Power line communications for smart meter networks
Power Line Communications is a technology that has been around for some time now and has been widely accepted as a solution that can meet the requirements of what a Smart Meter should do. Several countries in Europe have already rolled out Smart Meters in their regions to deliver the functions that are required by the utility and the consumer to proactively take action towards making the grid more efficient and smart. The PLC technology enables the utility to add value to their major assets – the distribution network that is already in place and using this as a means to facilitate the communication from the meter to the utility. By re-using the electricity distribution network for communication, the utility can also re-use maintenance tools and resources and thereby avoid costs for the maintenance of a specific communication network. With any extensions to the electricity distribution network made, the communication network grows accordingly.
It is broadly believed that the growth of energy demand has outpaced the rate at which energy generation can grow by traditional means. Additionally, many governments agree that greenhouse gas emissions need to be contained to control or prevent climate change. The necessity of modernizing the electric grid infrastructure around the world is both the consequence of the limited investments made in it in the last decades, as well as of the result of new requirements that emerge in the safe integration of utility scale renewable energy sources feeding into the transmission system. The active participation of consumers via Demand Side Management (DSM) and Demand Response (DR) programs, all of which are advocated as sustainable solutions to the energy crisis.
Balancing generation and demand at a very granular scale requires the integration of additional protection and control technologies that ensure grid stability. The concept of Smart Grid has emerged, along with the need for meters that provides information to the utility on the energy consumption so that the utility can act according to the demands placed on it. This has led to the concept of Smart Meters that enable the communication between the utility and the consumer. Because communications is such a fundamental element of the Smart Grid, it is important and crucial that the communication methodology chosen is reliable and consistent in its performance. Due to this basic requirement for very high reliability, wired communications are considered to be better than wireless communications. And within wired communications, Power Line Communications is the dominant technology that has been delivering the performance and reliability required for this market.
What is PLC?
Power Line Communications (PLC) systems operate by impressing a modulated carrier signal on the wiring system. Different types of power line communications use different frequency bands, depending on the signal transmission characteristics of the power wiring used. Data rates and distance limits vary widely over many power line communication standards. Low-frequency (about 100–200 k Hz) carriers impressed on high-voltage transmission lines may carry one or two analog voice circuits, or telemetry and control circuits with an equivalent data rate of a few hundred bits per second; however, these circuits may be many miles long. Higher data rates generally imply shorter ranges; a local area network operating at millions of bits per second may only cover one floor of an office building, but eliminates the need for installation of dedicated network cabling.
PLC offers the simplest type of installation out of all the neighborhood area network (NAN) access technologies and does not need any extra work other than installing the meter hardware. When competing solutions based on Wireless technology such as GPRS and RF Mesh only PLC offers the following advantages:
- No installation of additional communication wiring
- Communication is seamlessly established with powering up of the device
- No communication cables or equipment can be removed or tampered with during operation
Why PLC For Smart Meters?
In general, the distribution network made up of power lines are a hostile environment that makes the accurate propagation of communication signals difficult as they were designed to carry power and not data. When transmitting data over the power lines, there is a lot of exposure for this data to be negatively impacted because of the presence of many electrical devices connected to these lines. These other devices connected to the power lines are noise sources or noise impairments that can have an adverse effect on the communication of control data. Other factors that can impact the performance of a power line network is number and types of devices on the power lines and their switching functionality along with the distance between the transmitter and receiver of the PLC network. These factors have to be addressed to ensure that the PLC network is reliable and dependable. By overcoming the challenges of communicating over a PLC network, the data that is being communicated can now be used effectively to render the grid smart and make it work for the utility and the consumer.
Figure: Typical Architecture of a PLC Based Smart Metering Network
The European Committee for Electrotechnical Standardization (CENELEC) together with the ETSI and the European Committee for Standardization (CEN) form the European system for technical standardization that defined the narrow band frequencies to be in the range between 9 -150 KHz. The carrier frequency for CENELEC A-Band is between 9 – 95 KHz, for CENELEC B-Band the carrier frequency is between 95 – 125 KHz and the CENELEC C-Band is between 125 – 140 KHz. Power line transceivers can be used in the CENELEC A-band and CENELEC C-band. The A-band is reserved by law in CENELEC-regulated countries for the exclusive use of utilities and their licensees. The C-band is available for consumer and commercial use without restriction, but a common access protocol and co-existence protocol is mandated. When used in A-band mode, transceivers should support two channels within this band, one centered at 75 kHz and the other at 86 kHz. When used in C-band mode, transceivers also support two channels, one centered at 115 kHz and the other centered at 132 kHz. The rationale for two channels is that if one is blocked, it is unlikely that the other is blocked by a harmonic of the power line impairment.
Power Line Challenges and PLC
Intermittent noise sources, impedance changes, and attenuation make the power line a hostile signaling environment. Power Line Communications technology incorporate a variety of technical innovations to ensure reliable operation such as:
- Unique dual carrier frequency feature that automatically selects an alternate secondary communication frequency should the Highly efficient, patented, low-overhead forward error correction (FEC) algorithm to overcome errors induced by noise;
- Sophisticated digital signal processing, noise cancellation, and distortion correction algorithms integrated into the Power Line Communications transceiver that correct for a wide variety of signaling impediments, including impulsive noise, continuous tone noise, and phase distortion;
- High output, low distortion external amplifier circuits used on the transmission that can deliver 1Ap-p into low impedance loads, eliminating the need for expensive phase couplers in typical applications.
- Location of simple high-pass filter located between the Power Line Communications Transceiver and the power mains. This circuitry provides surge and line transient protection in addition to blocking the low frequency, 50Hz/60Hz AC mains signal.
The combination of these special features enable the Power Line Smart Transceivers to operate reliably in the presence of consumer electronics, power line intercoms, motor noise, electronic ballasts, dimmers, and other typical sources of interference. The Power Line Communications Transceivers can communicate over virtually any AC or DC power mains, as well as unpowered twisted pair, by way of a low-cost, external coupling circuit.Conclusion
With an installed basis of over several million metering points in Europe, PLC is by far the most commonly used communication technology for smart metering. The electricity network was not designed to be used as a communication channel; however, PLC technology is mature enough to deal with even the most challenging environments. Filter techniques, power line transceivers with special functional DSP blocks, filtering techniques and sophisticated routing algorithms all guarantee very robust communication.
Only a mature communication technology such as PLC offers the communication reliability necessary to read hundreds of thousands of metering points at an acceptable cost every day.
Additionally, meter installation is as simple as connecting the meter to the mains and requires no additional work and by using PLC technology, a utility has full control over its distribution network. Smart metering based on PLC is the first step towards fully realizing the full potential of a smart grid.
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