Collaborative Control and Protection Strategy for Bipolar Short-circuit Fault in VSC-HVDC Based on Active MMC Current Limiting

DC fault protection is one of the main challenges faced by the development of flexible DC transmission systems, and the use of flexible control of modular multilevel converters (MMCs) to achieve current limiting has become a current research hotspot. The active current limiting of MMC reduces the rate of change and amplitude of fault current, which can lead to difficulties in fault diagnosis and protection selection. In this paper, a flexible DC transmission system with symmetrical single-pole connection is taken as the research object. Using the collaborative control and protection strategy and combining the active current limiting control and fault identification, the method for identifying and cutting off fault areas based on active current limiting factor is proposed to achieve the identification and removal of bipolar short-circuit fault areas. Firstly, by adding a fault current target preset controller to the MMC current inner loop controller, the variation of fault current can be quickly tracked after a fault occurs, and the DC voltage output by the MMC can be adaptively adjusted to control the fault current near the preset target reference value. Secondly, the fault area is quickly determined based on the current limiting factors output by the fault current target preset controller at different fault locations. Finally, simulation analysis is conducted in different fault scenarios of the four-terminal flexible DC transmission system in PSCAD/EMTDC, verifying the feasibility and effectiveness of the proposed collaborative control and protection strategy. © 2024 Automation of Electric Power Systems Press. All rights reserved.