Dual-transformer type of dc-to-dc converter

• US 20080084714A1
• Filed: 10/04/2007
• Published: 04/10/2008
• Est. Priority Date: 10/04/2006
• Status: Active Grant

• Current Assignee: DENSO Corporation, Nippon Soken, Inc. (DENSO Corporation)
• Original Assignee: DENSO Corporation, Nippon Soken, Inc. (DENSO Corporation)
• Inventors: Kawasaki, Koji, Yamashita, Tsuyoshi
• Granted Patent: US 7,746,670 B2
• Time in Patent Office: Days
• US Class Current: 363/21.01
• CPC Class Codes: H02M 3/33576 having at least one active switching element at the secondary side of an isolation transformer

Abstract

A first AC/DC converter circuit is coupled via two transformers to a second AC/DC converter circuit, the first AC/DC converter circuit having a symmetrical configuration of two switching elements performing complementary opened/closed switching, to alternately connect positive and negative terminals of a DC source to a junction between transformer primary windings. Each primary winding alternates between a condition of transferring electrical power to a secondary winding and a condition of serving as a choke coil which temporarily stores electromagnetic energy when a current flows through that primary winding and a primary winding of the other transformer.

Claims

1. A two-transformer type of DC-to-DC converter comprising

a first transformer having a first winding, a second winding and a third winding, and a second transformer having a fourth winding, a fifth winding and a sixth winding, with respective first ends of said first and fourth windings connected to form a first winding pair, respective first ends of said second and fifth windings connected to form a second winding pair, and respective second ends of said fourth and fifth windings connected together,

a first DC terminal and second DC terminal for connecting said DC-to-DC converter to a first external circuit, and a third DC terminal and fourth DC terminal for connecting said DC-to-DC converter to a second external circuit,

a first AC/DC conversion circuit connected between said first and second DC terminals and said first, second, fourth and fifth windings, for performing conversion between DC electrical power and AC electrical power,

a second AC/DC conversion circuit connected between said third and fourth DC terminals and said second and third windings, for performing conversion between DC electrical power and AC electrical power, and

a control circuit adapted to control said conversion operations of said first A/D converter and said second AC/DC conversion circuit;

wherein said first AC/DC conversion circuit comprises;

a first switching element controlled to periodically switch between closed and opened states for respectively connecting and disconnecting said first DC terminal to/from a junction of said second ends of the fourth and fifth windings,

a second switching element controlled to periodically switch between said opened and closed states for respectively connecting and disconnecting said second DC terminal to/from said junction,

a first capacitor connected between said first DC terminal and a second end of said second winding, and

a second capacitor connected between said second DC terminal and a second end of said first winding.

2. A DC-to-DC converter as claimed in claim 1, comprising a diode connected in parallel with said first switching element.

3. A DC-to-DC converter as claimed in claim 2, wherein said first switching element is a semiconductor device and said diode is a parasitic diode which is intrinsic to said semiconductor device.

4. A DC-to-DC converter as claimed in claim 1, comprising a diode connected in parallel with said second switching element.

5. A DC-to-DC converter as claimed in claim 4, wherein said second switching element is a semiconductor device and said diode is a parasitic diode which is intrinsic to said semiconductor device.

6. A DC-to-DC converter as claimed in claim 1, wherein a DC voltage appearing between said first DC terminal and second DC terminal is higher than a DC voltage appearing between said third DC terminal and fourth DC terminal.

7. A DC-to-DC converter as claimed in claim 1, wherein a DC voltage appearing between said first DC terminal and second DC terminal is lower than a DC voltage appearing between said third DC terminal and fourth DC terminal.

8. A DC-to-DC converter as claimed in claim 1, wherein

said first AC/DC conversion circuit is adapted to operate as a power inverter circuit for converting DC electrical power applied between said first DC terminal and second DC terminal to AC electrical power,

said AC electrical power is transferred to said second AC/DC conversion circuit via said first transformer and second transformer, and

said second AC/DC conversion circuit is adapted to operate as a rectifier circuit for converting said AC electrical power to DC electrical power, to be outputted from said third DC terminal and fourth DC terminal.

9. A DC-to-DC converter as claimed in claim 8, wherein said second AC/DC conversion circuit comprises a smoothing circuit for smoothing said outputted DC electrical power and wherein said smoothing circuit in its entirety comprises a single capacitor.

10. A DC-to-DC converter as claimed in claim 8, wherein said third switching element is controlled to enter said opened and closed states in synchronism with said first switching element and said fourth switching element is controlled to enter said opened and closed states in synchronism with said second switching element, for thereby implementing synchronous rectification operation by said second AC/DC conversion circuit.

11. A DC-to-DC converter as claimed in claim 1, wherein said second AC/DC converter is adapted to operate as a power inverter circuit for converting DC electrical power applied between said third DC terminal and fourth DC terminal to AC electrical power,

said AC electrical power is transferred to said first AC/DC conversion circuit via said first transformer and second transformer, and

said first AC/DC conversion circuit is adapted to operate as a rectifier circuit for converting said AC electrical power to DC electrical power, to be outputted from said first DC terminal and second DC terminal.

12. A DC-to-DC converter as claimed in claim 1, wherein said control circuit is adapted to alternately set said first switching element in said closed and opened states with a specific duty ratio, and wherein designating said predetermined duty ratio as D, said control circuit is adapted to alternately set said second switching element in said closed and opened states with a duty ratio (1-D).

13. A DC-to-DC converter as claimed in claim 12, wherein said control circuit is adapted to set said duty ratio D at a value within a range of duty ratios whereby an amount of ripple in at least one of an output DC current and an output DC voltage produced by said DC-to-DC converter is below a predetermined value.

14. A DC-to-DC converter as claimed in claim 12, wherein said control circuit is adapted to set said duty ratio D at a value no greater than 50%.

15. A DC-to-DC converter as claimed in claim 12, wherein said control circuit is adapted to set said duty ratio D at a value greater than 50%.

16. A DC-to-DC converter as claimed in claim 12, wherein said control circuit is adapted to be operable for varying said duty ratio D to correspondingly vary a level of electrical power that is transferred by said DC-to-DC converter between said first external circuit and said second external circuit.

17. A DC-to-DC converter as claimed in claim 1, wherein said control circuit is adapted to control said first switching element and said second switching element for complementary opened/closed switching operation, and to establish a dead-time interval of predetermined duration in which both of said first switching element and second switching element are in said opened state, following each interval in which one of said first and second switching elements is in said closed state.

18. A two-transformer type of DC-to-DC converter comprising a power conversion circuit for converting input DC electrical power from a DC power source into AC electrical power, a rectifier circuit, and a first transformer and a second transformer each comprising two primary windings respectively connected to said power conversion circuit and each comprising a secondary winding connected to said rectifier circuit, with said power conversion circuit comprising a first input supply terminal and a second input supply terminal connected between a positive potential and a negative potential of said DC power source;

wherein;

a first primary winding and second primary winding of said first transformer are connected together at respective first ends thereof, a second end of said first primary winding of the first transformer is connected to a first end of a first primary winding of said second transformer and a second end of said second primary winding of the first transformer is connected to a first end of a second primary winding of said second transformer, and said power conversion circuit comprises

a first capacitor connected between said first input supply terminal and a second end of said first primary winding of said second transformer, and a second capacitor connected between said second input supply terminal and a second end of said second primary winding of said second transformer,

a first switching element connected between said first input supply terminal and a common connection of said first ends of said primary windings of first transformer,

a second switching element connected between said second input supply terminal and said common connection, and

a control circuit adapted to control said first switching element and said second switching element for performing complementary opened/closed switching operation.

19. A DC-to-DC converter as claimed in claim 18, comprising a first diode connected in parallel with said first switching element, for conducting a reverse-direction flow of current when said first switching element becomes closed, and a second diode connected in parallel with said second switching element, for conducting a reverse-direction flow of current when said second switching element becomes closed.

20. A DC-to-DC converter as claimed in claim 19, wherein said first switching element and second switching element are respective semiconductor devices and wherein said first diode and second diode are respective parasitic diodes that are intrinsic to said semiconductor devices.

21. A DC-to-DC converter as claimed in claim 18, wherein said rectifier circuit comprises a third switching element and a fourth switching element respectively coupled to said secondary winding of said first transformer and said secondary winding of said second transformer, and wherein said control circuit is adapted to control said third switching element and fourth switching element to perform complementary opened/closed switching operations in synchronism with said complementary witching operations of said first switching element and second switching element, for effecting synchronous rectification of said AC electrical power.