Three-level power conversion system and control method

1. A system comprising:

a first power conversion port including a three-level power factor correction device and a primary power conversion circuit, wherein the three-level power factor correction device includes input ports connected to a single-phase AC power source, a first output port connected to a first voltage bus, a second output port connected to a second voltage bus, and a third output port connected to a third voltage bus;

a first diode, a second diode connected in series with the first diode between the first voltage bus and the second voltage bus, a first capacitor, and a second capacitor connected in series with the first capacitor between the first voltage bus and the second voltage bus, and a relay connected between a common node of the first diode and the second diode, and a common node of the first capacitor and the second capacitor;

a second power conversion port including a three-level rectifier; and

a third power conversion port including a rectifier, the first power conversion port, the second power conversion port and the third power conversion port magnetically coupled to each other through a transformer.

2. The system of claim 1 , wherein the three-level power factor correction device is a three-level neutral point clamped (NPC) power factor correction converter, and the primary power conversion circuit includes a primary switching network of a three-level inductor-inductor-capacitor (LLC) converter and a resonant tank.

3. The system of claim 1 , wherein an output voltage of the three-level rectifier is regulated through adjusting a voltage across the first voltage bus and the second voltage bus.

4. The system of claim 1 , wherein the relay is configured to transition between a closed state and an open stage, and wherein the first diode, the second diode, the first capacitor, and the second capacitor form a voltage doubler when the relay is in the closed state.

5. The system of claim 1 , wherein the primary power conversion circuit includes a first primary switch, a second primary switch, a third primary switch and a fourth primary switch connected in series between a first voltage bus and a second voltage bus, and a resonant tank connected between a common node of the first primary switch and the second primary switch, and a first terminal of a primary winding of the transformer, and a second terminal of the primary winding of the transformer being connected to a common node of the third primary switch and the fourth primary switch.

6. A method comprising:

transferring energy from an AC power source to a first DC load through a three-level power factor correction device, a primary three-level power conversion circuit and a first secondary power conversion circuit that is magnetically coupled to the primary three-level power conversion circuit through a transformer;

configuring the three-level power factor correction device to generate a first voltage bus, a second voltage bus and a third voltage bus, wherein a first diode, a second diode connected in series with the first diode between the first voltage bus and the second voltage bus, a first capacitor and a second capacitor connected in series with the first capacitor between the first voltage bus and the second voltage bus, and a relay connected between a common node of the first diode and the second diode, and a common node of the first capacitor and the second capacitor; and

transferring energy from the AC power source to a second DC load through the three-level power factor correction device, the primary three-level power conversion circuit and a second secondary power conversion circuit that is magnetically coupled to the primary three-level power conversion circuit through the transformer.

7. The method of claim 6 , further comprising:

regulating a voltage across the first DC load through adjusting an output voltage of the three-level power factor correction device.

8. The method of claim 6 , further comprising:

configuring the first diode, the second diode, the first capacitor and the second capacitor and the relay as a voltage doubler through changing the relay from an open state to a closed state.

9. The method of claim 6 , further comprising:

configuring the second secondary power conversion circuit to operate as a linear regulator when an input voltage of the second secondary power conversion circuit is over a predetermined voltage threshold.

10. The method of claim 6 , further comprising:

configuring the first DC load as a power source to provide power for at least one of the second DC load and an AC load connected to terminals of the AC power source.

11. The method of claim 6 , further comprising:

configuring the second secondary power conversion circuit to operate in a boost converter mode by shorting a secondary side winding of the transformer through turning on two lower switches of the second secondary power conversion circuit.

12. A system comprising:

a three-port power conversion subsystem having a first port connected to an AC power source, a second port connected to a first DC load and a third port connected to a second DC load; and

a first two-port power conversion subsystem having a first port connected to the AC power source and a second port connected to the first DC load, the second port of the first two-port power conversion subsystem being a first unidirectional power port.

13. The system of claim 12 , wherein:

the first port of the three-port power conversion subsystem includes a first three-level power factor correction device and a first primary power conversion circuit connected in cascade between the AC power source and a first winding of a first transformer;

the second port of the three-port power conversion subsystem includes a three-level rectifier connected between a second winding of the first transformer and the first DC load; and

the third port of the three-port power conversion subsystem includes a first diode rectifier between a third winding of the first transformer and the second DC load.

14. The system of claim 13 , wherein the first three-level power factor correction device is a three-level neutral point clamped (NPC) power factor correction converter, and the first primary power conversion circuit and the three-level rectifier form a three-level inductor-inductor-capacitor (LLC) converter.

15. The system of claim 12 , wherein:

the first port of the first two-port power conversion subsystem includes a second three-level power factor correction device and a second primary power conversion circuit connected in cascade between the AC power source and a first winding of a second transformer; and

the second port of the first two-port power conversion subsystem includes a second diode rectifier connected between a second winding of the second transformer and the first DC load.

16. The system of claim 12 , further comprising:

a second two-port power conversion subsystem having a first port connected to the AC power source and a second port connected to the first DC load, the second port of the second two-port power conversion subsystem being a second unidirectional power port.