Violation-mitigation-based method for PV hosting capacity quantification in low voltage grids

Hosting capacity knowledge is of great importance for distribution utilities to assess the amount of PV capacity possible to accommodate without troubling the operation of the grid. In this paper, a novel method to quantify the hosting capacity of low voltage grids is presented. The method starts considering a state of fully exploited building rooftop solar potential. A downward process is proposed—from the starting state with expected violations on the grid operation to a state with no violations. In this process, the installed PV capacity is progressively reduced. The reductions are made sequentially and selectively aiming to mitigate specific violations: nodes overvoltage, lines overcurrent and transformer overloading. Evaluated on real data of fourteen low voltage grids from Austria, the method proposed exhibits benefits in terms of higher hosting capacities and lower computational costs compared to stochastic methods. Furthermore, it also quantifies hosting capacity expansions achievable by overcoming the effect of the violations. The usage of a potential different from solar rooftops is also presented, demonstrating that a user-defined potential allows to quantify the hosting capacity in a more general setting with the method proposed.publishedVersionPaid open acces

A simulation approach for multilocus aelection-migration models

Diese Diplomarbeit stellt eine Implementierung eines Software-Packets zur Simulation von Migrations-Selektionsmodellen vor. Die deterministische, diskrete Simulation iteriert die zugrunde liegende Differenzengleichung, um die Gleichgewichte des dynamischen Systems zu finden. Als Anwendungsfall wird die Gleichgewichtsstruktur einer Population unter quadratisch-stabilisierender Selektion untersucht. Zuerst wird das zugrunde liegende mathematische Modell eingeführt und die getroffenen biologischen Annahmen erklärt. Das untersuchte dynamische System wird definiert, Fitnessfunktionen, Rekombination und Migrationsmodelle werden abgehandelt. Weiters definieren wir wichtige Größen, die erlauben die genetische Zusammensetzung und die Differenzierung in Gleichgewichten zu messen. Danach werden relevante Publikationen besprochen, die Simulationen vorwärts in der Zeit und quadratisch stabilisierende Selektion betreffen. Weiters wird der Grenzfall starker Migration betrachtet. Dem folgt eine detailierte Beschreibung der Implementierung. Dies umfasst das Objekt-Modell, die Datenbankarchitektur und eine Diskussion algorithmischer Belange. Schließlich werden die Resultate duch Anwendung der vorgestellten Simulation auf den Fall quadratisch stabilisierender Selektion vorgestellt. Zuerst wird der Fall einer panmiktischen Population mit zwei Allelen auf zwei Loci untersucht, wobei das Optimum der Fitnessfunktion beliebig ist. Anschließend werden zwei Deme mit symmetrisch verschobenen Optima behandelt, um Migration anhand des Deakin-Modells zu untersuchen.In this diploma thesis, the implementation of a software package is presented, which facilitates the simulation and analysis of multilocus migration-selection models. The deterministic, discrete simulation iterates the underlying difference equation to find the equilibria of the dynamical system. As an application, the equilibrium structure of a population under quadratic stabilizing selection is investigated. First, we state the biological assumptions and introduce the mathematical model. We define the investigated dynamical system and introduce fitness functions, recombination, and migration models. Furthermore, we define important quantities to measure properties of the genetic composition and of differentiation at equilibrium. Then, we review related work concerning forward-time simulations and quadratic stabilizing selection. Moreover, we discuss the limiting case of strong migration. This is followed by a discussion of the implementation of the developed software. This comprises the object model, the database architecture, and a discussion of algorithmic issues. Finally, the results obtained by the application of the program to the case of quadratic stabilizing selection are presented. First, the case of a diallelic two-locus panmictic population is investigated, allowing for arbitrary optimum position. Then, two demes are considered, displacing the optima symmetrically within the demes, and assuming the Deakin migration model

Influence of usage and model inaccuracies on the performance of smart hot water heaters: lessons learned from a demand response field test

Domestic hot water heaters are considered to be easily integrated as flexible loads for demand response. While literature grows on reproducible simulation and lab tests, real-world implementation in field tests considering state estimation and demand prediction-based model predictive control approaches is rare. This work reports the findings of a field test with 16 autonomous smart domestic hot water heaters. The heaters were equipped with a retrofittable sensor/actuator setup and a real-time price-driven model predictive control unit, which covers state estimation, demand prediction, and optimization of switching times. With the introduction of generic performance indicators (specific costs and thermal efficiency), the results achieved in the field are compared by simulations to standard control modes (instantaneous heating, hysteresis, night-only switching). To evaluate how model predictive control performance depends on the user demand prediction and state estimation accuracy, simulations assuming perfect predictions and state estimations are conducted based on the data measured in the field. Results prove the feasible benefit of RTP-based model predictive control in the field compared to a hysteresis-based standard control regarding cost reduction and efficiency increase but show a strong dependency on the degree of utilization

Voltage-based droop control of electric vehicles in distribution grids under different charging power levels

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Optimal power tracking for autonomous demand side management of electric vehicles

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Optimal power tracking for autonomous demand side management of electric vehicles

Increasing electric vehicle penetration leads to undesirable peaks in power if no proper coordination in charging is implemented. We tested the feasibility of electric vehicles acting as flexible demands responding to power signals to minimize the system peaks. The proposed hierarchical autonomous demand side management algorithm is formulated as an optimal power tracking problem. The distribution grid operator determines a power signal for filling the valleys in the non-electric vehicle load profile using the electric vehicle demand flexibility and sends it to all electric vehicle controllers. After receiving the control signal, each electric vehicle controller re-scales it to the expected individual electric vehicle energy demand and determines the optimal charging schedule to track the re-scaled signal. No information concerning the electric vehicles are reported back to the utility, hence the approach can be implemented using unidirectional communication with reduced infrastructural requirements. The achieved results show that the optimal power tracking approach has the potential to eliminate additional peak demands induced by electric vehicle charging and performs comparably to its central implementation. The reduced complexity and computational overhead permits also convenient deployment in practice.publishedVersio

Heart rate detection from the supratrochlear vessels using a virtual reality headset integrated PPG sensor

An increasing amount of virtual reality (VR) research is carried out to support the vast number of applications across mental health, exercise and entertainment fields. Often, this research involves the recording of physiological measures such as heart rate recordings with an electrocardiogram (ECG). One challenge is to enable remote, reliable and unobtrusive VR and heart rate data collection which would allow a wider application of VR research and practice in the field in future. To address the challenge, this work assessed the viability of replacing standard ECG devices with a photoplethysmography (PPG) sensor that is directly integrated into a VR headset over the branches of the supratrochlear vessels. The objective of this study was to investigate the reliability of the PPG sensor for heart-rate detection. A total of 21 participants were recruited. They were asked to wear an ECG belt as ground truth and a VR headset with the embedded PPG sensor. Signals from both sensors were captured in free standing and sitting positions. Results showed that VR headset with an integrated PPG sensor is a viable alternative to an ECG for heart rate measurements in optimal conditions with limited movement. Future research will extend on this finding by testing it in more interactive VR settings

Sex-related differences in risk factors, type of treatment received and outcomes in patients with atrial fibrillation and acute stroke: Results from the RAF-study (Early Recurrence and Cerebral Bleeding in Patients with Acute Ischemic Stroke and Atrial Fibrillation)

Introduction: Atrial fibrillation is an independent risk factor of thromboembolism. Women with atrial fibrillation are at a higher overall risk for stroke compared to men with atrial fibrillation. The aim of this study was to evaluate for sex differences in patients with acute stroke and atrial fibrillation, regarding risk factors, treatments received and outcomes. Methods Data were analyzed from the “Recurrence and Cerebral Bleeding in Patients with Acute Ischemic Stroke and Atrial Fibrillation” (RAF-study), a prospective, multicenter, international study including only patients with acute stroke and atrial fibrillation. Patients were followed up for 90 days. Disability was measured by the modified Rankin Scale (0–2 favorable outcome, 3–6 unfavorable outcome). Results: Of the 1029 patients enrolled, 561 were women (54.5%) (p < 0.001) and younger (p < 0.001) compared to men. In patients with known atrial fibrillation, women were less likely to receive oral anticoagulants before index stroke (p = 0.026) and were less likely to receive anticoagulants after stroke (71.3% versus 78.4%, p = 0.01). There was no observed sex difference regarding the time of starting anticoagulant therapy between the two groups (6.4 ± 11.7 days for men versus 6.5 ± 12.4 days for women, p = 0.902). Men presented with more severe strokes at onset (mean NIHSS 9.2 ± 6.9 versus 8.1 ± 7.5, p < 0.001). Within 90 days, 46 (8.2%) recurrent ischemic events (stroke/TIA/systemic embolism) and 19 (3.4%) symptomatic cerebral bleedings were found in women compared to 30 (6.4%) and 18 (3.8%) in men (p = 0.28 and p = 0.74). At 90 days, 57.7% of women were disabled or deceased, compared to 41.1% of the men (p < 0.001). Multivariate analysis did not confirm this significance. Conclusions: Women with atrial fibrillation were less likely to receive oral anticoagulants prior to and after stroke compared to men with atrial fibrillation, and when stroke occurred, regardless of the fact that in our study women were younger and with less severe stroke, outcomes did not differ between the sexes

Prediction of early recurrent thromboembolic event and major bleeding in patients with acute stroke and atrial fibrillation by a risk stratification schema: the ALESSA score study

Background and Purposes—This study was designed to derive and validate a score to predict early ischemic events and major bleedings after an acute ischemic stroke in patients with atrial fibrillation. Methods—The derivation cohort consisted of 854 patients with acute ischemic stroke and atrial fibrillation included in prospective series between January 2012 and March 2014. Older age (hazard ratio 1.06 for each additional year; 95% confidence interval, 1.00–1.11) and severe atrial enlargement (hazard ratio, 2.05; 95% confidence interval, 1.08–2.87) were predictors for ischemic outcome events (stroke, transient ischemic attack, and systemic embolism) at 90 days from acute stroke. Small lesions (≤1.5 cm) were inversely correlated with both major bleeding (hazard ratio, 0.39; P=0.03) and ischemic outcome events (hazard ratio, 0.55; 95% confidence interval, 0.30–1.00). We assigned to age ≥80 years 2 points and between 70 and 79 years 1 point; ischemic index lesion >1.5 cm, 1 point; severe atrial enlargement, 1 point (ALESSA score). A logistic regression with the receiver-operating characteristic graph procedure (C statistic) showed an area under the curve of 0.697 (0.632–0.763; P=0.0001) for ischemic outcome events and 0.585 (0.493–0.678; P=0.10) for major bleedings. Results—The validation cohort consisted of 994 patients included in prospective series between April 2014 and June 2016. Logistic regression with the receiver-operating characteristic graph procedure showed an area under the curve of 0.646 (0.529–0.763; P=0.009) for ischemic outcome events and 0.407 (0.275–0.540; P=0.14) for hemorrhagic outcome events. Conclusions—In acute stroke patients with atrial fibrillation, high ALESSA scores were associated with a high risk of ischemic events but not of major bleedings