Parallel operation of multiple generators

• US 6,297,977 B1
• Filed: 09/12/2000
• Issued: 10/02/2001
• Est. Priority Date: 09/12/2000
• Status: Expired due to Fees

• Current Assignee: Hybrid Power Generation Systems, LLC
• Original Assignee: Honeywell Space Systems Incorporated
• Inventors: Lewis, David C., Huggett, Colin E.
• Primary Examiner(s): BERHANE, ADOLF D
• Application Number:
  US09/659,631
• Time in Patent Office: 385 Days
• Field of Search: 363/16, 363/95, 363/65, 363/71
• US Class Current: 363/65
• CPC Class Codes: H02M 7/493 the static converters being arranged for operation in parallel

Abstract

A power generation system includes multiple generators that are operated in parallel. An inverter of one of the generators is always operated in voltage mode. Inverters of the other generators are switched between voltage and current modes.

Claims

1. A power generating system comprising:

a group of generators, each generator including an inverter that is operable in a voltage mode and a current mode; and

a control system for switching at least one inverter between a current mode and a voltage mode, the control system switching between the two modes in response to a change in demanded power.

2. The system of claim 1, wherein each generator is part of a microturbine generator.

3. The system of claim 1, wherein at least one of the generators is designated as a follower;

wherein the control system operates a maximum number of follower inverters in current mode at maximum power output without exceeding the demanded power; and

wherein the control system operates the remaining inverters of active generators in voltage mode.

4. The system of claim 3, wherein the control system uses a synchronization signal to phase-lock the inverters of the followers.

5. The system of claim 4, wherein one of the generators is designated as a master;

wherein the synchronization signal is provided by the master; and

wherein the inverter of the master is always operated in voltage mode.

6. The system of claim of claim 5, wherein one of the generators is designated as a slave, the slave providing the synchronization signal if the master fails;

and wherein the slave is always operated in voltage mode.

7. The system of claim 5, further comprising a plurality of sensors for determining when the inverters should be switched between current and voltage modes, the sensors being cascaded.

8. The system of claim 1, further comprising a voltage regulator for sending the same voltage command to each inverter.

9. The system of claim 1, wherein the control system operates all of the inverters in voltage mode when demanded power is below the full power-generating capacity of a single generator.

10. The system of claim 1, further comprising at least one current sensor for comparing line current to first and second thresholds;

wherein a corresponding inverter is switched from voltage mode to current mode when the first threshold is crossed;

wherein the corresponding inverter is switched from current mode to voltage mode when the second threshold is crossed; and

wherein the first and second thresholds are not equal.

11. The system of claim 1, further comprising a plurality of sensors for determining when the inverters should be switched between current and voltage modes, the sensors being cascaded.

12. The method of claim 11, wherein each sensor corresponds to an inverter;

and wherein each inverter is switched solely on information provided by its corresponding sensor.

13. The system of claim 1, wherein the inverters are switched according to a hierarchy.

14. A method of using a set of generators to supply a power demand, the generators having inverters, the method comprising the steps of:

operating as many generators as possible at maximum power output without exceeding demanded power, wherein the inverters of the generators providing maximum power output are operated in current mode; and

operating inverters of the remaining generators in voltage mode.

15. The method of claim 14, further comprising the step of switching selected inverters between the current and voltage modes in response to changes in the power demand.

16. The method of claim 14, further comprising the step of supplying a reference signal to the generators, and phase-locking outputs of the inverters to the reference signal.

17. The method of claim 14, further comprising the step of sending the same voltage command to each of the inverters.

18. The method of claim 14, wherein the generators supply power to a distribution line;

wherein at least one generator inverter is switched from voltage mode to current mode when line current crosses a first threshold; and

wherein the at least one generator inverter is switched from current mode to voltage mode when line current crosses a second threshold, the first and second thresholds being different.

19. The method of claim 14, further comprising the step of sensing line current at the output of each generator;

and wherein each inverter is switched solely according to sensed current on the output of the corresponding generator.

20. The method of claim 14, wherein the generator inverters are independently switched according to a hierarchy.

21. A method of using a group of microturbine generators to supply current to a load, the method comprising the steps of:

operating one of the microturbine generators in the group as a master, the master always being operated in a voltage mode;

operating other microturbine generators in the group as followers;

combining power outputs of the master and the followers; and

switching a follower from voltage mode to current mode when load balance is greater than that follower'"'"'s maximum power rating, the follower then being operated in current mode at maximum power output.