Abstract：In order to solve the problem of large peak-to-peak inductor currents in dual active bridge converters

with mismatched input and output voltages，a four-degree-of-freedom modulation（FDFM）strategy was proposed

by combining symmetric duty cycle modulation and asymmetric duty cycle modulation. By analyzing the operating

modes of the four-degree-of-freedom modulation strategy，the peak-to-peak inductor current and transmission

power models were established，and the optimal solution with different transmission powers was solved by using

the Karush-Kuhn-Tucker（KKT）condition with the peak-to-peak inductor current as the optimization objective.

And the experimental prototype was built to verify the effectiveness of the proposed strategy. The experimental

results show that the proposed modulation strategy can effectively reduce the peak-to-peak inductor current of the

converter and improve the efficiency of the dual active bridge converter.

      Key words：converter；dual active bridge（DAB）；four-degrees-of-freedom；peak-to-peak current