This paper surveys expert systems (ES) development using a literature review and classification of articles from 1995 to 2004 with a keyword index and article abstract in order to explore how ES methodologies and applications have developed during this period. Based on the scope of 166 articles from 78 academic journals (retrieved from five online database) of ES applications, this paper surveys and classifies ES methodologies using the following eleven categories: rule-based systems, knowledge-based systems, neural networks, fuzzy ESs, object-oriented methodology, case-based reasoning, system architecture, intelligent agent systems, database methodology, modeling, and ontology together with their applications for different research and problem domains. Discussion is presented, indicating the followings future development directions for ES methodologies and applications: (1) ES methodologies are tending to develop towards expertise orientation and ES applications development is a problem-oriented domain. (2) It is suggested that different social science methodologies, such as psychology, cognitive science, and human behavior could implement ES as another kind of methodology. (3) The ability to continually change and obtain new understanding is the driving power of ES methodologies, and should be the ES application of future works.

http://www.sci.brooklyn.cuny.edu/~kopec/cis718/fall_2005/sdarticle5.pdf

Expert system methodologies and applications—a decade review from 1995 to 2004

The integration of distributed generation (DG) units in power distribution networks has become increasingly important in recent years. The aim of the optimal DG placement (ODGP) is to provide the best locations and sizes of DGs to optimize electrical distribution network operation and planning taking into account DG capacity constraints. Several models and methods have been suggested for the solution of the ODGP problem. This paper presents an overview of the state of the art models and methods applied to the ODGP problem, analyzing and classifying current and future research trends in this field.

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Optimal Distributed Generation Placement in Power Distribution Networks: Models, Methods, and Future Research

Natural disasters can cause large blackouts. Research into natural disaster impacts on electric power systems is emerging to understand the causes of the blackouts, explore ways to prepare and harden the grid, and increase the resilience of the power grid under such events. At the same time, new technologies such as smart grid, micro grid, and wide area monitoring applications could increase situational awareness as well as enable faster restoration of the system. This paper aims to consolidate and review the progress of the research field towards methods and tools of forecasting natural disaster related power system disturbances, hardening and pre-storm operations, and restoration models. Challenges and future research opportunities are also presented in the paper.

Research on Resilience of Power Systems Under Natural Disasters—A Review

Microgrids with distributed generation (DG) provide a resilient solution in the case of major faults in a distribution system due to natural disasters. This paper proposes a novel distribution system operational approach by forming multiple microgrids energized by DG from the radial distribution system in real-time operations to restore critical loads from the power outage. Specifically, a mixed-integer linear program is formulated to maximize the critical loads to be picked up while satisfying the self-adequacy and operation constraints for the microgrids formation problem by controlling the ON/OFF status of the remotely controlled switch devices and DG. A distributed multiagent coordination scheme is designed via local communications for the global information discovery as inputs of the optimization, which is suitable for autonomous communication requirements after the disastrous event. The formed microgrids can be further utilized for power quality control and can be connected to a larger microgrid before the restoration of the main grids is complete. Numerical results based on modified IEEE distribution test systems validate the effectiveness of our proposed scheme.

Resilient Distribution System by Microgrids Formation After Natural Disasters

DC microgrids and distribution systems: An overview

The goal to provide faster and faster restoration after a fault is pushing the technical envelope related to new algorithms. While many approaches use centralized strategies, the concept of multi-agent systems (MAS) is creating a new option related to distributed analyses for restoration. This paper provides details on a MAS that restores a power system after a fault. The development of agents and behaviors of the agents are described, including communication of agents. The MAS is tested on two test systems and facilitates both full and partial restoration, including load prioritization and shedding.

A Multi-Agent Solution to Distribution Systems Restoration

With the development of automation in distribution systems, distribution supervisory control and data acquisition (SCADA) and many automated meter reading (AMR) systems have been installed on distribution systems. Also distribution management system (DMS) have advanced and include more sophisticated analysis tools. The combination of these developments is providing a platform for development of distribution system state estimation (DSE). A branch-current-based three-phase state estimation algorithm for distribution systems has been developed and tested. This method chooses the magnitude and phase angle of the branch current as the state variables. Because of the limited number of real-time measurements in the distribution system, the state estimator can not acquire enough real-time measurements for convergence, so pseudo-measurements are necessary for distribution system state estimator. The load estimated at every node from the AMR systems is used as a pseudo-measurement for the state estimator. The algorithm has been tested on three IEEE radial test feeders. In addition to this new strategy for DSE, another issue is meter-placement. This topic includes the type of measurement as well as the location of the measurement. Our results show the impact of these two issues on accuracy. Several general meter rules based on this analysis are outlined.

A revised branch current-based distribution system state estimation algorithm and meter placement impact

With the increased installations of distributed generators (DGs) within power systems, load flow analysis of distribution systems needs special models and algorithms to handle multiple sources. In this paper, the development of an unbalanced three-phase load flow algorithm that can handle multiple sources is described. This software is capable of switching the DG mode of operation from constant voltage to constant power factor. The algorithm to achieve this in the presence of multiple DGs is proposed. Shipboard power systems (SPS) have other special characteristics apart from multiple sources, which make the load flow difficult to converge. The developed software is verified for a distribution system without DG using the Radial Distribution Analysis Package (RDAP). The developed software analyzes an IEEE test case and an icebreaker ship system. System studies for the IEEE 37-node feeder without the regulator show the effect of different models and varying DG penetration related to the increase in loading. System losses and voltage deviations are compared.

Development of Three-Phase Unbalanced Power Flow Using PV and PQ Models for Distributed Generation and Study of the Impact of DG Models

This paper presents a new online voltage stability index (VSI) that predicts the power system steady-state voltage stability limit. Starting with deriving a method to predict three types of maximum transferable power (real power, reactive power, and apparent power) of a single-source power system, a new VSI based on the calculated load margins is devised. In order to apply the VSI to large power systems, a method is developed to simplify the large network behind a load bus into a single source and a single transmission line using time-synchronized phasor measurements and network parameters. The simplified system model, to which the devised VSI can be applied, preserves power flow and voltage information of the particular load bus under study. The proposed VSI combined with the network simplification method provides the voltage stability margin of each individual load bus in an informative format and identifies the load bus that is the most vulnerable to voltage collapse. Test results from applying the VSI on two test systems validate its applicability for online applications

Synchrophasor-Based Real-Time Voltage Stability Index

A novel formulation for service restoration algorithm for unbalanced three phase distribution systems is described. This problem is a constrained multiobjective optimization formulated as a mixed integer non-linear programming problem. A comparison of the solutions with and without switch pairs has been made. The formulation was first validated using already developed three-phase unbalanced power flow software. The three-phase unbalanced power flow equations were embedded in the formulation, and hence separate calculations were not needed. Simulation results are presented for modified IEEE 13-node and IEEE 37-node test cases

Noel N. Schulz

Papers

A Multi-Agent Solution to Distribution Systems Restoration

A revised branch current-based distribution system state estimation algorithm and meter placement impact

Development of Three-Phase Unbalanced Power Flow Using PV and PQ Models for Distributed Generation and Study of the Impact of DG Models

Synchrophasor-Based Real-Time Voltage Stability Index

Optimized Restoration of Unbalanced Distribution Systems