Bidirectional dc-dc converter and control method thereof

Abstract

Disclosed is a small-size, high-efficiency, isolated, bidirectional DC-DC converter. The bidirectional DC-DC converter includes a transformer in which windings are magnetically coupled, switching circuits, a diode which is connected in parallel with a switch, smoothing capacitors, and a control section. First and second DC power supplies, which are connected in parallel with the smoothing capacitors, respectively, provide bidirectional electrical power transfer. When electrical power is to be transferred from the first DC power supply to the second DC power supply, the switch is maintained in the ON state. When, on the other hand, electrical power is to be transferred from the second DC power supply to the first DC power supply, the switch is maintained in the OFF state to prevent a reverse electrical power flow from the first DC power supply.

What is claimed is: 
     
         1 . A bidirectional DC-DC converter comprising:
 a first switching circuit to input electrical power from a first DC power supply, with which a first smoothing capacitor is connected in parallel, to an in-between terminal of DC terminals of the first switching circuit and to convert the electrical power to AC so as to supply the AC from an in-between terminal of AC terminals to a primary winding;   a second switching circuit to input electrical power from a second DC power supply, with which a second smoothing capacitor is connected in parallel, to an in-between terminal of DC terminals of the second switching circuit and to convert the electrical power to AC so as to supply the AC from an in-between terminal of AC terminals to a secondary winding;   a transformer which magnetically couples the primary winding to the secondary winding; and   control means for controlling the first and second switching circuits so as to transfer electrical power between the first and second DC power supplies,   wherein the first switching circuit includes:
 a first switching leg in which switching devices H 1  and H 2  are connected in series; and 
 a second switching leg in which switching devices H 3  and H 4  are connected in series and which is connected in parallel with the first switching leg, 
   wherein an in-between point of both ends of the first switching leg is the in-between terminal of the DC terminals while an interval between a point at which the switching devices H 1  and H 2  are connected in series and a point at which the switching devices H 3  and H 4  are connected in series is the in-between terminal of the AC terminals, and   wherein the control means is provided with a mode which keeps all the switching devices H 1  to H 4  in an ON state upon supplying electrical power from the second DC power supply to the first DC power supply.   
     
     
         2 . The bidirectional DC-DC converter according to  claim 1 ,
 wherein the second switching circuit is provided with a smoothing reactor to smooth electric current flowed into the second DC power supply, and   wherein energy of the second DC power supply accumulated in the smoothing reactor is discharged when the state of the switching devices provided with the second switching circuit is switched over to supply the electrical power of the second DC power supply to the secondary winding.