A distributed generation (DG) system with a photovoltaic (PV) source supported by energy storage devices and feeding dc-and ac-loads in islanded-mode operation, is considered and analyzed. As all the DG parts are interfaced through power electronic dc/dc or dc/ac converters, a control strategy is introduced which is applied directly on each individual duty-ratio converter input. The aim of the control design is to drive the PV-array energy production at the maximum power and to ensure instantaneous power balance in the limits of the storage capacity. In this scheme, critical quality demands are fulfilled, such as operation with constant ac-and dc-voltages at the load sides, independently from the power consumed. The particular controllers are implemented by applying the standard local cascaded structure with the inner-loops being fast nonlinear proportional-integral current-mode controllers. To avoid adverse impacts on the system performance, caused by contradictory actions between the individual controllers, the complete accurate DG model is considered as an isolated microgrid with the fast inner-loop controllers incorporated. Adopting a common modular inner-loop nonlinear controller form, a rigorous novel stability analysis is developed by constructing the appropriate Lyapunov function in a new sequential manner. Finally, the stability and convergence to the equilibrium are verified by simulation and experimental results.Index Terms-Lyapunov stability, microgrid control, nonlinear dynamic system, stability analysis of distributed generation systems.
The proliferation of heterogeneous computing platforms presents the parallel computing community with new challenges. One such challenge entails evaluating the efficacy of such parallel architectures and identifying the architectural innovations that ultimately benefit applications. To address this challenge, we need benchmarks that capture the execution patterns (i.e., dwarfs or motifs) of applications, both present and future, in order to guide future hardware design. Furthermore, we desire a common programming model for the benchmarks that facilitates code portability across a wide variety of different processors (e.g., CPU, APU, GPU, FPGA, DSP) and computing environments (e.g., embedded, mobile, desktop, server).As such, we present the latest release of OpenDwarfs, a benchmark suite that currently realizes the Berkeley dwarfs in OpenCL, a vendor-agnostic and openstandard computing language for parallel computing. Using OpenDwarfs, we characterize a diverse set of modern fixed and reconfigurable parallel platforms: multicore CPUs, discrete and integrated GPUs, Intel Xeon Phi co-processor, as well as a FPGA. We describe the computation and communication patterns exposed by a representative set of dwarfs, obtain relevant profiling data and execution information, and draw conclusions that highlight the complex interplay between dwarfs' patterns and the underlying hardware architecture of modern parallel platforms.
Background: Hypothesis generation in molecular and cellular biology is an empirical process in which knowledge derived from prior experiments is distilled into a comprehensible model. The requirement of automated support is exemplified by the difficulty of considering all relevant facts that are contained in the millions of documents available from PubMed. Semantic Web provides tools for sharing prior knowledge, while information retrieval and information extraction techniques enable its extraction from literature. Their combination makes prior knowledge available for computational analysis and inference. While some tools provide complete solutions that limit the control over the modeling and extraction processes, we seek a methodology that supports control by the experimenter over these critical processes.
In this paper we examine and compare the efficiency of four European electricity markets (NordPool, Italian, Spanish and Greek) of different microstructure and level of maturity, by testing the weak form of the Efficient Market Hypothesis (EMH). To quantify the level of efficiency deviation of each market from the ‘ideal’ or ‘benchmark market of random walk’, we have constructed a Composite Electricity Market Efficiency Index (EMEI), inspired by similar works on other energy commodities. The proposed index consists of linear and nonlinear components each one measuring a different feature or dimension of the market efficiency such as its complexity, fractality, entropy, long-term memory or correlation, all connected to the associated benchmark values of the Random Walk Process (RWP). The key findings are that overall, all examined electricity markets are inefficient in respect to the weak form of EMH and the less inefficient market, as measured by the EMEI is the NordPool, closely followed by the Spanish market, with the Italian being the third. The most inefficient market is the Greek one. These results are in accordance with the predominant view about the maturity of these markets. This study contributes significantly on improving the research framework in developing consistent and robust tools for efficiency measurement, while the proposed index can be a valuable tool in designing improved guidelines towards enhancing the efficiency of electricity markets.
The proliferation of heterogeneous computing platforms presents the parallel computing community with new challenges. One such challenge entails evaluating the efficacy of such parallel architectures and identifying the architectural innovations that ultimately benefit applications. To address this challenge, we need benchmarks that capture the execution patterns (i.e., dwarfs or motifs) of applications, both present and future, in order to guide future hardware design. Furthermore, we desire a common programming model for the benchmarks that facilitates code portability across a wide variety of different processors (e.g., CPU, APU, GPU, FPGA, DSP) and computing environments (e.g., embedded, mobile, desktop, server).As such, we present the latest release of OpenDwarfs, a benchmark suite that currently realizes the Berkeley dwarfs in OpenCL, a vendor-agnostic and open-standard computing language for parallel computing. Using OpenDwarfs, we characterize a diverse set of fixed and reconfigurable parallel platforms: multicore CPUs, discrete and integrated GPUs, Intel Xeon Phi coprocessor, as well as a FPGA. We describe the computation and communication patterns exposed by a representative set of dwarfs, obtain relevant profiling data and execution information, and draw conclusions that highlight the complex interplay between dwarfs' patterns and the underlying hardware architecture of modern parallel platforms.
The fundamental changes in power systems have led to an increased complexity in their operation and control. Wide area monitoring systems (WAMS) are considered as a key solution in order to deal with these challenges. In this paper, a general description of WAMS is presented along with a literature review on the topic. Emphasis is given on documenting real up to date applications of WAMS in the European power network. Moreover, wide area damping control systems for power system oscillations are also presented. A description is provided of two innovative WAMS combined with damping control using FACTS devices and Battery Energy Energy Storage Systems (BESS) that are currently implemented in the European network.
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