Isolated soft-switch single-stage AC-DC converter

1. An alternating current-to-direct current (AC-DC) converter comprising:

a transformer having a primary side and a secondary side;

a first bi-directional switch and a first inductor connected in series between a positive terminal of an AC source and a first terminal of the primary side of the transformer;

a second bi-directional switch and a second inductor connected between the positive terminal of the AC source and a second terminal of the primary side of the transformer and connected in parallel with the first bi-directional switch;

a first active switch connected between a first terminal of the secondary side of the transformer and a first terminal of a DC load;

a second active switch connected between the first terminal of the secondary side of the transformer and a second terminal of the DC load;

a third active switch connected between a second terminal of the secondary side of the transformer and the first terminal of the DC load; and

a fourth active switch connected between second terminal of the secondary side of the transformer and the second terminal of the DC load, and

wherein the third and fourth active switches are configured to alternatively turn on and off in a first predetermined sequence to regulate one of current and voltage on the primary side of the transformer,

wherein the first and second bi-directional switches are configured to alternatively turn on and off in a second predetermined sequence,

wherein when the third active switch is turned on, one of the first active switch and the second active switch is turned on, and one of the first bi-directional switch and second bi-directional switch is turned on, allowing a first current flow through one of the first inductor and second inductor, and

wherein when the fourth active switch is turned on, one of the first active switch and the second active switch is turned on, and one of the first bi-directional switch and second bi-directional switch is turned on, allowing a second current flow through one of the first inductor and second inductor.

2. The converter of claim 1 , wherein the first bi-directional switch and the second bi-directional switch are insulated-gate bipolar transistor (IGBT) switches.

3. The converter of claim 1 , wherein the first bi-directional switch and the second bi-directional switch are metal-oxide semiconductor field-effect transistors (MOSFETS).

4. The converter of claim 1 , wherein the first bi-directional switch and the second bi-directional switch are silicon-controlled rectifier switches (SCR).

5. The converter of claim 1 , wherein the transformer is a high frequency transformer.

6. The converter of claim 1 , wherein the transformer primary winding comprises one of a center-tapped winding or two separate windings.

7. The converter of claim 1 , further comprising a third bi-directional switch connected in series with the first bi-directional switch and the first inductor.

8. The converter of claim 1 , further comprising a fourth bi-directional switch connected in series with the second bi-directional switch and the second inductor.

9. The converter of claim 1 , wherein current is regulated on the primary side and voltage is regulated on the secondary side of the transformer.

10. The converter of claim 1 , wherein, when the first and second bi-directional switches of the primary side turn on, current flowing therethrough increases from zero, and when the first and second two bi-directional switches of the primary side turn off, the current has been decreased to zero.

11. A method of transmission in a bi-directional AC-DC converter having a bi-directional power stage that processes energy from an AC utility power grid to a passive DC load, the power stage including a first bi-directional switch and a second bi-directional switch on a primary side of a transformer, comprising the steps of:

providing a first active switch connected between a first terminal of a secondary side of the transformer and a first terminal of a DC load;

providing a second active switch connected between the first terminal of the secondary side of the transformer and a second terminal of the DC load;

providing a third active switch connected between a second terminal of the secondary side of the transformer and the first terminal of the DC load;

providing a fourth active switch connected between second terminal of the secondary side of the transformer and the second terminal of the DC load; and

controlling the third and fourth active switches to alternatively turn on and off in a first predetermined sequence to regulate one of current and voltage on the primary side of the transformer,

wherein the first and second bi-directional switches are configured to alternatively turn on and off in a second predetermined sequence,

wherein when the third active switch is turned on, one of the first active switch and the second active switch is turned on, and one of the first bi-directional switch and second bi-directional switch is turned on, allowing a first current flow through one of the first inductor and second inductor, and

wherein when the fourth active switch is turned on, one of the first active switch and the second active switch is turned on, and one of the first bi-directional switch and second bi-directional switch is turned on, allowing a second current flow through one of the first inductor and second inductor.

12. The method of claim 11 , wherein the power stage further includes:

a third bi-directional switch connected in series with the first bi-directional switch and a first inductor; and

a fourth bi-directional switch connected in series with the second bi-directional switch and a second inductor.

13. A bi-directional alternating current-to-direct current (AC-DC) converter comprising a bi-directional power stage that processes energy from an AC utility power grid to a passive DC load, the power stage comprising:

an input filter inductor and at least two bi-directional switches on a primary side of a transformer;

a first active switch connected between a first terminal of the secondary side of the transformer and a first terminal of a DC load;

a second active switch connected between the first terminal of the secondary side of the transformer and a second terminal of the DC load;

a third active switch connected between a second terminal of the secondary side of the transformer and the first terminal of the DC load; and

a fourth active switch connected between second terminal of the secondary side of the transformer and the second terminal of the DC load, and

wherein the third and fourth active switches are configured to alternatively turn on and off in a first predetermined sequence to regulate one of current and voltage on the primary side of the transformer,

wherein the first and second bi-directional switches are configured to alternatively turn on and off in a second predetermined sequence,

wherein when the third active switch is turned on, one of the first active switch and the second active switch is turned on, and one of the first bi-directional switch and second bi-directional switch is turned on, allowing a first current flow through one of the first inductor and second inductor, and

wherein when the fourth active switch is turned on, one of the first active switch and the second active switch is turned on, and one of the first bi-directional switch and second bi-directional switch is turned on, allowing a second current flow through one of the first inductor and second inductor.

14. The bi-directional AC-DC converter of claim 13 , wherein each of the at least two bi-directional switches comprise at least one of an insulated-gate bipolar transistor (IGBT), MOSFET, and SCR.

15. The bi-directional AC-DC converter of claim 13 , wherein the input filter inductor is configured to utilize the transformer leakage.

16. The bi-directional AC-DC converter of claim 13 , wherein each of the at least two bi-directional switches on the secondary side of the transformer comprise at least one of a metal-oxide-semiconductor field-effect transistor (MOSFET), IGBT, and SCR.

17. The bi-directional AC-DC converter of claim 13 , wherein, when the at least two bi-directional switches of the primary side turn on, current flowing therethrough increases from zero, and when the at least two bi-directional switches of the primary side turn off, the current has been decreased to zero.

18. The method of claim 11 , further comprising processing energy from a DC source to the AC utility grid.