1,721,075 research outputs found
A novel technique for online monitoring of photovoltaic devices degradation
No full textA novel methodology to assess the degradation of a photovoltaic module is presented. The degradation of the module can be represented by a progressive alteration of the equivalent One-Diode circuit model for the device. The involved circuit elements are the series and shunt resistances. It is possible to estimate the alterations for these elements by measuring the divergence between the model and the device behaviour. Two novelties are the key aspects of this work. First, the model is identified through a very accurate procedure. Second, the irradiance is estimated directly by means of the photovoltaic device, without need for additional sensors. The result is a completely on-line estimation of the module degradation that does not require any change in the operating point
An Overview of Non-Destructive Testing of Goss Texture in Grain-Oriented Magnetic Steels
No full textGrain oriented steels are widely used for electrical machines and components, such as transformers and reactors, due to their high magnetic permeability and low power losses. These outstanding properties are due to the crystalline structure known as Goss texture, obtained by a suitable process that is well-known and in widespread use among industrial producers of ferromagnetic steel sheets. One of the most interesting research areas in this field has been the development of non-destructive methods for the quality assessment of Goss texture. In particular, the study of techniques that can be implemented in industrial processes is very interesting. Here, we provide an overview of techniques developed in the past, novel approaches recently introduced, and new perspectives. The reliability and accuracy of several methods and equipment are presented and discussed
Modeling of hysteresis in magnetic multidomains
No full textIn this paper, the analysis of multi-domain nanostructures is made by means of numerical approaches. The Landau-Lifshitz-Gilbert LEG equation is used to compute the magnetic hysteresis loops for different alternate scalar polarizations. The data computed are then used to identify the parameters of a phenomenological model, based on the extension of the Preisach model in 2-D. The identification in this case is the evaluation of the size and the position of the hysterons in the H-plane. Each hysteron is associated to a domain of the nanostructure and the assembly of hysterons reproduces with satisfactory accuracy the hysteretic behavior of the nanostructure computed by the LLG equation with an extremely reduced computational time Some possible relationships between the magnetization nanostructure and the parameters of the hysteron are suggested. These relationship should be used for a "blind" prediction of the magnetization state of much larger magnetic structures, whose computation using the LLG equation is not possible in practice due to the enormous computational time, supposing that magnetic structures with the same aspect ratio exhibit a similar distribution of magnetic domains. The theory is applied here to an example of Permalloy nanostructure
Numerical simulations of vector hysteresis processes via the Preisach model and the Energy Based Model: An application to Fe-Si laminated alloys
No full textThe paper presents the state of the art and the problems already open in modelling the hysteresis phenomenon in 2-D for laminated soft ferromagnetic materials. Firstly, a thorough experimental investigation has been carried out at a very low frequency by a single disk tester (SDT) for a specimen of innovative NGO electrical steel sheet. Scalar, rotational and elliptic magnetization processes have been experimentally measured under controlled waveforms of the magnetic induction vector thanks to an effective digital feedback algorithm. Two numerical model of hysteresis have been taken into account to reproduce the measured magnetization processes: the vector Preisach model (VPM) and the Energy Based Model (EBM). The main advantages and limitations in the use of the two hysteresis models are comprehensively analysed and discussed, taking into consideration both the problem of identification and the simulation results. In particular, the effective capability of the models to reproduce the vector field trajectories and to predict the hysteresis power losses has been shown. Conclusive considerations involve the memory usage and the computational time for the low level of abstraction implementation of the two hysteresis models
Micromagnetic simulations of linewidth and nonlinear frequency shift coefficient in spin-torque nanoscillators
No full textThe dependence of the linewidth on the temperature and the applied magnetic field angle is studied in spin torque nano-oscillators (STNO) by means of full micromagnetic simulations. Linewidth behavior increases with the temperature in agreement with the analytical predictions by Tiberkevic et al. [Phys. Rev. B, 78, 092401 (2008)] and its slope depends on the applied field angle. Also, the nonlinear frequency shift coefficient, which gives a measure of the nonlinearity degree of STNO and indicates the strength of the transformation of amplitude into phase fluctuations, is foun
Pattern search approach to ferromagnetic material modelling
No full textThis paper deals with possible optimization-based techniques for the identification of the parameters of Preisach-inspired phenomenological model of vector hysteresis in ferromagnetic materials. After a summary of the key features of the phenomenological model mentioned above, the description of the identification technique proposed is given. The identification technique is based on a suitable pattern search algorithm and standard measurements. Results for the FeSi Non-Oriented Grains steel NOG are presented and discussed
Design procedures for series–series wpt systems: A comparative analysis
No full textThe Series–Series (SS) compensation is one of the most commonly employed topologies for enhancing the efficiency of Wireless Power Transfer (WPT) systems. In this topology, two capacitors are connected in series with the transmitter and receiver coils. Currently, in the literature, these capacitors are tuned to resonate with the self-inductance of the coils at the nominal frequency. Anyway, analyzing the circuit, another interesting possibility emerges: the calibration of the capacitors to resonate with the leakage inductances of the coupled coils. This approach, currently not investigated in the literature, leads to a system with significantly different characteristics. A comparative analysis between these two methods is lacking in the literature. Therefore, this paper aims to fill this gap by proposing an in-depth comparison between the two design procedures, with the aim of providing useful insights to designers in selecting the most appropriate design technique for their application. The analysis includes both steady-state and transient conditions. In particular, the input impedance, voltage transfer function and the transmission efficiency at different frequencies and coupling coefficients are compared. The theoretical results are validated experimentally. The results obtained are extremely interesting and are particularly useful for selecting the most appropriate sizing technique for a given application during the design phase
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