A Trigger Signals Modification Scheme for Common-Mode Conducted EMI Reduction of Modular Multilevel Converter

Modular multilevel converter (MMC), due to its features of modularization, high efficiency, and so on, has gradually become the mainstream multilevel converter. However, it can induce large electromagnetic interference (EMI) because of the high-level <inline-formula> <tex-math notation="LaTeX">$dv/dt$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$di/dt$ </tex-math></inline-formula> during its commutation transient. Therefore, it is significant to analyze the characteristics of common-mode (CM) conducted EMI of MMC and propose a suppression scheme accordingly. In this article, considering the voltage to ground of submodule (SM) as a direct noise source, the relationship between CM current and equivalent noise source of one phase, as well as that between the equivalent noise source of one phase and switching action of each SM are deduced. Furthermore, a trigger signals modification (TSM) scheme is proposed, which can effectively suppress the CM conducted EMI on the dc side without obviously affecting the operating performance of MMC. In particular, this scheme manipulates the trigger signals already generated by the modulation and capacitor voltage balancing control, thus enabling good applicability. Finally, experimental results verify the validity of the analysis and the effectiveness of the proposed TSM scheme.