Voltage Balancing Methods for Inner and Outer Switches of Three-level Resonant DC-DC Converter for Solid State Transformers

摘要

In the solid state transformers application, the three-level series resonant converter (TL-SRC) based on neural point clamped (NPC) half bridge has become popular in recently. Compared with the full bridge (FB), NPC half bridge can help adopt the low voltage IGBTs with excellent switching characteristics to build high voltage power module (PM) and reduce the number of medium frequency transformers (MFT). However, when TL-SRC operates in backward, there existed voltage imbalanced in the NPC half bridge between inner and outer switches, which increased a risk of overvoltage of the switches in the NPC half bridge. Therefore, this paper proposed two voltage balancing methods for inner and outer switches, and the experimental results verified the validity of the proposed voltage balancing methods through a 150kW back-to-back prototype.