The power grid is not only a network interconnecting generators and loads through a transmission and distribution system, but is overlaid with a communication and control system that enables economic and secure operation. This multilayered infrastructure has evolved over many decades utilizing new technologies as they have appeared. This evolution has been slow and incremental, as the operation of the power system consisting of vertically integrated utilities has, until recently, changed very little. The monitoring of the grid is still done by a hierarchical design with polling for data at scanning rates in seconds that reflects the conceptual design of the 1960s. This design was adequate for vertically integrated utilities with limited feedback and wide-area controls; however, the thesis of this paper is that the changing environment, in both policy and technology, requires a new look at the operation of the power grid and a complete redesign of the control, communication and computation infrastructure. We provide several example novel control and communication regimes for such a new infrastructure.

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Designing the Next Generation of Real-Time Control, Communication, and Computations for Large Power Systems

Load frequency control has been used for decades in power systems. Traditionally, this has been a centralized control by area with communication over a dedicated and closed network. New regulatory guidelines allow for competitive markets to supply this load frequency control. In order to allow an effective market operation, an open communication infrastructure is needed to support an increasing complex system of controls. While such a system has great advantage in terms of cost and reliability, the possibility of communication signal delays and other problems must be carefully analyzed. This paper presents a load frequency control method based on linear matrix inequalities. The primary aim is to find a robust controller that can ensure good performance despite indeterminate delays and other problems in the communication network.

Application of linear matrix inequalities for load frequency control with communication delays

Integration of renewable energy sources (RES) into traditional power system is one of the most viable technologies to meet the ever increasing energy demand efficiently. But, this technology arises a lot of challenges which are necessary to be taken care of for smooth operation of the network. Voltage regulation is the most significant technical challenge that tends to limit the amount of penetration of renewable distribution generators (DGs) into the distribution network. This paper attempts to present a detailed review of the control strategies that are being utilized to mitigate voltage regulation challenges when increased amount of renewable DGs are connected within the distribution network. This study analyses the direct impacts of increased accommodation of renewable DGs on the distribution network operation and evaluates current research status of voltage control strategies. Then qualitative analysis is performed for all kinds of voltage control approaches involving their pros and cons for the first time. The objective of this contribution is to present the latest research status of distribution system voltage control strategies with highly penetrated renewable DGs and a brief review of different control methodologies.

Review of control strategies for voltage regulation of the smart distribution network with high penetration of renewable distributed generation

Identifying coherent sub-graphs in networks is important in many applications. In power systems, large systems are divided into areas and zones to aid in planning and control applications. But not every partitioning is equally good for all applications; different applications have different goals, or attributes, against which solutions should be evaluated. This paper presents a hybrid method that combines a conventional graph partitioning algorithm with an evolutionary algorithm to partition a power network to optimize a multi-attribute objective function based on electrical distances, cluster sizes, the number of clusters, and cluster connectedness. Results for the IEEE RTS-96 show that clusters produced by this method can be used to identify buses with dynamically coherent voltage angles, without the need for dynamic simulation. Application of the method to the IEEE 118-bus and a 2383-bus case indicates that when a network is well partitioned into zones, intra-zone transactions have less impact on power flows outside of the zone; i.e., good partitioning reduces loop flows. This property is particularly useful for power system applications where ensuring deliverability is important, such as transmission planning or determination of synchronous reserve zones.

https://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/45758/Cotilla-SanchezEduardoElectricalEngineeringComputerScienceMultiAttributePartitioning.pdf;sequence=1

Multi-Attribute Partitioning of Power Networks Based on Electrical Distance

The topological (graph) structure of complex networks often provides valuable information about the performance and vulnerability of the network. However, there are multiple ways to represent a given network as a graph. Electric power transmission and distribution networks have a topological structure that is straightforward to represent and analyze as a graph. However, simple graph models neglect the comprehensive connections between components that result from Ohm's and Kirchhoff's laws. This paper describes the structure of the three North American electric power interconnections, from the perspective of both topological and electrical connectivity. We compare the simple topology of these networks with that of random, preferential-attachment, and small-world networks of equivalent sizes and find that power grids differ substantially from these abstract models in degree distribution, clustering, diameter and assortativity, and thus conclude that these topological forms may be misleading as models of power systems. To study the electrical connectivity of power systems, we propose a new method for representing electrical structure using electrical distances rather than geographic connections. Comparisons of these two representations of the North American power networks reveal notable differences between the electrical and topological structures of electric power networks.

Comparing the Topological and Electrical Structure of the North American Electric Power Infrastructure

In this paper, we present the design of a localized competitive market for reactive power ancillary services at the level of individual voltage-control areas. The concept of electrical distance has been used to identify the different voltage-control areas within a power system. The proposed reactive power market is settled on uniform price auction, using a modified optimal power-flow model. Uniform prices for various components of reactive power service are obtained for each voltage-control area. In the study cases described in the paper, we examine whether such a localized reactive power market is more desirable than a common system-wide reactive power market.

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Localized reactive power markets using the concept of voltage control areas

Summary form only given. In this paper, we present the design of a localized competitive market for reactive power ancillary services at the level of individual voltage-control areas. The concept of electrical distance has been used to identify the different voltage-control areas within a power system. The proposed reactive power market is settled on uniform price auction, using a modified optimal power-flow model. Uniform prices for various components of reactive power service are obtained for each voltage-control area. In the study cases described in the paper, we examine whether such a localized reactive power market is more desirable than a common system-wide reactive power market.

/pdf/localized-reactive-power-markets-using-the-concept-of-1q32g472rs.pdf

In the ongoing process to create a competitive electricity market, the problem of ancillary services is assuming a fundamental role. Ancillary services are those services performed by generators, transmission and control equipment, which are necessary to support basic services and to maintain reliable operations and system security. In this paper, we focus our attention on one of these services, load following, and propose a competitive way to provide this service through bilateral contracts between supplier and customer. In general, we assume that there will be both a competitive market for the provision of load following and an authority responsible for the amount of load following not met by bilateral contracts.

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Feasibility of a Bilateral Market for Load Following

Although the possibility of a competitive market for voltage control/reactive power ancillary service has been conceived in literature, electric power markets have so far only experimented with it. Usually the system operator obtains the right to some amount of reactive power capability and, with the assistance of analysis tools, determines what resources are needed and how to deploy them in an efficient manner. The optimal power flow (OPF) is often the main tool in such analysis. In this paper an area voltage control, to dynamically manage the reactive power available in a specific geographic region, is presented. This can be seen as an alternative, flexible tool to assist the system operator with the implementation of voltage control. The proposed scheme handles the issue as a localized problem and seems also suitable for the development of a local competitive marker for this ancillary service.

E. Nobile

Papers

Localized reactive power markets using the concept of voltage control areas

Localized reactive power markets using the concept of voltage control areas

Feasibility of a Bilateral Market for Load Following

An area-wise voltage control scheme suitable for setting up a Var ancillary market