Constant current to constant voltage dual active bridge LCL-transformer resonant DC-DC converter

1. A power converter comprising:

a primary H-bridge comprising semi-conductor switches;

an LCL-Transformer section comprising a first inductor L r with a first end connected to a first terminal A of the primary H-bridge, a capacitor C r connected between a second end of the first inductor L r and a second terminal B of the primary H-bridge, and a second inductor L g with a first end connected to the second end of the first inductor L r ;

a transformer with a primary side connected between a second end of the second inductor L g and the second terminal B of the primary H-bridge;

a secondary H-bridge comprising semi-conductor switches with an input connected to a secondary side of the transformer; and

an output capacitor C f connected across output terminals of the secondary H-bridge,

wherein the primary H-bridge is fed by a direct current (DC) constant current source and the output terminals of the secondary H-bridge are connected to a load and an output voltage of the secondary H-bridge regulated to maintain a constant DC output voltage, and

wherein the semi-conductor switches of the primary H-bridge are arranged in a leg A and a leg B, the semi-conductor switches of the secondary H-bridge are arranged in a leg D and a leg E and wherein:

the semi-conductor switches of the primary H-bridge are operated with symmetrical phase shift modulation with leg A leading leg B by an angle φ Ab ;

the semi-conductor switches of the secondary H-bridge are operated with symmetrical phase shift modulation with leg D leading leg E by an angle φ DE ;

an angle between leg A and leg D is angle φ AD ; and

the output voltage of the secondary H-bridge is maintained at a constant voltage by controlling angle φ AB , angle φ DE , and angle φ AD .

2. The power converter of claim 1 , wherein a switching frequency of the semi-conductor switches of the primary H-bridge and the secondary H-bridge is selected to be within 15 percent of a resonant frequency of the LCL-Transformer section.

3. The power converter of claim 2 , wherein a ratio g of the first inductor L r and the second inductor L g is set to be within a range of 0.2 to 5.

4. The power converter of claim 1 , wherein a relationship between angle φ AB , angle φ DE , and angle φ AD is:

φ

A

⁢

D

=

φ

A

⁢

B

2

+

π

2

-

φ

D

⁢

E

2

.

5. The power converter of claim 4 , wherein angle φ DE is 180 degrees and a relationship between angle φ AB and angle φ AD is:

φ

A

⁢

D

=

φ

A

⁢

B

2

.

6. The power converter of claim 5 , wherein one of:

angle φ AB is controlled as a function of the output voltage of the secondary H-bridge and angle φ AD is controlled to be half the angle φ AB ; and

angle φ AD is controlled as a function of the output voltage of the secondary H-bridge and angle φ AB is controlled to be twice the angle φ AD .

7. The power converter of claim 1 , wherein power flow is bidirectional.

8. The power converter of claim 7 , wherein

a power flow direction from the primary H-bridge to the secondary H-bridge is dependent on a phase angle φ PS , which is:

φ

P

⁢

S

=

φ

A

⁢

D

-

φ

A

⁢

B

2

+

φ

D

⁢

E

2

.

9. The power converter of claim 8 , wherein φ PS is within the range [0, π] for forward power flow where input current I 1 to the primary H-bridge and output current I 2 from the secondary H-bridge are positive, and φ PS is within the range [−π, 0] for reverse power flow where I 1 and I 2 are both negative.

10. The power converter of claim 8 , wherein angle φ DE is 180 degrees and a relationship between angle φ AB and angle φ AD is:

φ

A

⁢

D

=

φ

A

⁢

B

2

for forward power flow; and

φ

A

⁢

D

=

φ

A

⁢

B

2

-

1

⁢

8

⁢

0

∘

for reverse power flow.

11. The power converter of claim 10 , wherein one of:

for forward power flow, angle φ AB is one of set to a fixed value or controlled as a function of the output voltage of the secondary H-bridge and angle φ AD is controlled to be half the angle φ AB ;

for reverse power flow, angle φ AB is one of set to a fixed value or controlled as a function of the input current to the primary H-bridge and angle φ AD is controlled to be

φ

A

⁢

D

=

φ

A

⁢

B

2

-

18

⁢

0

∘

;

for forward power flow, angle φ AD is one of set to a fixed value or controlled as a function of the output voltage of the secondary H-bridge and angle φ AB is controlled to be twice the angle φ AD ; and

for reverse power flow, angleφ AD is one of set to a fixed value or controlled as a function of the input current to the primary H-bridge and angle φ AB is controlled to be φ AB =2(φ AD +180°.

12. The power converter of claim 1 , wherein a turns ratio n of the transformer is set at an optimal turns ratio n opt :

n

o

⁢

p

⁢

t

=

P

load_max

⁢

sin

⁢

(

φ

A

⁢

B

2

)

V

2

⁢

I

g

,

where

P load_max is a maximum load condition;

I g is a DC constant source current; and

V 2 is a constant output voltage of the secondary H-bridge.

13. The power converter of claim 1 , further comprising an input capacitor C in connected across input terminals of the primary H-bridge.

14. A power converter comprising:

a primary H-bridge comprising a first semi-conductor switch, a second semi-conductor switch, a third semi-conductor switch, and a fourth semi-conductor switch, wherein the first semi-conductor switch and the second semi-conductor switch are in leg A with terminal A between the first semi-conductor switch and the second semi-conductor switch in leg A and the third semi-conductor switch and the fourth semi-conductor switch are in leg B with terminal B between the third semi-conductor switch and the fourth semi-conductor switch in leg B, said terminal A and said terminal B forming an output of the primary H-bridge;

an LCL-Transformer section comprising a first inductor L r with a first end connected to said terminal A, a capacitor C r connected between a second end of the first inductor L r and said terminal B, and a second inductor L g with a first end connected to the second end of the first inductor L r ;

a transformer with a primary side connected between a second end of the second inductor L g and said terminal B, the transformer comprising a turns ratio n;

a secondary H-bridge comprising a fifth semi-conductor switch, a sixth semi-conductor switch, a seventh semi-conductor switch, and an eight semi-conductor switch with an input connected to a secondary side of the transformer, wherein the fifth and sixth semi-conductor switches are in leg D with terminal D between the fifth and sixth semi-conductor switches of leg D and the seventh and eighth semi-conductor switches are in leg E with terminal E between the seventh and eighth semi-conductor switches of leg E, said terminal D and said terminal E forming an output of the secondary H -bridge; and

an output capacitor C f connected across said terminal D and said terminal E,

wherein the primary H-bridge is fed by a direct current (DC) constant current source, and wherein said terminals D and E are connected to a load and an output voltage across said terminals D and E is regulated to maintain a constant DC output voltage, and

wherein:

the first, second, third and fourth semi-conductor switches of the primary H-bridge are operated with the symmetrical phase shift modulation with leg A leading leg B by an angle φ AB ;

the fifth, sixth, seventh, and eighth semi-conductor switches of the secondary H-bridge are operated with the symmetrical phase shift modulation with leg D leading leg E by an angle φ DE ;

an angle between leg A and leg D is angle φ AD ; and

the output voltage of the secondary H-bridge is maintained at a constant voltage by controlling angle φ AB , angle φ DE , and angle φ AD ,

wherein a relationship between angle φ AB , angle φ DE , and angle φ AD is:

φ

A

⁢

D

=

φ

A

⁢

B

2

+

π

2

-

φ

D

⁢

E

2

.

15. The power a switching frequency of the first, second, third and fourth semi-conductor switches of the primary H-bridge and the fifth, sixth, seventh, and eighth semi-conductor switches of the secondary H-bridge is selected to be within 15 percent of a resonant frequency of the LCL-Transformer section, and wherein a ratio g of the first inductor L r and the second inductor L g is within a range of 0.2 to 5.

16. The power converter of claim 14 , wherein angle φ DE is 180 degrees and a relationship between angle φ AB and angle φ AD is

φ

A

⁢

D

=

φ

A

⁢

B

2

,

and wherein one of:

angle φ AB is controlled as a function of the output voltage of the secondary H-bridge and angle φ AD is controlled to be half the angle φ AB ; and

angle φ AD is controlled as a function of the output voltage of the secondary H-bridge and angle φ AB is controlled to be twice the angle φ AD .

17. The power converter of claim 14 , wherein power flow is bidirectional, wherein

a power flow direction from the primary H-bridge to the secondary H-bridge is dependent on a phase angle φ PS , which is:

φ

P

⁢

S

=

φ

A

⁢

D

-

φ

A

⁢

B

2

+

φ

D

⁢

E

2

.

18. A bidirectional power converter comprising:

a primary H-bridge comprising a first semi-conductor switch, a second semi-conductor switch, a third semi-conductor switch, and a fourth semi-conductor switch, wherein the first semi-conductor switch and the second semi-conductor switch are in leg A with terminal A between the first semi-conductor switch and the second semi-conductor switch in leg A and the third semi-conductor switch and the fourth semi-conductor switch are in leg B with terminal B between the third semi-conductor switch and the fourth semi-conductor switch in leg B, said terminal A and said terminal B forming an output of the primary H-bridge;

an LCL-Transformer section comprising a first inductor L r with a first end connected to terminal A, a capacitor C r connected between a second end of the first inductor L r and said terminal B, and a second inductor L g with a first end connected to the second end of the first inductor L r ;

a transformer with a primary side connected between a second end of the second inductor L g and said terminal B, the transformer comprising a turns ratio n;

a secondary H-bridge comprising a fifth semi-conductor switch, a sixth semi-conductor switch, a seventh semi-conductor switch, and an eight semi-conductor switch with an input connected to a secondary side of the transformer, wherein the fifth and sixth semi-conductor switches are in leg D with terminal D between the fifth and sixth semi-conductor switches of leg D and the seventh and eighth semi-conductor switches are in leg E with terminal E between the seventh and eighth semi-conductor switches of leg E, terminal D and terminal E forming an output of the secondary H-bridge; and

an output capacitor C f connected across said terminal D and said terminal E,

wherein the primary H-bridge is fed by a direct current (DC) constant current source, and wherein said terminals D and E are connected to a load and an output voltage across said terminals D and E is regulated to maintain a constant DC output voltage,

wherein:

the first, second, third and fourth semi-conductor switches of the primary H-bridge are operated with symmetrical phase shift modulation with leg A leading leg B by an angle conductor φ AB ;

the fifth, sixth, seventh, and eighth semi-conductor switches of the secondary H-bridge are operated with symmetrical phase shift modulation with leg D leading leg E by an angle φ DE ;

an angle between leg A and leg D is angle φ AD ; and

a power flow direction from the primary H-bridge to the secondary H-bridge is dependent on a phase angle φ PS , which is:

φ

P

⁢

S

=

φ

A

⁢

D

-

φ

A

⁢

B

2

+

φ

D

⁢

E

2

.