The invention discloses a sub-module fault diagnosis method of a modular multilevel converter in the technical field of
power transmission and distribution. According to the technical scheme, the method includes: firstly, performing fault feature analysis aiming at typical faults of sub-modules; secondly, configuring an SFDU (sub-module fault diagnosis unit) in an SMC (sub-module controller), and combining provided sub-module fault diagnosis indexes by the aid of
capacitor voltage, bridge arm current and trigger signals at the moment so as to achieve diagnosis of faults of sub-module IGBT (insulated gate bipolar translator)
short circuit, IGBT open circuit, FWD (
freewheel diode)
short circuit,
capacitor failure and the like; and finally, adopting an exclusive method in a VBC (valve base controller) to achieve diagnosis of faults of sub-module FWD open circuit,
capacitor open
circuit failure, connection line open circuit and the like. The method has the advantages that diagnosis of sub-module faults is achieved on the base of
software, additional measuring points are not added to an original control
protection system, and the method is easy to implement, has quick and efficient sub-module fault diagnosis capability, and has coordination with other protection settings.