Analysis of a New Single-Stage AC/AC Converter for Solid-State Transformer

This work provides the analysis and design of a new single-stage high-frequency isolated AC/AC converter based on the resonant LLC structure. The proposed topology uses a semi-active bridge on the secondary side to eliminate the reverse power flow (RPF) and the secondary circulating current while maintaining power flow controllability using secondary phase-shift control. A detailed gain analysis is presented showing the capability of the converter to operate in buck and boost operating modes while maintaining soft-switching operation over a wide range. The fundamental harmonic approximation (FHA) method is applied for performing the steady-state analysis. A thorough analysis of the operating intervals of the converter is presented and the soft-switching constraints are derived. The modulation strategy of the proposed converter is also discussed in detail. Analytical expressions are derived for the power transferred and the peak resonant current. An experimental prototype of 1 kW rated power is developed, and the results are presented to substantiate the analysis.