Wind power facility and method
A DFIG wind power facility configured to be operated during grid faults is provided. The wind power facility includes a Doubly-Fed Induction Generator, a control system, an electric converter, a short-circuit controlled switch to selectively short-circuit the stator and a Stator Neutral Brake Chopper coupled to the stator. The DFIG includes a rotor and a stator, the stator including at least one three-phase winding. The electric converter includes a Machine Side Converter, a Grid Side Converter and a DC link connected therebetween. The SNBC includes a three-phase rectifier including three inputs, an impedance and an active high-frequency switch configured to vary the average value of the impedance by adjusting its duty cycle; each of the three inputs of the rectifier is connected to a phase of the at least one three-phase winding of the stator. Methods for operating a DFIG wind power facility during grid faults are also provided.
1 . A DFIG wind power facility configured to operate during grid faults, the DFIG wind power facility comprising:
a Doubly-Fed Induction Generator (DFIG) comprising a rotor and a stator, wherein the stator comprises at least one three-phase winding;
a control system configured to manage an operation of the DFIG wind power facility;
an electric converter comprising a Machine Side Converter (MSC), a Grid Side Converter (GSC) and a DC link connected therebetween;
a short-circuit controlled switch configured to selectively short-circuit the stator thereby allowing a current to flow through the stator upon decoupling the grid from the stator; and
a Stator Neutral Brake Chopper (SNBC) coupled to the stator, wherein the SNBC comprises a three-phase rectifier comprising three inputs, wherein each input corresponds to a phase; and
an impedance and an active high-frequency switch configured to vary an average value of the impedance by adjusting a duty cycle;
wherein each of the three inputs of the rectifier is connected to a phase of the at least one three-phase winding of the stator;
wherein the phases of the at least one stator three-phase winding are connected to the grid at one end and to the SNBC at the other end;
wherein, during a fault, the at least one stator three-phase winding is configured to remain connected to the grid.
2 . The DFIG wind power facility according to claim 1 , wherein the short-circuit controlled switch is an electromechanical switch or an electronic switch.
3 . The DFIG wind power facility according to claim 1 , wherein the three-phase rectifier comprises at least one thyristor.
4 . The DFIG wind power facility according to claim 3 , wherein the three-phase rectifier comprises a plurality of thyristors connected in series and/or in parallel.
5 . The DFIG wind power facility according to claim 1 , wherein the three-phase rectifier comprises at least a diode.
6 . The DFIG wind power facility according to claim 5 , wherein the three-phase rectifier comprises a plurality of diodes connected in series and/or in parallel.
7 . The DFIG wind power facility according to claim 5 , further comprising a stator-grid switch for selectively coupling/decoupling the stator and the grid.
8 . The DFIG wind power facility according to claim 1 , further comprising two or more SNBCs.
9 . The DFIG wind power facility according to claim 8 , wherein the two or more SNBCs are connected in parallel to the at least one winding of the stator.
10 . The DFIG wind power facility according to claim 8 , wherein the stator comprises a plurality of three-phase windings and the two or more SNBCs may be connected to a different three-phase winding of the stator or a combination thereof.
11 . The DFIG wind power facility according to claim 1 , further comprising an Energy Storage System in the DC link.
12 . The DFIG wind power facility according to claim 11 , wherein the ESS comprises a plurality of batteries in series and/or in parallel.
13 . The DFIG wind power facility according to claim 11 , wherein the ESS is connected parallel to the DC link capacitor.
14 . A method for operating the wind power facility according to claim 1 , during grid loss, wherein the DFIG wind power facility further comprises a plurality of blades, the method comprising:
monitoring a grid connection,
closing the short-circuit controlled switch and decoupling at least the stator from the grid upon detecting a grid loss;
increasing a pitch of the plurality of blades for gradually reducing a rotational speed of the rotor;
opening the active high-frequency switch of the at least one SNBC;
measuring the rotational speed of the rotor;
injecting a predetermined DC or AC current in the rotor for adapting a rotor frequency; and
opening the short-circuit controlled switch upon measuring the rotational speed of the rotor below a predetermined shutdown speed thereby allowing a controlled shutting down of the wind power facility.