Voltage-sharing method and device for sub-module capacitors in MMC

Abstract

The invention relates to a voltage-sharing method and device for sub-module capacitors in an MMC. The method comprises the steps of obtaining an initial switching state vector of a bridge arm sub-module, reading a capacitor voltage initial value vector of the bridge arm sub-module in a control period, and according to the capacitor voltage initial value vector of the bridge arm sub-module through a control method based on a voltage dispersion threshold value, dividing the sub-module capacitor voltage sequence into a plurality of large groups, and classifying the capacitor voltage initial value vector elements of the bridge arm sub-modules in the large groups into the subordinate sub-intervals to form a plurality of buckets, according to the initial switching state vector, performing capacitor voltage sharing on the bridge arm sub-module by applying a bucket sorting algorithm to obtain a bridge arm sub-module switching state vector of the control period, and controlling the switching of the bridge arm sub-modules according to the switching state vectors of the bridge arm sub-modules in the control period. In the whole process, the algorithm time complexity and the sub-module switching frequency can be effectively reduced, and efficient and accurate MMC sub-module capacitor voltage sharing is achieved.

Description

technical field [0001] The present application relates to the technical field of smart grid, in particular to a method, device, computer equipment and storage medium for equalizing voltage of sub-module capacitors in MMC (Modular Multilevel Converter, modular multilevel converter). Background technique [0002] In the field of long-distance large-capacity power transmission, direct current transmission is more economical than alternating current transmission. Therefore, there are many high-voltage direct current transmission projects that have been put into operation or are under construction in my country. In addition, the development of power electronics technology has promoted the application of flexible DC transmission technology (high voltage direct current based on voltage source converter, VSC-HVDC), which overcomes the problems of commutation failure in conventional DC transmission. In addition, VSC-HVDC It also has the advantages of flexible control mode and indepen...

AI Technical Summary

Problems solved by technology

[0004] The traditional pressure equalization algorithm is based on the bubble sorting method, but the bubble sorting method is a sorting algorithm with high time complexity. For the MMC-HVDC with n+1 level value, its time complexity is as high as o(n²)

For long-distance and large-capacity MMC-HVDC, the number of sub-modules is often as high as hundreds or even thousands. Therefore, with the increase of the number of sub-modules, the bubble sorting algorithm will greatly increase the amount of calculation, thus putting forward strict requirements on the control host hardware.

In addition, IGBT (Insulated Gate Bipolar Transistor, insulated gate bipolar transistor) components have certain switching losses during the turn-on and turn-off processes

In MMC-HVDC engineering applications, the frequent switching of a large number of sub-modules makes the switching loss cannot be ignored, even greater than the on-state loss. At the same time, too high switching frequency will obviously reduce the service life of power semiconductor components. The traditional voltage equalization algorithm is improved to reduce the switching frequency of sub-modules to achieve more efficient and accurate voltage equalization

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