MMC sub-module with fault current blocking and self-voltage-sharing capabilities

Abstract

The invention provides an MMC sub-module with fault current blocking and self-voltage-sharing capabilities. The MMC sub-module comprises a half-bridge sub-module consisting of switching tubes T1 and T2, diodes D1 and D2 and a capacitor C1, and a sub-module consisting of switching tubes T3, T4 and T5, diodes D3 to D8 and a capacitor C2, wherein the capacitor C1 and the capacitor C2 are connected inparallel through a diode; a connection part between the switching tubes T1 and T2 is connected with one wire outlet end of the MMC sub-module; and the lower end of a two-way switch formed by the diodes D5 to D8 and the switching tube T5 is connected with the other wire outlet end of the MMC sub-module. According to the MMC sub-module, only 2.5 IGBTs are needed for outputting unit level; and compared with an existing sub-module topology with a fault current blocking capacity, the MMC sub-module has the advantage of being more cost-effective. According to the invention, the difficulty of capacitor voltage balance control is simplified by the sub-module; after a fault is locked, when a forward fault current flows through, the capacitors are connected into a fault loop in series; and when a reverse fault current flows through, the sub-module connects the capacitors to the fault loop in parallel, thereby facilitating rapid recovery of a system after a fault.

Description

technical field [0001] The invention belongs to the technical field of power electronics, and in particular relates to an MMC sub-module equipped with fault current blocking and self-balancing voltage. Background technique [0002] Modular multilevel converter (MMC) has become one of the preferred topologies in the field of flexible DC transmission and distribution due to its advantages of high transmission efficiency, low harmonic content, and modular design. However, the MMC based on the traditional half-bridge submodule (HBSM) cannot block the DC fault current, and the power device faces the risk of breakdown due to the large fault current flowing. If the wind farm is connected to the AC system through the MMC, it may be difficult for the wind farm to achieve fault ride-through due to the long restart time of the fault. Therefore, how to block the DC fault current and quickly restart after a fault has become an urgent problem to be solved for MMC. [0003] There are cur...

AI Technical Summary

Problems solved by technology

[0005] In order to solve the problem that it is difficult for HBSM-MMC to block the DC fault current and the restart time is long after the fault is cleared, the present invention proposes an MMC sub-module with fault current blocking and self-balancing capabilities, which can output two positive level, compared with the traditional sub-module that outputs a positive level, when the number of AC voltage output levels is the same, the number of sub-modules proposed in this paper is less, and the capacitor voltage after the fault is more balanced, which is conducive to quickly clearing the DC fault current and Quick restart of MMC after failure

Images