Eddy Current Power Loss Research Articles

Analysis of power loss in heat pipes for integrated thermal management of next generation electrical machines

This paper presents analysis of eddy-current power loss in heat pipes (HPs) for integrated thermal management of electrical machines. Here, a close integration of HPs with winding body is considered. Such an arrangement is particularly attractive, as it targets the main heat source within the machine assembly. However, there are several challenges associated with the subsystem compatibility, which include electromagnetic, thermal, and mechanical design aspects. The HP’s power loss, which is generated as a results of the time varying stator and/or rotor slot magnetic flux leakage, requires careful considerations. Although, the HP-enabled thermal management of electrical machines (electrical windings) has been previously investigated, the additional HP generated power loss has had a very little attention. In this work, the author proposes alternative techniques for accurate predictions of HP generated power loss accounting for the HP’s wick structure. Three alternative custom-built HP constructions Copper-Water and Titanium-Water with sintered and mesh wicks have been investigated in this analysis. Both theoretical finite element (FE) electromagnetic and experimental methods are discussed in detail. The results show that the proposed experiment informed FE model of HP with an equivalent electrical resistivity wick region provides an accurate HP representation useful in design of electrical machines. Further to these, the proposed approach is demonstrated on an example custom vapor chamber (VC) highlighting the importance of accurate power loss predictions in HPs and VCs.

Frequency Response and Eddy Current Power Loss in Magneto-Mechanical Transmitters

Magneto-mechanical transmitters offer a compact and low-power solution for the generation of ultra-low frequency (ULF) magnetic signals for through-ground and through-seawater communications. Resonant arrays of smaller magneto-mechanical transmitters are particularly interesting in this context as the physical scaling laws allow for the increase of operating frequency and reduce the power requirements for ULF signal generation. In this work, we introduce a generalized model for accurate prediction of frequency and mode shape in generalized magneto-mechanical resonator arrays (MMRAs) that accounts for near-field magnetic interactions as well as magnetically induced nonlinearity. Using experiments, we demonstrate that our predictive capability is significantly improved compared against simplified dipole approximations. We additionally model the eddy current losses internal to the array and find that they are in agreement with experimental observations.

Effect of a YIG nanoparticle additive on the magnetic properties of MnZn ferrites for MHz frequency applications

AbstractIn this study, MnZn ferrites with added YIG nanoparticles were developed for MHz frequency applications. The effect of the magnetic YIG additive on the power loss, initial permeability, and cutoff frequency of MnZn ferrites was investigated. A small quantity of added YIG effectively reduces the power loss and concurrently increases the initial permeability. Compared to the results for the MnZn ferrite with no added YIG, the optimal MnZn ferrite with 600 ppm added YIG exhibits a reduction in the power loss at 25°C of 56.4% and 36.6% at 1 MHz/50 mT and 3 MHz/10 mT, respectively, and a 13.9% increase in the initial permeability. This sample also exhibits a good stability of the power loss against temperature. The power loss remains below 205 kW/m3 over temperatures ranging from 25 to 140°C. The effect mechanism of YIG addition on the magnetic properties of MnZn ferrites was studied. An analysis based on the equivalent circuit model showed that the reduction in the eddy current loss and power loss mainly results from the increase in the grain boundary resistance caused by the addition of highly resistive YIG.

Design Guidelines for interlocked stator cores made of CoFe sheets

CoFe lamination stacks used for high-performance electric motors can be manufactured economically in high volumes by interlocking. In order to ensure sufficient joint strength with minimized sheet thickness, a comprehensive knowledge of the influences of various process parameters, such as embossing depth, clearance and counter punch force, is essential. To analyze these parameters, which also influence the magnetic properties, experiments are carried out and resulting joint strengths are determined in top tensile tests. The negative influences of the cutting process on magnetic conductivity and thus hysteresis losses due to residual stresses and plastic deformation are well known. In the subsequent stacking step, an influence of embossing and pre-stresses on the material properties is expected. In addition, local electrical contacts between the sheets may occur due to the interlocking process, causing additional eddy currents. Loss measurements are conducted to investigate the effect of the joining process on the magnetic properties of the stack. In doing so, the influence of process parameters such as the embossing depth and clearance on eddy current power losses is analyzed.

Finite Element Modeling and Analysis of High Power, Low-loss Flux-Pipe Resonant Coils for Static Bidirectional Wireless Power Transfer

This paper presents the optimal modeling and finite element analysis of strong-coupled, high-power and low-loss flux-pipe resonant coils for bidirectional wireless power transfer (WPT), applicable to electric vehicles (EVs) using series-series compensation topology. The initial design involves the modeling of strong-coupled flux-pipe coils with a fixed number of wire-turns. The ohmic and core loss reduction for the optimized coil model was implemented by creating two separate coils that are electrically parallel but magnetically coupled in order to achieve maximum flux linkage between the secondary and primary coils. Reduction in the magnitude of eddy current losses was realized by design modification of the ferrite core geometry and optimized selection of shielding material. The ferrite core geometry was modified to create a C-shape that enabled the boosting and linkage of useful magnetic flux. In addition, an alternative copper shielding methodology was selected with the advantage of having fewer eddy current power losses per unit mass when compared with aluminum of the same physical dimension. From the simulation results obtained, the proposed flux-pipe model offers higher coil-to-coil efficiency and a significant increase in power level when compared with equivalent circular, rectangular and traditional flux-pipe models over a range of load resistance. The proposed model design is capable of transferring over 11 kW of power across an airgap of 200 mm with a coil-to-coil efficiency of over 99% at a load resistance of 60 Ω.

A new power MnZn ferrite for broad temperature range applications

The present study focuses on the targeted compositional and process design towards the development of a new MnZn ferrite material for high-efficiency power conversion systems that exhibits very low power losses at low frequencies across a broad temperature range extending from 25°C to 160°C. The MnZn ferrite powders were prepared by solid state processing, while the compositional design involved the investigation of several Co-doping levels (0 to 6000 ppm CoO) on the basic composition. Analysis of the contributions of hysteresis and eddy current power loss mechanisms to the overall power losses led to the design of further steps, targeting to the limitation of the chemical, morphological and microstructural defects, along with optimization of dopants distribution, through processing. This was achieved by the introduction of a primary heat treatment of the raw materials mixture and an optimization of the particle size distribution, both steps applied before the standard process of solid state reaction, resulting to an overall reduction of the power losses across the temperature range from 25 to 160°C. The developed MnZn ferrite material exhibits an initial permeability of 3200 at 10 kHz, 0.1 mT, 25°C, power losses <300 mW/cm3 at 100 kHz, 200 mT from 25 to 100°C and a superior magnetic performance at high temperatures, exhibiting the lowest reported power losses of 380 mW/cm3 at 100 kHz, 200 mT, 160°C, making it suitable for high energy-efficient products, independent of the environmental temperature and loading of the transformer.

Rotor eddy loss in high‐speed permanent magnet synchronous generators

Analytical and transient finite element analysis (FEA) methods are used to calculate on-load rotor eddy current power loss in permanent magnet machines taking into account the effect of the reaction of eddy currents. The effect of the phase advance angle between the back electromotive force, and the phase current on rotor eddy current power loss is investigated. Both magnet flux tooth ripple and magnetomotive force harmonics are considered in the analytical calculation of rotor loss; the harmonics of the magnet tooth ripple flux and armature reaction flux are added vectorially. Good agreement between analytical and FEA results is observed when the stator laminations are assumed to have a linear BH curve. However, a significant discrepancy is observed between the analytical and FEA solutions when a non-linear BH curve is used.

Calculation of No-Load Rotor Eddy-Current Power Loss in PM Synchronous Machines

Three analytical methods, and finite-element analysis (FEA), are used to calculate no-load flux harmonics traveling with respect to the rotor of a surface permanent magnet machine. Rotor eddy-current losses caused by each harmonic are calculated analytically using a multilayer eddy-current model of the machine, in which each harmonic is represented by an equivalent current sheet on the bore of a slotless stator. Losses are also calculated using transient time-stepping FEA coupled with the equation of motion of the rotor. Significant discrepancies are observed between the results obtained from the different methods and FEA, especially when the level of saturation in the stator core is significant.

Single domain wall dynamics in ferromagnetic wire with circular magnetization and conductive cover

The circular magnetization reversal process in a long ferromagnetic wire with a non-ferromagnetic conductive cover is theoretically analysed. The model of a single thin rigid 180° domain wall (DW) is used so that the wire is divided crosswise into two magnetic domains with opposite circular magnetization. It is presumed that after switching on direct electric current in the wire, the circular magnetization reversal occurs by means of the DW movement through the wire. The induced electric field and the eddy current power losses in all conductive parts are calculated in the model, from which the DW mobility is determined. It is shown that DW mobility is very sensitive to the thickness and the conductivity of the non-ferromagnetic cover. An experimental procedure for measuring DW mobility through the non-ferromagnetic conductive cover is proposed.

Rotor Eddy Current Power Loss in Permanent Magnet Synchronous Generators Feeding Uncontrolled Rectifier Loads

Analytical methods and transient finite element analysis (FEA) with rotating mesh are used to calculate rotor eddy current power loss in a permanent magnet synchronous generator connected to an uncontrolled bridge rectifier. Two winding and rectifier topologies are considered: a three-phase winding with a three-phase bridge rectifier and a double three-phase winding with a three-phase rectifier each, connected in series. Both magnet flux tooth ripple and stator magneto-motive force harmonics are considered in the calculation of rotor loss; the harmonics are added vectorially. Good agreement is observed between analytical and FEA for constant dc link current and constant voltage loads. The machine with double three-phase windings was found to have considerably lower rotor losses than the machine with one single three-phase winding.

Eddy Current Loss Estimation of Edge Burr-Affected Magnetic Laminations Based on Equivalent Electrical Network—Part I: Fundamental Concepts and FEM Modeling

Cutting and punching of the electrical steel can cause edge burrs which lead to interlaminar short circuits between the laminations. In this paper, based on an equivalent electric circuit of the eddy current path, an analytical method has been developed to estimate the eddy current power loss of the magnetic cores, caused by the interlaminar faults, in a wide range of flux density and magnetizing frequency. Important factors, such as skin effect, nonuniform flux density distribution, complex relative permeability, and the nonlinear relation of B (H), which are often neglected in the literature, are highlighted. Fundamental concepts of the interlaminar fault and its consequences, the effect of interlaminar faults on the configuration of magnetic cores, and finite-element method verification are presented in this Part I paper. Modeling of eddy current, together with experimental results of eddy current measurements of packs of shorted laminations, are reported in Part II.

Eddy Current Loss Estimation of Edge Burr-Affected Magnetic Laminations Based on Equivalent Electrical Network—Part II: Analytical Modeling and Experimental Results

In Part I of this two-part paper, fundamental concepts of interlaminar fault and its consequences on magnetic cores were presented. An equivalent configuration, which was proved by FEM modelling, was proposed for magnetic cores with interlaminar fault. In this Part II paper, based on the equivalent configuration of the core and equivalent circuit of eddy current path, an analytical model is developed to estimate eddy current power loss of magnetic cores with interlaminar faults in a wide range of magnetizing frequency. Important factors, such as skin effect, nonuniform flux density distribution, complex relative permeability and nonlinear relation of B (H), which are often neglected in the literature, are highlighted. Packs of two, three, and four Epstein-size laminations of conventional grain oriented were shorted together artificially to measure the extra power loss caused by the interlaminar fault and support the analytical modeling. It was found that in the magnetic cores affected by interlaminar fault, the skin effect is a determinant factor in the magnetic properties determinations, even at low frequencies.

A 3-D analytic eddy current model for a finite width conductive plate

Purpose – A 3-D analytic modeling technique for calculating the eddy current distribution, force and power loss in a conductive plate of finite width and thickness is presented. The derived equations are expressed in a general form so that any magnetic source can be utilized. The model assumes the length of the conductive plate is large and the thickness of the plate is thin but not negligible. The paper aims to discuss these issues. Design/methodology/approach – The conducting and non-conducting regions are formulated in terms of decoupled magnetic vector potential components. In order to accurately compute the eddy current fields and forces the source field only needs to be applied on the surface of the conducting plate. The primary focus is on reducing the eddy current computational time. Findings – The accuracy of the presented approach is verified by utilizing a magnetic rotor that has both a rotational and translational motion. The proposed method is computationally efficient and its accuracy is validated using the finite element method. Research limitations/implications – The conducting plate thickness is assumed to be thin (but not negligible), and this enables the field interaction through the edge of the plate to be neglected. The lateral force is not calculated in the proposed approach. Practical implications – The calculation procedure presented is computationally fast and therefore this can enable the 3-D eddy current forces to be computed in near real-time. Originality/value – This paper presents a fully 3-D analytic based eddy current formlation for computing the eddy current fields and forces in a conducting plate of finite thickness and finite width. The modeling approach is shown to be computationally accurate and relatively fast.

The Current Distribution, Resistance and Internal Inductance of Linear Power System Conductors—A Review of Explicit Equations

This paper reviews the present state of knowledge of explicit equations for calculating the dc and ac current distributions and the resistances and internal inductances per-unit length of linear electrical conductors used in power transmission and distribution systems. These conductors may be homogeneous wire or rod, tubular, triangular, elliptical or rectangular busbars, helically stranded nonmagnetic conductors (AAC or AAAC), or bimetallic stranded conductors, such as the commonly used aluminum conductor steel reinforced (ACSR). In general, the current density in an isothermal homogeneous conductor is uniform with direct current (dc), but with alternating current (ac), skin effect, and proximity effect, can cause nonuniform distribution of current, hence, increased resistance and decreased internal inductance. With stranded steel-cored conductors, the dc density within each section is inversely proportional to its resistivity. However, with ac at power frequency, the spiraling of the currents in the nonferrous layers causes a longitudinal magnetic flux in the steel core, which results in hysteresis and eddy current power loss in the core, and a circular magnetic flux in the nonferrous wires, which results in a nonuniform distribution of current density between the layers of nonferrous wires. These effects give rise to increased resistance and reduced internal inductance. The effects of current amplitude, frequency, temperature, and tensile stress on conductor properties are discussed.

Analysis and experiment of eddy current loss in Homopolar magnetic bearings with laminated rotor cores

This paper analyses the eddy current loss in Homopolar magnetic bearings with laminated rotor cores produced by the high speed rotation in order to reduce the power loss for the aerospace applications. The analytical model of rotational power loss is proposed in Homopolar magnetic bearings with laminated rotor cores considering the magnetic circuit difference between Homopolar and Heteropolar magnetic bearings. Therefore, the eddy current power loss can be calculated accurately using the analytical model by magnetic field solutions according to the distribution of magnetic fields around the pole surface and boundary conditions at the surface of the rotor cores. The measurement method of rotational power loss in Homopolar magnetic bearing is proposed, and the results of the theoretical analysis are verified by experiments in the prototype MSCMG. The experimental results show the correctness of calculation results.

A superconducting magnet mandrel with minimum symmetry laminations for proton therapy

The size and weight of ion-beam cancer therapy gantries are frequently determined by a large aperture, curved, ninety degree, dipole magnet. The higher fields achievable with superconducting technology promise to greatly reduce the size and weight of this magnet and therefore also the gantry as a whole. This paper reports advances in the design of winding mandrels for curved, canted cosine-theta (CCT) magnets in the context of a preliminary magnet design for a proton gantry. The winding mandrel is integral to the CCT design and significantly affects the construction cost, stress management, winding feasibility, eddy current power losses, and field quality of the magnet. A laminated mandrel design using a minimum symmetry in the winding path is introduced and its feasibility demonstrated by a rapid prototype model. Piecewise construction of the mandrel using this laminated approach allows for increased manufacturing techniques and material choices. Sectioning the mandrel also reduces eddy currents produced during field changes accommodating the scan of beam energies during treatment. This symmetry concept can also greatly reduce the computational resources needed for 3D finite element calculations. It is shown that the small region of symmetry forming the laminations combined with periodic boundary conditions can model the entire magnet geometry disregarding the ends.

Modeling of localized reflow in solder/magnetic nanocomposites for area-array packaging

We have modeled the reflow process of FeCo magnetic nanoparticle (MNP)-based solder composites with eddy current power loss of substrate and magnetic power losses of solder bumps. For an area array package without MNPs when subjected to 300 kHz ac magnetic field, the eddy current power loss can result in excessive temperatures that can cause substrate damage. Temperature profiles with different MNP concentration were simulated and the results showed localized reflow of solders to enable low-temperature assembly. The temperatures at different times and positions in solder composites were analyzed. We also modeled thermal profiles for solder composites with 0.2 wt. % MNP in 1 MHz and 3 MHz magnetic field. Such high field frequency generated larger power losses in MNPs and is shown to increase the heating efficiency.

Study of eddy current power loss in an RCS vacuum chamber

In a Rapid Cycling Synchrotron (RCS), power loss due to an eddy current on the metal vacuum chamber would cause heating of the vacuum chamber. It is important to study the effect for estimating eddy current induced power loss and temperature growth. Analytical formulas for eddy current power loss for various types of vacuum chambers are derived for dipole and quadrupole repectively. By using the prototype of dipole of CSNS/RCS, an experiment was done to test the analytical formula. The derived formulas were applied to calculating the eddy current power loss on some special structures of an RCS vacuum chamber.

Three-Dimensional–Two-Dimensional Coupled Model for Eddy Currents in Laminated Iron Cores

Eddy currents due to magnetic flux perpendicular to the sheets of a lamination iron core are represented on a number of 2D slice models, which are embedded in a 3D model of the entire device using a multi-scale technique. The choice of a different spatial resolution enables to attain an advantageous convergence of the discretization error for the eddy-current power losses, compared to a standard modelling technique using an anisotropic surrogate material.

A Measurement of HTS Cable Power Loss in a Sweeping Magnetic Field

Short sample HTS power cable composed of multiple 344C-2G strands and designed to energize a fast-cycling dipole magnet was exposed to a sweeping magnetic field in the (2-20) T/s ramping rate. The B-field orientation toward the HTS strands wide surface was varied from to -4° to 8°, in steps of 10. The test arrangement allowed measurements of combined hysteresis and eddy current power losses of the cable assembly. For the validity of these measurements, the power losses of a short sample cable composed of multiple LTS wire strands were also performed and compared with the known data. The test arrangement of the power cable is described, and the test results are compared with the projections for the eddy and hysteresis power losses using fine details of the test cable structures.