Power System Dynamic Simulations Using a Parallel Two-Level Schur-Complement Decomposition

As the need for faster power system dynamic simulations increases, it is essential to develop new algorithms that exploit parallel computing to accelerate those simulations. This paper proposes a parallel algorithm based on a two-level, Schur-complement-based, domain decomposition method. The two-level partitioning provides high parallelization potential (coarse- and fine-grained). In addition, due to the Schur-complement approach used to update the sub-domain interface variables, the algorithm exhibits high global convergence rate. Finally, it provides significant numerical and computational acceleration. The algorithm is implemented using the shared-memory parallel programming model, targeting inexpensive multi-core machines. Its performance is reported on a real system as well as on a large test system combining transmission and distribution networks

The robust design of complex systems

Robust Engineering Design has evolved as an important methodology for the integration of quality with the process of design. The methodology encompasses the disciplines of experimental design, model building and optimization. First an experiment is conducted on a system (or a simulation of the system), second a model is built to emulate the system and finally the emulation model is used to optimize the system design. Applying these methods to large problems can be difficult and time-consuming because of the complexity of most design problems. It is the goal of this thesis to introduce methods which reduce problem complexity and so make the application of Robust Engineering Design (RED) methodology easier for large design problems. By drawing from methods used in systems theory and circuit optimization several techniques are presented with the aim of reducing the complexity of performing experiments for Robust Engineering Design. A common framework for experimentation is created by combining a commercial circuit simulator with established methods for experimental design and model building. This provides the basis for experimentation in subsequent chapters. A method of design optimization with respect to quality is presented to complete the model-based Robust Engineering Design cycle. Three approaches to reducing problem complexity are adopted. First a method of system decomposition is applied directly to an electronic circuit to reduce the size of experiment required for RED. Second a method of modelling system response functions is described which integrates the action of the circuit simulator with the model building process. Third information about system topology is used in the design of experiments to enhance the model-building process. Conclusions are drawn about the effectiveness of the approaches described with respect to the impact on problem complexity

Challenges in using the actor model in software development, systematic literature review

Toimijamalli on hajautetun ja samanaikaisen laskennan malli, jossa pienet osat ohjelmistoa viestivät keskenään asynkronisesti ja käyttäjälle näkyvä toiminnallisuus on usean osan yhteistyöstä esiin nouseva ominaisuus. Nykypäivän ohjelmistojen täytyy kestää valtavia käyttäjämääriä ja sitä varten niiden täytyy pystyä nostamaan kapasiteettiaan nopeasti skaalautuakseen. Pienempiä ohjelmiston osia on helpompi lisätä kysynnän mukaan, joten toimijamalli vaikuttaa vastaavan tähän tarpeeseen. Toimijamallin käytössä voi kuitenkin esiintyä haasteita, joita tämä tutkimus pyrkii löytämään ja esittelemään. Tutkimus toteutetaan systemaattisena kirjallisuuskatsauksena toimijamalliin liittyvistä tutkimuksista. Valituista tutkimuksista kerättiin tietoja, joiden pohjalta tutkimuskysymyksiin vastattiin. Tutkimustulokset listaavat ja kategorisoivat ohjelmistokehityksen ongelmia, joihin käytettiin toimijamallia, sekä erilaisia toimijamallin käytössä esiintyviä haasteita ja niiden ratkaisuita. Tutkimuksessa löydettiin toimijamallin käytössä esiintyviä haasteita ja näille haasteille luotiin uusi kategorisointi. Haasteiden juurisyitä analysoidessa havaittiin, että suuri osa toimijamallin haasteista johtuvat asynkronisen viestinnän käyttämisestä, ja että ohjelmoijan on oltava jatkuvasti tarkkana omista oletuksistaan viestijärjestyksestä. Haasteisiin esitetyt ratkaisut kategorisoitiin niihin liittyvän lisättävän koodin sijainnin mukaan

Accelerated Simulation of Large Scale Power System Transients

RÉSUMÉ Le temps de simulation est un paramètre crucial de l’analyse des transitoires dans les réseaux électriques et il est en train de devenir l’un des facteurs les plus importants pour mesurer les performances et la fiabilité des logiciels. Actuellement, la vitesse et les performances des processeurs ont atteint un point où l’accélération de gain en vitesse et d’opérations en virgule flottante peut être réduite en se concentrant uniquement sur l’aspect vitesse des processeurs individuels. Au contraire, la recherche en informatique et le développement de matériel informatique tendent de plus en plus à rendre les processeurs parallèles plutôt que plus rapides. D'autre part, la simulation des systèmes électriques devient de plus en plus complexe avec l'introduction de modèles complexes tels que les énergies renouvelables, les composantes de réseaux intelligents et l'électronique de puissance. En outre, la demande de puissance sans cesse croissante et l’augmentation de la zone de couverture des réseaux de distribution d’énergie contribuent à l’augmentation de la taille des réseaux de distribution d’énergie et ralentissent encore plus la simulation électromagnétique transitoire de ces réseaux. De nombreux -logiciels de simulation de type EMT effectuent actuellement leurs opérations de manière séquentielle en utilisant un seul - processeur, plutôt que tous les processeurs de la machine. Ce comportement entraîne un temps de simulation long et introduit des difficultés pour simuler des réseaux de systèmes d'alimentation plus avancés et complexes. Ce type de délai devient un obstacle lorsque de grands réseaux, réels ou existants, sont utilisés. Par exemple, simuler le réseau d'Hydro-Québec doté d'une matrice de taille 41555 × 41555 et contenant un grand nombre de dispositifs de commutation et des éléments non linéaires nécessite 1765 secondes pour simuler une seconde avec un pas de temps de 50us. La programmation parallèle multithread est maintenant disponible dans les compilateurs modernes. Elle peut être utilisée pour améliorer de manière significative les performances des calculs EMT. La recherche actuelles dans ce domaine est principalement appliqué à des systèmes moins complexes qui nécessitent l'intervention de l'utilisateur pour le découpage parallèle et manque de généralisation pour toute topologie rencontrée dans les études réels. Cette thèse développe une méthode de parallélisation entièrement automatique applicable aux systèmes à grande échelle avec des topologies arbitraires sans aucune intervention de l'utilisateur.----------ABSTRACT Simulation time is a crucial parameter in power system transient analysis. The simulation needs for electromagnetic transients are continuously increasing. The electromagnetic transient (EMT) type tools are now also used for the simulation of slower electromechanical transients in large scale power systems. The EMT approach for power system analysis is the most accurate approach, but it suffers from computation performance issues. Research on this aspect is currently of crucial importance. Research is timely and should increase the application range of EMT-type tools. In fact very fast EMT-type tools can have a major impact on the simulation and analysis of modern power grids with increased penetration of renewables. Currently, computer processor speed and performance reached a point where not much speed gain and floating-point operation acceleration can be achieved by only focusing on the speed aspect of individual processors. Rather, the trend in computer research and hardware development is becoming more and more focused on making processors parallel rather than faster. Many EMT-Type simulation packages currently perform their operations sequentially by using only one CPU core rather than all machine processors. This behaviour results in long simulation time and introduces major difficulties when simulating large and complex power grids. This type of delay becomes a show stopper when large, real and existing networks are used. Multithreaded parallel programming is now available in modern compilers. It can be used to significantly improve the performance of EMT computations. Current research in this field has been mostly applied to less complicated systems and requires user intervention. This thesis develops a fully automatic parallelization method that is applicable to large scale systems with arbitrary topologies. This PhD thesis presents existing progress in the field of electromagnetic transient simulation acceleration and highlights the different approaches that are adopted to achieve faster EMT simulation. The focus is mainly on threading through CPU exclusively on modern desktop computers used by engineers on daily basis

Application of mathematical programming techniques to power system optimization

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Development and implementation of efficient segmentation algorithm for the design of antennas and arrays

Ph.DDOCTOR OF PHILOSOPH

Factorized solution of power system state estimation

In this thesis a general two-stage factorized solution for nonlinear WLS problems has been developed, with two main applications: a geographically distributed multilevel hierarchical state estimation algorithm, suitable for very large-scale power systems covering multiple control areas; and a factorized multi-stage version, which enhances the convergence speed and reduces the computational effort. In the multilevel hierarchical state estimation, the way the algorithm can be customized to the system decomposition is analyzed, particularizing the methodology for the distribution feeder, substation, and transmission or multi-area system levels. Tests are performed on benchmark and realistic large-scale networks, including the entire European transmission system. The main advantage of this method lies in the possibility of filtering raw measurements at the specific location where they are captured, and then sending only local estimates for further processing by higher level state estimators. This multilevel estimator will be of special interest in upcoming systems, where the increased introduction of ICTs at lower levels and widespread interconnections at the regional transmission level are leading to an explosion of information which could be hardly managed by a single energy management system. In the second case, different approaches are proposed, all of them sharing a first linear stage, clearly showing computational efficiency and enhanced convergence speed compared to the conventional estimator. After a two-stage algorithm, the dissertation develops a bilinear three-stage state estimation factorization which virtually eliminates the need to iterate yielding the same solution as that provided by the Gauss-Newton iterative method. This is also extended to the case in which equality constraints are to be enforcedPremio Extraordinario de Doctorado U

Choke management and production optimization in oil and gas fields

When a well is brought on production, the selection of the optimum choke management strategy should aim towards maximizing well productivity and minimizing the risk of completion or wellbore failures. Until recently, ramp-up practices were based on liquid rate recommendations or empirical guidelines on choke sizes for the early life of a well. The objective of this dissertation is to establish a systematic method for the design of choke management strategies and flowback operations under wellbore completion and reservoir constraints. In order to account for multi-well pressure interference through the surface facilities, an integration scheme is proposed for the effective coupling of the well models with the surface gathering network. Finally, an optimization framework is deployed to maximize the daily operating income by properly adjusting well and network controls. In the first part of the dissertation, we study choke management on an individual well basis. A general framework is introduced for comparing drawdown strategies for conventional and unconventional wells. Using analytical and numerical reservoir models we conclude that in conventional open-hole completions no more than 70% of the drawdown should be applied in less than 30% of the ramp-up period. In formations characterized by high diffusivity (e.g. high permeability gas formations), the bottom-hole-pressure should be reduced linearly with time. Using nodal analysis, a systematic method is proposed for translating a set of wellbore, completion and reservoir constraints into a choke management schedule. Illustrative examples are presented both for conventional and unconventional wells. For hydraulically fractured wells, we introduced a coupled rate-stress criterion for mitigating proppant flowback and fracture closure near the wellbore. Application of the method suggests drawdown rates which are in agreement with successfully implemented field practices (5-10 psi/hour). In order to capture well interference through the surface network, a multiphase (black-oil) pipeline network model has been developed. The network solver is formulated using fractional-flow theory, assuming steady state flow and concurrent flow of oil, water and gas phases. Using network topology, closed pipeline loops are unified into clusters where loop equations are solved using the Fletcher-Reeves conjugate gradient method. The network solver is validated using published network solutions, compared with field data and benchmarked against commercial network solvers. The well models are integrated with the surface gathering network using an explicit scheme that performs multi-point surface nodal analysis using fixed-point iteration. The integration scheme converges linearly and accurately captures well interference both for naturally flowing wells and wells on artificial lift. The integration scheme (forward model) is combined with various gradient based and derivative free optimization routines to optimize the well and network controls for a synthetic field. We observe that the use of integrated modeling can achieve significant improvements in terms of daily operating income (by up to 30%). Finally, we introduce a reduced variable range approach which can accelerate the performance of sampling and global search methods in complex production systems. This work introduces a systematic method for the design of choke management practices and presents new methods for integrating well models with the surface pipeline networkPetroleum and Geosystems Engineerin