The Voltage Clamping Based DC Circuit Breaker With Decoupled Fault Isolation and Energy Dissipation Processes

This paper proposes a DC Circuit Breaker (DCCB) topology for the DC fault clearance of the Modular Multilevel Converter based High Voltage Direct Current (MMC-HVDC) grid. By utilizing the voltage clamping and current limiting functions of the pre-charged capacitors in the DCCB, the DC-side short-circuit fault is isolated. First, the topological mechanism and operational principle of the unidirectional topology are analyzed, and the bidirectional topology is provided for backup protection. Then, the residual energy dissipation branch of the DC transmission line is introduced and the reclosing strategy after the deionization process is provided. Further, a step-insert method of the clamping branch is designed to relieve the sudden change of the electrical stresses during the voltage clamping based fault clearance process. Compared to the conventional DCCB schemes, the main advantage of the proposed topology is the decoupling of fast fault isolation and slow energy dissipation processes, which will accelerate the power recovery speed of the healthy parts of the HVDC grid. The proposed approaches are verified first by fully detailed Electro-Magnetic Transient (EMT) simulations on PSCAD/EMTDC then by a down-scaled hardware experiment.