Effect of placement of droop based generators in distribution network on small signal stability margin and network loss

For a utility-connected system, issues related to small signal stability with Distributed Generators (DGs) are insignificant due to the presence of a very strong grid. Optimally placed sources in utility connected microgrid system may not be optimal/stable in islanded condition. Among others issues, small signal stability margin is on the fore. The present research studied the effect of location of droop-controlled DGs on small signal stability margin and network loss on a modified IEEE 13 bus system, an IEEE 33-bus distribution system and a practical 22-bus radial distribution network. A complete dynamic model of an islanded microgrid was developed. From stability analysis, the study reports that both location of DGs and choice of droop coefficient have a significant effect on small signal stability, transient response of the system and network losses. The trade-off associated with the network loss and stability margin is further investigated by identifying the Pareto fronts for modified IEEE 13 bus, IEEE 33 and practical 22-bus radial distribution network with application of Reference point based Non-dominated Sorting Genetic Algorithm (R-NSGA). Results were validated by time domain simulations using MATLAB. (C) 2016 Elsevier Ltd. All rights reserved

Voltage Stability Analysis in Medium-Voltage Distribution Networks Using a Second-Order Cone Approximation

This paper addresses the voltage stability margin calculation in medium-voltage distribution networks in the context of exact mathematical modeling. This margin calculation is performed with a second-order cone (SOCP) reformulation of the classical nonlinear non-convex optimal power flow problems. The main idea around the SOCP approximation is to guarantee the global optimal solution via convex optimization, considering as the objective function the λ-coefficient associated with the maximum possible increment of the load consumption at all the nodes. Different simulation cases are considered in one test feeder, described as follows: (i) the distribution network without penetration of distributed generation; (ii) the distribution network with penetration of distributed generation; and (iii) the distribution grid with capacitive compensation. Numerical results in the test system demonstrated the effectiveness of the proposed SOCP approximation to determine the λ-coefficient. In addition, the proposed approximation is compared with nonlinear tools available in the literature. All the simulations are carried out in the MATLAB software with the CVX package and the Gurobi solver

MAGAN: Margin Adaptation for Generative Adversarial Networks

We propose the Margin Adaptation for Generative Adversarial Networks (MAGANs) algorithm, a novel training procedure for GANs to improve stability and performance by using an adaptive hinge loss function. We estimate the appropriate hinge loss margin with the expected energy of the target distribution, and derive principled criteria for when to update the margin. We prove that our method converges to its global optimum under certain assumptions. Evaluated on the task of unsupervised image generation, the proposed training procedure is simple yet robust on a diverse set of data, and achieves qualitative and quantitative improvements compared to the state-of-the-art

What happened to efficiency in electricity industries after reforms?

The last two decades have witnessed widespread power market reforms in both developed and developing countries that have cost billions of dollars. Among the key aims (and assumptions) of these reforms, there has always been realization of improvements in power sector efficiency. This paper questions the validity of this hypothesis. Using panel data from 92 countries covering the period 1982–2008, empirical models are developed and analyzed. The research findings suggest that the impact of the reforms on electricity industry performance is statistically significant but also limited. The results imply that, after controlling for country-specific variables, application of liberal market models in electricity industries slightly increases efficiency in power sector. Besides, we detect a positive relationship between reform process and the percentage share of network (transmission and distribution) losses in total electricity supplied; meaning that as countries take more reform steps the network losses as a fraction of power generated tend to increase. Moreover, the study puts forward that income level and other country specific features are more important determinants of industry efficiency than the reform process. Overall, contrary to expectations of substantial increases in sector efficiency, the paper concludes that introducing a decentralized market model with competition in the electricity sector has a limited increasing effect on power industry performance