State observer-based detection method of open-circuit fault of IGBT (insulated gate bipolar transistor) of MMC (modular multilevel converter)

The invention relates to the field of fault detection of power electronic and flexible HVDC (high voltage direct current), discloses a state observer-based detection method of an open-circuit fault of an IGBT (insulated gate bipolar transistor) of an MMC (modular multilevel converter) and aims to quickly diagnose reason and position of the open-circuit fault of the IGBT of the MMC. The state observer-based detection method includes as an error of an estimation value and a test value of bridge arm circulation excesses a threshold value for the moment of DeltaT1, judging that the fault occurs; comparing estimation values and actual values of the bridge arm current and output current and judging the bridge arm which the fault occurs to and fault type; monitoring voltage of capacitors of submodules, and in case that the voltage of the capacitor of one submodule is higher than the voltage threshold value for the moment of DeltaT2, judging that the fault occurs to the corresponding IGBT of the submodule. In this way, the state observer is provided for the output current and circulation of the MMC, and the submodule which the fault occurs is accurately positioned.