LAUSR

A MOSFET-based series-resonant indirect-matrix-type power electronic transformer (PET) consists of line-frequency-switching folding–unfolding bridges and series-resonant dc–dc converters (SRCs), which is an attractive choice to achieve ac–ac conversion due to its high efficiency and high power density. However, the conduction losses, switching losses, and core losses in each of the high-frequency switching cycles Ts are different due to the pulsating dc voltage |ac|, which introduces difficulties in the calculation of losses. In addition, the small dc capacitors also participate in the resonance, and the resonant current shape deviates from a pure sine. Therefore, the conventional loss model is not suitable for PETs. In this paper, the time-domain analysis of SRC resonant current considering the dc capacitor is developed. Then, the analytical expression of the resonant current RMS value in grid cycle Tg is derived, which is more accurate in calculating conduction loss than the conventional model. In addition, it avoids the calculating losses in each Ts. Next, an analytical switching loss model is developed based on the curve fitting of the capacitance–voltage relationship. A simplified analytical core loss model is provided. Each part of the loss of the PET is verified by thermal simulations, and the total losses are verified by efficiency tests on an experiment prototype.