System and methods to address drive train damper oscillations in a grid forming power generating asset

1. A method for providing grid-forming control of a double-fed generator connected to a power grid, the method comprising:

determining, via a frequency module of a controller, a stator-frequency error for the generator;

determining, via a controller shaping module of the frequency module, a torsional component and a stator component of the stator-frequency error, wherein the torsional component corresponds to a drivetrain torsional vibration frequency;

determining, via the frequency module, a power output requirement for the generator based, at least in part, on the stator component of the stator-frequency error;

combining, via the frequency module, the power output requirement with a damping power command to develop a consolidated power requirement for the generator, wherein the damping power command is generated in response to the drivetrain torsional vibration frequency;

determining, via the controller, at least one control command for the generator, based, at least in part, on the consolidated power requirement; and

changing an operating state of the generator in response to the at least one control command so as to output a grid-forming voltage and frequency.

2. The method of claim 1 , wherein the stator-frequency error comprises a difference between a reference frequency and a stator-output frequency.

3. The method of claim 2 , wherein determining the at least one control command for the generator further comprises:

determining, via the controller, a rotor voltage setpoint based, at least in part, on the consolidated power requirement.

4. The method of claim 2 , further comprising:

monitoring, via the controller, a three-phase stator voltage and current of the generator;

transforming the three-phase stator voltage and current via an abc-to-dq transfer module of the controller to a d-q reference frame so as to determine a d-component and a q-component for the current and voltage; and

determining, via a phase locked loop module of the controller, the stator-output frequency.

5. The method of claim 4 , wherein the stator component of the stator-output frequency comprises a DC value, and wherein the torsional component of the stator-output frequency comprises a sinusoidal frequency.

6. The method of claim 5 , wherein determining the torsional component and the stator component of the stator-frequency error further comprises:

establishing, via the frequency module, a gain value of zero at the torsional vibration frequency; and

establishing, via the frequency module, a non-zero gain value for values of the stator-frequency error which do not correspond to the torsional vibration frequency.

7. The method of claim 6 , wherein the non-zero gain value has a maximal value when the stator-frequency error has a minimal value and decreases with an increase in the stator-frequency error.

8. The method of claim 4 , further comprising:

determining, via a voltage module of the controller, a stator-voltage error for the generator, the stator-voltage error comprising a difference between a reference voltage and a stator-output voltage, wherein the stator-output voltage is the q-component of the stator voltage; and

determining, via the voltage module, a required rotor voltage d-component based, at least in part, on the stator-voltage error.

9. The method of claim 8 , wherein determining the at least one control command for the generator further comprises:

determining, via the frequency module, a required rotor voltage q-component based, at least in part, on the consolidated power requirement; and

combining, via a dq-to-abc transform module of the controller, the required rotor voltage d-component and the required rotor voltage q-component to generate a rotor voltage setpoint.

10. The method of claim 2 , further comprising:

receiving, via the controller, the reference frequency, wherein the reference frequency corresponds to an output frequency of the generator required to support the frequency of the power grid; and

receiving, via the controller, the reference voltage, wherein the reference voltage corresponds to an output voltage magnitude of the generator required to support the power grid.

11. The method of claim 1 , wherein the damping power command is generated by a drivetrain-damping module configured to damp torsional vibrations resulting from a transient grid event.

12. The method of claim 11 , further comprising:

detecting, via the controller, an oscillation in a power output of a power generating asset during a transient-event recovery phase following the transient grid event; and

in response to detecting the oscillation, storing at least a portion of the oscillatory power in an energy storage device operably coupled to the generator.

13. A system for operating a power generating asset so as to provide grid forming control, the system comprising:

a double-fed generator connected to a power grid; and

a controller communicatively coupled to the generator, the controller comprising at least one processor and a plurality of modules configured to perform a plurality of operations, the plurality of operations comprising:

determining, via a frequency module of the controller, a stator-frequency error for the generator, wherein the stator-frequency error comprises a difference between a reference frequency and a stator-output frequency;

determining, via a controller shaping module of the frequency module, a torsional component and a stator component of the stator-frequency error, wherein the torsional component corresponds to a drivetrain torsional vibration frequency;

determining, via the frequency module, a power output requirement for the generator based, at least in part, on the stator component of the stator-frequency error;

combining, via the frequency module, the power output requirement with a damping power command to develop a consolidated power requirement for the generator, wherein the damping power command is generated in response to the drivetrain torsional vibration frequency;

determining at least one control command for the generator, based, at least in part, on the consolidated power requirement; and

changing an operating state of the generator in response to the at least one control command so as to output a grid-forming voltage and frequency.

14. The system of claim 13 , wherein determining the at least one control command for the generator further comprises:

determining a rotor voltage setpoint based, at least in part, on the consolidated power requirement.

15. The system of claim 13 , wherein the plurality of operations further comprise:

monitoring a three-phase stator voltage and current of the generator;

transforming the three-phase stator voltage and current via an abc-to-dq transfer module of the controller to a d-q reference frame so as to determine a d-component and q-component for the current and voltage; and

determining, via a phase locked loop module of the controller, the stator-output frequency.

16. The system of claim 15 , wherein the stator component of the stator-output frequency comprises a DC value, and wherein the torsional component of the stator-output frequency comprises a sinusoidal frequency.

17. The system of claim 16 , wherein determining the torsional component and the stator component of the stator-frequency error further comprises:

establishing, via the frequency module, a zero gain value at the torsional vibration frequency; and

establishing, via the frequency module, a non-zero gain value for values of the stator-frequency error which do not correspond to the torsional vibration frequency.

18. The system of claim 15 , wherein the plurality of operations further comprise:

determining, via a voltage module of the controller, a stator-voltage error for the generator, the stator-voltage error comprising a difference between a reference voltage and a stator-output voltage, wherein the stator-output voltage is the q-component of the stator voltage; and

determining, via the voltage module, a required rotor voltage d-component based, at least in part, on the stator-voltage error.

19. The system of claim 18 , wherein determining the at least one control command for the generator further comprises:

determining, via the frequency module, a required rotor voltage q-component based, at least in part, on the consolidated power requirement; and

combining, via a dq-to-abc transform module of the controller, the required rotor voltage d-component and the required rotor voltage q-component to generate a rotor voltage setpoint.

20. The system of claim 18 , wherein the plurality of operations further comprise:

receiving the reference frequency, wherein the reference frequency corresponds to an output frequency of the generator required to support the frequency of the power grid; and

receiving a reference voltage, wherein the reference voltage corresponds to an output voltage magnitude of the generator required to support the power grid.