Magnetic Ripple Research Articles

Comparison and analysis of properties of V-type HV-LSPMSM with non-magnetic and magnetic-wedges

In order to improve the magnetic density distribution and torque ripple waveform of the motor and enhance its efficiency, the effect of slot wedge on motor performance is discussed in this paper. Taking 6 kV, 710 kW high-voltage line-start PMSM (HV-LSPMSM) as an example, the mathematical model is established, the influence mechanism of slot wedge on air gap density, loss, efficiency and torque ripple of motor is analyzed. The HV-LSPMSM prototype was manufactured, the deviations of several important motor parameters are less than 5% by comparing the test data and the finite element analysis (FEA) results, thus, the accuracy and reliability of the modified finite element model (FEM) are verified, it provides an experimental basis for further research on the effect of relative permeability variation on motor performance. The effects of nonmagnetic-wedges and magnetic-wedges on the motor’s performance are systematically compared. The research results show that compared with the non-magnetic wedges, the magnetic wedges are used to make the magnetic density more uniform, the eddy current loss with magnetic wedge (μ = 5) is reduced by 7.292 kW, and the motor efficiency is improved. The torque ripple rate with magnetic wedge (μ = 3) is reduced by 3.35%, and the torque waveform is significantly improved. And It is found that magnetic wedge (μ > 3) slowed down the iron loss reduction rate. The research provides an important theoretical and experimental basis for the design of HV-LSPMSM and the application of magnetic-wedge in motor.

Modelling and optimisation of the surface‐mounted permanent magnet machine with multi‐level array magnets

AbstractAn analytical and optimisation method is presented to improve the air‐gap magnetic field of the surface‐mounted permanent magnet machine with multi‐level array magnets, which can reduce air‐gap magnetic field harmonics and torque ripple. Different from the conventional analytical method (AM) around the entire single‐magnet pole, the modelling method of multi‐level equal‐thickness ferrite magnets with different remanences for improving the air‐gap flux density is investigated. Considering the influence of air‐gap relative permeability by stator slots and multi‐level magnet remanences on the air‐gap flux density, the proposed AM for improving air‐gap flux density is derived by analysing the slotless air‐gap flux density and slotted air‐gap relative permeability. The cogging torque is predicted with energy method by analysing the tangential magnetic field distribution at stator slots. Then, the back electromotive force is predicted by analysing the winding distribution and radial air‐gap flux density. Based on the proposed AM, the simulated annealing particle swarm optimisation algorithm is used by optimising the widths and thicknesses of the multi‐level array magnets to further reduce torque ripple and increase output torque. Finally, the accuracy of the proposed AM is verified by comparing with the finite element method.

Quasi-perpendicular shocks of galaxy clusters in hybrid kinetic simulations

Context. Cosmic ray acceleration in galaxy clusters is still an ongoing puzzle, with relativistic electrons forming radio relics at merger shocks and emitting synchrotron radiation. These shocks are also potential sources of ultra-high-energy cosmic rays, gamma rays, and neutrinos. Our recent work focuses on electron acceleration at low Mach number merger shocks in the hot intracluster medium which is characterized by high plasma beta. Using particle-in-cell (PIC) simulations, we previously showed that electrons are energized through the stochastic shock-drift acceleration process, which is facilitated by multi-scale turbulence, including ion-scale shock surface rippling. For the present work, we performed hybrid-kinetic simulations in a range of various quasi-perpendicular foreshock conditions, including plasma beta, magnetic obliquity, and the shock Mach number. Aims. We study the ion kinetic physics, which is responsible for the shock structure and wave turbulence, that in turn affects the particle acceleration processes. We cover the spatial and temporal scales, which allow the development of large-scale ion turbulence modes in the system. Methods. We applied a recently developed generalized fluid-particle hybrid numerical code that can combine fluid modeling for both electrons and ions with an arbitrary number of kinetic species. We limited this model to a standard hybrid simulation configuration with kinetic ions and fluid electrons. The model utilizes the exact form of the generalized Ohm’s law, allowing for an arbitrary choice of mass and energy densities, as well as the charge-to-mass ratio of the kinetic species. Results. We show that the properties of ion-driven multi-scale magnetic turbulence in merger shocks are in agreement with the ion structures observed in PIC simulations. In typical shocks with the sonic Mach number Ms = 3, the magnetic structures and shock front density ripples grow and saturate at wavelengths reaching approximately four ion Larmor radii. Only shocks with Ms ≳ 2.3 develop ripples. At very weak shocks with Ms ≲ 2.3, weak turbulence is formed downstream of the shock. We observed a moderate dependence of the strength of magnetic field fluctuations on the quasi-perpendicular magnetic field obliquity. However, as the field obliquity decreases, the shock front ripples exhibit longer wavelengths. Finally, we note that the steady-state structure of Ms = 3 shocks in high-beta plasmas shows evidence that there is little difference between 2D and 3D simulations. The turbulence near the shock front seems to be a 2D-like structure in 3D simulations.

Prototype development of a fully coreless multi-stage axial-flux permanent-magnet machine (AFPM) through the performance comparison between single-stator double-rotor (SSDR) and double-stator single-rotor (DSSR) configurations

Cascading rotor and stator in axial flux permanent magnet (AFPM) machine is a beneficial concept to increase the power density without increasing the diameter of the machine. Multi-stage AFPM can provide higher torque capability in applications requiring high power density. In this regard single-stator double- rotor (SSDR) and double-stator single-rotor (DSSR) are efficient machines compared to single -stage AFPM. Since SSDR and DSSR are also considered modular units to make multi-stage AFPM, like single-stage AFPM, this paper makes a comparison with analysis between SSDR and DSSR AFPM machines. Based on 3-D finite element analysis (FEA), the air-gap magnetic flux, voltage, current, torque, torque ripple, power and power density, efficiency are comparatively investigated to evaluate their performance. Results show that fully coreless topology only be achieved in SSDR AFPM machine with a higher power density. Finally, a prototype multi-stage coreless generator has been developed using a single stator double rotor (SSDR) configuration to justify the fully coreless concept. This prototype coreless generator eliminates eddy current losses and reduces weight, making it a suitable option for certain portable applications.

Effective Evaluation of the Impact of the Magnetic Ripple on the Field Line Topology in DTT: Preliminary Results

Effective Evaluation of the Impact of the Magnetic Ripple on the Field Line Topology in DTT: Preliminary Results

Resonant interaction between runaway electrons and the toroidal magnetic field ripple in TCV

This work explains the anomalously high runaway electron (RE) pitch angles inferred in the flat-top of dedicated Tokamak à Configuration Variable (TCV) experiments. Kinetic modelling shows that the resonant interaction between the gyromotion of the electrons and the toroidal magnetic field ripple will give rise to strong pitch angle scattering in TCV. The resulting increase in synchrotron radiation power losses acts as a RE energy barrier. These observations are tested experimentally by a magnetic field ramp-down, which gradually reduces the resonant parallel momentum at which the REs interact with the ripple. Resulting changes in synchrotron emission geometry and intensity are observed using three multi-spectral camera imaging systems, viewing the RE beam at distinct spatial angles in multiple wavelength ranges. Experimental reconstructions of the RE distribution in momentum- and real-space are consistent with kinetic model predictions.

Thrust Ripple Suppression Based on Negative Current Control for Short-Primary Low-Speed Large LIM Under Transient Operation

End effect of linear induction motor (LIM) leads to magnetic asymmetry and thrust ripple, which seriously restricts the performance and application of LIM. Existing methods for thrust ripple modeling and compensating have mostly focused on the steady state, which suffer from poor transient performance. Moreover, the influence of asymmetric currents on output thrust is not considered. In this paper, the thrust ripple characteristics and impact factors of a low-speed large LIM with negligible dynamic longitudinal end effect are analyzed in details, firstly. Then, a data-driven extracting and modeling method for transient thrust ripple is proposed. The non-stationary time-varying thrust ripple signal is extracted through wavelet decomposition and reconstruction, the polynomial parameters of thrust ripple model are trained off-line by particle swarm optimization algorithm. Finally, an improved suppressing scheme for transient thrust ripple is proposed, considering the decoupling and feedback control of positive and negative currents, based on the dynamic model of six-phase LIM. Full-scale experimental results have fully demonstrated the accuracy of proposed data-driven transient thrust ripple model is more than 90%. During the high-thrust operating stage, the axial vibration acceleration level of LIM within 100Hz is reduced by more than 12dB, with the adoption of improved control scheme.

Optimization of the operational domain for ICRH scenarios in WEST from statistical analysis

In the WEST tokamak, the Ion Cyclotron Resonance Heating (ICRH) system plays a substantial role in increasing the plasma temperature. However, its efficiency can be lowered by two main phenomena: ripple-induced fast ion losses and technical limits on the antenna current. In this work, a new technique using IR thermography was employed to measure the flux of particles coming from the trapping of fast ions in the toroidal magnetic field ripple. These measurements provided the opportunity to fit parametric scaling laws in order to predict the ion flux intensity and the total power loss for experiments with a plasma current of kA and a major radius of the cyclotron resonance layer of m depending on the heating power and the line-averaged electron density. Furthermore, another semi-empirical parametric scaling was developed to evaluate the coupling resistance depending on controllable parameters such as the line averaged electron density and the radial outer gap between the separatrix and the ICRH antenna. These laws were used to define an operational domain from the database of previous experiments made during campaign C4. The settled operational domain suggests that high power ( MW) and high electron density ( m−3) discharges are suitable for optimized steady-state high confinement scenarios in WEST using ICRH.

Variational methods for a singular SPDE yielding the universality of the magnetization ripple

AbstractThe magnetization ripple is a microstructure formed in thin ferromagnetic films. It can be described by minimizers of a nonconvex energy functional leading to a nonlocal and nonlinear elliptic SPDE in two dimensions driven by white noise, which is singular. We address the universal character of the magnetization ripple using variational methods based on Γ‐convergence. Due to the infinite energy of the system, the (random) energy functional has to be renormalized. Using the topology of Γ‐convergence, we give a sense to the law of the renormalized functional that is independent of the way white noise is approximated. More precisely, this universality holds in the class of (not necessarily Gaussian) approximations to white noise satisfying the spectral gap inequality, which allows us to obtain sharp stochastic estimates. As a corollary, we obtain the existence of minimizers with optimal regularity.

Vibration and Noise Optimization of Rotor Structure of Permanent Magnet Synchronous Motor for Vehicles

In order to improve the vibration and noise level of permanent magnet synchronous motor, based on the ANSYS workbench multi-physical field coupling platform, the motor structure is designed and simulated to optimize the vibration and noise of the motor. The spatial and temporal order of the vibration noise caused by the first order tooth harmonic is analysed, and the vibration noise caused by the first order tooth harmonic is reduced by slotting the rotor. By analysing the influence of rotor slots with different positions and different size parameters on the air gap magnetic flux density of the motor, the most suitable optimization method is found, and the optimization level of air gap magnetic flux density of rotor slots with different shapes under the same position and slot area is analysed and compared, so as to select the most suitable rotor slot shape. The simulation analysis shows that the air gap magnetic density and torque ripple of the optimized motor have been significantly improved, and the electromagnetic noise of 48-time order caused by 12 times the electromagnetic frequency of the motor in the 0 space order has been significantly reduced, which proves the reliability of the optimized scheme.

Contribution to Improve Magnetic Performance and Torque Ripple Reduction of the Low-Speed DSPM Machine

This article deals with the performance improvement of a toothed pole variable reluctance machine excited by permanent magnets housed in the stator yoke. The objective was to reduce the electromagnetic torque ripples caused by the structure geometry and by the supply technique. The machine was designed to meet the specifications of a small wind energy conversion system. The proposed solution improved the electromagnetic design of the new structure in order to minimize the variation of the reluctance. This improvement was obtained by action on the geometry of the structure (the location of the permanent magnets), by action on the stator and rotor tooth pitch, and by the application of an indirect control strategy called torque sharing function. The PSO optimization algorithm was applied in the first part for the optimization of the machine’s global parameters to maximize torque density and then, in the second part, for the research of the optimum tooth pitch parameters to minimize torque ripple. Static and dynamic performances were obtained using 2D-FEM and MATLAB/Simulink software. The results reveal that by action on the stator/rotor tooth pitch, the ripple torque was reduced by about 53%, and by approximately 76% with the used command technique.

Impact of magnetic ripple on neoclassical equilibrium in gyrokinetic simulations

The effect of magnetic field ripple on tokamak plasma without turbulence is studied numerically and augmented with a reduced analytical model that includes neoclassical processes in the presence of non-axisymmetric perturbation and stochastic transport. For this study, a magnetic field ripple perturbation has been implemented in the GYSELA gyrokinetic code. This implementation has been verified thanks to a test of toroidal angular momentum conservation. The GYSELA code was then successfully benchmarked against the NEO code, which solves the drift kinetic equation, and against the reduced model in the collisionality range [0.05–0.5] for several amplitudes of the magnetic ripple. An observation, shared by the model, the NEO code and GYSELA simulations is that the thermal drive of the mean poloidal velocity—measured by the coefficient—decreases sharply for large yet experimentally relevant magnetic ripple amplitudes, and may even change sign.

Toroidal magnetic field ripple in the presence of misaligned toroidal field coils on the COMPASS-U tokamak

Homogeneity of the toroidal magnetic field is a critical aspect of the tokamak fusion device. It is affected by the design of toroidal magnetic field coils and their manufacturing and assembly misalignments. The magnetic field of the COMPASS-U project is analysed using toroidal field ripple quantity. ANSYS modelling of bitter-plate-designed toroidal field coils is performed to prepare an accurate simplistic representation of the coils using a virtual current line. Toroidal field ripple is analysed using a Gaussian distribution of possible misalignments. The worst-case toroidal field ripple corresponding to the technical drawings only slightly exceeds the chosen limit of 0.5%.

Identification of fast ion wall loads in Wendelstein 7-X from thermographic measurements

Fast ion wall loads can result in excessively high heat fluxes to the plasma-facing components (PFCs). To allow for the development of mitigation strategies, and thereby protect the PFCs, the fast ion losses have to be predicted by faithful models. To ensure that fast ion models are an accurate representation of the real world, they need to be verified. The neutral-beam experiments performed in Wendelstein 7-X (W7-X) allow to investigate and verify models of the fast ion losses in the stellarator configuration. Infrared thermographic measurements were used to obtain the heat flux to both the baffle plates and the divertor. We found evidence of fast ion wall loads on the baffle plates, with loads between 100 kW m−2 and 1 MW m−2. The loads are attributed to fast ions which escape the main plasma via magnetic ripples. The fast ion wall loads on the baffle plates show up-down and toroidal asymmetry. The experimental results were compared to numerical simulations performed by the BEAMS3D and ASCOT codes. Qualitative agreement in up-down asymmetry is found, but the magnitude and toroidal asymmetry are not yet well predicted by the simulations. The asymmetries of the strike lines on the divertor suggest that fast ions also play a role here. Specifically, a second strike line emerged consistently in the high-iota configuration on the horizontal divertor. The shape and magnitude of the strike lines changed considerably during the neutral-beam injection (NBI) operation phase. Although no damage to steel components of W7-X was found, fast ion loads to the baffle plates could possibly limit the NBI operation in the upcoming campaigns of W7-X.

Magnetic Field Distribution and Ripple Loss Analysis of an Optimized Self-Shielding DC HTS Cable

Compared with AC HTS cable, DC high-temperature superconducting (HTS) cable has prominent advantages of low transmission loss, large current capacity and high controllability. The current directions in adjacent layers of “sandwich” cable with self-shielding characteristic are opposite, which can greatly reduce the magnetic field influence and the critical current degradation. In order to homogenize the magnetic field distribution of the cable, an optimized self-shielding DC HTS cable is proposed. Compared with the previous structure, the optimized self-shielding DC HTS cable has a larger critical current and smaller ripple loss. In this paper, the magnetic field distribution and the ripple loss of three different DC HTS cables with ripple current are studied by a two-dimensional (2D) finite element method (FEM) based on T-A formulation. The 2D simulation model offers a valuable reference for the design and operation of DC HTS cable with low voltage and large current.

On the interplay between interchange turbulence and sheared flows

The presence and the position of an X-point, namely, if the ion diamagnetic drift points toward it or not, strongly impact the edge plasma rotation in tokamaks. In the absence of kinetic effects such as magnetic ripple or ion orbit loss, the shape of the velocity profile results from the balance between neoclassical predictions and turbulent flow generation. In this contribution, we derive a reduced model of turbulence plunged in a shear flow. This model is based on (1) a description of the impact of a sheared flow on the interchange turbulence and (2) a prediction of the poloidal momentum generated by the turbulence. It includes the effects of both the magnetic topology and the finite shear layer width. The model is verified against 2D non-linear flux-driven simulations. Finally, the model predictions of the edge rotation resulting from the equilibrium between the neoclassical prediction and the poloidal momentum generation by the turbulence are invoked to describe the observations from experiment managed in the WEST tokamak. It points out the important role of the magnetic shear in the turbulence tilting and in the flow generation.

Simpler optimized stellarators using permanent magnets

A first-of-a-kind optimized stellarator for confining plasma has been designed and is being constructed with planar circular coils and permanent magnets composed of identical elements. The equilibrium is optimized to be quasi-axisymmetric for good particle confinement. The combination of permanent magnets and planar coils is significantly simpler to construct than fabricating three-dimensionally shaped coils, yet they are able to produce lower helical magnetic ripple than existing devices by two orders of magnitude in , a characteristic neoclassical transport metric.

Effect of Stator Slots on Electromagnetic Performance of a High-Voltage Line-Start Permanent Magnet Synchronous Motor

It is well known that the use of slotted stators in motors produces undesirable effects, such as magnetic flux distortion, additional losses, ripple torque, and vibration. However, a large number of studies pay more attention to stator slots and magnetic slot wedges (MSW) in asynchronous motors and permanent magnet motors, ignoring the same problems in large capacity high voltage line start permanent magnet synchronous motors (HVLSPMSM). In order to disclose the effect of the stator slot on HVLSPMSMs, the no-load air gap magnetic field distribution and stator leakage reactance are studied. Meanwhile, the differences in the starting torque, pull-in torque and pull-out torque of four slot models are compared, and the starting performance is more affected by stator slot. In practical manufacturing, the application of MSWs is the main way to change the electromagnetic performance of stator slots, so the influence of MSWs under different permeabilities on the performance of HVLSPMSMs is investigated. Finally, the effect of a stator slot on the motor starting performance and the rated performance are verified by prototypes and experimental tests, which provide a reference for the application of MSWs in HVLSPMSMs.

Simulation on formation process of field-reversed configuration

Collisional-merging is a way to form high-performance field-reversed configuration (FRC) plasma. An experiment device named HUST-FRC (HFRC) is under construction in Huazhong University of Science and Technology, which will be used to investigate the FRC formation through collisionalmerging. In this research, a magnetohydrodynamics simulation software called USim is used to study the effect of the initial density of plasma, the amplitude of the bias magnetic field, the configuration of the bias field, the rise time of the main field and the magnetic field ripple on the plasma parameters to facilitate the design and operation of HFRC. Preliminary simulation results show that cusp configuration, lower ripple, higher initial density, an initial bias field of −0.15 T or −0.2 T, and a rise time of 4 μs are conducive to the formation of high-performance FRC plasma in the HFRC device.

Design and Performance Benchmarking of Hybrid Tunnel FET/STT-MTJ-Based Logic In-Memory Designs for Energy Efficiency

With CMOS technology scaling and increased short channel effects, spin-transfer torque-magnetic tunnel junction (STT-MTJ)/CMOS-based logic-in-memory (LIM) designs consume significantly higher energy at scaled supply voltages. To enhance the energy efficiency of LIM circuit designs, this work proposes a hybrid tunnel FET (TFET)/MTJ-based digital circuit design approach at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathbf {DD}} = 0.3$ </tex-math></inline-formula> V. A Schmitt triggered pre-charge sense amplifier (ST-PCSA) with a strong feedback mechanism at the pull-down section is considered in TFET/MTJ-based LIM designs. The proposed LIM-MTJ designs are implemented using 20 nm TEFT technology and perpendicular anisotropy CoFeB/MgO/CoFeB MTJs. Two input and, or, xor logic gates, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times1$ </tex-math></inline-formula> multiplexer, 1-bit magnetic full adder (MFA), 4-bit magnetic ripple carry adder (RCA), and a simple 1-bit magnetic arithmetic and logical unit (M-ALU) are designed, exploring the proposed ST-PCSA-based hybrid TFET/MTJ logic. The proposed ST-PCSA-based hybrid TFET/MTJ LIM designs achieve ~47.2%–55.55% lower energy consumption in comparison with the PCSA-based TFET/MTJ LIM designs. Performance benchmarking with 20 nm FinFET designs demonstrates that the proposed TFET/MTJ LIM designs achieve 11.1%–25.9% lower energy consumption when compared with equivalent FinFET/MTJ-based LIM designs.