2,428,909 research outputs found
Reliability analysis of distribution systems with photovoltaic generation using a power flow simulator and a parallel Monte Carlo approach
This paper presents a Monte Carlo approach for reliability assessment of distribution systems with distributed generation using parallel computing. The calculations are carried out with a royalty-free power flow simulator, OpenDSS (Open Distribution System Simulator). The procedure has been implemented in an environment in which OpenDSS is driven from MATLAB. The test system is an overhead distribution system represented by means of a three-phase model that includes protective devices. The paper details the implemented procedure, which can be applied to systems with or without distributed generation, includes an illustrative case study and summarizes the results derived from the analysis of the test system during one year. The goal is to evaluate the test system performance considering different scenarios with different level of system automation and reconfiguration, and assess the impact that distributed photovoltaic generation can have on that performance. Several reliability indices, including those related to the impact of distributed generation, are obtained for every scenario.Postprint (published version
Voltage stability assessment for distrbuted generation in islanded microgrid system
The increasing energy demands are stressing the generation and transmission
capabilities of the power system. Distributed generation (DG), which generally
located in distribution systems, has the ability to meet some of the growing energy
demands. However, unplanned application of individual distributed generators might
cause other technical problems. The microgrid concept has the potential to solve
major problems arising from large penetration of DG in distribution systems. A
microgrid is not a forceful system when it is compared to a power system. This
project proposes a simulation approach to study voltage stability index (VSI) and
voltage stability analysis in microgrid system for the improvement of the dynamic
voltage stability in a microgrid in case of the dynamic voltage insufficiency. A
model of IEEE-14 Bus System has been presented as a case study of an islanded
microgird system. This project also presented line voltage stability index analysis
which accurately performs voltage stability analysis at each transmission line and
precisely predicts voltage collapse on power systems. A formula to calculate VSI has
been derived and applied on two cases on the system. To show the effectiveness of
the proposed voltage stability analysis method, this approach is implemented in a
microgrid test system (14-bus, 20 lines) in PSAT which is a MATLAB toolbox
environment. The test system has four diesel DGs and a wind turbine connected with
eleven constant loads. The dynamic simulation of the test system is carried out for
various types of disturbances. Islanded mode of operation is considered in this study.
Fast Voltage Stability Index (FVSI) and voltage stability analysis have been
successfully implemented and analysed
Distributed Leadership: challenging five generally held assumptions
This article reports on a study exploring a distributed perspective on school leadership through three head teacher case studies conducted in Scottish primary schools. Drawing from a sequence of in-depth, semi-structured and narrative style interviews conducted with each head teacher, as well as from a semi-structured questionnaire and sociometric analysis conducted with staff, the article analyses the experiences and the perceptions of head teachers. The paper finds that in practice, distributed leadership is more complex and challenging than often represented, challenging five generally held assumptions in the theoretical, policy and practice frames. Implications are drawn for educational leadership at both school and system levels
Model based code generation for distributed embedded systems
Embedded systems are becoming increasingly complex and more distributed. Cost and quality requirements necessitate reuse of the functional software components for multiple deployment architectures. An important step is the allocation of software components to hardware. During this process the differences between the hardware and application software architectures must be reconciled. In this paper we discuss an architecture driven approach involving model-based techniques to resolve these differences and integrate hardware and software components. The system architecture serves as the underpinning based on which distributed real-time components can be generated. Generation of various embedded system architectures using the same functional architecture is discussed. The approach leverages the following technologies – IME (Integrated Modeling Environment), the SAE AADL (Architecture Analysis and Design Language), and Ocarina. The approach is illustrated using the electronic throttle control system as a case study
Probabilistic model checking of complex biological pathways
Probabilistic model checking is a formal verification technique that has been successfully applied to the analysis of systems from a broad range of domains, including security and communication protocols, distributed algorithms and power management. In this paper we illustrate its applicability to a complex biological system: the FGF (Fibroblast Growth Factor) signalling pathway. We give a detailed description of how this case study can be modelled in the probabilistic model checker PRISM, discussing some of the issues that arise in doing so, and show how we can thus examine a rich selection of quantitative properties of this model. We present experimental results for the case study under several different scenarios and provide a detailed analysis, illustrating how this approach can be used to yield a better understanding of the dynamics of the pathway
Modeling and Reasoning over Distributed Systems using Aspect-Oriented Graph Grammars
Aspect-orientation is a relatively new paradigm that introduces abstractions
to modularize the implementation of system-wide policies. It is based on a
composition operation, called aspect weaving, that implicitly modifies a base
system by performing related changes within the system modules. Aspect-oriented
graph grammars (AOGG) extend the classic graph grammar formalism by defining
aspects as sets of rule-based modifications over a base graph grammar. Despite
the advantages of aspect-oriented concepts regarding modularity, the implicit
nature of the aspect weaving operation may also introduce issues when reasoning
about the system behavior. Since in AOGGs aspect weaving is characterized by
means of rule-based rewriting, we can overcome these problems by using known
analysis techniques from the graph transformation literature to study aspect
composition. In this paper, we present a case study of a distributed
client-server system with global policies, modeled as an aspect-oriented graph
grammar, and discuss how to use the AGG tool to identify potential conflicts in
aspect weaving
Implications of fault current limitation for electrical distribution networks
This paper explores the potential future need for fault current limitation in the UK's power system, and some of the technical implications of this change. It is estimated that approximately 300-400 distribution substations will require fault current limitation, based on the statistical analysis of the projected fault level "headroom" (or violation). The analysis uses a UK electrical system scenario that satisfies the Government's target for an 80% cut in CO2 emissions by 2050. A case study involving the connection of distributed generation (DG) via a superconducting fault current limiter (SFCL) is used to illustrate the potential protection and control issues. In particular, DG fault ride-through, autoreclosure schemes, and transformer inrush current can be problematic for SFCLs that require a recovery period. The potential solutions to these issues are discussed, such as the use of islanding or automation to reduce the fault level
Dynamic scaling in the 2D Ising spin glass with Gaussian couplings
We carry out simulated annealing and employ a generalized Kibble-Zurek
scaling hypothesis to study the 2D Ising spin glass with normal-distributed
couplings. The system has an equilibrium glass transition at temperature .
From a scaling analysis when at different annealing
velocities, we extract the dynamic critical exponent , i.e., the exponent
relating the relaxation time to the system length ; .
We find for both the Edwards-Anderson spin-glass order
parameter and the excess energy. This is different from a previous study of the
system with bimodal couplings [S. J. Rubin, N. Xu, and A. W. Sandvik, Phys.
Rev. E {\bf 95}, 052133 (2017)] where the dynamics is faster and the above two
quantities relax with different exponents (and that of the energy is larger).
We here argue that the different behaviors arise as a consequence of the
different low-energy landscapes---for normal-distributed couplings the ground
state is unique (up to a spin reflection) while the system with bimodal
couplings is massively degenerate. Our results reinforce the conclusion of
anomalous entropy-driven relaxation behavior in the bimodal Ising glass. In the
case of a continuous coupling distribution, our results presented here indicate
that, although Kibble-Zurek scaling holds, the perturbative behavior normally
applying in the slow limit breaks down, likely due to quasi-degenerate states,
and the scaling function takes a different form.Comment: 10 pages, 5 figure
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