Risk Of Demagnetization Research Articles

Enhancing capacity utilization of Li|LiCl-KCl-CsCl|Bi (300 °C) liquid metal batteries through the application of external magnetic fields

Long-cycle-life, high-safety liquid metal batteries (LMBs) are considered competitive alternatives for large-scale energy storage applications. LMBs typically operate at high temperatures, and reducing their operating temperature has been a focus of research. In this study, we adopt a multi-cation molten salt LiCl-KCl-CsCl as the electrolyte for LMBs and achieve the stable operation of Li|LiCl-KCl-CsCl|Bi battery at 300 °C for the first time. However, the lower operating temperature significantly deteriorates the kinetic performance, resulting in a capacity utilization of only about 30 %. To address this issue, we apply a certain intensity of magnetic field to the battery using Helmholtz coils, which increases the capacity utilization to 100 %. This study combines the strategy of low-temperature LMBs with external magnetic field regulation, not only achieving a low operating temperature but also ensuring complete capacity release. Furthermore, this approach paves the way for the potential use of permanent magnets within battery modules to provide the magnetic field environment, without the risk of demagnetization.

Intraindividual Comparison of Image Artifacts of Two Generations of Rotatable Cochlear Implant Magnets.

In cochlear implant recipients, the diagnostic value of magnetic resonance imaging (MRI) scans is reduced by image artifacts. The static magnetic field of a 3.0T scanner is associated with the risk of implant demagnetization. The development of rotatable implant magnets aimed to support the advancement of 3.0T MRI scanners and eliminate the risk of demagnetization of cochlear implant magnets. This study aimed to compare the image artifacts caused by first-t and second-generation rotatable cochlear implant magnets in 3.0T MRI. Three Tesla MRI T2W TSE sequences were performed on 3 subjects with first- and second-generation rotatable cochlear implant magnets. The cochlear implant was fixed to the head at the implantation position by a swim cap. The size of the image artifact was determined in the transverse plane. Intraindividual comparative analyses showed that within the margin of combined uncertainty of 5 mm at a resolution of 2 mm, the cochlear implant-induced image artifacts in all subjects showed for both (first- and second-generation rotatable cochlear implant magnets), the same maximum image artifact dimension of 125 mm. We could show that no difference in image artifact size was detected within the margin of error determined by resolution, localized induced shift of the scan, and reproducibility of the tilt angle of the head relative to the chest in a living subject. Assumed improved magnet attachment can be reached without compromising of the magnet artifact size.

Electromagnetic Design Optimization Integrated with Mechanical Stress Analysis of PM-Assisted Synchronous Reluctance Machine Topologies Enabled with a Blend of Magnets

Permanent Magnet-Assisted Synchronous Reluctance Machines (PMASynRM) provide a low-cost alternative to Surface PM Machines due to the use of relatively lower grades of rare-earth (RE) or RE-free magnets, as the performance degradation due to weaker magnets is compensated by the presence of reluctance torque. However, the weaker magnets suffer from a high risk of demagnetization, leading to unreliable motor operation. Using a blend of RE and RE-free magnets has the potential to overcome this issue. This paper proposes to blend different grades of various rare-earth (RE) and rare-earth-free (RE-free) magnets in six different combinations and utilizes them in two-layer and three-layer U-shaped PMASynRM topologies with both eight-pole and six-pole variations. The rotor of the various designs is then optimized using a differential evolution (DE) based optimization algorithm to obtain low-cost designs with reduced RE magnet volume and minimum demagnetization risk. The optimization of each design is also integrated with the evaluation of mechanical stresses in the rotor laminations so as to maintain the stresses below the material yield strength. Furthermore, the various performance metrics, such as toque–speed/power–speed characteristics, demagnetization, and efficiency maps, are evaluated for each of the optimized and mechanically feasible designs. A quantitative comparison of the various optimized designs is also obtained to highlight the various trade-offs. The results indicate the feasibility of meeting the baseline torque requirement across the entire speed range, even with a 100% reduction in RE magnet volume and less than 5% demagnetization risk, while achieving a cost reduction exceeding 50%. Moreover, the two-layer, eight-pole designs exhibit relatively higher performance, whereas the three-layer, eight-pole designs are found to be the most economical option.

Design and Performance Analysis of an Outer-Rotor PMaSynRM

Permanent magnet synchronous motors (PMSMs) are consciously used as traction motors in electric vehicles (EVs) and hybrid electric vehicles (HEVs). The rotor position (inner-rotor, outer-rotor) and topology of PMSMs significantly impact their torque profile, efficiency, and demagnetization characteristics. This article focuses on designing an outer-rotor permanent-magnet-assisted synchronous reluctance motor (PMaSynRM) under traction motor requirements and investigating its electromagnetic performance using the finite element method (FEM). This study's primary challenge is achieving optimal machine performance, considering high maximum torque and the risk of demagnetization at low levels. The design, derived from analytical calculations, was subjected to Finite Element Method (FEM) analyses. These analyses investigated motor performance in terms of efficiency, the ability to generate torque at different drive currents, and the risk of demagnetization. As a result of the study, the proposed PMaSynRM design was obtained that provides an adequate demagnetization performance even under 300% loading, has a maximum torque exceeding 35 Nm, and achieves an efficiency of 90% at rated conditions.

Vector hysteresis loops of rare earth magnets measured in a biaxial vibrating sample magnetometer

Vector hysteresis loops of rare earth magnets measured in a biaxial vibrating sample magnetometer

Electromagnetic–Thermal Characteristics Analysis of a Tubular Permanent Magnet Linear Generator for Free-Piston Engines

Temperature rise of the tubular permanent magnet linear generator (TPMLG) might lead to insulation failure and demagnetization of permanent magnets, affecting the safe and stable operation of other equipment and the entire system. Herein, a bidirectional electromagnetic–thermal coupling method for analyzing the electromagnetic loss and thermal characteristics of a TPMLG considering the effect of increased temperature on the permanent magnet was proposed. To study the electromagnetic–thermal characteristics of the TPMLG under stable power generation, a two-dimensional electromagnetic field model and a three-dimensional temperature field model were established and coupled. The temperature field of the TPMLG was numerically calculated using computational fluid dynamics over finite volume method under natural air cooling and forced air cooling conditions. Effects of loss and air flow velocity on the steady temperature field were investigated. Results indicated that copper loss increased by 24.5% considering the influence of temperature rise. The windings’ top central position in the TPMLG was the spot with the highest temperature of 127.8 °C and there was a potential demagnetization risk for the permanent magnets. Some reference for future research of clarifying thermal characteristics and cooling design was provided.

Risk of irreversible demagnetisation under transient states of the line start permanent magnet synchronous motor taking into account magnet temperature

Risk of irreversible demagnetisation under transient states of the line start permanent magnet synchronous motor taking into account magnet temperature

Comparative analysis of a mining truck motor with permanent magnets in a rotor and a synchronous homopolar motor without magnets in a drive

The relevance. Increasing need for using mining trucks with a diesel-electric (hybrid) drive for development of minerals. Improving operational and cost characteristics of the electric drive of mining trucks helps to reduce costs in the development of minerals. The main aim. To compare theoretically the performance of synchronous traction motors of various designs (a conventional design with permanent magnets inside a rotor and a homopolar design without permanent magnets with an excitation winding on a stator), optimized by the same method, in the drive of a mining truck. To optimize the motor design to reduce power loss and required inverter power, as well as to limit torque ripple and reduce the risk of permanent magnet demagnetization. Objects. Design of twelve-pole nine-phase synchronous AC motors with a rated power of 370 kW of various designs: a homopolar motor without permanent magnets with an excitation winding on the stator and a motor of a traditional design with permanent magnets in the rotor. Methods. Derivative-free optimization method; equivalent circuit method; mathematical modeling; two-dimensional finite element method. Results. Based on the analysis, the advantages and disadvantages of the considered motors were revealed. The advantage of the motor with permanent magnets in the rotor is reduction in active part length by 30 %. The advantage of the homopolar motor with an excitation winding on the stator are 4.6 times lower cost of active materials. In addition, the homopolar motor has a more reliable design, without the risk of overheating, demagnetization or deterioration of the properties of permanent magnets over time

A Novel Consequent-Pole Contra-Rotating Machine With Zero-Sequence Current Excitation

A novel hybrid excitation consequent-pole contra-rotating machine with zero-sequence current excitation is presented in this paper. The stator windings carry both the DC field winding current and the AC armature current, making the machine more compact. Further, the flux can be weakened or enhanced without the risk of demagnetization by controlling the zero-sequence current excitation in the integrated winding. Finally, the segmented stator can effectively reduce iron loss and simplify the manufacture processing.

PM Eddy-Current Loss Reduction of Axial Flux PM Wheel Motor With Arc Incompletion Segmentation

The high permanent magnet (PM) eddy-current loss will inevitably cause the risk of irreversible demagnetization, and the PM complete segmentation (CS) method is a common method to reduce the PM eddy-current loss. However, PM CS design will increase the cost and difficulty of assembly process, especially for axial flux PM (AFPM) machines. To address this issue, a new arc incompletion segmentation (AIS) method is proposed to reduce the PM eddy current loss and cost, including double-side AIS and single-side AIS designs. Then, some of the key parameters are optimized. In addition, the PM eddy current loss, cost, and torque performance are studied and compared with different segmentation methods under different conditions based on 3-D finite element method (FEM). Finally, two different 25kW prototypes are manufactured and tested to validate the proposed method and analysis.

Toroidal Field Excitation for Axial-Field Double-Rotor Flux-Reversal DC Motors With Magnetic Differential

In order to provide differential action for electric vehicles performing reliable cornering, the axial-field (AF) double-rotor (DR) flux-reversal (FR) motor shows a good ability of torque output along with magnetic differential (MagD) control on its two rotors. Apart from using the permanent magnet (PM) excitation, which suffers from high PM cost and risk of accidental demagnetization, this paper proposes the toroidal DC (TDC) windings for field excitation to avoid the problems associated with PMs. The TDC windings not only serve as the source of the magnetic field but also regulate the flux on two rotors to produce MagD action. By using three-dimensional finite element analysis, motor performances between using the TDC windings and the conventional concentrated DC (CDC) windings are quantitatively compared, which validates that the proposed AF-DR-FR-TDC motor takes definite advantages over the CDC counterpart while offering the desired MagD action.

Design and Analysis of Double-Sided Flux Concentrated Permanent Magnet Linear Machine With Saturation Relieving Effect

This paper proposes a double-sided flux concentrated permanent magnet linear machine (DS-FCPMLM) with saturation relieving effect. With the adoption of slot PMs, DS-FCPMLM can effectively relieve the primary saturation and greatly improve the thrust force density. First, the machine topology and operation principle are introduced. Then, the flux generation mechanism under dual PMs and complementary structure is analytically calculated based on magnetomotive force-permeance model, and further verified by finite element analysis. In addition, some electromagnetic performances including open-circuit characteristic, thrust force performances, demagnetization risk and power factor are comparatively studied. With the help of slot PMs, DS-FCPMLM can significantly improve the thrust force density by 63.4% compared with that only has yoke PMs, and the overload capability can be extended to nearly 4 times of the rated value. More importantly, DS-FCPMLM only consumes 1/30 PM volumes while can achieve 72.2% thrust force density compared with conventional PMLMs for a long stroke with 10 meters. Finally, a prototype of the DS-FCPMLM is carried out for experimental validation.

Design and Analysis of Wide Speed Regulation of Variable Leakage Flux Reverse Salient-Pole Motor

In this article, a new variable leakage flux reverse salient-pole motor (VLF-RSPM) is raised to widen the speed range. The innovation is to realize both reverse salient-pole characteristics and variable leakage flux characteristics by using a method of adding magnetic bridges and magnetic barriers. Firstly, the evolution of the topological structure and working principle of the motor are introduced. Secondly, based on 2D Finite Element Analysis (FEA), the electromagnetic properties and noise of the motor are analyzed in detail, and the electromagnetic properties are contrasted with that of the conventional V-type synchronous motor (CVTSM). The results show that VLF-RSPM has the advantages of small torque ripple, strong magnetic weakening ability, low noise, high efficiency, and low risk of permanent magnet demagnetization under different conditions. In addition, it is verified that the proposed motor extends the speed range.

Fast Determination of Transient Short-Circuit Current of PM Synchronous Machines via Magnetostatic Flux Maps

The three-phase symmetric short-circuit is a reference fault condition for the qualification of a newly designed permanent magnet (PM) synchronous machine against the risk of irreversible demagnetization. To date, the accurate determination of the peak transient short-circuit current condition requires coupled circuital and transient Finite Element Analysis (FEA) to properly account for magnetic saturation, and several simulations to determine the worst-case pre-fault conditions. This work presents a method for the fast evaluation of the transient short-circuit current of a PM synchronous machine by manipulation of extended flux linkage maps, obtained with magnetostatic FEA or experimental measures. Besides providing a fast and accessible computational tool, the flux-map based method gives insights into the effect of pre-fault conditions, showing that the higher the pre-fault torque and thus flux amplitude, the higher the transient peak current after a fault. Moreover, the paper shows that braking is a more severe pre-fault condition. Finally, the hyper-worst-case short circuit current is also defined as the magnetic property of the machine under test and computed by means of quick FEA iterations without the need for pre-determined flux-linkage maps. The proposed methods are validated against transient FEA using a commercial software and verified experimentally on a commercial motor for traction applications.

Effect of multicomponent Tb-Cu films diffusion on the magnetic properties and thermal stability of sintered Nd-Fe-B magnets

In order to improve the diffusion characteristics of heavy rare earth in the grain boundary, effects of the diffusion process as well as the ratio of Tb and Cu (RTb/Cu) during the layered deposition process on the magnetic properties of Tb-Cu diffused Nd-Fe-B magnets were systematically investigated. The coercivity of the diffused magnet with RTb/Cu = 4:1 was enhanced most, which increased from 10.86 kOe to 21.80 kOe. Cu greatly improved the composition homogenization of diffused magnets. For the present designed diffused magnet, the highest utilization efficiency of Tb reached 43.96 kOe/wt%. Moreover, the reduced demagnetization risk of sintered Nd-Fe-B magnets was verified by using finite element method based on the experimentally obtained temperature characteristics of the magnet.

Design Criterion and Analysis of Hybrid-Excited Vernier Reluctance Linear Machine With Slot Halbach PM Arrays

This paper proposes a hybrid-excited vernier reluctance linear machine (HEVRLM) with slot halbach PM arrays. By utilizing halbach PM arrays, leakage flux that existing in the consequent pole structure can be greatly reduced. Besides, the dc excitation can enhance both the flux regulation capability and force density. First, the machine topology and working principle are introduced. Then, magnetomotive force (MMF)-permeance model is established to analytically calculate the air gap flux density under hybrid excitation. Moreover, the flux regulation capability, thrust force characteristic and PM demagnetization risk of the proposed machine are comparatively studied based on finite element method (FEM). It shows that halbach PM arrays can effectively reduce the leakage flux and further significantly improve the thrust force density by more than 30%. In addition, hybrid excitation is a feasible approach to further improve the thrust force density by distributing the optimal dc and ac currents. Moreover, the proposed HEVRLM exhibits high thrust force density compared with other three types of hybrid-excited linear machines. Finally, a prototype of HEVRLM is manufactured and tested for experimental validation.

Shape optimization and demagnetization analysis of interior permanent magnet synchronous machine with hybrid cores

With designing stator teeth by using grain oriented silicon sheets (GO) and other parts still with non-grain oriented silicon sheets (NGO), the electromagnetic performance of interior permanent magnet synchronous machine (GO-IPMSM) can be improved greatly, however its torque ripple will be increased as well. For reducing its torque ripple, optimizing its rotor barrier shape is an effective way. In this paper, the polynomial method is proposed to establish the rotor barrier shape, and the genetic algorithm (GA) method is employed for the optimization process. In case the optimized GO-IPMSM can work normally, its anti irreversible demagnetization ability is analyzed as well. As shown, with the GO is adopted for designing the stator teeth and its rotor barrier shape is optimized, though its torque ability and efficiency have been increased, its anti irreversible demagnetization risk ability is reduced, however the proposed machine can still operate safely.

Novel Mechanical Flux-Weakening Design of a Spoke-Type Permanent Magnet Generator for Stand-Alone Power Supply

In this paper, a novel mechanical flux-weakening design of a spoke-type permanent magnet generator for a stand-alone power supply is proposed. By controlling the position of the adjustable modulator ring mechanically, the total induced voltage, i.e., the amplitude of the back EMF vector sum can be effectively adjusted accordingly by the modulation effect. Consequently, the variable-speed constant-amplitude voltage control (VSCAVC) with a large speed range can be achieved. Compared to the electrical flux-weakening method, the mechanical flux-weakening method is easier to operate without the risk of PM demagnetization. The analytical model is presented, and the operation principles are illustrated. To analyze the performance of different combinations of stator/rotor pole pairs, four cases are optimized and analyzed using the finite element method for comparison. The characteristics of VSCAVC are analyzed.

Temperature Field Analysis and Cooling Structure Optimization for Integrated Permanent Magnet In-Wheel Motor Based on Electromagnetic-Thermal Coupling

Aiming at the impact of heat generation and temperature rise on the driving performance of a permanent magnet (PM) motor, taking the PM in-wheel motor (IWM) for electric vehicles as an object, research is conducted into the temperature distribution of the electromagnetic–thermal effect and cooling structure optimization. Firstly, the electromagnetic–thermal coupling model considering electromagnetic harmonics is established using the subdomain model and Bertotti’s iron loss separation theory. Combined with the finite element (FE) simulation model established by Ansoft Maxwell software platform, the winding copper loss, stator core loss and PM eddy current loss under the action of complex magnetic flux are analyzed, and the transient temperature distribution of each component is obtained through coupling. Secondarily, the influence of the waterway structure parameters on the heat dissipation effect of the PM-IWM is analyzed by the thermal-fluid coupled relationship. On the basis, the optimization design of waterway structure parameters is carried out to improve the heat dissipation effect of the cooling system based on the proposed chaotic mapping ant colony algorithm with metropolis criterion. The comparison before and after optimization shows that the temperature of key components is significantly improved, the average convection heat transfer coefficient (CHTC) is increased by 23.57%, the peak temperature of stator is reduced from 95.47 °C to 82.73 °C, and the peak temperature of PM is decreased by 14.26%, thus the demagnetization risk in the PM is improved comprehensively. The research results can provide some theoretical and technical support for the structural optimization of water-cooled dissipation in the PM motor.

Analysis of Split-Tooth Stator PM Vernier Machines With Zero-Sequence Current Excitation

This article proposes a series of split-tooth stator permanent magnet (PM) Vernier machines with zero-sequence current excitation, which integrates enhanced torque density and flux adjustment capability. The key is to design the split tooth to exert desired dual magnetic field modulation effect so as to efficiently utilize the hybrid magnetic fields by the PM and zero-sequence current. Meanwhile, with the split-tooth design, the paralleled flux paths are achieved to offer improved flux regulation capability and reduced PM demagnetization risk. In this article, the machine topologies and operation principle are introduced. Hybrid excitation magnetic field is analyzed with the consideration of dual magnetic field modulation of split-tooth structure. Influences of split tooth and PM on torque and flux regulation capability are analyzed. Electromagnetic performances of the proposed machine are analyzed and compared. A prototype is manufactured and tested to validate the theoretical analysis.