A Novel Hybrid Modular Multilevel Converter for DC Grid Operation with Integrated DC Fault Blocking

This paper presents a novel hybrid Modular Multilevel Converter for DC grid applications with DC fault blocking capabilities. The unique topology of the converter integrates Half-Bridge Submodules and Full-Bridge Submodules in addition to three additional switches to achieve efficient DC-DC conversion and balanced arm energy. The distinctive feature of the proposed design is the parallel connectivity of the arm capacitors, which ensures balanced capacitor voltages and energy transfer between the arms through two modes of operation. The proposed converter works successfully as a DC transformer which provides two-way power flow and effective DC fault blocking. Various simulation scenarios are investigated using MATLAB/SIMULINK to demonstrate the performance of the converter, including a DC Transformer operation for a converter with rated power 4MW at DC voltage ratio 10kV/4kV. The results validate the successful operation of the converter to sustain efficient DC-DC conversion, arm energy equalization, and robust fault protection. This offers a promising solution for enhancing the reliability and efficiency of DC grid systems.