A Novel Calculation Method for Steady-State Short-Circuit Currents in Meshed DC-Grids

DC grids can be found at different levels of the energy system, from DC railway networks to HVDC grids. However, there is currently no standard for calculating the short-circuit currents in meshed DC-grids. This paper proposes a calculation method for steady-state short-circuit currents for DC-grids with arbitrary topology. These grids are fed by converters, which behave like an uncontrolled six-pulse bridge rectifier in case of a short-circuit. Due to different number of diodes conducting simultaneously, these converters exhibit a nonlinear behaviour. The proposed calculation method uses a piecewise linear VI-characteristic to describe the nonlinear converter behaviour with different linear Thevenin equivalents. Thus, the nonlinear network is reduced to a linear network, which minimises computational cost. An iterative algorithm is used to determine the correct Thevenin equivalent for each converter. The accuracy of the proposed calculation method is demonstrated relative to detailed simulations in PSCAD.