MMC capacitor voltage-sharing strategy with low switching frequency and complexity

Abstract

The invention provides an MMC capacitor voltage-sharing strategy with low switching frequency and complexity. The MMC capacitor voltage-sharing strategy comprises the steps of S1, rapidly monitoring acapacitor voltage value of each sub-module; S2, determining the number of input and removed sub-modules, and judging the charging and discharging conditions of the input sub-modules in the bridge arm; S3, continuing to use the sorting result of the last period, grouping the sub-modules in the input state and the cut-off state to perform insertion sorting correction for limiting the step number, the step number being determined by the maximum voltage difference, and the larger the difference value is, the larger the step number is; S4, according to the charging and discharging conditions, introducing a retention factor to the capacitor voltage of the corresponding sub-module; S5, merging the two sub-sequences in the input state and the cut-off state in two paths, and updating and recordinga sorting result; S6, generating the trigger pulse. According to the invention, dual optimization of the sorting algorithm operation speed and the device switching frequency is realized, and the problems of large sorting algorithm operation amount and high device switching frequency in the traditional sub-module capacitor voltage-sharing strategy are solved.

Description

technical field [0001] The patent of the present invention relates to an MMC capacitor voltage equalization strategy with relatively low switching frequency and complexity, which belongs to the field of electric power technology. Background technique [0002] Modular multilevel converter (MMC) is the core device of flexible direct current transmission technology, and the sub-module capacitor voltage equalization problem of MMC is one of the key issues for the stable operation of the transmission system. In the traditional sub-module capacitor voltage balancing strategy, the amount of computation of the sorting algorithm increases exponentially with the number of sub-modules. When the number of sub-modules is large, hardware design is difficult and costly. At the same time, when the modular multilevel converter (MMC) is applied to a flexible HVDC transmission system, it has the characteristics of a large number of power modules and a large bridge arm current, which leads to ...

AI Technical Summary

Problems solved by technology

When the number of sub-modules is large, hardware design is difficult and costly

At the same time, when the modular multilevel converter (MMC) is applied to the flexible HVDC transmission system, it has the characteristics of a large number of power modules and a large bridge arm current, which leads to high switching losses of the converter valve and difficulty in heat dissipation of the switching devices.

The switching of power modules with the traditional sorting voltage equalization algorithm is a random process, and the switching frequency is very high, which is difficult to meet the actual engineering needs

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