Aiming at the problems of modulation nonlinearity and large backflow power in single-stage isolated alternating current-direct current（AC-DC） converters

this paper proposes a minimum backflow power modulation strategy based on virtual frequency. A time-domain analysis is conducted on the extended phase shift (EPS) modulation strategy for dual active bridge (DAB) converters. The power transmission characteristics are obtained. On this basis

the nonlinearity problem of the converter and the influence of backflow power are analyzed. To solve the aforementioned problems

the concept of virtual frequency is introduced. A linearized modulation and minimum backflow power optimization strategy based on virtual frequency is put forward. This modulation strategy can not only reduce the modulation complexity of the converter

but also effectively decrease the backflow power of converters. Meanwhile

it ensures that the switches achieve zero current switching (ZCS) turn-off or zero voltage switching (ZVS) turn-on over the entire range. Finally

the effectiveness of the proposed modulation strategy is verified through simulations and experiments.