METHOD FOR CONTROLLING THE OPERATION OF A WIND TURBINE AND WIND TURBINE

Abstract

A method is provided for controlling the operation of a wind turbine, the wind turbine including a generator, a converter, a converter control unit, a wind turbine controller and a connection device to an external electrical power grid, wherein electrical power generated by the generator is input into the power grid via the converter, wherein the wind turbine controller is configured to determine a fault condition according to a fault condition signal and to active a safe operating mode in response to the fault condition signal indicating a fault condition, wherein the fault condition signal is determined by evaluating changes in an available output power signal generated by the converter control unit, the available output power signal describing the active output power available from the converter.

Claims

1. A method for controlling the operation of a wind turbine, the wind turbine comprising a generator, a converter, a converter control unit, a wind turbine controller and a connection device to an external electrical power grid, wherein electrical power generated by the generator is input into the power grid via the converter, wherein the wind turbine controller is configured to determine a fault condition according to a fault condition signal and to activate a safe operating mode in response to the fault condition signal indicating the fault condition, wherein the fault condition signal is determined by evaluating changes in an available output power signal generated by the converter control unit, the available output power signal describing the active output power available from the converter.

2. The method according to claim 1, wherein the available output power signal is received by the wind turbine controller and a Boolean power change signal indicating the presence of a drop or increase in the available output power is determined from the available output power signal in the wind turbine controller, wherein the fault condition signal is set to indicating a fault condition if the power change signal changes from false to true.

3. The method according to claim 2, wherein a Boolean recovery signal indicating a recovery from the drop or increase in the available output power is determined from the available output power signal in the wind turbine controller, wherein the fault condition signal is set to indicating no fault condition when the recovery signal changes from false to true.

4. The method according to claim 3, wherein the power change signal; and/or the recovery signal are determined from at least one filtered signal, wherein the at least one filtered signal is determined by filtering using a smoothing filter, wherein the power change signal and/or the recovery signal are determined by comparing a respective of the at least one filtered signal with a respective threshold value.

5. The method according to claim 4, wherein the at least one filtered signal is normalized, by a per-unit transformation.

6. The method according to claim 4, wherein, before filtering, frequency dependent processing of the available output power signal is performed, emphasizing changes and/or variations on a predetermined time scale.

7. The method according to claim 4, wherein a first filtered signal is determined for the power change signal and a second filtered signal is determined for the recovery signal by applying different smoothing filters.

8. The method according to claim 1, wherein the safe operating mode comprises at least one measure for reducing the occurrence of mechanical load due to the fault condition.

9. The method according to claim 8, wherein the at least one measure comprises: commanding to move the pitch angle of the blades towards feather position with a specific rate, delivering a maximum active power generation value by the converter control unit to the wind turbine controller after the available output power recovers, setting a saturation value of the set points for the drive train to assure a correct drive train damper action application, the saturation value set by the converter control unit depending on the maximum active power, ramping up the power or torque set points with different rates according to the drive train damper action to come up with a ramped value of the power taking into account network operator's settling time restrictions, applying a first order filter to the ramped value of the power to soften more the torque overshoot, and applying the drive train damper torque command to the ramped power reference to reduce the mechanical load in the wind turbine and to damp the oscillation in the generator.

10. The method according to claim 1, wherein the available output power is the total available output power of at least one power converter assembly of the converter of the wind turbine.

11. A wind turbine, comprising a generator, a converter, a converter control unit, a wind turbine controller and a connection device to an external electrical power grid, wherein electrical power generated by the generator is input into the power grid via the converter, wherein the wind turbine controller is configured to determine a fault condition according to a fault condition signal and to activate a safe operating mode in response to the fault condition signal indicating the fault condition, wherein the wind turbine controller is further configured to receive an available output power signal generated by the converter control unit, the available output power signal describing the active output power available from the converter, and determine the fault condition signal from the available power output signal.

Description

BRIEF DESCRIPTION

[0044] Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

[0045] FIG. 1 shows a schematical view of a wind turbine according to the invention;

[0046] FIG. 2 shows a schematical view of the control structure of the wind turbine according to an example;

[0047] FIG. 3 shows a flow chart of an embodiment of a method according to the invention;

[0048] FIG. 4 shows a flow chart for determining a power change signal according to an embodiment;

[0049] FIG. 5 shows a flow chart for determining a recovery signal according to an embodiment; and

[0050] FIG. 6 shows graphs illustrating principles of the current invention according to an embodiment.

DETAILED DESCRIPTION

[0051] FIG. 1 is a schematical view of a wind turbine 1 according to embodiments of the invention. The wind turbine 1 comprises a rotor having, in this case, three wind turbine blades 2 attached to a rotor hub 3. The rotor is connected to a drive train 4 comprising a rotor shaft 5, a gear box 6, a generator shaft 7 and a wind turbine generator 8, which may be coupled to the generator shaft 7 via a coupling (not shown).

[0052] If wind impinges on the wind turbine blades 2 along the rotational axis of the rotor, the rotor begins to rotate such that mechanical power is input to the generator 8. The generator 8 converts the mechanical power into electrical power, which is fed to a converter 9 converting it into electrical power fulfilling requirements to be input via a connection device 10 (only indicated in FIG. 1) into an external electrical power grid 11 (only indicated in FIG. 1).

[0053] In the wind turbine of FIG. 1, the drive train components as well as the converter 9 are housed in a nacelle 12, which is pivotably carried by a tower 13 of the wind turbine 1. The wind turbine 1 may be an offshore wind turbine or an onshore wind turbine.

[0054] The wind turbine 1 may further comprise a control system 14 shown in FIG. 2. The control system 14 may comprise a converter control unit 15 (CCU) and a wind turbine controller 16, which may, for example, be implemented as a PLC. The wind turbine controller 16 may also be called wind turbine generator control device or wind turbine generator (WTG) controller. The wind turbine controller 16 controls operation of the wind turbine 1. It receives input from the converter control unit 15 and sends control signals to the converter control 15 and other components, for example a pitch system (not shown), an uninterruptable power supply (not shown), and the like. According to embodiments of the invention, the wind turbine controller 16, in particular, receives an available output power signal according to arrow 17 from the converter control unit 15. In an evaluation unit 18 of the wind turbine control unit 16, a Boolean fault condition signal may be derived from the available output power signal and provided to an operation control unit 19 according to arrow 20.

[0055] The available output power signal describes the active output power available in the converter 9. The fault condition signal may indicate various types of fault conditions relating to the occurrence a torque mismatch and can hence also be called torque mismatch signal. The fault condition signal may in particular indicate at least the following types of fault conditions, namely a low voltage or high voltage event (voltage dip or voltage peak) of the external electrical power grid 11, a frequency event of the external electrical power grid 11, a high temperature event in the component of the wind turbine 1 leading to power derating, and a partial failure of the power converter 9, in particular failure in a power converter module. While the available active output power of the converter 9 is normally the rated power plus auxiliary consumptions and losses, in case of a fault condition, the signal drops its value to the maximum that the converter 9 can produce under the circumstances of the fault condition.

[0056] If the fault condition signal indicates a fault condition (true), the operating control unit 19 may change the operating mode from a default or normal operating mode to a special safe operating mode to protect components of the wind turbine 1. In embodiments, measures for protecting components from mechanical load can be effected, like adjusting a pitch angle of the wind turbine blades 2, in particular to a feather position. Furthermore, an uninterruptable power supply can be activated and the like. In embodiments, measures like those described in EP 2 835 529 B1 can be used.

[0057] The wind turbine controller 16 is hence configured to perform a method according to embodiments of the invention. An embodiment of such a method will now be discussed with respect to FIGS. 3 to 6. Here, FIG. 3 is a general flow chart of the method.

[0058] In a step S1, the wind turbine controller 16 may receive the available output power signal from the converter control unit 15. In a step S2, two further signals may be derived from the available output power signal, namely a power change signal indicating the presence of an, in particular abrupt, power change which marks the beginning of a fault condition, and a recovery signal indicating the return of the dropped available active output power to its normal value (as discussed above, normally rated power plus auxiliary consumptions and losses). The power change signal and the recovery signal may be evaluated in step S3 to determine the fault condition signal. In embodiments, if the power change signal indicates a power change, that is, flips from false to true while the fault condition signal is false, the fault condition signal is set to true, indicating a fault condition. If the false condition signal is true and the recovery signal switches from false to true, indicating recovery, a fault condition signal is set to false once again.

[0059] In a step S4, a safe operating mode may be activated if the fault condition signal changes from false to true, and a return to the previous, in particular default, operating mode is initiated when the fault condition signal changes from true to false.

[0060] FIG. 4 shows the determination of the power change signal. As indicated by arrow 21, the available output power signal is provided by the converter control unit 15. In an optional step S5, changes and/or variations of the available output power signal in a predetermined time scale are emphasized by frequency-dependent processing. In concrete embodiments, two low pass filters may be used, one having a lower cutoff frequency and thus being slower. The result of the one filter may be subtracted from the result of the other low pass filter. Instead of low pass filters, slew limiters may also be used.

[0061] In a step S6, a smoothing filter FP1 may be applied to the available output power signal or the result output in step S5, if processed. The smoothing filter decreases noise introduced by the change and/or variation emphasis operation in step S5, if performed, as well as other high-frequency fluctuations already present in the available output power signal.

[0062] In a step S7, a per-unit transformation may be applied to the filtered signal, which may then be forwarded to step S8, where the filtered signal may be compared to a per-unit threshold, in this case per-unit drop limit provided according to arrow 22, wherein the power change signal is output as false as long as the per-unit filtered signal is larger than the per-unit threshold, and else as true, according to arrow 23.

[0063] Steps S6 and S7 may also be applied in the opposite order, i.e., performing the per-unit transformation first and then applying the smoothing filter.

[0064] FIG. 5 shows the determination of the recovery signal, which may follow the same general structure. The main difference is modified step S6, where a different smoothing filter FP2 may be used. The smoothing filters FP1 and FP2, which may comprise at least one low-pass filter, are chosen to optimize the detectability of the features determining the presence of a power change and recovery, respectively. In some embodiments, step S5 may also be replaced by a step S5, to apply a change and/or variation emphasis optimized regarding recovery detection.

[0065] In modified step S8, the second per-unit filtered signal may be compared to a different per-unit threshold supplied according to arrow 24, wherein, if the per-unit filtered signal is larger than the per-unit threshold, in this case a per-unit recovery limit, the recovery signal is output as true and else as false, as indicated by arrow 25.

[0066] FIG. 6 illustrates this principle exemplarily for a simplified available output power signal 26 shown in the uppermost graph. At a time shortly before time point 27, the available output power W begins to drop to a lower value 28 and recovers at a later time to again reach its normal value 29 at time point 30.

[0067] The second graph shows the corresponding fault condition signal 31, while the third and the fourth graph explain the determination of the fault condition signal 31. In the third graph, the corresponding first per-unit filtered signal 32 for the power change signal 33 in the fourth graph is shown, as well as the second per-unit filtered signal 34 for the recovery signal 35 shown in the fourth graph. As can be seen, the power change signal 33 is set to true (1) once the first per-unit filtered signal 32 drops below a first per-unit threshold 36 and is again set to false (0) as the first per-unit filtered signal 32 again exceeds the first per-unit threshold 36, see points 37, 38. Likewise, the recovery signal 35 is set to false, that is 0, as soon as the second per-unit filtered signal 34 drops below a second per-unit threshold 39 and again set to 1, that is true, as the second per-unit filtered signal 34 exceeds the second per-unit threshold 39, see points 40, 41.

[0068] That is, at point 37, while the fault condition signal is false, the power change signal 33 changes from false to true, such that the fault condition signal 31 also changes from false to true. At point 41, recovery signal 35 changes from false to true while the fault condition signal 31 is true, such that the fault condition signal 31 is again set to false.

[0069] Although the present invention has been disclosed in the form of 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.

[0070] 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.