Impedance interaction between islanded parallel voltage source inverters and the distribution network

In an islanded microgrid consisting of parallel-connected inverters, the interaction between an inverter’s output impedance (dominated by the inverter’s filter and voltage controller) and the impedance of the distribution network (dominated by the other paralleled inverters’ output impedances and the interconnecting power cables) might lead to instability. This paper studies this phenomenon using root locus analysis. A controller based on the second derivative of the output capacitor voltage is proposed to enhance the stability of the system. Matlab simulation results are presented to confirm the validity of the theoretical analysis and the robustness of the proposed controlle

Fission barriers in covariant density functional theory: extrapolation to superheavy nuclei

Systematic calculations of fission barriers allowing for triaxial deformation are performed for even-even superheavy nuclei with charge number $Z=112-120$ using three classes of covariant density functional models. The softness of nuclei in the triaxial plane leads to an emergence of several competing fission pathes in the region of the inner fission barrier in some of these nuclei. The outer fission barriers are considerably affected by triaxiality and octupole deformation. General trends of the evolution of the inner and the outer fission barrier heights are discussed as a function of the particle numbers.Comment: 24 pages, 8 tables, 12 figure

Spectroscopy of the heaviest nuclei (theory)

Recent progress in the applications of covariant density functional theory (CDFT) to the description of the spectroscopy of the heaviest nuclei is reviewed. The analysis of quasiparticle spectra in actinides and the heaviest A ~ 250 nuclei provides a measure of the accuracy of the description of single-particle energies in CDFT and an additional constraint for the choice of effective interactions for the description of superheavy nuclei. The response of these nuclei to the rotation is rather well described by cranked relativistic Hartree+Bogoliubov theory and it serves as a supplementary tool in configuration assignment in odd-mass nuclei. A systematic analysis of the fission barriers with allowance for triaxial deformation shows that covariant density functional theory is able to describe fission barriers on a level of accuracy comparable with the best phenomenological macroscopic+microscopic approaches.Comment: 10 pages, 7 figures, invited talk of A.V. Afanasjev at the International Nuclear Physics Conference (INPC 2010), Vancouver, Canada, July 4-9, 2010, to be published in Journal of Physics G: Conference Series (JPCS

Time-odd mean fields in covariant density functional theory I. Non-rotating systems

Time-odd mean fields (nuclear magnetism) are analyzed in the framework of covariant density functional theory (CDFT). It is shown that they always provide additional binding to the binding energies of odd-mass nuclei. This additional binding only weakly depends on the RMF parametrization reflecting good localization of the properties of time-odd mean fields in CDFT. The underlying microscopic mechanism is discussed in detail. Time-odd mean fields affect odd-even mass differences. However, our analysis suggests that the modifications of the strength of pairing correlations required to compensate for their effects are modest. In contrast, time-odd mean fields have profound effect on the properties of odd-proton nuclei in the vicinity of proton-drip line. Their presence can modify the half-lives of proton-emitters (by many orders of magnitude in light nuclei) and affect considerably the possibilities of their experimental observation.Comment: 20 pages, 19 figure

Hyperdeformation in the cranked relativistic mean field theory: the Z=40-58 part of nuclear chart

The systematic investigation of hyperdeformation (HD) at high spin in the $Z=40-58$ part of the nuclear chart has been performed in the framework of the cranked relativistic mean field theory. The properties of the moments of inertia of the HD bands, the role of the single-particle and necking degrees of freedom at HD, the spins at which the HD bands become yrast, the possibility to observe discrete HD bands etc. are discussed in detail.Comment: 22 pages, 25 figure

High-spin transition quadrupole moments in neutron-rich Mo and Ru nuclei: testing γ\gamma softness?

The transition quadrupole moments, $Q_{t}$, of rotational bands in the neutron-rich, even-mass $^{102-108}$Mo and $^{108-112}$Ru nuclei were measured in the 8 to 16 $\hbar$ spin range with the Doppler-shift attenuation method. The nuclei were populated as fission fragments from $^{252}$Cf fission. The detector setup consisted of the Gammasphere spectrometer and the HERCULES fast-plastic array. At moderate spin, the $Q_{t}$ moments are found to be reduced with respect to the values near the ground states. Attempts to describe the observations in mean-field-based models, specifically cranked relativistic Hartree-Bogoliubov theory, illustrate the challenge theory faces and the difficulty to infer information on $\gamma$ softness and triaxiality from the data.Comment: 17 pages, 4 figure

Chondrocyte Deformations as a Function of Tibiofemoral Joint Loading Predicted by a Generalized High-Throughput Pipeline of Multi-Scale Simulations

Cells of the musculoskeletal system are known to respond to mechanical loading and chondrocytes within the cartilage are not an exception. However, understanding how joint level loads relate to cell level deformations, e.g. in the cartilage, is not a straightforward task. In this study, a multi-scale analysis pipeline was implemented to post-process the results of a macro-scale finite element (FE) tibiofemoral joint model to provide joint mechanics based displacement boundary conditions to micro-scale cellular FE models of the cartilage, for the purpose of characterizing chondrocyte deformations in relation to tibiofemoral joint loading. It was possible to identify the load distribution within the knee among its tissue structures and ultimately within the cartilage among its extracellular matrix, pericellular environment and resident chondrocytes. Various cellular deformation metrics (aspect ratio change, volumetric strain, cellular effective strain and maximum shear strain) were calculated. To illustrate further utility of this multi-scale modeling pipeline, two micro-scale cartilage constructs were considered: an idealized single cell at the centroid of a 100×100×100 μm block commonly used in past research studies, and an anatomically based (11 cell model of the same volume) representation of the middle zone of tibiofemoral cartilage. In both cases, chondrocytes experienced amplified deformations compared to those at the macro-scale, predicted by simulating one body weight compressive loading on the tibiofemoral joint. In the 11 cell case, all cells experienced less deformation than the single cell case, and also exhibited a larger variance in deformation compared to other cells residing in the same block. The coupling method proved to be highly scalable due to micro-scale model independence that allowed for exploitation of distributed memory computing architecture. The method’s generalized nature also allows for substitution of any macro-scale and/or micro-scale model providing application for other multi-scale continuum mechanics problems

Design and control of a grid-connected interleaved inverter

This paper is concernedwith the design and control ofa three-phase voltage source grid-connected interleaved inverter. This topology enables the use of low-current devices capable of switching at high frequency, which together with the ripple cancelation feature reduces the size of the output filter and the inverter considerably compared to an equivalent classical two-level voltagesource inverter with an LCL output filter using high-currentdevices with considerably lower switching frequency. Due to its higher switching frequency and low-filter component values, the interleaved inverter also has a much higher bandwidth than the classical inverter, which improves grid voltage harmonics disturbance rejection and increases the speed of response of the inverter and its capability to ride through grid disturbance (e.g., voltage sags and swells). The paper discusses the selection of the numberof channels and the filter component values of the interleaved inverter. The design of the digital control system is then discussed in detail. Simulation and practical results are presented to validate the design and demonstrate its capabilities

DFIG Driven Wind Turbine with Grid Supporting Battery Storage System

This is the author accepted manuscript.Grid operators face challenges with the increasing integration of wind energy into electric grids, necessitating uninterrupted wind power generation during outages to maintain system stability. Due to voltage dips there is a significantly impact on grid-connected Doubly Fed Induction Generators(DFIG). Hence, Integrating DFIG with Grid Battery Storage System(GBSS) is to provide essential active and reactive power support at the CommonCoupling Point(PCC), aligning requirement of Low Voltage Ride Through(LVRT) and other services to the electricgrid. The paper proposes and experimentally validates a coordinated control scheme between the Grid Side Converter(GSC) of the DFIG and the GBSS. In this dynamic adjustment of power set points within the outer control loop responds to voltage and frequency changes at the PCC. The control scheme facilitates multiple services to grid by seamless plug-and-play functionality between DFIG and GBSS converters. The proposed method, utilizing GBSS, achieves significant voltage improvement and enhanced reactive power injection, while effectively managing stator voltage, rotor-side converter current, and DC link voltage oscillations. The study incorporates Hardware-in-theLoop(HIL) testing using Real-Time Digital Simulator(RTDS) with hardware setup of 2.5 kW DC motor emulating a wind turbine interconnected via Power Amplifier(PA). Simulation and experimental results demonstrate the effectiveness of proposed coordinated control scheme indicating its potential significance in grid conditions by withstanding voltage dips and load variations