Wind Farm and Method for Controlling the Same

• US 20090096211A1
• Filed: 05/12/2006
• Published: 04/16/2009
• Est. Priority Date: 05/13/2005
• Status: Active Grant

• Current Assignee: Siemens Gamesa Renewable Energy A/S (Siemens AG)
• Original Assignee: Siemens AG
• Inventors: Stiesdal, Henrik
• Granted Patent: US 7,808,126 B2
• Time in Patent Office: Days
• US Class Current: 290/44
• CPC Class Codes: H02J 2300/28 The renewable source being wind energy wind motors F03D
• CPC Class Codes: H02J 3/1835 with stepless control
• CPC Class Codes: H02J 3/1878 using tap changing or phase shifting transformers
• CPC Class Codes: H02J 3/38 Arrangements for parallely feeding a single network by two or more generators, converters or transformers
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02M 7/5395 by pulse-width modulation
• CPC Class Codes: Y02E 10/76 Power conversion electric or electronic aspects
• CPC Class Codes: Y02E 40/30 Reactive power compensation

Abstract

A method for controlling dynamic power factor or the reactive power of a wind farm is provided. The wind farm comprises a number of wind turbines connected to a utility grid driven with a requested power factor or a requested reactive power. The wind turbine output voltage is controlled to a specific voltage set point. In the method, the wind farm power factor is measured and compared with the power factor requested for the utility grid, or the wind farm reactive power is measured and compared with the reactive power requested for the utility grid, respectively; the ratio of the wind farm voltage to the utility grid voltage is adjusted, and the output voltage of the individual wind turbines is regulated to correspond to the specific voltage set point; the steps are repeated until the power factor of the wind farm electricity corresponds to the requested reactive power.

Claims

1-17. -17. (canceled)

18. A method of controlling the dynamic power factor or the reactive power of a wind farm having a plurality of wind turbines connected to a utility grid driven with a requested power factor or a requested reactive power, the output voltage of the electricity supplied by an individual wind turbine controlled to a specific voltage set point, comprising:

measuring and comparing the wind farm power factor with the power factor requested for the utility grid, or measuring and comparing the wind farm reactive power with the reactive power requested for the utility grid;

adjusting the ratio of the wind farm voltage to the utility grid voltage;

regulating the output voltage of the individual wind turbines to correspond to the specific voltage set point; and

repeating the adjusting and regulating until the power factor of the electricity supplied by the wind farm corresponds to the requested power factor or the reactive power of the electricity supplied by the wind farm corresponds to the requested reactive power, respectively.

19. The method as claimed in claim 18, wherein the ratio of the wind farm voltage to the utility grid voltage is adjusted via a main transformer tap.

20. The method as claimed in claim 19, wherein the ratio of the wind farm voltage to the utility grid voltage is additionally adjusted via a supplementary dynamic power factor control system.

21. The method as claimed in claim 20, wherein the ratio of the wind farm voltage to the utility grid voltage is additionally adjusted via an adjustable capacitor bank.

22. The method as claimed in claim 21, wherein individual wind turbines are equipped with a power electronic converter that converts at least a portion of the electricity supplied by the wind turbine, and the power electronic converter is programmed to control the output voltage of the electricity supplied by an individual wind turbine to the specific voltage set point and regulate the output voltage of the individual wind turbines to correspond to the specific voltage set point.

23. The method as claimed in claim 22, wherein the method steps are repeatedly performed in discrete steps until the power factor of the electricity supplied by the wind farm corresponds to the requested power factor or the reactive power of the electricity supplied by the wind farm corresponds to the requested reactive power, respectively.

24. The method as claimed in claim 23, wherein the voltage set point is adjustable.

25. A wind farm with a plurality of wind turbines for collectively connecting to a utility grid, comprising:

a power electronic converter assigned to an individual wind turbine for converting at least a portion of the electricity supplied by the wind turbine, the power converter having a controller programmed for controlling the output voltage of the electricity supplied by the wind turbine to a specific voltage set point;

a measuring device configured to measure the wind farm power factor or the wind farm reactive power;

a comparing device configured to compare the measured wind farm power factor or the wind farm reactive power with a requested power factor or the requested reactive power, respectively;

an adjusting device that adjusts the ratio of the wind farm voltage to the utility grid voltage; and

a substation that connects the wind farm to the utility grid, the substation having a substation controller connected to or including the measuring device for receiving a difference signal representing the deviation of the wind farm power factor from the requested power factor or the deviation of the wind farm reactive power from the requested reactive power, respectively, and to the adjusting device for outputting an adjustment signal, the substation controller programmed to iteratively establish an adjustment signal based on the received difference signal.

26. The wind farm as claimed in claim 25, wherein the adjustment device comprises a main transformer having a plurality of taps and a tap changer.

27. The wind farm as claimed in claim 26, wherein the adjustment device further comprises a supplementary dynamic power factor control system.

28. The wind farm as claimed in claim 27, wherein the dynamic power factor control system comprises a variable capacitor bank.

29. The wind farm as claimed in claim 28, wherein a capacity of the supplementary dynamic power factor control system corresponds to a change in reactive power from the wind farm resulting from a change in the ratio of the wind farm voltage to the utility grid voltage caused by one tap change at the main transformer.

30. The wind farm as claimed in claim 29, wherein the power electric converter which comprises:

an inverter having an inverter input and an inverter output, the inverter input connected to a DC link of the power electronic converter and the inverter output connected to the substation, and

an inverter controller programmed for controlling the output voltage of the inverter to the specific voltage set point.

31. The wind farm as claimed in claim 30, wherein the inverter comprises a plurality of switches connecting the inverter input to the inverter output, and

the inverter controller comprises:

a voltage measurement unit connected to the inverter output for measuring the output voltage of the inverter and for producing a voltage signal representing the measured output voltage,

a memory that stores the voltage set point,

a comparator unit connected to the voltage measurement unit for receiving the voltage signal and connected to the memory for receiving the voltage set point, the comparator unit designed for comparing the output voltage to the voltage set point and for producing a deviation signal that represents the deviation of the measured voltage from the voltage set point,

a processing unit connected to the comparator unit for receiving the deviation signal programmed to establish a modulation signal representing a pulse width modulation of commutation signals for the switches based on the deviation signal, and

a pulse width modulation unit connected to the processing unit for receiving the modulation signal, the pulse width modulation unit designed for modulating the pulse width of commutation signals and connected to a drive circuit of the switches for outputting pulse width modulated commutation signals.

32. The wind farm as claimed in claim 31, further comprising a set point adjustment unit connected to the substation for receiving a set point signal representing a certain value for the voltage set point from the substation and further connected to the power electric converter of the individual wind turbines for delivering a setting signal to the power electric converter causing the voltage set point to be adjusted to the value represented by the set point signal.