A Novel DC Fault Current Limiting Control of the Improved Hybrid Modular Multilevel Converter

In the event of a DC-side short circuit fault, the traditional modular multilevel converters (MMC) based on half-bridge submodule (HBSM) designs are unable to clear the fault, leading to system blocking. To deal with these challenges, this paper proposes an improved hybrid MMC (HMMC) to limit and clear the fault current without blocking the HBSMs when the DC pole-to-pole (P2P) fault happens. In the proposed typology, a number of full-bridge submodule (FBSM) cluster are added in the DC bus of the HBSM-based MMC. With the capability of FBSM to output negative voltage, the proposed HMMC system can ride through the DC P2P faults. This ensures that the system remains in normal operation during DC P2P fault. The FBSM cluster operates in two modes: steady-state operation mode and fault ride through mode. Finally, the proposed topology and control strategy's effectiveness and feasibility are verified through MATLAB/Simulink simulation.