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A single-stage isolated ac–ac converter without the commutation problem is proposed. The proposed converter has the step-up/down function dependence on the phase shift control which provides zero-voltage switching zero-voltage switching (ZVS) for all switches in rated condition. Also, the commutation paths of the secondary side switches are provided for any switching case by adding a single capacitor; originally, a filter capacitor is used for the switching mode power supply input, and in this case, this filter capacitor also solves the primary-side commutation problem. The ZVS and solving the commutation problem increase the power efficiency and reliability. The proposed converter achieves high power quality with a simple control algorithm. A 1 kW/ 220 Vrms prototype is implemented to verify the theoretical analysis and performance of the proposed converter. The California energy commission efficiency is 97.3%, the total harmonic distortion (THD) of the input current is 2.45% at full load, and the THD of the output voltage is 1.07% at full load. [ABSTRACT FROM AUTHOR]