CONTROL METHOD AND APPARATUS

• US 20100148508A1
• Filed: 12/11/2009
• Published: 06/17/2010
• 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
• Granted Patent: US 8,615,331 B2
• Time in Patent Office: Days
• US Class Current: 290/44
• 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 wind motors F03D
• 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 wind power generation system connected to a grid at a point of connection, wherein the system is devised to feed reactive power to the grid, comprising:

determining a Q-V characteristic for the grid at the point of connection by injecting a disturbance at the point of connection; and

controlling the feeding of reactive power based on the Q-V characteristic.

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

determining a nose point for the Q-V characteristic; and

determining a minimum reactive current, I_Qmin, which is safe from the nose point; and

wherein

the controlling of the feeding of reactive power includes keeping the reactive current higher than the minimum reactive current, I_Qmin.

3. A method according to claim 1, wherein the feeding of reactive power to the grid is controlled by controlling rotor currents of a double fed induction generator, DFIG.

4. A method according to claim 1, wherein the feeding of reactive power to the grid is controlled by controlling switches of an AC/DC/AC converter configuration connecting a generator with the grid.

5. A method according to claim 1, wherein the method is used in transient conditions.

6. A method according to claim 1, wherein the method is used in steady state conditions.

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

a power regulator for injecting 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; and

a controller controlling the feeding of reactive power based on the Q-V characteristic.

8. A controller according to claim 7, wherein the controller further comprises:

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

a determination unit determining a minimum reactive current, I_Qmin, which is safe from the nose point; and

wherein

the controller is devised to keep the reactive current higher than the minimum reactive current, I_Qmin.

9. A wind power generating system comprising a controller according to claim 7.