Current resonant dc/dc converter

A three-phase current resonant DC/DC converter comprising:

• a transformer unit including a first transformer circuit, a second transformer circuit, and a third transformer circuit, each of the transformer circuits including a primary-side coil and a secondary-side coil;
• a primary-side switching circuit including a first leg, a second leg, and a third leg connected in parallel, each of the legs includes an upper arm and a lower arm connected in series, and each of the arms includes a switching element, a reverse connected diode, and a partial resonant capacitor connected in parallel;
• a primary-side resonant circuit includes a first resonant circuit connected to the first leg and the primary-side coil of the first transformer circuit, a second resonant circuit connected to the second leg and the primary-side coil of the second transformer circuit, and a third resonant circuit connected to the third leg and the primary-side coil of the third transformer circuit, each of the resonant circuits including a resonant coil and a resonant capacitor;
• a secondary-side switching circuit including a fourth leg, a fifth leg, and a sixth leg connected in parallel, each of the legs includes a switching element, a reverse connected diode, and a partial resonant capacitor connected in parallel;
• and
• a control unit that controls the primary-side switching circuit and the secondary-side switching circuit;
• and
• the three-phase current resonant DC/DC converter performing forward power transmission from the primary-side switching circuit to the secondary-side switching circuit, wherein the control unit performs, when a driving frequency of the primary-side switching circuit is higher than a first frequency, frequency modulation control of controlling the driving frequency according to an output of the secondary-side switching circuit, and performs, when the driving frequency is equal to or lower than the first frequency, boost control to generate a boost period in which the secondary-side switching circuit is brought into a short-circuit state, and the control unit, during the boost control, turns on one of the switching elements of the secondary-side switching circuit to generate the boost period within a period in which a resonant current flows through the first resonant circuit and the second resonant circuit, within a period in which a resonant current flows through the second resonant circuit and the third resonant circuit, and within a period in which a resonant current flows through the third resonant circuit and the first resonant circuit.