Analysis and control of resonances in HVDC connected DFIG-based offshore wind farm

Wechselwirkungen zwischen den weit verbreiteten wechselrichtergekoppelten Netzkomponenten und den passiven Netzkomponenten können einen breiten Frequenzbereich von Resonanzen aufweisen, wodurch massive harmonische Verzerrungen hervorgerufen und sogar die Systemstabilität gefährdet werden. Ihre Folgen könnten die Trennung erneuerbarer und konventioneller Stromerzeuger vom Netz oder die physische Beschädigung empfindlicher Netzanlagen sein. Motiviert durch die Resonanzereignisse der letzten Jahre in windintegrierten Stromversorgungssystemen, untersucht diese Dissertation die resonanzinduzierten harmonischen Verzerrungs- und Stabilitätsprobleme in einem Offshore-Windpark (OWF) mit doppelt gespeisten Asynchrongeneratoren (DFIG) und Netzanschluss mittels Hochspannungsgleichstromübertragung (HGÜ). Ziel dieser Dissertation ist es, die Resonanzen genau zu charakterisieren, ihre Risiken zu bewerten und Lösungen für die Gestaltung der Minderungsstrategie bereitzustellen. Um die dynamischen Eigenschaften eines DFIG-basierten Windparks genau zu erfassen, wird eine umfassende Impedanzmodellierung unter Berücksichtigung des detaillierten PIRegelkreises und der Gleichstromdynamik der Windkraftanlage sowie der Kabelverbindungen des Mittelspannungskollektorsystems (MV) durchgeführt. Durch schrittweise Simulationsüberprüfungen hat sich die aggregierte Modellierung des MVKollektorsystems für die Breitbandresonanzanalyse als geeignet erwiesen. Auf dieser Grundlage wurden sowohl die Bode-Plot-Methode als auch der Ansatz der Resonanzmodusanalyse (RMA) angewendet, um die Resonanzprobleme unter Berücksichtigung verschiedener Betriebsbedingungen des Windparks und Änderungen der Netz-Topologie anzugehen. Ihre Auswirkungen auf die Resonanzfrequenz, die harmonische Verzerrungen und die Dämpfungen zu Resonanzen werden untersucht. Die Orte, an denen Resonanzen am einfachsten angeregt werden können, werden durch die Busbeteiligungsfaktoranalyse identifiziert. Darüber hinaus wird der Einfluss der Frequenzkopplungseffekte von Steuerungs- und Schaltvorgängen für asymmetrische Wandler auf subsynchrone Resonanz- (SSR), Mittel- und Hochfrequenzresonanzen unter Verwendung der aggregierten Modelle analysiert, die aus einem praktischen HGÜverbundenen DFIG-basierten OWF abgeleitet wurden. Für den Frequenzbereich von mehreren Hz bis zu einigen kHz werden große harmonische Verzerrungs- und Stabilitätsprobleme gezeigt. Um den negativen Einfluss von Resonanzen auf die Stromqualität und die Systemstabilität zu verhindern, wurde eine Reihe aktiver Dämpfungsmöglichkeiten untersucht und in das untersuchte windintegrierte Stromnetz implementiert, und es wird eine koordinierte Dämpfungsstrategie vorgeschlagen, mit der Breitbandresonanzen effektiv gedämpft werden können. Schließlich validieren Simulationen in MATLAB / Simulink die Ergebnisse der Impedanzmodellierung, der Resonanzanalyse sowie die Wirksamkeit der Breitbandresonanzdämpfungsstrategie.Interactions among the widely utilised converter-interfaced grid components and passive grid components can introduce wide-frequency range of resonances, thus induce massive harmonic distortions and even endanger system stability. Their consequences might be the tripping of renewable and conventional generation units or the physical damage of sensitive grid assets. Motivated by recent years’ resonance incidents in wind-integrated power systems, this study investigates the resonance-induced harmonic distortion and stability issues in doubly fed induction generator (DFIG)-based offshore wind farm (OWF) with high-voltage direct current (HVDC) grid connection. The objective of this study is to accurately characterize the resonances, evaluate their risks and provide solutions for the design of mitigation strategy. To accurately capture the dynamic characteristics of DFIG-based wind farm, a comprehensive impedance modelling considering the detailed PI control loop and DC dynamics of wind turbine as well as the cable connections of the medium-voltage (MV) collector system is conducted. Through stepwise simulation verifications, aggregated modelling of MV collector system is proved to be suitable for wideband resonance analysis. On this basis, both Bode-plot method and resonance mode analysis (RMA) approach have been adopted to address the resonance issues taking into account various wind farm operating conditions and grid topology changes. Their impacts on resonance frequency, harmonic amplification level and damping level are investigated. The locations where resonances can be most easily excited are identified through bus participation factor analysis. Moreover, the impact of the frequency-coupling effects from asymmetrial converter control and switching operations on subsynchronous resonance (SSR), middleand high-frequency resonances is analyzed using the aggregated models derived from a practical HVDC connected DFIG-based OWF. Large harmonic distortion and stability issues are demonstrated for the frequency range from several Hz to a few kHz. In order to prevent the negative impact of resonances on power quality and system stability, a series of active damping possibilites have been studied and implemented in the studied wind-integrated power system, and a coordinated damping strategy which can effectively damp wideband resonances is proposed. Finally, simulations in MATLAB/Simulink validate the results of impedance modelling, resonance analysis as well as the effectiveness of the wideband resonance damping strategy

Voltage noise analysis with ring oscillator clocks

Voltage noise is the main source of dynamic variability in integrated circuits and a major concern for the design of Power Delivery Networks (PDNs). Ring Oscillators Clocks (ROCs) have been proposed as an alternative to mitigate the negative effects of voltage noise as technology scales down and power density increases. However, their effectiveness highly depends on the design parameters of the PDN, power consumption patterns of the system and spatial locality of the ROCs within the clock domains. This paper analyzes the impact of the PDN parameters and ROC location on the robustness to voltage noise. The capability of reacting instantaneously to unpredictable voltage droops makes ROCs an attractive solution, which allows to reduce the amount of decoupling capacitance without downgrading performance. Tolerance to voltage noise and related benefits can be increased by using multiple ROCs and reducing the size of the clock domains. The analysis shows that up to 83% of the margins for voltage noise and up to 27% of the leakage power can be reduced by using local ROCs.Peer ReviewedPostprint (author's final draft

Impact of particles on the Planck HFI detectors: Ground-based measurements and physical interpretation

The Planck High Frequency Instrument (HFI) surveyed the sky continuously from August 2009 to January 2012. Its noise and sensitivity performance were excellent, but the rate of cosmic ray impacts on the HFI detectors was unexpectedly high. Furthermore, collisions of cosmic rays with the focal plane produced transient signals in the data (glitches) with a wide range of characteristics. A study of cosmic ray impacts on the HFI detector modules has been undertaken to categorize and characterize the glitches, to correct the HFI time-ordered data, and understand the residual effects on Planck maps and data products. This paper presents an evaluation of the physical origins of glitches observed by the HFI detectors. In order to better understand the glitches observed by HFI in flight, several ground-based experiments were conducted with flight-spare HFI bolometer modules. The experiments were conducted between 2010 and 2013 with HFI test bolometers in different configurations using varying particles and impact energies. The bolometer modules were exposed to 23 MeV protons from the Orsay IPN TANDEM accelerator, and to $^{241}$Am and $^{244}$Cm $\alpha$-particle and $^{55}$Fe radioactive X-ray sources. The calibration data from the HFI ground-based preflight tests were used to further characterize the glitches and compare glitch rates with statistical expectations under laboratory conditions. Test results provide strong evidence that the dominant family of glitches observed in flight are due to cosmic ray absorption by the silicon die substrate on which the HFI detectors reside. Glitch energy is propagated to the thermistor by ballistic phonons, while there is also a thermal diffusion contribution. The implications of these results for future satellite missions, especially those in the far-infrared to sub-millimetre and millimetre regions of the electromagnetic spectrum, are discussed.Comment: 11 pages, 13 figure

Performance analysis and optimization of automotive GPUs

© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Advanced Driver Assistance Systems (ADAS) and Autonomous Driving (AD) have drastically increased the performance demands of automotive systems. Suitable highperformance platforms building upon Graphic Processing Units (GPUs) have been developed to respond to this demand, being NVIDIA Jetson TX2 a relevant representative. However, whether high-performance GPU configurations are appropriate for automotive setups remains as an open question. This paper aims at providing light on this question by modelling an automotive GPU (Jetson TX2), analyzing its microarchitectural parameters against relevant benchmarks, and identifying specific configurations able to meaningfully increase performance within similar cost envelopes, or to decrease costs preserving original performance levels. Overall, our analysis opens the door to the optimization of automotive GPUs for further system efficiency.This work has been partially supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under grant TIN2015-65316-P, the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 772773) and the HiPEAC Network of Excellence. Pedro Benedicte and Jaume Abella have been partially supported by the MINECO under FPU15/01394 grant and Ramon y Cajal postdoctoral fellowship number RYC-2013-14717 respectively and Leonidas Kosmidis under Juan de la Cierva-Formacin postdoctoral fellowship (FJCI-2017-34095).Peer ReviewedPostprint (author's final draft

Devices and architectures for large scale integrated silicon photonics circuits

We present DWDM nanophotonics architectures based on microring resonator modulators and detectors. We focus on two implementations: an on chip interconnect for multicore processor (Corona) and a high radix network switch (HyperX). Based on the requirements of these applications we discuss the key constraints on the photonic circuits' devices and fabrication techniques as well as strategies to improve their performance

Frequency and duration of low-wind-power events in Germany

In the transition to a renewable energy system, the occurrence of low-wind-power events receives increasing attention. We analyze the frequency and duration of such events for onshore wind power in Germany, based on 40 years of reanalysis data and open software. We find that low-wind-power events are less frequent in winter than in summer, but the maximum duration is distributed more evenly between months. While short events are frequent, very long events are much rarer. Every year, a period of around five consecutive days with an average wind capacity factor below 10% occurs, and every ten years a respective period of nearly eight days. These durations decrease if only winter months are considered. The longest event in the data lasts nearly ten days. We conclude that public concerns about low-wind-power events in winter may be overrated, but recommend that modeling studies consider multiple weather years to properly account for such events.Comment: This is an update version after peer revie

Grid integration of intermittent renewable energy sources using price-responsive plug-in electric vehicles

Plug-in electric vehicles (PEVs) are expected to balance the fluctuation of re-newable energy sources (RES). To investigate the contribution of PEVs, the availability of mobile battery storage and the control mechanism for load man-agement are crucial. This study therefore combined the following: a stochastic model to determine mobility behavior, an optimization model to minimize vehicle charging costs and an agent-based electricity market equilibrium model to esti-mate variable electricity prices. The variable electricity prices are calculated based on marginal generation costs. Hence, because of the merit order effect, the electricity prices provide incentives to consume electricity when the supply of renewable generation is high. Depending on the price signals and mobility behavior, PEVs calculate a cost minimizing charging schedule and therefore balance the fluctuation of RES. The analysis shows that it is possible to limit the peak load using the applied control mechanism. The contribution of PEVs to improving the integration of intermittent renewable power generation into the grid depends on the characteristic of the RES generation profile. For the Ger-man 2030 scenario used here, the negative residual load was reduced by 15 to 22 percent and the additional consumption of negative residual load was be-tween 34 and 52 percent. --Plug-in electric vehicles,demand-side management,variable prices,intermittent generation

How Will Hydroelectric Power Generation Develop under Climate Change Scenarios?

Climate change has a large impact on water resources and thus on hydropower. Hydroelectric power generation is closely linked to the regional hydrological situation of a watershed and reacts sensitively to changes in water quantity and seasonality. The development of hydroelectric power generation in the Upper Danube basin was modelled for two future decades, namely 2021-2030 and 2051-2060, using a special hydropower module coupled with the physically-based hydrological model PROMET. To cover a possible range of uncertainties, 16 climate scenarios were taken as meteorological drivers which were defined from different ensemble outputs of a stochastic climate generator, based on the IPCC-SRES-A1B emission scenario and four regional climate trends. Depending on the trends, the results show a slight to severe decline in hydroelectric power generation. Whilst the mean summer values indicate a decrease, the mean winter values display an increase. To show past and future regional differences within the Upper Danube basin, three hydropower plants at individual locations were selected. Inter-annual differences originate predominately from unequal contributions of the runoff compartments rain, snow-and ice-melt