Multi-mode control for a DC-to-DC converter

1. An apparatus comprising:

a voltage regulation module that controls output voltage of a direct current (“DC”) to DC converter to an output voltage reference over an output current range between an operating condition where output power of the converter reaches a positive power reference and output power of the converter reaches a negative power reference, the converter comprising a bidirectional converter;

a positive power regulation module that controls output power of the converter to the positive power reference over a positive constant power range between the output voltage of the converter being at the output voltage reference and output current of the converter being at a positive output current reference;

a negative power regulation module that controls output power of the converter to the negative power reference over a constant power range between output voltage of the converter being at the output voltage reference and a maximum negative power limit of the converter; and

a constant current module that limits output current to a positive output current reference in a range between a minimum output voltage and output power of the converter reaching the positive power reference.

2. The apparatus of claim 1 , wherein the constant current module comprises a current feedback control loop that limits output current to below the positive output current reference.

3. The apparatus of claim 2 , wherein the positive power regulation module, the negative power regulation module, and the voltage regulation module comprise feedback control loops and wherein the current feedback control loop comprises an inner feedback control loop and the feedback control loops of the positive power regulation module, the negative power regulation module, and the voltage regulation module comprise an outer feedback loop.

4. The apparatus of claim 2 , wherein the constant current feedback loop further comprises compensation implemented using a gain scheduled feedback controller, the gain scheduled feedback controller comprising one or more output control signals that vary over a plurality of control regions, the gain scheduled feedback controller implementing a different compensation equation for each control region.

5. The apparatus of claim 4 , wherein the converter comprises one or more phase shift modulators controlled by the one or more output control signals, wherein the one or more output control signals control according to a minimum current trajectory (“MCT”) control technique, the MCT substantially minimizing circulating current within the converter.

6. The apparatus of claim 4 , wherein the gain scheduled feedback controller maintains the converter in a zero-voltage switching (“ZVS”) region while minimizing circulating current by following a trajectory a fixed distance from an MCT.

7. The apparatus of claim 1 , wherein the constant current module further limits the output current to a negative output current reference in a range between a minimum output voltage and output power of the converter reaching the negative power reference.

8. The apparatus of claim 1 , wherein the output voltage reference varies with output current such that the output voltage reference decreases as output current increases.

9. The apparatus of claim 8 , wherein the output voltage reference varies based on the equation:

V Set ( I O )= V Set (0)− I OUT R V

where:

V Set (I O ) is the output voltage reference as a function of output current

V Set (0) is the output voltage reference at zero output current;

R V is a resistance representing a slope of the output voltage reference; and

I OUT is output current of the converter.

10. The apparatus of claim 1 , wherein the positive output current reference varies with output voltage such that the positive output current reference decreases as output voltage increases.

11. The apparatus of claim 10 , wherein the positive output current reference varies based on the equation:

I

Set

⁡

(

V

OUT

)

=

I

Set

⁡

(

0

)

-

V

OUT

R

I

where:

I Set (V OUT ) is the positive output current reference as a function of output voltage;

I Set (0) is the positive output current reference at zero output voltage;

V OUT is the output voltage; and

R I is a resistance representing a slope of the positive output current reference.

12. The apparatus of claim 1 , wherein the converter comprises a resonant power converter.

13. The apparatus of claim 12 , wherein the resonant power converter comprises at least one stage of a dual active bridge series resonant converter (“DABSRC”).

14. A system comprising:

a direct current (“DC”) to DC converter, the converter comprising a bidirectional converter;

one or more phase shift modulators controlling one or more phase angles within the converter;

a voltage regulation module that controls output voltage of the converter to an output voltage reference over an output current range between an operating condition where output power of the converter reaches a positive power reference and output power of the converter reaches a negative power reference;

a positive power regulation module that controls output power of the converter to the positive power reference over a positive constant power range between the output voltage of the converter being at the output voltage reference and output current of the converter being at a positive output current reference;

a negative power regulation module that controls output power of the converter to the negative power reference over a constant power range between output voltage of the converter being at the output voltage reference and a maximum negative power limit of the converter; and

a constant current module that limits output current to a positive output current reference in a range between a minimum output voltage and output power of the converter reaching the positive power reference.

15. The system of claim 14 , wherein the constant current module comprises a current feedback control loop that limits output current to below the positive output current reference.

16. The system of claim 15 , wherein the constant current feedback loop further comprises compensation implemented using a gain scheduled feedback controller, the gain scheduled feedback controller comprising one or more output control signals that vary over a plurality of control regions, the gain scheduled feedback controller implementing a different compensation equation for each control region.

17. The system of claim 16 , wherein the one or more output control signals control according to a minimum current trajectory (“MCT”) control technique, the MCT substantially minimizing circulating current within the converter, wherein the gain scheduled feedback controller maintains the converter in a zero-voltage switching (“ZVS”) region while minimizing circulating current by following a trajectory a fixed distance from an MCT.

18. A method comprising:

controlling output voltage of a direct current (“DC”) to DC converter to an output voltage reference over an output current range between an operating condition where output power of the converter reaches a positive power reference and output power of the converter reaches a negative power reference, the converter comprising a bidirectional converter;

controlling output power of the converter to the positive power reference over a positive constant power range between the output voltage of the converter being at the output voltage reference and output current of the converter being at a positive output current reference;

controlling output power of the converter to the negative power reference over a constant power range between output voltage of the converter being at the output voltage reference and a maximum negative power limit of the converter; and

limiting output current to a positive output current reference in a range between a minimum output voltage and output power of the converter reaching the positive power reference.

19. The method of claim 18 , wherein limiting output current to a positive output current reference comprises using a current feedback control loop that limits output current to below the positive output current reference.

20. The method of claim 18 , wherein controlling output voltage of the converter to an output voltage reference, controlling output power of the converter to the positive power reference, and controlling output power of the converter to the negative power reference comprise using one or more outer feedback control loops to the current feedback control loop, which comprises an inner feedback control loop.

21. The method of claim 18 , wherein limiting output current to a positive output current reference comprises generating one or more output control signals that vary over a plurality of control regions, wherein each control region comprises a different compensation equation.

22. The method of claim 18 , further comprising varying the output voltage reference with output current such that the output voltage reference decreases as output current increases, wherein the output voltage reference varies based on the equation:

V Set ( I O )= V Set (0)− I OUT R V

where:

V Set (I O ) is the output voltage reference as a function of output current

V Set (0) is the output voltage reference at zero output current;

R V is a resistance representing a slope of the output voltage reference; and

I OUT is output current of the converter.

23. The method of claim 18 , further comprising varying the positive output current reference with output voltage such that the positive output current reference decreases as output voltage increases, wherein the positive output current reference varies based on the equation:

I

Set

⁡

(

V

OUT

)

=

I

Set

⁡

(

0

)

-

V

OUT

R

I

where:

I Set (V OUT ) is the positive output current reference as a function of output voltage;

I Set (0) is the positive output current reference at zero output voltage;

V OUT is the output voltage; and

R I is a resistance representing a slope of the positive output current reference.