Modeling and Power Transfer Characteristics of MMC-H based Solid State Transformer with Sine-Square Wave Modulation

Compared with traditional solid-state transformers (SSTs) with multiple dual-active bridge modules, the MMC-H based SST only requires one transformer and has high control flexibility and strong fault-tolerant capability. However, existing methods mainly adopt the square-square wave modulation technique in SSTs, rendering high dv/dt voltage stress and large harmonics. This paper takes advantage of the sine-square wave technique with MMCs to enhance the voltage and current performance. An accurate power transfer model for the MMC-H SST with the sine-square wave is proposed. The transferred power and current characteristics are revealed, and the maximum power transfer point is identified. Validated by the simulation results, the proposed model has high accuracy with an average error of less than 3%, and transfer current harmonics is reduced by 12% under heavy load.