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The distribution network (DN) reconfiguration is a well-known optimal power flow (OPF) problem. However, with the transition of DN from 'passive' to 'active', new technical challenges arise in DN reconfiguration. This article addresses two key issues in this regard. Firstly, the integration of local renewable generation (LRG) introduces uncertainty into the system-wide power flow of the DN. Secondly, the coupling between DN and the external power grid (EPG) affects the determination of DN root voltage. Consequently, a novel DN reconfiguration approach is proposed in this article. To begin with, an explicit mixed-integer convex OPF model is constructed that incorporates both the EPG and DN sides. Notably, the OPF model embeds the function of local droop control that is provided by LRG. Subsequently, the original OPF model is decomposed, and the distributed optimization methods based on the augmented Lagrangian relaxation are employed. The article comprehensively discusses parallel processing and asynchronous implementation as parts of the distributed optimization procedure. Furthermore, to address the uncertainty related to LRG integration, the extreme scenario method is used to provide a robust decision regarding DN reconfiguration. The application of the extreme scenario method in the distributed OPF model concerning DN reconfiguration is successively developed. Finally, numerical results are presented to demonstrate the acceptable performance of the distributed optimization methods, in terms of optimality and convergence. Also, these are validated that the proposed DN reconfiguration approach exhibits robustness to LRG integration, the system-wide voltage profile is improved, and the active power loss is effectively reduced using the proposed DN reconfiguration approach., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Intelligent Electrical Power Grids

This article presents an accurate DC fault location method that applies parameter fitting. This technique first discusses the traveling wave (TW) propagation process in the decoupled line-mode network. We obtain the exact fault distance equation based on the analytical expressions for the wavefront of backward line-mode voltage TW. The adaptive multi-step Levenberg- Marquardt's (AMLM) algorithm is used for parameter fitting due to its fast processing speed and accuracy. The exact fault location can then be estimated using the parameter fitting results. The proposed fault location method is validated using a three-terminal HVDC system modeled on a real-time digital simulator (RTDS) platform. Based on the experimental results, the proposed method accurately detects the fault location, with all estimated errors smaller than 1%, and can withstand 40 dB noise interference. Moreover, the proposed method does not need a high sampling frequency and communication device. Its accuracy is independent of fault resistance and type compared to existing methods., Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Intelligent Electrical Power Grids

The significance of battery energy storage systems (BESSs) technology has been growing rapidly, mostly due to the need for microgrid applications and the integration of renewables. Relevant to the importance of utilization of BESS in microgrids, the protection of the BESS during microgrid faults has become a concern too. The short circuit in a microgrid cause overcurrent for all of the integrated sources. BESS, as one of the sources in the microgrid, is heavily influenced by fault occurrence. The overcurrent can easily damage power electronic converter switches, battery management systems, and damage battery banks. Fault current limiters are appropriate protection devices that have been massively studied. In this article, we propose a controllable reactor fault current limiter (CRFCL) to protect the BESS against fault currents. The proposed CRFCL can control the fault current value supplied by BESS during a fault condition as a current regulator. It is realized by means of the operation of solid-state switches and series dc-reactor behavior. The main achievement of CRFCL is the protection of BESS against fault currents without delay. The simulations of the proposed structure are carried out in a MATLAB/Simulink platform, and they are confirmed and validated by experimental test results., Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Intelligent Electrical Power Grids, High Voltage Technology Group

Reliable Power Electronic Systems (PES) are vital for enabling energy transition technologies of the future. Power hardware-in-the-Loop (PHIL) test bed can be used to validate such systems cost-effectively and time-efficiently. In general, the Real Time Digital Twin (RTDT) is a virtual representation of the PES and its operating environment that mimics its behavior in real-time to provide adequate flexibility to the test bed. The workflow of alternating between the prototype and twin, for instance, overcomes the dilemma of needing 100 % details (due to fast dynamics), but optimization during design choices requires cheap flexibility. In this paper, some use cases in applications of RTDT-based PHIL test bed such as fault tolerant converters, power electronic interface for green technologies, survivable all-electric ships, mission profile-based reliability testing, protection of multi terminal dc systems and reconfigurable hybrid ac-dc links is discussed. Furthermore, the co-simulation potential of real-time platforms is briefly described., Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., DC systems, Energy conversion & Storage, Intelligent Electrical Power Grids, Electrical Sustainable Energy

Overvoltage instability is a growing concern in a standalone low-voltage (LV) microgrid (MG) with non-dispatchable intermittent renewable energies such as residential and commercial photovoltaic generators (PVGs). Several overvoltage controllers used in PV arrays have adopted the concept of standard deviation from the maximum power point (MPP) to curtail the generated power. However, these solutions lack presenting analytical expression for the MPP deviation size, settings tuning independent of the MG's/PV's characteristics, scalability, and accurate power-sharing in the same control structure. To overcome these limitations, this paper proposes a new analytical MPP tracking (MPPT)-based overvoltage and power-sharing control method using the series equivalent resistance of the PV module model. By applying this analytical expression, the size of the PV array voltage shift to the right-hand side of the MPP is obtained in terms of overvoltage level, while all PVGs proportionally curtail the active power output. The effectiveness of the proposed methodology is shown in various low-demand and high-PV generation cases through a real time digital simulator (RTDS) platform. In addition to the fast and accurate performance, the presented method benefits from the straightforward and communication-free structure as it solely exploits the point of common coupling (PCC) voltage. Also, the method's threshold does not require re- tuning after MG restructure, ensuring scalability. Without relying on other microgrid facilities, the proposed methodology is accordingly an effective solution for practical PV-based LV MGs., Intelligent Electrical Power Grids

Bisbibenzyls represent chemical class of compounds containing two bibenzyl units mutually connected by an oxygen atom and/or directly by the “C-C” bonds. They are chemical markers of liverworts, the ancestors of higher vascular plants. Marchantin A from Marchantia polymorpha was the first discovered bisbibenzyl. More than 120 chemically characterized bisbibenzyls were reported up to 2020 with numerous biological activities [1]. The first report on bisbibenzyls in higher (vascular) plants was published in 2007, when Kosenkova et al. (2007) isolated riccardin C in Primula veris subsp. macrocalyx from Mt. Altay in Russia as the dominant compound in the extract of the whole plant [2]. In the repeated study of the same species, Kosenkova et al. (2009) confirmed their findings discovering an additional bisbibenzyl constituent, perrottetin E [3]. In this investigation from the CH2Cl2/CH3OH (1:1) extract of the air-dried, powdered roots nine isbibenzyls, five new, have been isolated from P. veris subsp. columnae and P. acaulis using dry column flash chromatography followed by semipreparative HPLC chromatography and identified on the basis of 1D and 2D NMR, IR, UV and HRESIMS data. This investigation widens the knowledge about the presence of bisbibenzyls in vascular plants since only two bisbibenzyls have been previously found in vascular plants, in Primula veris subsp. macrocalyx.

Euphorbia cyparissias L. (cypress spurge) is one of the many species of the genus Euphorbia. Like other plant species of the genus, E. cyparissias is a source of biologically active compounds [1, 2]. The aim of this research was to profile the chloroform-methanol latex extract and detect the type of secondary metabolites of Serbian E. cyparissias, collected in Deliblato Sand (Serbia) in May 2022, using liquid chromatography – electrospray ionisation mass spectrometry. Based on the obtained results, terpene derivatives have been found as the most abundant in the latex extract, mainly diterpenes (jatrophanes and ingenanes) and triterpenes. Also, the anticancer activ ity of the latex extract on the cell lines NCI-H460, NCI-H460/R, U87, U87/ TxR and MRC-5, as well as the ability to inhibit P-gp, were examined. Latex extract exhibited anticancer activity against all tested cell lines, and also proved to be a strong P-gp inhibitor. The obtained results are in accordance with the literature data because jatrophanes are well-known strong P-gp inhibitors [3]. These preliminary results indicate that this plant material is a rich source of biologically active compounds and detailed phytochemical research of E. cyparissias is further planned.

U ovom radu ispitani su različiti tipovi kompozitnih materijala, koji su po sastavu većim delom od cementa, a jednim delom od recikliranog otpadnog praškastog materijala, neutrala. Ispitivanja su obuhvatila uticaj kompozitnih materijala na kvalitet vode u šaržnom sistemu. Ispitani su ključni parametri na osnovu kojih se može oceniti uticaj na promenu kvaliteta vode. Deo materijala čini i reciklirani otpadni materijal koji ima komercijalni naziv „neutral“. Neutral nastaje od sirovine koju predstavljaju različiti tipovi (često opasnog) otpada, koji se u reaktoru sa kalcijum-oksidom prevodi u prah koji se može koristiti kao beozopasan. Ovo istraživanje predstavlja preliminarna ispitivanja koaj će ukazati na mogućnost korišćenja neutrala kao materijal koji bi, u kontaktu sa vodom, otpuštao zagađujuće materije u ekološki prihvatljivom obimu i/ili ne.

Two conventional experimental procedures for determination of the water permeability of saturated porous medium are the constant and the falling head permeability tests. The first one is more applicable on more permeable materials where the outflow from the sample is measured at variety of constant water heads, while the second one is more convenient for low permeable materials, utilizing the continuous measurements of the water head falling due to filtration through the saturated sample. However, neither of the two is useful for materials of high permeability and large cross-sectional area. The constant head permeability test faces technical issues since a significant and continuous water discharge is required, while the falling head permeability test has limitations due to neglection of the Forchheimer's high-velocity flow through the sample, but also the influence of inertia on the fluid mass. Here we proposed an approach for determination of the water permeability of saturated porous medium based on the agreement between the measured water level change in two connected reservoirs containing a porous sample and the new semi-analytical expression describing that change by accounting for the mentioned theoretical deficiencies. This efficient approach has been tested on four pervious paver samples, and results showed satisfactory agreement with the constant head permeability data. It has been also confirmed the proposed semi-analytical solution is more accurate than the falling head permeability approach in case of highly pervious materials, while for low permeable materials it reduces to the conventional approach.

High local electric field intensity in transformer windings originating from transient signals is one of the reasons for transformer failures. Due to the integration of renewable energy sources into the power grids and the increased number of transients, the likelihood of transformer catastrophic failure increases accordingly. Therefore, to ensure the reliable performance of transformers and associated power networks studying their behavior during these events is required. Accordingly, there is a need for accurate modeling of transformer windings capable of simulating electromagnetic transients. Using these models, it is possible to identify frequencies that can be dangerous to the transformer windings and to study different protection schemes. This paper aims to find an accurate analytical model of transformer winding validated by experimental measurements and to study the performance of the R-L protection device during the transient phenomena. The protection device is designed based on the winding model to introduce an impedance comparable to that of the transformer winding at critical frequencies where voltage amplification in the winding is significant. This approach ensures enhanced protection against potential transformer damage to the transformer. By using this protection scheme, the high inter-turn voltage originating from transient signals may be mitigated. At the same time, it does not affect the grid's performance during normal conditions., Intelligent Electrical Power Grids, High Voltage Technology Group

This paper explores the possibilities of providing fast frequency support as an emergency support service to the disturbed AC system through the MTDC grid. A two-layer hierarchical control structure of the MTDC grid is proposed to assure the minimum cost of the frequency control actions, the minimum voltage deviations, or the minimal impact on the frequencies of not-affected AC systems while ensuring the stable operation of MTDC grid. An optimization algorithm is executed at the secondary control level to find the optimal reference values for the voltage-droop characteristics of the voltage-regulating converters, and consequently their DC voltages and active power references. Then, at the primary control level, the reference values are tuned with the optimization results. Implemented control structure confirms that MTDC can provide set values at its terminals without endangering its stability. The secondary control layer is implemented in MATLAB, while the performance of the controller is successfully evaluated through simulation in RSCAD., Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Intelligent Electrical Power Grids