Background: In developing and maintaining a large-scale system-of-systems (SoS), interface coordination & control (ICC) among interdependent subsystems is crucial for evolving individual subsystems and the overall SoS. However, the available literature offers little or no support to guide ICC in practice. Objectives: To describe how ICC can be done in the context of a large-scale SoS.We aimed to explore and analyze Ericsson’s (an example of a typical large-scaleSoS) current process and practices. To identify any limitations of the process, we investigated the challenges faced by practitioners regarding ICC, their reasons, and implications. Furthermore, we researched and proposed improvement possibilities to overcome the identified challenges. Method: We conducted a case study research and used observations, interviews, focus groups, and archival analysis for data collection. We used coding techniques from grounded theory and descriptive statistics to analyze qualitative and quantitative data, respectively. Moreover, the tabulation technique was employed to identify improvement opportunities. Results: We found that ICC is part of an overall technical coordination process. ICC is implemented through a recurrent cycle of activities. It brings together stakeholders to present upcoming changes, discuss their impact, and plan mitigation strategies. The outcome of ICC is a list of agreed-upon changes, impacted subsystems, and version numbers of interacting objects for the next release. We categorised the identified challenges in three groups: "people & subsystems", "tools, artifacts & technique", and "organization & management". These challenges impeded the effectiveness of the ICC process, quality of the SoS, and overall efficiency of the ICC and development process. Need for training, tool support, and stronger governance were identified as possible improvements to address multiple categories of identified challenges. Conclusion: The studied ICC process is well adapted for the large-scale SoS context. It is reasonably effective in minimizing the impact of evolving subsystems on the functioning and quality of SoS (as evident from the defect report analysis in this thesis). It also helps in cost-saving through early detection of compatibility-related issues. This thesis describes an ICC process used in practice, a novel contribution to the software configuration management (SCM) literature. In addition, companies in similar contexts can use the ICC description. The described ICC process is generalizableas as it is agnostic of the underlying development technologies used in a company.

The high penetration of renewable energy and the emerging concept of micro-grid system raises challenges to the high power conversion techniques. Multilevel converter plays the key role in such applications and is studied in detail in the dissertation. The topologies and modulation techniques for multilevel converter are categorized at first by a thorough literature survey. The pros and cons for various multilevel topologies and modulation techniques are discussed. The 3-level neutral point clamped (NPC) topology is selected to build a 200kVA, 20 kHz power conversion system. The modularized phase leg building block of the converter is carefully designed to achieve low loss and stress for high frequency and high power operation. The switching characteristics for all the commutation loops of 3-level phase leg are evaluated by double pulse tests. The switching performance is optimized for loss and stress tradeoff. A detailed loss model is built for system loss distribution and loss breakdown calculation. Loss and stress for the phase leg and 3-phase system are quantified at all power factors. The space vector modulation (SVM) for 3-level NPC converter is investigated to achieve loss reduction, neutral voltage balance and noise reduction. The loss model and simulation model provides a quantitative analysis for loss and neutral voltage ripple tradeoff. An improved SVM method is proposed to reduce NP imbalance and switching loss simultaneously. This method also ensures an evenly distributed device loss in each phase leg and gives a constant system efficiency under different power factors. Based on the improved modulation strategy, a new modulation scheme is then proposed with largely reduced conduction loss and switching stress. Moreover, the device loss and stress distribution on a phase leg is more even. This scheme also features on the simplified implementation. The improved switching characteristics for the proposed method are verified by double pulse tests. Also the system loss breakdown and the phase leg loss distribution analysis shows the loss reduction and redistribution result. The harmonic filter for the grid interface converter is designed with LCL topology. A detailed inductor current ripple analysis derives the maximum inductor current ripple and the ripple distribution in a line cycle. The inverter side inductor is designed with the optimum loss and size trade-off. The grid side inductor is designed based on grid code attenuation requirement. Different damping circuits for LCL filter are evaluated in detail. The filter design is verified by both simulation and hardware experiment. The average model for the 3-level NPC converter and its equivalent circuit is derived with the consideration of damping circuit in both ABC and d-q frame. The modeling and control loop design is verified by transfer function measurement on real hardware. The control loops design is also tested and verified on real hardware. The interleaved DC/DC chopper is introduced at last. The different interleaving methods and their current ripple are analyzed in detail with the coupled and non-coupled inductor. An integrated coupled inductor based on 3-dimentional core structure is proposed to achieve high power density and provide both CM and DM impedance for the inductor current and output current. / Ph. D.

Dans le processus de conception des véhicules, la vibration et le bruit sont des sujets d’étude très importants. En effet, les vibrations sont susceptibles d’affecter le comportement dynamique des structures et le bruit dégrade le confort acoustique des passagers. L’objectif principal de la thèse est de proposer un ensemble de méthodes pour l’optimisation du comportement dynamique des systèmes complexes afin de réduire les vibrations des structures et le bruit dans l’habitacle. À cet effet, on s’intéresse à des stratégies de contrôle des interfaces, comme le collage de couches viscoélastiques sur les zones les plus déformées, ou l’introduction de dispositifs frottants calibrés pour ajouter de l’amortissement à certaines fréquences de résonance. Les structures assemblées résultantes sont étudiées numériquement par une méthode de synthèse modale généralisée. La méthode de synthèse modale proposée contient plusieurs niveaux de condensation. Le premier concerne les degrés de libertés (DDL) internes de chaque sous-structure. La deuxième condensation s’effectue sur les modes de branches, de sorte à réduire le nombre de DDL aux interfaces entre les sous-structures. Pour les systèmes couplés fluide/structure, une troisième condensation portant sur les DDL du fluide est proposée. Suite à ces condensations, la dimension du système est fortement réduite. Cette méthode permet alors d’obtenir aussi bien la réponse forcée de la structure que les fluctuations du champ de pression dans le fluide. Les chemins de transmission acoustiques et vibratoires peuvent également être déduits des contributions modales intermédiaires. On montre que ces paramètres modaux peuvent être utilisés comme fonctions objectif pour une démarche d’optimisation des interfaces. Le front de Pareto des conceptions optimales est obtenu avec un algorithme génétique multi-objectif élitiste, appliqué à une approximation par krigeage de la fonction objectif. Cette approche modale est étendue à l’étude de systèmes non-linéaires. L’hypothèse fondamentale est que les modes non-linéaires sont faiblement couplés. Les paramètres modaux non-linéaires (fréquences propres, amortissements...), dépendent des amplitudes modales. L’idée est alors de calculer des modes normaux non-linéaires en fonction de leur amplitude et de superposer leurs réponses pour obtenir celle de la structure. La méthode est appliquée à des systèmes incorporant des non-linéarités de type Duffing et de frottement sec. Le cas particulier du frottement sec est considéré à travers un modèle de Masing généralisé. Deux approches modales sont développées : l’une basée sur les modes complexes, et l’autre basée sur les modes réels. L’utilisation de modes complexes ou réels dans la synthèse modale conduit à des termes d’amortissement par frottement différents. On montre que la synthèse modale non-linéaire combinée au modèle de Masing généralisé aboutit à une méthode numérique simple, rapide et efficace pour décrire le comportement non-linéaire de structures soumise à du frottement sec. / Noise and vibration are important topics in the automotive industry for several reasons, including passenger comfort and structural integrity. The main objective of this thesis is to propose a series of appropriate methods to optimize structural system characteristics, so that the vibration and noise can be reduced. To achieve this goal, interface control strategies are employed, including bonding viscoelastic layers onto the most heavily deformed zones and introducing frictional damping devices calibrated on certain resonance frequencies. Such built-up structural systems are numerically investigated via a generalized modal synthesis approach that incorporates several groups of modes. The employed modal synthesis approach consists of several levels of condensation. The first one is on the internal degrees of freedoms (DOFs) of each substructure, and the second condensation is on the branch modes so as to reduce the boundary DOFs among substructures. For coupled fluid-structural systems, a third condensation on the fluid DOFs is suggested. With these condensation techniques, the system dimension can be significantly reduced. The method allows us to obtain the forced response of the structures as well as the pressure variation of the fluids. Additionally, modal parameters characterizing vibration and noise transmission paths can be deduced as mid-stage results. We show that these modal parameters can be used as optimization objective during the interface configuration design. The Pareto front of the optimal design is achieved by employing Kriging approximations followed with an elitist multi-objective genetic algorithm. Another advantage of the modal approach is that a modal overview on the system characteristics is provided by analyzing the natural frequencies, modal damping ratios and the aforementioned modal parameters. The modal synthesis approach is further extended to study nonlinear systems. The basic assumption is that the nonlinear modes are weakly coupled. Nonlinear modal parameters, such as modal frequency and modal damping ratio, contain the essential nonlinear information and depend on modal amplitude. The main idea is to compute nonlinear normal modes according to their modal amplitude and superimpose the response of several nonlinear modes to obtain the overall forced response. The method is applied to systems involving Duffing and dry friction nonlinearities. In the case of dry friction, a generalized Masing model is considered to capture the dry friction nature. Both complex modes and real modes are used in the modal synthesis, leading to different frictional damping terms. We show that the nonlinear modal synthesis combined with the generalized Masing model yields a simple, fast and efficient numerical method to describe nonlinear performance of structures with dry friction.

With a big picture view of increasing the accessibility of space, standardization is applied within a service-oriented space program. The development of standardized spacecraft interfaces for numerous and varied payloads is examined through the lens of the creation of an Interface Control Document (ICD) within the Peregrine Lunar Lander project of Astrobotic Technologies, Inc. The procedure is simple, transparent, and adaptable; its applicability to other similar projects is assessed. / För en ökad tillgång till rymden finns det behov av standardisering för en förbättrad service. Utvecklingen av standardiserade rymdfarkostgränsytor för flera och olika nyttolaster har undersökts via ett dokumentet för gränssnittskontroll (ICD) inom projektet Peregrine Lunar Lander för Astrobotic Technologies, Inc. Proceduren är enkel, transparent och anpassningbar; dess användning för andra liknande projekt har värderats.