Solid-state switch-mode rectification converters have reached a matured level for improving power quality in terms of power-factor correction (PFC), reduced total harmonic distortion at input AC mains and precisely regulated DC output in buck, boost, buck-boost and multilevel modes with unidirectional and bidirectional power flow. This paper deals with a comprehensive review of improved power quality converters (IPQCs) configurations, control approaches, design features, selection of components, other related considerations, and their suitability and selection for specific applications. It is targeted to provide a wide spectrum on the status of IPQC technology to researchers, designers and application engineers working on switched-mode AC-DC converters. A classified list of more than 450 research publications on the state of art of IPQC is also given for a quick reference.

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A review of single-phase improved power quality AC-DC converters

This paper investigates (i) preplanned switching events and (ii) fault events that lead to islanding of a distribution subsystem and formation of a micro-grid. The micro-grid includes two distributed generation (DG) units. One unit is a conventional rotating synchronous machine and the other is interfaced through a power electronic converter. The interface converter of the latter unit is equipped with independent real and reactive power control to minimize islanding transients and maintain both angle stability and voltage quality within the micro-grid. The studies are performed based on a digital computer simulation approach using the PSCAD/EMTDC software package. The studies show that an appropriate control strategy for the power electronically interfaced DG unit can ensure stability of the micro-grid and maintain voltage quality at designated buses, even during islanding transients. This paper concludes that presence of an electronically-interfaced DG unit makes the concept of micro-grid a technically viable option for further investigations.

Micro-grid autonomous operation during and subsequent to islanding process

As solar photovoltaic power generation becomes more commonplace, the inherent intermittency of the solar resource poses one of the great challenges to those who would design and implement the next generation smart grid. Specifically, grid-tied solar power generation is a distributed resource whose output can change extremely rapidly, resulting in many issues for the distribution system operator with a large quantity of installed photovoltaic devices. Battery energy storage systems are increasingly being used to help integrate solar power into the grid. These systems are capable of absorbing and delivering both real and reactive power with sub-second response times. With these capabilities, battery energy storage systems can mitigate such issues with solar power generation as ramp rate, frequency, and voltage issues. Beyond these applications focusing on system stability, energy storage control systems can also be integrated with energy markets to make the solar resource more economical. Providing a high-level introduction to this application area, this paper presents an overview of the challenges of integrating solar power to the electricity distribution system, a technical overview of battery energy storage systems, and illustrates a variety of modes of operation for battery energy storage systems in grid-tied solar applications. The real-time control modes discussed include ramp rate control, frequency droop response, power factor correction, solar time-shifting, and output leveling.

Battery Energy Storage for Enabling Integration of Distributed Solar Power Generation

This paper presents a comprehensive review on the unified power quality conditioner (UPQC) to enhance the electric power quality at distribution levels. This is intended to present a broad overview on the different possible UPQC system configurations for single-phase (two-wire) and three-phase (three-wire and four-wire) networks, different compensation approaches, and recent developments in the field. It is noticed that several researchers have used different names for the UPQC based on the unique function, task, application, or topology under consideration. Therefore, an acronymic list is developed and presented to highlight the distinguishing feature offered by a particular UPQC. In all 12 acronyms are listed, namely, UPQC-D, UPQC-DG, UPQC-I, UPQC-L, UPQC-MC, UPQC-MD, UPQC-ML, UPQC-P, UPQC-Q, UPQC-R, UPQC-S, and UPQC-VA. More than 150 papers on the topic are rigorously studied and meticulously classified to form these acronyms and are discussed in the paper.

Enhancing Electric Power Quality Using UPQC: A Comprehensive Overview

This paper addresses the problem of voltage rise mitigation in distribution networks with distributed generation. A distributed automatic control approach is proposed to alleviate the voltage rise caused by active power injection. The objective of the proposed approach is not to control bus voltage but to guarantee that generator injections alone do not cause significant voltage rise: a solution in which distribution network operators (DNOs) are kept to their traditional task of voltage regulation for load demand. The approach is discussed in the perspective of effectiveness and adequacy. Its consequences to DNO control effort are evaluated. Illustration is provided for a single feeder with stochastic generation and transformer on-load tap-changing voltage regulation.

Distributed Reactive Power Generation Control for Voltage Rise Mitigation in Distribution Networks

Transient overvoltage protection during live maintenance of high voltage transmission lines is necessary to prevent line-line sparkovers due to possible transient overvoltages. Portable protective air gaps(PPAGs) along a transmission line under maintenance are proposed to limit the line-ground voltage transients. Previous work has shown that a 41 inch rod gap installed along the line for sparkover protection will provide protection at approximately 1.7 per unit on a 500 kV system. The PPAG had not previously been used to provide protection line-line, however. This paper presents the results from a study that confirms whether PPAGs installed line-ground could also provide adequate protection from line-line overvoltages, and to determine the optimal installation scheme of sets of PPAGs over the length of the line or line section.

Control of line-to-line overvoltages for helicopter-based live work on a 500 kV transmission line

A modular reconfigurable medium voltage transformer configured for data centers, VOLT/VAR control, AC and DC charging, and vehicle-to-grid applications is disclosed. The modular reconfigurable transformer includes a plurality of modules configured to be connected to or disconnected from each other to provide multiple transformer configurations. Each of the modules are configured for bi-directional or uni-directional power flow to allow the transformer to provide power from a power source to an application or from the application back to the power source

Modular reconfigurable medium voltage transformer for data centers, volt/var control, ac and dc charging, and vehicle-to-grid applications

Numerous analyses, including the “Prism” analysis at the Electric Power Research Institute (EPRI), show that energy conservation and distributed resource integration are critical elements of an overall strategy to reduce carbon emissions. The smart grid is the enabling infrastructure that makes much higher levels of distributed resource integration possible. The value is maximized by leveraging Distributed Resources at both the local and overall system level as a “virtual power plant” to better match energy supply with demand along with related value-added benefits. Due to the complexity, number and scale of the systems and devices involved in creating a demand-side virtual power plant, interoperability between the various systems is the key to success. An interoperable smart grid fosters increased competition among suppliers, innovation, choice, reduced costs and reduced capital risk caused by technology or vendor obsolescence, and enables automation resulting in increased value and improved reliability. Unfortunately, interoperability cannot realistically be achieved by a single entity and requires collaboration from numerous organizations including utilities, regulatory bodies, standards bodies, vendors and more. An approach of structured regional utility demonstrations designed to promote and evaluate integration of distributed resources at all levels of power system operations will further smart grid interoperability. Utilizing a standardized approach like the IntelliGrid® methodology to develop use cases and standard functional requirements can further communication, information, and control infrastructures required to support integration of emerging technologies as well as identify critical gaps in existing standards providing focus for future research and development.

https://smartgrid.epri.com/doc/Achieving%20Smart%20Grid%20Interoperability%20through%20Collaboration.pdf

Achieving smart grid interoperability through collaboration

As utilities modernize their distribution systems to include wider use of advanced distribution automation (ADA) schemes, they need to assess the relevant distribution circuit configurations and reconfiguring capabilities, including the associated control and protection systems. The simulation of these ADA schemes along with the associated control systems overlay can lead to a better understanding of the value of these emerging capabilities and the ways they can be most effectively used. This panel presentation summary discusses using the control system overlay feature of an open-source distribution system simulator for modeling distribution automation schemes.

Modelling distribution automation schemes with a control systems overlay

Power monitoring systems (power quality monitors, digital fault recorders, digital relays, advanced controllers, etc.) continue to get more powerful and provide a growing array of benefits to overall power system operation and performance evaluation. Permanent monitoring systems are used to track ongoing performance, to watch for conditions that could require attention, and to provide information for utility and customer personnel when there is a problem to investigate. An important development area for these monitoring systems is the implementation of intelligent systems that can automatically evaluate disturbances and conditions to make conclusions about the cause of a problem or even predict problems before they occur. This paper describes the development of a Next Generation Power Information System that will provide an open platform for implementing advanced monitoring system applications that involve integration with many different data sources. The work builds on many years of experience with software for management and analysis of large power quality monitoring systems. BENEFITS Interoperability and open access to data are cornerstones to successful development and implementation of advanced smart-grid applications at the enterprise level. An integrated platform is needed that includes access to power quality data and disturbance data in addition to traditional data stores such as historians, GIS, and electrical models. Key benefits that are realized when this integration occurs include: • Advanced applications that are based on disparate utility information systems. • Automated data analysis using intelligent algorithms. • Enterprise wide (web-based) data access, reporting, and alarming . • Improved performance of transmission and distribution systems through advanced applications, such as fault location and equipment diagnostics. In operating and maintaining a power system, the timeliness and accuracy of available information has a direct impact on the efficiency and effectiveness of the system. It also has a direct impact on the safety of employees and the public. Seamlessly integrated and automated processes that take advantage of newer and smarter remote data gathering devices reduce the time that is required to understand system dynamics and return to the optimum state. BACKGROUND Monitoring and recording power quality data can result in especially large databases. And, applications like PQView operate on these databases for data management, analysis, and reporting. Figure 1 is an example of a typical power quality monitoring system. Example of System Monitoring Concept Transmission Distribution Substation Substation Monitoring System Customer Monitoring System Customer Monitoring System Monitoring Database Local Network Data Collection Data Collection Database Management/ Local Data Analysis Corporate Intranet Internet/ World Wide Web Power Quality/ Energy Information Service Power Quality/ Reliability Performance and Data Analysis le of System it ri oncept s is ion i tribution st tion

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Mark McGranaghan

Papers

Control of line-to-line overvoltages for helicopter-based live work on a 500 kV transmission line

Modular reconfigurable medium voltage transformer for data centers, volt/var control, ac and dc charging, and vehicle-to-grid applications

Achieving smart grid interoperability through collaboration

Modelling distribution automation schemes with a control systems overlay

Next generation power information system