다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

A communication infrastructure is an essential part to the success of the emerging smart grid. A scalable and pervasive communication infrastructure is crucial in both construction and operation of a smart grid. In this paper, we present the background and motivation of communication infrastructures in smart grid systems. We also summarize major requirements that smart grid communications must meet. From the experience of several industrial trials on smart grid with communication infrastructures, we expect that the traditional carbon fuel based power plants can cooperate with emerging distributed renewable energy such as wind, solar, etc, to reduce the carbon fuel consumption and consequent green house gas such as carbon dioxide emission. The consumers can minimize their expense on energy by adjusting their intelligent home appliance operations to avoid the peak hours and utilize the renewable energy instead. We further explore the challenges for a communication infrastructure as the part of a complex smart grid system. Since a smart grid system might have over millions of consumers and devices, the demand of its reliability and security is extremely critical. Through a communication infrastructure, a smart grid can improve power reliability and quality to eliminate electricity blackout. Security is a challenging issue since the on-going smart grid systems facing increasing vulnerabilities as more and more automation, remote monitoring/controlling and supervision entities are interconnected.

https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1315&context=electricalengineeringfacpub

A Survey on Smart Grid CommunicationInfrastructures: Motivations, Requirements andChallenges

The significant benefits associated with microgrids have led to vast efforts to expand their penetration in electric power systems. Although their deployment is rapidly growing, there are still many challenges to efficiently design, control, and operate microgrids when connected to the grid, and also when in islanded mode, where extensive research activities are underway to tackle these issues. It is necessary to have an across-the-board view of the microgrid integration in power systems. This paper presents a review of issues concerning microgrids and provides an account of research in areas related to microgrids, including distributed generation, microgrid value propositions, applications of power electronics, economic issues, microgrid operation and control, microgrid clusters, and protection and communications issues.

State of the Art in Research on Microgrids: A Review

This paper proposes a novel comprehensive operation and self-healing strategy for a distribution system with both dispatchable and nondispatchable distributed generators (DGs). In the normal operation mode, the control objective of the system is to minimize the operation costs and maximize the revenues. A rolling-horizon optimization method is used to schedule the outputs of dispatchable DGs based on forecasts. In the self-healing mode, the on-outage portion of the distribution system will be optimally sectionalized into networked self-supplied microgrids (MGs) so as to provide reliable power supply to the maximum loads continuously. The outputs of the dispatchable DGs will be rescheduled accordingly too. In order to take into account the uncertainties of DG outputs and load consumptions, we formulate the problems as a stochastic program. A scenario reduction method is applied to achieve a tradeoff between the accuracy of the solution and the computational burden. A modified IEEE 123-node distribution system is used as a test system. The results of case studies demonstrate the effectiveness of the proposed methodology.

Self-Healing Resilient Distribution Systems Based on Sectionalization Into Microgrids

This paper proposes a novel control strategy for coordinated operation of networked microgrids (MGs) in a distribution system. The distribution network operator (DNO) and each MG are considered as distinct entities with individual objectives to minimize the operation costs. It is assumed that both the dispatchable and nondispatchable distributed generators (DGs) exist in the networked MGs. In order to achieve the equilibrium among all entities and take into account the uncertainties of DG outputs, we formulate the problem as a stochastic bi-level problem with the DNO in the upper level and MGs in the lower level. Each level consists of two stages. The first stage is to determine base generation setpoints based on the load and nondispatchable DG output forecasts and the second stage is to adjust the generation outputs based on the realized scenarios. A scenario reduction method is applied to enhance a tradeoff between the accuracy of the solution and the computational burden. Case studies of a distribution system with multiple MGs of different types demonstrate the effectiveness of the proposed methodology. The centralized control, deterministic formulation, and stochastic formulation are also compared.

Coordinated Energy Management of Networked Microgrids in Distribution Systems

Load demand management in the context of grid-connected microgrids is the scope of this paper. This issue is formulated as a power dispatching problem between distributed power sources with the objective of grid operational cost minimization. Under the assumption of time-varying demands and supplies at individual microgrids, a cooperative power dispatching algorithm of interactions among microgrids is proposed for power sharing within the grid. This is done through a communication infrastructure in the grid and a set of defined parameters known as purchase prices at individual microgrids. As a result of this algorithm, power flows within the grid are regulated to smooth power generations at microgrids despite the stochastic load demands. Numerical results demonstrate the effectiveness of the proposed load management scheme in comparison with no power sharing scheme in the grid operational cost point of view. Moreover, optimal solution of the power problem verifies these results.

Statistical Cooperative Power Dispatching in Interconnected Microgrids

Communication infrastructure (CI) in microgrids (MGs) allows for the application of different control architectures for the secondary control (SC) layer. The use of new SC architectures involving CI is motivated by the need to increase MG resilience and handle the intermittent nature of distributed generation units. The structure of SC is classified into three main categories, including centralized SC (CSC) with a CI, distributed SC (DISC) generally with a low-data-rate CI, and decentralized SC (DESC) with communication-free infrastructure. To meet the MGs’ operational constraints and optimize performance, control and communication must be utilized simultaneously in different control layers. In this survey, we review and classify all types of SC policies from CI-based methods to communication-free policies, including CSC, averaging-based DISC, consensus-based DISC methods, containment pinning consensus, event-triggered DISC, washout-filter-based DESC, and state-estimation-based DESC. Each structure is scrutinized from the viewpoint of the relevant literature. Challenges such as clock drifts, cyber-security threats, and the advantage of event-triggered approaches are presented. Fully decentralized approaches based on state-estimation and observation methods are also addressed. Although these approaches eliminate the need of any CI for the voltage and frequency restoration, during black start process or other functionalities related to the tertiary layer, a CI is required. Power hardware-in-the-loop experimental tests are carried out to compare the merits and applicability of different SC structures.

/pdf/on-the-secondary-control-architectures-of-ac-microgrids-an-151dix7731.pdf

On the Secondary Control Architectures of AC Microgrids: An Overview

Energy consumption scheduling to achieve low-power generation cost and a low peak-to-average ratio is a critical component in distributed power networks. Implementing such a component requires the knowledge of the whole power demand throughout the network. However, due to the diversity of power demands, this requirement is not always satisfied in practical scenarios. To address this inconsistency, this paper addresses energy consumption scheduling in a distribution network with connected microgrids consisting of a local area with a determined demand and neighboring areas with an uncertain demand. The total cost and peak-to-average ratio minimizations are formulated as a multi objective optimization problem. In addition to a deterministic optimal solution, an adaptive scheduling approach is provided with online stochastic iterations to capture the randomness of the uncertain demand over time. Numerical results demonstrate the effectiveness of the proposed adaptive scheduling schemes in the following results obtained from optimal solutions.

Adaptive Energy Consumption Scheduling for Connected Microgrids Under Demand Uncertainty

This paper proposes a decentralized optimal secondary controller for frequency regulation and accurate active power sharing in autonomous microgrids. This optimal controller does not require any communication network. Unlike most of the existing works, a systematic approach of secondary controller design is introduced based on a quadratic cost function in the form of a linear quadratic regulator (LQR) solution. The design procedure only depends on the cut-off frequency of the power calculation filter. Decentralized behavior, simplicity, optimality based on a quadratic cost function, and straight forward design procedure are the main advantages of this approach. Using the proposed solution, frequency can be restored immediately following any disturbance in the system, without need of any event-driven and time-dependent protocol. Experimental results validate the effectiveness of the proposed controller.

Mohammad Fathi

Papers

Statistical Cooperative Power Dispatching in Interconnected Microgrids

On the Secondary Control Architectures of AC Microgrids: An Overview

Adaptive Energy Consumption Scheduling for Connected Microgrids Under Demand Uncertainty

Decentralized Optimal Frequency Control in Autonomous Microgrids

Facile synthesis of ternary MnO2/graphene nanosheets/carbon nanotubes composites with high rate capability for supercapacitor applications