Analysis of coupling effect on LCC-MCC hybrid HVDC from parallel AC lines in close proximity

As the demand for electric power grows continuously, there are more AC and DC lines sharing the same corridor because of economic and ecological reasons. One of the problems is the induced fundamental frequency voltages and consequent circulating current on the DC lines by the coupled parallel AC lines. The LCC-MMC hybrid transmission system is quite suitable to transmit bulk power over long distance with overhead lines, which has many advantages over conventional HVDC topology. In the stage of planning a new hybrid system, comprehensive study need to be carried out on the possible coupling effect from the nearby AC lines. However, unlike LCC and VSC, the research is limited on the characteristic of MMC converters under fundamental frequency voltage from DC side. This paper proposes a computational efficient method to study the coupling effect on LCC-MMC hybrid system from the parallel AC lines. The MMC inverter and LCC rectifier are represented by equivalent models. The coupled line model is adopted to calculate the impedance and admittance matrices of the transmission lines. A typical case is chosen to illustrate the calculation results. The induced voltage and circulating current on LCC and MMC sides are carefully studied based on the chosen case.