Modular multilevel converter with ac fault protection capability and control method

CN116599371BActive Publication Date: 2026-07-14SOUTHEAST UNIV

Patent Information

Authority / Receiving Office: CN · China
Patent Type: Patents(China)
Current Assignee / Owner: SOUTHEAST UNIV
Filing Date: 2023-06-15
Publication Date: 2026-07-14

AI Technical Summary

Technical Problem

In a bipolar HVDC system, when there is a single-phase ground fault in the AC circuit, the AC current has no zero-crossing point, making it difficult for the AC circuit breaker to disconnect the fault current, damaging the converter and power electronic devices. At the same time, the full-bridge submodule increases power loss and cost.

Method used

A modular multilevel converter structure is adopted, which includes one unipolar full-bridge submodule and N-1 half-bridge submodules per phase. Combined with eight thyristor branches, the AC fault current is disconnected within 20 milliseconds through a control method to avoid submodule capacitor overvoltage and bridge arm overcurrent.

Benefits of technology

It enables rapid disconnection of AC fault current, avoids overvoltage of submodule capacitors and overcurrent of bridge arms, reduces converter losses and infrastructure costs, and maintains low losses during normal operation.

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Abstract

The application discloses a modular multilevel converter with AC fault protection capability and a control method, and relates to the technical field of multilevel power electronic converters.The application comprises three phases A, B and C, each phase comprising an upper bridge arm and a lower bridge arm, and each bridge arm comprising N sub-modules connected in series, characterized in that the N sub-modules in each bridge arm comprise one unipolar full-bridge sub-module and N-1 half-bridge sub-modules; the upper ends of the upper bridge arms of the three phases A, B and C are short-circuited and connected to the DC side of a power transmission line through a first isolating switch, and the lower ends of the lower bridge arms of the three phases A, B and C are short-circuited and grounded through a second isolating switch; and the modular multilevel converter further comprises eight thyristor branches.The application can achieve the same output characteristics as traditional modular multilevel converters, and when an AC single-phase ground fault occurs at the valve side, the application can quickly clear the fault, avoid capacitor overvoltage and bridge arm overcurrent, and realize AC fault protection.

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