Method for controlling hybrid MMC sub-module to block and clear DC short circuit fault current

By controlling the submodule lockout method of the hybrid MMC, the bridge arm current and the improved submodule voltage are balanced, solving the problems of bridge arm overcurrent and overvoltage, and improving the safety and fault clearing efficiency of the converter.

CN117155097BActive Publication Date: 2026-07-24NANJING UNIV OF SCI & TECH
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Patent Information

Authority / Receiving Office
CN · China
Patent Type
Patents(China)
Current Assignee / Owner
NANJING UNIV OF SCI & TECH
Filing Date
2023-08-21
Publication Date
2026-07-24

AI Technical Summary

Technical Problem

In the process of blocking and clearing DC short-circuit fault current, the overcurrent problem of the bridge arm and the overvoltage problem of the improved submodule were not effectively solved by the hybrid MMC, which threatened the safety of the converter.

Method used

By measuring the AC three-phase voltage and DC voltage, the voltage required by each bridge arm from the improved submodule is calculated. This allows for partial submodule blocking, rather than complete blocking, balancing the bridge arm current and the improved submodule voltage, and avoiding reducing the minimum reverse voltage of the fault current path.

Benefits of technology

It effectively alleviates the problems of excessive bridge arm current and excessive voltage of improved submodules, balances current and voltage, and avoids the extended DC fault clearing time caused by reducing bridge arm voltage.

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Abstract

The application discloses a method for controlling hybrid MMC sub-modules to clear DC short-circuit fault current. The method detects the real-time size of AC voltage, calculates the bridge arm voltage according to the principle of limiting AC current change and not affecting the speed of DC fault current clearing, and determines the number of improved sub-modules (sub-modules capable of providing counter electromotive force, such as full-bridge sub-modules) in each bridge arm according to the bridge arm voltage. Compared with the conventional method of directly locking all sub-modules to clear DC fault current, the application reduces the bridge arm current during the DC fault current clearing process, alleviates the overvoltage of the improved sub-modules, limits the influence on the speed of DC fault clearing, and improves the safety of the hybrid modular multilevel converter during the process of clearing DC fault current.
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Citation Information

Patent Citations

  • Hybrid sub-module MMC converter with direct-current fault ride-through capability

    CN104320011A

  • Protection method for modular multilevel converter during bridge arm short circuit fault

    WO2015074620A1