Estimating Relevant Portion of Stability Region using Lyapunov Approach and Sum of Squares

Traditional Lyapunov based transient stability assessment approaches focus on identifying the stability region (SR) of the equilibrium point under study. When trying to estimate this region using Lyapunov functions, the shape of the final estimate is often limited by the degree of the function chosen, a limitation that results in conservativeness in the estimate of the SR. More conservative the estimate is in a particular region of state space, smaller is the estimate of the critical clearing time for disturbances that drive the system towards that region. In order to reduce this conservativeness, we propose a methodology that uses the disturbance trajectory data to skew the shape of the final Lyapunov based SR estimate. We exploit the advances made in the theory of sum of squares decomposition to algorithmically estimate this region. The effectiveness of this technique is demonstrated on a power systems classical model.Comment: Under review as a conference paper at IEEE PESGM 201

Sistemas multi-agentes aplicados a proteção adaptativa de linhas de transmissão com três terminais

Este artigo discute o uso de agentes para a adaptação de ajustes de relés de distância para linhas com três terminais. Agentes são processos baseados em softwares capazes de buscar informações em redes de comunicação, interagindo com equipamentos e realizando tarefas em seu favor (neste caso os próprios relés). Resultados ilustrando o desempenho do método adaptativo proposto, e os comparando com métodos convencionais, são apresentados. É mostrado que os relés digitais em conjunto com sistemas agentes, agindo dentro de um sistema de comunicação, podem alterar os ajustes adaptativos e assim assegurar o correto funcionamento do sistema de proteção sobre uma larga variedade de condições de operação. O esquema proposto para proteção adaptativa também pode ser utilizado para a transferência de abertura de disjuntor através da rede dedicada para proteção de primeira zona ao longo da extensão total da linha.This paper discusses the adaptation of the settings of distance relays for three-terminal lines employing agents. Agents are software processes capable of searching for information in networks, interacting with pieces of equipment and performing tasks on behalf of their owners (relays). Results illustrating the performance of the adaptive method proposed, compared to conventional fixed settings, are presented. It is shown that the digital relays and agents acting within a communication structure can alter adaptive settings to ensure correct performance over a wide variety of operation conditions. The proposed relaying scheme can also be utilized for transferring the trip of the first zone, clearing over the entire line

Transient Stability Assessment of Cascade Tripping of Renewable Sources Using SOS

There has been significant increase in penetration of renewable generation (RG) sources all over the world. Localized concentration of many such generators could initiate a cascade tripping sequence that might threaten the stability of the entire system. Understanding the impact of cascade tripping process would help the system planner identify trip sequences that must be blocked in order to increase stability. In this work, we attempt to understand the consequences of cascade tripping mechanism through a Lyapunov approach. A conservative definition for the stability region (SR) along with its estimation for a given cascading sequence using sum of squares (SOS) programming is proposed. Finally, a simple probabilistic definition of the SR is used to visualize the risk of instability and understand the impact of blocking trip sequences. A 3-machine system with significant RG penetration is used to demonstrate the idea.Comment: To appear in PESGM 2018, Portland, OR, 201

Coordinated interchange scheduling and opportunity cost payment: a market proposal to seams issues

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Characterizing the Cool KOIs. VI. H- and K-band Spectra of Kepler M Dwarf Planet-Candidate Hosts

We present H- and K-band spectra for late-type Kepler Objects of Interest (the "Cool KOIs"): low-mass stars with transiting-planet candidates discovered by NASA's Kepler Mission that are listed on the NASA Exoplanet Archive. We acquired spectra of 103 Cool KOIs and used the indices and calibrations of Rojas-Ayala et al. to determine their spectral types, stellar effective temperatures and metallicities, significantly augmenting previously published values. We interpolate our measured effective temperatures and metallicities onto evolutionary isochrones to determine stellar masses, radii, luminosities and distances, assuming the stars have settled onto the main-sequence. As a choice of isochrones, we use a new suite of Dartmouth predictions that reliably include mid-to-late M dwarf stars. We identify five M4V stars: KOI-961 (confirmed as Kepler 42), KOI-2704, KOI-2842, KOI-4290, and the secondary component to visual binary KOI-1725, which we call KOI-1725 B. We also identify a peculiar star, KOI-3497, which has a Na and Ca lines consistent with a dwarf star but CO lines consistent with a giant. Visible-wavelength adaptive optics imaging reveals two objects within a 1 arc second diameter; however, the objects' colors are peculiar. The spectra and properties presented in this paper serve as a resource for prioritizing follow-up observations and planet validation efforts for the Cool KOIs, and are all available for download online using the "data behind the figure" feature.Comment: Accepted for publication in the Astrophysical Journal Supplement Series (ApJS). Data and table are available in the sourc

Riverine macrosystems ecology: sensitivity, resistance, and resilience of whole river basins with human alterations

Riverine macrosystems are described here as watershed-scale networks of connected and interacting riverine and upland habitat patches. Such systems are driven by variable responses of nutrients and organisms to a suite of global and regional factors (eg climate, human social systems) interacting with finer-scale variations in geology, topography, and human modifications. We hypothesize that spatial heterogeneity, connectivity, and asynchrony among these patches regulate ecological dynamics of whole networks, altering system sensitivity, resistance, and resilience. Long-distance connections between patches may be particularly important in riverine macrosystems, shaping fundamental system properties. Furthermore, the type, extent, intensity, and spatial configuration of human activities (eg land-use change, dam construction) influence watershed-wide ecological properties through effects on habitat heterogeneity and connectivity at multiple scales. Thus, riverine macrosystems are coupled social–ecological systems with feedbacks that influence system responses to environmental change and the sustainable delivery of ecosystem services