Fault mode operation strategies for dual H-bridge current flow controller in meshed HVDC grid

Current flow controllers (CFCs) can remove grid bottlenecks or extend grid operation area by changing amount of power flowing through DC transmission lines. This study focuses on behavior of interline H-bridge CFC in a DC grid in fault condition. In addition to the CFC circuit level fault studies, non-linear and linearized simplified models are developed for system level analysis. The analysis and fault study shows that the interline H-bridge CFC cannot survive during DC transmission line and bus faults due to an overvoltage occurring in its capacitor. Further investigation figures out that this overvoltage cannot be avoided even in presence of fast HVDC circuit breakers. Hence, an improved control system together with circuit level modifications are proposed to improve the CFC post-fault operation and to retain its components from possible damages.