Current Calculation and Characteristics Analysis of Fault Current in Hybrid Grids

As a crucial component for the New Power Systems, the Modular-Multilevel-Converter-based High Voltage Direct Current (MMC-HVDC) girds face challenges of short-circuit faults caused by the lightning strike. Calculating fault current and analyzing characteristics are of vital significance to the dc protection. However, the accurate calculation requires multiple iterating simulations in Electromagnetic Transient (EMT) type software. Therefore, a method of calculating dc fault currents in the rising stage in the MMC- HVDC grids is proposed. It contains equivalent modeling, basic-cutset-matrix equations formation in complex frequency domain, and inverse Laplace transformation. By employing the proposed calculation method, the computing amount is hugely decreased and can be extended to the MMC-HVDC grids with arbitrary topology. Finally, the proposed method is verified in comparison with the simulation results based on EMT software, and the influence of system parameters on fault current characteristics are further analyzed based on the proposed method.