Calculation method of short-circuit fault current in flexible DC grid

Abstract

The flexible DC grid has the capability to transport and distribute electric energy in multiterminal power system, and avoid the adverse impact on AC power grid in reactive power consumption and current harmonic. Unfortunately, because of the discharge of submodule capacitor facing the short-circuit fault of the overhead line, The overcurrent problem caused by the fault restricts the further development of the DC grid. At present, the research on short-circuit fault of flexible DC grid is mainly based on computer software simulation without mathematical expression to describe failure process quantitatively. This paper proposes a short-circuit fault current calculation method describing flexible DC grid fault process. Firstly, the linearized equivalent model of the MMC converter station is obtained by considering the discharge characteristics of the submodule capacitors. Secondly, considering the DC grid space topology, the parsed expression of overcurrent in short circuit fault is derived. Finally, the analysis results of the paper are compared with the software simulation results of the PSCAD/EMTDC platform to verify the validity and accuracy of the overcurrent algorithm.