Performance evaluation of G3 narrowband PLC standard for transmission through single and paired transformer

摘要

This paper evaluates the transmission of narrow-band PLC signals using the G3 PLC standard as it passes through transformers which is crucial in automatic meter reading and demand side applications deployment for Smart Grid. Three typical laboratory step down transformers with different secondary voltages are utilized to compare the modem performance at various modulation schemes with SNR, BER and data rate used as the metric. The PLC modem utilized and configured to operate in the G3-PLC standard is C2000 from Texas Instrument. The tests done include file transfer through single and paired transformer using BPSK, QPSK, D8PSK, and ROBO modulation schemes, distance test, and gain test. It was observed that transmission through a step down transformer with lower secondary voltage generated higher SNR and RSSI. It is also noted that transmission from high voltage side to the low voltage side (downlink) of the transformer provides better SNR and BER than transmitting from low to high side (uplink). This is due to the unequal impedance seen by the two modems, one is seeing an impedance Z, while the other is seeing an impedance equal to the impedance Z at the other side times the square of the turns ratio. This is validated in the transmission on paired transformers, where both modems see the same impedance, hence, successful transmission is achieved. Thus, it is advisable to design the coupling circuit of the modem that would match the impedance of the power line where the signal is expected to pass through a single transformer only. The other remedy is to use the ROBO modulation scheme, a repeated BPSK transmission, that shows successful transmission in both uplink and downlink transmission of the modem. Although it is relatively slower than the other modulation schemes, it maintains a constant value up to a modem-to-modem distance of 100 m.