This paper presents the operation principle and the properties of a single-phase DC-AC converter with medium frequency transformer and soft commutation. The influence of the non-dissipative snubber capacitor and the transformer parasitic components for ZVS and ZCS are explained in relation with their influence of the output characteristic. Additionally the effect of the semiconductor voltage drop is considered to get a precise circuit model for steady-state continuous operation. Finally efficiency improvements of this phase-shift PWM DC-AC converter are achieved by actively short-circuiting the circulating current at the AC-side during full load operation.