A Novel MMC Topology Integrated DC Fault Current Blocking and Energy Dissipation Equipment for Offshore Wind VSC-HVDC System

The offshore wind power system based on HVDC transmission technology demands exceptional reliability. To ensure system stability while minimizing the number of fault ride-through devices and simplifying system complexity, this study proposes a Sub-Module(SM) topology of MMC that combines DC-side fault current blocking and surplus energy dissipation function. The study analyzes DC-side bipolar short-circuit faults and AC-side voltage sag faults and further explores the operational mechanism of the proposed structure. Without altering the operation scheme, a simple control method is employed to change the switching states of the IGBTs within the SM, enabling the reverse activation of the SM capacitor and the switching of energy dissipation resistors. Under the same number of submodules and a DC side voltage of 6400 kV, the proposed DBSSM achieves a 5 ms reduction in DC fault current blocking time. Compared to other energy dissipation methods, this method eliminates the need for additional fault ride-through devices and avoids the construction costs of offshore platforms, significantly reducing the construction timeline. Furthermore, without adding extra hardware components, the DBSSM structure also facilitates the passive voltage balancing of SM capacitors, thereby alleviating the burden associated with sorting algorithms. Simulations of the proposed topology were conducted using MATLAB/Simulink, and hardware-in-the-loop tests were performed using the dSPACE1202 and FPGA, validating the feasibility of the proposed structure.