AC Loss Analysis Research Articles

AC Loss Analysis of 35-kV Superconducting Cables Operating at Full Load

AC Loss Analysis of 35-kV Superconducting Cables Operating at Full Load

AC loss analysis on an HTS field winding of the generator with T-A formulation

In this study, we proposed a coupling model utilizing finite element software to estimate AC loss on the high-temperature superconducting (HTS) field winding of a 1 MW generator. The model comprises three distinct physical modules: rotating machinery and magnetic (RMM), electrical circuit (CE) and partial differential equation (PDE). These modules collaborate to resolve the generator's magnetic field distribution, rated output parameters and degree of current magnetization on the HTS field winding, employing Maxwell equations and T-A formulation. Given the placement of the HTS field winding on the rotor core, accurately calculating its loss in an electromagnetic field that varies both temporally and spatially presents a considerable challenge. To address this issue, we adjust the coordinate system within the PDE module to vary with the material rather than space. Our analysis reveals that the instantaneous AC loss of an HTS field winding comprises two primary components: the attenuation envelope and the oscillatory variation, resulting from the charging process and external harmonic magnetic fields. Additionally, we comprehensively discuss and analyze the influence of current excitation speed on instantaneous AC loss. Accurately estimating AC loss in HTS field windings is a critical and meaningful aspect of preliminary machine design. This study provides an essential reference for addressing this issue.

Analysis of AC Losses in KSTAR Superconducting PF Magnets at Low Current Ramp Rates

Analysis of AC Losses in KSTAR Superconducting PF Magnets at Low Current Ramp Rates

AC Loss and Thermal Analysis of a Curved DCT Super-Conducting Magnet for Carbon Ion Therapy

AC Loss and Thermal Analysis of a Curved DCT Super-Conducting Magnet for Carbon Ion Therapy

AC Loss Analysis of the Central Solenoid Charge and Discharge

AC Loss Analysis of the Central Solenoid Charge and Discharge

Optimization of HTS Transformer Parameters and Analysis of AC Losses Under Harmonic Conditions

Optimization of HTS Transformer Parameters and Analysis of AC Losses Under Harmonic Conditions

AC loss study of high-temperature superconducting stacked conductors based on parameter identification method

Fusion magnets generate significant AC loss during the processes of excitation and demagnetization. The electrical measurement was predominantly employed as the method for estimating the AC loss. However, the phase-locked amplifier method and integral method (IM) can access the average power across one or multiple current cycles but leave the instantaneous power value unrecorded. In this study, the AC loss of two types of high-temperature superconducting (HTS) stacked conductors composed of REBCO and Bi-2223 were measured. An AC loss analysis method based on parameter identification method is employed to study AC loss in REBCO and Bi-2223 stacked conductors by identifying their instantaneous inductance and instantaneous resistance. Unlike the integral method, the AC loss analysis method based on parameter identification method can analyze the average power, and also the instantaneous power at any given time using a fixed forgetting factor which can affect the accuracy of the calculation. The experimental data suggest that, under identical frequency and current, the AC loss of the REBCO stacked conductor is approximately three times that of the Bi-2223 stacked conductor.

Analysis of AC Losses in Flat-Wire Windings of Dual-Rotor Axial-Flux PM Machines with Segmented Stators

Analysis of AC Losses in Flat-Wire Windings of Dual-Rotor Axial-Flux PM Machines with Segmented Stators

Equivalent 2-D FEA Modeling Method for AC Loss Analysis of High-Speed Electrical Machines With Litz Winding Considering Incomplete Transposition

In high-speed electrical machines, litz wire shows great performance on reducing the AC loss under complete transposition, which is well-known. However, due to technological limitation, its pitch cannot be made to match the stack length in small aspect ratio machines, bringing significant AC loss. And 3D FEA modeling method is too complicated for its twisted structure and time-consuming. This paper proposed an equivalent 2D FEA modeling method for high-speed electrical machines with litz winding. The machine is divided into several parts along the axial equally, and each part is established by a 2D FEA model approximatively in which litz winding transposition is considered. All 2D models are connected in series in field-circuit coupling model. The influences of structural parameters on AC loss are also analyzed, providing guidance for the optimal design of litz winding in high-speed electrical machines.

AC losses calculation of parallel multi‐strand flat wire windings for automotive drive motor

AbstractAutomobile drive motor with flat wire winding has improved the slot fill factor and efficiency. However, under the current environment of drive motors development to high frequency and voltage, the increase in winding AC loss has weakened those advantages. Accurate analysis of AC loss and the design of high‐performance windings have become the key issues and difficulties in the design process of drive motors. Based on the winding AC loss generation mechanism, the authors propose a winding AC loss analysis method, which can effectively separate DC loss, eddy current loss, and circulating current loss. The method is used to analyse winding AC loss of 60 kW flat wire winding permanent magnet synchronous motor (PMSM). In addition, parallel multi‐strand flat wire windings are proposed to reduce the winding AC loss and eliminate the limitation of the magnetic load of the motor on the selection of winding layers. The AC loss of the parallel multi‐strand flat wire windings at different frequencies is calculated, which demonstrates the effectiveness of the proposed winding topology in reducing the winding AC loss. In addition, the correctness of the simulation model was verified through experiments, and the loss calculation method was verified through finite element analysis.

AC Loss Analysis in Superconducting Cables Carrying Characteristic and Noncharacteristic Harmonic Currents

Harmonic distortions - especially in current waveform - are the inherent nature of any power system such as urban grids, wind farms, electric aircraft, and other electrified transportation units that could change the AC loss value in High Temperature Superconducting (HTS) cables. The aim is to investigate the impact of non-sinusoidal currents with different integer-harmonics, inter-harmonics, and sub-harmonics on the AC loss characteristics of a 22.9 kV, 50 MVA HTS cable. This was accomplished by using an Equivalent Circuit Model (ECM). To do so, current waveforms containing different harmonic components were passed to the ECM of HTS cable. For evaluating the impact of distorted current waveforms on the AC loss of the HTS cable, the ECM was validated by means of Finite Element Method (FEM) in tape level. The results of validation phase have shown a good agreement between the AC loss value derived by ECM and those calculated by FEM published in literature. The results showed that when current waveform was distorted by harmonics, the value of AC loss was changed significantly with respect to variations of harmonic phase angle, order, and amplitude. Results also indicated that 5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> harmonic order has the highest impact on the AC loss value and could increase 6% to 80% of AC loss in comparison to pure sinusoidal current. Sub-harmonics and inter-harmonics could also increase the AC loss value to maximum 88% and 64% higher than that of sinusoidal condition.

An electromagnetic-thermal-mechanical analysis model for high temperature superconducting magnets

High temperature superconducting magnets are the core component of superconducting power devices, and their stability is the key factor that restricts the safe operation of superconducting power devices. In order to accurately and effectively evaluate the stability of superconducting magnets during operation, an electromagnetic-thermal-mechanical numerical simulation method for high temperature superconducting magnets is studied in this paper. Based on the model, the 150 kJ SMES magnet as case is studied, the magnetic field and current density distribution are solved during its operation, and its temperature rise, AC loss and stress analysis of the magnet are achieved. In addition, this work further analyses the critical current degradation of superconducting tapes in the 150 kJ HTS magnet under multi-field coupling, the dangerous region in operation is obtained and suggestions are put forward to avoid quench. The electromagnetic-thermal-mechanical model may provide an appropriate stability assessment with rapid and real-time calculations for high temperature superconducting magnets.

Performance Analysis of HTS Armature Axial Flux Magnetic Field Modulation Direct Drive Wind Generator

Axial flux electrical machine has higher power density than the radial flux electrical machine, showing a promising application in the field of offshore wind power generation. However, the conventional copper armature winding will suffer from severe joule loss when improving the electrical loading, resulting in that the further improvement of the power density of axial flux electrical machine is limited. In order to overcome the limitation of the electrical loading improvement of the copper armature winding, this paper uses the high-temperature superconducting (HTS) armature winding instead of the conventional copper armature winding, proposes an HTS armature axial flux magnetic field modulation direct-drive wind generator (HTSAAFFM-DDG). In this paper, the topology and operational principle of the proposed HTSAAFFM-DDG is clearly demonstrated. Meanwhile, the electromagnetic performances are carefully analyzed, including airgap magnetic field, basic electromagnetic characteristics, and AC loss analysis of the HTS armature winding. The research results show that the torque density of the proposed HTS armature axial flux machine can be 24% higher than that of the copper armature axial flux machine with the same size and topology. Besides, the superconducting (SC) shielding layer used in the proposed HTSAAFFM-DDG exhibits an excellent inhibition effect on the PM excited field, and can reduce the AC loss of the armature winding obviously.

$H$-$\phi$ Formulation in Sparselizard Combined With Domain Decomposition Methods for Modeling Superconducting Tapes, Stacks, and Twisted Wires

The growing interest in the modeling of superconductors has led to the development of effective numerical methods and software. One of the most utilized approaches for magnetoquasistatic simulations in applied superconductivity is the $H$ formulation. However, due to the large number of degrees of freedom (DOFs) present when modeling large and complex systems (e.g. large coils for fusion applications, electrical machines, and medical applications) using the standard $H$ formulation on a desktop machine becomes infeasible. The $H$ formulation solves the Faraday's law formulated in terms of the magnetic field intensity $\mathbf{H}$ using edge elements in the whole modeling domain. For this reason, a very high resistivity is assumed for the non-conducting domains, leading to an ill-conditioned system matrix and therefore long computation times. In contrast, the $H$-$\phi$ formulation uses the $H$ formulation in the conducting region, and the $\phi$ formulation (magnetic scalar potential) in the surrounding non-conducting domains, drastically reducing DOFs and computation time. In this work, we use the $H$-$\phi$ formulation in 2D for the magnetothermal (AC losses and quench) analysis of stacks of REBCO tapes. The same approach is extended to a 3D case for the AC loss analysis of a twisted superconducting wire. All the results obtained by simulations in Sparselizard are compared with results obtained with COMSOL. Our custom tool allows us to distribute the simulations over hundreds of CPUs using domain decomposition methods, considerably reducing the simulation times without compromising accuracy.

Analysis for AC Loss by Electromagnetic Disturbance in HTS Magnet for Maglev Train

Research on Hyper Tube, a Korean high-speed HTS Maglev train, has reached the verification stage for actual operation, and electromagnetic dynamic characteristics analysis of the train is required accordingly. Depending on the winding type of the propulsion armature, the HTS magnet experiences the harmonic that causes AC loss. Beside the static thermal losses by thermal conduction, current leads et al., the AC loss should be take account for the thermal battery design depending on operation conditions. This study describes the AC loss analysis of the HTS magnet induced by the harmonic using the homogeneous <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T-A</i> formulation widely used in recent. In consideration of acceleration and cruise conditions, the effect of the AC loss by harmonics on the capacity of the solid nitrogen thermal battery was discussed.

AC Loss Analysis and Measurement of a Hybrid Transposed Hairpin Winding for EV Traction Machines

To address the problem of high-frequency AC loss of hairpin winding, a hybrid transposed hairpin winding (HTHW) scheme, which combines flat wire and litz wire, is proposed. The HTHW can effectively reduce the high-frequency AC loss, while maintaining a relatively high slot fill factor. In this paper, the AC loss generation mechanism under high-frequency excitation is firstly analyzed. Then, based on the field-circuit-coupled finite element method, the current density distribution and AC loss of hairpin winding with different transposed topologies are calculated and compared. Finally, an experimental platform enabling direct measurement of hairpin winding loss is built to verify the simulation. The simulation and experimental results show that the AC loss of the proposed HTHW is much lower than that of the traditional hairpin winding, for medium to high running frequency. In our case, the AC and DC resistance ratio of the presented HTHW is 2.12 at the frequency of 1200 Hz, contrasting that of the ratio of traditional hairpin winding, which is 10.2.

AC Loss Analysis and Modular Cryostat Design of a 10-MW High-Temperature Superconducting Double Stator Flux Modulation Machine

Superconducting (SC) machines are one of the best candidates for large-scale direct-drive wind power generation because of its high torque density. In a traditional SC synchronous machine, either armature windings or field windings need to rotate, which makes the structure of the machine complicated. To solve this problem, a high temperature superconducting (HTS) double stator flux modulation (DSFM) machine was proposed. In this machine, the armature windings and SC field windings are placed in outer stator and inner stator, respectively, and the machine works through flux modulation effect by reluctance rotor. Due to modulation effect, there is a high content of harmonic in this machine. Thus, it is important to analyze harmonics influence on SC coils, especially the SC coils ac loss. In this article, the losses of a 10MW HTS-DSFM machine are calculated and analyzed. It turns out that the ac losses of SC coils in this machine is higher compared with the traditional SC synchronous machine. From analytical calculation, the ac magnetic field perpendicular to the tape surface have strong impacts on the SC coils. In order to reduce the ac losses, some suppression methods are adopted on machine structures and SC thermostat. Then, cryostats are designed and the cooling budgets are evaluated. At last, the comprehensive performances of the machine are calculated and its economy in the long term is verified.

Analysis and Mitigation of AC Losses in High Performance Propulsion Motors

In this paper, the AC copper losses in classical random windings are investigated and mitigated using several techniques across a range of permanent magnet synchronous motor designs. At high operating frequencies, AC copper losses can represent a substantial share of the total loss in electrical machines, thus, reducing the machine’s overall performance, and increasing the thermal loading. Recently, different approaches for modelling AC copper losses have been proposed. This paper utilises simulation software to quantify the expected AC losses in six different propulsion motor designs. The motor designs are then modified to reduce the AC winding losses through the implementation of five different methods. Using two-dimensional finite element analysis, the magnetisation direction, magnet to airgap ratio, copper stranding, magnetic wedges and the motor slot openings are modified to reduce AC losses. The paper considers distributed, fractional, slot and concentrated windings, and the results show promising reductions across these different winding configurations.

Development of a Roebel structure transposed cable with in-plane bending of REBCO tapes

A compact High Temperature Superconductor (HTS) cable that can carry large current is crucial for developing high field superconducting accelerator magnets. Herein, we are reporting a high current and low AC loss REBCO cable that adopts the Roebel structure, but it is implemented by in-plane bending stacked REBCO tapes directly to realize the transposition, instead of by punching REBCO tapes to the desired shape. The cable maximizes the utilization of the original REBCO tapes, so that the material cost is significantly reduced comparing with the present “Roebel” REBCO cable. Recently, a prototype cable has been successfully fabricated. The critical current of each REBCO tape after cabling shows no degradation, and the cable’s measured critical current is 1939.8 A at 77 K and self-field, which is very close to the predicted critical current by simulation. Calculations also show that the AC loss of the cable is lower compared with that of a simple REBCO stack with the same cross-section and current-carrying capacity. In this paper, we first introduce the fabrication process of the cable. What follows is the measurement of the in-plane bending performance of REBCO tapes. Then, we present the design and fabrication of the prototype cable together with current-carrying performance tests. Finally, the AC loss calculation and analysis of the cable are reported.

Computationally Efficient Stator AC Winding Loss Analysis Model for Traction Motors Used in High-Speed Railway Electric Multiple Unit

The aim of this proposed work is to develop a computationally efficient and accurate AC winding loss analysis model for the traction motors for use in high-speed railways (HSRs). The goal of the model is to be able to study AC winding loss under both sinusoidal and pulse width modulated (PWM) inverter voltage sources. The traction motor model considered for the proposed study is a form wound winding permanent magnet (PM) assisted synchronous reluctance motor (PMaSynRM). The traction motor uses an open slot with two-layer winding. First, a flux linkage table is built using finite element analysis (FEA) with sinusoidal current as the input. The machine model then includes the effect of the PWM inverter voltage source with the current controller. For the AC winding loss analysis, the fundamental component and the harmonics due to PWM are considered separately. To find the loss due to the fundamental component only, the vector potential of the slot region is mapped to the subconductors of the form wound winding and the eddy current distribution and the AC winding loss are calculated. The effect of the harmonics due to the PWM switching is then added in the post-processing stage by analytically evaluating the individual harmonic effect. The whole AC loss analysis model proposed in this work is computationally more efficient than the conventional FEA because the transient state of the system is removed. Moroover, the PWM voltage source effect is divided into the effects of the fundamental component and switching harmonics by combining the vector potentia mapping and post-processing analytical calculation.