Control of small distributed energy resources

US 7,687,937 B2
Filed: 03/18/2005
Issued: 03/30/2010
Est. Priority Date: 03/18/2005
Status: Active Grant

First Claim

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1. A method of controlling distributed energy resources, the method comprising:

providing a microsource, wherein the microsource is located in a microgrid, and further wherein the micro source is configured to deliver a power P1 at a frequency ω

1;

operating the microsource in a grid mode in which the microsource is connected to a utility grid, wherein during operation in the grid mode the frequency ω

1 is approximately equal to a frequency ω

_oand the power P1 is equal to a power P1_o, wherein the frequency ω

_ois an operating frequency of the utility grid; and

transferring the microsource from the grid mode to an island mode such that the microsource is disconnected from the utility grid, wherein ω

1 is equal to ω

_islandand P1 is equal to P1_islandduring the island mode;

wherein ω

_island>

ω

₀, and P1_island<

P1₀if the microgrid was exporting power prior to the transfer from the grid mode to the island mode;

wherein ω

_island<

ω

₀, and P1_island>

P1₀if the microgrid was importing power prior to the transfer from the grid mode to the island mode; and

wherein the microsource delivers a maximum power output level P1_maxat a frequency ω

_min, wherein the microsource has a slope switch frequency ω

_switch, and $ω_{island} \approx ω_{0} (\frac{ω_{0} - ω_{\min}}{P 1_{0} - P 1_{\max}}) (P 1_{0} - P 1_{island}) . if [ω_{0} - (\frac{ω_{0} - ω_{\min}}{P 1_{0} - P 1_{\max}}) (P 1_{0} - P 1_{island})] < ω_{\max} .$

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Abstract

A method of controlling the output inverter of a microsource in a distributed energy resource system is disclosed. Embodiments of the invention include using unit or zone power controllers that reduce the operating frequency of the inverter to increase its unit output power. Preferred embodiments includes methods wherein the inverter reaches maximum output power and minimum operating frequency at the same time, and further comprising using a voltage controller implementing a voltage vs. reactive current droop. Other aspects of this embodiment relate to an inverter that implements such methods, and a microsource containing such an inverter. These methods can be extended to control inverters in a plurality of microsources, organized in a single zone or in a plurality of zones.

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27 Claims

1. A method of controlling distributed energy resources, the method comprising:
- providing a microsource, wherein the microsource is located in a microgrid, and further wherein the micro source is configured to deliver a power P1 at a frequency ω
  
  1;
  
  operating the microsource in a grid mode in which the microsource is connected to a utility grid, wherein during operation in the grid mode the frequency ω
  
  1 is approximately equal to a frequency ω
  
  _oand the power P1 is equal to a power P1_o, wherein the frequency ω
  
  _ois an operating frequency of the utility grid; and
  
  transferring the microsource from the grid mode to an island mode such that the microsource is disconnected from the utility grid, wherein ω
  
  1 is equal to ω
  
  _islandand P1 is equal to P1_islandduring the island mode;
  
  wherein ω
  
  _island>
  
  ω
  
  ₀, and P1_island<
  
  P1₀if the microgrid was exporting power prior to the transfer from the grid mode to the island mode;
  
  wherein ω
  
  _island<
  
  ω
  
  ₀, and P1_island>
  
  P1₀if the microgrid was importing power prior to the transfer from the grid mode to the island mode; and
  
  wherein the microsource delivers a maximum power output level P1_maxat a frequency ω
  
  _min, wherein the microsource has a slope switch frequency ω
  
  _switch, and $ω_{island} \approx ω_{0} (\frac{ω_{0} - ω_{\min}}{P 1_{0} - P 1_{\max}}) (P 1_{0} - P 1_{island}) . if [ω_{0} - (\frac{ω_{0} - ω_{\min}}{P 1_{0} - P 1_{\max}}) (P 1_{0} - P 1_{island})] < ω_{\max} .$
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
- - 2. The method of claim 1, wherein the microsource delivers a maximum power output level P1_maxat a frequency ω
    - _min, and wherein
3. The method of claim 1, $wherein$
- ⁢
  
  ω
  
  island ≈
  
  ω
  
  0 - ( ω
  
  0 - ω
  
  min P ⁢
  
  ⁢
  
  1 0 - P ⁢
  
  ⁢
  
  1 max ) ⁢
  
  ( P ⁢
  
  ⁢
  
  1 0 - P ⁢
  
  ⁢
  
  1 island ) $if [ω_{0} - (\frac{ω_{0} - ω_{\min}}{P 1_{0} - P 1_{\max}}) (P 1_{0} - P 1_{island})] \geq ω_{switch} .$
4. The method of claim 1, wherein the microsource delivers a maximum output level P1_maxat a frequency ω
- _minwherein the microsource has a maximum operating frequency ω
  
  _max, $wherein ω_{island} \approx ω_{0} - (\frac{ω_{0} - ω_{\min}}{P 1_{0} - P 1_{\max}}) (P 1_{0} - P 1_{island})$ $if [ω_{0} - (\frac{ω_{0} - ω_{\min}}{P 1_{0} - P 1_{\max}}) (P 1_{0} - P 1_{island})] < ω_{\max}; and$ $wherein$ $ω_{island} \approx ω_{\max} if [ω_{0} - (\frac{ω_{0} - ω_{\min}}{P 1_{0} - P 1_{\max}}) (P 1_{0} - P 1_{island})] \geq ω_{\max} .$
5. The method of claim 1, wherein the microsource delivers a maximum power output level P1_maxat a frequency ω
- _min, wherein the microsource has a slope switch frequency ω
  
  _switch, wherein the microsource has a maximum operating frequency ω
  
  _max, $wherein ω_{island} \approx ω_{0} - (\frac{ω_{0} - ω_{\min}}{P 1_{0} - P 1_{\max}}) (P 1_{0} - P 1_{island})$ $if [ω_{0} - (\frac{ω_{0} - ω_{\min}}{P 1_{0} - P 1_{\max}}) (P 1_{0} - P 1_{island})] < ω_{switch};$ $wherein ω_{island} < ω_{0} - (\frac{ω_{0} - ω_{\min}}{P 1_{0} - P 1_{\max}}) (P 1_{0} - P 1_{island})$ $if ω_{switch} \leq [ω_{0} - (\frac{ω_{0} - ω_{\min}}{P 1_{0} - P 1_{\max}}) (P 1_{0} - P 1_{island})] < ω_{\max}; and$ $wherein$ $ω_{island} \approx ω_{\max} if [ω_{0} - (\frac{ω_{0} - ω_{\min}}{P 1_{0} - P 1_{\max}}) (P 1_{0} - P 1_{island})] \geq ω_{\max} .$
6. The method of claim 1, wherein the microsource delivers a maximum power output level P1_maxat a frequency ω
- _min, wherein the microsource has a minimum power output level P1_min, $wherein$ $P 1_{island} \approx P 1_{0} - (\frac{P 1_{0} - P 1_{\max}}{ω_{0} - ω_{\min}}) (ω_{0} - ω_{island})$ $if$ $P 1_{0} - (\frac{P 1_{0} - P 1_{\max}}{ω_{0} - ω_{\min}}) (ω_{0} - ω_{island}) > P 1_{\min};$ $and wherein$ $P 1_{island} \approx P 1_{\min}$ $if$ $P 1_{0} - (\frac{P 1_{0} - P 1_{\max}}{ω_{0} - ω_{\min}}) (ω_{0} - ω_{island}) \leq P 1_{\min} .$
7. The method of claim 6, wherein the microsource includes power storage such that P1_min<
- 0.
8. The method of claim 1, further comprising:
- providing a second microsource, wherein the second microsource is located in the microgrid, and further wherein the second microsource is configured to deliver a power P2 at a frequency ω
  
  2;
  
  operating the second microsource in the grid mode in which the second microsource is connected to the utility grid, wherein during operation in the grid mode, the frequency ω
  
  2 is approximately equal to the frequency ω
  
  _oand the power P2 is equal to a power P2_o; and
  
  transferring the second microsource from the grid mode to the island mode such that the second microsource is disconnected from the utility grid, wherein ω
  
  2 is approximately equal to ω
  
  _islandand P2 is equal to P2_islandduring operation in the island mode;
  
  wherein ω
  
  _island>
  
  ω
  
  _oand P2_island<
  
  P2_oif the microgrid was exporting power prior to the transfer from the grid mode to the island mode; and
  
  wherein ω
  
  _island<
  
  ω
  
  _oand P2_island>
  
  P2_oif the microgrid was importing power prior to the transfer from the grid mode to the island mode.
9. The method of claim 8, wherein (P1_island−
- P1₀)≈
  
  (P2_island−
  
  P2₀) such that an amount of change of P1 when the microsource is transferred from the grid mode to the island mode is approximately equal to an amount of change of P2 when the second microsource is transferred from the grid mode to the island mode.
10. The method of claim 8, further comprising providing a power slope m, and wherein ω
- _island≈
  
  ω
  
  ₀−
  
  m(P1₀−
  
  P1_island)≈
  
  ω
  
  ₀−
  
  m(P2₀−
  
  P2_island).
11. The method of claim 8, further comprising providing a power slope m, wherein the microsource has a minimum operating frequency ω
- min, wherein ω
  
  _island≈
  
  ω
  
  ₀−
  
  m(P1₀−
  
  P1_island)>
  
  ω
  
  _min; and
  
  wherein ω
  
  _island≈
  
  ω
  
  _minif ω
  
  ₀−
  
  m (P1₀−
  
  P1_island)≦
  
  ω
  
  _min.
12. The method of claim 8, further comprising providing a power slope m, wherein the microsource has a maximum operating frequency ω
- _max, wherein ω
  
  _island≈
  
  ω
  
  ₀−
  
  m(P1₀−
  
  P1_island)>
  
  ω
  
  _max; and
  
  wherein ω
  
  _island≈
  
  ω
  
  _maxif ω
  
  ₀−
  
  m(P1₀−
  
  P1_island)≦
  
  ω
  
  _max.
13. The method of claim 8, further comprising providing a power slope m, wherein the microsource has a minimum operating frequency ω
- _minand a maximum operating frequency ω
  
  _max, wherein ω
  
  _island≈
  
  _minif ω
  
  −
  
  m(P1₀−
  
  P1_island)≦
  
  ω
  
  _minwherein ω
  
  _island≈
  
  ω
  
  _max−
  
  m(P1₀−
  
  P1_island)>
  
  ω
  
  _min; and
  
  wherein ω
  
  _island≈
  
  ω
  
  _maxif ω
  
  ₀−
  
  m (P1₀−
  
  P1_island)≦
  
  ω
  
  _max.
14. The method of claim 1, wherein the microsource has a maximum power output level P1_max, a minimum power output level P1_min, and a minimum operating frequency ω
- _min, and wherein $ω_{island} \approx ω_{0} - (\frac{ω_{0} - ω_{\min}}{P 1_{\min} - P 1_{\max}}) (P 1_{0} - P 1_{island}) .$
15. The method of claim 1, wherein the microsource has a maximum power output level P1_max, a minimum power output level P1_min, and a minimum operating frequency ω
- _min, $Wherein$ $P 1_{island} \approx P 1_{0} - (\frac{P 1_{\min} - P 1_{\max}}{ω_{0} - ω_{\min}}) (ω_{0} - ω_{island})$ $if$ $P 1_{0} - (\frac{P 1_{\min} - P 1_{\max}}{ω_{0} - ω_{\min}}) (ω_{0} - ω_{island}) > P 1_{\min}$ $and wherein$ $P 1_{island} \approx P 1_{\min}$ $if$ $P 1_{0} - (\frac{P 1_{\min} - P 1_{\max}}{ω_{0} - ω_{\min}}) (ω_{0} - ω_{island}) \leq P 1_{\min} .$
16. The method of claim 1, wherein the microsource has a maximum power output level P1_max, a minimum power output level P1_min, and a minimum operating frequency ω
- _min, $wherein$ $P 1_{island} \approx P 1_{0} - (\frac{P 1_{\min} - P 1_{\max}}{ω_{0} - ω_{\min}}) (ω_{0} - ω_{island})$ $if$ $P 1_{0} - (\frac{P 1_{\min} - P 1_{\max}}{ω_{0} - ω_{\min}}) (ω_{0} - ω_{island}) < P 1_{\max}$ $and wherein$ $P 1_{island} \approx P 1_{\max}$ $if$ $P 1_{0} - (\frac{P 1_{\min} - P 1_{\max}}{ω_{0} - ω_{\min}}) (ω_{0} - ω_{island}) \leq P 1_{\max} .$
17. The method of claim 1 wherein the microsource has a maximum power output level P1_max, a minimum power output level P1_min, and a minimum operating frequency ω
- _min, $wherein$ $P 1_{island} \approx P 1_{\min}$ $if$ $P 1_{0} - (\frac{P 1_{\min} - P 1_{\max}}{ω_{0} - ω_{\min}}) (ω_{0} - ω_{island}) \leq P 1_{\min};$ $wherein$ $P 1_{island} \approx P 1_{0} - (\frac{P 1_{\min} - P 1_{\max}}{ω_{0} - ω_{\min}}) (ω_{0} - ω_{island})$ $if$ $P 1_{\min} < P 1_{0} - (\frac{P 1_{\min} - P 1_{\max}}{ω_{0} - ω_{\min}}) (ω_{0} - ω_{island}) < P 1_{\max};$ $and wherein$ $P 1_{island} \approx P 1_{\max}$ $if$ $P 1_{0} - (\frac{P 1_{\min} - P 1_{\max}}{ω_{0} - ω_{\min}}) (ω_{0} - ω_{island}) \geq P 1_{\max} .$

18. A microgrid comprising:
- a microsource comprising a power controller configured tocontrol a frequency ω
  
  1 and a power P1 of the microsource;
  
  operate the microsource in a grid mode in which the microsource is connected to a utility grid, and wherein the frequency ω
  
  1 is approximately equal to an operating frequency ω
  
  _oof the utility grid and the power P1 is equal to P1_o; and
  
  transfer the microsource to operate in an island mode in which the microsource is disconnected from the utility grid, wherein the frequency ω
  
  1 is equal to ω
  
  _islandand the power P1 is equal to P1_islandin the island mode;
  
  wherein ω
  
  _island>
  
  ω
  
  ₀, and P1_island<
  
  P1₀if the microgrid was exporting power prior to the transfer from the grid mode to the island mode;
  
  wherein ω
  
  _island<
  
  ω
  
  ₀, and P1_island>
  
  P1₀if the microgrid was importing power prior to the transfer from the grid mode to the island mode; and
  
  wherein the microsource delivers a maximum power output level P1_maxat a frequency ω
  
  _min, wherein the microsource has a slope switch frequency ω
  
  _switch, wherein $ω_{island} \approx ω_{0} - (\frac{ω_{0} - ω_{\min}}{P 1_{0} - P 1_{\max}}) (P 1_{0} - P 1_{island})$ $if [ω_{0} - (\frac{ω_{0} - ω_{\min}}{P 1_{0} - P 1_{\max}}) (P 1_{0} - P 1_{island})] < ω_{switch};$
- View Dependent Claims (19, 20, 21, 22, 23, 24, 25, 26, 27)
- - 19. The microgrid of claim 18, wherein the microsource delivers a maximum power output level P1_maxat a frequency ω
    - _min, and wherein
20. The microgrid of claim 18, $wherein$ $ω$
- island <
  
  ω
  
  0 - ( ω
  
  0 - ω
  
  min P ⁢
  
  ⁢
  
  1 0 - P ⁢
  
  ⁢
  
  1 max ) ⁢
  
  ( P ⁢
  
  ⁢
  
  1 0 - P ⁢
  
  ⁢
  
  1 island ) $if [ω_{0} - (\frac{ω_{0} - ω_{\min}}{P 1_{0} - P 1_{\max}}) (P 1_{0} - P 1_{island})] \geq ω_{switch} .$
21. The microgrid of claim 18, wherein the microsource delivers a maximum power output level P1_maxat a frequency ω
- _min, wherein the microsource has a slope switch frequency ω
  
  _switch, wherein the microsource has a maximum operating frequency ω
  
  _max, $wherein$ $ω_{island} \approx ω_{0} - (\frac{ω_{0} - ω_{\min}}{P 1_{0} - P 1_{\max}}) (P 1_{0} - P 1_{island}) if [ω_{0} - (\frac{ω_{0} - ω_{\min}}{P 1_{0} - P 1_{\max}}) (P 1_{0} - P 1_{island})] < ω_{switch};$ $wherein$ $ω_{island} < ω_{0} - (\frac{ω_{0} - ω_{\min}}{P 1_{0} - P 1_{\max}}) (P 1_{0} - P 1_{island})$ $if ω_{switch} \leq [ω_{0} - (\frac{ω_{0} - ω_{\min}}{P 1_{0} - P 1_{\max}}) (P 1_{0} - P 1_{island})] < ω_{\max};$ $wherein$ $ω_{island} \approx ω_{\max} if [ω_{0} - (\frac{ω_{0} - ω_{\min}}{P 1_{0} - P 1_{\max}}) (P 1_{0} - P 1_{island})] \geq ω_{\max} .$
22. The microgrid of claim 18, wherein the microsource delivers a maximum power output level P1_maxat a frequency ω
- _min, wherein the microsource has a minimum power output level P1_min, $wherein$ $P 1_{island} \approx P 1_{0} - (\frac{P 1_{0} - P 1_{\max}}{ω_{0} - ω_{\min}}) (ω_{0} - ω_{island})$ $if P 1_{0} - (\frac{P 1_{0} - P 1_{\max}}{ω_{0} - ω_{\min}}) (ω_{0} - ω_{island}) > P 1_{\min}; and$ $wherein$ $P 1_{island} \approx P 1_{\min} if P 1_{0} - (\frac{P 1_{0} - P 1_{\max}}{ω_{0} - ω_{\min}}) (ω_{0} - ω_{island}) \leq P 1_{\min} .$
23. The microgrid of claim 22, wherein the microsource further comprises a power storage unit such that P1_min<
- 0.
24. The microgrid of claim 18, wherein the microsource has a maximum power output level P1_max, a minim urn power output level P1_min, and a minimum operating frequency ω
- _min, and wherein $ω_{island} \approx ω_{0} - (\frac{ω_{0} - ω_{\min}}{P 1_{\min} - P 1_{\max}}) (P 1_{0} - P 1_{island}) .$
25. The microgrid of claim 18, wherein the microsource has a maximum power output level P1_max, a minimum power output level P1_min, and a minimum operating frequency ω
- _min, $P 1_{island} \approx P 1_{0} - (\frac{P 1_{\min} - P 1_{\max}}{ω_{0} - ω_{\min}}) (ω_{0} - ω_{island})$ $if P 1_{0} - (\frac{P 1_{\min} - P 1_{\max}}{ω_{0} - ω_{\min}}) (ω_{0} - ω_{island}) > P 1_{\min};$ $and wherein$ $P 1_{island} \approx P 1_{\min}$ $if$ $P 1_{0} - (\frac{P 1_{\min} - P 1_{\max}}{ω_{0} - ω_{\min}}) (ω_{0} - ω_{island}) \leq P 1_{\min} .$
26. The microgrid of claim 25, wherein the microsource further comprises a power storage unit such that P1_min<
- 0.
27. The microgrid of claim 18, wherein the microsource has a maximum power output level P1_max, a minimum power output level P1_min, and a minimum operating frequency ω
- _min, $P 1_{island} \approx P 1_{0} - (\frac{P 1_{\min} - P 1_{\max}}{ω_{0} - ω_{\min}}) (ω_{0} - ω_{island})$ $if P 1_{0} - (\frac{P 1_{\min} - P 1_{\max}}{ω_{0} - ω_{\min}}) (ω_{0} - ω_{island}) < P 1_{\max};$ $and wherein$ $P 1_{island} \approx P 1_{\max}$ $if$ $P 1_{0} - (\frac{P 1_{\min} - P 1_{\max}}{ω_{0} - ω_{\min}}) (ω_{0} - ω_{island}) \geq P 1_{\max} .$

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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)
Paladini; Albert W
Assistant Examiner(s)
KAPLAN, HAL IRA

Application Number

US11/084,737
Publication Number

US 20060208574A1
Time in Patent Office

1,838 Days
Field of Search

307/65, 307/69
US Class Current

307/69
CPC Class Codes

H02J 3/38 Arrangements for parallely ...

H02J 3/388 Islanding, i.e. disconnecti...

Control of small distributed energy resources

First Claim

3 Assignments

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Abstract

Citations

27 Claims

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Control of small distributed energy resources

First Claim

3 Assignments

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Abstract

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27 Claims

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