A Modified Middle Point Clamped (MMPC) DC-DC Converter for All-DC Wind Generation Systems

In this paper a modified middle point clamped (MMPC) dc-dc converter is proposed for a high-voltage wind turbine (WT) conversion in an all-dc wind generation system. The proposed high-voltage WT system uses a two-port hybrid generator whose output is rectified using two cascaded passive rectifiers before connecting to a medium voltage dc (MVDC) collector grid via two cascaded MMPC converters. The MMPC converter topology offers two operational scenarios with different duty cycles that result in a 3-level unipolar dc output voltage, while the cascade connection of two MMPC converters results in a 5-level output voltage thereby meeting the rated voltage requirements of WTs using off-the-shelf semiconductor switches. A conceptual space modulation diagram (C-SMD) is developed that is used to synthesize a dc voltage in a space vector modulation (SVM) domain. Switching strategy and related mathematical models for the corresponding duty cycles are derived while the effectiveness of the proposed topology and proposed C-SMD are verified by the simulation results.