DC-MMC with fault-blocking capability


When a fault occurs in the low voltage (LV) grid, to avoid fault propagation, the DC MMC should include a number of SM in upper arms large enough to withstand the rated voltage of the high voltage (HV) grid. In some cases, the fault blocking capability comes with an oversizing of the upper arms. Otherwise, a DC circuit breaker (DCCB) will be needed. The proposed solution consists in controlling the converter to make the HV current going to zero and using a switch.  As the current to break is almost zero, the switch cost will be reduced compared to a DCCB. With the proposed control, the upper arm current is controlled with the lower arms thanks to the energy stored in the SM capacitors. The lower arms overcurrent is prevented thanks to the output filtering inductances. The sizing of the inductances and capacitors could be as well designed accordingly to switch opening time of the available technology. Finally the number of SM is significantly reduced.




  • Provide fault blocking capability for the DC MMC without increasing the number of SM in the upper arms


  • HVDC multiterminal systems


  • Patent application FR1915048, filling date: dec 20th 2019
  • Report
  • Simulation files
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