A Short-Circuit Current Calculation Method Based on Discrete Model for VSC-HVDC Grids

A numerical calculation method for short-circuit current of voltage source converter based high voltage direct current (VSC-HVDC) grid based on discrete model is proposed in this paper. For VSC-HVDC grid based on modular multilevel converter (MMC), the equivalent circuit after DC short-circuit fault is analyzed. Based on the Backward Euler Method, the discrete models of inductance and capacitor in converter and lines is established. Besides, discrete model of converter stations under different fault types is formed. On this basis, the numerical solution algorithm for different types of fault currents in DC grids is designed. Based on the RT-lab platform, a four-terminal VSC-HVDC grid simulation model is built. The numerical solution calculation and electromagnetic model simulation results are compared and analyzed. It is verified that the fault current value can be accurately obtained based on the proposed model and fault current numerical solution algorithm. The calculation error is less than 5.5% compared to the simulation results.