A modified submodule of modular multilevel converter using active power decoupling method for reducing capacitor voltage ripple under low‐frequency operation

In this paper, a modified submodule (MSM) method is proposed to reduce capacitor voltage fluctuation by integrating bidirectional buck-boost type active power decoupling (APD) circuit into each SM for the low-frequency operation of converter system. The MSM-MMC can be significantly reduced compared conventional SMs with same capacitance transferring ripple components auxiliary energy storage capacitor, resulting in lower main SM, which requires total capacitance. Additionally, closed-loop controller control APD voltages inheriting advantages repetitive and proportional-integral (PI) enhance performance suppression. improve start-up medium drives without injecting high-frequency components, avoid common-mode imposed on AC side operating principle, control, suppression are analyzed detail. feasibility has been confirmed simulation results based case studies using MATLAB/SIMULINK software further verified hardware-in-the-loop (HILS) real-time simulator OPAL-RT platform.