Low-voltage ride-through techniques for DFIG-based wind turbines: State-of-the-art review and future trends

This paper deals with low-voltage ride-through (LVRT) capability of wind turbines (WTs) and in particular those driven by a doubly-fed induction generator (DFIG). This is one of the biggest challenges facing massive deployment of wind farms. With increasing penetration of WTs in the grid, grid connection codes in most countries require that WTs should remain connected to the grid to maintain the reliability during and after a short-term fault. This results in LVRT with only 15% remaining voltage at the point of common coupling (PCC), possibly even less. In addition, it is required for WTs to contribute to system stability during and after fault clearance. To fulfill the LVRT requirement for DFIG-based WTs, there are two problems to be addressed, namely, rotor inrush current that may exceed the converter limit and the dc-link overvoltage. Further, it is required to limit the DFIG transient response oscillations during the voltage sag to increase the gear lifetime and generator reliability. There is a rich literature addressing countermeasures for LVRT capability enhancement in DFIGs; this paper is therefore intended as a comprehensive state-of-the-art review of solutions to the LVRT issue. Moreover, attempts are made to highlight future issues so as to index some emerging solutions

Modified Direct Torque Control of PMSM Drives using Dither Signal Injection and Non-Hysteresis Controllers

International audienceThe DTC of voltage source inverter fed PMSM is based on hysteresis controllers of torque and flux. It has several advantages, namely, elimination of the mandatory rotor position sensor, less computation time and fast torque response. In addition, the stator resistance is the only parameter, which should be known and no reference frame transformation is required. The implementation of DTC in PMSM drives is described and the switching tables specific for an interior PMSM are derived. The conventional eight voltage-vector switching table, which is namely used in the DTC of induction motor, does not seem to regulate the torque and stator flux in PMSM well when the motor operates at low speed. Modelling and simulation studies have both revealed that a six voltage-vector switching table is more appropriate for PMSM drive at low speed. Different switching algorithms using hysteresis and non-hysteresis controllers are proposed and the effectiveness of the strategies are analyzed and discussed. In addition, a modified method is propoed which introduces dither signal injection so that the flux and torque ripples are reduced

ADEPOS: Anomaly Detection based Power Saving for Predictive Maintenance using Edge Computing

In industry 4.0, predictive maintenance(PM) is one of the most important applications pertaining to the Internet of Things(IoT). Machine learning is used to predict the possible failure of a machine before the actual event occurs. However, the main challenges in PM are (a) lack of enough data from failing machines, and (b) paucity of power and bandwidth to transmit sensor data to cloud throughout the lifetime of the machine. Alternatively, edge computing approaches reduce data transmission and consume low energy. In this paper, we propose Anomaly Detection based Power Saving(ADEPOS) scheme using approximate computing through the lifetime of the machine. In the beginning of the machines life, low accuracy computations are used when the machine is healthy. However, on the detection of anomalies, as time progresses, the system is switched to higher accuracy modes. We show using the NASA bearing dataset that using ADEPOS, we need 8.8X less neurons on average and based on post-layout results, the resultant energy savings are 6.4 to 6.65XComment: Submitted to ASP-DAC 2019, Japa

Synthetic and analytical investigations related to vegetable oils and fats.

The work presented here has developed along two lines: analysis and synthesis of triacylglycerols. A new application is reported in the use of the infrared detector in HPLC for the detection and preparative and quantitative separation of triacylglycerols of seed fats and oils, acylglycerols from lipolysis mixtures and synthetic acylglycerols. The composition of the total triacylglycerol of some of these fats and oils, and the distribution of fatty acids in the sn-2 position m them are determined for the first time The n-hydrocarbon composition of most of these fats and oils is also determined for the first time. Three new routes, namely, the tosylate, the silyl ether and the phosphate route, have been explored, in the tosylate route best conditions are found for the preparation of glycerol-1,3-ditosylate and its subsequent conversion into 1,3-diacylgiycerols by nucleophilic substitution. From the 1,3-diacylglycerols, five symmetrical diacid tnacylglycerois have been prepared by reaction with an appropriate acid chloride. By the silyl ether route symmetrical diacylglycerols have been prepared from the 1,3-disilyl derivative of 1,3-dihydroxv acetone. In this regard, it is noted that selective silylation of glycerol does not take place, and the 1,3-disilyl derivative of glycerol (prepared indirectly) does not undergo nucleophilic substitution. However, this route does hot offer any advantage over existing routes. In connection with the phosphate route, preliminary experiments have shown that the diphenyl phosphate group can be substituted easily and under mild conditions by a carboxylate anion in a primary alkyl phosphate derivative in both non-polar and polar protic and aprotic solvents. The product from the reaction of diphenyl phosphoryl chloride and glycerol contained only a small amount of the desired 1,3-diphosphate derivative which has been converted into the 1,3-diacylglycerols by nucleophilic substitutio

Coordinate Transformation-Free Observer-Based Adaptive Estimation of Distorted Single-Phase Grid Voltage Signal

© 2013 IEEE. This paper studies the phase and frequency estimation problem of single-phase grid voltage signal in the presence of DC offset and harmonics. For this purpose, a novel parameterized linear model of the grid voltage signal is considered where the unknown frequency of the grid is considered as the parameter. Based on the developed model, a linear observer (Luenberger type) is proposed. Then using Lyapunov stability theory, an estimator of the unknown grid frequency is developed. In order to deal with the grid harmonics, multiple parallel observers are then proposed. The proposed technique is inspired by other Luenberger observers already proposed in the literature. Those techniques use coordinate transformation that requires real-time matrix inverse calculation. The proposed technique avoids real-time matrix inversion by using a novel state-space model of the grid voltage signal. In comparison to similar other techniques available in the literature, no coordinate transformation is required. This significantly reduces the computational complexity w.r.t. similar other techniques. Comparative experimental results are provided with respect to two other recently proposed nonlinear techniques to show the dynamic performance improvement. Experimental results demonstrate the suitability of the proposed technique

Dacryocystorhinostomie endonasale Vs Dacryocystorhinostomie externe : La Préférence patient

Introduction :La prise en charge des sténoses lacrymo-nasales est exclusivement chirurgicale par Dacryocystorhinostomie (DCR), ce procédé peut être réalisé par voie externe longtemps considéré comme le gold-standars dans la prise en charge de ces pathologies ou alors par voie endonasale (end), plus esthétique. Le but de notre étude était entre autres d’analyser la préférence patient pour la voie endonasale.Matériels & Méthode :C’est une étude monocentrique, prospective de 117 DCR-end (97 patients). Ce travail consiste, à Comparer les résultats post-opératoires suivant les deux techniques (voie externe et voie endoscopique) et d’évaluer la préférence patient pour la voie endonasale.Résultats & commentaires : Le taux de réussite enregistré dans notre série était de 89,7% (105/117), un résultat moyen (perméabilité de la voie lacrymale à l’examen clinique avec persistance de la symptomatologie dans certaines situations) était considéré comme un échec soit 4,2% des cas (5/117).Seul des complications mineurs sont observé dans notre série à type de douleurs post-opératoire 5 cas (5,2%), hémorragie post-opératoire 3 cas (3,2%), synéchies du cornet inférieur 4 cas (4,1)Au dernier contrôle, de 6 mois ; 4 patients n’étaient pas satisfaits, et était indécis concernant le conseil de l’intervention à un ami, soit 95,9% de patients Satisfaits.Conclusion :La DCR endonasale est moyen sure et efficace dans la prise des sténoses lacrymo-nasales. Malheureusement elle ne fait toujours pas partie de l’arsenal thérapeutique dans beaucoup de centres hospitaliers qui traite de ces pathologies

Bank credit risk and macro-prudential policies: role of counter-cyclical capital buffer

This paper investigates the impact of macro-prudential policy (proxied by the counter-cyclical capital buffer (CCyB)) on bank credit risk during uncertain times, as banking sector stability is crucial in promoting financial intermediation. Using a unique daily data set consisting of 4939 credit default swaps (CDS) of 70 banks from 25 countries over the period 2010–2019, we find that CCyB tightening decreases bank-level CDS spreads, while CCyB loosening increases CDS spreads. This heterogeneous effect of CCyB arises due to its asymmetric effect on the capital ratio (i.e., the equity-to-total assets ratio) of banks. Tightening CCyB significantly increases capital, whereas loosening CCyB does not impact capital. Thus, the risks that emanate from the banking sector during periods of heightened uncertainty and financial distress can be significantly dampened when CCyB regulation is enabled. Consequently, macro-prudential policies for banks to hold higher levels of capital during good times are justified to contain financial market risks during downturns

EXPERIMENTAL INVESTIGATION ON THE POWER ELECTRONIC TRANSISTOR PARAMETERS INFLUENCE TO THE NEAR-FIELD RADIATION FOR THE EMC APPLICATIONS

Abstract—With the increases of the module integration density and complexity in electrical and power electronic systems, serious problems related to electromagnetic interference (EMI) and electromagnetic compatibility (EMC) can occur. For the safety, these disturbing effects must be considered during the electronic equipment design process. One of the concerns on EMC problems is induced by unintentional near-field (NF) radiations. The modeling and measurement of EM NF radiations is one of the bottlenecks which must be overcome by electronic engineers. To predict the unwanted different misbehaviors caused by the EM radiation, NF test benches for the reconstitution of scanning maps at some millimeters of electrical/electronic circuits under test were developed at the IRSEEM laboratory. Due to the difficulty of the design with commercial simulators, the prediction of EM NF emitted by active electronic systems which are usually based on the use of transistors necessitates more relevant and reliable analysis techniques. For this reason, the main focus of this article is on the experimental analysis of EM NF radiated by an MOSFET transistor with changing electrical parameters. Descriptions of the experimental test bench for the EM map scan of transistors radiation are provided. This experimental setup allows not only to detect the EM NF emission but also to analyze the influence of the excitation signal parameter

Do country-level financial structures explain bank-level CDS spreads?

The existing literature has typically focused on bank-level characteristics to uncover the main drivers of bank CDS spreads. In this paper, we use data for 58 banks from 15 countries over the period 2004–2011 to assess whether country-level factors also explain variations in bank CDS spreads. In particular, we focus on financial structure indicators (namely, financial stability, depth, access and efficiency) and country risks (i.e. economic, financial and political rating risks) to explain why some banks experience higher levels of credit risk relative to others across countries. We find that while country-level financial instability is associated with higher credit risk; bank-level profitability, liquidity and improved asset quality are linked with lower credit risk. In addition, although country-level financial depth (as an indicator of credit bubble) contributes to higher CDS spreads, house price appreciation tends to dampen credit risk