Methods, systems, computer program products, and devices for renewable energy site power limit control

• US 9,270,164 B2
• Filed: 06/19/2013
• Issued: 02/23/2016
• Est. Priority Date: 06/19/2013
• Status: Active Grant

• Current Assignee: TMEIC Corp. Americas
• Original Assignee: Tmeic Corporation (Toshiba Corporation)
• Inventors: Bixel, Paul S., Rudolph, Benjamin D.
• Primary Examiner(s): Pham, Emily P
• Application Number:
  US13/921,788
• Publication Number:
  US 20140376289A1
• Time in Patent Office: 979 Days
• US Class Current: 1/1
• CPC Class Codes: H02J 2300/20 The dispersed energy generation being of renewable origin
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02J 3/46 Controlling of the sharing of output between the generators, converters, or transformers
• CPC Class Codes: H02M 1/42 Circuits or arrangements for compensating for or adjusting power factor in converters or inverters
• CPC Class Codes: H02M 7/493 the static converters being arranged for operation in parallel
• CPC Class Codes: Y02E 10/76 Power conversion electric or electronic aspects

Abstract

The present invention provides methods, systems, computer program products, and devices for renewable energy site power limit control that address conditions of plant saturation and loop delay. In an exemplary embodiment, power limit control of the present invention is broken into two levels of control: a site-wide real power limit control that produces a single site-wide command, SitePlimCom, for all inverters, and inverter-level power limit control that outputs a command, Inv[x].PlimCom[k], for individual inverters. In some embodiments, the invention has one or more of the following features: an integrator with nonlinear gains, limit based anti-windup, a power limit control term based on the sum of both integrator and feed-forward terms, and an inverter-level controller designed to meet slew rate and site power overshoot constraints. The invention can be used at any renewable energy site employing inverters wherein improved dynamic control performance is needed, including solar, wind, and tidal energy sites.

Claims

1. A method of power limit control for a renewable energy site comprising:

generating a site-wide power limit command by;

calculating a feed-forward power limit reference PlimRef[k];

integrating an error integral term; and

adding said feed-forward power limit reference to said error integral term to yield said site-wide power limit command for the renewable energy site; and

dividing said site-wide power limit command by a number of enabled inverters at the renewable energy site to obtain an individual inverter command.

2. The method of claim 1 comprising Loop Delay compensation wherein said Loop Delay compensation is implemented by setting delay term D to a nonzero number corresponding to loop delay in either of two cases:

subtracting present inverter feedback signal from a corresponding reference generated LoopDelay seconds prior in order to compute an integration error increment;

or

basing inverter level power limit maximum on an inverter command generated LoopDelay seconds prior.

3. The method of claim 1 comprising generating an individual inverter power limit command from either:

i) a maximum based on said inverter power limit command and feedback;

or ii) a slew rate limit to said site-wide power limit command.

4. The method of claim 1 comprising calculating a power limit integrator limit and calculating a power limit integrator increment.

5. The method of claim 1, wherein said calculating of said feed-forward power limit reference is performed by a power limit reference slew control process comprising:

providing site inverter power feedback and an operator power limit reference; and

calculating said power limit reference based on;

i) an upper limit based on said site inverter power feedback and said operator power limit reference;

ii) a slew increment; and

iii) said operator power limit reference.

6. The method of claim 1 comprising loop delay compensation of said feed-forward power limit reference, wherein said loop delay compensation comprises offsetting said feed-forward power limit reference by a delay term D to yield PlimRef[k-D].

7. The method of claim 6, wherein said loop delay compensation is implemented by setting the delay term D to a nonzero number corresponding to a loop delay.

8. The method of claim 4, wherein said power limit integrator limit is calculated based on one or more of:

i) a PlimRef[k-D];

ii) maximum inverter power feedback;

iii) number of enabled inverters; and

iv) site rated power limit reference.

9. The method of claim 4 wherein said power limit integrator increment is calculated by performing one or more of:

i) multiplying a site power error and a gain which depends on a number of saturated inverters;

or ii) subtracting site inverter power feedback from said PlimRef[k] or PlimRef[k-D] to generate an error term and scaling said error term by a saturation gain term and a constant Ki to generate a scaled error term.

10. The method of claim 9, wherein said scaled error term is integrated by:

i) providing said scaled error term; and

ii) integrating said scaled error term until it reaches an integrator limit to provide said error integral term.

11. The method of claim 10, wherein windup of said scaled error term integration is minimized:

i) by said integrator limit;

or ii) by halting the scaled error term integration when one or more applies;

(a) a number of inverters free to produce more power (NumInvFree) is zero;

or (b) said scaled error term reduces an absolute value of said error integral term.

12. The method of claim 10, wherein said error integral term is added to said PlimRef[k] to provide a numerator for a power limit command distribution.

13. The method of claim 12, wherein said power limit command distribution comprises dividing said numerator by said number of enabled inverters to generate a distributed site power limit command.

14. The method of claim 1, wherein an inverter power limit command upper limit is calculated as a function of said inverter power limit command and inverter power feedback.

15. The method of claim 1, wherein said inverter power limit command is calculated based on an inverter power limit command slew control process as a function of:

i) an inverter power command upper limit;

or

ii) a slew rate limit, which is applied when the inverter is detected as open loop and is a function of a slew rate increment; and

iii) said site-wide power limit command.

16. A system of power limit control for a renewable energy site comprising:

one or more inverters; and

a power limit controller in operable communication with at least one of the one or more inverters and operably configured to generate a site-wide power limit command by;

calculating a feed-forward power limit reference PlimRef[k];

integrating an error integral term;

adding said feed-forward power limit reference to said error integral term to yield said site-wide power limit command for the renewable energy site; and

dividing said site-wide power limit command by a number of enabled inverters at the renewable energy site to obtain an individual inverter command.

17. The system of claim 16 comprising distributing said site power limit command among some or all of said one or more inverters which are enabled at the renewable energy site.

18. The system of claim 16 wherein the power limit controller is operably configured to generate an inverter power limit command.