Four-Level MMC Cell Type with DC Fault Blocking Capability for HVDC

Inhalt:
The Modular Multilevel Converter (MMC) is a well-suited converter topology for high-voltage direct current (HVDC) transmission. This converter is assembled with a large amount of in series connected cells, such as the half bridge, full bridge or clamp double cell type. In this paper, a four-level MMC cell type with a DC fault blocking capability is presented and its functional principle is described. Furthermore, a detailed analysis on different cell types is performed. The semiconductor losses are calculated in combination with an evaluation of the junction temperature by means of a proven thermal model. Thus, the maximum thermal admissible current and consequently the power transmission capability of each cell type is derived. Finally, a comparison of the different cell types with regard to the utilization of the installed switching power, the efficiency and power transmission capability is presented.