Introduction  With the rapid development of AC/DC distribution networks and distributed generation technology, the role of DC microgrids in distribution networks is becoming increasingly important and will become an important component of future distribution networks. Due to the small coverage area and low line impedance of the DC microgrid, when an inter pole short circuit fault occurs, the fault current increases rapidly and has a large amplitude, which can reach more than 10 times the rated working current. This makes it difficult to set the protection of DC microgrids and requires high equipment selection, which restricts the rapid development of DC microgrids.

  Method  In response to the above issues, taking the DC microgrid as the research object, starting from the working principle of inter pole faults in the DC microgrid, the fault characteristics on the DC side of the DC microgrid were analyzed. In response to the shortcomings of existing main current limiting methods, a voltage controllable fault current controller was proposed to achieve precise control of fault current. The simulation model of DC microgrid and fault current controller was built for simulation verification.

  Result  The simulation results show that the fault current controller can significantly reduce the fault current and achieve precise control of the fault current, making the system controllable before and after the fault without locking the protection. During steady-state operation, the fault current controller can also assist the VSC (Voltage Source Converter) in further stabilizing the DC bus voltage.

  Conclusion  To cooperate with the normal operation of the relay protection device and avoid VSC triggering overcurrent protection blocking, it is recommended to set the fault current control range between 1~2 pu.