A converter apparatus includes: a first transformer with two windings; a first full-bridge circuit with four switches, DC input/output units connected to a first DC power supply, and AC input/output units connected via an inductor to one winding of the first transformer; a second full-bridge circuit with four switches, DC input/output units connected to a second DC power supply, and AC input/output units connected via an inductor to another winding of the first transformer; a second transformer with two windings, one being connected via an inductor to the AC input/output units of the first circuit; a third full-bridge circuit with four switches, DC input/output units connected to a third DC power supply, and AC input/output units connected via an inductor to another winding of the second transformer; and a control unit for controlling the switches to supply power between the first to third DC power supplies.