Adaptive Single-Pole Autoreclosing Concept with Advanced DC Fault Current Control for Full-Bridge MMC VSC Systems

This paper presents an adaptive autoreclosing concept for HVDC transmission systems with modular multilevel converters in full-bridge topology for single pole-to-ground faults. Since HVDC transmission will be used in the German energy transmission system to support the heavily loaded ac grid for energy transport over far distances, the interruption time has to be kept as short as possible to preserve system stability. Within the presented autoreclosing concept, the necessary interruption time is determined adaptively. After fault detection, the converter control drives the fault current to zero and injects a low-level ac current. The nonlinear interdependence between the fault arc resistance and the current is used to detect the final arc extinction and to start the voltage recovery, enabling a fast resumption of the power transmission. PSCAD|EMTDC is used to model the electric arc behavior and the dielectric recovery inside an exemplary point-to-point HVDC grid model as an evaluation of the concept. The minimum required ac current is identified related to the used fault detection method. Additionally, the influences of fault position, line length, and fault resistance on fault detection are investigated. The results show that the required interruption time can be determined adaptively for transmission line length up to 400 km.