Symmetric Components Research Articles

A novel adaptive frequency extraction method for fast and accurate connection between inverters and microgrids

Renewable energy is being rapidly developed and extensively utilized, which are commonly interfaced to the microgrids through the inverters. Therefore, the proper and fast extraction of the synchronous phases, frequency and amplitudes of the sequence voltages have brought major requirements under unbalanced and distorted microgrid voltage. In this regard, this paper presents a novel adaptive frequency method to improve the instantaneous sequence components detection method, which can significantly improve the accuracy of positive and negative sequence voltages. Based on the symmetric component method and the virtual vector construction module, the positive and negative sequence voltages with errors are calculated. The harmonic suppression module filters out the harmonics and random noise in the sequence voltages with errors. Then, the real-time difference frequency phase information of the sequence voltages is obtained by the difference frequency adjustment. With the closed-loop control of the difference frequency phase information, the microgrid frequency can be quickly and accurately obtained. The frequency information is fed back to the virtual vector construction module and the harmonic suppression module to obtain the frequency, amplitudes and synchronous phases of the positive and negative sequence voltages for inverter control in unbalanced and distorted microgrids. When the microgrid frequency changes greatly, the frequency detection module of this method can improve the accuracy of obtaining the positive and negative sequence voltages. Simulation results show that the proposed method can quickly and accurately capture the real-time sequence voltages in the three-phase asymmetric and distorted environment, and the validity and robustness of the proposed method are verified.

Forecasting exchange rates with elliptically symmetric principal components

We extract elliptically symmetric principal components from a panel of 17 OECD exchange rates and use the deviations from the components to forecast future exchange rate movements, following the method in Engel et al. (2015). Instead of using standard factor models, we apply elliptically symmetric principal component analysis (ESPCA), introduced by Solat and Spanos (2018), which captures both contemporaneous and temporal co-variation among the exchange rates. We find that ESPCA is more accurate than forecasts generated by existing standard methods and the random walk model, with or without including macroeconomic fundamentals.

ПРОДОЛЬНОЕ СОПРОТИВЛЕНИЕ ОДНОЦЕПНОЙ ЛЭП С ДВУМЯ ГРОЗОЗАЩИТНЫМИ ТРОСАМИ В ЗАДАЧЕ ДИСТАНЦИОННОГО ОМП

One of the most important tasks in remote fault location in a 110 kV+ network is modeling the power lines taking into account the electromagnetic and electrostatic interaction of their conductive elements. A common approach is to use the mathematical models recommended by the guidelines for calculating short-circuit currents for relay protection. However, these models of power transmission lines take into account the geometric mean distance between the wires and the lightning protection cables, which means they average the values of the mutual induction impedances. In cases where wires and cables are located asymmetrically relative to each other, this leads to an overestimation of the zero-sequence impedance of power lines and, as a consequence, to an underestimation of the single-phase short-circuit current. This situation can affect the results of remote fault location. To eliminate this drawback, the article proposes a combined equivalent circuit for a single-circuit power transmission line with two lightning protection cables, based on a combination of methods of phase coordinates and symmetric components. The given equivalent circuit of power transmission lines allows calcula¬ting the mode parameters using the method of symmetric components and, at the same time, simulating those of interest for calculating power lines using phase coordinates.

Uticaj zaštitnih užadi na aktivnu otpornost i reaktansu visokonaponskih nadzemnih vodova

In this paper, the influence of ground wires on the resistance and reactance (longitudinal impedance) of high voltage overhead power lines (OPLs) is considered and the method for its calculation is described in detail. This is important considering the power flow calculation and the design of the protection system of OPLs, especially those which use distance relays. In addition to symmetric, asymmetric operating conditions of OPLs are also studied, for the analysis of which symmetric components are used. Specifically, this meant the calculation of longitudinal impedances of OPL for positive, negative and zero sequences in each considered case. Special attention is paid to the symmetric system with zero sequences, because the influence of ground wires on the change of longitudinal impedance of OPLs is the greatest in that case. The cases of OPLs with one (110 kV OPL) and two (400 kV OPL) ground wires are considered, using the values o f their parameters that can be found in real systems. Values of longitudinal impedances, obtained with and without ground wires influence or the influence of some of their parameters, are compared, based on which appropriate conclusion is made.

The prevalence of posterolateral tibial baseplate overhang: An anatomical CT study

IntroductionTotal Knee Arthroplasty (TKA) is used in patients with osteoarthritis who have failed conservative management to reduce pain, improve functional outcomes and ultimately quality of life. However, less than optimal patient satisfaction has led to continued improvements in design and technology of TKA. One factor that can limit patient satisfaction is postero-lateral overhang of the tibial baseplate. The purpose of our study is to utilize pre-operative CT scans to assess the prevalence of posterolateral tibial overhang with the use of a symmetric tibial baseplate component in a popular knee system with robotic assistance. MethodsNinety-eight (98) consecutive patients who underwent robotic-assisted total knee arthroplasty (TKA) were included in this study. Using both the most medial aspect of the tibial tubercle and the medial ⅓ of the tibial tubercle as reference points, we quantified the extent of posterolateral overhang when determining the rotation of the tibial component. ResultsUsing the most medial aspect of the tibial tubercle as a reference point for rotation of the tibial baseplate, 63% of the instances of reviewed CT scans (369/588) had posterolateral overhang. Furthermore, 81% (406/588) had posterolateral overhang when using the medial ⅓ aspect of the tibial tubercle as the reference for rotation of the tibial baseplate. The average posterolateral tibial baseplate overhang was 1.5 mm (range 0–8 mm) when using the most medial aspect of the tibial tubercle and 2.4 mm (range 0–8 mm) when using the medial ⅓ tibial tubercle as the centering point for the tibial baseplate. DiscussionTibial baseplate overhang could lead to potential pain from irritation of soft tissues. To our knowledge, this is the first study that was able to valencquantify the amount of tibial baseplate overhang using pre-operative CT scans. Rotational alignment of the tibial baseplate needs to be balanced to ensure minimal lateral overhang while achieving sufficient external rotation of the tibial component. An asymmetric tibial component may provide a compromise in certain situations. Level of evidenceDiagnostic level IV case series.

An Angular Speed and Position FLL-Based Estimator Using Linear Hall-Effect Sensors

This paper proposes using a frequency-locked loop-based detector to estimate rotational speed and angle position for an electric machine rotor shaft. The measurement system consists of arrays of permanent magnets fixed to the rotor shaft together with linear Hall-effect sensors attached to a fixed frame. Parametric uncertainties on the sensor assembly lead to significantly noisy signals, exhibiting unbalance and harmonic distortion. To accurately estimate rotational speed and angle, it is proposed to use a frequency-locked loop scheme based on a fourth-order harmonic oscillator (FOHO) to allow the processing of the symmetric components, thus dealing with the unbalance. The scheme also includes an adaptive law to reconstruct the fundamental frequency. Moreover, a harmonic compensation mechanism comprising parallel FOHOs is included; each FOHO is tuned at the spectral component under concern for its cancellation. The proposed algorithm delivers a clean estimate of the positive sequence fundamental component despite the disturbances at the signals provided by the Hall-effect sensor, which is used to reconstruct the rotation angle. The described approach could enhance low-cost sensing solutions in applications where position feedback is mandatory and sensorless control is impossible, not requiring special installation considerations.

Study on Power Quality Evaluation of Traction Power Supply System of High-speed Railway

With the continuous development and progress of China's high-speed railway system, the power supply of high-speed railway has become an important load of the power system. The introduction of large load will bring certain voltage fluctuation, harmonic interference and other random problems to the power system. In this paper, the positive sequence, negative sequence and zero sequence component models of current and voltage are established to solve the problem of equivalent modeling for power quality assessment of high-speed railway power supply system. Firstly, the positive sequence, negative sequence and zero sequence component models of current and voltage based on symmetric component method are established. Through Fourier transform, the phase Angle of fundamental wave is solved, and the positive sequence, negative sequence, zero sequence component, sequence component diagram and current spectrum diagram of current and voltage under three actual working conditions are obtained Through the analysis of the whole train operation process, the amplitude graphs of the positive sequence, negative sequence and zero sequence components of the current and the curves of the third harmonic possession with time are obtained by using the above methods.

An Improved Detection Algorithm of Three-phase Unbalanced Voltage Sag Detection Method for Improving Power Supply Reliability

With the popularization of high-power power electronic switching equipment and the technical update of electrical equipment, voltage sags have become a major problem affecting power quality, which seriously affects the reliability of power supply in power systems. In the case where the voltage sags failure cannot be avoided, rapid and accurate detection of the voltage sag has become a key technology for improving the reliability of the power supply of the power system. Based on the symmetrical component method, an improved detection algorithm for three-phase unbalanced voltage sag is proposed in this paper, which can significantly improve the detection speed and the reliability of power supply. The method firstly constructs the virtual orthogonal signal of the grid voltage and uses the symmetric component method to realize the fast and accurate extraction of the positive and negative sequence components of the grid voltage fundamental. In addition, an improved method for constructing virtual orthogonal signals is proposed in this paper, which effectively improves the accuracy of the constructed orthogonal signals. Finally, the feasibility and priority of the improved detection method have been verified by MATLAB/Simulink.

Устранение несимметрии трехфазного напряжения с помощью твердотельного трансформатора в интеллектуальных сетях электроснабжения

The use of nonconventional power supplies featuring unstable quality of the electricity produced and fluctuations in the output power, on the one hand, and the availability of various consumers connected to power supply grids, on the other hand, are factors that give rise to phase unbalances in the grids. These circumstances complicate the operation of smart grids, especially in microgrids. One of possible ways to improve the quality of smart power supply grids is to use a three-stage solid-state transformer with galvanic isolation and two DC links, an arrangement that makes it possible to connect power supply sources and consumers, and to arrange backup storage of electricity in storage batteries. The aim of the study is to analyze the electric power quality at the output of a three-stage solid-state transformer powered by an unbalanced three-phase voltage source. The study was carried out by numerical modeling using the Matlab/Simulink software package. The modeling parameters are given, and the current and voltage waveforms at the solid-state transformer output are obtained. Phasors of the input and output voltages are constructed with expanding them into zero-, positive-, and negative sequence harmonic components. The harmonic distortion coefficients for current and voltage in each phase, and the voltage unbalance coefficients for the zero and negative sequences at the solid-state transformer input and output are determined using the method of symmetric components. It has been shown that by using solid-state transformers it becomes possible to obtain noticeably better quality of electric energy and eliminate the unbalance to the levels stipulated by the relevant state standard. It is shown that solid-state transformers are a promising technology as part of smart power supply grids, which opens the possibility to control and adjust power supply parameters, improve the power supply quality, distribute power flows between the sources and consumers, and integrate DC and AC grids of various voltage and power levels.

Convolutional neural network with group theory and random selection particle swarm optimizer for enhancing cancer image classification.

As an epitome of deep learning, convolutional neural network (CNN) has shown its advantages in solving many real-world problems. Successful CNN applications on medical prognosis and diagnosis have been achieved in recent years. Their common goal is to recognize the insights from the subtle details from medical images by building a suitable CNN model with maximum accuracy and minimum error. The CNN performance is extremely sensitive to the parameter tuning for any given network structure. To approach this concern, a novel self-tuning CNN model is proposed with a significant characteristic of having a metaheuristic-based optimizer. The most optimal set of parameters is often found via our proposed method, namely group theory and random selection-based particle swarm optimization (GTRS-PSO). The insights of symmetric essentials of model structure and parameter correlation are extracted, followed by the hierarchical partitioning of parameter space, and four operators on those partitions are designed for moving neighborhoods and formulating the swarm topology accordingly. The parameters are updated by a random selection strategy at each interval of partitions during the search process. Preliminary experiments over two radiology image datasets: breast cancer and lung cancer, are conducted for a comprehensive comparison of GTRS-PSO versus other optimization algorithms. The results show that CNN with GTRS-PSO optimizer can achieve the best performance for cancer image classifications, especially when there are symmetric components inside the data properties and model structures.

Моделювання асиметричних динамічних режимів трифазних трансформаторів

The paper analyses the aspects of the need to research the dynamic modes of transformers, which are the most important element of power grids. The types of mathematical models that are used to research the dynamic modes of transformers are considered. Arguments in favour of 3-axial mathematical models are presented, which have wider possibilities for modelling various operating modes. The paper aims to determine a universal variant of a mathematical model suitable for studying asymmetric operating modes of a transformer. The paper proposes a variant of a 3-axial mathematical model based on a generalized electric machine model. A modernized variant of the model was used, which takes into account the power losses in the magnetic core. To be able to model asymmetric modes with its help, a phase-by-phase separation of parameters was performed and the corresponding calculated coefficients were introduced. The equations of currents are presented taking into account the phase-by-phase separation of their parameters. For the proposed model, transients for one symmetric (switching on the transformer at full load) and two asymmetric (switching on when a short circuit in one phase and switching on when phase failure) modes were calculated. As sources of asymmetry, the accidents in the secondary circuit of the transformer were considered. Modelling was performed on alternating current. The analysis of the obtained curves showed that the proposed model and methods of its application make it possible to adequately model a wide spectrum of dynamic modes of a transformer without the need to use the decomposition of asymmetric systems of quantities into a set of symmetric components, which essentially simplifies the modelling process. The analysis of asymmetric modes showed that they are characterized by an asymmetry of the transformer currents in amplitude and angle, and in the case of a phase failure, a significant difference in the pattern of currents in the primary and secondary windings is observed.

Charge-spin conversion signal in WTe2 van der Waals hybrid devices with a geometrical design

The efficient generation and control of spin polarization via charge-spin conversion in topological semimetals are desirable for future spintronic and quantum technologies. Here, we report the charge-spin conversion (CSC) signals measured in a Weyl semimetal candidate WTe2-based hybrid graphene device with a geometrical design. Notably, the geometrical angle of WTe2 on the graphene spin-valve channel yields contributions to symmetric and anti-symmetric CSC signal components. The spin precession measurements of the CSC signal at different gate voltages and ferromagnet magnetization show the robustness of the CSC in WTe2 at room temperature. These results can be useful for the design of heterostructure devices and in the architectures of two-dimensional spintronic circuits.

Size and shape regulation during larval growth in the lepidopteran Pieris brassicae.

By adopting a longitudinal study design and through geometric morphometrics methods, we investigated size and shape regulation in the head capsule during the larval development of the cabbage butterfly Pieris brassicae under laboratory conditions. We found evidence of size regulation by compensatory growth, although not equally effective in all larval stages. Size compensation is not attained through the regulation of developmental timing, but rather through the modulation of per-time growth rate. As for the shape, neither the variance of the symmetric component of shape, nor the level of fluctuating asymmetry show any evidence of increase across stages, either at the population or individual level, which is interpreted as a mark of ontogenetic shape regulation. In addition, also the geometry of individual asymmetry is basically conserved across stages. While providing specific documentation on the ontogeny of size and shape variation in this insect, this study may contribute to a more general understanding of developmental regulation and its influence on phenotypic evolution.

Virtual Damping Control Design of Three-Phase Grid-Tied PV Inverters for Passivity Enhancement

The interconnection stability of a grid-tied inverter system can be investigated not only based on classical control theory, e.g., Nyquist criterion, but also from the energy dissipation point of view. If a critical resonance occurs within the regions, where the system equivalent impedance behaves passively, i.e., has only nonnegative real parts, the system stability can be guaranteed. Thus, it is preferred to design systems with passive regions over a wide-frequency range. This article investigates passivity properties influenced by different control loops and operating points in the dq frame, which facilitates the stability assessment in the frequency domain. Based on this, a virtual damping control method is proposed to improve the stability by enhancing the system passivity. By implementing a damping transfer function in the d- and q-axis individually, nonpassive regions can be accordingly reduced over a specific frequency range. Asymmetrical designs can be considered in the d- and q-axis according to corresponding passivity properties, which is impossible to be realized through symmetric physical filter components. The design procedure is elaborated based on a 2 MW inverter system, which is based on a combined graphical and analytical approach. Verifications are conducted based on a 1 kW prototype including both simulations and experimental results. The method applies to all types of grid-tied inverters with multiple control loops. This article is accompanied by a video demonstrating the validations.

Comparison of Tropical Cyclone Center Positions Determined from Satellite Observations at Infrared and Microwave Frequencies

AbstractDetermining tropical cyclone (TC) center positions is of interest to many researchers who conduct TC analysis and forecasts. In this study, we develop and apply a TC centering technique to Cross-Track Infrared Sounder (CrIS) and Advanced Technology Microwave Sounder (ATMS) observations of brightness temperature and report on an improvement of accuracy by adding a TC spectral analysis to the state of the art [Automated Rotational Center Hurricane Eye Retrieval (ARCHER)], especially for ATMS. We show that the ARCHER TC center-fixing algorithm locates TC centers more successfully based on the infrared channel with center frequency at 703.75 cm−1 (channel 89) of the CrIS than the ATMS channel 22 (183.31 ± 1.0 GHz) due to small-scale features in ATMS channel’s brightness temperature field associated with strong convective clouds. We propose to first apply the ARCHER TC center-fixing algorithm to ATMS channel 4 (51.76 GHz) that is less affected by small-scale convective clouds, and then to perform a set of the azimuthal spectral analysis of the ATMS channel-22 observations with tryout centers within a squared box centered at the ATMS channel-4-determined center. The center that gives the largest symmetric component is the final ATMS-determined center. Compared to the National Hurricane Center best track, the root-mean-square center-fixing errors determined from the two ATMS channels (one single CrIS channel) are 29.9 km (35.8 km) and 28.0 km (30.9 km) for 104 tropical storm and 81 hurricane cases, respectively, in the 2019 hurricane season.

Modeling Of Calculation Of Voltage Unbalance Factor Using Simulink (Matlab)

This paper presents the problem of power quality in asymmetric modes in low-voltage electrical networks. The modeling of determination of power value, voltages and currents and, accordingly, their symmetric components, using the Simulink package in the MatLab program is shown.

Geometric properties of adiabatic quantum thermal machines

We present a general unified approach for the study of quantum thermal machines, including both heat engines and refrigerators, operating under periodic adiabatic driving and in contact with thermal reservoirs kept at different temperatures. We show that many observables characterizing this operating mode and the performance of the machine are of geometric nature. Heat-work conversion mechanisms and dissipation of energy can be described, respectively, by the antisymmetric and symmetric components of a thermal geometric tensor defined in the space of time-dependent parameters generalized to include the temperature bias. The antisymmetric component can be identified as a Berry curvature, while the symmetric component defines the metric of the manifold. We show that the operation of adiabatic thermal machines, and consequently also their efficiency, are intimately related to these geometric aspects. We illustrate these ideas by discussing two specific cases: a slowly driven qubit asymmetrically coupled to two bosonic reservoirs kept at different temperatures, and a quantum dot driven by a rotating magnetic field and strongly coupled to electron reservoirs with different polarizations. Both examples are already amenable for an experimental verification.

DBEM computation of T-stress and mixed-mode SIFs using interaction integral technique

In this paper, dual boundary element method (DBEM) is combined with interaction integral (I-integral) to evaluate stress intensity factors (SIFs) and T-stress simultaneously for mixed-mode crack analyzing. DBEM is proved to be one of the most efficient boundary element methods (BEM) for solving crack problems with boundary-only discretization, however its current implementation is in lack of efficient methods to evaluate fracture parameters. The available geometrical extrapolation method and J-integral technique for calculating fracture parameters in combination with DBEM are imprecise and difficult to be implemented in mix-mode crack analysis. The presented combined DBEM and I-integral approach can be easily used to extract SIFs and T-stress for mixed-mode cracks, which does not need the decomposition of elastic field into symmetric and antisymmetric components. The fundamental basis lies in the introduction of auxiliary fields for some proper defined single mode crack, then fracture parameters are calculated by evaluating the formulated I-integral in terms of DBEM solution and auxiliary elastic fields. In this paper, the basis of DBEM is illustrated at first, then the explicit expressions for auxiliary fields of displacement gradients are derived, then an automatic scheme for generating the path of I-integral is presented. Several numerical examples are given to validate correctness of the presented method.

Symmetric and Asymmetric Components of Shape Variation in the Diatom Genus Frustulia (Bacillariophyta)

Irregularities in cell division can produce asymmetry in symmetric structures, such as outlines of diatom cells, which can reflect genetic, environmental, or random variability in developmental processes. This study examined 12 phylogenetic lineages of the diatom genus Frustulia using landmark-based geometric morphometrics to assess the variation between cell segments separated by apical and transapical axes. Although asymmetric variation within cells differed in some lineages, these irregularities most likely did not reflect the evolutionary history of the lineages. The intraclonal phenotypic plasticity of diatom frustules was induced rather by nongenetic factors, i.e., inherited valve abnormalities, constraints of siliceous cell walls, and random developmental instability during morphogenesis. The positive correlations between the symmetric and asymmetric components of shape variation indicated that the morphogenesis of diatom cell walls affected irregularities within cells and variability among the symmetrized cells to a similar extent.

Phenotypic plasticity of leaf shape in selected and semi-domesticated genotypes as new tool of Argania spinosa L. Skeels breeding

Leaves are part of the plant organs that are important to sustain its life. These organs are sensitive to climate changes and may present phenotypic plasticity in response to environmental conditions. However, affirmation of the leaves morphological plasticity and their regulation in different environments is still little studied up to date. In the present research, we evaluated performance of 20 different groups of Argania spinosa (L.) Skeels genotypes (half-sibling). Each group contains 3 half-sibs. Genotype × environment interactions (GxE) were evaluated as well, for shape and size leaves. To perform this, geometric morphometric principles were applied to analyze genotypes morphology in three locations (Central, North-Western and South-Western of Morocco). Univariate and multivariate analysis was used for data analysis. Results showed significant variation of symmetric and asymmetric components for genotypes, half-sibling and location with relatively high variation coefficient (ca 60%). Shape and size differences among genotypes, suggest that they were the main source in leaf morphology variation. Canonical Variate Analysis of leaf shapes reveals that the regions are clearly distinct from each other. For symmetric component analysis, Mahalanobis distances values among locations reached 35.53 between South-Western and North-Western locations, 21.88 North-Western and Central locations and 18.29 for South-Western and Central location. The differentiation between the groups using the Canonical Variations value showed a significant effect of the environment on the studied argan tree genotypes. Small leaves and narrow blades were observed in Central location compared to others. However, leaves originated from South-Western location had mainly an ovate shape. The same genotypes presented a high spectrum of shape variation varying from obovate to ovate in the other regions. This study highlights the strong correspondence between leaf morphology and genotype within different environments, and demonstrates that GxE interaction shave an impact to take into consideration in breeding programs.