AC Loss Research Articles

Parametric AC Loss Study on 7 MW Fully Superconducting Direct-Drive Wind Turbine Generators With Concentrated Stator Winding

Parametric AC Loss Study on 7 MW Fully Superconducting Direct-Drive Wind Turbine Generators With Concentrated Stator Winding

Calculation and Measurement of Transport AC Loss of ReBCO CORC Cables for Electric Aircraft

Calculation and Measurement of Transport AC Loss of <i>Re</i>BCO CORC Cables for Electric Aircraft

Modeling of AC Losses in DEMO RW2rutstab Conductor

Modeling of AC Losses in DEMO RW2rutstab Conductor

AC Loss Analysis of the Central Solenoid Charge and Discharge

AC Loss Analysis of the Central Solenoid Charge and Discharge

Comparison of AC Loss Reduction Methods Based on Striation of Ag-Stabilized REBCO Tapes

Comparison of AC Loss Reduction Methods Based on Striation of Ag-Stabilized REBCO Tapes

Experimental AC loss study on REBCO coil assemblies coupled with an iron cylinder

In high-temperature superconducting (HTS) power devices, the presence of iron cores changes the magnetic field profile around the HTS coil windings, potentially affecting their AC loss characteristics. AC loss measurements for HTS coil windings coupled with an iron core using the electrical method can lead to a significant error, owing to the indirect estimation of the iron core loss through using a copper test coil. To investigate the cause of the experimental error and the influence of an iron core on coil AC losses, transport AC losses of REBCO double pancake coil (DPC) assemblies coupled with an iron cylinder were measured. A 40-turn 1DPC and an 80-turn 2DPC assembly wound with 4 mm SuperPower wire were employed in the measurements. To ensure the same iron core loss using the HTS coil assembly and the copper coil, 2D finite element method simulations were conducted iteratively to design the iron core and the copper coil to get the same local magnetic field distributions in the designed iron core for the two cases. The main cause of the error is due to the difference in local magnetic flux densities in the iron core generated by the HTS coil assembly and the copper coil even when the ampere-turns of the coils are identical. We showed that the simulation-guided measurement method can assure accurate AC loss measurement in the HTS coil assemblies coupled with iron cores. Compared with the AC losses in the 1DPC and 2DPC coil assemblies without the iron cylinder, the presence of the iron cylinder significantly increases the coil losses. Frequency dependence is observed in the coil AC losses of the 1DPC and 2DPC assemblies when coupled with the iron cylinder. This is due to the eddy current induced in the iron cylinder generating a magnetic field, which influences the coil AC loss.

The Study of Multi-Terminal DC Systems in an Offshore Wind Environment: A Focus on Cable Ripple Analysis

This paper studies the THD and AC losses on the DC cables of offshore wind farm-based multi-terminal HVDC systems when they extract and deliver power from and to more than one connection point. In the paper, the study of a full system PLECS + Simulink model with two branches, including a wind resource, a wind turbine, a Permanent Magnet Synchronous Generator (PMSG), a Pulse Width Modulation (PWM) rectifier, a Single Active Bridge (SAB) DC–DC converter, an Input Parallel Output Series (IPOS) DC–DC converter, HVDC cables, and a simplified onshore system, is presented. It focuses on the investigation of the output ripple content of multiple DC–DC converters on DC cables under different wind conditions with different voltage and power ratings. The importance of the study is providing a general understanding of the operation of the innovative offshore wind farm-based DC system, as well as the interaction between different DC–DC converters and their influence on cable ripple content under different situations.

Study on the frequency response characteristic of superconducting/tunnel magnetoresistance composite magnetic sensors

The superconducting/tunnel magnetoresistance (TMR) composite magnetic sensor is expected to have great application prospects in the field of weak magnetic field detection due to its ultra-high detectivity. For some special applications such as bio-magnetic measurement, it is of necessity to study the frequency response characteristic. Therefore, a superconducting/TMR composite sensor was fabricated and its frequency response was systematically studied in this paper. Firstly, the sensitivity of composite magnetic sensors was found to decrease rapidly with the magnetic field frequency. After excluding the influence of the TMR device itself at different temperatures, the sensitivity decay with magnetic field frequency was attributed to the AC loss of the superconducting loop. Finally, the minimum detectable field of the composite magnetic sensor was obtained by combining the sensitivity and noise spectrum. The sensor exhibits superior magnetic field detectivity, particularly in the low-frequency range, which indicates the suitability for the application of bio-magnetic field detection.

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 on a 3-phase HTS 1 MVA transformer coupled with a three-limb iron core

High-temperature superconducting (HTS) technology provides an alternative approach to achieve compact transformers. Addressing AC loss in the HTS winding is crucial for HTS transformer applications. Most numerical AC loss studies on HTS transformers have neglected the influence of iron cores. This work carries out an AC loss study to explore the impact of an iron core on the HTS windings in a 3-phase HTS 1 MVA transformer coupled with it. AC loss simulations for the transformer winding both with and without the iron core are conducted by adopting the three-dimensional (3D) T-A homogenization method. When the iron core is incorporated, the saturation magnetic fields of iron materials, flux diverters (FDs) with different geometries, and variations in turn spacings in the LV winding composed of Roebel cables are considered to investigate their influence on the AC loss of the transformer winding. The inclusion of the iron core leads to a 1.2% increase in AC loss for the transformer winding while simulating at the rated current. We attribute this slight difference to the non-inductive winding structure of the transformer winding, where a strong magnetic field generated in the space between the LV and HV windings effectively shields the influence of the iron core.

Transmission Expansion Planning Considering Storage, Flexible AC Transmission System, Losses, and Contingencies to Integrate Wind Power

To meet future load projection with the integration of renewable sources, the transmission system must be planned optimally. Thus, this paper introduces a comparative analysis and comprehensive methodology for transmission expansion planning (TEP), incorporating the combined effects of wind power, losses, N-1 contingency, a FACTS, and storage in a flexible environment. Specifically, the optimal placement of the FACTS, known as series capacitive compensation (SCC) devices, is used. The intraday constraints associated with wind power and energy storage are represented by the methodology of typical days jointly with the load scenarios light, heavy, and medium. The TEP problem is formulated as a mixed-integer nonlinear programming (MINLP) problem through a DC model and is solved using a specialized genetic algorithm. This algorithm is also used to determine the optimal placement of SCC devices and storage systems in expansion planning. The proposed methodology is then used to perform a comparison of the effect of the different technologies on the robustness and cost of the final solution of the TEP problem. Three test systems were used to perform the comparative analyses, namely the Garver system, the IEEE-24 system, and a real-world Colombian power system of 93 buses. The results indicate that energy storage and SCC devices lead to a decrease in transmission requirements and overall investment, enabling the effective integration of wind farms.

Оптимизация ВТСП кабелей постоянного и переменного тока с учетом эффекта продольного магнитного поля

It is known that in magnetic fields parallel to the transport current, an increase of the critical current is observed in most low-temperature and high-temperature superconductors — the effect of a longitudinal magnetic field (LMFE). LMFE has been theoretically predicted and experimentally confirmed in many studies. This article presents various methods for optimizing power coaxial cables based on high-temperature superconductors (HTS), considering LMFE. LMFE provides a higher current-carrying capacity of HTS DC cables and higher stability for HTS power AC cables, including lower AC losses. The results of optimization of HTS cables for both DC and AC applications with consideration of LMFE are presented and discussed. Two methods for calculating the magnetic field in coaxial HTS cables are presented: analytical and using the finite element method. The results of AC loss calculations and measurements for HTS cables are also presented.

AC Loss Analytic Method and Optimization of Litz Winding for High-Speed Electrical Machines

AC Loss Analytic Method and Optimization of Litz Winding for High-Speed Electrical Machines

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.

AC Losses Analysis and Design Guidelines for Hairpin Windings With Segmented Conductors

In the last years, hairpin windings are amongst the most studied and implemented winding topologies to increase torque and power densities of electrical machines, especially in the traction field. However, their main drawback remains the elevated ohmic losses generated at high frequency operations. Recently, hairpin windings with segmented conductors have been proposed to overcome this challenge, but an analytical model to predict the losses in such unconventional winding is missing, as well as a critical analysis on the extra manufacturing complexities needed. In this paper, first a simple analytical formulation for the estimation of AC losses in segmented hairpin conductors is proposed, developed and validated at various operating frequencies, both through finite element analyses and experimental measurements. Then, an in-depth analysis of the main advantages and disadvantages of this winding topology is proposed with the aim at providing guidelines and recommendations for their practical realization, adopting standard methodologies for their connection and transposition.

Calculation of AC Loss in a High-Speed Coreless Axial-Flux Machine Under No Load and Load Conditions Using a Hybrid Method

Calculation of AC Loss in a High-Speed Coreless Axial-Flux Machine Under No Load and Load Conditions Using a Hybrid Method

Analytical Calculation and Experimental Validation of Litz Wires Axial Thermal Conductivity

Litz wires are widely used in electrical machines with reduced AC losses, compared to traditional random winding. The reduced AC losses can improve both electrical machines electromagnetic performance, such as efficiency and thermal performance. Thermal aspect is identified as a key enabler for next generation high power density electrical machines, where thermal modelling plays a critical role. Equivalent slot thermal conductivity is one of the most challenging parameters to be determined in the process of thermal model development, due to various components, such as copper, insulation, and impregnation resin. There are extensive literatures where the litz wire thermal conductivity in the radial direction are reported. However, the thermal conductivity in the axial direction is not well studied, which is critical to determine the heat transfer, such as for electrical machines with end winding spray-cooling system. In this paper, the axial thermal conductivity is investigated with analytical calculations and experimental validation. Firstly, 9 litz wire samples are selected with various types, such as rectangular and circular shapes, with varnish process and without. Two different analytical methods are then introduced and presented to calculate the litz wire thermal conductivity in axial direction, based on equivalent length theory and equivalent medium theory, respectively. Finally, experimental tests are conducted, and results are compared to those obtained from the proposed analytical methods. Guidelines are also provided to predict the litz wire axial thermal conductivity in this field.

Fast and accurate electromagnetic modeling of non-insulated and metal-insulated REBCO magnets

REBCO high-temperature superconductors are promising for all-superconducting high-field magnets, including ultra-high field magnets. Non-insulated (NI) and metal-insulated (MI) windings are a good solution for protection against electro-thermal quench. Design and optimization requires numerical modelling of REBCO inserts for high-field magnets. Here, we detail a fast and accurate two-dimensional cross-sectional model for the electromagnetic response of NI and MI coils, which is based on the minimum electro magnetic entropy production. Benchmarking with an A − V formulation method on a double pancake coil shows good agreement. We also analyse a fully superconducting 32 T magnet with a REBCO insert and a low-temperature superconducing outsert. In particular, we analyse the current density, the screening current induced field (SCIF), and the AC loss. We have shown that metal-insulated coils enable transfer of angular current in the radial direction, and hence magnet protection, while keeping the same screening currents and AC loss of insulated coils, even at relatively high ramp rates of 1 A s−1. Surprisingly, soldered coils with low resistance between turns present relatively low AC loss for over-current configuration, which might enable higher generated magnetic fields. The numerical method presented here can be applied to optimize high-field magnets regarding SCIF in MI or NI magnets. It also serves as the basis for future electro-thermal modelling and multi-physics modelling that also includes mechanical properties.

Numerical study on the electromagnetic characteristics of multi-layer CORC cables

Due to the high isotropy and low AC losses, the multi-layer conductor on round core (CORC) cable is a good candidate for high field magnets, such as central solenoid magnets in fusion. Considering the difficulty in experimental measurement, numerical model is an effective way to illustrate the electromagnetic characteristics of the multi-layer CORC cable and provide further insights into its working performance. In this work, a 3D finite element model based on H formulation is proposed to simulate a CORC cable with as many as 18 layers considering electromagnetic coupling. The validity of the model has been verified by experimental results. Based on the proposed model, the DC transport current distribution characteristics and charge-discharge loss characteristics of multi-layer CORC cables wound in the same and opposite winding directions are investigated respectively. This work can provide an important reference for the design of multi-layer CORC cables for high-current or high-field application.

Improved single‐layer powder core inductor design procedure for DC‐DC converters

AbstractOne of the early design decisions for DC‐DC converters is the choice of an appropriate magnetic core material. Powder cores in particular are suitable due to their saturation flux density of up to 1.5 T. However, high DC currents constitutes a significant problem since the winding cross‐section rises with the current, which consequently increases AC losses due to skin effects. Another challenge is the reduction of winding layers to decrease proximity losses. This paper presents an improved single‐layer winding design procedure for DC‐DC converter powder cores. The procedure determines the optimum number of parallel cores and stacks. This way, the procedure enables a predefined maximum wire cross‐section for copper loss optimisation and single‐layer winding. The introduced approach defines the optimum switching frequency as a trade‐off between core loss and core volume. Finally, experimental tests with two setups validate 27 kW DC‐DC converters and hence the design procedure using Si‐IGBTs and SiC‐MOSFETs. The results demonstrate that SiC‐MOSFETs reduce core volume by a factor of 3 compared to Si‐IGBTs. Further, the SiC setup reaches high efficiencies of up to 98.53% compared to 98.17% for the Si‐based converter.