System and method for controlling an active harmonic filter in an inverter-based resource

1. A method for controlling an active harmonic filter of an inverter-based resource, the method comprising:

receiving, via a maximum compensation tracker module, a grid feedback signal;

determining, via the maximum compensation tracker module, a phase shift signal based, at least in part, on the grid feedback signal;

applying, via the maximum compensation tracker module, a phase shift offset signal to the phase shift signal to obtain a modified phase shift signal;

determining, via the maximum compensation tracker module, a voltage reference signal for the active harmonic filter based, at least in part, on the grid feedback signal and the modified phase shift signal, wherein determining the voltage reference signal for the active harmonic filter based, at least in part, on the grid feedback signal and the modified phase shift signal further comprises:

rotating the grid feedback signal from an abc reference frame to a dq reference frame to obtain a rotated dq feedback signal;

filtering the rotated dq feedback signal to obtain a filtered dq feedback signal;

applying a gain to the filtered dq feedback signal to determine a dq voltage reference signal;

rotating the dq voltage reference signal from the dq reference frame back to the abc reference frame to obtain an abc voltage reference signal, the abc voltage reference signal being synonymous with the voltage reference signal; and

controlling, via the maximum compensation tracker module, the active harmonic filter using the voltage reference signal, wherein the phase shift offset signal ensures that the active harmonic filter injects a current out of phase of a targeted harmonic.

2. The method of claim 1 , wherein the grid feedback signal comprises at least one of voltage feedback, a current feedback, a frequency feedback, or combinations thereof.

3. The method of claim 1 , wherein determining the phase shift signal based, at least in part, on the grid feedback signal further comprises:

determining, via a proportional integral controller, an angular frequency based on an initial frequency signal and a d component of the filtered dq feedback signal; and

integrating the angular frequency to obtain the phase shift signal.

4. The method of claim 1 , further comprising determining, via the maximum compensation tracker module, an optimal value of the phase shift offset for maximum harmonic compensation per unit ampere for the active harmonic filter.

5. The method of claim 4 , wherein determining the optimal value of the phase shift offset signal for maximum harmonic compensation per unit ampere for the active harmonic filter further comprises:

setting a default value for the phase shift offset signal;

disturbing the phase shift offset signal by an offset parameter;

checking a harmonic compensation of the active harmonic filter using a discrete Fourier transform;

if the harmonic compensation has improved, maintaining the phase shift offset signal at the default value; and

if the harmonic compensation has not improved, incrementally changing the offset parameter by a certain amount to obtain a revised offset parameter, disturbing the phase shift offset signal by the revised offset parameter, and rechecking the harmonic compensation of the active harmonic filter.

6. The method of claim 1 , wherein the maximum compensation tracker module is one of a plurality of maximum compensation tracker modules, the method further comprising:

generating, via the plurality of maximum compensation tracker modules, a plurality of phase offset signals; and

applying the plurality of phase offset signals to respective specific harmonic compensators.

7. The method of claim 6 , further comprising coupling the active harmonic filter between a line-side converter of the wind turbine power system and an electrical grid.

8. The method of claim 1 , wherein the inverter-based resource comprises a wind turbine power system.

9. A wind turbine power system connected to an electrical grid, the wind turbine power system comprising:

a power converter comprising a rotor-side converter and a line-side converter;

a generator comprising a rotor and a stator;

an active harmonic filter coupled between the generator and the electrical grid; and

a controller for controlling the wind turbine power system, the controller comprising a maximum compensation tracker module, the maximum compensation tracker module configured to perform a plurality of operations, the plurality of operations comprising:

receiving a grid feedback signal;

determining a phase shift signal based, at least in part, on the grid feedback signal;

applying a phase shift offset signal to the phase shift signal to obtain a modified phase shift signal;

determining a voltage reference signal for the active harmonic filter based, at least in part, on the grid feedback signal and the modified phase shift signal, wherein determining the voltage reference signal for the active harmonic filter based, at least in part, on the grid feedback signal and the modified phase shift signal further comprises:

rotating the grid feedback signal from an abc reference frame to a dq reference frame to obtain a rotated dq feedback signal;

filtering the rotated dq feedback signal to obtain a filtered dq feedback signal;

applying a gain to the filtered dq feedback signal to determine a dq voltage reference signal;

rotating the dq voltage reference signal from the dq reference frame back to the abc reference frame to obtain an abc voltage reference signal, the abc voltage reference signal being synonymous with the voltage reference signal; and

controlling the active harmonic filter using the voltage reference signal, wherein the phase shift offset signal ensures that the active harmonic filter injects a current substantially out of phase of a targeted harmonic.

10. The wind turbine power system of claim 9 , wherein the grid feedback signal comprises at least one of voltage feedback, a current feedback, a frequency feedback, or combinations thereof.

11. The wind turbine power system of claim 9 , wherein determining the phase shift signal based, at least in part, on the grid feedback signal further comprises:

determining, via a proportional integral controller, an angular frequency based on an initial frequency signal and a d component of the filtered dq feedback signal; and

integrating the angular frequency to obtain the phase shift signal.

12. The wind turbine power system of claim 9 , wherein the plurality of operations further comprise:

determining, via the maximum compensation tracker module, an optimal value of the phase shift offset for maximum harmonic compensation per unit ampere for the active harmonic filter.

13. The wind turbine power system of claim 12 , wherein determining the optimal value of the phase shift offset signal for maximum harmonic compensation per unit ampere for the active harmonic filter further comprises:

setting a default value for the phase shift offset signal;

disturbing the phase shift offset signal by an offset parameter;

checking a harmonic compensation of the active harmonic filter using a discrete Fourier transform;

if the harmonic compensation has improved, maintaining the phase shift offset signal at the default value; and

if the harmonic compensation has not improved, incrementally changing the offset parameter by a certain amount to obtain a revised offset parameter, disturbing the phase shift offset signal by the revised offset parameter, and rechecking the harmonic compensation of the active harmonic filter.

14. The wind turbine power system of claim 9 , wherein the maximum compensation tracker module is one of a plurality of maximum compensation tracker modules, the method further comprising:

generating, via the plurality of maximum compensation tracker modules, a plurality of phase offset signals; and

applying the plurality of phase offset signals to respective specific harmonic compensators.