Hybrid Magnet Research Articles

Investigation of Torque Characteristics of Switched Flux Hybrid Magnet Memory Machine by a Coupled Solution

This article investigates the torque characteristics of a switched flux hybrid magnet memory machine (SF-HMMM) by employing a coupled solution combining a quasi-linear hysteresis model (QLHM) of low coercive force (LCF) magnet and frozen-permeability method (FPM). This provides an in-depth understanding of the torque production of SF-HMMM. The QLHM is utilized to characterize the repetitive remagnetizing/demagnetizing behaviors of LCF permanent magnets (PMs), while the FPM is employed to separate and quantify the torque contributions due to two sets of PMs and armature windings. The machine topology and analysis methodology are described, respectively. The torque segregation results accounting for magnetization state variation are analyzed by the proposed coupled solution. The influence of the LCF PM property on the torque segregation result is investigated to facilitate the establishment of general design guidelines. Finally, the prototype is tested to experimentally validate the theoretical analysis.

Design of the Resistive Insert for the Nijmegen 45 T Hybrid Magnet

This paper presents the design of the resistive insert magnet for the 45 T hybrid magnet under construction at the High Field Magnet Laboratory (HFML) in Nijmegen. We describe the design process and tools used to obtain the coil and disk design, and we describe the mechanical design aspects of the housing for the magnet. We address the end turn issue and introduce an innovative new element to provide sufficient clamping of the coil at all times. Finally, we address possible fault scenarios and the magnetic misalignment forces associated with such faults and their impact on the housing.

Comparative Study on Variable Flux Memory Machines With Different Arrangements of Permanent Magnets

Compared with conventional permanent magnet synchronous motor, variable flux memory motor (VFMM) possesses the advantage of adjusting the magnetization state online. Because of its wide speed range and large high-efficiency region, it becomes a competitive candidate for the electric drive system. This paper presents a novel parallel hybrid magnets VFMM which is obtained by updating a conventional series hybrid permanent magnets VFMM. The proposed motor adopts a new permanent magnet arrangement and the combination of low coercive force permanent magnet and high coercive force permanent magnet is used. The proposed parallel hybrid permanent magnets VFMM and the series hybrid permanent magnets VFMM are compared. The equivalent magnetic circuit models of the motors are used to explain the principle of the motors. The finite element analysis method is used to study the fundamental properties, such as open circuit radial flux density, unintentional demagnetization with q-axis current, intentional demagnetization with d-axis current, torque capability, and efficiency characteristics. It was shown the efficiency of the parallel hybrid permanent magnets VFMM is higher in the high-speed region and the magnetization state adjustment range of the parallel hybrid permanent magnets VFMM is larger.

Suspension power optimization of unbalanced structure permanent magnet electromagnetic hybrid magnet using genetic algorithm

Suspension power optimization of unbalanced structure permanent magnet electromagnetic hybrid magnet using genetic algorithm

Magnetic Performance of (Nd,Ce)-Fe-B-type Die-upset Hybrid Magnet Composed of Melt-spun and HDDR-treated Materials

Ce-containing (Nd,Ce)-Fe-B-type hybrid magnet was fabricated by die-upset technique using two different types of materials: Ce-substituted (NdSUB0.55/SUBCeSUB0.45/SUB)SUB15/SUBFeSUB72.2/SUBCoSUB6.6/SUBGaSUB0.6/SUBBSUB5.6/SUB HDDR powder and melt-spun Nd1SUB3.6/SUBFeSUB73.6/SUBCoSUB6.6/SUBGaSUB0.6/SUBBSUB5.6/SUB flakes. Magnetic performance of the hybrid magnet was superior to that of the single alloy magnet when they had identical overall composition: SUBi/SUBHSUBc/SUB = 6.8 kOe, Mr = 10.6 kG, and (BH)SUBmax/SUB = 19.8 MGOe for the Ce-containing hybrid magnet and iHc = 3.9 kOe, Mr = 9.8 kG, and (BH)SUBmax/SUB = 11.6 MGOe for the magnet from the single alloy HDDR powder. Die-upset hybrid magnet consisting of two constituent materials showed smooth and single-material-like demagnetization behavior, and this was attributed to the exchange interaction between neighbouring grains in the magnet.

Texture Development in (Nd,Ce)-Fe-B-type Die-upset Hybrid Magnet Consisted of Two Hard Magnetic Constituents

Texture development in the Ce-substituted Nd-Fe-B-type die-upset hybrid magnet, which was fabricated using starting materials of Ce-substituted (NdSUB0.55/SUBCeSUB0.45/SUB)SUB15/SUBFeSUB72.2/SUBCoSUB6.6/SUBGaSUB0.6/SUBBSUB5.6/SUB HDDR-treated alloy powder and meltspun NdSUB13.6/SUBFeSUB73.6/SUBCoSUB6.6/SUBGaSUB0.6/SUBBSUB5.6/SUB flakes (MQU-F) without Ce, was investigated. Noticeably better texture developed in die-upset magnet from the MQU-F flakes alone with respect to magnet from the HDDR-treated powder alone. Better texture developed also in the MQU-F flake regions in the die-upset hybrid magnet with respect to the HDDR particle regions, and overall texture in the hybrid magnet was dominantly controlled by the texture in the MQU-F flake regions. Overall texture in the hybrid magnet was not as good as the weighted average of texture expected from texture of the single alloy magnets from the HDDR powder alone and the MQU-F flakes alone.

On-load demagnetization effect of high-coercive-force PMs in switched flux hybrid magnet memory machine

In the previous researches of hybrid magnet memory motors (HMMMs), the demagnetization characteristics of low-coercive-force (LCF) magnets have been already investigated extensively. Nevertheless, the possible irreversible demagnetization of high-coercive-force (HCF) magnets remains unexplored hitherto. In this paper, the demagnetization behaviour of HCF magnets in switched flux hybrid magnet memory machines (SF-HMMMs) accounting for the high-level current pulse is revealed and investigated. A simplified magnetic circuit model is built to illustrate when and how the DC current pulse poses the risk of irreversible demagnetization to the HCF magnets. Furthermore, the influences of temperature, DC current amplitude and HCF magnet thickness on the irreversible demagnetization effect of HCF magnets in the investigated SF-HMMM are analyzed based on finite-element (FE) analyses. The theoretical and FE results are experimentally verified by the tests on an SF-HMMM prototype.

A Lightweight Magnetorheological Actuator Using Hybrid Magnetization

This article presents the design and validation of a lightweight magnetorheological (MR) clutch, called hybrid magnetorheological (HMR) clutch. The clutch utilizes a hybrid magnetization using an electromagnetic coil and a permanent magnet. The electromagnetic coil can adjust the magnetic field generated by the permanent magnet to a desired value and fully control the transmitted torque. To achieve the maximum torque-to-mass ratio, the design of the HMR clutch is formulated as a multiobjective optimization problem with three design objectives, namely the transmitted torque, the mass of the clutch, and the magnetic field strength within the clutch pack. A prototype of the HMR clutch is fabricated, and its dynamic performance is experimentally validated. Experimental results clearly demonstrate the advantages of the HMR clutch in applications requiring fast and precise motion and torque control.

Design Considerations of Switched Flux Memory Machine with Partitioned Stators

This paper presents general design considerations of a partitioned stator switched flux hybrid magnet memory machine (PS-SF-HMMM). The armature windings and permanent magnets (PMs) are placed on two separate stators, respectively, in the PS-SF-HMMM, and thus both high torque density and wide flux regulation capability can be obtained. The topology and working principle of the machine are introduced briefly first, and then different magnet arrangements and stator/rotor pole combinations are investigated. In addition, various design parameters are optimized based on finite element (FE) methods. Finally, a prototype is fabricated to experimentally validate the FE results.

Coercivity enhancement and uncoordinated deformation in PrCu-doped PrFeB/PrCo5 hybrid magnets

PrFeB/PrCo5 hybrid magnet has excellent magnetic properties and better thermal stability. In this paper, anisotropic nanocomposite PrFeB/PrCo5 hot-deformed magnets with and without doping PrCu eutectic alloy were prepared by spark plasma sintering (SPS) technique. With the addition of 6 wt% PrCu, the coercivity of the magnet (10.8 kOe) is almost double than that of undoped magnet (5.6 kOe), with an enhancement of the remanence (9.1 kG versus 8.4 kG). For the magnet with PrCu, the nonmagnetic PrCu phase is mainly distributed in the phase boundary regions, introducing a coupling effect of demagnetization on the hard-magnetic phases, which obtained an enhancement of the coercivity. The deformed Pr2Fe14B grains of the hybrid magnet have elongated platelet shapes, but the PrCo5 grains are not easy to be deformed, which affects the overall degree of deformation texture of the hybrid magnet. This implies that there is uncoordinated deformation for the PrFeB/PrCo5 hybrid magnet.

A Novel $In-Situ$ Radiation Damage Diagnostic System for Undulators

Radiation damage has been a known problem at many synchrotron radiations and free-electron lasers facilities, especially those that use hybrid or pure permanent magnet undulators to produce high brightness light. Field strength loss due to demagnetization makes it necessary to remove the insertion device from the tunnel for inspection and repair, which brings several inconveniences. We aimed to develop an in situ radiation damage detection system for undulators capable of diagnosing relative field changes of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> (100 ppm) or smaller. The system measures the flux change in a flexible printed circuit board coil attached to the undulator magnet array by periodically measuring the integral flux change during the opening and closing of the undulator gap. If the magnet block damage occurs, the signal from the coil will decrease proportionally to the damage. First tests performed on variable gap hybrid undulators for the Linac Coherent Light Source II (LCLS-II) at SLAC National Accelerator Laboratory showed that the system is capable of measuring flux changes with a relative precision of approximately 0.7 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> over several days. Relative field changes smaller than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> were detected in short-term measurements. The novel system that we propose here opens the possibility of detecting radiation damage in undulators during operation.

A variable-temperature scanning tunneling microscope operated in a continuous flow cryostat.

We present a continuous flow cryostat scanning tunneling microscope (STM) which can be operated at temperatures between 4.9 K and 300 K. A variable temperature insert with 20 mm aperture is installed in the cryostat. A base temperature of 4.9 K at the STM head was achieved with helium exchange gas cooling. By using a novel design of zirconia structure, the size of the STM head was minimized to 9.2 mm in outer diameter. The high compactness and rigidity of the STM head make it less sensitive to vibrations, contributing to the high stability of the tip-sample junction. The drifting rates of the STM at 4.9 K in the X-Y plane and Z direction are 1.96 and 3.05 pm/min, respectively. The performance of the STM was demonstrated by atomically resolved imaging of graphite and NbSe2 without using external vibrational isolation. Furthermore, the dI/dV spectra of NbSe2 were resolved near its critical temperature, illustrating the formation process of the superconducting gap as a function of temperature. This STM is ultrahigh vacuum and strong magnetic field compatible, making it promising for direct application in the extreme conditions involving water-cooled magnets and hybrid magnets.

Hybrid excited permanent magnet machines for electric and hybrid electric vehicles

This paper reviews various hybrid excited (HE) machines from the perspective of location of PM and DC excitation, series/parallel connection of PM and DC excited magnetic fields, and 2D/3D magnetic fields, respectively. The advantages as well as drawbacks of each category are analyzed. Since an additional control degree, i.e. DC excitation, is introduced in the HE machine, the flux weakening control strategies are more complex. The flux weakening performance as well as efficiency are compared with different control strategies. Then, the potential to mitigate the risk of uncontrolled overvoltage fault at high speed operation is highlighted by controlling the field excitation. Since additional DC coils are usually required for HE machines compared with pure PM excitation, the spatial confliction inevitably results in electromagnetic performance reduction. Finally, the technique to integrate the field and armature windings with open-winding drive circuit is introduced, and novel HE machines without a DC coil are summarized.

Influence of magnetic field strength of hybrid magnet on vibration isolation of quarter car model

This work studies the vibration isolation of a single degree of freedom (SDOF) quarter car model under the influence of the magnetic field strength of electromagnet of a hybrid electromagnet (EM) and permanent magnet (PM) combination. Furthermore, the time history plot helps to study the influence of the relative movement of the electromagnet and the permanent magnet on the top plate, base plate, stiffness of the system and damping coefficient. A laboratory scale model of a SDOF quarter car with a hybrid magnet is tested on an open loop type shaker table at different frequencies of base excitation. Data acquisition and analysis have been carried out with the aid of two piezoelectric accelerometers and Lab VIEW software. Also, the theoretical analysis is carried out in MATLAB Simulink. From the experimental and Simulink results, it is found that the repulsive force between the electromagnet and permanent magnet varies the base and top plate amplitude, the stiffness of the system and damping coefficient of the suspension elements.

A Novel Hybrid-Magnetic-Circuit Variable Flux Memory Machine

This article proposes a novel hybrid-magnetic-circuit variable flux memory machine (HMC-VFMM) by combining series and parallel hybrid magnet structures. Thus, the synergies of wide flux regulation range in parallel type and excellent on-load demagnetization withstand capability in series type can be simultaneously obtained with the proposed HMC design. Meanwhile, two sets of the permanent magnets (PMs) with high coercive force and low coercive force (LCF), i.e., NdFeB and AlNiCo PMs, are employed to achieve high torque density and energy-efficient magnetization state adjustment. The topologies and tradeoffs of traditional parallel and series VFMMs are addressed first. In addition, the structure evolution, features and operating principle of the proposed HMC-VFMM are described, respectively. A simplified equivalent magnetic circuit is modeled to reveal the performance improvement of the machine. Then, the design improvements with q-axis barriers are presented to elevate the LCF PM working point for preventing the on-load demagnetizing effect, while maintaining the torque capability. The electromagnetic characteristics of the HMC design are investigated and compared with the parallel/series counterparts. Finally, the experiments have been carried out to validate the finite-element analyses.

A Novel Hybrid Magnet Made of HTS Tape Stacks and Permanent Magnets for Motor Applications

High-temperature superconducting (HTS) tape stacks could be used in motors as a substitute for permanent magnets (PMs) to improve the power density. However, the magnetization difficulty and safety concern limit its wider application. A novel hybrid magnet made of HTS tape stacks and PMs is proposed in this paper and investigated in experimental and numerical modeling methods. A hybrid magnet sample is manufactured and tested using pulsed field magnetization (PFM) at 77.3 K. Then, a 3-D electromagnetic-thermal coupled model is built and verified to simulate the field performance at lower temperatures. After the optimization process of the thickness ratio, an optimal 5-mm hybrid magnet of 0.5-mm tape stack +4.5 mm PM is obtained. Compared with the PM, the optimal hybrid magnet could enhance the magnetic field by 114%. Compared with the pure tape stack of the same size, the hybrid magnet could be magnetized with relatively small pulsed field, could reduce the consumption of the HTS tapes, and could enhance the operation safety especially encountering a cooling system failure. The results offer a novel perspective to introduce the HTS material into the conventional motor applications and provide a possible reference to the future study of HTS motors.

Mechanical Utility Structure for Testing High Field Superconducting Dipole Magnets

The U.S. Magnet Development Program (MDP) collaboration is designing a utility mechanical structure for testing various high-field superconducting dipole coils. The design uses a shell-based structure concept, which allows applying preload in two steps: during a room temperature assembly and during a cool down to a cryogenic temperature. The structure is designed to accommodate various coil designs-including Nb3Sn Cosine Theta (CT) and Canted CT magnets as well as hybrid magnets with high temperature superconductor cables. Superconducting coils, enclosed by bolted pads to form an octagonal coil pack, will be inserted into a reusable yoke-shell subassembly and precisely preloaded during the assembly using a bladder-and-key technology. Due to a differential thermal contraction between an external aluminum shell and the magnet core, the coil preload increases during the cool down up to level required for 17-T excitation. Such a reusable structure will serve as a testing fixture supporting goals of the MDP program, decreasing cost and simplifying coil performance testing at different preload levels. We present a finite-element analysis of the structure preloading various coil designs and examine the predicted coil stress at each step of the magnet assembly and excitation.

Fabrication of the Nb3Sn/Cu CICC Coil and Cold Mass for the Radboud University HFML 45 T Hybrid Magnet

The High Magnetic Field Laboratory in Nijmegen has been collaborating with the National High Magnetic Field Laboratory (NHMFL) in Florida on a 45 T hybrid magnet project. The primary scope of the collaboration was the design and manufacture of the hybrid magnet's superconducting cold mass. The 7.5 ton cold mass includes a single 13 T solenoid wound with high JC RRP Nb 3 Sn/Cu cable-in-conduit conductor. The coil will be forced flow supercritical helium and operated in parallel with a set of Bitter-disk resistive coils. Coil winding, reaction heat treatment, epoxy impregnation, and cold mass assembly has been completed at the NHMFL. The full cold mass has been delivered to Radboud University and will be assembled with the cryostat and interfaced with the system utilities.

A Tear-Drop Bifilar Sample Holder for Full Excitation and Stability Studies of HTS Cables at 4.2 K Using a Superconducting Transformer

HTS cables proposed for next-generation main, hybrid, and insert magnets will have very high I c (>10 kA) at 14 T and above. Determining the quench, current-sharing, and other properties of these cables will require measurement systems, which will likely incorporate a superconducting transformer. The utilization of high-field persistent mode solenoids will make size and cost less prohibitive, allowing a higher frequency of measurements within a larger number of research facilities. Additionally, a system designed for use with solenoids will allow for experiments at higher maximum fields than those achievable using dipoles and split coils. Proposed in this document is a bifilar sample probe, which fits within a 77-mm bore solenoid capable of measuring up to a 6-mm outer diameter conductor-on-round-core REBCO cables or wires up to 20 kA in transverse fields at 12 T and 4.2 K. Splices and mechanical considerations will be discussed.

Comparative Study of Partitioned Stator Memory Machines With Series and Parallel Hybrid PM Configurations

In this paper, the partitioned stator (PS) structure is extended to variable-flux memory machines, forming two newly emerged PS switched-flux memory machines (PS-SFMMs) with series and parallel hybrid magnet configurations. From the perspective of geometry, both two PS-SFMMs share identical outer stator and rotor segments, while two different types of permanent magnet (PM) arrangements are employed in the inner stationary part. Thus, the developed machines can inherent the geometric separation of the armature winding and PM excitations from the PS design, thus achieving acceptable torque capability, and excellent air-gap flux control. A comparative study between PS-SFMMs with series and parallel structures is established. First, the topologies and operating principle are introduced, respectively. In addition, the design tradeoffs and PM sizing of the two PS machines are revealed and optimized with a simplified magnetic circuit model. Then, the electromagnetic characteristics of PS-SFMMs with different magnetic circuits are investigated and compared with the finite-element (FE) method. The FE results are validated by the experiments on a parallel prototype.