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Power-line communication (PLC) is a communication protocol that uses electrical wiring to simultaneously carry both data, and Alternating Current (AC) electric power transmission or electric power distribution. It is also known as power-line carrier, power-line digital subscriber line (PDSL), mains communication, power-line telecommunications, or power-line networking (PLN).
A wide range of power-line communication technologies are needed for different applications, ranging from home automation to Internet access which is often called broadband over power lines (BPL). Most PLC technologies limit themselves to one type of wire (such as premises wiring within a single building), but some can cross between two levels (for example, both the distribution network and premises wiring). Typically transformers prevent propagating the signal, which requires multiple technologies to form very large networks. Various data rates and frequencies are used in different situations.
A number of difficult technical problems are common between wireless and power-line communication, notably those of spread spectrum radio signals operating in a crowded environment. Radio interference, for example, has long been a concern of amateur radio groups.
Narrowband power-line communications began soon after electrical power supply became widespread. Around the year 1922 the first carrier frequency systems began to operate over high-tension lines with frequencies of 15 to 500 kHz for telemetry purposes, and this continues. Consumer products such as baby alarms have been available at least since 1940. In the 1930s, ripple carrier signalling was introduced on the medium (10–20 kV) and low voltage (240/415 V) distribution systems.
Électricité de France (EDF) developed a system called "spread frequency shift keying" or S-FSK. See IEC 61334. It is a simple low cost system with a long history, however it has a very slow transmission rate, between 200 and 800 bits per second. In the 1970s, the Tokyo Electric Power Co ran experiments which reported successful bi-directional operation with several hundred units.
Since the mid-1980s, there has been a surge of interest in using the potential of digital communications techniques and digital signal processing. The drive is to produce a reliable system which is cheap enough to be widely installed and able to compete cost effectively with wireless solutions. But the narrowband powerline communications channel presents many technical challenges, a mathematical channel model and a survey of work is available.
Principle of Operation
Power line networking uses existing electrical wiring, whether in a building or in the utility grid, as network cables, meaning they also carry data signals. It can be a means of extending an existing network into new places without adding new wires.
For example, a computer could be wired to a router as follows: an adapter is connected to a router of an existing wired local-area network, via its network port. A second adapter is connected to an Ethernet-ready device like a computer. When both adapters are plugged into their wall sockets they will have a network connection via the electrical wiring in between the two wall sockets being used. Some networking devices, such as routers or switches, also have power line connectivity built in. This adds no new wires since they need to be plugged into the wall to operate anyway.
The power line is transformed into a data line via the superposition of a low energy information signal to the power wave. Since electricity is 50 or 60 Hz, data is transmitted at at least 3 kHz to ensure that the power wave does not interfere with the data signal. A technical challenge is that because the power wiring is unshielded and untwisted, the wiring acts as an antenna. So that the wiring emits radio energy, causing interference to the existing users of the same frequency band. The power lines can also act as receiving antennas, and receive interference from radio signals. In many jurisdictions such transmissions are illegal. The U.S. is an exception, permitting limited-power wide-band signals to be injected into unshielded wiring, as long as the wiring is not designed to propagate radio waves in free space.
A PLC connection has many advantages to a wireless connection, however the quality of the connection will still depend on the quality of the domestic electrical system. Improper wiring and circuit breakers in between the connected cables can negatively affect the performance, and can cause connection interruptions.
PLC (along with 12 other product categories) has been implicated in the production of "undue interference with wireless telegraphy apparatus". There were 158 and 114 complaints in 2013 and 2014 respectively across all 13 product categories. These product categories are under increasing scrutiny to ensure this is avoided.
Types of PLC
PLC can be broadly grouped as narrowband PLC and broadband PLC, also known as low frequency and high frequency respectively. They may also be grouped as AC or DC. Functionally, there are four basic forms of powerline communications:
- Narrowband in-house applications: where household wiring is used for low bit rate services like home automation and intercoms.
- Narrowband outdoor applications. These are mainly used by the utility companies for automatic meter reading and remote surveillance and control.
- Broadband In-house mains power wiring can be used for high speed data transmission for home networking.
- Broadband over Power Line: outdoor mains power wiring can be used to offer broadband internet access.
Narrowband PLC works at lower frequencies (3–500 kHz), lower data rates (up to 100s of kbps), and has longer range (up to several kilometers), which can be extended using repeaters. It can be applied in the Smart Grid in smart energy generation, particularly in micro-inverters for solar panels. Data rates and distance limits vary widely over many power-line communication standards. Low-frequency (about 100–200 kHz) 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.
Applications in the smart grid
Power-line carrier communication (PLCC) is mainly used for telecommunication, tele-protection and tele-monitoring between electrical substations through power lines at high voltages, such as 110 kV, 220 kV, 400 kV. This can be used by utilities for advanced energy management techniques (such as OpenADR and OpenHAN), fraud detection and network management, automatic meter reading (AMR), advanced metering infrastructure, demand side management. load control, and demand response.
A project of EDF includes demand management, street lighting control, remote metering and billing, customer specific tariff optimisation, contract management, expense estimation and gas applications safety.
A coupling capacitor is used to connect the transmitters and receivers to the high voltage line. Both one-way and two-way systems have been successfully used for decades. In a one-way (inbound only) system, readings "bubble up" from end devices (such as meters), through the communication infrastructure, to a "master station" which publishes the readings. A one-way system might be lower-cost than a two-way system, but also is difficult to reconfigure should the operating environment change.
In a two-way system, commands can be broadcast out from the master station to end devices (meters) – allowing for reconfiguration of the network, or to obtain readings, or to convey messages, etc. This type of broadcast allows the communication system to simultaneously reach many thousands of devices—all of which are known to have power, and have been previously identified as candidates for load shed. PLC also may be a component of a Smart Grid.
A PLC carrier repeating station is a facility at which a PLC signal on a powerline is refreshed. Therefore, the signal is filtered out from the powerline, demodulated and modulated on a new carrier frequency, and then reinjected onto the powerline again. As PLC signals can carry long distances (several 100 kilometres), such facilities only exist on very long power lines.
The Distribution Line Carrier (DLC) System technology used a frequency range of 9 to 500 kHz with data rate up to 576 kbit/s.
In 2009, a group of vendors led by principal sponsor Iberdrola formed the PoweRline Intelligent Metering Evolution (PRIME) alliance. As delivered, the physical layer is OFDM, sampled at 250 kHz, with 512 differential phase shift keying channels from 42–89 kHz. Its fastest transmission rate is 128.6 kilobits/second, while its most robust is 5.4 kbit/s. It uses a convolutional code for error detection and correction. PRIME supports IPv6.
In 2011, several companies including distribution network operators (ERDF, Enexis), meter vendors (Sagemcom, Landis&Gyr) and chip vendors (Maxim Integrated, Texas Instruments, STMicroelectronics) founded the G3-PLC Alliance to promote G3-PLC technology. G3-PLC is the low layer protocol to enable large scale infrastructure on the electrical grid. G3-PLC may operate on CENELEC A band (35 kHz to 91 kHz) or CENELEC B band (98 kHz to 122 kHz) in Europe, on ARIB band (155 kHz to 403 kHz) in Japan and on FCC (155 kHz to 487 kHz) for the US and the rest of the world. The technology used is OFDM sampled at 400 kHz with adaptative modulation and tone mapping. Error detection and correction is made by both a convolutional code and Reed-Solomon error correction. The required media access control is taken from IEEE 802.15.4, a radio standard. In the protocol, 6loWPAN has been chosen to adapt IPv6 an internet network layer to constrained environments which is Power line communications. 6loWPAN integrates routing, based on the mesh network LOADng, header compression, fragmentation and security. G3-PLC has been designed for extremely robust communication based on reliable and highly secured connections between devices, including crossing Medium Voltage to Low Voltage transformers. In December 2011, G3 PLC technology was recognised as an international standard at ITU in Geneva where it is referenced as G.9903. Narrowband orthogonal frequency division multiplexing power line communicationtransceivers for G3-PLC networks.
With the use of IPv6, both PRIME and G3 enable communication between meters, grid actuators as well as smart objects.
Home automation and networking
- Universal powerline bus, introduced in 1999, uses pulse-position modulation.
- LonTalk, part of the LonWorks home automation product line, was accepted as part of some automation standards.
Typically home-control power-line communication devices operate by modulating in a carrier wave of between 20 and 200 kHz into the household wiring at the transmitter. The carrier is modulated by digital signals. Each receiver in the system has an address and can be individually commanded by the signals transmitted over the household wiring and decoded at the receiver. These devices may be either plugged into regular power outlets, or permanently wired in place. Since the carrier signal may propagate to nearby homes (or apartments) on the same distribution system, these control schemes have a "house address" that designates the owner. A popular technology known as X10 has been used since the 1970s.
PLC can be used for transmitting radio programs over powerlines in the AM radio band.
Higher data rates generally imply shorter ranges; a local area network operating at millions of bits per second (Mbps) may only cover one floor of an office building, but eliminates the need for installation of dedicated network cabling.
Broadband PLC works at higher frequencies (1.8-250 MHz), high data rates (up to 100s of Mbps) and is used in shorter-range applications. High frequency communication may (re)use large portions of the radio spectrum for communication, or may use select (narrow) band(s), depending on the technology.
Power line communications can also be used in a home to interconnect home computers and peripherals, and home entertainment devices that have an Ethernet port. Adapters allowing for such connectivity are often marketed as "Ethernet over power" (EOP). Powerline adapter sets plug into power outlets and establish an Ethernet connection using the existing electrical wiring in the home. (Power strips with filtering may absorb the power line signal.) This allows devices to share data without the inconvenience of running dedicated network cables. Protocols are:
- HomePlug AV, introduced in 2005, has speed from 20Mbit/s to 60Mbit/s. HomePlug AV is ratified by the IEEE 1901 specification which assures interoperability between adapters from different vendors.
- Powerline AV 500 offers speeds from 90Mbit/s to 200Mbit/s.
Other companies and organizations back different specifications for power line home networking and these include the Universal Powerline Association, SiConnect, the HD-PLC Alliance, Xsilon and the ITU-T’s G.hn specification. Within homes, the HomePlug AV and IEEE 1901 standards specify how existing AC wires should be used for data. IEEE 1901 products interoperate with HomePlug. Some limitations in household use are that performance can be degraded by certain home appliances including motorized devices, switchmode AC-to-DC converters, and fluorescent lamps; and using them in an apartment building might lead to a security risk.
Broadband PLC works at higher frequencies (1.8-250 MHz), high data rates (up to 100s of Mbps) and is used in shorter-range applications.
Broadband over power line (BPL) is a system to transmit two-way data over existing AC MV (medium voltage) electrical distribution wiring, between transformers, and AC LV (low voltage) wiring between transformer and customer outlets (typically 110 to 240V). This avoids the expense of a dedicated network of wires for data communication, and the expense of maintaining a dedicated network of antennas, radios and routers in wireless network.
BPL uses some of the same radio frequencies used for over-the-air radio systems. Modern BPL employs frequency-hopping spread spectrum to avoid using those frequencies actually in use, though early pre-2010 BPL standards did not. The criticisms of BPL from this perspective are of pre-OPERA, pre-2005 standards.
The BPL OPERA standard is used primarily in Europe by ISPs. In North America it is used in some places (Washington Island, WI, for instance) but is more generally used by electric distribution utilities for smart meters and load management.
Advanced techniques are needed to overcome noisy direct current environments. Prototypes are operational in vehicles, using CAN-bus, LIN-bus over power line (DC-LIN) and DC-BUS. LonWorks power line based control has been used for an HVAC system in a production model bus. The SAE J1772 committee is developing standard connectors for plug-in electric vehicles proposes to use power line communication between the vehicle, off-board charging station, and the smart grid, without requiring an additional pin; SAE and the IEEE Standards Association are sharing their draft standards related to the smart grid and vehicle electrification.
- HomePlug Powerline Alliance
- IEEE 1675-2008
- KNX (standard)
- List of broadband over power line deployments
- Multimedia over Coax Alliance
- National Emergency Alarm Repeater
- Residential gateway
- Universal Powerline Association
- IEC 61334
- List of PLC manufacturers
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