A survey on the communication architectures in smart grid(1)

（原文来自IEEE）

Abstract

The next-generation electric power systems (smart grid)arestudied intensively as apromising solution for energy crisis(有前途的能源危机解决方案). One importantfeature of the smart grid is the integration of high-speed, reliable and securedata communication networks to manage the complex power systems effectively andintelligently.We provide in this paper a comprehensive survey on thecommunication architectures(通信架构) inthe power systems, including the communication network compositions,technologies, functions, requirements, and research challenges.As these communication networks are responsible fordelivering power system related messages, we discuss specifically thenetworkimplementation considerations（网络实施的考虑） and challenges in the power system settings. This survey attempts to summarize the current state of researchefforts in the communication networks of smart grid, which may help us  identify theresearch problems in the continued studies.

1.Introduction

The currentelectric power systems have been serving us for more than five decades. They rely heavily on the fossil fuels, including oil, coal, and natural gas, as theenergy sources. These fossil fuels are nonrenewable and the reserves（储量） onthe earth are being consumed rapidly. The emerging energy crisis has called for global attention on finding alternative energy resources that can sustain long-term industry development. The identified renewable energy resources include wind, small hydro, solar, tidal(潮汐),geothermal（地热）, and waste [1], which are also called green energy for the fact that they do not release carbon dioxide(CO2) into the atmosphere in the process of electric energy generation.The renewable energy resources are important complements to and replacements of the fossil fuels for their exploitation durability andenvironment friendliness.In fact, active research studies anddeployment activities（部署活动）are underway across the world [1,2] for effective harness of the renewable energy resources（可再生能源的有效治理）.In the next-generation electricpower systems that incorporate diversified renewable energy resources, automatedand intelligent management is a critical component that determines theeffectiveness and efficiency of these power systems.The management automation and intelligence are envisioned to offer a variety of advantages over the current systems in terms of digitalization,flexibility,intelligence, resilience（回弹性）, sustainability, and customization（用户化[3],which entitles the name Smart Grid to the next generation power systems. The smart control centers are expected to monitor and interact theelectric devices remotely in real time; thesmart transmissioninfrastructures（智能传输设施） expected to employ newtechnologies to enhance the power quality; and the smart substations （变电站）are expected to coordinate their local devices self-consciously [3].Enabled by the significant advancements in systemautomation and intelligence, the concept ofEnergy Internet[4] has beenproposed that envisions an exciting prospect of the futureenergyutilization paradigm（范例）throughout all the energy generation, storage,transmission and distribution phases. As one of theenabling technologies, a fast, reliable and secure communication network playsa vital role in the power system management.The network is required to connect the magnitude of elecric devices（级电子设备） in distributed locations and exchange their status information andcontrol instructions. The system-wide（系统范围的）intelligence is feasible only if the information exchange among the variousfunctional units（功能部件）is expedient（权宜）, reliable and trustable. The current communication capabilities ofthe existing power systems are limited to small-scale local regions thatimplement basic functionalities（实现基本功能） for system monitoringand control, such as power-line communications [5–8]and the Supervisory control and data acquisition (SCADA，监测控制和数据采集) systems [9–12],which do not yet meet thedemanding communication requirements for the automated and intelligentmanagement in the next-generation electric power systems.The future power systems comprise of a diversity ofelectric generators and power consumers that are located distributively overvast areas and connected all together into the same management network.Real-time bidirectionalcommunications（实时双向通信） arethe foundations to support the comprehensive power system management taskswhich, in certain cases, require time-sensitive（时效性） and data-intensive（数据密集型） information exchange. Apart frompower systems, networking technologies have gained tremendous development inthe past decades as a separate industry sector. The creation of the Internet, mobilecellular networks, satellite networks, community networks, wired and wirelesslocal area and personal networks, as well as the invention of diversifiednetworking services has enormously enhanced our capability for

informationexchange. However, the modern networking technologies have not beenleveraged sufficiently in power systems for optimizedmanagement. When we develop the smart grid, it is critical to take advantage ofthe advancements in networking technologies to enable the automated andintelligent system management. Although the currently available networkingtechnologies have greatly satisfied our personalcommunication needs, applying them to power systems andaddressing the specific requirements（解决特定的要求） for powercommunications are challenging by all means.We need to identify thecommunication scenarios(通信场景)and characteristics in power systems and develop practically usable networksolutions. Particularly, our network infrastructures should be able to meet thepromptness, reliability and security expectations of the power systemcommunications.At this transitional phase（过渡阶段） of shifting to the next-generation electric power systems, thestudy on the communication architectures for automated and intelligent system managementis still at a primitive stage. Many technicalchallenges are awaiting solutions. To position our current research work anddirect our future research effort, we are motivated to present this survey onthe network infrastructures to be used in the next-generation electric power systems.As the research and development of these power systems areevolutionary（对当前电力系统的研究和开发正在发展）, this survey may not include all the relevant informationexhaustively, but it provides a preliminary summary of the current status andthe future expectation of the smart grid research.

Therest of this survey is organized as follows. Section 2 describes the smart gridstructures and expectations.Section 3 presents the communication architecturein the

smart grid andthe communication requirements. Sections 4 and 5 discuss the most challengingcommunication issues in the smart grid, namely, the delay, reliability and

security.Section 6 describes the typical communication scenarios. The communicationstandards and experiments are discussed in Sections 7 and 8 respectively.Section 9

concludesthis survey.

 

2. Smartgrid framework and expectations

The communicationarchitectures（通信架构） to be used in the smart grid provide the platformto build the automated and intelligent management functions in power systems. Thefunctional requirements of communication architectures depend on the expectedmanagement tasks. To better understand our research goals on the communicationnetworks that support the system management, we first discuss the vision andframework of smart grid. For ease of presentation, we list in Table 1 all thesmart grid related acronyms（首字母缩略词）used in this article.

2.1. Smart grid reference model（智能电网参考模型）

In the smart grid, many distributed renewable energysources will be connected into the power transmission and distribution systemsas integral components. The typical renewable energy sources include wind,solar, small

hydro, tidal, geothermal, and waste. These sources generate extra electricity that supplementsthe electricity supply from large power plants and, when the electricity generatedby distributed small energy sources exceeds the local needs, the surplus issold back to the power grid.

 

Table 1

Acronyms in smart grid.Acronym Definition

AMI        Automatic metering infrastructure（自动计量设施）

AMR      Automaticmeter reading（自动读表系统）

BAS       Buildingautomation system

DER       Distributedenergy resource(分布能源源)

DLC       Directload control（直接负载控制）

DMS      Distributionmanagement system

DR         Demandresponse（需求回应）

EMS      Energymanagement system

ESI        Energyservices interface

GPS       Globalpositioning system

IED        Intelligentelectronic device

IEM        Intelligentenergy management

IFM        Intelligentfault management（智能故障管理）

IHD        In-homedisplay（家用显示器）

ISO        Independentsystem operator

LMS       Loadmanagement system

MDMS    Meteringdata management system

OMS      Outagemanagement system（停电管理系统）

PEV       Plug-inelectric vehicle 

PLC       Powerline communication（电线通信）

PMU      Phasormeasurement unit（矢量测量单元）

PTP       Precisiontime protocol

RTO       Regionaltransmission operator（区域传输操作者）

 

RTP       Real Time Pricing（实时定价）

RTU       Remote terminal unit

SCADA  Supervisory control and data acquisition（监测控制和数据采集）

STNP     Simple time network protocol

WACS    Wide area control system

WAMS   Wide area monitoring system

WAPS    Wide area protection system

WASA    Widearea situational awareness（广域态势感知）

 

With the addition of renewable energy sources,bi-directional dynamic energy flows are observed in the power grid. Weillustrate in Fig. 1 the framework of smart grid.Toeffectively manage this complex power system that involves an enormous numberof diversely functional devices,aco-locatedcommunication infrastructure（同地协作通信设施） isrequired to coordinate the distributed functions across the entire powersystem. This system consists of seven functional blocks [13,14], which are,namely, bulk generation, transmission, distribution, operation, market,customer and service provider.

 

2.1.1. Bulk generation（容量产生）

Electricity is generated by using resources likeoil, coal, nuclear fission, flowing water, sunlight, wind, tide, etc. This domainmay also store electricity to manage the variability of renewable resourcessuch that the surplus electricity generated at times of resource richness canbe stored up for redistribution at times of resource scarcity. The bulk generationdomain is connected to the transmission domain. It also communicates with themarket domain through amarket services interfaceover Internet and with the operations domainover the wide area network. It is required to communicate key parameters likegeneration capacity and scarcity to the other domains. It comprises ofelectrical equipments including RTUs（终端）, programmable logic controllers,equipment monitors, and fault recorders.

2.1.2. Transmission

The generated electricity is transmitted to thedistribution domain via multiple substations and transmission lines. Thetransmission is typically operated and managed by a RTO（区域传输操作者） or an ISO.The RTO is responsible for maintaining the stability ofregional transmission lines by balancing between the demand and supply. Thetransmission domain

may also support small scale energygeneration and storage. To achieve self-healing functions and enhance wide areasituational awareness and control, a lot of information will be captured fromthe grid and sent to the control centers. The control centers will also send responses to

the devices in remote substations. The bidirectional communications between control centersand substations are handled in the transmission domain too.

2.1.3. Distribution

The dispatch of electricity（电力调度） to end usersin the customer domain is implemented by making use of the electrical and communicationinfrastructures that connect the transmission and customer domains. This domain includes distribution feeders andtransformers（？配电馈线和变压器） to supply electricity. It interactswith many different equipment, such as DERs(分布能源源),PEVs, AMI, and sensors with communicationcapability. The distribution domain takes the responsibility of delivering electricityto energy consumers according to the user demands and the energy availability.In order to provide quality electricity, the stability of this domain ismonitored and controlled.

2.1.4. Operation

This domain maintains efficient andoptimal operations of the transmission and distribution domains using an EMS（能源管理系统） in thetransmission domain and a DMS（分配管理系统） in thedistribution domain. It uses field area and wide area networks in the transmissionand distribution domains to obtain information of the power system activitieslike monitoring,

control, fault management, maintenance, analysis andmetering. The information is obtained using the SCADA systems. The operationsdomain may be subdivided into sub-domains for transmission, distribution, andRTO/ISO operations. These sub-domains may be controlled by different organizations.

2.1.5. Market

The balance between the supply and the demand of electricityis maintained by the market domain. This domain consists of retailers whosupply electricity to end users, suppliers of bulk electricity, traders who buyelectricity from suppliers and sell it to retailers, and aggregators（整合者）who combine smaller DERresources for sale.Effective communicationsbetween the bulk producers（批量生产商） of electricity,the DERs and the market is essential to match the production of electricitywith its demand.

2.1.6. Customer

Customers consume, generate (using DERs), or store electricity.This domain includes home, commercial or industrial buildings. It iselectrically connected to the distribution domain and communicates with thedistribution, operation, service provider and market domains. The customer domainalso supports the demand response process.To allow customers to activelyparticipate in the grid, a two-way communication interface between thecustomer premises（用户驻地） and the distribution domainin required. This is generally referred to as an ESI（能源服务接口） and is present at the customer premises.Acommunication network within the customer premises is required to allowexchange of data and control commands between the utility（公共设施） and the smart customer devices.This network is referred to as a home area network. It is expectedto support applications such as remote load control, DER monitoring andcontrol, IHD（家用显示器） support for customer usages,reading of non-energy meters, and integration with building management systems.

2.1.7. Service provider

Electricity is provided to customers and utilities throughservice providers. They manage services likebilling and customer account management for utility companies. It communicateswith the operation domain to get the metering information and for situationalawareness and system control. It must also communicate with HANs in thecustomer domain through the ESI interface to provide smart services likemanagement of energy uses and home energy generation.

2.2. Smart grid expectations

The next-generation electric power systems will not onlyaddress the existing problems in the current power systems, but also add inadvanced new features. Visions and expectations of such modernized powersystems have been proposed and endorsed by a number of independent organizationsall over the world [15–17]. We summarize them below.

2.2.1. Support for diverse devices

Unlike the existing electricity distribution grid,the future grids will accommodate different kinds of electricity generation andstorage devices and allow for bidirectional energy exchange on the existinggrid. This will involve support not only for the DERs like the photovoltaic cells（光电管）, storage batteries and windenergy, but also for the traditional electric loads, smart devices (loads withcommunication capability) in households and PEVs. The use of DERs will have environmental and monetary benefits for thecustomers, as they can use the electricity generated and stored by themselvesor sell it back to the grid. The bidirectionalenergy

exchange mechanism will be useful intimes of electricity shortage at the customer or utility end and will haveoperational benefits（经济效益） for the both of them.

2.2.2. Superior power quality

Power quality is the ability of thesupplied electricity on the distribution grid to adhere to the specified peaklevels orroot mean square (RMS，均方根) voltages. Anydeviation（偏差） in the level (e.g. increasing, decreasingor random RMS voltage) can harm the loads attached to the grid which aregenerally designed to function at specified levels of electric voltage andfrequency. The affected load in turn can harm the gird. Forexample, it might cause a dip in the voltage levels on the grid affecting othercustomers that share the infrastructure with the affected site. In severecases, it might even lead to apower outage（停电） resulting in revenue loss. Oneof the ways to avoid such a situation is tomakethe loads more resistant to transients（使负载更抗瞬变）in the electric distribution network. The other way is to improve the powerquality. The modern grid handles such problems by improving the power qualitythrough monitoring (using sensors) and conditioning. It provides power qualityin accordance with load sensitivity（和负载灵敏度一致）. Thusthere could be different levels of power quality at different prices. Thedigital appliances andgadgets（配件） of today require higher power quality than what is provided by thetraditional grid.

2.2.3. Operation efficiency and optimization（操作效率和优化）

The smart grid will use information technology for extensivefacility and electrical field equipment monitoring. This information can beused to operate the grid efficiently by minimizing system losses. The dataobtained from the monitoring process will also be helpful in carrying out need-based maintenance（按需维护） and for improving the designof electrical power systems.

2.2.4. Grid security

The future grid will rely extensively on the use ofcommunication technologies forcriticalfunctionalities such as control, protection and monitoring of electricalequipments. Hence the security of such a connected structure from any cyberattack is ofparamount importance（至关重要）. Security against anyphysical attack would also be a concern. In case ofany breach of security, it is expected that the grid will be able to detect andisolate such a breach to minimize its effect and raise an alarm to speedservice restoration.

2.2.5. Grid self-correction

The future grid is expected to detect, analyze andrespond automatically to changes where human intervention may not be requiredor the action is too critical to wait for human input. Thus the grid will beable to detect the occurrence or predict the possibility of a fault in thetransmission or distribution system at the earliest. This would improve thereliability, power quality and efficiency of the grid and minimize service disruption（最小化服务中断）.

2.2.6. Consumer participation

In future grids, bymaking use of the two-way communications and control capability, the utilitycompanies can involve consumers by offering them dynamic electricity pricingwith low rates in times of low load on the grid and temporary load reductionprograms like demand response.

The communication capability also allows consumers tomonitor, using web-based EMS, the efficiency of individual smart applianceswhich can communicate with the grid and choose to replace or repair theinefficient ones. These features will be highly useful when used along

with devices with storage backup. For example, PEVs,where the users can monitor the charging of the vehicles or DERs with storagewhere the users can monitor the stored electric charge.

2.2.7. Market boost（市场提高）

The future grid will allow a lot of new services tobe offered to the consumers including the capability to sell and purchaseelectricity from different suppliers. In such a scenario, the markets shallbecome a way to connect the suppliers of electricity to the consumers ofelectricity. The competing price of electricityfrom various suppliers will keep the price of electricity in favor of theconsumers. At the same time by using variable pricing, the market vendors cancoordinate the demand of electricity with its availability（协调电量的供求）. The markets will need to have detailed information abouta particular distribution region to which it caters to, for example, capacityof the system, rate of capacity change, available electricity from suppliers,electricity demand, etc. The use of open standards of communication will allowthe user data to be received by the authorized market vendor for processing andbilling activities.