Modeling of Inverter-Based Microgrid for Small-Signal and Large-Signal Stability Analysis

Integration of inverter-based resources (IBRs) such as solar photovoltaic, wind, and battery storage, is both a boon and a bane for electric power systems. On one hand, IBRs have helped in making electrical energy a clean (carbon-free) source of energy. On other hand, the dynamics of IBRs have changed the way power system studies have been carried out. With the advantages IBRs offer over conventional resources, it is assumed that a small distribution power system (microgrid) will have a 100% IBRs penetration in the future. Such a microgrid can operate in grid-connected mode or in an islanded mode. Both modes of operation bring challenges to system stability due to faster control dynamics of IBRs and can pose problems such as blackouts if the dynamics are not studied and mitigated properly. IBRs in a microgrid can operate in a grid-following (GFL) mode or grid-forming mode (GFM). We studied the effect of GFM inverters, GFL inverters, and elements of microgrid (such as lines, and transformers) on microgrid stability. We studied how solar radiation affects the bus voltage and how the inverter gains and line impedance can make a system unstable. Based on the study stable limits for a single inverter connected to a strong point of common coupling (PCC) were established. Since the study of a microgrid is still an evolving topic it has been observed that some elements such as a transformer are not modeled in detail for the stability study of the system. It was shown how detailed modeling of different transformer models will help in understanding the cause of high frequencies in the system following a disturbance. Droop type GFM inverters mimic the droop characteristics of the synchronous generator to control the frequency and voltage. Droop control is best suited for a power system where lines are highly inductive which is not the case for lines of a microgrid that are highly resistive. This results in a weak microgrid system. A modified primary control technique was developed for improving reactive power sharing between the inverters and thus making the microgrid system strong. Virtual Synchronous Generator (VSG) type of control of GFM inverters is another widely used control technique for GFM type of inverters. In an islanded microgrid GFM and GFL inverters work in parallel and interaction between these different types of inverter controls plays a huge role in system stability. Therefore, it is necessary to study the interactions of dynamics between GFM and GFL inverters to understand and define the stability limits of a microgrid system. We studied the inter-inverter dynamics in an islanded microgrid and demonstrated how in a deregulated market one inverter can aid another inverter to make the overall system more stable and reliable. A nonlinear study of inverters for large-signal stability was also performed for islanded microgrid system

Harvest: An Integrated Set of Tools for a Digital Library

This paper discusses the problems in organization and retrieval due proliferation resources in digital format over the web. It presents the harvest systems which tackles the problems through a set of customizable tools for gathering information from diverse repositories, building topic specific content indexes, flexibly searching indexes, widely replicating them, and caching objects as they are retrieved across the Internet. Harvest permits flexible construction of information services that use both the network and information servers efficiently. It is easily configurable system and can be deployed to automatically collect and summarize related objects from around the Internet into digital library collections

Identifying and Separating Interaction Concerns from Distributed Feature Components

Implementation of distributed applications over the internet needs the interaction among homogenous/ heterogeneous subcomponents to a great extent. This interaction among heterogeneous components can be implemented by considering the semantic issues of its related compositions. The coordination and cooperation between services at the two ends of application make the problem of interaction more significant. The term interaction can formerly be described in terms of features and services of the application or of the subcomponent

Representing Aspect Model as Graph Transformation

In this paper we discussed a new method for representing aspect models. This method uses the basics of UML to devise a new way for specifying the model level aspects and transformations among them. The resultant model is effective from both expression and scaling point of view. The work in this paper is based on assumed transaction processing system in a bank

Comparative Performance of DVR and STATCOM for Voltage Regulation in Radial Microgrid with High Penetration of RES

In recent years, the penetration of renewable energy sources (RES) in microgrids and distribution system feeders has increased manifold. Moreover, the advancement of power electronics-based devices in the distribution system has significantly increased the number of sensitive loads. Variations in the voltage under intermittent RES create functional problems with sensitive loads, necessitating voltage regulators (VR) installation. In this paper, two custom power devices: dynamic voltage restorer (DVR) and static synchronous compensator (STATCOM), used for voltage regulation in a microgrid, are investigated under different operating conditions. The efficacy of DVR and STATCOM for voltage regulation in an 11-node radial microgrid with high penetration of RES is simulated under a MATLAB Simulink environment. Furthermore, the simulated microgrid voltage profile results are analyzed to evaluate the efficacy of both voltage regulators

Analysing the Security Aspects of IoT using Blockchain and Cryptographic Algorithms

Technological advancement is a never-ending field that shows its evolution from time to time. In 1832, with the invention of the electromagnetic telegraph, the era of the Internet of Things (IoT) began. Within the time of 190 years, this technological domain has revolutionized IoT and made it omnipresent. However, with this evolved and omnipresent nature of IoT, many drawbacks, privacy, interoperability, and security issues have also been generated. These different concerns should be tackled with some newer technologies rather than the conventional ones as somehow, they are only the generator of those issues. Outdated Security could be an appropriate issue of IoT along with the centralized point of failure. It also possesses more concerns and challenges to tackle. On the other side, there is a visible solution to address the challenges of IoT in this developing domain of technology. The visible approach is Blockchain which acted as the backbone in securing Bitcoin in 2008, which was created by the pseudo group named Satoshi Nakamoto. Blockchain has evolved from Blockchain 1.0 to Blockchain 4.0 as the latest one depicts its amalgamation with another component of Industry 4.0 i.e., Artificial Intelligence (AI). AI will give the ability to think logically and like humans. In addition to this SMART solution, there is also an advanced cryptographical technique known as the Elliptic Curve Digital Signature Algorithm (ECDSA) which can enhance the security spectrum of IoT if applied appropriately. This paper produces a vision to enhance and optimize the security of IoT using a network peer-to-peer technology Blockchain along with advanced cryptography

Improved Contextual Grounding by Combining Multiple Speech Transcription Hypotheses

Processing a user’s voice command includes parsing the command to derive the components referred to therein. These identified components or arguments are then mapped to items or objects in the real world in a process known as “grounding.” In some cases, transcription inaccuracies can make it infeasible for a virtual assistant or other application to achieve accurate grounding, thus making it impossible to service the user’s command. This disclosure describes techniques to improve grounding by taking into account the top N highest-likelihood transcriptions for a user’s voice command along with contextual information accessed with the user’s permission. Improved query interpretation can enable a virtual assistant or other application to accurately interpret the command and thereby improve user experience