This paper introduces the power line carrier (PLC) technology and its development process, and compares the traditional narrowband single carrier FSK modulation scheme with the new OFDM-based PRIME and G3 schemes.
Introduction
The traditional grid is changing. In the past century, the grid was a system used to transfer electrical energy from a certain number of power stations to a large number of different levels of users. The standard for designing and operating a grid is to transfer electrical energy from hundreds of power plants to millions of users in an efficient manner. The system's ability to store power is limited, so how to predict the user's power consumption becomes critical. The control of the grid is based on daily forecasts, and the power is delivered by the power station to the distribution network via the transmission network. Most of the power generation needs to be controlled by a regulator.
Now, in some countries, and in more countries in the future, green energy will contribute more and more to the power grid. Its share of the grid, from the original 5% of hydropower, rose to 40% of solar and wind power. In most green power, the regulator has little control. In addition, electric vehicles have joined the changing team. The large-scale promotion of electric vehicles will double the power consumption of the grid and bring large storage capacity on a large scale. The rise in electricity consumption, the promotion of green power and uncontrolled power generation, and the storage capacity of electric vehicles are considered to be the perfect storm for the power grid. This solution is called the smart grid. It combines embedded intelligence with real-time communication and control to communicate with any user and control their load at any time. To achieve such communication functions, PLC technology using the power grid as the main communication medium is required.
PLC technology was used in the medium voltage field to control the power grid more than 20 years ago. However, the large-scale use of PLC on the low-voltage side is closer. A typical success story of PLC technology is that the Italian ENEL power supply company uses a narrowband PLC system based on FSK and BPSK modulation to build an AMM (Automatic Meter Management) system for 35 million users. This system automatically reads 35 million meters every 2 months. However, its average baud rate is not enough to support more real-time communication and control, as well as future applications based on communication protocols such as IPv6.
For more real-time communication and control, as well as future applications based on communication protocols such as IPv6, a new generation of PLC technology based on OFDM modulation is needed. Two of the main OFDM schemes are the current G3 and PRIME technologies. The G3 is a solution developed by the French EDF Power Company, developed by MAXIM and SAGEMCOM. This program was announced in 2009, and EDF plans to test 2,000 electric meters using G3 technology in 2013.
PRIME is an open multi-vendor solution from the PRIME Alliance that includes more than 30 members of power supply companies, meter manufacturers and chip suppliers such as ADD Semiconductor, FUJITSU, STM and TI. The watch manufacturers include SAGEMCOM, ITRON, LANDIS+GYR, ISKRA-MECO, ZIV and SOGECAM. IBERDROLA was the first power company to promote this solution, but now EDP, CEZ MERENI and ITRI are also joining the camp.
IBERDROLA began installing 100,000 PRIME-enabled meters in 2010. The power supply company also plans to release a new standard for the demand of 1 million meters by the end of 2010, and complete the installation of 10 million meters in Spain in the next 3-5 years. Other power supply companies have begun to adopt PRIME technology. Both G3 and PRIME are OFDM solutions, but the history of development is different. The G3 originally used a chip designed by MAXIM that provides IEEE 802.15.4 2006 communication for the PHY layer and some existing software layers, 6LowPAN for the MAC layer, and IPv6 communication for the network layer.
PRIME is a consortium of power companies, industry players and university research institutes that collaborate to develop a new open standard for OFDM power line technology. The alliance uses a systematic design process for the PHY layer, starting with meeting the most basic requirements. The next step is to define the physical medium from the elements of noise level, noise rhythm, signal attenuation and impedance mode. Industry manufacturers have developed new automation products for these purposes and have cooperated with power companies. This resulted in a large database containing elements such as noise levels, noise cadence, signal attenuation and impedance modes, as well as an accurate data statistics model for the grid.
In the second step, they use this model to estimate different combinations of multiple parameters such as head implementation, bandwidth allocation, number of subcarriers, subcarrier modulation and error correction of OFDM technology, and use new equipment in the field. Test to come to * estimate the best solution. After repeated iterations and extensive field tests, they selected the best combination of parameters based on the conditions of the European grid and the specifications of the power supply company. In addition, the MAC and upper communication layers were developed by a consortium of chip vendors, watch manufacturers and power companies.
After hard work, they developed the PHY, MAC, and centralized communication layers. The PHY layer transceives MPDUs between adjacent nodes. It uses a high frequency 47.363 kHz bandwidth in the CENELEC A band with an average transmission rate of 70 kbps and a maximum rate of 120 kbps. Under this condition, the probability of direct communication between nodes in the network is 92%. At other times, routing ensures 100% connectivity is successful.
The MAC layer provides core MAC functions such as system access, bandwidth allocation, connection creation/maintenance, and topology resolution.
A service-specific centralized layer (CL) can classify information transmissions and associate them with appropriate MAC connections. It can measure any data transmission that may be included in the MAC SDU, or it can have payload header compression. At the same time, multiple subset layers are used to implement various data transmissions in the MAC SUD.
In a basic FSK or BPSK scheme, information is transmitted on a single carrier. The baud rate of the transmission depends on the size of the bandwidth, while the reduction in noise and selectivity limits communication. In the OFDM scheme, information is transmitted over multiple subcarriers. The baud rate of the transmission depends on the bandwidth and the complexity of the DBPSK, DQPSK or D8PSK subcarrier modulation. Noise and selectivity reduction in communication is better eliminated by employing multiple subcarriers, coding and error correction.
The size of the symbol is determined by the sampling frequency and the number of subcarriers. The larger the symbol, the more reliably the impulse noise can be suppressed. Encoding improves stability, but it also adds complexity and power. The more subcarriers, the higher the communication stability, but it does not mean that the baud rate is higher.
The G3 technology uses 36 subcarriers, a 0.735 ms classification symbol, a 6.79 ms sequence, and a 9.5 ms beginning. Repeating methods and RS error correction are required to improve communication stability.
PRIME uses 97 subcarriers, a long symbol of 2.24ms, a 2ms order, and a beginning of 4.48. In order to avoid the complexity of the iterative method and RS error correction, it uses a symbol that is three times more energy efficient to improve communication stability. This is a solution that provides stability but is less costly.
In summary, traditional power grids are evolving toward smart grids that require more advanced communications capabilities. PLC technology is a more convenient technology for achieving the necessary functions and stability. PLC technology is also changing towards OFDM solutions, while G3 and PRIME are the two main solutions.
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