Modularized multi-level current converter asymmetric double sub-module midpoint electric potential equalization control method

Abstract

A modularized multi-level current converter asymmetric double sub-module midpoint electric potential equalization control method. In an MMC formed by asymmetric double sub-modules and half-bridge sub-modules, each phase is formed by an upper bridge arm and a lower bridge arm, and each of the upper bridge arm and the lower bridge arm is formed by connecting i half-bridge sub-modules and N-i asymmetric double sub-modules in series; each half-bridge sub-module comprises two IGBTs, two diodes and one capacitor; each asymmetric double sub-module comprises four IGBTs, four diodes and two capacitors; when a fault occurs on a direct current side of MMC, all IGBTs are locked, capacitor voltage is used for forcing switched-on diodes to cut off and block a fault current in a reverse direction, asymmetric double sub-module midpoint electric potential equalization control is adopted, asymmetric double sub-module midpoint electric potential equalization of MMC comprising the asymmetric double sub-modules and the half-bridge sub-module is maintained, and operational reliability and security of MMC based on the asymmetric double sub-modules and the half-bridge sub-modules can be improved.

Description

technical field [0001] The present invention relates to the technical field of power electronics, in particular to a method for controlling midpoint potential equalization of asymmetric twin sub-modules of a modular multi-lever converter (hereinafter referred to as MMC). Background technique [0002] Due to the lack of high-voltage DC circuit breaker technology, short-circuit faults on the DC side are an important problem faced by flexible HVDC transmission, which seriously affects the development of flexible HVDC transmission technology. In the flexible HVDC transmission system using modular multi-level converter technology, in the case of a short-circuit fault on the DC side, the sub-module of the half-bridge MMC has the ability to continue current. The DC fault point is fed into the fault current to provide a path, and the three-phase virtual short occurs on the AC system side. There are currently three methods for dealing with DC side faults: [0003] (1) Use the AC si...

AI Technical Summary

Problems solved by technology

The asymmetric twin-submodule structure with DC fault self-blocking capability is favored because of its better economy, but the unbalanced midpoint potential of the asymmetric twin-submodule affects its safe operation

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