Parallel open-circuit fault diagnosis method suitable for carrier phase-shifting modulation cascade full-bridge NPC inverter

The invention discloses a parallel open-circuit fault diagnosis method suitable for a carrier phase-shifting modulation cascade full-bridge NPC inverter, and relates to the field of flexible direct-current power transmission of a power system. According to the invention, rapid detection and accurate positioning of a fault device are realized by using a corresponding relation of different abnormal changes generated by voltage deviation of two capacitors in a sub-module after open-circuit faults of different IGBTs. The parallel open-circuit fault diagnosis method disclosed by the invention has the advantages that a plurality of open-circuit fault devices in different sub-modules of the carrier phase-shifting modulation cascade full-bridge NPC inverter are independently diagnosed, the complexity and the diagnosis time are kept unchanged along with the increase of the number of the sub-modules, and compared with a serial method, the calculated amount is small, and the diagnosis time is short; fault diagnosis and