Research on the Interaction Mechanism of DC Side Ripple Based on MMC Wide Frequency Domain Model

The DC voltage of the flexible DC transmission system is prone to the problem of excessive ripple during the transmission process, which leads to the instability of the system. The existing mathematical model of modular multilevel converter (MMC) is insufficient in the description of its internal harmonic dynamic characteristics, and cannot reflect the electrical coupling between the AC and DC sides of the MMC. Based on this, this paper proposes a wide frequency domain dynamic phasor model based on complex Fourier series, and studies the interaction mechanism between the frequency characteristics of MMC DC impedance and the switching frequency of its sub-module power devices. Finally, a single-ended flexible DC transmission simulation is built in Matlab/Simulink to verify the interaction mechanism between the DC impedance and the switching frequency of the sub-modules, which provides a reference for the DC voltage ripple problem in the actual flexible direct current transmission project.