Research on the Design of Main Circuit Parameters of CSC-MMC DC Transformer

The DC transformer is the core equipment to realize the DC collection and transmission of new energy sources, and the CSC-MMC DC transformer (CSC-MMC) is mixed with the controllable current source converter (CSC) and the modular multilevel converter (MMC), which can realize high controllable commutation, high power density design and high efficiency power transmission. The CSC two degrees of freedom fundamental frequency modulation (TDFFFM) has the advantages of low switching frequency, low transmission loss, and independent regulation of active and reactive power. In this paper, for the CSC-MMC based on TDFFFM, the main circuit parameter design method is proposed: the CSC smoothing reactor is designed with the DC current fluctuation rate as the constraint, the filter capacitor is constrained by the CSC modulation ratio; the MMC submodule capacitor is designed with the voltage fluctuation rate of capacitor, and the bridge arm inductance is designed from the transmission power and circulation avoidance. At the same time, the influence of AC frequency on loss is explored.