This project is about GRIDNET - Powerline Communication over the low-voltage grid, which has interested several researchers and utilities during the last decade, trying to achieve higher bit-rates and more reliable communication over the power lines. In the last decade there was a large growth in small communication networks in the home & in the office places. Several computers & their peripherals interconnected together resulting the network to expand globally to the state of Internet.A number of networking technologies are invented which purely concentrates on home networks. But users are limited due to its nature of high cost. Some are over engineered or difficult to install in per-existing buildings. This report is based on one such communication medium, which has a very high potential growth. i.e, the power line, which give rise to power line carrier communication.
Power line carrier communication refers to the concept of transmitting information using the mains as a communications channel.Power Line Carrier communication systems consist of a high frequency signal injection over the electrical power lines. This kind of technology has been used since the 1950 decade in order to provide signalling and ripple control in high voltage lines, at transmission level. In the last years the interest for this technology has suffered a revival because the impressing increase of the mobile telecommunications has brought a big development in transmission technologies for this kind of communications. In particular, new modulation technologies used for wireless communication are especially suitable for PLC communication and make massive data transmissions possible. Besides, the opening of the market, the need to integrate Distributed Energy Resources (DER) and the increase of the power supply demand create a new scenario in which the approach of the energy distribution system has to change.
In such a scenario, the distribution system needs to be automated in order to give a satisfactory response to the problems that will eventually appear. The actual automation ratio of the Spanish distribution system is of approximately a 2% or 3% and the prevision is that it should increase to more than a 50% in the following years. Currently PLC communications can be broadband as well as narrowband and both cases present successful transmissions. In the case of Narrowband PLC there are the CENELEC standards EN50065 and EN50065-1, for signals between 3 kHz and 148 kHz over low voltage public and/or private grids. For Broadband PLC, European Commission funded OPERA IST and Opera 2 projects are working towards the standard development currently. In this case the used signals range from 1MHz to 34MHz with a bandwidth between 10 and 30MHz and a bit rate of 200mbps. The results of the both above mentioned projects will feed the ETSI Broadband Power line Telecommunications standard. Thus, it would be possible to think of an automated distribution scenario with PLC used as a communication link used for multiple applications. Our project mainly aims at applicability of power line carrier communication techniques towards home networking. Communication over the power line will have the following advantages.
The modern electric grids are well maintained & far superior to any of the wired communication networks. No of electrical consumers are higher than telephone, cable or other wired communication customers. This will give a high potential market for the investors. The analog spread spectrum waves have much greater bandwidths or carrying capacity than the digital switched systems.
A basic PLC transmitter consists of five main sub-stages: a data source, a serial to parallel converter, a carrier frequency oscillator, a digital modulator and an interfacing circuit. The transmitter function is to modulate the data signal using one of the digital modulation techniques and then to load it to the power-line network. A PLC receiver is connected to the power-line network via an interfacing circuit. A preamplifier is used to compensate for the losses in the power lines. The amplified signal is demodulated to recover the original data, and then passed to a data sink.
This section is used to enter the code of the device to switch ON / OFF. This section consists of more than one push to on switches; each of them will be allotted with a unique number. The key board will be scanned and encoded with the help of a microcontroller.
The microcontroller controls the entire actions of both transmitter unit and receiver unit. The microcontroller in the transmitter unit scans the key board in order to detect the closed key and encodes the key value. The key value will be an hexadecimal code in the parallel format. The µC in the transmitter also performs the parallel to serial conversion so that the code can be transmitted over a wireless channel. The microcontroller in the receiver unit will perform a serial to parallel conversion in order the retrieve the code of the closed key. Also the microcontroller in the receiver unit analyzes the received code and switches ON/ OFF the load according to the received code.
This section generates the high frequency carrier wave which is used to modulate with the data. The frequency is set around.
This section modulates the serial data out of the microcontroller with the carrier waver. The OOK modulation is usually used because it provides a reliable and yet a simple system. OOK modulation is a special case of ASK (Amplitude Shift Keying) modulation, where no carrier is present during the transmission of a zero.
This section demodulates the data from power line carrier signal. A phase locked loop will be the best choice.
Power Line Interface
An interfacing circuit is used to isolate the 220 V/50 Hz from the low voltage environment.
Relay And Relay Drivers
The relays are used to isolate both the controlling and controlled equipments. The relay is an electromagnetic device, which consumes comparatively large amount of power. Hence it is impossible for the interface IC to drive the relay satisfactorily. To enable this, a driver circuitry, which will act as a buffer circuit, is to be incorporated between of them. The Driver circuitry senses the presence of a “high” level at the input and drives the relay from another Voltage source. Here the relay is used to switch the electrical supply to the appliances.
The system requires a regulated voltage of +5V along with an unregulated 12V supply for relay. These low voltages are obtained from the domestic supply with the help of this block.