Derating operation method and device for modular multilevel converter

Abstract

The invention provides a derating operation method and device for a modular multilevel converter. The method comprises the steps that the number of submodules input by the upper bridge arm of the modular multilevel converter is acquired; and if the number of the submodules input by the upper bridge arm of the modular multilevel converter is less than N / 2 or greater than N / 2, whether the number ofthe submodules input by the upper bridge arm is in an increasing phase or a decreasing phase is judged, and corresponding bridge arm reactor switching control is carried out. Derating operation of themodular multi-level converter is realized, and the derating effect is remarkable. According to the invention, the process is simple and free of complicated operation; the requirement on the controller of the modular multilevel converter is low; the investment cost is low; only a few thyristors need to be added; compared with a CCSC, the method can reduce the fundamental frequency and double frequency components of the capacitor voltage waveform of the submodules to a greater extent; the capacitor voltage fluctuation of the submodules is reduced; and the method has certain significance for further reducing the weight of the submodules of the converter.

Description

Technical field [0001] The invention relates to the technical field of direct current transmission, in particular to a method and device for reducing the capacity of a modular multilevel converter. Background technique [0002] High voltage DC transmission technology based on voltage source converters, especially modular multilevel converters, is called flexible DC transmission in China. Due to many advantages, it has received more and more attention and is applied in high voltage and UHV DC Power transmission field. The many advantages of inverters are due to the low inertia of power electronic devices. The DC side voltage of the converter is supported by the capacitor voltage of the sub-modules that are input by controlling the corresponding power electronic devices. The volume of the converter station is determined by the number of sub-modules and the volume of each sub-module. The energy storage capacitor accounts for 80% of the sub-module volume. As the transmission volta...

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Problems solved by technology

[0003] In order to overcome the disadvantages of poor derating effect in the above-mentioned prior art, the present invention provides a derating operation method and device for a modular multi-level converter, which obtains the input voltage of the upper bridge arm of the modular multi-level converter. The number of modules, and then the number of sub-modules invested in the upper bridge arm of the modular multi-level converter is less than N / 2 and the number of sub-modules invested in the upper bridge arm of the modular multi-level converter is greater than N / 2. , it is judged that the number of sub-modules invested in the upper bridge arm is in the increasing stage or decreasing stage, and the switching control of the corresponding bridge arm reactor is carried out to realize the derating operation of the modular multilevel converter, and the derating effect is remarkable

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