Hasil untuk "Electricity and magnetism"

Chaobo DAI, Guoliang ZHAO, Zhichang YANG et al.

It is required for grid-connected converters to obtain synchronous information quickly and accurately when a short-circuit fault occurs in the grid. Compared with the phase locked loop (PLL), the second order generalized integrator (SOGI)-frequency locked loop (FLL) promises faster detection of the phase, amplitude and frequency of the grid voltage, but becomes susceptible to the effect of a direct current (DC) offset. Modified schemes based on the suppression method and the filtering method have drawback of slower response. A modified scheme based on the subtraction method is proposed with an addition of a SOGI block in the FLL. The basic scheme based on SOGI-FLL, the modified scheme based on the suppression method and the proposed scheme based on the subtraction method are analyzed and compared by transfer functions theoretically and simulations of PSCAD commercial software. Comparison results illustrate that the subtraction-based scheme promises faster detection of the phase, amplitude and frequency of the grid voltage, and better suppression of the DC offset and low frequency components. Taking account of respective transient and steady-state response characteristics, the subtraction-based scheme has the best comprehensive properties.

C. A. S. Vieira, B. J. Santos, J. G. Duque et al.

The Iridium-based oxides are the subject of great recent interest due to the non-conventional physics that may emerge from the strong spin-orbit coupling present in 5d ions. Here, we explore the coupling between Ir and Co in the La2-xBaxCoIrO6 perovskites (x = 0, 0.5, 0.75 and 1.0), where the structural, electronic, and magnetic properties of the series are investigated by means of x-ray powder diffraction and magnetometry. The system's crystal structure evolves from the monoclinic P2_1/n to the triclinic I-1 space group as the Ba concentration increases. Measurements of magnetization revealed ferrimagnetic behavior in x = 0, 0.5 and 0.75 compounds, possibly resulting from antiferromagnetic coupling between Co2+/3+ and Ir4+. In contrast, for x = 1.0 a clear collinear antiferromagnetic character is observed for the Co2+ ions, resulting from the quenching of the Ir5+ magnetic moment. The evolution of the magnetic properties of the series is discussed in terms of the structural and electronic changes, as well as the spin-orbit coupling in Ir.

Shurui LIU, Peiqiang LI, Jiayu CHEN et al.

In the context of rapid development of clean energy, the stochasticity and volatility of wind power output have significant impacts on the stability of power system, so wind power fluctuation smoothing is a basic problem for the current clean energy development. A hybrid energy storage capacity allocation strategy based on SCNGO-VMD is proposed to smooth wind power fluctuations. After variational mode decomposition (VMD) of the wind power parameter optimization, the Pearson correlation analysis is used to judge the boundary points of strong and weak correlation, and the grid-connected power and hybrid energy storage power are obtained after two allocations; The hybrid energy storage power is allocated based on T-test frequency division (T-tFD) algorithm, and the capacity configuration of battery/ultra-capacitor is obtained. Based on this strategy, the annual comprehensive cost of energy storage components is used as the model to evaluate the economics through case study. And the fluctuation of grid-connected power and the superiority of the SCNGO are analyzed. The results show that the energy storage capacity allocation strategy based on SCNGO-VMD can effectively smooth wind power fluctuations. The maximum fluctuation of the smoothed grid-connected power for 1 minute and 10 minutes is only 18.2% and 45.52% of the national requirements, and the corresponding energy storage configuration cost is the lowest among traditional configuration strategies. The configured hybrid energy storage capacity is more economical. Meanwhile, it is verified that the SCNGO is superior to the traditional intelligent optimization algorithm in iteration speed and accuracy.

Chong Li, Feng Tian, Erwei Cheng et al.

Abstract An S‐band near‐field focused array is designed and implemented. Consisting of 4 × 4 metallic Vivaldi elements, the array is designed for focusing the E‐field of several kilovolts per metre within its near‐field region. To minimise the power loss and enhance the synthesis effectiveness, elements are arranged on a sphere surface and oriented towards the sphere centre. When exciting the elements, the waves will be focused to a specific area on the observation plane. By adjusting the excitation phase, the focus position can be tuned. A systematic analysis has been carried out to illustrate the focus scanning process across the entire observation plane. Near‐field two‐dimensional scanning is performed to measure the E‐field distribution of the array. While scanning the focus, the diameter of 3 dB focal area is about 0.3 m, and the maximum field strength in the focus ranges from 1184 to 2129 V/m, which can be used for the radiated susceptibility testing.

Joanna Marciniak, Mirosław Werwiński

In previous experiments, thin films of L1$\mathrm{_0}$ FeNi with different surfaces, including (001), (110) and (111), were produced and studied. Each surface defines a different alignment of the crystallographic tetragonal axis with respect to the film's plane, resulting in different magnetic anisotropies. In this study, we use density functional theory calculations to examine three series of L1$\mathrm{_0}$ FeNi films with surfaces (001), (010), and (111), and with thicknesses ranging from 0.5 to 3 nm (from 4 to 16 atomic monolayers). Our results show that films (001) have perpendicular magnetic anisotropy, while (010) favor in-plane magnetization, with a clear preference for the tetragonal axis [001]. We propose calling this type of in-plane anisotropy fixed in plane. A film with surface (111) and a thickness of four atomic monolayers has the magnetization easy axis almost perpendicular to the plane of the film. As the thickness of the (111) film increases, the direction of magnetization rotates towards a tetragonal axis [001], positioned at an angle of about 45$^{o}$ to the plane of the film. Furthermore, the magnetic moment of ultrathin films increases by a maximum of 5%, and the most significant changes in spin and orbital magnetic moments occur at a depth of about three near-surface atomic monolayers. The presented results could be useful for experimental efforts to synthesize ultrathin L1$\mathrm{_0}$ FeNi films with different surfaces. Ultrathin L1$\mathrm{_0}$ FeNi films with varying magnetic anisotropies may find applications in spintronic devices.

Muhammad Junaid, Wenqing Yu, Shuzhi Cao et al.

Abstract With the development of a distributed generation, direct current (DC) load and energy‐storage equipment, voltage‐source‐converter‐based medium‐voltage DC systems (VSC‐MVDC) have attracted more attention due to its low power consumption, high reliability, independent power control and so on. However, VSC‐MVDC has the problem of DC fault isolation, which requires the fast‐acting DC circuit‐breakers to isolate faulty lines and ensure low cost. This problem can be solved by coordinating resistive type superconducting‐fault‐current‐limiter (R‐SFCL) and integrated‐gate‐commutated‐thyristor (IGCT) based hybrid circuit breaker. Based on this, IGCT based superconducting DC circuit breaker (SDCCB) is proposed and analysed. Combining R‐SFCL with IGCT could realise large current limiting and interruption and ensure low cost. In addition, the IGCT based hybrid DC circuit breaker (IGCT‐HDCCB) is compared with the traditional insulated gate bipolar transistor (IGBT) based hybrid DC circuit breaker (IGBT‐HDCCB) to evaluate which circuit breaker is more suitable for VSC‐MVDC. The results show that, coordination based on R‐SFCL and SDCCB, the fault current is successfully limited from 17.6 to 2.1 kA, and then interrupted within 3.8 ms. In addition, IGCT‐HDCCB overcomes the disadvantage that IGCT has less interrupting capacity than IGBT, retains the advantage of low cost of IGCT and is more suitable for MVDC system.

Arun Kumar Jaiswal, Robert Eder, Di Wang et al.

With its potential for drastically reduced operation power of information processing devices, electric field control of magnetism has generated huge research interest. Recently, novel perspectives offered by the inherently large spin-orbit coupling of 5d transition metals have emerged. Here, we demonstrate non-volatile electrical control of the proximity induced magnetism in SrIrO3 based back-gated heterostructures. We report up to a 700 % variation of the anomalous Hall conductivity σ_AHE and Hall angle θ_AHE as function of the applied gate voltage Vg. In contrast, the Curie temperature TC = 100K and magnetic anisotropy of the system remain essentially unaffected by Vg indicating a robust ferromagnetic state in SrIrO3 which strongly hints to gating-induced changes of the anomalous Berry curvature. The electric-field induced ferroelectric-like state of SrTiO3 enables non-volatile switching behavior of σ_AHE and θ_AHE below 60 K. The large tunability of this system, opens new avenues towards efficient electric-field manipulation of magnetism.

Dongwook Kim, Seungyoung Ahn

A microrobot that could continuously receive both electrical energy and propulsion force from a wireless power transfer system would offer tremendous benefits. However, wireless powering systems produce a time-varying magnetic field that can be harmful if the generated magnetic field needed for microrobot movement is large. To limit exposure, power transfer efficiency must be enhanced. This paper derived and analyzed the magnetic force applied to a microrobot from a wireless power transfer system. Unlike previously introduced Lorentz force-based microrobot propulsion, the proposed method is independent of a wireless power transfer system’s frequency. Therefore, this frequency can be determined considering maximum power transfer efficiency. The theoretical analysis and simulation by numerical analysis were compared, and results were verified though actual fabrication and measurement. Analyses of the transmitting and receiving coils were conducted. The optimum force, with less than 9% discrepancy, was determined while achieving a 3.6% improvement in power transfer efficiency.

Ju Seong Park, Ji Hun Hong, Kang Wook Kim

A new design method for an ultra-wideband circularly polarized microstrip-fed monopole antenna with a ground defect is proposed in this paper. To achieve ultra-wideband circular polarization performance, a parallelogram-shaped ground defect is employed in the bottom layer. The analysis of the ultra-wideband axial ratio (AR) and the impedance bandwidth of the proposed antenna is performed both in the top and bottom layers. A semi-circular aperture is designed to achieve impedance matching in the 24–40 GHz frequency range. Then, the AR bandwidth is discussed considering the surface current distribution produced by the parallelogram-shaped ground defect to rote current in each orthogonal phase. A prototype of the proposed circularly polarized antenna with a 50% ultra-wide bandwidth (from 24 to 40 GHz), a 10-dB return loss, and a 3-dB AR was fabricated and measured. A 6-dBic right-hand circular polarization gain was also achieved.

Endre J. Szili, Bethany L. Patenall, Adrian Fellows et al.

The study compares how acetyl donor molecules tetraacetylethylenediamine (TAED) and pentaacetate glucose (PAG) improve the antibacterial efficacy of solutions activated with a low-temperature atmospheric-pressure argon plasma jet. Plasma activation of solubilised TAED and PAG produce solutions with different chemical compositions and oxidative potentials. Both acetyl donor molecules enhance the hydrogen peroxide (H₂O₂) concentration in solution with TAED being more effective compared to PAG. However, PAG is more effective at forming peracetic acid (PAA) from reaction of its acetyl donor groups with plasma generated H₂O₂. The enhanced oxidative potential of plasma activated TAED and PAG solutions were shown to significantly improve bactericidal activity against common wound pathogens Gram-negative <i>Pseudomonas aeruginosa</i> and Gram-positive <i>Staphylococcus aureus</i> compared to plasma activated water produced without acetyl donors. Furthermore, the oxidative capacity of plasma activated PAG was least affected by the bacterial oxidative defence enzyme catalase, attributed to the high concentration of PAA produced in this formulation. Overall, the above data show that acetyl donors may help improve next generation of antimicrobial formulations produced by plasma, which might help combat increasing problems of antimicrobial resistance.

Liangyuan Huang, Guoji Shen, Niaoqing Hu et al.

Induction motors are complex energy conversion systems across the domains of dynamics, electricity, and magnetism. Most existing models mainly consider unidirectional coupling, such as the effect of dynamics on electromagnetic properties, or the effect of unbalanced magnetic pull on dynamics, while in practice it should be a bidirectional coupling effect. The bidirectionally coupled electromagnetic-dynamics model is beneficial to the analysis of induction motor fault mechanisms and characteristics. This paper proposes a coupled electromagnetic-dynamic modeling method that introduces unbalanced magnetic pull. By using the rotor velocity, air gap length, and unbalanced magnetic pull as the coupling parameters, the coupled simulation of the dynamic and electromagnetic models can be effectively realized. Simulation results for bearing faults show that the introduction of magnetic pull induces a more complex dynamic behavior of the rotor, which in turn leads to modulation in the vibration spectrum. The fault characteristics can be found in the frequency domain of the vibration and current signals. Through the comparison between simulation and experimental results, the effectiveness of the coupled modeling approach and the frequency domain characteristics caused by the unbalanced magnetic pull are verified. The proposed model can help to obtain a variety of information that is difficult to measure in reality and can also serve as a technical basis for further research on nonlinear characteristics and chaos in induction motors.

V. I. Klyukhin, A. Ball, C. P. Berriaud et al.

The conceptual design study of a hadron Future Circular hadron-hadron Collider (FCC-hh) with a center-of-mass energy of the order of 100 TeV assumes using in the experimental detector the superconducting magnetic system with a central magnetic flux density of an order of 4 T. A superconducting magnet with a minimal steel yoke was proposed as an alternative to the baseline iron-free solenoids. In a present study, both designs are modeled with Cobham's program TOSCA and compared. All the main parameters are discussed.

C. S. Davies, J. H. Mentink, A. V. Kimel et al.

We review and discuss the process of single-shot helicity-independent all-optical switching of magnetization by which a single suitably-ultrafast excitation, under the right conditions, toggles magnetization from one stable state to another. For almost a decade, this phenomenon was only consistently observed in specific rare-earth-transition-metal ferrimagnetic alloys of GdFeCo, but breakthrough experiments in recent years have revealed that the same behavior can be achieved in a wide range of multi-sublattice magnets including TbCo alloys doped with minute amounts of Gd, Gd/Co and Tb/Co synthetic ferrimagnets, and the rare-earth-free Heusler alloy Mn$_2$Ru$_x$Ga. Aiming to resolve the conditions that allow switching, a series of experiments have shown that the process in the ferrimagnetic alloys GdFeCo and Mn$_2$Ru$_x$Ga is highly sensitive to the pulse duration, starting temperature and the alloy composition. We argue here that the switching displayed by these two very different ferrimagnetic alloys can be generally understood within a single phenomenological framework describing the flow of angular momentum between the constituent sublattices and from the sublattices to the environment. The conditions that facilitate switching stem from the properties of these channels of angular momentum flow in combination with the size of the angular momentum reservoirs. We conclude with providing an outlook in this vibrant research field, with emphasis on the outstanding open questions pertaining to the underlying physics along with noting the advances in exploiting this switching process in technological applications.

Bo Zhang, Qifeng Kuang, Hua Pang et al.

In this work, we present detailed $^{57}$Fe Mössbauer spectroscopy investigations of (Co$_{0.97}$$^{57}$Fe$_{0.03}$)$_{4}$Nb$_{2}$O$_{9}$ compound to study its possible magnetic structures. We have shown that the previously reported magnetic structures can not satisfactorily describe our low temperature Mössbauer spectra. Therefore, in combination with theoretical calculations, we have proposed a modulated helicoidal magnetic structure that can be used to simulate the whole series of our low temperature Mössbauer spectra. Our results suggest that the combination of previously reported different magnetic structures are only approximations of the average magnetic structure from our modulated helicoidal model. We anticipate that the proposed modulated non-collinear magnetic structure might shed light on the understanding of the complex magnetoelectric effects observed in this system.

Jin-bo YU, Cai ZHANG, Ze-ting ZHANG et al.

The intrinsically disordered alpha-synuclein (α-synuclein) directly affects mitochondrial dynamics, morphology and function, and is closely related to Parkinson's disease. Studying the interactions between α-synuclein and mimic mitochondrial membranes/intact mitochondria is an effective way to understand how α-synuclein affects mitochondria. It has been reported that α-synuclein interacts with the mimic inner membrane of mitochondria (IMM), but not with the outer membrane of mitochondria (OMM), and the N-terminal plays an important role in binding with the mitochondria. However, little is known about the positions of interaction. Here, the interactions between α-synuclein and intact mitochondria isolated from rat liver were investigated by nuclear magnetic resonance (NMR). It was found that, different from the previous report, α-synuclein interacted with the OMM and the first 60 residues of N-terminus were crucial for the binding. It was postulated that the interaction between α-synuclein and OMM might depend not only on the lipid composition of the membrane, but also on other factors which were not reflected in the mimic membrane, such as the curvature of membrane and/or other components of the OMM. Our study also indicated that NMR is an effective method for studying the interaction of proteins with intact mitochondria.

Yalin Wang, Jiandong Wu, Tao Han et al.

Abstract Form‐wound windings in electric machines designed for electric aircraft propulsion face reliability challenges due to the severe operating environment, such as high temperature and low pressure. This study proposes a forewarning method for insulation condition monitoring of form‐wound windings based on partial discharge (PD) and deep learning neural network. Three PD features are extracted from the PD profile, which provides information about physics‐of‐failure and reflects the degree of insulation degradation. An algorithm fusion extracted from auto‐encoder and long short‐term recurrent neural network is proposed to synthesize one failure precursor from these three features and make multi‐time‐step prediction through historical data to provide forewarning. An electrical and thermal accelerated ageing test is performed on the form‐wound windings at 0.2 atm to simulate working environment of electric aircraft. The proposed method is validated on the accelerated ageing dataset and shows better prediction accuracy than some existing time‐series prediction methods, indicating the advantages of the proposed method. Moreover, an on‐line hardware setup using a deep learning processor is recommended to implement the forewarning method. The proposed approach has the potential to be widely applied to other insulation systems and contribute to work on condition monitoring.

Marco Bosi, Albert-Miquel Sánchez, Francisco Javier Pajares et al.

This paper presents a study and proposes a new methodology to analyze, evaluate and reduce the overall uncertainty of instrumentations for EMC measurements. For the scope of this work, the front end of a commercial EMI receiver is chosen and variations due to tolerances, temperature and frequency response of the system are evaluated. This paper illustrates in detail how to treat each block composing the model by analyzing each discrete component, and how to evaluate their influence on the measurand. Since a model can have hundreds or even thousands of parameters, the probability distribution functions (PDFs) of some variable might be unknown. So, a method that allows to obtain in a fast and easy way the uncertainty of the measurement despite having so many variables, to then being able to evaluate the influence of each component on the measurand, is necessary for a correct design. In this way, it will be possible to indicate which discrete components have the most influence on the measurand and thus set the maximum tolerances allowed and being able to design a cost-effective solution. Furthermore, this works presents a methodology which can easily be extended and applied to estimate and compute the uncertainty for electromagnetic interferences, energy storage systems (ESS), energy production, electric machines, electric transports and power plants in general.

Yongqiang REN, Defu CHE, Shisen XU et al.

As the coal power still remains dominant in China's current energy structure, the highly efficient and clean IGCC technology has demonstrated a wide application prospect in China. In this paper, the process flow of air separation technology, coal gasification, the high-temperature purification, and combined cycle technologies of five typical IGCC power plants with installed capacity greater than 250MW are analyzed. Particularly, the overall objectives, development stages as well as system parameters and the operation of the Tianjin IGCC project are described, which is expected to have certain reference value for the future development of IGCC technology in our country.

Julan MING, Hengchang XU, Hongling ZHONG et al.

The detection of active chlorine content in the phosphate ester fire-resistant fluids is of great importance for the electro-hydraulic control system. In this paper, the principles, instruments and operating conditions of automatic potentiometric titration method to detect active chlorine content in the phosphate ester fire-resistant fluids are studied. The inter-laboratory experiments involving eight laboratories and five samples are conducted and the results are evaluated. In terms of repeatability and reproducibility, limit of detection, recovery rate and accuracy of measurement, the proposed automatic potentiometric titration testing method is capable of detecting the active chlorine content in the phosphate ester fire-resistant fluids with high accuracy and efficiency as well as fast analysis of measurement but simple sample treatment procedures and low requirements for instrument configuration. Therefore it can be promoted for practical usage in the field of power industry.

Aquil Ahmad, Srimanta Mitra, S. K. Srivastava et al.

Co2FeAl (CFA) nanoparticles (NPs) of different sizes were synthesized by chemical route. The effect of the size of NPs upon the structure and magnetization compared to its bulk counterpart was investigated. The structure and composition were determined from X-ray diffraction (XRD) and electron microscopy. XRD analysis shows that the samples are having single (A2-type) disordered phase. Magnetization measurements suggest that the samples are soft ferromagnetic in nature with very low coercivity. Enhanced magnetic properties like saturation magnetization, coercive force, retentivity, and Curie-temperature are observed with a decrease in particle size. The effect of particle size on hysteresis losses is also discussed. The smallest particles of size 16 nm exhibited the highest saturation magnetization and transition temperature of 180.73 emu/g and 1261 K, respectively. The origin of enhancement in the magnetization of Co2FeAl nano-alloy is attributed to the strong Co-Co exchange interaction due to disorder present in the systems.