DC bus strength in DC grid protection

Fast detection and isolation of DC faults is recognized as the main challenge in developing DC transmission grids. Voltage source converter blocking must be prevented which can be very difficult given the large rate-of-rise of fault currents. The concept of multi-converter DC bus is introduced as a grid design approach aimed towards increasing robustness of DC grids to DC faults. Behavior of a multi-converter DC bus under DC fault conditions is analyzed using newly defined parameters such as peak fault current increase and bus voltage drop. Critical inductor size and critical fault neutralization time are studied and their implications discussed. The impact of converter rating on fault current sharing and voltage drop on a multi-converter bus is investigated. Theoretical studies are substantiated by simulation results using a 10-converter bus model in PSCAD.