Impact of Transformer Leakage Inductance on the Soft-Switching Solid-State Transformer

Leakage inductance is inevitable in high frequency (HF) transformer design for solid-state transformer applications. Managing the energy trapped in leakage is very crucial for a safe and efficient operation of Solid-State Transformer (SST) converters. In the soft-switching solid-state transformer (S4T), leakage energy management is achieved in a passive way by having it absorbed in the two auxiliary resonant circuits, one on each side of the HF transformer. However, this could lead to an additional voltage/current stress on the resonant circuit and could impact various elements of the S4T design. This paper presents a detailed analysis of the resonant circuit operation and analytically derived relations between the leakage inductance and the peak voltage/current stress in the S4T converter. Simulation and experimental results verifying the analysis are presented. Using the derived relations, the design considerations for the S4T resonant circuit parameters are also discussed.