System and method for providing grid-forming control for a double-fed wind turbine generator

1. A method for controlling a wind turbine power system connected to an electrical grid, the wind turbine power system having a double-fed wind turbine generator coupled to a power converter having a line-side converter and a rotor-side converter coupled together via a DC link, the method comprising:

determining, via a controller, at least one non-linear magnetizing parameter of the double-fed wind turbine generator, wherein determining the at least one non-linear magnetizing parameter of the double-fed wind turbine generator comprises:

(a) providing a plurality of data arrays comprising, at least, a data array of operating data points and a data array of non-linear magnetizing parameter data points;

(b) enabling rotor control of the double-fed wind turbine generator with a stator switch open;

(c) setting an operating set point of the double-fed wind turbine generator equal to a first operating data point in the data array of operating data points;

(d) controlling the rotor-side converter to the operating set point and frequency for a time period;

(e) collecting current and voltage feedbacks for the time period; and

(f) calculating the at least one non-linear magnetizing parameter based on the current and voltage feedbacks for the time period;

developing, via the controller, a model of the at least one non-linear magnetizing parameter of the double-fed wind turbine generator; and,

using, via the controller, the model in a stator voltage regulator of the double-fed wind turbine generator to provide grid-forming control of the double-fed wind turbine generator.

2. The method of claim 1 , wherein the at least one non-linear magnetizing parameter comprises magnetizing reactance.

3. The method of claim 1 , further comprising:

(g) storing the operating set point and the at least one non-linear magnetizing parameter together in a data array;

(h) setting the operating set point of the double-fed wind turbine generator equal to a remainder of the operating data points in the data array for subsequent time periods; and,

(i) repeating steps (d) through (g) for each of the operating data points in the data array for the subsequent time period.

4. The method of claim 1 , wherein determining the at least one non-linear magnetizing parameter of the double-fed wind turbine generator further comprises:

averaging the collected current and voltage feedbacks for the time period to remove noise; and,

calculating the at least one non-linear magnetizing parameter based on the averaged current and voltage feedbacks for the time period.

5. The method of claim 1 , wherein the data array of operating data points comprises at least one of flux data points or stator voltage data points.

6. The method of claim 1 , wherein the data array of operating data points comprise, at least, a range of expected operating data points that the double-fed wind turbine generator is expected to operate during normal operation.

7. The method of claim 1 , wherein the data array of operating data points further comprise one or more additional data points to capture operating data points beyond the normal operation to estimate one or more characteristics of the double-fed wind turbine generator for at least one of abnormal conditions or temporary conditions.

8. The method of claim 1 , wherein developing the model of the at least one non-linear magnetizing parameter of the double-fed wind turbine generator further comprises:

creating a saturation curve of the at least one non-linear magnetizing parameter versus the operating set point.

9. The method of claim 8 , wherein the saturation curve comprises a piecewise-linear curve fit.

10. The method of claim 1 , further comprising determining the at least one non-linear magnetizing parameter automatically using existing converter hardware and feedbacks.

11. The method of claim 8 , wherein using the model in the stator voltage regulator of the double-fed wind turbine generator to provide grid-forming control of the double-fed wind turbine generator further comprises:

calculating an expected magnetizing reactance at a desired flux level using a stator flux command with slopes and y-intercepts of the saturation curve;

calculating a magnetizing current feed forward signal based on the expected magnetizing reactance;

calculating a magnetizing current command signal based on the magnetizing current feed forward signal and a magnetizing current correction signal; and,

calculating a rotor current command signals using the magnetizing current command signal and a stator current feedback signals.

12. A system for controlling a wind turbine power system connected to an electrical grid, the wind turbine power system having a double-fed wind turbine generator coupled to a power converter having a line-side converter and a rotor-side converter coupled together via a DC link, the system comprising:

a controller comprising at least one processor, the at least one processor configured to perform a plurality of operations, the plurality of operations comprising:

determining at least one non-linear magnetizing reactance of the double-fed wind turbine generator, wherein determining the at least one non-linear magnetizing parameter of the double-fed wind turbine generator comprises:

(a) providing a plurality of data arrays comprising, at least, a data array of operating data points and a data array of non-linear magnetizing parameter data points;

(b) enabling rotor control of the double-fed wind turbine generator with a stator switch open;

(c) setting an operating set point of the double-fed wind turbine generator equal to a first operating data point in the data array of operating data points;

(d) controlling the rotor-side converter to the operating set point and frequency for a time period;

(e) collecting current and voltage feedbacks for the time period; and

(f) calculating the at least one non-linear magnetizing parameter based on the current and voltage feedbacks for the time period;

developing a model of the at least one non-linear magnetizing reactance of the double-fed wind turbine generator; and,

using the model in a stator voltage regulator of the double-fed wind turbine generator to provide grid-forming control of a double-fed wind turbine generator.

13. The system of claim 12 , further comprising:

(g) storing the operating set point and the at least one non-linear magnetizing reactance together in a data array;

(h) setting the operating set point of the double-fed wind turbine generator equal to a remainder of the operating data points in the data array for subsequent time periods; and,

(i) repeating steps (d) through (g) for each of the operating data points in the data array for the subsequent time period.

14. The system of claim 12 , wherein determining the at least one non-linear magnetizing reactance of the double-fed wind turbine generator further comprises:

averaging the collected current and voltage feedbacks for the time period to remove noise; and,

calculating the at least one non-linear magnetizing reactance based on the averaged current and voltage feedbacks for the time period.

15. The system of claim 12 , wherein the data array of operating data points comprises at least one of flux data points or stator voltage data points.

16. The system of claim 12 , wherein developing the model of the at least one non-linear magnetizing reactance of the double-fed wind turbine generator further comprises:

creating a saturation curve of the at least one non-linear magnetizing reactance versus the operating set point.

17. The system of claim 12 , further comprising determining the at least one non-linear magnetizing reactance automatically using existing converter hardware and feedbacks.

18. The system of claim 16 , wherein using the model in the stator voltage regulator of the double-fed wind turbine generator to provide grid-forming control of the double-fed wind turbine generator further comprises:

calculating an expected magnetizing reactance at a desired flux level using a stator flux command with slopes and y-intercepts of the saturation curve;

calculating a magnetizing current feed forward signal based on the expected magnetizing reactance;

calculating a magnetizing current command signal based on the magnetizing current feed forward signal and a magnetizing current correction signal; and

calculating a rotor current command signals using the magnetizing current command signal and a stator current feedback signals.