Data Communication through Distribution Network for Smart Grid Applications

Abstract

This work investigates a novel solution for overcoming excessive signal attenuation in distribution transformers for power line communication (PLC) applications in smart grids. The proposed solution avoids classical hardware bypassing and does not require sophisticated modulation schemes like Orthogonal Frequency Division Multiplexing (OFDM). It explores the resonance that occurs in transformer windings at the kHz range to transmit the communication signal. The transformer is modeled as a network of resistors, inductors and capacitors. This results in several resonance frequencies in the kHz and MHz ranges that can be used to pass the communication signal. Several methods can be used to obtain the frequency response of distribution transformers. In this work, the Frequency Response Analysis (FRA) technique is implemented. This technique measures the amplitude and phase response due to the application of a swept sinusoid at one terminal of the transformer winding. FRA measurement of a 20kVA (220/20kV) transformer indicated that there is a resonance at 490 kHz with a gain of 2 V/V and a bandwidth of 40 kHz. The captured frequency response is then modelled as a communication channel. Then digital modulated Binary Phase Shift Keying (BPSK) signals (at resonance and nonresonance frequencies) are transmitted through the modeled transformer. Sending data at 490 kHz within the 40 kHz bandwidth resulted in Bit Error Rate (BER) values that appear better than the Additive White Gaussian Noise (AWGN) channel because of the associated gain in the transformer. In addition, the simulation verified that sending data at non-resonance frequencies or outside the resonance bandwidth resulted in poor BER. The final issue investigated in this work is the effect of distribution cables from the utility substation up to the customers' distribution transformers. The simulation confirmed that the cable at high frequency acts as an attenuator with a value of attenuation that depends on the cable length. The BER was calculated for variable cable lengths cascaded with the transformer. By sending a BPSK signal at resonance with a bandwidth of 20 kHz, the BER was zero for cases where the attenuation was less than 40 dB. The research results showed that sending data at resonance frequencies has the potential to be an effective method for improving data communication using PLC for smart grid applications.