DC-Side Impedance Modeling of Modular Multilevel Converters Based on the Multi-Harmonic Linearization Method

In recent years, modular multilevel converters (MMC) have been widely used in remote and large-scale new energy grid connection due to their technical advantages, which have driven the rapid development of the new energy power generation industry. However, the broad frequency oscillation issue with MMC is currently gaining prominence and poses a severe danger to the power system's ability to operate safely and steadily. This paper employs the multi-harmonic linearization method to construct a small-signal impedance model for the DC side of the MMC. Firstly, a steady-state average model considering the multi-harmonic coupling characteristics of MMC is established, and its steady-state harmonic characteristics are analyzed. Next comes the establishment of the small signal frequency domain model for the control loop and main circuit, followed by the derivation of the dc-side impedance model. For the purpose of confirming that the impedance analysis model is accurate, a frequency sweep is performed in MATLAB/Simulink.