A power conversion method of a power conversion apparatus including plural primary side ports disposed in a primary side circuit and a secondary side port disposed in a secondary side circuit magnetically coupled to the primary side circuit through a transformer, the method adjusting transmission power transmitted between the primary and secondary side circuits by changing a phase difference between switching of the primary and secondary side circuits, and changing a first duty ratio of the switching of the primary side circuit or a second duty ratio of the switching of the secondary side circuit, the method including: determining whether a value obtained by dividing the phase difference by 360° is greater than a third duty ratio; and setting the second duty ratio to be equal to or greater than the value obtained by dividing the phase difference by 360° when the value is greater than the third duty ratio.