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

The most significant challenge in distribution management associated with the so called “smart grid” is that the distribution system becomes an active system-with distributed generation, smart customer loads, electric vehicle charging, smart inverters, distributed storage, and so on. The challenge of an active distribution system affects both the planning functions and the real-time operations of the system. The transition to an active distribution system does not change the need to maintain and improve reliability.

http://ieeexplore.ieee.org/iel5/8014/5989937/05989945.pdf

Sim City

Utility distribution systems are becoming increasingly intelligent, with continued advancements in sensors, monitoring, and controls. In some cases, these improvements make it possible for the utility to isolate faults and reenergize sections of line from alternative points of feed. Under normal circumstances, utilities may dynamically reconfigure their system to optimize overall operating efficiency. With these capabilities comes increased need for detailed three phase models of the distribution system that identify existing equipment and loads on a per-phase basis. This granularity is needed in order to make informed decisions regarding distribution switching, optimization, and control. This paper presents a technique and preliminary test results for a method of automatically identifying the phase of each customer by correlating voltage information from the utility's SCADA system with voltage information from customer electricity meters.

Automatic identification of service phase for electric utility customers

Although capacitor switching transient events are one of the most common disturbance events on distribution systems, information on whether the capacitor bank is energized properly or as desired is often not available. The capacitor switching performance tracker is designed to examine capacitor switching transient events and determine the condition relative to the events. The module identifies if the root cause of the event is due to energizing a capacitor bank. It then determines the relative location of the bank, i.e., upstream or downstream from the monitoring location, and examines if the kVAr generated from the capacitor bank is added properly to the system and if the kVAr is distributed evenly among all phases. By determining the kvar changes, it is possible to identify unsuccessful energization, blown fuses, or even failed capacitor cans on one of the phases.

Signature analysis to track capacitor switching performance

Fault location is of considerable interest for utilities to improve their reliability and speed storm restorations. Power quality recorders, relays, and other monitors can provide information to help locate faults. In this paper, some basic impedance-based fault-location methods are evaluated on utility measurement data with known fault locations. The main finding is that reasonably accurate fault locations are possible on a wide range of distribution circuits with either feeder-level or bus-level substation monitoring. Another important finding described is how monitoring can be used to estimate the parameters of the fault arc. This can improve fault locations and help with accident investigations, equipment failure forensics, and other hazards related to the power and energy created by the arc

Using PQ Monitoring and Substation Relays for Fault Location on Distribution Systems

The role and operation of the electric power system is evolving to accommodate changes in the ways electricity is produced, delivered, and used. Consumers have increasing choice and control over their electricity service. The range of choice is diverse: owning or leasing generating systems [such as photovoltaic (PV), solar, thermal, wind, and biomass] and using storage options and technology to manage when and how they use electricity to manage costs. A power system that makes these distributed energy resources (DER) part of the performance optimization is referred to as an integrated grid (Figure 1).

Mark McGranaghan

Papers

Sim City

Automatic identification of service phase for electric utility customers

Signature analysis to track capacitor switching performance

Using PQ Monitoring and Substation Relays for Fault Location on Distribution Systems

Enabling the Integrated Grid: Leveraging Data to Integrate Distributed Resources and Customers