Design of DC Reactors for DC Fault Ride-through on MMC-based Bipolar DC Grid

This paper provides the design criteria of the DC reactors for the most promising configuration option that is bipolar DC grid. The DC reactors on bipolar grid are divided into pole reactor and neural line reactor. The configurations of DC reactor are compared and shows the distributed configuration is suitable for neutral line reactor and pole reactor. Furthermore, the difference of these two reactors is investigated, showing that pole reactor is superior in limiting the fault injected by the non-fault stations and hold the dc voltage during the fault. Neutral line reactor would not affect the dynamic characteristics of the system and can protect the system from valve-side or dc bus fault that pole reactor can not. The design constraints of choosing DC reactor about hybrid DC circuit breaker (DCCB), protection requirement, additional fault current limiter (FCL) and stability are discussed. Finally, a three terminal meshed DC grid as a case study to verify the design method. For completeness, all fault analysis results are based on PSCAD/EMTDC.