A Bidirectional Self-Blocking Novel MMC Bridge Arm and Current Limiting Control Coordination Strategy

To solve the problem of dc fault clearance in flexible dc grids while balancing critical factors such as fault clearance velocity, hardware-related expenses, and power losses, this article presents an innovative modular multilevel converter (MMC) bridge arm topology, referred to as the improved bridge arm MMC (IBA-MMC). Additionally, a tailored current-limiting control strategy is designed for severe dc fault scenarios. The IBA-MMC topology reduces the number of insulated gate bipolar transistors (IGBTs) by incorporating additional devices. It employs improved bridge submodules (IBSMs) for fault current interruption and device voltage withstand capabilities, along with supplementary diodes for fault current redirection and charging of submodule capacitors. In comparison to other schemes, the IBA-MMC demonstrates superior competitiveness in terms of capital investment and fault clearance efficacy. The proposed current-limiting control strategy is capable of self-adapting to variations in the arm current and reducing the dc voltage to suppress the fault current. This mechanism creates favorable conditions for the IBA-MMC to expeditiously clear dc faults. To assess the feasibility and effectiveness of the IBA-MMC topology and its current-limiting control, a comprehensive model was developed using MATLAB/Simulink. Subsequent experiments were conducted on the RT-LAB platform, encompassing scenarios of normal system operation, transient faults, and permanent faults.