Power line communication(PLC)

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Saurabh GuptaIDD Part-IV

Roll No-07020408

What is PLC?

Power line communication or power line carrier (PLC), also known as Power line Digital Subscriber Line (PDSL), are systems for carrying data on a conductor also used for “electric power transmission”.

It is the technology that enables data transfer at narrow or broad band speeds through power lines by using advanced modulation technology.

Why PLC? By use of power line carrier digitalization and

networking of existing facilities could be organized at low cost. Because there is no need for any further construction of communication lines, given that home appliances, information devices and other various kinds of control devices therein related are digitalized easily.

Power-line communication systems greatly reduce the complexity and effort of installation.

Use of existing power lines as a communication medium eliminates installation costs for adding dedicated communication wiring to existing structures.

Some facts about PLC60%+ U.S. homes have Internet

access10% broadband

◦Inaccessible and costlyPLC = No new wires:

◦Extensive infrastructure "Every" building

◦Emerging Technology◦Use of Power grid for communication

Power line characteristics

Not designed for high frequenciesPower line "hostile" to signal

propagationPower line is one of the most

electrically contaminated environments, which makes reliable data communication via this medium extremely difficult.

Operating principle of PLC

Superimposing a high frequency signal (1.6 to 30 MHz) at low energy levels over the 50 Hz electrical signal.

This second signal is transmitted via the power infrastructure and can be received and decoded remotely.

PLC signal is received by any PLC receiver located on the same electrical network.

Components used in PLC

Power line network components use existing electrical power lines as carriers for data communications signals. These components are:

Directional couplers:

A directional coupler is a power component used for developing high flatness and directivity on the waveguide band.

Fixed power attenuators: An attenuator is a power component that is

used to lower the amplitude value of the electrical signal passing through a wire.

Contd….

Line trap: It is also called "Wave trap". It is connected in series with the power (transmission) line. It blocks the high frequency carrier waves and let power waves (50 Hz - 60 Hz) to pass through. It is basically an inductor of rating in milli Henry.

Coupling capacitor: It provides low impedance path for carrier energy to HV line and blocks the power frequency circuit by being a high impedance path.

Power line modems: A power line modem can be used in residential and commercial applications for transmitting and receiving data through power lines.

Directional coupler

How is PLC implemented All power line communications systems operate by

impressing a modulated carrier signal on the wiring system.

As the losses in the grid are also proportional to distance, high voltages are used for long-distance

transmission, medium voltages are used for intermediate

distances, and low voltages are used for transmission over

short distances and within the target building or environment.

Different types of power line communications use different frequency bands, depending on the signal transmission characteristics of the power wiring used.

Contd…

HV lines are excellent carriers for radio frequency (30 kHz-300GHz) communications signals, as they feature open wires with very few crossovers over quite long distances. An RF transmission power of about 10 watts is often sufficient to cover distances of more than 500 km.

MV and LV lines are characterized by a large number of cross-connections and different conductor types (e.g., open wire and cable). Long-distance RF signal propagation is extremely poor in such an environment, primarily due to the high attenuation and impedance mismatch.

Orthogonal Frequency DivisionModulation Scheme - OFDM

AdvantagesHigh bandwidth efficiency.Scalable to high data rates.Channel equalization not required.Efficient implementation using Fast Fourier

Transform (FFT).Used in Home Plug 1.0Design of OFDM transmission schemes is

based on the selection of the number of carriers and the cyclic prefix length.

Block diagram for OFDM modem:

Multicarrier modulation is used.

Robust against narrowband interference.

The bandwidth is divided into a number of sub-channels, which can be viewed as many independent modulated carriers with orthogonal carrier frequencies.

The data is divided into several parallel data streams or channels, one for each sub-carrier.

Contd..

Each sub-carrier is modulated with a conventional modulation scheme (such as quadrature amplitude modulation or phase-shift keying) at a low symbol rate, maintaining total data rates similar to conventional single-carrier modulation schemes in the same bandwidth.

Channel equalization is simplified because OFDM may be viewed as using many slowly-modulated narrowband signals rather than one rapidly-modulated wideband signal.

Disadvantages: Sensitive to frequency synchronization problems. Loss of efficiency caused by cyclic prefix/guard

interval.

Limitations of PLC Power line wiring was designed for transmission of

electrical power, nominally in the 50–60 Hz range and at most at about 400 Hz; thus, the use of this medium for data transmission at high frequencies presents some technically challenging problems.

Attenuation in the PLC Channel: Maximum signal power is received only when the

impedance of the transmitter, power line, and receiver match.

Power line networks usually consist of a variety of conductor types and cross sections joined randomly; therefore, a wide variety of characteristic impedances are encountered in the network.

This impedance mismatch results in a multipath effect with destructive interference at certain frequencies.

Contd… In a typical home environment, the attenuation on a typical

power line is 20 to 60 dB and depends heavily on the load.

Noise in the PLC channel: The major sources of noise in the PLC channel are electrical

appliances that utilize the 50 Hz electric supply and generate noise components extending well into the high-frequency spectrum as harmonics of the line frequency.

Induced radio frequency signals from broad cast, commercial, military, citizen band, and amateur stations severely impair certain frequency bands on the PLC channel.

PLC Electromagnetic Compatibility: The use of power lines for communications involves

transmission of information modulated on carrier frequencies in the 9 kHz to 30 MHz range. The skin depth effect at these frequencies causes the power lines to radiate high-frequency electromagnetic signals that make them leaky. The placement of any wireless service near PLC systems is bound to be subjected to interference. The interference is directly proportional to the transmission power and the distance between the installation and the power line.

Regulatory ConstraintsRegulatory agencies

◦ Federal Communications Commission (FCC)

◦ European Committees for Electro technical Standardization (CENELEC)

North America◦ 0 to 500 kHz and part of 2 to 30 MHz

unlicensed spectrum are used for PLCGeneral -- Regulate

◦ Band allocation◦ Radiation emission◦ Power transmission on band

European Regulations Frequencies / Use1. 3-9 kHz: energy providers; customers premises2. 9-95 kHz (A-band): energy providers & concession holders3. 95-125 kHz (B-band): energy provider's customers4. 125-140 kHz (C-band): energy provider's customers5. 140-148.5 kHz (D-band): energy provider's customers

◦ B & D-band no access protocol defined

6. 2-30 MHz◦ Home plug 1.0 uses◦ Unlicensed by FCC◦ Europe: efforts to develop a standard for

electromagnetic compatibility with PLC

General: Regulate◦ Band allocation

Applications of PLCPower 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.

Automatic meter reading (AMR) technology allows energy suppliers to exploit their own infrastructure to bill their customers in an efficient and economical way using Power Line Communications (PLC).

Contd…

PLCC can be used for interconnecting PBXs(Private branch exchange). The electricity board in India have an internal network PLCC between PBXs.

PLC modems can satisfy services like load and alarm management, remote monitoring and disconnection, etc., provide high throughput and keep a low cost.

Applications of PLC based on frequency spectrum used:

1. High-frequency communication (≥MHz)

◦ Home networking (LAN)◦ Internet access (broadband over power lines)

2. Medium frequency (kHz)◦ Home control (narrowband)◦ Low-speed narrow-band communication◦ Transmitting radio programs◦ Utility applications

3. Low frequency (<kHz)◦ Utility

Automatic meter reading Load control Demand response

Under Research/Development

By Home Plug AllianceGoal 100 Mb/s for in home PL

network◦Necessary for multimedia (e.g.

HDTV)◦Rivals wired network protocols

(Ethernet)Accommodates new hybrid

power lines & wireless network .Simple, reliable, cost-effectivePlug-and-play

PLC -- SummaryTremendous potential

◦ Existing infrastructure◦ Much research -- many companies◦ Relatively low cost

Obstacles◦ Compatibility, security, reliability◦ Bandwidth◦ Regulatory issues

THANKYOU!!!