A Survey on Smart Grid Communication Infrastructures: Motivations, Requirements and Challenges

Abstract

А 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.

BACKGROUND

Many technologies to be adopted by smart grid have already been used in other industrial applications, such as sensor networks in manufacturing and wireless networks in telecommunications, and are being adapted for use in new intelligent and interconnected paradigm. In general, smart grid communication technologies can be grouped into five key areas: advanced components, sensing and measurement, improved interfaces and decision support, standards and groups, and integrated communications.

Figure 1 illustrates a general architecture for smart grid communication infrastructures, which includes home area networks (HANs), business area networks (BANs), neighborhood area networks (NANs), data centers, and substation automation integration systems [4]. Smart grids distribute electricity between generators (both traditional power generation and distributed generation sources) and end users (industrial, commercial, residential consumers) using bi-directional information flow to control intelligent appliances at consumers’ side saving energy consumption and reducing the consequent expense, meanwhile increasing system reliability and operation transparency. With a communication infrastructure, the smart metering/monitoring techniques can provide the real-time energy consumption as a feedback and correspond to the demand to/from utilities. Network operation center can retrieve those customer power usage data and the on-line market pricing from data centers to optimize the electricity generation, distribution according to the energy consumption.

In a complex smart grid system, through wide deployment of new smart grid components and the convergence of existing information and control technologies applied in the legacy power grid, it can offer sustainable operations to both utilities and customers [5]. It can also enhance the efficiency of legacy power generation, transmission and distribution systems and penetrate the usage of clean renewable energy by introducing modern communication systems into smart grids.

The cornerstone of a smart grid is the ability for multiple entities (e.g. intelligent devices, dedicated software, processes, control center, etc) to interact via a communication infrastructure. It follows that the development of a reliable and pervasive communication infrastructure represents crucial issues in both structure and operation of smart grid communication systems [6], [7]. In this connection, a strategic requirement in supporting this process is the development of a reliable communication infrastructure for establishing robust real-time data transportation through Wide Area Networks (WANs) to the distribution feeder and customer level [8].

Existing electrical utility WANs are based on a hybrid of communication technologies including wired technologies such as fiber optics, power line communication (PLC) systems, copper-wire line, and a variety of wireless technolo-gies (i.e. data communications in cellular networks such as GSM/GPRS/WiMax/WLAN and Cognitive Radio [9]). They are designed to support some monitoring/controlling applications as Supervisory Control and Data Acquisition (SCADA)/Energy Management Systems (EMS), Distribution Management Systems (DMS), Enterprise Resource Plan-ning (ERP) systems, generation plant automation, distribution feeder automation and physical security for facilities in wide range areas with very limited bandwidth and capacity in closed networks.

Many applications such as energy metering on the smart grid, have emerged from a decade of research in wireless sensor networks. However, the lack of an IP-based network architecture precluded sensor networks from interoperating with the Internet, limiting their real-world impact. The IETF chartered the 6LoWPAN and RoLL working groups to specify standards at various layers of the protocol stack with the goal of connecting low-power devices to the Internet. In [10] the authors present the standards proposed by these working groups, and describe how the research community actively participates in this process by influencing their design and providing open source implementations.

Power Line Communications

Power line communications (PLCs) uses the power feeder line as communication media. First generation ripple control systems provide one-way communications, in which centralized load control and peak shaving have been performed for many years. The European standards body CENELEC restricted the use of frequencies between 3 kHz and 95 kHz for two-way communications for electricity distributor use. A number of second generation PLC systems with low data rates were proposed in the 1990’s, and Automatic Meter Reading systems have been deployed based on this technology. Third generation systems based on OFDM with much higher data rates are currently being developed and deployed for Smart Grids, Distribution Automation and Advanced Metering Management [12].

With the development of smart grids, the PLC on the power transmission and distribution networks have become one of the potential technologies to exchange the information between the end users and the utilities. In order to provide communication services with different priorities under the smart grid environment, it is a must to design a PLC system with variable data rates supported, which means understanding of the PLC physical channel characteristics become vital. The testing results in [13] show that the main reason influencing the reliable communication of high-speed data on power line is the attenuation of the high-frequency signal, which exhibits more obviously in the branch of power line. It is almost impossible to use the frequency range from 10 to 20 MHz for the reliable communications from distribution transformer to end user, so it must be solved with the aid of means such as the repeater and the modulation schemes.

Beside the fact that feeder cables are not designed for data transmission, they are also prone to be interfered by the inverter’s outcome. Therefore, PLC modems developed for domestic applications may not be suitable. Limitations and difficulties that obstruct transmission are revealed in [14]. Also, it underlines the possibility of communicating in such an environment and discusses the possible solutions such as the use of a pulsewidth modulation filter to overcome those limitations. The majority of recent contributions have discussed PLC for high-data-rate applications like Internet access or multimedia communication serving a relatively small number of users. However, it lacks the consideration with PLC as an enabler for sensing, control, and automation in large systems comprising tens or even hundreds of components spread over relatively wide areas. In [15], the authors discussed communication network requirements common to such systems and presented transmission concepts for PLC to make use of the existing power transmission and/or distribution infrastructure resources (i.e., power lines) to meet these requirements. In [16] the authors give an overview of DLC+VIT4IP (Distribution Line Carrier: Verification, Integration and Test of PLC Technologies and IP Communication for Utilities), a EU funded project under the 7th Framework Programme (FP7) that aims to extend the existing PLC technologies by developing efficient transport of IPv6 protocol, automatic measurement, configu-ration and management, and security. In addition, the project DLC+VIT4IP also exploits frequency ranges up to 500 kHz, to support systems serving larger smart grid applications.

Distributed Energy Resources

The legacy power generation and transmission concept is converting to a massively distributed energy generation landscape integrating an extensive number of variable and small renewable energy resources (DERs) such as wind [17]–[19], solar [20]–[22] installations with all their challenging effects on the smart grid. Meta PV [23] is a project demonstrated the provision of electrical benefits from photovoltaics (PV) on a large scale, showing the way toward cities powered by renew-able energy sources. The project also demonstrates enhanced control capacities implemented into PV inverters, including active voltage control, low-voltage ride-through capability, autonomous grid operation, and interaction of distribution system control with PV systems. Smart control should enable an increase of the PV penetration in existing power grids and promote the use of more renewable energy sources in cities and industries at minimum additional investment costs. The MetaPV project is funded by the European Commission in the 7th Framework Programme, which consists of six partners from four EU countries.

New stakeholders (e.g. energy resource aggregators), more flexibility for the consumers (energy market place), and totally new concepts (loading of Electric Vehicles (EVs), usage of EVs as flexible power storage) have to be respected. Innovative monitoring and control concepts are required to operate these distributed energy resources in a reliable and safe way, so the communication technologies must support it. A key require-ment for facilitating the distributed production of future grids is that communication and information are standardized to ensure interoperability. For example, the IEC 61850 standard, which was originally aimed at substation automation, has been expanded to cover the monitoring and control of DERs. By having a consistent and well-defined data model the standard enables a DER aggregator, such as a Virtual Power Plant (VPP), in communicating with a broad array of DERs. If the data model of IEC 61850 is combined with a set of contemporary web protocols, it can result in a major shift in how DERs can be accessed and coordinated. [24] describes how IEC 61850 can benefit from the REpresentational State Transfer (REST) service concept and how a server using these technologies can be used to interface with DERs as diverse as EVs and micro Combined Heat and Power (µCHP) units.

There are some works (e.g., [25]–[27]) in integrating DER generation into the traditional centralized carbon fuel based generation power grid. These energy sources include biomass etc. A key observation made in [25] is that existing power grids were designed in a one-direction radial mode without considering the communication with the emerging distributed renewable resource generation. In [26] it discussed the broader implications of the social acceptance of these new energy gen-eration technologies, as they represent a significant departure from incumbent approach of traditional monolithic large scale energy generation. In addition, the implications of regulatory and economic factors also contribute to potential take-up and various deployment models to increase the adoption of these distributed renewable resource generators [27]. Every DER includes an Electronic Power Processor (EPP) to govern the power exchange with the smart grid and Switching Power Interface (SPI) to control the currents drawn from the smart grid. Such distributed EPPs and SPIs should perform cooperatively to take full advantage of smart grid potentiality (exploitation of renewable energy sources, power quality and transmission efficiency). To achieve this goal dif-ferent approaches can be adopted, depending on the available communication capability. In [28] it discussed various control solutions applicable in absence of supervisory control, e.g., in residential micro-grids, where communication is possible between neighbor units only (surround control) or is not available at all (plug & play control). In micro-grids, where number and type of DERs and loads is unpredictable and may vary during time, cooperative operation can be achieved by simple cross-communication among neighbor EPPs, without centralized supervisor. In [29], it describes principles of co-operative operations with existing information and communication architectures, which allows exploitation of micro-grid capabilities without additional infrastructure investments.

Smart Metering

The Advanced Metering Infrastructure (AMI) is a key factor in the smart grid which is the architecture for automated, two-way communications between a smart utility meter and a utility company. A smart meter is an advanced meter which identifies power consumption in much more detail than a conventional meter and communicates the collected information back to the utility for load monitoring and billing purposes. Consumers can be informed of how much power they are using so that they could control their power consumption and the consequent carbon dioxide emission. By managing the peak load through consumer participation, the utility will likely provide electricity at lower and even rates for all.

AMI has already gained great attraction within the industry, with the advantages in accuracy and process improvement of on-line meter reading and control. In [30], additional benefits are suggested to be gained in managing power quality and asset management with AMI. This paper also discussed how reliability, operational efficiency, and customer satisfaction can be addressed with an AMI deployment. However, the benefits of AMI are countered by increasing cyber security issues [31]. The technologies require a communication infrastructure to provide interconnectivity. Hence, the vulnerabilities that ex-pose other internetworking systems will ultimately lead to security threats to AMI systems.

Monitoring and Controlling

SCADA systems have been implemented to monitor and control electrical power grids for decades. The industrial experience shows that practical deployment of SCADA based systems may restrict it to the high voltage transmission net-works only. In [32] the authors made the observation that existing monitoring and control systems are restricted to the (high-voltage) transmission network and not suitable for larger scale monitoring and control of the entire electrical grid. A distributed monitoring control system is proposed to manage the power grid. A grid computing solution is proposed to address these monitoring control needs and the results of the research for an off-line test environment is discussed. The key motivations also include the need to support sustainable and renewable energy source at the micro-generation level. As SCADA systems evolve, there is much interest in exploring the security vulnerabilities posed to these systems over com-munication network and/or internet technologies [33]–[35]. In [36], the solution applies existing Information and Communication Technology (ICT) systems in a hierarchical decomposition of the power grid into logical zones for monitoring and control. It outlines the impact to the control center responsible for management and control of the electrical network. It also proposes a framework for future control center in order to monitor and manage the smart grid. The EU FP6 project ADINE [37] is based on the Active Network Management (ANM) concept, where automation, ICT and power electronics are used to integrate more distributed gener-ators by exploiting active resources instead of just reinforcing the network. The resources are mobilized through ancillary services or requirements. Five enabling solutions within ANM are pushed forward in the project: Protection relay and fault location applications, coordinated protection planning, voltage control with microturbine, centralized voltage control with SCADA/DMS.

The rest of this paper is organized as follows: the key motivations of smart grid communication infrastructures are discussed in section II. Several industrial trials are shown in section III. The detailed requirements are presented in section IV. The challenges are discussed in section V. Conclusions are drawn in section VI.

MOTIVATIONS

In this section, we briefly highlight the key motivations of communication infrastructures in smart grid systems. As illustrated in Figure 2, the motivations are related to system, operation and environment aspects in emerging smart grid paradigm through communication infrastructures [38].

A key objective for communication infrastructures in smart grid systems is to improve service reliability and quality to customers which includes reduced outage times when a power system is interrupted, improved notification of electricity net-work problems and providing customers with proper options and tools to understand and optimize their energy usage to curtail the peak-hour usage to avoid power quality degradation or blackout [39].

CASE STUDIES

The industry has recently undergone a significant transformation of their ICT systems to support both current and future business models of smart grid operations. Moreover, the power industry is transforming from the traditional models of business to embrace a number of new and enhanced technologies that support future smart grid operations. This section summaries several smart grid industry projects which include energy web infrastructure for power generation and electricity market information exchange, smart metering infrastructure which support monitoring and retrieving both real-time and historical data, smart community for real-time power consumption monitoring and managing, ZigBee-based recording system with capability for consumers to view and manage their power consumption online, and future control center for power generation and distribution managing and deciding between utilities through public networks such as internet.

The increasing electricity demand and sustainable devel-opment of renewable energy resources offer opportunities for both utilities, brokers, customers to participate into the development of the emerging energy web. The basic idea of energy web is to use the Internet to gain bandwidth, reliability and interconnection for the smart grid. It realizes the on-demand and demand response in local area by establishing the balance of power generation and consumption.

In Figure 3, each power generator is interconnected with an adapted power supplier which has the proper capability of interpreting the real-time price signal received from the energy web infrastructure [45]. In order to match the consumption and generation, the participant strategy is adapted. In the power market model, each electricity user has option to become a power generator. The electricity price is generated real-time and sent to every participants by utility operators using the smart grid communication infrastructure from the electricity market. The electricity flows generated by the participants are monitored in real-time mode by utility operators who also operate the real-time metering infrastructures such as automatic meter reading (AMR) or AMI for establishing the energy demand and supply balance. While the historical records of both the power consumption and generation with their corresponding price are periodically sent to the related offices of the participants for financial settlement.

Security

Based on the evolution of power system communication infrastructures and the concern of cyber security, many new issues have arisen in the context of smart grid.

A domain is a specific area, wherein specific activities/business operations are going on and they can be grouped together. The security domains are introduced in Figure 10 [99].

When communicating across power utilities, different organizations and companies, using communication networks, the security domains should be recognized. For example, a power utility company could define a security domain and related policies and procedures for its telecontrol activity to assure compliance with legislative or regulatory requirements. If similar definitions, procedures, policies, etc. were developed by other power utility companies, it would be easier to discuss and define common rules for the information exchange or the usage of common resources in a communication infrastructure. However today, there are no common definitions including the term security. Also, there are no common control system security policies or procedures, although groups such as IEC [100], ISA [101], and NIST [102], [103], are working on generic policies and procedures. A government coordination action between different authorities and agencies were started in [104], focusing on SCADA security. The action is based on the participation of the power utilities, water companies, and railway systems, which have SCADA systems as the critical part of operations. Also, the security policies are represented. Here, the expertise is gathered and experiences are shared, including both domestic and international knowledge; everything with the purpose of securing the SCADA systems being part of the critical information infrastructures. As a natural step, the SCADA Security Guideline has been developed in [105]. Also, technical guidelines and administrative recommendations are developed which are available for free downloading, that support the securing actions of the SCADA systems in the different areas of operations: power, water, and transportation.

The fact that SCADA/EMS systems are now being interconnected and integrated with external systems creates new possibilities and threats in cyber security. Some of these new issues have been emphasized in [98] and [106]. The various interconnections of a substation were investigated in [107], as shown in Figure 11. All the numbered access points (1-10) elucidates the possible points where to the substation can be accessed. This number creates an operational environment that implies possible digital entrances and hence digital vulnerabilities at the same time. As presented in [108], using a wireless sensor network (WSN) in AMI in a smart grid is so vulnerable to be attacked by an intelligent adversary even with an ordinary microwave stove. Brodsky et al. [109] documented a denial-of-service attack on IEEE 802.15.4 wireless sensor networks used within the smart grid. The equipment needed for such an attack is inexpensive (about $70). The privacy of terminal customers and smart metering networks is important to the eventual acceptance by the public. Research in this area is going on and smart meter users will need to be reassured that their data is secure. In [110] the authors describe a method for securely anonymizing frequent (e.g., every few minutes) electrical metering data sent by a smart meter. Although such frequent metering data may be required by a utility or electrical energy distribution network for operational reasons, this data may not necessarily need to be attributable to a specific smart meter or consumer. However, it needs to be securely attributable to a specific location (e.g. a group of houses or apartments) within the smart grid.

CONCLUSION

In this paper, we presented the background and motivation for smart grid communication infrastructures. We showed that a smart grid built on the technologies of sensing, communications, and control technologies offer a very promising future for utilities and users. We reviewed several industrial trials and summarized the basic requirements of communication infrastructures in smart grid paradigm. Efficiency, reliability and security of interconnected devices and systems are critical to enabling smart grid communication infrastructures. Interoperability must be achieved while avoiding being isolated into noncompetitive technical solutions and the need for wholesale replace of existing power communication systems. Alignment behind technical standards must be balanced with creating an environment that encourages innovation so that the overall communication infrastructure may continue to evolve. Based on the above survey, we can focus on those challenges to smart grid communication infrastructures in both system design and operations to make it more efficient and secure.

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