Pole-to-Ground Fault Current Calculation for MMC-HVDC Grid with Symmetrical Component Decomposition

Pole-to-ground (PTG) fault current calculation is of vital importance for modular multilevel converter based high voltage direct current (MMC-HVDC) grid. However, considering the difference between metallic return conductor and positive/negative dc line, both the fault boundary condition and dc line parameters are asymmetrical, which challenges the PTG fault current calculation. In this paper, a novel analysis method that based on three-dimensional symmetrical component decomposition is proposed to overcome the double asymmetric issue. With the proposed method, analytical expressions of the PTG fault currents can be obtained. The calculated PTG fault current can provide insights on the fault mechanism and is applicable for sizing of the dc equipment and setting of protection relays. Finally, the proposed analysis method is verified by PSCAD/EMTDC simulation.