Architectures and algorithms for voltage control in power distribution systems

In this thesis, we propose a hierarchical control architecture for voltage in power distribution networks where there is a separation between the slow time-scale, in which the settings of conventional voltage regulation devices are adjusted, and the fast time-scale, in which voltage regulation through active/reactive power injection shaping is accomplished. Slow time-scale devices will generally be existing hardware, e.g., voltage regulation transformers, which will be dispatched at appropriate time intervals to reduce the wear on their mechanical parts. In contrast, fast time-scale devices are considered to be devices that connect to the grid through power electronics, e.g., photovoltaic (PV) installations. In the slow time-scale control, we propose a method to optimally set the tap position of voltage regulation transformers. We formulate a rank-constrained semidefinite program (SDP), which is then relaxed to obtain a convex optimization that is solved distributively with the Alternating-Direction Method of Multipliers (ADMM). In the fast time-scale control, we propose the following schemes: (i) a feedback-based approach to regulate system voltages, and (ii) an optimization-based approach that maintains the desired operating state through a quadratic program developed from a linear distribution system model. Finally, we showcase the operation of the two time-scale control architecture in an unbalanced three-phase distribution system. The test system in the case studies is derived from the IEEE 123-bus test system and has a high penetration of residential PV installations and electric vehicles (EVs). We provide several examples that demonstrate the interaction between the two time-scales and the impact of the proposed control on component behaviors

Earth history and the passerine superradiation.

Avian diversification has been influenced by global climate change, plate tectonic movements, and mass extinction events. However, the impact of these factors on the diversification of the hyperdiverse perching birds (passerines) is unclear because family level relationships are unresolved and the timing of splitting events among lineages is uncertain. We analyzed DNA data from 4,060 nuclear loci and 137 passerine families using concatenation and coalescent approaches to infer a comprehensive phylogenetic hypothesis that clarifies relationships among all passerine families. Then, we calibrated this phylogeny using 13 fossils to examine the effects of different events in Earth history on the timing and rate of passerine diversification. Our analyses reconcile passerine diversification with the fossil and geological records; suggest that passerines originated on the Australian landmass ∼47 Ma; and show that subsequent dispersal and diversification of passerines was affected by a number of climatological and geological events, such as Oligocene glaciation and inundation of the New Zealand landmass. Although passerine diversification rates fluctuated throughout the Cenozoic, we find no link between the rate of passerine diversification and Cenozoic global temperature, and our analyses show that the increases in passerine diversification rate we observe are disconnected from the colonization of new continents. Taken together, these results suggest more complex mechanisms than temperature change or ecological opportunity have controlled macroscale patterns of passerine speciation

Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures

Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo

Distributed Algorithms for Voltage Control in Electrical Networks

This thesis proposes a method to utilize distributed energy resources to provide the reactive power support required to stabilize and control voltage in electric power systems. As the number of distributed energy resources continues to increase, traditional approaches to the design and control of distribution networks will no longer be adequate. For example, on a clear day with high incident irradiance, it is possible for the active power injections from photovoltaic systems to reverse the flow of power and cause over-voltages on certain buses. The impacts of photovoltaic systems and plug-in hybrid electric vehicles on distribution networks are of particular interest due to the potentially high penetration of these devices in the years to come. Although the contribution of each device is small, collectively, they can have a significant impact on system reliability and performance. Since the placement and number of these devices are unknown to system operators, a decentralized-distributed control strategy is desired to determine the reactive power support provided for ancillary services. This thesis presents a resource allocation algorithm and an adpative algorithm that modifies its behavior to respond to voltage limits on a radial line. The ability of these distributed algorithms to control voltages is illustrated in a series of case studies

Data assembly notes

Notes on data assembly with PHYLUC

RAxML gene trees

Newick file of gene trees estimated using RAxM

Supplementary File S3

Subsampling and trimming strategy for phylogenetic analysi

Files for dating analyses in BEAST, MCMCTree

Files for dating analyses in BEAST (BEAUTI files and nucleotide data sets) and MCMCTree (control files and calibrated tree file