In view of the problems of fault protection for the multi-terminal DC system

the DC fault characteristics and the challenges that multi-terminal DC system protection are facing are analyzed

and the existing fault protection methods for multi-terminal DC system are summarized. Based on a typical topology of the multi-terminal DC system

the partition principles of DC zones and a coordinated partition-based protection strategy are proposed

with the objective of using a minimum number of DC breakers. The method uses the DC breakers to separate the faulted DC zone from the healthy DC zones. Thus the healthy DC zones can be restored to normal operation quickly after the fault

and the faulted zone can be protected by AC breakers and DC switches which are already installed at the AC and DC side of modular multilevel converters(MMC). Finally

the simulation results based on MATLAB/Simulink platform show that the coordinated partition based protection strategy is effective and economical.