Generator set adaptive droop control method

• US 8,841,787 B1
• Filed: 03/15/2013
• Issued: 09/23/2014
• Est. Priority Date: 03/15/2013
• Status: Active Grant

• Current Assignee: Caterpillar Incorporated
• Original Assignee: Caterpillar Incorporated
• Inventors: Folken, Keith, Meinhart, Matthew Joseph, Schroeder, Edward Maurer, Black, Andrew William
• Primary Examiner(s): Cuevas, Pedro J
• Application Number:
  US13/832,946
• Publication Number:
  US 20140265354A1
• Time in Patent Office: 557 Days
• Field of Search: 290/7, 290/40.E, 700/287, 700/292, 700/295, 363/71, 307/84
• US Class Current: 290/40.E
• CPC Class Codes: H02J 3/46 Controlling of the sharing of output between the generators, converters, or transformers
• CPC Class Codes: H02P 9/42 to obtain desired frequency without varying speed of the generator

Abstract

A method of controlling a plurality of gensets during a failsafe condition is provided. The method may include operating one or more of the gensets according to a modified isochronous control scheme, and operating a remainder of the gensets according an adaptive droop control scheme. The modified isochronous control scheme may include varying the frequency of each isochronous genset with respect to load for lower-range loads and upper-range loads, and maintaining the frequency of each isochronous genset at nominal frequencies for mid-range loads. The adaptive droop control scheme may include adjusting the frequency of each droop genset to match the frequency of the isochronous gensets, and varying the load of each droop genset with respect to frequency for lower-range loads and upper-range loads.

Claims

1. A method of controlling a plurality of gensets during a failsafe condition, the method comprising:

operating a remainder of the gensets according an adaptive droop control scheme, the adaptive droop control scheme adjusting the frequency of each droop genset to match that of one or more isochronous gensets, and varying the load of each droop genset with respect to frequency for lower-range loads and upper-range loads.

2. The method of claim 1, wherein the method further comprises operating one or more of the gensets according to a modified isochronous control scheme, the modified isochronous control scheme varying the frequency of each isochronous genset with respect to load for lower-range loads and upper-range loads, and maintaining the frequency of each isochronous genset at nominal frequencies for mid-range loads.

3. The method of claim 1, wherein the failsafe condition is triggered by at least a loss of communication between one or more of the gensets.

4. The method of claim 1, wherein a modified isochronous control scheme is employed to increase the frequency of each isochronous genset for lower-range loads, and decreases the frequency of each isochronous genset for upper-range loads, while the adaptive droop control scheme decreases the load of each droop genset if the frequency is increased, and increases the load of each droop genset if the frequency is decreased.

5. The method of claim 1, wherein the frequency of each isochronous genset is varied with respect to load for lower-range loads and for upper-range loads at substantially the same rate.

6. The method of claim 1, wherein lower-range loads correspond to loads at which the gensets exhibit resistance to decreases in load, and upper-range loads correspond to loads at which the gensets exhibit resistance to increases in load.

7. The method of claim 1, wherein the load of each droop genset is varied with respect to frequency at a first rate for lower-range loads and at a second rate for upper-range loads, each of the first rate and the second rate being adaptively calculated based on a predefined droop limit, a last-known frequency of the droop genset, and a last-known load of the droop genset.

8. The method of claim 7, wherein the droop limit defines at least a lower frequency limit corresponding to a maximum load, and an upper frequency limit corresponding to a minimum load, the first rate being calculated based on a difference between the upper frequency limit and the last-known frequency and a difference between the minimum load and the last-known load of the droop genset, the second rate being calculated based on a difference between the lower frequency limit and the last-known frequency and a difference between the maximum load and the last-known load of the droop genset.

9. An adaptive droop control system for controlling a plurality of gensets during a failsafe condition, the adaptive control system comprising:

at least one controller in electrical communication with one or more of the plurality of gensets, the common bus, and the load, the controller being configured to;

operate one or more of the gensets according to an adaptive droop control scheme, the adaptive droop control scheme configuring the controller to adjust the frequency of each droop genset to match that of one or more isochronous gensets, and vary the load of each droop genset with respect to frequency for lower-range loads and upper-range loads.

10. The adaptive droop control system of claim 9, wherein the controller further operates one or more remaining gensets according to a modified isochronous control scheme, the modified isochronous control scheme configuring the controller to vary the frequency of each isochronous genset with respect to load for lower-range loads and upper-range loads, and maintain the frequency of each isochronous genset at nominal frequencies for mid-range loads.

11. The adaptive droop control system of claim 9, wherein the failsafe condition is triggered by at least a loss of communication between one or more of the gensets, the controller being configured to detect the loss of communication.

12. The adaptive droop control system of claim 9, wherein a modified isochronous control scheme is employed to configure the controller to increase the frequency of each isochronous genset for lower-range loads, and decrease the frequency of each isochronous genset for upper-range loads, while the adaptive droop control scheme configures the controller to decrease the load of each droop genset if the frequency is increased, and increase the load of each droop genset if the frequency is decreased.

13. The adaptive droop control system of claim 9, wherein lower-range loads correspond to loads at which the gensets exhibit resistance to decreases in load, and upper-range loads correspond to loads at which the gensets exhibit resistance to increases in load.

14. The adaptive droop control system of claim 9, wherein controller is configured to vary the frequency of each isochronous genset with respect to load for lower-range loads and for upper-range loads at substantially the same rate.

15. The adaptive droop control system of claim 9, wherein the controller is configured to vary the load of each droop genset with respect to frequency at a first rate for lower-range loads and at a second rate for upper-range loads, each of the first rate and the second rate being adaptively calculated based on a predefined droop limit, a last-known frequency of the droop genset, and a last-known load of the droop genset.

16. The adaptive droop control system of claim 15, wherein the droop limit defines at least a lower frequency limit corresponding to a maximum load, and an upper frequency limit corresponding to a minimum load, the controller being configured to calculate the first rate based on a difference between the upper frequency limit and the last-known frequency and a difference between the minimum load and the last-known load of the droop genset, and calculate the second rate based on a difference between the lower frequency limit and the last-known frequency and a difference between the maximum load and the last-known load of the droop genset.

17. A genset system, comprising:

a plurality of gensets, each genset having a primary power source and an electric machine configured to generate electrical power;

a common bus coupled to each of the gensets and configured to communicate the electrical power generated by the gensets to a connected load; and

at least one controller in electrical communication with one or more of the plurality of gensets, the common bus, and the load, the controller being configured to operate one or more of the gensets according to an adaptive droop control scheme during a failsafe condition, the adaptive droop control scheme varying load with respect to frequency for lower-range loads and upper-range loads.

18. The genset system of claim 17, wherein the controller is configured to operate any one or more remaining gensets according to a modified isochronous control scheme, the modified isochronous control scheme varying frequency with respect to load for lower-range loads and upper-range loads.

19. The genset system of claim 17, wherein one or more of the gensets are operated according to a modified isochronous control scheme, the modified isochronous control scheme configuring the controller to increase the frequency of each isochronous genset for lower-range loads, maintain the frequency of each isochronous genset at nominal frequencies for mid-range loads, and decrease the frequency of each isochronous genset for upper-range loads, while the adaptive droop control scheme configures the controller to decrease the load of each droop genset if the frequency is increased, and increase the load of each droop genset if the frequency is decreased.

20. The genset system of claim 17, wherein the controller is further configured to:

vary the load of each droop genset with respect to frequency at a first rate for lower-range loads and at a second rate for upper-range loads, each of the first rate and the second rate being adaptively calculated based on a predefined droop limit, a last-known frequency of the droop genset, and a last-known load of the droop genset, the droop limit defining at least a lower frequency limit corresponding to a maximum load, and an upper frequency limit corresponding to a minimum load,

calculate the first rate based on a difference between the upper frequency limit and the last-known frequency and a difference between the minimum load and the last-known load of the droop genset, and

calculate the second rate based on a difference between the lower frequency limit and the last-known frequency and a difference between the maximum load and the last-known load of the droop genset.