A hybrid half-bridge submodule-based DC-DC modular multilevel converter with a single bidirectional high-voltage valve

Modular Multilevel Converters (MMCs) are promising candidates for high-voltage high-power applications. The main challenge of the MMCs is the zero-frequency operation. To achieve a successful DC-DC conversion process with balanced capacitors' voltages with limited voltage ripple, this paper suggests the employment of the conventional two-leg half-bridge submodule-based MMC structure in conjunction with a single bidirectional high-voltage (HV) valve across the low-voltage side. In the suggested structure, the HV valve is controlled on and off to ensure energy equalization for the MMC arms. In addition, soft-switching for the HV valve is proposed to reduce the switching losses. Detailed illustration and design of the proposed concept are presented. Simulation and experimentation results are elucidated to show the effectiveness of the proposed DC-DC hybrid MMC. The results showed efficient performance of the suggested converter. Here, the conventional two-legs half-bridge submodule-based MMC structure is employed in conjunction with a single bidirectional high-voltage (HV) valve to perform the DC-DC conversion successfully. In the suggested structure, the HV valve is controlled on and off to ensure energy equalization for the MMC arms. In addition, soft-switching for the HV valve is proposed to reduce the converter switching losses.image