Capacitor Voltage Ripple Suppression Strategy of MMC Submodule based on High Harmonic Injection

As the energy storage component of the modular multilevel converter (MMC), the voltage fluctuation of the sub-module capacitor determines the selection of the switching device and its safe operating range. In order to suppress the capacitor voltage ripple in the control strategy, this paper analyses the voltage ripple characteristics of sub-module capacitor, and introduces zero sequence voltage as another degree of freedom to suppress the capacitor voltage ripple based on the relationship between capacitor energy current amplitude and phase current amplitude and frequency. Combined with the third harmonic theory, an improved voltage ripple suppression strategy of MMC sub-module capacitor with high frequency harmonic injection is proposed. Finally, a system simulation model is established based on the PLECS simulation platform, and a 200V experimental prototype is built for verification. The experimental results verify that the improved MMC sub-module capacitor voltage ripple suppression strategy has the ability to effectively suppress the capacitor voltage ripple.