, leads to intensification in the one-sided flux in a much sinusoidally waveform that consequently increases the magnetic torque. These all lead to gain higher torques in constant volumes of magnets. Besides, the magnetic torque ripple and the modulators’ losses are decremented. The new model is based on the variation of the magnetisation angles of the adjacent permanent magnet blocks, in the array. Various states of the magnetisation angles in the array are optimised based on a heuristic method. This is studied in the whole trigonometric range for magnetisation angles characteristics. The prototype is fabricated based on the optimised magnetic gear design and complies with the results.

Comparative Study of Dual PM Vernier Machines

In this paper, two types of dual permanent magnet (PM) machines, i.e., stator slot dual-PM (SSDPM) machine and split-tooth dual-PM (STDPM) machine, are investigated and compared. Both machines have consequent pole structure with Halbach array PMs. Their difference lies in the position of stator PM. The SSDPM machine has Halbach array PMs in the stator slots, while the STDPM machine has PMs between the split teeth. Torque characteristics, i.e., average torques and torque ripples, of different slot/pole number combinations of the two machines are compared. The 24 stator slots/20 rotor slots/4 armature pole pair (24S20R4Pa) SSDPM machine with distributed windings and the 24 stator slots/10 rotor slots/4 armature pole pair (12S20R4Pa) STDPM machine with concentrated windings are compared under both open-circuit and on-load conditions. The results show that the SSDPM machine is more competitive by delivering higher torque density and higher power density.

Time- and Frequency-Domain Steady-State Solutions of Nonlinear Motional Eddy Currents Problems

This paper presents a comparison of different time- and frequency-domain solvers for the steady-state simulation of the eddy current phenomena, due to the motion of a permanent magnet array, occurring in the soft-magnetic stator core of electrical machines that exhibits nonlinear material characteristics. Three different dynamic solvers are implemented in the framework of the isogeometric analysis, namely the traditional time-stepping backward-Euler technique, the space-time Galerkin approach, and the harmonic balance method, which operates in the frequency domain. Two-dimensional electrical machine benchmarks, consisting of both slotless and slotted stator core, are considered to establish the accuracy, convergence, and computational efficiency of the presented solvers.

Comparative study of partitioned stator flux-modulation motors with different permanent magnet arrays

By incorporating the merits of partitioned stator and flux modulation techniques, the partitioned stator flux modulation motors featuring high torque, have attracted much attention. This paper investigates four partitioned stator flux modulation motors with different types of PM arrays, including surface-mounted type, consequent-pole type, Halbach-array type, and half-Halbach type. The influences of key parameters on the average electromagnetic torque is conducted and compared. Then, based on the optimal designs, four motors are compared in terms of magnetic field distribution, back-electromotive force, torque characteristics, loss and overload ability. The result reveals that the half-Halbach motor is capable of utilizing more PM to improve electromagnetic torque. Also, the consequent-pole motor achieves the highest torque per PM usage. In addition, performance comparison under the same PM usage is carried out. The result shows that the half-Halbach motor not only exhibits the highest average torque but also achieves the highest PM utilization. Last, the prototype of half-Halbach motor is built for experimental verification.

An Angular Speed and Position FLL-Based Estimator Using Linear Hall-Effect Sensors

This paper proposes using a frequency-locked loop-based detector to estimate rotational speed and angle position for an electric machine rotor shaft. The measurement system consists of arrays of permanent magnets fixed to the rotor shaft together with linear Hall-effect sensors attached to a fixed frame. Parametric uncertainties on the sensor assembly lead to significantly noisy signals, exhibiting unbalance and harmonic distortion. To accurately estimate rotational speed and angle, it is proposed to use a frequency-locked loop scheme based on a fourth-order harmonic oscillator (FOHO) to allow the processing of the symmetric components, thus dealing with the unbalance. The scheme also includes an adaptive law to reconstruct the fundamental frequency. Moreover, a harmonic compensation mechanism comprising parallel FOHOs is included; each FOHO is tuned at the spectral component under concern for its cancellation. The proposed algorithm delivers a clean estimate of the positive sequence fundamental component despite the disturbances at the signals provided by the Hall-effect sensor, which is used to reconstruct the rotation angle. The described approach could enhance low-cost sensing solutions in applications where position feedback is mandatory and sensorless control is impossible, not requiring special installation considerations.

Unidirectional Shear Horizontal Wave Generation With Side-Shifted Periodic Permanent Magnets Electromagnetic Acoustic Transducer.

Periodic permanent magnet (PPM) array electromagnetic acoustic transducers (EMATs) can efficiently generate and receive shear horizontal (SH) ultrasonic waves. Conventional PPM EMATs typically generate waves which simultaneously propagate both forward and backward. This can complicate the received signals and make it difficult to locate the position of scatterers. Unidirectional generation of ultrasounds can be achieved if two ultrasonic sources are separated by a predefined distance and are excited with the proper delay. Relying on this principle, EMATs have been previously designed aiming to generate other modes of ultrasonic waves. The main challenge when extending this conception to an SH-wave EMAT is how to restrict each coil to its specific magnet array. We present the concept of a unidirectional SH EMAT consisting of two racetrack coils and two interlaced PPM arrays, that are slightly shifted sideways, in such a way that the generated wavefronts still properly interfere. The design was fabricated and experimentally evaluated in an aluminum plate generating the SH0 guided wave mode. The forward to backward generated wave ratio is above 20 dB and well agrees with finite element simulations.