FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
& THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
WIND-POWER GENERATION SYSTEM AND OPERATION CONTROL METHOD THEREFOR;
MITSUBISHI HEAVY INDUSTRIES, LTD., A CORPORATION ORGANIZED AND EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 16-5, KONAN 2-CHOME, MINATO-KU, TOKYO 1088215, JAPAN.
THE FOLLOWING * SPECIFICATION
PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH (T IS TO BE PERFORMED.

DESCRIPTION
Technical Field
The present invention relates to wind-power generation systems and operation control methods therefor.
Background Art
In power factor control at an interconnection node of a wind farm, conventionally, a predetermined power-factor command value is determined by, for example, consultation with the grid operator so as to satisfy the range of, for example, a leading power factor of 0.95 to a lagging power factor of 0.95, and generation systems of individual wind turbines perform power factor control so as to maintain the determined predetermined power-factor command. In addition, if the power factor at the interconnection node deviates from the above range despite such control, the power factor at the interconnection node is adjusted by the opening/closing of a capacitor bank or reactors at a substation.
In addition, Patent Citation 1 discloses that a central

controller for controlling the power at the interconnection node and so on transmits a uniform reactive power command to the individual wind turbines so that the individual wind turbines perform control based on the reactive power command.
Patent Citation 1:
U.S. Pat. No. 7,166,928, specification
Disclosure of Invention
To increase the voltage stability of a utility grid, the accuracy of power factor adjustment at an interconnection node must be improved. The conventional technique described above, however, is disadvantageous in that the accuracy of power factor adjustment cannot be further improved because a uniform reactive power command value is provided to the individual wind turbines.
An object of the present invention is to provide a wind-power generation system and an operation control method therefor in which the accuracy of power factor adjustment can be improved.
To solve the above problem, the present invention employs the following solutions.
A first aspect of the present invention is an operation

control method for a wind-power generation system including a plurality of wind turbines and a central controller for providing control commands to the individual wind turbines, and output powers of the individual wind turbines are supplied to a utility grid via a common interconnection node. Power-factor command values corresponding to the individual wind turbines are determined by correcting a predetermined power-factor command value for the interconnection node using power factor correction levels set for the individual wind turbines.
According to the present invention, because the predetermined power-factor command value for the interconnection node is corrected using the power factor correction levels corresponding to the individual wind turbines, different power-factor command values can be set for the individual wind turbines. This allows power factor control of the individual wind turbines based on appropriate power-factor command values taking into account, for example, the properties related to the individual wind turbines, thus improving the accuracy of power factor control at the grid node.
In the above operation control method for the wind-power generation system, the power factor correction levels may be determined based on reactance components present between the

individual wind turbines and the interconnection node.
Thus, because the power-factor command values for the individual wind turbines are determined using the power factor correction levels taking into account the reactance components present between the wind turbines and the interconnection node, the actual power factor at the interconnection node can be efficiently adjusted to the predetermined power-factor command value.
For example, if simple feedback control is performed to adjust the actual power factor at the interconnection node to the power-factor command value without taking into account the reactance components present between the individual wind turbines and the interconnection node, it is possible to adjust the power factors at output ends of generation systems of the individual wind turbines to the power-factor command value provided to the individual wind turbines, although it is difficult to adjust the power factor at the interconnection node to the predetermined power-factor command value. This is because the power factor varies depending on, for example, the reactances of power lines connecting the output ends of the wind turbines to the interconnection node. In this respect, according to the present invention, the power factor at the interconnection node can be controlled efficiently and accurately because the individual wind turbines are controlled

based on the power-factor command values taking into account the reactance components present between the individual wind turbines and the interconnection node.
A second aspect of the present invention is an operation control method for a wind-power generation system including a plurality of wind turbines and a central controller for providing control commands to the individual wind turbines, and outputs of the individual wind turbines are supplied to a utility grid via a common interconnection node. If the plurality of wind turbines include both variable-speed wind turbines and fixed-speed wind turbines, the overall power factor of the fixed-speed wind turbines at the interconnection node is calculated, the difference between the calculated power factor and a predetermined power-factor command value for the interconnection node is calculated, the predetermined power-factor command value is corrected using the calculated difference, and power-factor command values for the individual variable-speed wind turbines are determined based on the corrected predetermined power-factor coinmand value.
According to the above method, because the power-factor command values for the variable-speed wind turbines are determined by taking into account variations in power factor due to the fixed-speed wind turbines, the variations in power

factor due to the fixed-speed wind turbines can .be absorbed by power factor control of the variable-speed wind turbines. This improves the accuracy of power factor control at the interconnection node even if fixed-speed wind turbines and variable-speed wind turbines are both present.
In the above operation control method for the wind-power generation system, the power-factor command values corresponding to the individual variable-speed wind turbines may be determined by correcting the corrected predetermined power-factor command value using power factor correction levels set for the individual variable-speed wind turbines.
Thus, because the power-factor command values for the individual variable-speed wind turbines are determined by further correcting the predetermined power-factor command value for the interconnection node, corrected by taking into account the variations in the power factors of the fixed-speed wind turbines, using the power factor correction levels set for the individual variable-speed wind turbines, different power-factor command values can be set for the individual variable-speed wind turbines. This allows power factor control of the individual variable-speed wind turbines based on appropriate power-factor command values taking into account, for example, the properties related to the individual

variable-speed wind turbines, thus further improving the accuracy of power factor control at the interconnection node.
In the above operation control method for the wind-power generation system, the power factor correction levels corresponding to the individual variable-speed wind turbines may be determined based on reactance components present between the individual variable-speed wind turbines and the interconnection node.
Thus, because the power-factor command values for the individual variable-speed wind turbines are determined by taking into account the reactance components present between the wind turbines and the interconnection node, the actual power factor at the interconnection node can be efficiently adjusted to the power-factor command value.
A third aspect of the present invention is a wind-power generation system including a plurality of wind turbines and a central controller for providing control commands to the individual wind turbines, and output powers of the individual wind turbines are supplied to a utility grid via a common interconnection node. Power-factor command values corresponding to the individual wind turbines are determined by correcting a predetermined power-factor command value for

the interconnection node using power factor correction levels set for the individual wind turbines.
A fourth aspect of the present invention is a wind-power generation system including a plurality of wind turbines and a central controller for providing control commands to the individual wind turbines, and outputs of the individual wind turbines are supplied to a utility grid via a common interconnection node. If the plurality of wind turbines include both variable-speed wind turbines and fixed-speed wind turbines, the central controller calculates the overall power factor of the fixed-speed wind turbines at the interconnection node, calculates the difference between the calculated power factor and a predetermined power-factor command value for the interconnection node, corrects the predetermined power-factor command value using the calculated difference, and determines power-factor command values for the individual variable-speed wind turbines based on the corrected predetermined power-factor command value.
The present invention provides the advantage of improving the accuracy of power factor adjustment.
Brief Description of Drawings

[FIG. 1] Fig. 1 is a diagram showing the entire configuration of a wind-power generation system according to a first embodiment of the present invention.
[FIG. 2] Fig. 2 is a diagram illustrating power factor correction levels according to the first embodiment of the present invention.
[FIG. 3] Fig. 3 is a flowchart showing a procedure of an operation control method for the wind-power generation system according to the first embodiment of the present invention.
[FIG. 4 ] Fig. 4 is a diagram illustrating an operation control method for a wind-power generation system according to a second embodiment of the present invention. Explanation of Reference:
1: wind-power generation system
10: central controller
2 0: generation system
30: power line
WTG1, WTG2, WTGn: wind turbine
Best Mode for Carrying Out the Invention
Individual embodiments of wind-power generation systems and operation control methods therefor according to the present invention will be described below with reference to

the drawings.
First Embodiment
Fig. 1 is a block diagram showing the entire configuration of a wind-power generation system according to this embodiment. As shown in Fig. 1, a wind-power generation system 1 includes a plurality of wind turbines WTG1, WTG2, ..., WTGn (hereinafter denoted simply by the reference sign "WTG" when all wind turbines are referred to and denoted by the reference signs "WTG1", "WTG2", etc. when the individual wind turbines are referred to) and a central controller 10 for providing control commands to the individual wind turbines WTG. In this embodiment, all wind turbines WTG are variable-speed wind turbines.
Each wind turbine WTG includes a generation system 20. The generation system 20 includes, as the main configuration thereof, for example, a generator, a variable-frequency converter excitation system capable of controlling the active power and the reactive power of the generator, and a wind turbine controller for providing a power command value to the variable-frequency converter excitation system.
The powers output from the generation systems 20 of the individual wind turbines are supplied through respective power lines 30 to a utility grid via a common interconnection node

A.
The central controller 10 sets a power-factor command value for the interconnection node A based on a requested-power-factor command for the interconnection node A provided from a power management room managing grid power (for example, an electric utility). The power-factor command value is corrected using power factor correction levels set for the individual wind turbines WTG1, WTG2, ..., WTGn, and the corrected power-factor command values are transmitted to the respective wind turbines. Here the details of the power factor correction levels set for the individual wind turbines will be described later.
The generation system 20 of each wind turbine WTG1, WTG2, ..., WTGn sets an active-power command value and a reactive-power command value so as to satisfy the power-factor command value provided from the central controller 10. Specifically, the wind turbine controller of the generation system 20 monitors the rotational speed of the generator to set an active-£jower command value corresponding to the rotational spe^d. In addition, a reactive-power command value satisfying the power-factor command value is determined from the active-powor command value and the relational expression shown in equation (1) below. At this time, the wind turbine

controller sets the reactive-power command value within the operating range depending on thermal constraints and voltage limitations. In addition, if the power-factor command is given priority, the setting may be such that the necessary reactive power is supplied by reducing the active power.
[Equation 1]
P
Power factor = , — {1)
In equation (1) above, P is the active power, and Q is the reactive power.
The wind turbine controller provides the set active-power command value and the set reactive-power command value to the variable-frequency converter excitation system. The variable-frequency converter excitation system controls the generator based on the active-power command value and the reactive-power command value provided from the wind turbine controller.
With the above power factor control, active powers and reactive powers satisfying the power-factor command values provided to the individual wind turbines are output from the respective wind turbines WTG and are supplied to the common interconnection node A through the power lines 30.
Next, the power factor correction levels set for the

individual wind turbines WTG1, WTG2, ..., WTGn described above will be described in detail.
The above power factor correction levels are determined based on reactance components present between the individual wind turbines WTG1, WTG2, ..., WTGn and the interconnection node A. In a wind farm having many wind turbines, for example, the lengths of the power lines 30 connecting the individual wind turbines WTG1, WTG2, ..., WTGn and the interconnection node A differ largely. Accordingly, the powers output from the wind turbines are affected by the reactances corresponding to the distances over the respective power lines 30 before reaching the interconnection node A.
As a result, for example, if a uniform power-factor command value is provided to the individual wind turbines, variations in the reactive power at the interconnection node A can occur and decrease the power factor accuracy. In that respect, this embodiment takes into account the power variations, described above, due to the reactance components of the power lines 30 to correct the power-factor command value provided to the individual wind turbines using the power factor correction levels corresponding to the individual wind turbines, more specifically, the reactance components of the power lines 30 connecting the individual wind turbines and the interconnection node A.

First, as shown in Fig. 2, let the powers at the output ends of the individual wind turbines WTG1, WTG2, . .., WTGi, ..., WTGn be Pi+jQi, P2+JQ2, •■•, Pi+jQi, . .., Pn+jQn, respectively. In addition, let the reactances of the power lines between the individual wind turbines WTGI, WTG2, . .., WTGn and the interconnection node A be jx1, jx2, . . . , jx1 ..., jxn, respectively, and the powers of the individual wind turbines at the interconnection node A are defined as Pi'+jQi', P2'+JQ2'/ --., Pi'+jQi', .-., Pn'+jQn'/ respectively.
Next, power flow calculation is performed for each wind
turbine. Here the i-th wind turbine will be described as an
example. For convenience, let interconnection node voltage
Vgrid = 1 pu and grid = 0. In addition, let the
direction from each wind turbine toward the interconnection node A be positive in sign for both the active power P and the reactive power Q. The sign of the power factor also corresponds thereto; for example, power factor pf > 0 if P > 0 and Q > 0, and power factor pf < 0 if P > 0 and Q < 0.
Under such conditions, the active power Pi and the reactive power Qi at the output end of the wind turbine WTGi and the active power Pi' and the reactive power Q1' at the interconnection node A are represented, respectively, as follows.


[Equation 2]
In this power flow calculation, the active powers have the same value, namely, Pi = Pi', because only the reactance components of the power lines 30 are taken into account. Letting Pi and Q± be known, Pi and Qi' can be solved from equation (2) above.
As Pi and Qif appropriate values (for example, averages) are set by, for example, acquiring the active power Pi and the reactive power Qi at the output end of the wind turbine over a past predetermined period of time (for example, one month, three months, or one year) and analyzing the acquired data.
The power factor pfi at the output end of the wind turbine is represented by equation (3) below, and the power factor pfi1 at the interconnection node A is represented by equation (A) below.
[Equation 3]


As a result, the power factor correction level pf± for the i-th wind turbine can be determined by equation (5) below: pfi = pfgrid - pfi' (5)
In equation (5) above, pfgrid is the power-factor command value for the interconnection node A.
The power factor correction levels pfi determined for the individual wind turbines by the method described above are stored in a memory of the central controller 10 in association with the respective wind turbines and are used for correction of the power-factor command value in the operation of the wind turbines.
The above power factor correction levels stored in the memory may be updated, for example, at predetermined time intervals (for example, every one year or three months). For updating, the active powers P± and the reactive powers Q± of the wind turbines may be set to appropriate values (for example, as described above, set using the analytical results of data over a past predetermined period of time), and these values may be substituted into the above equations to update

the power factor correction levels for the individual wind turbines.
Next, an operation control method for the wind-power generation system having the above configuration will be described.
First, upon acquisition of the power-factor command value pfgrid for the interconnection node (Step SA1 in Fig. 3), the central controller 10 reads the power factor correction levels
pfi corresponding to the individual wind turbines WTG1, WTG2, ..., WTGn from the memory and corrects the power-factor command value pfgrid using the power factor correction levels
pfi (Step SA2). The corrected power-factor command values pfi (= pfgrid + pfi) are transmitted to the respective wind turbines WTG1, WTG2, ..., WTGn (Step SA3).
The wind turbine controllers of the individual wind turbines WTG1, WTG2, ..., WTGn set active-power command values and reactive-power command values so as to satisfy the respective power-factor command values pfi, pf2 ■ • • /
pfi, ..., pfn received from the central controller 10 and provide the set active-power command values and the set reactive-power command values to the variable-frequency converter excitation systems. The variable-frequency converter excitation systems control the generators based on

the provided active-power command values and the provided reactive-power command values. Thus, the active powers and the reactive powers satisfying the power-factor command values corresponding to the individual wind turbines are output from the respective wind turbines and are supplied to the common interconnection node A through the power lines 30.
The central controller 10 detects the reactive power and the active power at the interconnection node A to calculate the actual power factor pfgrid' from the detected values. The difference between the calculated actual power factor pfgrid' and the power-factor command value pfgrid is then calculated, and new power-factor command values are calculated so as to offset that difference and are provided as the next power-factor command values to the respective wind turbines (Step SA4) .
The new power-factor command values are determined by further adding the difference between the actual power factor pfgrid' and the power-factor command value pfgrid and the power factor correction levels pf1 to the power-factor command value pfgrid, as in equation (6) below.
pfi = pfgrid + Pfi + (Pfgrid " pf grid ' ) (6)
The power-factor command values corresponding to the individual wind turbines may be calculated thereafter by

detecting the actual power factor at the interconnection node A at predetermined time intervals and substituting the difference in power factor determined from the detection results, namely, pfgrid = pfgrid - pfgrid' , and the power factor correction levels pfi into equation (6) above.
In this way, feedback control can be performed to stabilize the power factor at the interconnection node A.
As described above, because the wind-power generation system 1 and the operation control method therefor according to this embodiment determine power-factor command values appropriate for the individual wind turbines by correcting the power-factor command value for the interconnection node A using the power factor correction levels corresponding to the reactances present between the individual wind turbines and the interconnection node A, power factor control taking into account the reactances related to the power lines 30 can be performed in the individual wind turbines. This improves the accuracy of power factor control at the interconnection node A.
Second Embodiment
Next, a second embodiment of the present invention will be described using Fig. 4.
While the case where all wind turbines are variable-speed

wind turbines has been described in the first embodiment described above, the case where some wind turbines are fixed-speed wind turbines will be described in this embodiment.
A wind-power generation system according to this embodiment includes at least one fixed-speed wind turbine and at least one variable-speed wind turbine. As shown in Fig. 4, for example, the first to i-th wind turbines are variable-speed wind turbines, whereas the i+l-th to n-th wind turbines are fixed-speed wind turbines. In this case, first, the active powers Pi and the reactive powers Q1' at the interconnection node A are determined by power flow calculation based on the same procedure as in the first embodiment described above.
Subsequently, the sums of the active powers and the reactive powers of the fixed-speed wind turbines alone at the interconnection node A are determined as shown in equations (7) and (8) below.


Subsequently, the above sums of the active powers and the reactive powers are used to calculate the overall power factor pffix' of the fixed-speed wind turbines.

Next, the difference between the power-factor command value for the interconnection node A and the above overall power factor pffiXf of the fixed-speed wind turbines is calculated.
pf = pfgrid " pffix' (9)
To absorb that difference in the variable-speed wind turbines, pf is set as a command value correction level, and a value obtained by adding the command value correction level
pf to the above power-factor command value pfgr±d is set as a new power-factor command value. Based on the power-factor command value, as in the first embodiment described above, the power-factor command values for the individual wind turbines are determined using the power factor correction levels pfi,
pf2, - . . , pf± corresponding to the individual variable-speed wind turbines WTG1, WTG2, ..., WTGi, and the corrected power-factor command values are transmitted to the respective wind turbines.

As described above, if fixed-speed wind turbines and variable-speed wind turbines are both present, because the wind-power generation system and the operation control method therefor according to this embodiment determine power-factor command values for the variable-speed wind turbines by taking into account variations in the power factors of the fixed-speed wind turbines, the variable-speed wind turbines can absorb the variations in power factor due to the fixed-speed wind turbines. This improves the accuracy of power factor control even if fixed-speed wind turbines are included.
In this embodiment, the overall power factor of the fixed-speed wind turbines is determined and is used to correct the power-factor command value for the interconnection node A, and the corrected power-factor command value is further corrected using the power factor correction 'levels pf± set for the individual variable-speed wind turbines; instead, for example, the power-factor command value corrected using the overall power factor of the fixed-speed wind turbines may be provided as a power-factor command value for the individual variable-speed wind turbines. Although in this case variations in power factor due to reactors present between the individual variable-speed wind turbines and the interconnection node A are not offset, a considerable

advantage can be achieved in that the variations in power factor due to the fixed-speed wind turbines can be offset.
Although the embodiments of the present invention have been described above in detail with reference to the drawings,' specific configurations are not limited to those of the embodiments; design .changes etc. are encompassed without departing from the spirit of the present invention.
For example, although the central controller 10 corrects the power-factor command value in the embodiments described above, the power-factor command value may instead be corrected, for example, in the individual wind turbines. In this case, a uniform power-factor command value is transmitted from the central controller 10 to the individual wind turbines, and the power-factor command value received from the central controller 10 is corrected in the individual wind turbines using the respective power factor correction levels possessed by the individual wind turbines.
In addition, although the corrected power-factor command values etc. are transmitted from the central controller 10 by communication in this embodiment, a configuration may be employed in which, for example, the operator -manually inputs and sets the power-factor command values to the respective

wind turbines.


We Claim :
1. An operation control method for a wind-power generation
system comprising a plurality of wind turbines and a central
controller for providing control commands to the individual
wind turbines, output powers of the individual wind turbines
being supplied to a utility grid via a common interconnection
node,
wherein power-factor command values corresponding to the individual wind turbines are determined by correcting a predetermined power-factor command value for the interconnection node using power factor correction levels set for the individual wind turbines.
2. The operation control method for the wind-power generation system according to Claim 1, wherein the power factor correction levels are determined based on reactance components present between the individual wind turbines and the interconnection node.
3. An operation control method for a wind-power generation system comprising a plurality of wind turbines and a central controller for providing control commands to the individual wind turbines, outputs of the individual wind turbines being supplied to a utility grid via a common interconnection node, wherein

if the plurality of wind turbines include both variable-speed wind turbines and fixed-speed wind turbines, the overall power factor of the fixed-speed wind turbines at the interconnection node is calculated;
the difference between the calculated power factor and a predetermined power-factor command value for the interconnection node is calculated;
the predetermined power-factor command value is corrected using the calculated difference; and
power-factor command values for the individual variable-speed wind turbines are determined based on the corrected predetermined power-factor command value.
4. The operation control method for the wind-power generation system according to Claim 3, wherein the power-factor command values corresponding to the individual variable-speed wind turbines are determined by correcting the corrected predetermined power-factor command value using power factor correction levels set for the individual variable-speed wind turbines.
5. The operation control method for the wind-power generation system according to Claim 4, wherein the power factor correction levels corresponding to the individual variable-speed wind turbines are determined based on reactance

components present between the individual variable-speed wind turbines and the interconnection node.
6. A wind-power generation system comprising a plurality of wind turbines and a central controller for providing control commands to the individual wind turbines, output powers of the individual wind turbines being supplied to a utility grid via a common interconnection node,
wherein power-factor command values corresponding to the individual wind turbines are determined by correcting a predetermined power-factor command value for the interconnection node using power factor correction levels set for the individual wind turbines.
7. A wind-power generation system comprising a plurality of wind turbines and a central controller for providing control commands to the individual wind turbines, outputs of the individual wind turbines being supplied to a utility grid via a common interconnection node,
wherein, if the plurality of wind turbines include both variable-speed wind turbines and fixed-speed wind turbines,
the central controller:
calculates the overall power factor of the fixed-speed wind turbines at the interconnection node;
calculates the difference between the calculated power

factor and a predetermined power-factor command value for the interconnection node;
corrects the predetermined power-factor command value using the calculated difference; and
determines power-factor command values for the individual
variable-speed wind turbines based on the corrected
predetermined power-factor command value.
Dated this 15th day of February, 2010
FOR MITSUBISHI HEAVY INDUSTRIES, LTD. By their Agent