A Multi-scale Suppression Method for Capacitor Voltage Ripple of MMC Half-Bridge Sub-Module

Abstract

A multi-scale suppression method for capacitor voltage ripple of MMC half-bridge sub-module, firstly collecting three-phase voltage signal and current signal u on AC side sj , i sj , three-phase upper and lower bridge arm current signal i pj , i nj , the DC bus voltage signal u dc , calculate the instantaneous power P of the upper and lower arms pj , P nj The expression of , the sum of the instantaneous power of the upper and lower bridge arms is controlled to zero, and the circulating current injection value is obtained through the modulation function s of the upper and lower bridge arms pj and s nj Take the derivative and make it equal to 0, and get the time t corresponding to the peak value of the modulated wave max with m 3 , φ 3 The functional relationship between , supplemented by the maximum modulation ratio and the sum of the number of sub-modules put into the upper and lower bridge arms at time t as constraints, the optimal injected third harmonic is obtained. The coordination of the two injection methods can effectively improve the DC voltage utilization rate of the MMC, and ensure that the peak value of the modulation wave of the system will not increase due to the circulating current injection, so as to achieve better capacitor voltage fluctuation suppression effect.

Description

technical field [0001] The invention relates to the field of direct current transmission control, in particular to a multi-scale suppression method for capacitor voltage ripple of an MMC half-bridge sub-module. Background technique [0002] The flexible DC transmission technology based on MMC (Modular Multilevel Converter) has become an effective solution for large-capacity offshore wind power transmission due to its advantages of flexible controllability, good stability, convenient regional interconnection, modular structure characteristics, and low loss. . As the core equipment of flexible DC transmission technology, the capacity and voltage level of MMC converter valve continue to increase with the needs of the project, resulting in a great increase in the weight, area and cost of the MMC converter valve. The volume and weight of the capacitor in the MMC half-bridge sub-module account for 60% of the entire sub-module. Therefore, it is very feasible to reduce the capacit...

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