As work progresses on building a smarter grid, we’ll need to take a fresh look at existing technologies, even as we invent new ones. Many existing technologies, once thought to have limited applications and an uncertain future – even serious drawbacks – can be tweaked to provide viable and valuable technical options in a smart grid that demands flexibility.
A case in point is Power Line Communication or PLC, a blanket term that covers several technical approaches to sending a modulated signal over transmission, distribution and/or premise wiring for a variety of communication purposes for monitoring and control, including smart metering and myriad smart grid applications.
PLC’s properties found initial success in specific circumstances where legacy equipment meshed with its strengths. Objections to its wider use have largely been based on two main, intrinsic
hurdles. Transmission, distribution and premise wiring generally is designed for transmitting AC power in 50 Hz and 60 Hz cycles, with limited ability to carry signals in higher frequencies, such as PLC’s traditional signal in the 1.6 MHz to 30 MHz range. This property could limit signal propagation from one point to another. The other main objection to PLC has been that, in many cases, it runs on unshielded wires that have the potential to emit radio signals and many if not most countries have laws that forbid such interference with other uses of those frequencies.
The “good news,” if you will, is that years ago the IEEE Standards Association (IEEESA) set out to improve PLC and harmonize its proprietary flavors. To do so, the IEEE P1901.2™ Working Group examined PLC’s strengths and optimized them for smart grid applications, and addressed PLC’s real and perceived shortcomings to make it a suitable medium for smart grid. The Intended outcome of this standards-based work also provides the flexibility and scalability needed to serve applications needed for smart cities and the Internet of Things. That’s quite a leap for a communication medium that many had considered passé or possessing a geographically limited future.
History meets new challenges
PLC for voice telephony began in the early 20th century and became widespread in Europe and the United States by the end of the 1920s. In the smart grid era, which required first one-way, then two-way data transmission over power lines, Echelon (which has since focused on industrial IoT technology) used PLC for low-frequency, low data rate (sub 1Kbps) smart metering projects in Italy, starting around 2000, and more recently a higher data rate (sub 50Kbps Cenelec data rates) PRIME OFDM PLC technology for Spain, along with G3-PLC OFDM PLC installations in France and Japan (also with sub 50Kbps Cenelec data rates).
Echelon performed similar installations in Scandinavia and Eastern Europe. Reliability and robustness of the solution were two key drivers in these successful implementations. Europe remains one of the leading target markets for PLC’s use. In terms of smart meters, PLC can be added as an additional communication module and is easily upgradeable if and when that’s needed, so existing meter designs can accommodate PLC without altering meter design. One obvious advantage of PLC is that it relies on existing wiring and precludes the time and expense needed to rewire a premise. The drawbacks include the fact that performance quality can depend on the quality of legacy wiring, particularly in a premise environment. Wiring that doesn’t meet code, or circuit breakers between wiring sections, can interrupt a PLC signal.
Optimizing for Smart Grid
In order to optimize PLC for smart grid, the IEEE 1901™ Standard for Broadband over Power Line Networks: Medium Access Control and Physical Layer specifications provides a flexible architecture that supports applications for high-speed communications over electric power distribution systems (medium and low voltage power lines), smart metering/grid, smart buildings – including homes and businesses – and vehicles.
The modulation format employed by PLC for smart grid applications is an important element. Most often in smart grid applications the modulation format is OFDM – orthogonal frequency division multiplexing. OFDM offers a more robust signal-to-noise ratio by operating in larger frequency bands than other options, such as binary phase-shift keying (BPSK) or spread frequency-shift keying (S-FSK). OFDM also provides higher bit rates and lower latency where data packet repetition is needed. The radio interference potentially caused by broadband PLC has been resolved by the “notching” capability of OFDM, which removes PLC signals from amateur radio bands.
Security, reliability, scalability
Security, system reliability, robustness, availability, scalability and quality of service (QoS) are all qualities avidly sought in smart grid-related technologies, including PLC. IEEE 1901 provides state-of-the-art data security and privacy by supporting Internet Protocol version 6 (IPv6) and various transport levels of security. IEEE 1901 offers high robustness to noise with a specific mechanism to cope with noise on medium voltage lines. In terms of scalability, PLC technology is scalable from a few kilobitsper-second (kbps) to hundreds of megabitsper-second (Mbps), as previously noted.
In addition, IEEE 1901 was developed to cope with various electrical topologies, including both medium voltage and low voltage power lines. For the meter environment, specifically, low frequency PLC succeeds in the typical configurations found in European cities and rural areas that can have 100-200 or more homes per transformer, as compared to the United States which averages between two and four homes per transformer, depending on the area. One key feature of PLC is that it’s plug-and play, which significantly cuts the cost of meter installation by as much as a halfhour at each meter. In a typical European installation, PLC typically requires limited repeaters, saving associated capital costs.
Because IEEE 1901 is typically associated with network management systems that enable remote management of devices utilizing this standard, operation and maintenance costs are limited.
Another attractive characteristic of PLC is that it complements wireless and other communication networks. PLC works as a standalone technology but, combined with wireless communication in a mesh network, it can increase coverage and data rates.
Looking ahead to IoT
The IoT will accelerate the convergence of communication technologies. IEEE 1905.1™ Standard for a Convergent Digital Home Network for Heterogeneous Technologies provides a common interface to widely deployed networking technologies such as IEEE 1901 (Broadband PLC), IEEE 802.11™ for wireless, Ethernet over twisted pair cable, and MoCA 1.1 over coaxial cable. IEEE 1905.1 was extended to support other networking technologies such as IEEE 1901.2 (Narrow band PLC). In addition, PLC’s support for IPv6, which may well be integral to IoT, is a crucial addition to low-frequency PLC solutions. So PLC flavors are designed to support IoT applications.
The standards process
As is often the case, when myriad, sometimes proprietary standards appear in the marketplace, harmonization of these defacto standards is often needed. For instance, for Low Frequency OFDM there were two main, proprietary technologies in production in 2009, PRIME and GE-PLC. With the introduction of efforts by the IEEE-SA, both technologies changed significantly. The updated PRIME and GE-PLC specifications now support up through FCC band and include various features developed in IEEE-SA. The “new G3-PLC” has been altered significantly with various additions. For instance, advanced modulations have been added, coherent solution has been added, frequency bands have been added. The International Telecommunication Union (ITU) also adopted these same features for ITU directed solutions.
In short, PLC has been optimized and made more robust and flexible, related, proprietary solutions have been improved and PLC technology has been updated to provide capabilities that will prove useful in markets beyond Europe, including North America and Asia. Equipment that can work with PLC is being produced more widely and swiftly than many were aware.
Jean Philippe Faure is chair of the IEEE 1901 Broadband over Power Line (BPL) Working Group and the IEEE ComSoc Power Line Communication Standards Committee. Jim LeClare is chair of the IEEE 1901.2 Low-Frequency Narrowband Power Line Communications Working Group.
This article first appeared in Metering & Smart Energy International Issue 5 2015.