A Setting-Free Single-Ended Fault Detection Method for Multiterminal DC Systems Based on Active Boundary Control

The increasing integration of power electronic equipment into modern power systems has led to the gradual weakening or elimination of boundary components, posing significant challenges for single-ended whole-line fault identification. To address this issue, this paper employs coordinated active boundary control and signal injection control during the fault steady-state to enhance fault characteristics and establish series-connected boundary properties. A fault analysis is established using modal network modeling for both pole-to-ground (P2G) and pole-to-pole (P2P) faults. The results demonstrate that the injected characteristic frequency current magnitude at the protection point increases or remains unchanged in the case of internal faults, while it decreases under external faults. Based on this, a novel single-ended setting-free protection criterion is proposed, which is independent of system parameters, simulations, and complex calculations. Its performance is validated on a multi-terminal hybrid HVDC transmission system. Simulation and experimental results confirm that the method achieves whole-line fault identification under fault resistances up to 500 Ω, noise levels up to 20 dB, and parameter variations, demonstrating high robustness and reliability even in weak or non-boundary scenarios.