C onventional worldwide power systems produce a significant amount of greenhouse gas emis-sions mainly due to their use of fossil fuels for power generation.
In addition, the typical power grid in most countries consists of an aged infra-structure. Although the power grid has provided several decades of useful ser-vice, its dependence on fossil fuels can be reduced. The next-generation power grid is generally referred to as the “smart grid.” The smart grid is envisioned as a cyberphysical system that will utilize modern communication technologies
extensively to maximize operational effi-ciency of energy production, transmis-sion, and delivery.
Twenty-first century communication technologies can facilitate the operational effectiveness of the power system by ena-bling demand response functionality as well as improving reaction time during power outages. The use of the existing power system infrastructure itself, as a medium for data communications, has gen-erated worldwide appeal. Despite healthy competition from wireless technology, powerline communications (PLC) remains viable as a smart grid enabling tool. In par-ticular, narrowband powerline communica-tions (NB-PLCs) show incredible potential. There are a plethora of NB-PLC standards,
Digital Object Identifier 10.1109/MPOT.2013.2249691
Anim AmArsingh,
hAniph A. lAtchmAn,
And duotong yAng
Narrowband power line communications:
Enabling the smart grid
JANuAry/FEbruAry 2014 17
each with their inherent advantages and disadvantages. This article will explore some of the various NB-PLC standards as an enabler for the smart grid.
Eyeing advantagesPerhaps the salient advantage of PLC
over wireless technology lies in commu-nication performance in highly urban-ized areas. In these metropolitan areas, attenuation losses to wireless communi-cations are high, and signal strength is low or non-existent. Figure 1 illustrates the interference of signals that can occur in metropolitan areas due to physical objects. Fading causes a problem since communication with the electric meter may not be available in all locations or at all times.
On the other hand, high-rise apart-ments are common in these highly built-up areas. In these high-rise apartments, the electricity meters are typically located in the basement. Communication with meters in an underground location provides another challenge. PLCs pro-vide a viable communication solution with these meters. Figure 2 illustrates the location of electricity meters in the basement of a typical high-rise apart-ment building. The pervasive nature of power lines within buildings makes NB-PLC an effective solution for com-munication with electric meters, espe-cially when they are located in areas where wireless coverage would be poor.
The world is undergoing the largest wave of urban growth in history. In 2008, for the first time in history, more than half
of the world’s population was living in towns and cities. By 2030 this number will increase to almost 5 billion. With such a large population concentrated in urbanized areas, a communications solu-tion that provides reliable metering within highly urban areas is desired. Furthermore, since the power system infrastructure is maintained by the utility, PLC communi-cations would incur no additional costs such as those associated with using exter-nal communication options provided via wireless service providers. PLCs can be divided into two large classes: narrow-band and broadband.
Narrowband PLCsNarrowband PLCs typically operate in
the frequency range from 3 KHz to 500 kHz. This narrowband technology is further subdivided into those that make use of multicarrier-based technology such as orthogonal frequency division multi-
plexing (OFDM) and those that utilize single carrier technology. In fact, the mul-ticarrier-based technologies offer higher data rates. Examples of these multicarrier narrowband technologies are Powerline Intelligent Metering Evolution (PRIME) and G3-PLC. Both PRIME and G-3 PLC were developed specifically with utility applications in mind. Additionally, IEEE 1901.2 and ITU-T G.hnem are two prom-ising, next generation NB-PLC standards because of their improved data rates compared to PRIME and G3-PLC. ITU-T G.hnem and IEEE 1901.2 are based on two proven OFDM technologies, PRIME and G-3 PLC.
Broadband PLCsBroadband PLCs usually function in
the frequency range from 1.8 MHz to 250 MHz and offer data speeds of up to several hundred megabits per second. Some examples of broadband PLC
Fig. 1 An example of physical obstacles causing interference in urban areas.
Example of anApartment
Basement
ElectricalMeters
PowerStorageBatteries
Dryerand WashingMachine
DataConcentrator
Air Conditioner
Fig. 2 Electricity meters in the basement of a high-rise apartment complex.
18 IEEE POTENTIALS
technology include HomePlug AV, HomePlug Green PHY, IEEE 1901, and HD-PLC.
Unlike broadband PLCs, some NB-PLC technologies offer the advantage of being able to communicate through transform-ers. Lower frequencies are able to cross the transformer more effectively than the higher frequencies utilized by broadband PLCs. This feature is advantageous in that NB-PLC technology can be utilized for longer distances on the electric power grid without the need for repeaters. The installation of repeaters can increase the cost of PLC deployment substantially.
Enabling the smart gridNB-PLC can potentially form the
communication core of an intelligent power system. For instance, NB-PLC can be used to transmit energy con-sumption data from the residential side to the utility in real time. This data enables the utility to have an increased awareness of the demand on the power grid. Additionally, if there is a fault on the power system, bidirectional com-munications, provided by NB-PLC can facilitate faster and more efficient resto-ration of power. Figure 3 provides a basic schematic for the use of NB-PLC as a backhaul technology and for the control of devices at the residential end.
With the advent of bidirectional com-munications in the smart grid, the poten-tial for a host of other energy manage-ment applications becomes possible. For instance, the electric meter at the house-hold can function as a central access point to modulate the use of certain appliances in response to time of use pricing from the utility company.
Time-of-use pricing enables the utility to set higher prices for electricity con-sumption during peak times and reduced
prices during off-peak times. The aim of time-of-use pricing is to encourage cus-tomers to shift their energy consumption away from peak times. Reduction in peak demand reduces the need for bringing inefficient peaking power plants online.
PLC essentialsAlthough PLCs may differ in terms of
physical layer (PHY) and medium access control (MAC) specifications, they essen-tially function in the same way. A cou-pler is used to inject the PLC signal into the electric power line. These couplers may be inductive or capacitive. Inductive couplers do not require a physical con-nection with the bare wire, while capaci-tive couplers require a physical connec-tion. Additionally, in the deployment of PLC systems, data concentrators are uti-lized to convert the power line signals from the individual electric meters into a form that is more acceptable to a central-ized data server.
Additionally, PLCs are a form of infor-mation communications technology and, as such, error detection and error correc-tion mechanisms are important. Forward error correction (FEC) enables errors to be corrected without the need for retrans-mission of data. Another error control technique used by some PLC technology is automatic repeat request (ARQ). ARQ instantly requests a retransmission when errors are detected. This ability to correct data without retransmission is key in applications where retransmission may be too time consuming or impossible. There are several types of FEC available. Some examples of FEC coding include Reed-Solomon coding and convolutional coding. Different PLC standards use dif-ferent levels of FEC. The more robust the FEC employed, the more processing power that is typically required at each
node. With increased processing power requirements, the chipsets needed would be more expensive. Many PLC systems employ both FEC and ARQ schemes to satisfy performance requirements.
Government regulations concerning PLC operation
NB-PLC technology has a larger potential to be deployed worldwide as a smart grid communication tool from a government regulation standpoint. In addition to the power-system topology, it is vital to understand that government regulations within a specific country would influence the PLC technology that would be deployed within that country.
For instance, Galli et al. report that Japan’s regulatory polices prevent the use of broadband PLC outdoors. Therefore, in Japan, PLC operating in the frequency range between 2 and 30 MHz would not be allowed outdoors. However, NB-PLC is a potential candidate for outdoor use in Japan. Due to its abilities to cross the transformer and its potential for providing reliable communications at low power consumption and cost, this article will survey some of the most popular NB-PLC technologies available.
Some European countries have agreed that certain frequencies on the power line be allocated for certain pur-poses. For instance, Galli et al. report that CENELEC EN 50065 (a European standard) allows communication over low voltage (LV) distribution power line in the frequency range from 3 kHz to 148.5 kHz. Razazian et al. reported that in the United States, the Federal Communications Commission has allot-ted the spectrum between 14 and 480 kHz as one wideband channel. It can be observed that it is difficult for one specific standard to be the best choice as each power system topology and the respective regulations of each country provides unique challenges.
PrimE PRIME is a narrowband OFDM PLC
technology that achieves data rates of up to 130 kb/s. PRIME was conceptualized in 2006 with the needs of utility companies in mind and utilizes a nonproprietary PHY/MAC specification that has the potential to become a globally recog-nized industry standard. PRIME uses a convolutional code as its FEC mechanism. Berganza et al. indicated that PRIME allows for cost-effective seamless integra-tion with established standard metering protocols such as device language
UtilityControlCenter
DataConcentrator
Central Access Point
Transmission
Backhaul (NB-PLC Communications)(System 2)
Home Area Network(PLC Enabled)Low VoltagePower Generation
Meters
Node
Node
Node
Fig. 3 The potential use for NB-PLC as a smart grid enabler (backhaul communication).
JANuAry/FEbruAry 2014 19
message specification/companion specifi-cation for energy metering (DLMS/COSEM). Furthermore, Berganza et al. reported that this compatibility with DLMS/COSEM is a significant benefit of PRIME. The DLMS/COSEM standard suite is the most widely accepted international standard for utility meter data exchange. Fundamentally, DLMS/COSEM is a stan-dardized “message” that allows for interoperability with different types of communications media.
Essentially, the PRIME Alliance is responsible for promoting PRIME as a global power line standard and for encouraging multivendor interoperabil-ity for markets/equipment. As of 2011, Iberdrola, a Spanish-based multinational utility company, had deployed 100,000 PRIME compliant meters in its electricity distribution network in Castellon, Spain.
In their field deployment, Ibedrola gained considerable insight into the challenges faced with PRIME technol-ogy. In fact, Berganza et al. identified wideband interfering noise sources as the single most common and serious challenge involving PRIME deployments. In particular, Berganza et al. identified equipment such as garage ventilation systems and defective lighting systems as being a major contributor to this noise on the power line. Noise on the power line reduces data rates and, in some situ-ations, can even impede communica-tions. Berganza et al. proposed that fil-ters at customers’ residences could resolve the problem. Iberdrola is one of the top five electric utility companies in the world and has a worldwide market of 30 million customers. As a principal member of the PRIME alliance, Iberdrola is actively promoting the PRIME NB-PLC specification for smart grid applications on the LV grid.
G3-PLCG3-PLC is an NB-PLC specification
developed to operate in the frequency range from 35.9 kHz to 90.6 kHz. G3-PLC uses fast Fourier transform-based OFDM. The G3-PLC specification was developed by Maxim Integrated Products in collab-oration with the French utility company Électricité Réseau Distribution France. One of the outstanding features of G3 PLC technology is its use of adaptive tone mapping, whereby the system auto-matically uses the part of the spectrum that has the least amount of noise in order to maximize data rate. Due to vari-ous frequency regulations in different countries, there are different versions of
G3-PLC. For instance, G3 FCC has been developed to take advantage of the legally available PLC spectrum in the United States. Kaveh Razazian and fellow researchers at Maxim Integrated Research indicated that G3-PLC with D8PSK mod-ulation can achieve data rates of up to 208 kb/s. Moreover, G-3 PLC is a PLC specification intended for both medium and LV networks.
Additionally, there is G-3 PLC Lite that offers similar performance capabilities of the G3-PLC chip set. G-3 PLC lite appears to be more cost effective and, as a result, does not support some features of G3-PLC. These features that are lacking include QPSK and 8PSK modulations, adaptive tone mapping, as well as sup-port for IPv6. Incidentally, Razazian et al. conducted field trials in the U.S. distribu-tion grid utilizing G-3 PLC Lite technol-ogy. On one field trial, it was determined that transformers can attenuate the G3 PLC Lite signal by more than 50 dB. Razazian et al. demonstrated that the received signal is the same level as noise and highlighted the need for a power line specification with a robust FEC mechanism as provided by the G3-PLC specification.
Another rea l p rob lem, which Razazian et al. identified in their study, is the impact of capacitor banks during PLC over medium voltage (MV) lines. Certainly, on the MV grid, it is critical that long distance communication be achieved with minimum use of repeat-ers. Undoubtedly, using fewer repeat-ers would enable cost savings to the utility. Razazian et al. informed that these capacitor banks limit communica-tion distances and data rates when they are turned on. Moreover, Razazian et al. reported that in a real-world test per-formed in which a capacitor bank was active, G3-PLC Lite achieved a data rate of 33 kb/s at a communication distance of 1 km. However, the aforesaid
researchers conceded that the capacitor bank problem would need to be addressed by the use of repeaters. Indeed, the aforementioned research provides valuable insight for the future deployment of G-3 PLC technology.
iTU-T G.hnem G.hnem is an NB-PLC standard initi-
ated by the telecommunications sector of the International Telecommunications Union. The G.hnem project was insti-gated in January 2010 with the intention of developing a unified next generation, worldwide standard for NB-PLC technol-ogy. The G.hnem standard was specifi-cally designed to facilitate smart grid applications such as demand response (DR) and advanced metering infrastruc-ture (AMI).
Essentially, G.hnem integrates fea-tures from both PRIME and G-3 PLC standards and adds novel features for claimed enhancements in coverage, throughput, and reliability. G.hnem sup-ports a data rate of 1 Mb/s and utilizes Reed-Solomon and convolutional coding as its FEC mechanism. Additionally, G.hnem transceivers are highly parame-terized and can be programmed to oper-ate in the different frequency bands as required by the regulatory bodies in various countries. Therefore, it is possi-ble that one G.hnem transceiver design can be mass manufactured and individu-ally programmed for the desired country of use. This feature is notable when compared to transceivers based on other NB-PLC standards.
Markedly, G3-PLC FCC utilizes a dif-ferent setup that is compatible in the United States but not in Europe. This use of a single design may reduce manufac-turing costs for the G.hnem transceiver and simplify global deployments of PLC systems for the smart grid. However, there are some disadvantages with G.hnem. For instance, G.hnem is a newer standard, and it has not been tested as extensively in field deployment as PRIME and G-3 PLC. Although G.hnem promises a substantially higher data rate than PRIME and G-3 PLC, the actual data rate of G.hnem and its immunity to noise needs to be tested in field deploy-ment. Further research needs to be per-formed to ascertain the cost effective-ness of deploying G.hnem transceivers as compared to the deployment of trans-ceivers based on other NB-PLC technol-ogies. Dr. Vladimir Oksman, director of technical marketing at Lantiq, reported that G.hnem coexistence with other
NB-PLC can be used to transmit energy consumption data from the residential side
to the utility in real time. This data enables the utility
to have an increased awareness of the demand
on the power grid.
20 IEEE POTENTIALS
NB-PLC networks such as PRIME and G-3 PLC, as well as IEEE 1901.2, is cur-rently under study.
iEEE 1901.2 IEEE 1901.2 is a standard for low fre-
quency NB-PLC under development by IEEE. IEEE 1901.2 is similar to ITU-T G.hnem in that IEEE 1901.2 also adds technological advances to G-3 PLC and PRIME specifications. For instance, IEEE Standards Association Marketing Man-ager Shang Yu reports that IEEE 1901.2 is designed to support smart grid appli-cations that include grid to utility meter communications, electric vehicle to charging station, home area networking, and solar panel communications. IEEE 1901.2 promises data rates of up to 500 kb/s. IEEE 1901.2 is designed to work on LV lines of fewer than 1,000 V and on MV lines of up to 72 kV.
As with other NB-PLC technologies, IEEE 1901.2 supports communication through transformers and promises to support interoperability with existing PRIME and G3-PLC OFDM technologies. IEEE 1901.2 is designed to work in the frequency band of 10–490 kHz and accommodates various country band regulations. IEEE 1901.2 utilizes Reed-Solomon and convolutional coding as its FEC mechanisms.
Challenges in field deployment There are various power system topol-
ogies and communication regulations around the world. As a result, some NB-PLC technologies may be more effec-tive than others in certain environments. For instance, in several urban areas in European countries, the MV line goes to a substation room, and a few transformers may serve a large number of homes in this configuration. However, in countries with lower population densities such as the United States and Canada, the feeders are basically the MV lines. These homes are typically served by an aerial trans-former. In these situations, only a few homes may be served by a single trans-former. These various configurations would impact the power line specifica-tion that a utility would deem most suit-able for its specific market.
Although NB-PLC technologies have the ability to cross the transformer, there is a significant reduction in the signal-to-noise ratio. A lower signal-to-noise ratio increases the chance of errors during data transmission. Therefore, in applica-tions where the power line signal has to be transmitted across a large number of
transformers, a PLC technology with more robust FEC is desired.
For instance, G3-PLC has more rigor-ous FEC mechanisms than PRIME. Mark-edly, G3-PLC facilitates the Reed-Solomon code and convolutional code as its FEC mechanisms. Simulations performed by Martin Hoch of the Friedrich-Alexander-Universitat Erlangen-Nuremberg indi-cated that due to its additional FEC, G3-PLC performs better than PRIME when subjected to the noise environment typical of a power line. Razazian et al. confirmed that G3-PLC is able to transmit across the transformer.
PRIME may not be as effective as G3-PLC in communicating across the transformer since PRIME does not have a FEC mechanism that is as robust. If a power line technology is unable to pene-trate the transformer effectively, additional equipment is required to enable commu-nications around the transformer. On the other hand, utilizing a more robust FEC mechanism requires additional processing power. Therefore, the chip set required at each node in a G3-PLC network may be more sophisticated in order to handle additional processing, and thus, it is more expensive. There are several cost and per-formance tradeoffs in NB-PLC technolo-gies that need to be examined by utilities for their specific needs.
When deploying PLCs, utilities need to decide on the extent of the smart grid services they wish to deploy. For instance, the U.S. Department of Energy reported that AMI and DR data-rate requirements are expected to be around 100 kb/s and 500 kb/s for backhaul. Based on the requirements, PRIME and G3-PLC appear to be appropriate for data communications to the individual nodes but insufficient for the backhaul.
On the other hand, next-generation NB-PLC standards ITU-T G.hnem and IEEE 1901.2 promise data rates that would be sufficient for both the individual
electric meters and the backhaul. However, ITU-T G.HNEM and IEEE 1901.2 are newer standards and thus need to be tested more extensively in field deploy-ments in order to fully prove their merit.
ConclusionWithout question, information and
communication technologies will play a vital role in enabling the next-generation power systems to be more energy efficient and reliable than currently existing power systems. In particular, on the LV and MV grids, NB-PLC technologies are particularly attractive as a communications solution due to their low cost of deployment and ability to communicate across the trans-former. This ability to cross the transformer is vital in power system topologies with lower population densities. It was ascer-tained that wideband interfering noise sources, such as defective lighting systems, hampered communication in both PRIME and G3-PLC systems.
Additionally, the next-generation NB-PLC standards ITU-T G.hnem and IEEE 1901.2 were investigated. ITU-T G.hnem and IEEE 1901.2 seek to unify NB-PLC technologies and promise higher data rates than PRIME or G3-PLC. Surely, narrowband PLC technologies have a critical role in enabling a more efficient and reliable power grid.
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Twenty-first century communication technologies can facilitate the operational effectiveness of the power
system by enabling demand response functionality as well
as improving reaction time during power outages.
JANuAry/FEbruAry 2014 21
stamp.jsp?tp=&arnumber=6102336& isnumber=6102296 • (2012, Apr. 22). 09-3 DLMS/COSEM for Smart Metering. [Online]. Available: URL: http://www.dlms.com/news/09-3-dlms-cosem-for-smart-metering.html • (2012, Apr. 14). S Iberdrola looks to prime PLC standard. [Online]. Avail-able: URL: http://www.greentechmedia.com/articles/read/iberdrola-looks-to-prime-plc-standard/ • K. Razazian, A. Kamalizad, M. Umari, Q. Qu, V. Loginov, and M. Navid. (2011, Apr. 3–6). G3-PLC field trials in U.S. distribution grid: Initial results and requirements. presented at IEEE Int. Symp. Power Line Com-munications Applications. pp. 153–158. [Online]. Available: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber= 5764382&isnumber=5764369 • V. Oksman and J. Zhang. (2011, Dec.). G.HNEM: The new ITU-T stand-ard on narrowband PLC technology. IEEE Commun. Mag. [Online]. 49(12), pp. 36–44. Available: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber= 6094004&isnumber=6093994
• A. Rossello-Busquet. (2012, Jan–Feb. 30–2). G.hnem for AMI and DR. presented at Int. Conf. Computing, Net-working Communications. pp. 111–115. [Online]. Available: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber= 6167382&isnumber=6167355 • (2012, June 7). IEEE P1901.2™ standard for low-frequency, narrow-band power l ine communicat ions enters letter balloting. [Online]. Avail-able: http://www.businesswire.com/news/home/20120110005295/en/IEEE-P1901.2%E2%84%A2-Standard-Low- Frequency-Narrowband-Power-Line • M. Hoch. (2011, Apr.). Compari-son of PLC G3 and PRIME. presented at IEEE Int. Symp. Power Line Communi-cations Applications. pp. 165–169. [On-line]. Available: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber= 5764384&isnumber=5764369
About the authorsAnim Amarsingh (animamarsingh@
ufl.edu) earned his B.Sc. degree in elec-trical engineering (summa cum laude) from Morgan State University in 2011.
He is currently a Ph.D. student in elec-trical engineering at the University of Florida. His research interests include smart grids, information and com-munications technology, and energy management.
Haniph A. Latchman ([email protected]) earned his Ph.D. degree from Oxford University (Rhodes scholar) in 1986 and his B.Sc. degree (first class honors) from the University of the West Indies–Trinidad and Tobago in 1981. He is a professor of electri-cal and computer engineering at the University of Florida and director of the Laboratory for Information Systems and Telecommunications (LIST).
Duotong Yang ([email protected]) earned his B.Sc. degree in elec-trical engineering from North China Electric Power University in 2011. He is currently pursuing his M.S. degree in electrical engineering at the Uni-versity of Florida. His research inter-ests include dynamic pricing for smart grids, net-metering based on power line communication, and renewable energy adaptation.
Digital Object Identifier 10.1109/MPOT.2013.2295161
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