Indirect Power Decoupling Control Strategy for Submodules of a Modified MMC Topology to Reduce Capacitor Voltage Ripple

Recently, a full-bridge submodule (FB-SM) with an active power decoupling (APD) circuit (called APD-SM) was introduced to suppress the voltage ripple of modular multilevel converter (MMC) SM capacitor while also possessing fault handling capabilities. However, it is accompanied by two inherent flaws: the APD circuit inductor is not involved in system operation and the transient performance of ripple suppression controller cannot be guaranteed. In this paper, the APD circuit inductor is further reused by the arm of MMC and an indirect power decoupling control (IPDC) strategy for the APD-SM is proposed. By controlling the ripple power of the APD-SM port and the APD-SM capacitor, the control of the ripple power transferred by the APD circuit is indirectly achieved, thereby suppressing the SM capacitor voltage ripple. The topology and operating mode of the novel APD-SM are analyzed in detail, and the design process of the IPDC strategy is also introduced step by step. Finally, simulation and prototype experimental platforms are designed to verify the steady-state and transient performance of the proposed IPDC strategy.