Method and apparatus for controlling the feed of reactive power in a wind power generation system

• US 8,615,331 B2
• Filed: 12/11/2009
• Issued: 12/24/2013
• Est. Priority Date: 12/12/2008
• Status: Active Grant

• Current Assignee: Vestas Wind Systems A/S
• Original Assignee: Vestas Wind Systems A/S
• Inventors: Garcia, Jorge Martinez
• Primary Examiner(s): Ali, Mohammad
• Assistant Examiner(s): Booker, Kelvin
• Application Number:
  US12/636,196
• Publication Number:
  US 20100148508A1
• Time in Patent Office: 1,474 Days
• Field of Search: 700/287, 290/44
• US Class Current: 700/287
• CPC Class Codes: F03D 9/255 connected to electrical distribution networks; Arrangements therefor
• CPC Class Codes: G05F 1/70 Regulating power factor; Regulating reactive current or power
• CPC Class Codes: H02J 2300/28 The renewable source being wind energy
• CPC Class Codes: H02J 3/16 by adjustment of reactive power
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02J 3/50 Controlling the sharing of the out-of-phase component
• CPC Class Codes: H02P 2101/15 for wind-driven turbines
• CPC Class Codes: H02P 9/04 Control effected upon non-electric prime mover and dependent upon electric output value of the generator
• CPC Class Codes: H02P 9/102 for limiting effects of transients
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
• CPC Class Codes: Y02E 10/72 Wind turbines with rotation axis in wind direction
• CPC Class Codes: Y02E 10/76 Power conversion electric or electronic aspects
• CPC Class Codes: Y02E 40/30 Reactive power compensation

Abstract

A method and a controller for controlling a wind power generation system is disclosed. The system is connected to a grid at a point of connection, and is devised to feed reactive power to the grid in order to improve grid stability. A Q-V characteristic is determined for the grid at the point of connection as well as a nose point for the Q-V characteristic. A minimum reactive current, I_Qmin, which is safe from the nose point, is determined, and the feeding of reactive power is controlled such that the reactive current is kept higher than the minimum reactive current. This ensures that the reactive current does not make the Q-V characteristic reverse, and thereby the stability of the system is improved.

Claims

1. A method for controlling a feed of reactive power in a wind power generation system to a grid, wherein the wind power generation system is connected to the grid at a point of connection, comprising:

injecting a disturbance at the point of connection;

determining a Q-V characteristic for the grid at the point of connection based on the injected disturbance at the point of connection, wherein the Q-V characteristic is a relation between reactive power injected to the grid at the point of connection and grid voltage at the point of connection;

determining a minimum reactive current, I_Qmin; and

controlling the feeding of reactive power to the grid based on the Q-V characteristic, wherein controlling the feeding of reactive power to the grid comprises maintaining the reactive current greater than the minimum reactive current, I_Qmin.

2. The method according to claim 1, wherein the method further comprises:

determining a nose point for the Q-V characteristic,

wherein the minimum reactive current, I_Qmin, corresponds to a point on the Q-V characteristic that is a predetermined distance from the nose point.

3. The method according to claim 1, wherein controlling the feeding of reactive power to the grid comprises:

controlling rotor currents of a double fed induction generator (DFIG).

4. The method according to claim 1, wherein controlling the feeding of reactive power to the grid comprises:

controlling switches of an alternating current/direct current/alternating current (AC/DC/AC) converter configuration connecting a generator with the grid.

5. The method according to claim 1, wherein determining the Q-V characteristic for the grid and controlling the feeding of reactive power to the grid occurs while the wind power generation system is operating in a transient state.

6. The method according to claim 1, wherein determining the Q-V characteristic for the grid and controlling the feeding of reactive power to the grid occurs while the wind power generation system is operating in a steady state.

7. The method of claim 1, wherein the Q-V characteristic is represented by a parabolic function with the form:

a*Q=V²+b*V+c.

8. The method of claim 1, wherein injecting a disturbance at the point of connection comprises:

injecting current at the point of connection.

9. The method of claim 8, wherein determining the Q-V characteristic for the qrid comprises:

increasing the injected current to determine parameter a, parameter b, and parameter c from a parabolic function representing the Q-V characteristic;

a*Q=V²+b*V+c.

10. The method of claim 9, further comprising:

determining a nose point for the Q-V characteristic by determining a point on the parabolic function representing the Q-V characteristic having a derivative that is substantially equal to zero.

11. A controller for controlling a feed of reactive power in a wind power generation system to a grid, wherein the wind power generation system is connected to the grid at a point of connection, comprising:

a power regulator configured to inject a disturbance at the point of connection;

a Q-V characteristic detector for determining the Q-V characteristic for the grid at the point of connection based on an injected disturbance at the point of connection, wherein the Q-V characteristic is a relation between reactive power injected to the grid at the point of connection and grid voltage at the point of connection;

a determination unit for determining a minimum reactive current, I_Qmin; and

a current controller configured to feed reactive power to the grid based on the Q-V characteristic,

wherein the current controller is configured to maintain the reactive current greater than the minimum reactive current, I_Qmin.

12. The controller according to claim 11, wherein the controller further comprises:

a nose point detector for detecting a nose point of the Q-V characteristic

wherein the minimum reactive current, I_Qmin, corresponds to a point on the Q-V characteristic that is a predetermined distance from the nose point.

13. The controller of claim 11, wherein the controller is further configured to control switches of an alternating current/direct current/alternating current (AC/DC/AC) converter configuration.

14. The controller of claim 11, wherein the controller is further configured to operate when the wind power generation system in a transient state.

15. The controller of claim 11, wherein the controller is further configured to operate when the wind power generation system in a steady state.

16. The controller of claim 11, wherein the Q-V characteristic is represented by a parabolic function with the form:

a*Q=V²+b*V+c.

17. The controller of claim 11, wherein the power regulator is further configured to inject current at the point of connection.

18. The controller of claim 17, wherein the power regulator is further configured to increase the injected current to determine parameter a, parameter b, and parameter c from the parabolic function of the Q-V characteristic:

a*Q=V²+b*V+c.

19. The controller of claim 18, wherein the nose point detector is configured to detect a point on the parabolic function of the Q-V characteristic with a derivative that is substantially equal to zero.

20. A method for controlling a feed of reactive power in a wind power generation system to a grid, wherein the wind power generation system is connected to the grid at a point of connection, comprising:

injecting a disturbance at the point of connection;

determining a Q-V characteristic for the grid at the point of connection based on the injected disturbance at the point of connection,

wherein the Q-V characteristic is a relation between reactive power injected to the grid at the point of connection and grid voltage at the point of connection, and

wherein the Q-V characteristic is represented by a parabolic function with the form;

a*Q=V²+b*V+c;

determining a minimum reactive current, I_Qmin; and

controlling the feeding of reactive power to the grid based on the Q-V characteristic, wherein controlling the feeding of reactive power to the grid comprises maintaining the reactive current greater than the minimum reactive current, I_Qmin.