Smart Grids Data Processing Analysis [Step 10]
Communication on dedicated power lines
Systems on the PLC protocol exchange data on dedicated power lines. It is also possible to communicate via "cold" wire. Data exchange protocols on power lines are based on such basic modulation schemes as FSK (frequency manipulation) and multiplexing with orthogonal frequency division of channels (OFDM).
FSK is a modulation scheme used for purposes such as one-way transmission from the meter to the concentrator. Among the significant disadvantages of the FSK scheme is the loss of the signal from the receiver side when the interference frequency coincides with one of the transmission frequencies.
Thus, the communication speed is reduced, because the frequency manipulation switches between the two frequencies, which causes delays in the bandwidth. In the case where the system architecture involves a bidirectional communication channel (intelligent networks), frequency manipulation is unacceptable.
Often several hundred meters are connected to a single data concentrator over a high voltage network segment. For this reason, data must be exchanged via low/high voltage (LV/MV) transformers.
Typically these transformers can cause a signal attenuation of several tens of decibels (frequency selective attenuation). Modulation schemes such as OFDM are used to compensate for attenuation. Orthogonal frequency division multiplexing is used in communication systems such as digital radio and television, Wi-Fi and WiMAX networks, and in PRIME (one of the narrowband protocols of the first generation).
With OFDM, PLC networks can provide sufficient bandwidth for smart grids without additional equipment costs. The G3-PLC technology uses OFDM modulation to improve quality, as this modulation eliminates interference at a specific frequency and also prevents frequency selective attenuation by increasing the number of carriers. In this way, the reliability and volume of transmitted information is increased.
Solutions based on OFDM modulation use two levels of error-corrected coding - the Reed-Solomon Brief Encoding and the Reed-Solomon Coding.
Since impulse interference and packet errors can occur on the channel, the data are intermittent in the frequency and time areas of the OFDM carriers. Some security solutions on the MAC level use the AES-128 encryption mechanism, and to find the optimal path between network nodes - mesh routing (mesh routing protocol) . Due to the high reliability of G3-PLC, communication on transformers takes place through an inexpensive connector. In this way it is possible to reduce the number of hubs, which makes this solution an affordable alternative to advanced wireless measurement infrastructures (AMI).
The communication channel distance over high and low voltage networks is 6 km, which allows monitoring even over long distances. At high noise levels, e.g. in apartment buildings, the RS-485 bus architecture is used so that it is less susceptible to external interference due to the differential transmission of signals on the channel.
This architecture also supports multi-point configurations, for connecting several meters to the same bus. Thus, based on this architecture, in apartment buildings the readings of apartment meters are transferred to the central unit, where the accumulated information is sent over a wireless channel or PLC lines. When transmitting data over short distances, the RS-232 protocol is used (e.g. when a meter is connected to a computer, modem or remote display at two points). If communication protocols are not known in advance, boards with the same layout are used for data exchange as for different protocols.
Measuring energy consumption
Power management in smart grids involves measuring both total consumption (whole building) and the load point (household appliances). Based on this data, utility companies offer customers discounts and different pricing rates. The term Power Usage Effectiveness - PUE is also used to measure the efficiency of the production infrastructure. This indicator is a ratio of total data center power consumption to equipment power consumption.
For this purpose, measurements are made at multiple points within the data centre. Microcontrollers, discrete circuitry, or crystal-based solutions can be used to measure power consumption.Among the serious disadvantages of general-purpose microcontrollers are low accuracy and narrow dynamic range, so when using microcontrollers are used 10, 12-bit ADC.
The use of discrete circuitry for measurement involves a significant number of additional components, as well as significant time for architecture development. ZigBee-based solutions allow you to capture data from an outlet (which indicates the time of measurement) and send the information over a wireless communication channel for further graphical analysis. When measuring currents from 10 mA to 20 A in the temperature range of -40°C +85°C, the error of the based systems is 0.5%.
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To be continued