UPPER LIMIT FOR A WIND PARK CONTROLLER

Abstract

Provided is a method of determining an upper limit value for an active power controller of a wind park including plural wind turbines connected at a point of common coupling, the method including: estimating a cumulative loss of active power occurring between output terminals of the plural wind turbines and the point of common coupling; determining the upper limit value based on the estimated loss of active power.

Claims

1. A method of controlling an active power controller of a wind park comprising plural wind turbines connected at a point of common coupling, the method comprising: performing a method of determining an upper limit value for the active power controller, the method comprising: estimating a cumulative loss of active power occurring between output terminals of the plural wind turbines and the point of common coupling; determining the upper limit value based on the estimated loss of active power, wherein the method of controlling the active power controller further comprises: supplying an error signal of active power, determined as difference between a wind park active power reference and a measured active power at the point of common coupling, to the active power controller; determining, by the active power controller, a controller output signal based on the error signal and restricted to be not greater than the determined upper limit value.

2. The method according to claim 1, wherein estimating the loss of active power includes estimating the loss of active power in dependence of a reference active power or a measured active power at the point of common coupling.

3. The method according to claim 2, wherein according to the dependence the loss of active power increases with increasing active power at the point of common coupling, wherein the loss of active power increases stronger or faster than linear with increasing active power at the point of common coupling.

4. The method according to claim 1, wherein estimating the loss of active power includes: establishing a relationship between the loss of active power and the active powder at the point of common connection.

5. The method according to claim 4, wherein the relationship is expressible as a mathematical equation describing the power loss as a polynomial of at least first power or at least second power of the active power at the point of common connection.

6. The method according to claim 5, wherein the polynomial is a second order polynomial.

7. The method according to claim 5, wherein the polynomial comprises coefficients which are adjusted to comply with experimental data including measured active power at the point of common connection and measured loss of active power.

8. The method according to claim 1, wherein determining the upper limit value includes calculating the upper limit value as a sum of the estimated loss of active power and a wind park active power reference at the point of common coupling.

9. The method of controlling a wind park comprising plural wind turbines connected at a point of common coupling, the method comprising: performing a method of controlling an active power controller of the wind park according to claim 1; determining plural active power wind turbine reference signals based on the controller output signal; and distributing the plural active power wind turbine reference signals to the plural wind turbines.

10. The method according to claim 9, further comprising: operating the wind park at low wind condition at a wind park active power reference such that the controller output signal substantially equals the upper limit value; operating the wind park at high wind condition at the same wind park active power reference restricting overshoot to be lower than the estimated power loss estimated for the wind park active power reference.

11. A control system for controlling an active power of a wind park comprising plural wind turbines connected at a point of common coupling, the control system comprising: an arrangement for determining an upper limit value for an active power controller, the arrangement comprising: a processor adapted: to estimate a cumulative loss of active power occurring between output terminals of the plural wind turbines and the point of common coupling; and to determine the upper limit value based on the estimated loss of active power, the control system further comprising: the active power controller, connected to the arrangement.

12. A wind park comprising: plural wind turbines connected at a point of common coupling; and a control system according to the claim 11.

Description

BRIEF DESCRIPTION

[0028] Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

[0029] FIG. 1 schematically illustrates a wind park according to an embodiment of the present invention including a wind park controller according to an embodiment of the present invention; and

[0030] FIG. 2 illustrates a relationship between active power output and loss of active power as considered in embodiments of the present invention.

DETAILED DESCRIPTION

[0031] The wind park 1 according to an embodiment of the present invention illustrated in FIG. 1 comprises plural wind turbines 3 which are connected to a common point of common coupling 5 to which the wind turbines 3 provide their individual active power output streams 7. The wind turbines 3 may also additionally provide reactive power to the point of common coupling 5. The point of common coupling 5 is connected (e.g. via a wind park transformer) to a utility grid 10. Each of the wind turbines 3 comprises a respective wind turbine controller 9 which controls the operation of the wind turbine 3.

[0032] The wind turbine controllers 9 receive each an active power wind turbine reference signal 11 which is provided by a control system 13 according to an embodiment of the present invention.

[0033] The control system (also referred to as wind park controller) 13 comprises an arrangement 15 for determining an upper limit value 33 for an active power controller 17 according to an embodiment of the present invention and further comprises the active power controller 17. The active power controller 17 outputs a controller output signal 19 and provides it to a distribution module 21 which derives from the controller output signal 19 the active power wind turbine reference signals 11 and provides them to the wind turbine controllers 9.

[0034] The control system 13 receives from an external entity a wind park active power reference 23 (Pref) which defines a desired total active power output at the point of common coupling 5. The actual active power output at the point of common coupling 5 is measured using a measurement sensor 25 and is provided as a measurement signal 27 to a difference element 29 with a negative sign. To the difference element 29 also the wind park active power reference 23 is provided such that the difference element 29 outputs a difference 31 between the wind park active power reference 23 (Pref) and the measured active power (represented by the measurement signal 27) at the point of common coupling 5. The error signal 31 is supplied to the active power controller 17. The active power controller 17 determines based on the error signal 31 the controller output signal 19 which is restricted to be within the upper limit value 33 and a lower limit value 35. The lower limit value 35 may for example be 0 MW.

[0035] The upper limit value is determined according to a method according to an embodiment of the present invention for which the arrangement 15 is used. The arrangement 15 comprises a processor 16 which is adapted to estimate a cumulative loss 18 of active power occurring between output terminals of the plural wind turbines 3 and the point of common coupling 5 and to determine the upper limit value 33 based on the estimated loss of active power.

[0036] The processor 16 may comprise for example an electronic storage in which a relationship between the cumulated loss of active power and the active power at the point of common coupling or the reference active power at the point of common coupling is stored.

[0037] According to an embodiment of the present invention the loss estimate may be done offline, i.e. the loss estimate may be done once offline, and the parameters may just be entered as parameters into the controller. According to another embodiment of the present invention the loss estimate may be done online, thereby continuously providing updates of the parameters to the controller.

[0038] The processor 16 may for example utilize the relationship between the active power at the point of common coupling and the loss of active power which may be described by a mathematical equation or may be obtained from a look-up table for example.

[0039] Therefore, the arrangement 15 or in particular the processor 16 may estimate the losses of active power as a function of the active power at the point of common coupling, as is illustrated in FIG. 2. Therein, the abscissa of the graph of FIG. 2 labelled with reference sign 37 indicates the desired active power at the point of common coupling, while the ordinate 39 indicates the loss of active power due to the transition of electric active power from the respective wind turbines 3 to the point of common coupling 5. The scattered data points each represent measurements of the estimated loss of active power in dependence of the active power at the point of common coupling. The measurement data points are labelled by reference sign 41. For establishing a relationship between the active power at the point of common coupling and the loss of active power, an n-th order polynomial may be estimated using known fitting algorithms. In the illustrated example, a second order polynomial has been fitted to the data points 41, wherein the best fit polynomial is labelled with reference sign 43. Based on the curve 43 for every active power at the point of common coupling, the corresponding loss of active power may be obtained.

[0040] Thereby, the upper limit value 33 may be calculated using the curve 43 for every wind park active power reference 23 or 37. According to embodiments of the present invention, the upper limit 33 is calculated as a sum of the estimated loss of active power 18 and the wind park AC power reference 23 (Pref). The sum is calculated using the summation element 20 which is comprised within the arrangement 15. Thereby, the upper limit value 33 is calculated as the sum of the estimated loss 18 and the wind park active power reference 23.

[0041] According to an embodiment of the present invention, the estimated cumulative loss 18 may be calculated using the curve 43. According to other embodiments of the present invention, the estimated cumulative loss 18 may be calculated using one of the curves 45 or 47 which are shifted by constant amounts relative to the best fit curve 43. The offset of the curves 45, 47 can be selected or chosen such as to reduce the risk of overshooting (for example subtracting a value from the best fit curve 43) arriving at curve 47 or such as to reduce the risk of not reaching the set point in the point of common coupling (for example by adding a positive value to the best fit curve 43) in order to arrive at the curve 45.

[0042] According to an embodiment of the present invention, the estimated loss of active power may be calculated according to following equation:

P.sub.wind-up,offset(P.sub.ref)A.Math.P.sub.ref.sup.2+B.Math.P.sub.ref+C

[0043] Herein, A, B and C are coefficients for example to be determined by fitting a curve to experimental data points, such as data points 41 illustrated in FIG. 2. P.sub.wind-up,offset may correspond to the estimated cumulative loss 18 illustrated in FIG. 1.

[0044] Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

[0045] For the sake of clarity, it is to be understood that the use of a or an throughout this application does not exclude a plurality, and comprising does not exclude other steps or elements. The mention of a unit or a module does not preclude the use of more than one unit or module.