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The spectral proper orthogonal decomposition (SPOD) is a newly introduced extension of snapshot POD that recently gained attention but also brought up controversial issues. Within the first proposition, the approach was mainly presented in a methodological and phenomenological way. The present paper will detail the relations between SPOD and related POD approaches from an analytical point of view. To allow for a better grasp of the approach, an alternative formulation is given that is based on the classic idea from Lumley that was carried on by George. As will be shown, SPOD is closely related to POD with a prior segmentation and Fourier transformation in time. Moreover, the SPOD is shown to be equivalent to snapshot POD combined with time delay embedding.

Zusammenfassung In diesem Artikel werden Ergebnisse der optimalen Steuerung eines Schmelzcarbonat- Brennstoffzellensystems unter Lastwechseln präsentiert. Den umfangreichen Berechnungen liegt ein detailliertes, validiertes mathematisches Modell zugrunde, das die zeitliche und örtliche Dynamik der Gasströme, deren elektro-chemische Reaktionen und die in der Zelle herrschenden Temperaturen und elektrischen Spannungen beschreibt. Das mathematische Modell besteht aus einem hochdimensionalen, nichtlinearen partiell differential-algebraischen Gleichungssystem mit einer parabolischen Gleichung für die Wärmeleitung im Elektrolyten der Zelle sowie hyperbolischen Transportgleichungen für den reaktiven Gastransport. Die Potentialfelder werden in jedem Ortspunkt durch ein differential-algebraisches Gleichungssystem beschrieben. Darüber hinaus gehen in die rechten Seiten der Differentialgleichungen Integralterme ein. Der Gasstrom zwischen Anode und Kathode wird über einen katalytischen Nachbrenner und eine Mischkammer geführt, sodass die Verknüpfung von Anode zu Kathode durch ein differential- algebraisches Gleichungssystem beschrieben wird. Die Einlassbedingungen am Anodeneingang und am Lufteinlass bieten die Möglichkeit der Steuerung der Brennstoffzelle. Damit sind numerische Simulationen und extrem zeitaufwändige optimale Steuerungen, z. B. eines Lastwechsels möglich, die den Brennstoffzellenstapel optimal von einem stationären Zustand in einen anderen überführen. Die numerischen Resultate belegen die Leistungsfähigkeit moderner Methoden der Optimalen Steuerung. Hier kommt eine Methode zum Tragen, bei der alle Gleichungen erst diskretisiert, dann optimiert werden.

Power flow partitioning is a topic of interest for European transmission system operators because of the increasing amount of Unscheduled Flows, which can cause congestions. Unscheduled Flows are caused by the transition to more and more renewable energy sources and the rising complexity of the European transnational energy market with insufficient price signals. To identify different flow types, the Full Line Decomposition (FLD) method can be used. The trend of grid extension goes more towards flexible AC transmission systems (FACTS) which have to be considered in a special way, since the actively changed power flow cannot be identified by FLD. New methods have to be developed. This publication presents a way to calculate and to classify partial power flows caused by FACTS, especially by high voltage DC (HVDC) transmission systems using the proportional sharing principle.

Abstract So far, organizations had no authoritative guidance on circular economy (CE) principles, strategies, implementation, and monitoring. Consequentially, the British Standards Institution recently launched a new standard “BS 8001:2017 – Framework for implementing the principles of the circular economy in organizations”. BS 8001:2017 tries to reconcile the far-reaching ambitions of the CE with established business routines. The standard contains a comprehensive list of CE terms and definitions, a set of general CE principles, a flexible management framework for implementing CE strategies in organizations, and a detailed description of economic, environmental, design, marketing, and legal issues related to the CE. The guidance on monitoring CE strategy implementation, however, remains vague. The standard stipulates that organizations are solely responsible for choosing appropriate CE indicators. Its authors do not elaborate on the links between CE strategy monitoring and the relevant and already standardized quantitative tools life cycle assessment (LCA) and material flow cost accounting (MFCA). Here a general system definition for deriving CE indicators is proposed. Based on the system definition and the indicator literature a dashboard of new and established quantitative indicators for CE strategy assessment in organizations is then compiled. The dashboard indicators are mostly based on material flow analysis (MFA), MFCA, and LCA. Steel cycle data are used to illustrate potential core CE indicators, notably, the residence time of a material in the techno-sphere (currently 250–300 years for steel). Moreover, organizations need to monitor their contribution to in-use-stock growth, a central driver of resource depletion and hindrance to closing material cycles.

Electrically powered buses reduce CO$_{2}$ and noise emissions in urban areas and thus promote the trend towards more livable cities. Upon this reason, more and more cities are introducing their first electrified lines as pilot projects. However, no standardized technology has yet emerged, which is why statements on interactions between vehicle, operation and infrastructure in public transport are proving to be difficult to make. In order to be able to make statistically significant statements in this respect, a simulation model was developed that depicts the three subsystems vehicle, operation and infrastructure. On the basis of measurement data from the PRIMOVE research project in Mannheim, in which an urban bus line is operated with two electrically powered buses, the simulation model was validated and a data basis was laid for further investigations. As a result, simulation studies with more than 700 simulated operating days could be carried out, the results of which represent the input for the following statistical analysis. Based on this analysis, the interactions described above will be demonstrated in the design of the main technical parameters, the battery lifespan and the energy demand of electrical bus lines. Through the findings of these simulations, an optimized version of the already electrified bus line in Mannheim will then be presented. Finally, a novel design methodology for electrification based on a multi-objective optimization is introduced. All parameters of the system are variable in order to apply the presented methodology to other projects and thus underline the general validity of the work.

AbstractThe number of inverter-fed motors is increasing due to the good controllability of the motor and the meanwhile low acquisition costs. As a result of the discrete switching states of the power transistors, the average of the three output voltages of a two-level inverter is a common mode voltage, which differs from zero. The common mode voltage is impressed into the motor winding by the inverter, and an image of the common mode voltage is produced across the bearings via the winding-to-rotor capacitance. The voltage applied to the motor bearings can exceed the dielectric strength of the lubricating film of the bearings and lead to discharge currents resulting in damage to the motor bearings. The winding-to-rotor capacitance is composed of a slot and an end-winding portion. In this article, an analytical determination of the end-winding portion of the winding-to-rotor capacitance is presented, which, in addition to the rotor geometry, considers the influence of materials with different permittivities. The method is validated by means of FEM simulations for different geometries and materials.

Wind energy represents one of the leading renewable energy sectors and is considered instrumental in the ongoing decarbonization process. Accurate forecasts are essential for a reliable large-scale wind power integration, allowing efficient operation and maintenance, planning of unit commitment, and scheduling by system operators. However, due to non-stationarity, randomness, and intermittency, forecasting wind power is challenging. This work investigates a multi-modal approach for wind power forecasting by considering turbine-level time series collected from SCADA systems and high-resolution Numerical Weather Prediction maps. A neural architecture based on stacked Recurrent Neural Networks is proposed to process and combine different data sources containing spatio-temporal patterns. This architecture allows combining the local information from the turbine’s internal operating conditions with future meteorological data from the surrounding area. Specifically, this work focuses on multi-horizon turbine-level hourly forecasts for an entire wind farm with a lead time of 90 h. This work explores the impact of meteorological variables on different spatial scales, from full grids to cardinal point features, on wind power forecasts. Results show that a subset of features associated with all wind directions, even when spatially distant, can produce more accurate forecasts with respect to full grids and reduce computation times. The proposed model outperforms the linear regression baseline and the XGBoost regressor achieving an average skill score of 25%. Finally, the integration of SCADA data in the training process improved the predictions allowing the multi-modal neural network to model not only the meteorological patterns but also the turbine’s internal behavior.

Solar power appears to be one of the most promising resources to meet the medium and long term renewable energy targets. The integration of large amounts of photovoltaic (PV) generation into distribution networks faces some limitations due to the network constraints. The PV community became well aware of these limitations in the last years. While first solutions have been pointed out mainly for large installations connected to the medium voltage network, the specificities of low voltage networks are still not fully understood. This paper aims at explaining the challenges associated to the planning and operation of low voltage network with high PV penetration. The actual impact of PV infeed is quantified on the basis of real and accurate network, load and generation data. Results from unsymmetrical load-flow computations are presented and the implementation of reactive power-based voltage control is shortly discussed. 26th European Photovoltaic Solar Energy Conference and Exhibition; 4469-4478