Generator dispatching or load shedding control method and system for microgrid applications

Patent metadata

Field	Value
Publication number	US-10008853-B2
Application number	US-201615265017-A
Country	US
Kind code	B2
Filing date	Sep 14, 2016
Priority date	Oct 8, 2012
Publication date	Jun 26, 2018
Grant date	Jun 26, 2018

Abstract

A microgrid power generation system includes a plurality of generators having a plurality of different rated capacities and a plurality of distribution nodes, at least some of the distribution nodes being powered by the generators. A grid is formed by the distribution nodes, the grid includes a system frequency. A plurality of loads are powered by the grid through the distribution nodes, the loads have a power demand. A processor includes a plurality of efficiency bands, each of the efficiency bands being for a corresponding one of the generators and including a plurality of generator switching points based upon droop of the system frequency and the power demand of the loads. The processor is structured to operate the generators and the loads under transient conditions based upon the efficiency bands.

First claim

What is claimed is:

1. A load shedding control method for a microgrid, said method comprising:
employing a plurality of generators;
employing a plurality of distribution nodes;
powering at least some of said distribution nodes by said generators;
forming a grid by said distribution nodes, said grid including a system frequency;
powering a plurality of loads by said grid through said distribution nodes; and
measuring the system frequency of said grid, comparing the measured system frequency to a frequency threshold to generate a comparison result representing a difference between the system frequency and the frequency threshold, and responsive to and based on the comparison result shedding by a processor a number of said loads from said grid or prohibiting additional load to said grid.

2. The load shedding control method of claim 1 further comprising:
providing at least one of:
not shedding said loads for transient frequency dips of the system frequency from which the microgrid will recover,
immediately shedding a number of said loads in order to prevent stalling of a number of said generators, and
permitting the measured system frequency to be less than the frequency threshold for a predetermined period of time before a number of said loads are shed.

3. The load shedding control method of claim 1 further comprising:
defining an input value equal to the system frequency less the frequency threshold;
providing an output having a value of zero if the input value is greater than or equal to zero, or otherwise said input value;
feeding the value of said output through a function having a value;
subtracting a value from the value of said function to provide a result;
adding the result to an accumulator or a discrete-time integration function having a value;
normalizing the value of the accumulator to a maximum value;
assigning said loads corresponding shedding thresholds; and
shedding a number of said loads based upon the value of said accumulator and the corresponding shedding thresholds.

4. The load shedding control method of claim 1 further comprising:
employing as said frequency threshold a rated droop frequency of one of said generators.

5. The load shedding control method of claim 3 further comprising:
employing as said function having the value a squaring function.

6. A load shedding system comprising:
a plurality of generators;
a plurality of distribution nodes, at least some of said distribution nodes being powered by said generators;
a grid formed by said distribution nodes, said grid including a system frequency;
a plurality of loads powered by said grid through said distribution nodes; and
a processor including a frequency-based load shedding routine structured to measure the system frequency of said grid, compare the measured system frequency to a frequency threshold to generate a result representing a difference between the system frequency and the frequency threshold, and responsive to and based on the result shed a number of said loads from said grid or prohibit additional load to said grid.

7. The load shedding system of claim 6 wherein said frequency-based load shedding routine is further structured to define an input value equal to the system frequency less the frequency threshold, provide an output having a value of zero if the input value is greater than or equal to zero, or otherwise said input value, feed the value of said output through a function having a value, subtract a value from the value of said function to provide a result, add the result to an accumulator or a discrete-time integration function having a value, normalize the value of the accumulator to a maximum value, assign said loads corresponding shedding thresholds, and shed a number of said loads based upon the value of said accumulator and the corresponding shedding thresholds.

8. The load shedding system of claim 6 wherein said grid is a microgrid operating in an islanded mode.

9. The load shedding system of claim 6 wherein the frequency-based load shedding routine is further structured to provide emergency load shedding to immediately shed a number of said loads in order to prevent a number of said generators from stalling, and non-emergency load shedding.

10. The load shedding system of claim 6 wherein the frequency-based load shedding routine is further structured to not shed said loads for transient frequency dips of said system frequency from which the load shedding system will recover.

11. The load shedding system of claim 6 wherein the frequency-based load shedding routine is further structured to immediately shed a number of said loads in order to prevent stalling of a number of said generators.

12. The load shedding system of claim 6 wherein the frequency-based load shedding routine is further structured to permit the measured system frequency to be less than the frequency threshold for a predetermined period of time before a number of said loads are shed.

13. The load shedding system of claim 12 wherein after said predetermined period of time, said number of said loads are shed until said system frequency is greater than the frequency threshold.

14. The load shedding system of claim 12 wherein said predetermined period of time permits dispatching of extra generation.

15. The load shedding system of claim 7 wherein the frequency-based load shedding routine includes a table having a high threshold value and a low threshold value for each of said loads; wherein a corresponding one of said loads is shed when the value of said accumulator is greater than the high threshold value of the corresponding one of said loads; and wherein the corresponding one of said loads is reapplied to said grid when the value of said accumulator is less than the low threshold value of the corresponding one of said loads.

16. The load shedding system of claim 8 wherein one of said distribution nodes is powered by an energy store and a DC/AC inverter or battery interface module.

Assignees

• Eaton Corp
• Eaton Intelligent Power Ltd

Inventors

• Piyabongkarn Damrongrit
• Buck Edward F
• Dimino Steven A

Classifications

• H02J3/04

  Arrangements for connecting networks of the same frequency but supplied from different sources · CPC title

• G05F1/66

  Regulating electric power · CPC title

• Y02P80/14

  District level solutions, i.e. local energy networks · CPC title

• H02J3/381 Primary

  Dispersed generators · CPC title

• H02J3/38

  Arrangements for feeding a single network from two or more generators or sources in parallel; Arrangements for feeding already energised networks from additional generators or sources in parallel · CPC title