MMC Modeling and Internal Electromagnetic Interference Mechanism Analysis

During the operation of the Modular Multilevel Converter (MMC) system, when encountering extreme working conditions, a large number of sub-modules may be switched on and off at the same time. At this time, the electromagnetic environment is very harsh. This paper develops a common-mode (CM) electromagnetic interference (EMI) noise model for MMC system. Through modeling, we found that when the sub-modules in different positions are switched on and off, the voltage to ground is different, so the dv/dt is also different. The dv/dt of the sub-module close to the DC side is small, and the common-mode current generated should also be small. The sub-module close to the AC side has a large dv/dt and the common-mode current generated should also be large. Experimental results verify our conjecture. However, we found that the voltage jump of the sub-modules will produce a great voltage spike, and the voltage spikes are mainly caused by the cable parameters of the DC bus. At the same time, based on the EMI model, the mechanism of the common-mode current is explored, and the effect of CM noise paths on CM noise is discussed.