Active Power Decoupling Control Strategy for MMCs with Split-Capacitor Sub-modules

Although modular multilevel converters (MMCs) are more and more widely used, low frequency ripple voltage appears in sub-module (SM) capacitors due to the operating mode, and the fundamental frequency and double frequency are the main ones. Based on the split-capacitor sub-module (SC-SM) structure, an easy double closed loop active power decoupling control strategy is proposed in this paper. Firstly, the ripple power of MMC arm is deeply analyzed, and the operation principle of split-capacitor is introduced accordingly. Then, a mathematical model based on MMC split-capacitor is established in detail. Finally, the control strategy of voltage outer loop and current inner loop is proposed, and the AC and DC voltage decoupling is realized. The effectiveness and accuracy of the control scheme are verified by simulation experiments. The experiment results show that the voltage ripple of the split-capacitor sub-module is well suppressed in the steady state, and the voltage ripple is reduced to 3%.