Supply Restoration in Active Distribution Networks Based on Soft Open Points with Embedded DC Microgrids

As disturbances due to natural disasters or man-made attacks intensify awareness regarding power systems’ resilience enhancement, the scientific community concentrates on exploring state-of-the-art technologies for emergency supply restoration strategies. Recent studies are increasingly focusing on the expanded flexibility of soft open points (SOPs) compared to conventional tie-switches to increase the restoration rate of critical loads; however, the potential of this novel technology is not limited to this aspect, with SOPs being used to improve the voltage level and increase the hosting capacity of renewable energy sources (RESs). This paper proposes a deterministic model for the optimal coordination of SOPs and distributed resources in an active distribution network (ADN) aiming at re-establishing the energy supply to critical loads after a prolonged interruption occurrence. At the same time, the support of DC microgrids with integrated RESs, embedded in SOPs, for the restoration process is explored. The efficiency of the proposed optimization model is verified based on a 24-h analysis performed on the modified IEEE 33-bus system, while considering the load and generation uncertainties as well.

Investigation of problems in modeling critical loads on a composite model of a wind turbine blade

This article deals with the problems of designing and analysis of the deformed state of the wind turbine blade under critical loads. A three-dimensional shell simulation model is built, taking into account the complex curvilinear geometry and the presence of reinforcing internal parts. The determination of the parameters of the stress-strain state under the influence of wind load was carried out on the basis of the finite element method. A shell ten-node isoparametric finite element was used. The constructed finite element model of the blade allows taking into account the composite structure and reproduced the presence of a different number of composite layers along the thickness of the shell, the diversity of fibers on individual layers, in particular, the curvilinear orthotropy of mechanical properties was modeled. The procedure of multi-layer structure setting is presented, which provides for superimposition of layers of composite one on the other in places of joint, which ensures compliance of model with technological peculiarities. Static analysis of structural deformation calculation is carried out taking into account lifting force and air head force. The strength analysis was performed for each of the layers according to the criterion of maximum deformations. Key words: composite material, wind turbine blade, strength, finite-elemental analysis, orthotropy of characteristics.

Energy Resilience Impact of Supply Chain Network Disruption to Military Microgrids

The ability to provide uninterrupted power to military installations is paramount in executing a country’s national defense strategy. Microgrid architectures increase installation energy resilience through redundant local generation sources and the capability for grid independence. However, deliberate attacks from near-peer competitors can disrupt the associated supply chain network, thereby affecting mission critical loads. Utilizing an integrated discrete-time Markov chain and dynamic Bayesian network approach, we investigate disruption propagation throughout a supply chain network and quantify its mission impact on an islanded microgrid. We propose a novel methodology and an associated metric we term “energy resilience impact” to identify and address supply chain disruption risks to energy security. The proposed methodology addresses a gap in the literature and practice where it is assumed supply chains will not be disrupted during incidents involving microgrids. A case study of a fictional military installation is presented to demonstrate how installation energy managers can adopt this methodology for the design and improvement of military microgrids. The fictional case study shows how supply chain disruptions can impact the ability of a microgrid to successfully supply electricity to critical loads throughout an islanding event.

Research on Voltage Stabilizing Control Strategy of Critical Load in Unplanned Island Based on Electric Spring

Aiming to solve the problem of voltage fluctuation of critical load caused by lack of control when an unplanned island occurs in a microgrid, a voltage stabilizing control strategy of critical load based on electric spring is proposed in this paper. When unplanned islanding occurs in a microgrid system, the system bus voltage fluctuates dramatically due to instantaneous power imbalance, compromising the power supply safety of important loads on the bus. In this paper, the electric spring control mode is integrated into the voltage stabilizing control strategy of critical loads in an unplanned island for the first time to realize the protection of critical loads. First of all, a model of an optical storage AC/DC hybrid microgrid is built, the overall system architecture is determined, and the microgrid is divided into four working states. Second, the working principle of electric spring is introduced, and a decoupling control strategy based on double closed loop is proposed. Finally, the experimental simulation of the proposed control strategy is experimentally simulated in Matlab/Simulink environment. The simulation findings show that when the bus voltage and current of microgrid change due to an unplanned island, the proposed control strategy based on electric spring may achieve the stability of voltage and current on critical loads.

Geometrically nonlinear analysis of the stability of the stiffened plate taking into account the interaction of eigenforms of buckling

The aims of this work are a detailed consideration in a geometrically nonlinear formulation of the stages of the equilibrium behavior of a compressed stiffened plate, taking into account the interaction of the general form of buckling and local forms of wave formation in the plate or in the reinforcing ribs, comparison of the results of the semi-analytical solution of the system of nonlinear equations with the results of the numerical solution on the Patran-Nastran FEM complex of the problem of subcritical and postcritical equilibrium of a compressed stiffened plate. Methods. Geometrically-nonlinear analysis of displacement fields, deformations and stresses, calculation of eigenforms of buckling and construction of bifurcation solutions and solutions for equilibrium curves with limit points depending on the initial imperfections. An original method is proposed for determining critical states and obtaining bilateral estimates of critical loads at limiting points. Results. An algorithm for studying the equilibrium states of a stiffened plate near critical points is described in detail and illustrated by examples, using the first nonlinear (cubic terms) terms of the potential energy expansion, the coordinates of bifurcation points and limit points, as well as the corresponding values of critical loads. The curves of the critical load sensitivity are plotted depending on the value of the initial imperfections of the total deflection. Equilibrium curves with characteristic bifurcation points of local wave formation are constructed using a numerical solution. For the case of action of two initial imperfections, an algorithm is proposed for obtaining two-sided estimates of critical loads at limiting points.

Robust topology optimization of graphene platelets reinforced functionally graded materials considering hybrid bounded uncertainties

An efficient scheme for the robust topology optimization considering hybrid bounded uncertainties (RTOHBU) is proposed for the graphene platelets (GPLs) reinforced functionally graded materials (FGMs). By introducing the concept of the layer-wise FGMs, the properties of the GPLs reinforced FGMs are calculated based on the Halpin-Tsai micromechanics model. The practical boundedness of probabilistic variables is naturally ensured by utilizing a generalized Beta distribution in constructing the robust topology optimization model. To address the issue of lacking the information of critical loads in existing topology optimization approaches considering hybrid uncertainties, a gradient-attributed search is carried out at first based on the hypothesis of linear elasticity to determine the critical loads leading to the worst structural performance. Subsequently, the statistical characteristics of the objective structural performance under such critical loads are efficiently evaluated by integrating the univariate dimension reduction method and the Gauss-Laguerre quadrature, the accuracy of which is verified by the comparison analysis utilizing the results of Monte Carlo simulation as references. Furthermore, a novel realization vector set is constructed for the bounded probabilistic uncertainties to parallelize the sensitivity analysis and accelerate the optimization process. All the proposed innovations are integrated into the robust topology optimization scheme, the effectiveness and efficiency of which are verified by three illustrative examples.

Scratch Properties of Clear Coat for Automotive Coating Comprising Molecular Necklace Crosslinkers with Silane Functional Groups for Various Environmental Factors

Automotive coatings, which comprise multiple layers, i.e., primer, base coating, and clear coat layers, are exposed to various environmental conditions that pose various types of damages to them. In particular, the outer layer of the automotive coating, i.e., the clear coat, is affected significantly by such damages. Therefore, a reliable and durable clear coat must be developed to improve the appearance of automobiles. In this study, a new clear coat based on an acrylic-based clear coat modified using polyrotaxane crosslinkers, which are necklace-shaped supramolecules composed of ring-shaped host molecules, is developed and characterized. The effects of polyrotaxane and silane on the scratch properties and mechanisms of the clear coating are analyzed. It is observed that the critical loads of the clear coat from scratch tests can be improved by adding optimal molecular necklace crosslinkers comprising silane functional groups. The improvement in the scratch properties of the modified acrylic-based clear coat may be attributed to the crosslinking characteristics and dynamic molecular movements of the polyrotaxane. In addition, the effects of environmental factors on the scratch characteristics of the modified acrylic-based clear coat are investigated by addressing the scratch durability of the clear coat.

Comparison of Existing Legal Assessment Values for Heavy Metal Deposition in Western Europe and Calculation of Assessment Values for Luxembourg

The protection against eco- and human-toxicological impairments caused by atmospheric deposition of heavy metals requires legally defined assessment values. Since such values are missing for Luxembourg, the aim of this investigation was to evaluate different approaches to derive assessment values for the regulation of heavy metals that are in accordance with scientific and legal standards. To this end, assessment values for heavy metals were derived from the compilation of respective values implemented in European countries. In addition, (1) precipitation-related assessment values for the protection of soil for Cr, Zn, and Cu and (2) precautionary assessment values (critical loads for Cr, Zn, and Cu, as well as As, Cd, Ni, and Pb) for the protection of human health and ecosystems were calculated. The calculation of the regionally differentiated precipitation-related assessment values resulted in ranges of 17–272 g Cu ha−1 a−1, 167–2672 g Zn ha−1 a−1 and 17–272 g Crtotal ha−1 a−1. The critical loads for drinking water protection vary in the ranges from 1.23 to 2.14 g Cd ha−1 a−1, from 4.05 to 8.63 g Pb ha−1 a−1, from 2.6 to 5.9 g As ha−1 a−1, from 258 to 564 g Cu ha−1 a−1, from 1292 to 2944 g Zn ha−1 a−1, and from 12.9 to 29.9 g Crtotal ha−1 a−1. Ecosystems are significantly more sensitive to Pb, Cu, and Zn inputs than humans. For As and Cr, humans react much more sensitively than ecosystems. For Cd, the critical loads for drinking water, ecosystems, and wheat products are about the same.

A Single-Stage Three Phase CT-Type MLI for Grid Integration and for Supplying Critical Loads

Power system reliability and resiliency involves availability of uninterrupted power supply to loads. With ever-increasing natural and man-made disturbances in power grid, the need of alternate renewable based source of supply is gaining more attention. This paper presents an efficient renewable energy-based single stage configuration for standalone application to provide uninterrupted power supply to critical loads in case of grid power interruption. This configuration can also be used for grid integration during peak load demand of power. The advancement in research of Multilevel Inverter (MLI) relating to high voltage with high power energy control enabled increased use of MLI in renewable energy, especially PV and fuel cell-based systems. The renewable energy-based configuration proposed in this paper uses Cross T-Type (CT-Type) MLI which provides quality output power from solar PV, fuel cell etc. Moreover, the absence of any DC-DC converter reduces complexity and makes the system more economical for grid integration. The overall system performance improves compared to existing methods in terms of total harmonic distortion (THD), total standing voltage (TSV), number of levels, number of components requirement and efficiency.