Generator with DC boost and split bus bidirectional DC-to-DC converter for uninterruptible power supply system or for enhanced load pickup

• US 20040155526A1
• Filed: 02/07/2003
• Published: 08/12/2004
• Est. Priority Date: 02/07/2003
• Status: Active Grant

• Current Assignee: Cummins Power Generation Limited (Cummins Incorporated)
• Original Assignee: Cummins Power Generation Limited (Cummins Incorporated)
• Inventors: Bax, Randall, Naden, Mark
• Granted Patent: US 7,786,616 B2
• Time in Patent Office: Days
• US Class Current: 307/43
• CPC Class Codes: H02J 3/28 Arrangements for balancing of the load in a network by storage of energy
• CPC Class Codes: H02J 9/062 for AC powered loads
• CPC Class Codes: H02J 9/08 requiring starting of a prime-mover

Abstract

A local power generation system generates a substantially DC voltage at an inverter input, which is modulated to generate a resulting output AC power signal to a load. The inverter input voltage may be obtained from an engine generator, providing an AC power signal that is rectified. An energy storage device helps maintain the DC voltage at the inverter input when load power draw increases or during engine startup or acceleration, for example, until the engine accommodates the increased power demand. The system may also be used in an uninterruptible power supply (UPS) application, in which the load draws power from a utility-provided AC power source until a fault condition appears. When the fault condition appears, the load switches its power draw from the utility-provided AC power source to the inverter output. The energy storage device is charged through a bidirectional DC-to-DC converter and through an inverter that operates in a rectifier mode to rectify a utility-provided AC electrical power signal.

Claims

1. A system providing AC electrical power to a first load device, the system including:

a generator, including a generator output;

an inverter circuit, including an inverter input and an inverter output, the inverter input coupled to the generator output, the inverter output adapted to be coupled to the first load device;

an energy storage device;

a first bidirectional DC-to-DC converter circuit, including first and second converter terminals that permit a DC-to-DC voltage conversion therebetween, the first converter terminal coupled to the energy storage device, and the second converter terminal coupled to the inverter input; and

an AC controller circuit, including an AC controller input and an AC controller output, wherein the AC controller input is configured to be coupled to a utility-provided AC power source, and the AC controller output is adapted to be coupled to the first load device for providing power from the utility-provided AC power source to the first load device, and wherein the AC controller output is coupled to the inverter output to provide an operating mode that supplies power from the utility-provided AC power source to the inverter output and through the inverter to the inverter input and through the bidirectional DC-to-DC converter to the energy storage device for charging the energy storage device.

2. The system of claim 1, in which the first converter terminal of the bidirectional DC-to-DC converter includes a first positive node, a first neutral node, and a first negative node, and in which the second converter terminal of the bidirectional DC-to-DC converter includes a second positive node, a second neutral node, and a second negative node.

3. The system of claim 2, in which the first neutral node is electrically connected in common with the second neutral node.

4. The system of claim 3, in which the generator output includes a floating neutral node, and in which first and second neutral nodes are electrically connected in common with the floating neutral node.

5. The system of claim 3, in which the bidirectional DC-to-DC converter includes:

a first inductor, the first inductor including first and second inductor terminals, the first inductor terminal coupled to the first positive node;

a second inductor, the second inductor including third and fourth inductor terminals, the third inductor terminal coupled to the first negative node;

a first switching transistor, coupled between the second inductor terminal and the first neutral node;

a second switching transistor, coupled between the fourth inductor terminal and the second neutral node;

a third switching transistor, coupled between the second inductor terminal and the second positive node; and

a fourth switching transistor, coupled between the fourth inductor terminal and the second negative node.

6. The system of claim 5, in which the bidirectional DC-to-DC converter includes:

a first diode, an anode of the first diode coupled to the first neutral node, a cathode of the first diode coupled to the second inductor terminal;

a second diode, an anode of the second diode coupled to the fourth inductor terminal, a cathode of the second diode coupled to the first neutral node;

a third diode, an anode of the third diode coupled to the second inductor terminal, a cathode of the third diode coupled to the second positive node; and

a fourth diode, an anode of the fourth diode coupled to the second negative node, a cathode of the fourth diode coupled to the fourth inductor terminal.

7. The system of claim 6, in which the bidirectional DC-to-DC converter includes a controller, the controller including:

a boost mode, in which power is provided from the first terminal to the second terminal, the boost mode providing switching of the first and second switching transistors and preventing switching of the third and fourth switching transistors, the boost mode permitting power to be conducted through the third and fourth diodes; and

a charger mode, in which power is provided from the second terminal to the first terminal, the charger mode providing switching of the third and fourth switching transistors and preventing switching of the first and second switching transistors, the charger mode permitting power to be conducted through the first and second diodes.

8. The system of claim 1, further including a rectifier coupled between the generator output and the inverter input, the rectifier configured to convert AC power provided by the generator at the generator output to a DC voltage provided to the inverter input.

9. The system of claim 1, configured for charging the energy storage device when the utility-provided AC power source is operating to provide adequate power to the first load, said charging including operating the inverter in a non-switching rectifier mode, and wherein the system is configured to turn on the generator in response to a failure of the utility-provided AC power source to provide adequate power to the load, and wherein the system is configured to provide power from the energy storage device to the inverter input during a startup period of the generator.

10. A bidirectional DC-to-DC converter including:

a first converter terminal, including a first positive node, a first neutral node, and a first negative node;

a second converter terminal, including a second positive node, a second neutral node, and a second negative node;

a first inductor, the first inductor including first and second inductor terminals, the first inductor terminal coupled to the first positive node;

a second inductor, the second inductor including third and fourth inductor terminals, the third inductor terminal coupled to the first negative node;

a first switching transistor, coupled between the second inductor terminal and the first neutral node;

a second switching transistor, coupled between the fourth inductor terminal and the second neutral node;

a third switching transistor, coupled between the second inductor terminal and the second positive node; and

a fourth switching transistor, coupled between the fourth inductor terminal and the second negative node.

11. The bidirectional DC-to-DC converter of claim 10, further including:

a first diode, an anode of the first diode coupled to the first neutral node, a cathode of the first diode coupled to the second inductor terminal;

a second diode, an anode of the second diode coupled to the fourth inductor terminal, a cathode of the second diode coupled to the first neutral node;

a third diode, an anode of the third diode coupled to the second inductor terminal, a cathode of the third diode coupled to the second positive node; and

a fourth diode, an anode of the fourth diode coupled to the second negative node, a cathode of the fourth diode coupled to the fourth inductor terminal.

12. The bidirectional DC-to-DC converter of claim 11, further including a controller that includes:

a first mode, in which power is provided from the first terminal to the second terminal, the first mode providing switching of the first and second switching transistors and preventing switching of the third and fourth switching transistors, the first mode permitting power to be conducted through the third and fourth diodes; and

a second mode, in which power is provided from the second terminal to the first terminal, the second mode providing switching of the third and fourth switching transistors and preventing switching of the first and second switching transistors, the second mode permitting power to be conducted through the first and second diodes.

13. A system providing AC electrical power to a first load device, the system including:

an energy storage device;

a first bidirectional DC-to-DC converter circuit, including first and second converter terminals that permit a bidirectional DC-to-DC voltage conversion therebetween, the first converter terminal coupled to the energy storage device; and

an inverter circuit, including an inverter input coupled to the second converter terminal, and including an inverter output adapted to be coupled to the first load device, the inverter circuit configured for providing a switching mode for providing energy from the inverter input to the inverter output, and the switching mode configured for converting a substantially DC signal at the inverter input to an AC signal at the inverter output, the inverter circuit also configured for providing a nonswitching rectifier mode for providing energy from the inverter output to the inverter input, and the nonswitching rectifier mode configured for converting an AC signal at the inverter output to a substantially DC signal at the inverter output.

14. The system of claim 13, further comprising a generator including a generator output that is coupled to the inverter input.

15. The system of claim 14, further including a utility connection between the first load and a utility-provided AC power source.

16. The system of claim 15, in which the utility connection includes an AC controller circuit between the utility-provided AC power source and the first load, wherein the AC controller circuit is also coupled between the utility-provided AC power source and the inverter output.

17. The system of claim 16, further including a rectifier coupled between the generator output and the inverter input.

18. The system of claim 13, in which the first converter terminal includes a first positive node, a first neutral node, and a first negative node, and in which the second converter terminal includes a second positive node, a second neutral node, and a second negative node, and wherein the bidirectional DC-to-DC converter further includes:

a first inductor, the first inductor including first and second inductor terminals, the first inductor terminal coupled to the first positive node;

a second inductor, the second inductor including third and fourth inductor terminals, the third inductor terminal coupled to the first negative node;

a first switching transistor, coupled between the second inductor terminal and the first neutral node;

a second switching transistor, coupled between the fourth inductor terminal and the second neutral node;

a third switching transistor, coupled between the second inductor terminal and the second positive node; and

a fourth switching transistor, coupled between the fourth inductor terminal and the second negative node.

19. A system providing AC electrical power to a first load device, the system including:

a utility connection terminal, adapted to be connected to a utility-provided AC power supply;

a generator connection terminal, including a three phase generator output and a floating neutral generator output;

a DC bus, including a positive DC bus node, a negative DC bus node, and a neutral DC bus node, the neutral DC bus node electrically connected in common with the floating neutral generator output;

a rectifier, including a rectifier input coupled to the three phase generator output, the rectifier also including a rectifier output coupled to the positive DC bus node and to the negative DC bus node;

a dual inverter/rectifier circuit, including an inverter input and an inverter output, the inverter input coupled to the positive DC bus node and the negative DC bus node, and the inverter output coupled to the first load device, and the inverter output also coupled to the utility connection terminal;

an energy storage device, including a positive energy storage node, a negative energy storage node, and a neutral energy storage node, the neutral energy storage node electrically connected in common with the floating neutral generator output; and

a first bidirectional DC-to-DC converter circuit, including first and second converter terminals that permit a DC-to-DC voltage conversion therebetween, the first converter terminal coupled to the positive energy storage node, the negative energy storage node, and the floating neutral generator output, the second converter terminal coupled to the positive DC bus node, the negative DC bus node, and the floating neutral generator output.

20. The system of claim 19, further including a generator connected to the three phase generator output and the floating neutral generator output.

25. The method of claim 20, in which the charging the energy storage device includes converting a higher level of a substantially DC power signal received from the utility-provided AC power source through the inverter operating as a rectifier to a lower level of a substantially DC power signal for storing on the energy storage device.

26. The method of claim 25, in which the providing power to the first load from the energy storage device includes converting a lower level of a substantially DC power signal received from the energy storage device to a higher level of a substantially DC power signal that is used for inverting into an AC power signal provided to the first load.

21. A method of providing AC power to a first load, the method including:

charging an energy-storage device from a utility-provided AC power source through a switched-mode inverter that is configured in a mode to prevent switching and provide rectification; and

if the utility-provided AC power source fails to provide adequate power to the first load, then providing power to the first load from the energy-storage device and through the inverter.

22. The method of claim 21, further including, if the utility-provided AC power source fails to provide adequate power to the first load, generating electrical power to provide to the first load through the inverter.

23. The method of claim 21, in which the providing power to the first load from the energy-storage device includes providing said power during a turn-on period of a generator.

24. The method of claim 21, in which the generating electrical power to provide to the first load through the inverter includes:

generating an AC power signal;

rectifying the AC power signal into a substantially DC power signal; and

inverting the substantially DC power signal.