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.
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.
Courtesy of EETimes Europe
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