Power conversion device and power conversion method

A power conversion method of a power conversion device including a plurality of primary side ports disposed in a primary side circuit and a plurality of secondary side ports disposed in a secondary side circuit magnetically coupled to the primary side circuit with a transformer, the power conversion device adjusting transmission power transmitted between the primary side circuit and the secondary side circuit by changing a phase difference between switching of the primary side circuit and switching of the secondary side circuit, the power conversion method comprising:

• setting the phase difference to a calculated value;
• determining whether power is transmitted from the secondary side circuit to the primary side circuit;
• calculating a transmission efficiency based on a primary side power calculated value of the primary side circuit and a secondary side power calculated value of the secondary side circuit;
• setting an adjustment value of the phase difference to a value that is obtained by dividing the transmission efficiency by a specified efficiency;
• determining whether the adjustment value is less than a specified value;
• and
• setting the phase difference to a value that is obtained by dividing the calculated value by the adjustment value when the adjustment value is less than the specified value.