Fault-Isolation Scheme for Flexible DC Distribution Networks With Multiple Types of Converters

Complete fault-isolation schemes for flexible DC distribution networks with multiple types of converters are rare. In this work, a fault-isolation scheme based on the new-type multi-port DC circuit breaker (MP-DCCB) and improved converters (modular multi-level converters, voltage source converters, and DC transformers) with current-limiting and fault-isolation capability is proposed. The fault currents are limited by the thyristor-based fault current limiter. Thereafter, multi-type faults are isolated by the coordination of MP-DCCB and improved converters. The working principle of the new scheme is analyzed by establishing equivalent models, and its validity under different scenarios is verified by simulations. Moreover, its advantages are demonstrated by comparing its performance with other typical schemes in terms of economy and functionality.