Inverter based storage in dynamic distribution systems including distributed energy resources

• US 7,787,272 B2
• Filed: 03/01/2007
• Issued: 08/31/2010
• Est. Priority Date: 03/01/2007
• 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.
• Primary Examiner(s): Laxton; Gary L
• Assistant Examiner(s): QUDDUS, NUSRAT
• Application Number:
  US11/681,024
• Publication Number:
  US 20080212343A1
• Time in Patent Office: 1,279 Days
• Field of Search: 363/15, 363/19, 363/21.03, 363/21.15, 363/21.16, 363/39, 363/118, 363/74, 363/78, 363/79, 363/95, 363/97, 363/98, 318/798
• US Class Current: 363/98
• CPC Class Codes: H02J 2300/20 The dispersed energy generation being of renewable origin
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• CPC Class Codes: H02J 2300/28 The renewable source being wind energy wind motors F03D
• CPC Class Codes: H02J 2300/30 The power source being a fuel cell
• CPC Class Codes: H02J 3/30 using dynamo-electric machines coupled to flywheels
• CPC Class Codes: H02J 3/32 using batteries with converting means
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02J 3/50 Controlling the sharing of the out-of-phase component
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers
• CPC Class Codes: Y02E 10/76 Power conversion electric or electronic aspects
• CPC Class Codes: Y02E 60/16 Mechanical energy storage, e.g. flywheels or pressurised fluids
• CPC Class Codes: Y02E 70/30 Systems combining energy storage with energy generation of non-fossil origin

Abstract

A microsource is provided, which includes an inverter, an energy storage device, and a controller. The controller calculates a maximum frequency change for the inverter based on a first comparison between a first power set point and a measured power from the inverter. The first power set point is defined based on a charge level of the energy storage device. A minimum frequency change for the inverter is calculated based on a second comparison between a second power set point and the measured power from the inverter. An operating frequency for the inverter is calculated based on a third comparison between a power set point and a measured power flow. A requested frequency for the inverter is calculated by combining the maximum frequency change, the minimum frequency change, and the operating frequency. The requested frequency is integrated to determine a phase angle of a voltage of the inverter to control a frequency of an output power of the inverter.

Claims

1. A controller for controlling a charge and/or a discharge of an energy storage device used in a distributed energy resource, the controller comprising circuitry:

to calculate a maximum frequency change for an inverter based on a first comparison between a first power set point and a measured power from the inverter, wherein the first power set point is defined based on a charge level of an energy storage device coupled to the inverter;

to calculate a minimum frequency change for the inverter based on a second comparison between a second power set point and the measured power from the inverter;

to calculate an operating frequency for the inverter based on a third comparison between a power set point and a measured power flow;

to calculate a requested frequency for the inverter by combining the calculated maximum frequency change, the calculated minimum frequency change, and the calculated operating frequency; and

to integrate the calculated requested frequency to determine a phase angle of a voltage of the inverter to control a frequency of an output power of the inverter.

2. The controller of claim 1, wherein calculating the operating frequency comprises use of m(F_o−

F), where m is a slope of an F-ω

characteristic, _o is the power set point, and F is the measured power flow.

3. The controller of claim 1, wherein calculating the operating frequency comprises use of m(P_o−

P), where m is a slope of a P-ω

characteristic, P_o is the power set point, and P is the measured power flow.

4. The controller of claim 3, wherein the measured power is the measured power flow.

5. The controller of claim 1, wherein calculating the maximum frequency change comprises subtracting the measured power from the first power set point to determine a power differential.

6. The controller of claim 5, wherein calculating the maximum frequency change further comprises applying the determined power differential to a proportional-integral controller.

7. The controller of claim 1, wherein calculating the minimum frequency change comprises subtracting the measured power from the second power set point to determine a power differential.

8. The controller of claim 7, wherein calculating the minimum frequency change further comprises applying the determined power differential to a proportional-integral controller.

9. The controller of claim 1, wherein the second power set point is defined based on the charge level of the energy storage device.

10. The controller of claim 1, further comprising regulating an output voltage of the inverter using a voltage versus reactive power droop controller.

11. The controller of claim 1, wherein the first power set point is set to a maximum discharge rate of the energy storage device during a transition to island mode.

12. The controller of claim 1, wherein the first power set point is set to a preferred discharge rate of the energy storage device after a transition to island mode.

13. The controller of claim 12, wherein the second power set point is set to the preferred discharge rate of the energy storage device after the transition to island mode.

14. The controller of claim 1, wherein the first power set point is set to a preferred discharge rate of the energy storage device when an energy level of the energy storage device exceeds a maximum energy reserve level.

15. The controller of claim 1, wherein the first power set point is set to approximately zero when an energy level of the energy storage device falls below a minimum energy reserve level.

16. The controller of claim 1, further comprising measuring a current drawn by the inverter from the energy storage device.

17. The controller of claim 16, further comprising holding a power rate from the energy storage device to a maximum power ramp rate.

18. A method of controlling a charge and/or a discharge of an energy storage device used in a distributed energy resource, the method comprising:

calculating a maximum frequency change for an inverter using a controller based on a first comparison between a first power set point and a measured power from the inverter, wherein the first power set point is defined based on a charge level of an energy storage device coupled to the inverter;

calculating a minimum frequency change for the inverter using the controller based on a second comparison between a second power set point and the measured power from the inverter;

calculating an operating frequency for the inverter using the controller based on a third comparison between a power set point and a measured power flow;

calculating a requested frequency for the inverter using the controller by combining the calculated maximum frequency change, the calculated minimum frequency change, and the calculated operating frequency; and

integrating the calculated requested frequency to determine a phase angle of a voltage of the inverter to control a frequency of an output power of the inverter.

19. A microsource, the microsource comprising:

an inverter;

an energy storage device operably coupled with the inverter; and

a controller operably coupled with the energy storage device and the inverter, the controller including circuitry configured

to calculate a maximum frequency change for the inverter based on a first comparison between a first power set point and a measured power from the inverter, wherein the first power set point is defined based on a charge level of the energy storage device;

to calculate a minimum frequency change for the inverter based on a second comparison between a second power set point and the measured power from the inverter;

to calculate an operating frequency for the inverter based on a third comparison between a power set point and a measured power flow;

to calculate a requested frequency for the inverter by combining the calculated maximum frequency change, the calculated minimum frequency change, and the calculated operating frequency; and

to integrate the calculated requested frequency to determine a phase angle of a voltage of the inverter to control a frequency of an output power of the inverter.

20. The microsource of claim 19, further comprising a power storage device operably coupled with the inverter, wherein the controller is operably coupled with the power storage device and further includes circuitry configured to limit a power rate of the energy storage device and to control an amount of power output from the power storage device to the inverter.

21. The microsource of claim 20, wherein the controller further includes circuitry configured to measure a current drawn by the inverter from the energy storage device to limit the power rate of the energy storage device.