Control of small distributed energy resources

• US 20040051387A1
• Filed: 09/17/2002
• Published: 03/18/2004
• Est. Priority Date: 09/17/2002
• Status: Active Grant

• Current Assignee: Wisconsin Alumni Research Foundation (University of Wisconsin System)
• Original Assignee: Wisconsin Alumni Research Foundation (University of Wisconsin System)
• Inventors: Piagi, Paolo, Lasseter, Robert H.
• Granted Patent: US 7,116,010 B2
• Time in Patent Office: Days
• US Class Current: 307/80
• CPC Class Codes: H02J 2300/10 The dispersed energy generation being of fossil origin, e.g. diesel generators
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02J 3/472 For selectively connecting the AC sources in a particular order, e.g. sequential, alternating or subsets of sources

Abstract

A power electronics interface in a microsource controller allows efficient connection in a power system of small, low cost and reliable distributed generators such as microturbines, fuel cells and photovoltaic. Power electronics provide the control and flexibility to insure stable operation for large numbers of distributed generators. The power electronics controls are designed to insure that new generators can be added to the system without modification of existing equipment. A collection of sources and loads can connect to or isolate from the utility grid in a rapid and seamless fashion, each inverter can respond effectively to load changes without requiring data from other sources, and voltage sag and system imbalances can be corrected.

Claims

1. A microsource system providing power in any one of an isolation mode and a grid mode and being configured to couple to a power system without modification of existing equipment in the power system, the microsource system comprising:

a microsource power source configured to provide electrical power; and

a controller coupled to the microsource power source to control the microsource power source based only on information available locally at the microsource power source.

2. The microsource system of claim 1 wherein the controller includes a voltage controller and a power controller.

3. The microsource system of claim 2 wherein the voltage controller and the power control receive inputs from a real power and reactive power calculator and a flux vector or phasor calculator.

4. The microsource system of claim 3 wherein the real power and reactive power calculator receive inputs from voltage at a connection point, current injected by the microsource power source, and current in a feeder from a utility supply.

5. The microsource system of claim 2 wherein the power controller includes a frequency droop governor where if frequency (ω

₁) decreases below ω

_o power increases linearly by a coefficient m.

6. The microsource system of claim 1 wherein the microsource power source is a fuel cell.

7. The microsource system of claim 1 wherein the microsource power source is a microturbine.

8. The microsource system of claim 1 wherein the controller reduces a local voltage set point as reactive current generated by the microsource power source become more capacitive.

9. The microsource system of claim 1 wherein the controller increases a local voltage set point as current generated by the microsource power source becomes more inductive.

10. The microsource system of claim 1 wherein the microsource power source includes a prime mover, a DC interface, and a voltage source inverter.

11. A microsource system configured for use in a microgrid which is capable of separation from a power grid while continuing to operate independently when problems occur and reconnecting to the power grid once the problems are solved, the system comprising:

a microsource including a prime mover, a DC interface, and a voltage source inverter;

means for controlling real and reactive power coupled to the microsource; and

means for regulating voltage through droop control to the microsource.

12. The system of claim 11 further comprising means for fast load tracking and storage coupled to the microsource.

13. The system of claim 11 further comprising means for frequency droop control for power sharing coupled to the microsource.

14. The system of claim 11 wherein the means for regulating voltage through droop reduces a local voltage set point as reactive current generated by the microsource becomes more capacitive.

15. The system of claim 11 wherein the means for regulating voltage through droop increases a local voltage set point as current generated by the microsource becomes more inductive.

16. A power system comprising:

a microsource including a voltage source inverter, the microsource being configured to connect to a utility grid, the utility grid coupling a plurality of power sources; and

a controller coupled to the voltage source inverter and configured to control reactive and active power independently from the plurality of power sources coupled to the utility grid.

17. The power system of claim 16 wherein the microsource includes a high frequency AC source that is rectified.

18. The power system of claim 16 wherein the microsource includes a DC battery storage source.

19. The power system of claim 16 wherein the controller includes a droop controller.

20. The power system of claim 19 wherein the droop controller comprises means for reducing a local voltage set point as reactive current generated by a microsource becomes more capacitive;

and

means for increasing the local voltage set point as current generated by the microsource becomes more inductive.

21. A method of controlling a microsource in a microgrid system where the microgrid can operate independently from a power grid or in cooperation with the grid, the method comprising:

receiving inputs from voltage at a connection point, current injected by the microsource, and current in a feeder from a utility supply;

reducing a local voltage set point as current injected by the microsource becomes more capacitive; and

increasing the local voltage set point as current generated by the microsource becomes more capacitive.

22. The method of claim 21 further comprising controlling voltage and power of the microsource using the inputs.

23. The method of claim 22 wherein controlling the power of the microsource includes using a frequency governor.

24. The method of claim 22 wherein constant power is provided during microgrid connected mode.

25. The method of claim 22 wherein dynamic load tracking is provided during island mode.