A New Approach for Hybrid ac-dc Circuit Fault Analysis

Classical fault analysis is a powerful tool for the ac power system fault analysis, which provides the short circuit currents for an effective protection system design. With the rise of dc circuits within the ac grid and the presence of dc loads and power sources, new fault analysis that includes the hybrid system has become an immediate need. Faults at the ac side of the circuit are affected by the dc loads and sources. Thus, a fast and accurate scheme that can analyze the effects of the dc circuit on the ac grid is required. The existing methods for fault analysis of the ac-dc hybrid grids are complex and require different modeling for the ac and dc circuits. This paper aims to extend the results of the classical ac fault analysis to the ac-dc hybrid grids. This will make available the well-developed ac fault analysis methods to the hybrid circuit with accuracy and simplicity. The proposed method finds a Thevenin equivalent of the dc laterals applied to the ac circuit; thus, avoids multiple analyses currently used in ac-dc circuits.