Modular multilevel converter system and voltage detection method and open-circuit fault diagnosis method thereof

A voltage detection method of a modular multilevel converter system, comprising:

• configuring N sub-modules sequentially cascaded, where N is an integer greater than or equal to 2, each of the sub-modules comprising at least one bridge arm and a capacitor connected in parallel to the bridge arm, the capacitor having a positive terminal and a negative terminal;
• and
• configuring a voltage detection unit for detecting a voltage between at least two adjacent sub-modules in the N sub-modules and connected in parallel between the positive terminal of the capacitor of the first sub-module and the negative terminal of the capacitor of the last sub-module in the at least two sub-modules.

An open-circuit fault diagnosis method of a modular multilevel converter system, wherein the modular multilevel converter system comprises a plurality of sub-modules sequentially cascaded, each of the sub-modules comprising at least one bridge arm and a capacitor connected in parallel to the bridge arm, the capacitor having a positive terminal and a negative terminal, and a voltage detection unit for detecting a voltage between a first sub-module and a second sub-module connected adjacent in the plurality of sub-modules, the voltage detection unit being connected in parallel between the positive terminal of the capacitor of the first sub-module and the negative terminal of the capacitor of the second sub-module in the two sub-modules, comprising:

• detecting the voltages between the two sub-modules in a switch-on state and a switch-off state by the voltage detection unit;
• determining the sub-module with an open-circuit fault in the two sub-modules according to the detected result.