Capacitor voltage balancing control strategy for MMC submodule in flexible DC converter station based on fractional-order supercapacitor

In response to the problems of repeated module switching and significant voltage fluctuations in the capacitor voltage balancing control strategy of MMC submodules in ultra-high voltage flexible DC converter stations, this paper focuses on the operation of fractional order super-capacitors, focusing on the transmission power and non-transmission power of the converter. A mathematical model of MMC submodule was established based on the study of capacitor voltage below and above the reference wave set voltage, and a dual closed-loop control strategy for capacitor voltage was proposed. The effectiveness and feasibility of this method in voltage balancing control of sub modules in ultra-high voltage flexible DC converter stations were verified by constructing a simulation model of sub module capacitor voltage balancing control using Simulink.