We claim:
1. A method for operating a wind turbine generator (120) connected to a
power grid (184) using direct-quadrature (d-q) control technology, the method
comprising:
measuring an alternating-current (a-c) quantity of the power grid (184);
converting the a-c quantity to a d-q quantity in a controller (174) of the wind
turbine generator (120);
providing the d-q quantity to a d-q control loop (200) within the controller
(174);
altering, with a symmetric control component (202, 204), a transfer function of
the d-q control loop (200);
generating at least one d-q reference signal for the wind turbine generator
(120) based on the altered transfer function so as to achieve symmetric control of the
wind turbine generator (120);
generating a control signal for the wind turbine generator (120) based, at least
in part, on the at least one d-q reference signal; and,
operating the wind turbine generator (120) based on the control signal so as to
stabilize sub-synchronous interaction of the wind turbine generator (120).
2. The method as claimed in claim 1, wherein the symmetric control
component (202, 204) comprises at least one of one or more filters or a control
compensator.
3. The method as claimed in claim 2, wherein the one or more filters
comprise at least one of a notch filter, a low-pass filter, a high-pass filter, or
combinations thereof.
4. The method as claimed in claim 1, wherein the wind turbine generator
(120) comprises a doubly-fed generator having a stator and a rotor, the rotor being
coupled to the power grid (184) via a power conversion assembly (162), the power
conversion assembly (162) comprising a rotor-side power converter (166) and a gridside power converter (168), wherein the d-q control loop (200) is configured to
control a voltage of the rotor via the rotor-side power converter (166).
5. The method as claimed in claim 4, wherein the d-q reference signal
comprises at least one of a d-axis current reference, a d-axis voltage reference, a qaxis current reference, or a q-axis voltage reference.
6. The method as claimed in claim 5, wherein generating the control
signal for the wind turbine generator (120) based on the d-q reference signal further
comprises providing the d-axis current reference and the q-axis current reference to
the rotor-side converter, determining the control signal as a function of the d-axis
current reference and the q-axis current reference via the rotor-side converter (166),
and providing the control signal to the wind turbine generator (120), wherein the
symmetric control component (202, 204) alters the transfer function of the d-axis
current reference and the q-axis current reference so as to achieve symmetric control
of the wind turbine generator (120).
7. The method as claimed in claim 6, wherein the q-axis current reference
regulates voltage of the wind turbine generator (120) and the d-axis current reference
regulates torque of the wind turbine generator (120).
8. The method as claimed in claim 6, further comprising calculating the
q-axis current reference by determining a proportional integral derivative of a
terminal voltage of the wind turbine generator (120) and filtering the derivative.
9. The method as claimed in claim 6, further comprising calculating the
d-axis current reference as a function of a torque reference and a magnetic flux,
wherein the method further comprises determining the magnetic flux as a function of
a terminal voltage of the wind turbine generator (120), filtering the terminal voltage,
and multiplying the filtered terminal voltage by a multiplier.
10. A method for improving sub-synchronous interaction (SSI) damping of
a doubly-fed generator of a wind turbine connected to a power grid (184), the method
comprising:
altering, with a symmetric control component (202, 204), a transfer function of
a d-q control loop (200) within a controller (174) of the generator;
generating at least one d-q reference signal for the generator based on the
altered transfer function so as to achieve symmetric control of the wind turbine
generator (120); generating a control signal for the wind turbine generator (120) based, at least
in part, on the d-q reference signal; and,
operating the wind turbine generator (120) based on the control signal.
11. A system as claimed in operating a doubly-fed generator connected to
a power grid (184) using direct-quadrature (d-q) control technology, the system
comprising:
one or more sensors configured to measure an alternating-current (a-c)
quantity of the power grid (184);
a controller (174) communicatively coupled to a processor, the processor
comprising a d-q control loop (200) having at least one symmetric control component
(202, 204), the d-q control loop (200) being configured to perform one or more
operations, the one or more operations comprising:
converting the a-c quantity to a d-q quantity;
providing the d-q quantity to a d-q control loop (200) within the controller
(174);
altering, with a symmetric control component (202, 204), a transfer function of
the d-q control loop (200);
generating at least one d-q reference signal for the wind turbine generator
(120) based on the altered transfer function so as to achieve symmetric control of the
wind turbine generator (120);
generating a voltage-current signal for the wind turbine generator (120) based,
at least in part, on the at least one d-q reference signal; and,
operating the wind turbine generator (120) based on the voltage-current signal
so as to stabilize sub-synchronous interaction of the wind turbine generator (120).
12. The system as claimed in claim 11, wherein the symmetric control
component (202, 204) comprises at least one of one or more filters or a control
compensator.
13. The system as claimed in claim 12, wherein the one or more filters
comprise at least one of a notch filter, a low-pass filter, a high-pass filter, or
combinations thereof.
14. The method as claimed in claim 11, wherein generating the voltagecurrent signal for the wind turbine generator (120) based on the d-q reference signal further comprises providing a d-axis current reference and a q-axis current reference
to a rotor-side converter, determining the voltage-current signal as a function of the daxis current reference and the q-axis current reference via the rotor-side converter,
and providing the voltage-current signal to the doubly-fed generator, wherein the
symmetric control component (202, 204) alters the transfer function of the d-axis
current reference and the q-axis current reference so as to achieve symmetric control
of the wind turbine generator (120), wherein the q-axis current reference regulates
voltage of the wind turbine generator (120) and the d-axis regulates torque of the wind
turbine generator (120).
15. The method as claimed in claim 14, further comprising calculating the
q-axis current reference by determining a proportional integral derivative of a
terminal voltage of the wind turbine generator (120) and filtering the derivative.