Starting method of full bridge and half bridge mixed type modular multilevel converter

Abstract

The invention discloses a starting method of a full bridge and half bridge mixed type modular multilevel converter. The converter is subjected to alternating current uncontrolled charging firstly; when the voltage of each sub module of the converter reaches a working threshold value of a power-taking loop, an IGBT of a full-bridge sub module is triggered to enable the external characteristic of the full-bridge sub module to be consistent to that of a half-bridge sub module, and the system performs secondary uncontrolled charging to all sub modules through a starting resistor; after the secondary uncontrolled charging is completed, the voltage balance of the full-bridge sub module and the half-bridge sub module is realized through valve-control voltage-sharing control; and finally, direct current voltage control is started to complete starting of the converter. By adoption of the starting method, the condition of inconsistent charging voltages among different sub modules caused by inconsistency of charging characteristics among different sub modules can be solved, current impact caused by direct unlocking of the parallel serial type modular multilevel after uncontrolled charging can be lowered, and starting failure and protection lockout caused by uneven capacitive voltages of different sub modules can be avoided.

Description

technical field [0001] The invention relates to the field of flexible direct current transmission, in particular to a method for starting a full-bridge and half-bridge hybrid modular multilevel converter. Background technique [0002] Modular multilevel converter (MMC) is a flexible DC power transmission topology that is developing rapidly in the world. At present, most of the modular multilevel structures used in engineering are half-bridge types. Relatively few, low loss, low cost and other advantages are widely used, but they cannot isolate DC faults, are not suitable for long-distance overhead lines, and reduce the operational reliability and scope of application of flexible DC transmission systems. [0003] The full-bridge sub-module has the ability to isolate DC faults, but it has more switching devices than the half-bridge sub-module, resulting in high loss and high cost, which increases the construction cost of the system and reduces the operating income of the syste...

AI Technical Summary

Problems solved by technology

[0007] In order to solve the deficiencies in the prior art, the present invention discloses a method for starting a full-bridge and half-bridge hybrid modular multilevel converter, which is used to solve the problem of full-bridge and half-bridge hybrid modular multilevel converters. The charging voltage of different sub-modules is inconsistent during the uncontrolled charging process of the AC side; ensure the voltage consistency of the sub-modules during the start-up process, and avoid start-up failure and protection lockout caused by uneven capacitor voltages of different sub-modules

Images