Frequency-Domain Analysis of Linear Time-Periodic Systems

In this paper, we study convergence of truncated representations of the frequency-response operator of a linear time-periodic system. The frequency-response operator is frequently called the harmonic transfer function. We introduce the concepts of input, output, and skew roll-off. These concepts are related to the decay rates of elements in the harmonic transfer function. A system with high input and output roll-off may be well approximated by a low-dimensional matrix function. A system with high skew roll-off may be represented by an operator with only few diagonals. Furthermore, the roll-off rates are shown to be determined by certain properties of Taylor and Fourier expansions of the periodic systems. Finally, we clarify the connections between the different methods for computing the harmonic transfer function that are suggested in the literature

An Aggregated Approach to Harmonic Modelling of Loads in Power Distribution Networks

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A Harmonic Transfer Function Model for a Diode Converter Train

A method for analysis of electric networks with nonlinear and switching components is presented. The method is based on linearization around the nominal AC voltage, which results in linear time periodic (LTP) models. For nonlinear and switching components, there is coupling between different frequencies, which may cause stability and resonance problems. The models capture this coupling and can thus be used for small signal stability and robustness analysis. A short introduction to transfer functions for LTP systems is given. To illustrate the method, an LTP model for the Adtranz locomotive Re 4/4 is derived. The system consists of an AC-side with a transformer, and a DC-side with a DC motor and a smoothing choke. The AC-side and the DC-side are connected by a diode bridge rectifier. The model clearly shows the coupling between frequencie

"Men heder är ju inte bara en sak" : En studie om samverkan kring hedersrelaterat våld

The purpose with this study was to investigate how professionals in social services, school, youth clinic and women shelter in a municipality describes and are experiencing collaboration on honor-related violence with qualitative interviews as methods with six professionals. New Institutionalism and especially decoupling together with institutional logics and accounts was used as theoretical framework. The result of the study showed that decoupling was used by a number of the participating actors within the collaboration and despite this, the collaboration was described as functional according to the participating actors

Model Based Residual Policy Learning with Applications to Antenna Control

Non-differentiable controllers and rule-based policies are widely used for controlling real systems such as telecommunication networks and robots. Specifically, parameters of mobile network base station antennas can be dynamically configured by these policies to improve users coverage and quality of service. Motivated by the antenna tilt control problem, we introduce Model-Based Residual Policy Learning (MBRPL), a practical reinforcement learning (RL) method. MBRPL enhances existing policies through a model-based approach, leading to improved sample efficiency and a decreased number of interactions with the actual environment when compared to off-the-shelf RL methods.To the best of our knowledge, this is the first paper that examines a model-based approach for antenna control. Experimental results reveal that our method delivers strong initial performance while improving sample efficiency over previous RL methods, which is one step towards deploying these algorithms in real networks

I en värld där smala väger tyngst : övervikt som en medial konstruktion

“I en värld, där smala väger tyngst - Övervikt som medial konstruktion” är författad av Jeanette Berga och Mikaela Möllerstedt vid institutionen för Medie- och kommunikationsvetenskap vid Lunds universitet. I studien undersöks Svenska Dagbladets representation av överviktiga barn och övervikt under år 2015. Empirin utgörs av 76 artiklar vilka, utifrån textanalytiskt angreppssätt analyseras för att studera och tolka betydelser, förutfattade meningar gällande överviktiga barn och övervikt. Studiens ansats görs utifrån ett socialkonstruktivistiskt perspektiv och baseras på symtomal läsart för att urskilja representationer av övervikt. Syftet med studien är att, utifrån ett socialkonstruktivistiskt perspektiv öka kunskap om och synliggöra representationen av övervikt i en svensk morgontidning. Studiens mål är att undersöka representationen av överviktiga barn och hur den skiljer sig mellan överviktiga barn och vuxna samt att studera vilka motsättningar till representationen av övervikt som beskrivs. Övervikt representeras som avvikande och den överviktiga kroppen beskrivs underlägsen den smala, det är gemensamt för både överviktiga barn och vuxna. Överviktiga barn kategoriseras, precis som vuxna och tilldelas negativa karaktärsdrag. Både överviktiga barn och vuxna påstås vara avvikande och som bör korrigeras. Medier påstås ha en viktig roll i hur överviktiga barn representeras. Kroppspositivism representeras som en motståndsrörelse som kämpar för att överviktiga ska forma en gemensam stolthet över sina kroppar. Denna rörelse beskrivs växa fram och sprida sig, men kroppspositivism beskrivs möta motstånd och kritik, något som påstås grundas i att föreställningarna gällande den överviktiga kroppen och vad som tolkas som verklighet är svåra att förändra över tid och att få utrymme i medier

Dynamic Analysis of Harmonics in Electrical Systems

Frequency domain analysis and design of power systems is complicated in the presence of harmonics, switching dynamics, nonlinearities, unbalances, and for systems with mixed ac/dc dynamics. The reason is that linearization of the system does not lead to a time invariant system, but a system with periodically time varying dynamics, which implies that there is coupling between different frequencies. Often one has to rely on simplifying assumptions and simulation. The thesis uses linear time periodic (LTP) models to analyze power systems. The harmonic transfer function (HTF) for LTP systems is introduced. Using the HTF, the system can be treated as an infinitely dimensional linear time invariant system, which means that the system, under certain convergence conditions, can be analyzed using the well developed theory for LTI systems. The thesis contains four papers with power system applications. Paper I describes the modeling and analysis of networks including components with switching dynamics, such as diodes and thyristors. An algorithm for parameter estimation from experimental data is presented. Papers II and III treats modeling and analysis of single-phase railway systems. The modeling of the locomotives is performed in collaboration with industry. Paper IV treats analysis and control aspects of a converter for grid connection of a micro-turbine used for distributed power generation. This is a three-phase application done in collaboration with the industry