Single-Terminal Quantity Based Line Protection for Ring Flexible DC Distribution Grids

The fast and reliable identification of DC faults is of great significance for the development of multi-terminal flexible DC distribution networks. With regard to MVDC lines in a multi-terminal ring DC distribution network with modular multilevel converters and two-level voltage source converter, a fault identification approach based on the voltage of the additional inductor was proposed. First, the calculation method of the initial voltage across the additional inductor after faults was elaborated based on modulus networks. Subsequently, the difference of the initial voltage across the additional inductor between internal and external faults was utilized to accomplish the fault identification. Furthermore, the faulty pole is discriminated based on the difference between the initial voltage across the additional inductor of the faulted pole and that of the healthy pole. The proposed scheme can identify the fault quickly and reliably. Finally, the proposed calculation method and the feasibility of the protection scheme are verified via PSCAD/EMTDC-based simulation.