Method for starting flexible high-voltage direct-current (HVDC) system of modularized multi-level converter

Abstract

The invention provides a method for starting a flexible HVDC (high-voltage direct-current) system of a modularized multi-level converter, which is utilized to control a switch, a breaker, a converter and the like, so that the submodule voltage and DC voltage are ensured to reach rated values; and control strategies are formulated properly to restrain impulse currents generated in a charging process. By using the method, a charging control method is simplified, a modulation algorithm is optimized, the problem that a far-end converter submodule is short of capacitor voltages when an alternating-current system at one end charges two stations is solved, and the problem of the charging of a DC line is solved as well.

Description

Technical field: [0001] The invention relates to the technical field of flexible direct current transmission in power systems, in particular to a starting method for a modular multilevel converter flexible direct current transmission system. Background technique: [0002] The Modular Multilevel Converter (MMC) used for flexible direct current transmission adopts a new type of multilevel topology that is currently popular in the world. Its core unit - sub-module (Sub Module, SM), such as figure 1 As shown, it is a half-bridge structure composed of two self-turn-off power electronic switching devices with anti-parallel diodes and a capacitor. The basic topology of the novel multilevel topology is as figure 2 As shown, similar to the H-bridge cascaded multi-level structure, it consists of three phase units (Phase Module or Phase Unite, figure 2 1) in the composition, each phase unit includes a vertically symmetrical converter leg (ConverterLeg), and each converter leg is c...

AI Technical Summary

Problems solved by technology

[0006] The common disadvantages of the above two sub-module methods are: first, during the charging process of each bridge arm / phase of the converter, only a single sub-module is put into charging. Under the same current limiting resistance, the charging time of the converter Second, whether it is other excitation charging of the DC voltage source or self-excitation charging of the AC system, a control program specially designed for converter charging is required, which increases the complexity of the controller design; third, From the perspective of the start-up of the flexible DC transmission system, the above technologies only focus on the charging method of the converter, and the charging process of the DC line and other equipment in the system has not been involved.

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