Impact of DC Circuit Breakers on Transient Stresses within Modular Multilevel Converters in Bipolar HVDC Systems

DCCB is analyzed to characterize benchmark stress values, including converter-internal voltages, component currents and surge arrester energies. Building on this, multiple DCCB integration scenarios with varied DCCB locations and designs are evaluated. Through comparison with the benchmark values, conclusions are drawn on whether existing converter designs for PtP systems can be translated to MTDC systems comprising DCCBs. The results indicate that DCCB integration leads to increased terminal-to-ground voltage stresses in the converter station, thus increasing the requirements on the installed surge arresters. By contrast, worst-case current and submodule stack voltage stresses remain comparable to PtP designs.

Faster DCCBs systematically reduce voltage stresses across all investigated faults. The effect of added inductance depends on the fault location: it increases converter-internal overvoltages for converter-internal faults but reduces voltage stresses for faults at the DCCB terminals. These findings indicate that PtP converter hardware is largely transferable to MTDC systems with

DCCBs, provided surge-arrester capability is adapted and breaker dynamics are considered.