Analysis and Evaluation of Modular Multilevel Converters for DC-DC Solid-State Transformer Based on Different Operating Conditions

In modular multilevel converter (MMC) based solid-state transformer (SST), the MMC dominates total volume and power loss. The loss and volume of MMC are influenced by various factors, such as operating frequencies, waveforms of ac-link voltage, numbers of submodules, as well as modulation methods. Their impacts on loss and volume of MMC have not been comprehensively analyzed and evaluated. To investigate and evaluate the loss and volume of MMC based on various operating conditions, the computational model is developed for MMC-SST according to its operational principles. The developed model considered the parameter design of MMC to determine the capacitance and arm inductance based on various operating conditions, which are essential parameters to solve state variables. Then, with the developed computational model, the methodology is developed to comprehensively evaluate the losses and volume of MMC-SST under various operating conditions, and to investigate the impacts of the above-mentioned factors. The proposed analysis and methodology serve as a guidance and basis for the future optimal design of MMC-SST by providing insights into its performance. The proposed model and analysis are verified by experimental results.