Soft switching full-bridge phase-shifted DC-DC converter

1. A DC-DC converter ( 1 ), comprising

a first input connection (E 1 );

a second input connection (E 2 );

a first switching element (S 1 ) which is arranged between the first input connection (E 1 ) and a first node point (K 1 );

a second switching element (S 2 ) which is arranged between the first input connection (E 1 ) and a second node point (K 2 );

a third switching element (S 3 ) which is arranged between the first node point (K 1 ) and the second input connection (E 2 );

a fourth switching element (S 4 ) which is arranged between the second node point (K 2 ) and the second input connection (E 2 ),

freewheeling diodes (D 1 -D 4 ) arranged in parallel to each of the switching elements (S 1 -S 4 );

a transformer (T) with a primary side and a secondary side, wherein a first connection of the primary side is electrically coupled to the first node point (K 1 ) and a second connection of the primary side is electrically coupled to the second node point (K 2 );

a first inductance (L 1 ) positioned between a first connection of the secondary side of the transformer (T) and a third node point (K 3 );

a rectifier circuit ( 10 ) configured to rectify an electrical voltage which is applied between the third node point (K 3 ) and a second connection of the secondary side of the transformer and to provide a rectified voltage between a first output connection (A 1 ) and a second output connection (A 2 );

a current sensor configured to detect an electric current through the first switching element (S 1 ) and also through the second switching element (S 2 ); and

a control device ( 20 ) configured

to initially, at a first time, close the first switching element (S 1 ) and the fourth switching element (S 4 ) together while the second switching element (S 2 ) and the third switching element (S 3 ) are open;

to, at a second time subsequent to the first time, open the fourth switching element (S 4 ) after a predetermined first time period (t 1 ) while keeping the first switching element (S 1 ) closed and the second switching element (S 2 ) and the third switching element (S 3 ) open;

to, at a third time subsequent to the second time, open the first switching element (S 1 ) once an electric current through the first switching element (S 1 ) or an electric current through the secondary side of the transformer (T) falls below a prespecified threshold value while keeping the second switching element (S 2 ), the third switching element (S 3 ), and the fourth switching element (S 4 ) open;

to subsequently close the second switching element (S 2 ) and the third switching element (S 3 ) after a predetermined second time period (t 2 ) while keeping the first switching element (S 1 ) and the fourth switching element (S 4 ) open;

to subsequently open the third switching element (S 3 ) after the predetermined first time period (t 1 ) while keeping the second switching element (S 2 ) closed and the first switching element (S 1 ) and the fourth switching element (S 4 ) open;

to then open the second switching element (S 2 ) once an electric current through the second switching element (S 2 ) or an electric current through the secondary side of the transformer (T) falls below the prespecified threshold value while keeping the first switching element (S 1 ), the third switching element (S 3 ), and the fourth switching element (S 4 ) open.

2. The DC-DC converter ( 1 ) as claimed in claim 1 , wherein an input voltage (Uin) between the first input connection (E 1 ) and the second input connection (E 2 ) is smaller than a product of a transformation ratio between the primary side and the secondary side of the transformer (T) and a setpoint output voltage (Uout) which is to be output between the first output connection (A 1 ) and the second output connection (A 2 ).

3. The DC-DC converter ( 1 ) as claimed in claim 2 , wherein the predetermined first time period (t 1 ) is adjusted depending on the input voltage (Uin) and the setpoint output voltage (Uout).

4. The DC-DC converter ( 1 ) as claimed in claim 2 , wherein the predetermined first time period (t 1 ) is adjusted depending on the input voltage (Uin).

5. The DC-DC converter ( 1 ) as claimed in claim 2 , wherein the predetermined first time period (t 1 ) is adjusted depending on the setpoint output voltage (Uout).

6. The DC-DC converter ( 1 ) as claimed in claim 1 , wherein the rectifier circuit ( 10 ) comprises an active synchronous rectifier circuit.

7. The DC-DC converter ( 1 ) as claimed in claim 6 , wherein the control device ( 20 ) is further configured to control additional switching elements (S 5 -S 8 ) of the rectifier circuit depending on the switching states of the first switching element (S 1 ) and of the second switching element (S 2 ).

8. A method ( 100 ) for controlling a DC-DC converter ( 1 ), comprising a first input connection (E 1 ), a second input connection (E 2 ), a first switching element (S 1 ) which is arranged between the first input connection (E 1 ) and a first node point (K 1 ), a second switching element (S 2 ) which is arranged between the first input connection (E 1 ) and a second node point (K 2 ), a third switching element (S 3 ) which is arranged between the first node point (K 1 ) and the second input connection (E 2 ), a fourth switching element (S 4 ) which is arranged between the second node point (K 2 ) and the second input connection (E 2 ), wherein a freewheeling diode (D 1 -D 4 ) is arranged in parallel in relation to each of the switching elements (S 1 -S 4 ), a transformer (T) with a primary side and a secondary side, wherein a first connection of the primary side is electrically coupled to the first node point (K 1 ) and a second connection of the primary side is electrically coupled to the second node point (K 2 ), a first inductance (L 1 ) which is arranged between a first connection of the secondary side of the transformer (T) and a third node point (K 3 ), a rectifier circuit ( 10 ) which is designed to rectify an electrical voltage between the third node point (K 3 ) and a second connection of the secondary side of the transformer (T), and to provide a rectified voltage between a first output connection (A 1 ) and a second output connection (A 2 ), a current sensor configured to detect an electric current through the first switching element (S 1 ) and also through the second switching element (S 2 ); wherein the method comprises:

initially, at a first time, closing ( 120 ) the first switching element (S 1 ) and the fourth switching element (S 4 ) together while keeping the second switching element (S 2 ) and the third switching element (S 3 ) open;

opening ( 130 ), at a second time subsequent to the first time, the fourth switching element (S 4 ) once the fourth switching element (S 4 ) has been closed for a predetermined first time period (t 1 ) while keeping the second switching element (S 2 ) and the third switching element (S 3 ) open and the first switching element (S 1 ) closed;

monitoring ( 140 ) an electric current through the first switching element (S 1 ) or an electric current through the secondary side of the transformer (T);

opening ( 150 ), at a third time subsequent to the second time, the first switching element (S 1 ) once the monitored electric current through the first switching element (S 1 ) or through the secondary side of the transformer (T) is smaller than a prespecified threshold value while keeping the fourth switching element (S 4 ), the second switching element (S 2 ), and the third switching element (S 3 ) open;

closing ( 160 ) the second switching element (S 2 ) and the third switching element (S 3 ) once the first switching element (S 1 ) has been open for a predetermined second time period (t 2 ) while keeping the first switching element (S 1 ) and the fourth switching element (S 4 ) open;

opening ( 170 ) the third switching element (S 3 ) once the third switching element (S 3 ) has been closed for the predetermined first time period (t 1 ) while keeping the second switching element (S 2 ) closed and the first switching element (S 1 ) and the fourth switching element (S 4 ) open;

monitoring ( 180 ) an electric current through the second switching element (S 2 ) or an electric current through the secondary side of the transformer (T); and

opening ( 190 ) the second switching element (S 2 ) once the monitored electric current through the second switching element (S 2 ) or through the secondary side of the transformer (T) is smaller than the prespecified threshold value while keeping the first switching element (S 1 ), the third switching element (S 3 ), and the fourth switching element (S 4 ) open.

9. The method ( 100 ) as claimed in claim 8 , wherein the second time period (t 2 ) is adjusted depending on a dead time of the first switching element (S 1 ) and a dead time of the second switching element (S 2 ).

10. The method ( 100 ) as claimed in claim 8 , wherein the second time period (t 2 ) is adjusted depending on a dead time of the first switching element (S 1 ).

11. The method ( 100 ) as claimed in claim 8 , wherein the second time period (t 2 ) is adjusted depending on a dead time of the second switching element (S 2 ).