Hochschule Bonn-Rhein-Sieg

Grid-forming inverters (GFIs) have emerged as key enablers for establishing and stabilizing power grid voltage in inverter-dominated grids. International activities increasingly emphasize verification-oriented specifications for GFIs to support secure integration. The recent FNN note on grid-forming inverters provides structured requirements and test considerations to define and prove grid-forming behavior. However, while core properties and current limiting are addressed, it offers limited guidance for transition process between current-limiting and normal operation. This work investigates a representative GFI employing a voltage phasor-based limiting mechanism. Based on the FNN note on grid-forming behavior, we performed further experimental tests transitioning the GFI between current-limiting and normal grid-forming operation. The test framework was extended to include fault ride-through (FRT) combined with islanding, which reveals the voltage source characteristics of the GFI during limiting conditions. The employed current-limiting approach demonstrates adequate transition performance across these test scenarios. Even though, further investigations and finetuning have been identified as necessary to achieve optimised release from current limiting mode.

The increasing integration of renewable energy sources into power grids requires adaptive strategies to maintain stability, espe-cially in island and distribution grids. This paper presents the development of a 200 kVA battery inverter with grid-forming control for the integration of photovoltaics (PV) into island grids. The inverter uses a three-phase ANPC topology with two interleaved legs and a DC-DC converter with flying capacitor topology. Usually, PV systems shut down as soon as they detect an island grid. However, the integration of renewable energy is crucial for future grid reliability, especially in isolated or disaster-affected regions. The energy management system aims to integrate PV systems into the grid during island grid operation, prevent battery overcharging and ensure grid-serving functionalities. Using the VDE 4105 guidelines, the system controls PV active power by adjusting the grid frequency and optimizes the battery's state of charge (SoC) for reliability and durability. Laboratory tests with Power-Hardware-in-the-Loop (P-HiL) demonstrate the effectiveness of the system in maintaining uninterrupted grid operation and adapting PV power generation to the needs of the microgrid.

Arbovirus infection outbreaks are becoming more widely reported in Africa. However, it is still difficult and crucial to better understand arbovirus transmission patterns, disease trends, and burdens. The epidemiology of these infections-dengue virus (DENV), Zika virus (ZIKV), chikungunya virus (CHIKV), West Nile virus (WNV), Rift Valley fever virus (RVFV), and yellow fever virus (YFV)-is unfortunately not well understood. This review provides an epidemiological inventory of DENV, ZIKV, CHIKV, WNV, RVFV, and YFV infections in Africa, with helpful results for risk mapping and upcoming prevention and control initiatives. This systematic review protocol implements the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and an expert-evaluated design, laboratory assay and reporting evaluation (DARE) concept. Two independent reviewers conducted preliminary literature searches in PubMed in May 2023 to improve search keywords, strategy, and inclusion criteria while considering the context and scientific significance. The final search will be conducted using PubMed, ScienceDirect (SCOPUS), Web of Science Core Collection, African Journal Online, and Google Scholar. Two reviewers will simultaneously and independently conduct searches, screen studies, and extract data. Quality assessment will be performed by two independent epidemiology experts, and discrepancies will be handled by consensus or by consulting a third reviewer. Meta-analysis will be performed to determine the pooled estimate of arboviruses circulation and transmission patterns in Africa. With this review, we want to present an epidemiological inventory with information that will be relevant for risk assessment, future arbovirus infection outbreak prevention, and arbovirus infection outbreak control in Africa. This will include estimating the patterns, trends, and burden of arboviral infection across Africa, as well as identifying the regions with the highest risk of transmission. This will be crucial for developing well-informed policies for epidemic prevention. PROSPERO CRD42023434939.

Abstract Advances in large language models (LLMs) have enabled conversational agents (CAs) to invoke external functions dynamically, yet little is known about how different tool-calling (TC) strategies affect user experience. This study compares two approaches – automatic execution based on conversational context versus user-confirmed execution – using a German-language CA in a business-travel scenario. In a between-subjects experiment, 451 employed adult participants (aged 18–65) were randomly assigned to one of the two TC conditions, completed a structured travel request interaction, and then rated their perceived trust (PTru), autonomy (PA), transparency (PTrn), ease of use (PEU), and usefulness (PU). Our findings indicate that TC strategy had a significant overall impact on users’ combined perceptions, and that demographic factors – particularly age – played a critical role in shaping these responses, highlighting the need for adaptive, inclusive design practices that balance automation with user control. CCS Concepts • Human-centered computing → Human computer interaction (HCI) → Interactive systems and tools • Human-centered computing → Interaction design → Systems and tools for interaction design.

Reliable determination of elastic properties is essential for the structural use of polymer composites in engineering applications. This work aims to evaluate the impulse excitation technique (IET) as a method for determining elastic constants of glass bead‑reinforced polyamide 66 (PA66) and polybutylene terephthalate (PBT), and to compare its performance to tensile testing (TT), dynamic mechanical analysis (DMA), and oscillatory torsion (OT). Commercial PA66 and PBT grades with 0-40 wt% glass beads were injection‑molded and annealed; the addition of glass beads increased Young's moduli by 60-70% for PA66 and 40-60% for PBT compared to the neat matrices, depending on filler content. IET, supported by finite element analysis, provided dynamic flexural and longitudinal moduli, shear modulus, and Poisson's ratio which were comparable to those obtained from TT, DMA and OT. In the linear elastic regime IET data differed within the standard deviations of TT, DMA and OT. The moduli determined by flexural excitation using IET and DMA agreed within experimental uncertainty only above an amplitude threshold of approximately 110μm, while Young's moduli from TT and IET showed good agreement, though TT exhibited greater variability. Consistent trends were also found for shear modulus and Poisson's ratio. The higher longitudinal moduli (4 to 8% for PA66 and 2 to 4% for PBT) measured by IET are explained by higher frequencies (3 to 4 orders of magnitude) and cross-sectional microstructural anisotropy and crystallinity differences confirmed by microscopy and calorimetry. The results demonstrate that IET is a much faster, non‑destructive and accurate method for obtaining elastic constants of thermoplastic composites particularly suited for the design and dimensioning of load‑bearing structural components.

Accelerometry provides more objective estimates of physical activity and sleep parameters than self-report data. However, the use of accelerometry may suffer from reactivity to measurement, that is, changes in behaviour under study due to the awareness of being observed. In two field-experimental studies, we examined reactivity to measurement in physical activity and sleep parameters estimated with accelerometry. We used within-subjects designs and manipulated if participants were made aware of the measurement intention or if it was concealed. During a 2-week study, participants received a red accelerometer for one of the weeks and were informed that their physical activity would be monitored in this week. In the other week, participants received a black accelerometer and were informed that it would monitor sleep. In fact, both the red and the black accelerometers monitored both physical activity and sleep. We consistently found no evidence for reactivity to measurement for any indicator of physical activity (moderate to vigorous physical activity, steps) or sleep (duration, efficiency). Accelerometry can provide unbiased measures of indicators of physical activity and sleep and is therefore a valuable addition to the common use of self-report data.