OSCILLATION DAMPING IN WIND POWER INSTALLATIONS

Abstract

Provided is a control unit for a converter, in particular of a wind power installation and/or of a wind farm, comprising: an input for receiving a detected voltage and/or a detected current, an input for receiving a voltage set point and/or a current set point, an input for receiving a correction value and a feedback control system which is set up, depending on the detected voltage and/or the detected current and the voltage set point and/or the current set point and the correction value, to produce a reactive power set point for a modulated, preferably amplitude-modulated reactive and/or active power of the converter.

Claims

1. A controller for a converter, comprising: a first input configured to receive a detected voltage value and/or a detected current value; a second input configured to receive a voltage set point and/or a current set point; and a third input configured to receive a correction value, and wherein the controller is configured to determine a reactive power set point for a modulated reactive and/or active power of the converter depending on the detected voltage value and/or the detected current value, the voltage set point and/or the current set point and the correction value.

2. A wind power installation and/or wind farm, comprising: the controller as claimed in claim 1.

3. The controller as claimed in claim 1, wherein the modulated reactive and/or active power of the converter is an amplitude-modulated reactive and/or active power of the converter.

4. The controller as claimed in claim 1, wherein: the correction value includes at least one control value; or the at least one control value is formed from the correction value.

5. The controller as claimed in claim 1, wherein the controller is configured to perform filtering on a potentially critical frequency to determine the correction value.

6. The controller as claimed in claim 5, wherein, the controller is configured to determine the correction value based on at least one comparative value that enables an identification of a critical frequency.

7. The controller as claimed in claim 5, wherein the controller is configured to: apply a Kalman filter to determine a problem vector from the potentially critical frequency; and perform phase correction to correct the problem vector to obtain a phase-corrected vector that forms a basis for the correction value.

8. The controller as claimed in claim 5, wherein the controller is configured to: perform the filtering system in αβ coordinates; and identify the critical frequency in response to at least one amplitude response threshold being exceeded.

9. The controller as claimed in claim 1, wherein the controller is configured to: identify, from a plurality of frequencies, at least one potentially critical frequency.

10. The controller as claimed in claim 9, wherein the at least one potentially critical frequency indicates a network oscillation in an electrical supply network.

11. The controller as claimed in claim 9, wherein the controller is configured to operate in one of at least two different modes in order to identify the at least one potentially critical frequency.

12. A method for controlling a converter, comprising: detecting at least one voltage and/or at least one current; receiving a voltage set point and/or a current set point; receiving a correction value; determining a reactive power set point for a modulated reactive and/or active power of the converter depending on the detected at least one voltage value and/or the detected at least one current value, the voltage set point and/or the current set point and the correction value; and exchanging the modulated reactive power with an electrical supply network to dampen or counteract a network oscillation.

13. The method as claimed in claim 12, wherein the converter is a wind power installation and/or a wind farm.

14. A method for controlling an electrical supply network, comprising: setting a frequency or a frequency range by a network operator; determining whether vibrations that represent a network oscillation occur within the frequency or the frequency range; and controlling reactive power in the electrical supply network to dampen the vibrations.

15. The method as claimed in claim 14, wherein controlling the reactive power includes: detecting at least one voltage and/or at least one current; receiving a voltage set point and/or a current set point; receiving a correction value; and determining, by a controller of at least one wind power installation or a wind farm, a reactive power set point for the reactive and/or an active power depending on the detected at least one voltage value and/or the detected at least one current value, the voltage set point and/or the current set point and the correction value.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0047] The present invention is now explained in greater detail hereinafter in an exemplary manner using exemplary embodiments with reference to the accompanying figures, wherein the same reference symbols are used for the same or similar components.

[0048] FIG. 1 shows a schematic view of a wind power installation according to one embodiment.

[0049] FIG. 2 shows a schematic structure of a control unit (controller) of a wind power installation and/or of a wind farm according to one embodiment.

[0050] FIG. 3 shows a schematic structure of a frequency block of a control unit, in particular as shown in FIG. 2.

[0051] FIG. 4 shows a schematic structure of a filter block of a control unit, in particular as shown in FIG. 2.

[0052] FIG. 5 shows a schematic structure of a controller block of a control unit, in particular as shown in FIG. 2.

[0053] FIG. 6 shows an amplitude-modulated reactive power.

DETAILED DESCRIPTION

[0054] FIG. 1 shows a schematic view of a wind power installation 100 according to one embodiment.

[0055] For this purpose, the wind power installation 100 has a tower 102 and a nacelle 104. An aerodynamic rotor 106 with three rotor blades 108 and a spinner 110 is arranged on the nacelle 104. The rotor 106 is transferred into a rotational movement by the wind during operation and thus drives a generator in the nacelle 104.

[0056] A control unit (controller) which is described previously or hereinafter is further provided for operating the wind power installation.

[0057] FIG. 2 shows a schematic structure of a control unit (controller) 200 of a wind power installation and/or of a wind farm according to one embodiment.

[0058] The control unit 200 comprises a frequency block (frequency stage or circuitry) 300, a filter block (filter stage or circuitry) 400 and a controller block (controller stage or circuitry) 500.

[0059] The frequency block 300 has as an input variable at least one frequency fi, for example in the form of a frequency set point or a frequency specification.

[0060] In this case, the input variable fi is in particular used for monitoring a specific frequency range of the electrical supply network, for example frequencies in ranges between 0.1 Hz and 5 Hz.

[0061] The input variable is particularly preferably designed as a vector and in particular comprises at least one specification of the network operator, for example in the form of a frequency specification vector fGO, or a frequency band, for example comprising a lower limit value f.sub.Low and/or an upper limit value f.sub.High.

[0062] In addition, the operating mode of the frequency block can preferably be set via a further input value, for example the control value MOD, for example between an operation with fixed frequency specifications and an operation with limit values f.sub.Low and f.sub.High, which define a frequency window.

[0063] In addition, the frequency block 300 has at least one measurement input in particular for current and/or voltage which preferably has a three-phase design.

[0064] In one particularly preferred embodiment, the frequency block is additionally designed to examine in particular the currents and/or voltages detected by the measurement input 310 for vibrations within a frequency window, for example the frequency window between f.sub.Low and f.sub.High. In this case, the fundamental vibration (e.g., 50 Hz) used for power transport in the network is preferably faded out in a targeted manner, and it is examined for significant amplitudes below and/or above the fundamental vibration frequency.

[0065] The frequency block 300 determines at least one potentially critical frequency fpi from the input variable.

[0066] In this case, a potentially critical frequency fpi is intended to be understood to mean all those frequencies or frequency ranges in which a damping is to be achieved by means of the control unit. These are typically frequencies in which network areas of a large electrical supply network or individual production units in the electrical supply network oscillate against one another, for example by the rotor angle of synchronous machines vibrating in opposite directions at this frequency. These oscillations, also referred to as network oscillations, can result in undesired current flows between network areas or production units which under certain circumstances are damaging to operating equipment within the electrical supply network, such as transformers or lines, for example. Network oscillations of this type may also result in mechanical torsional loads on the shafts of power stations which reduce the life span of the power station shaft.

[0067] In addition, the potentially critical frequency fpi is used as an input signal for the filter block 400.

[0068] A further embodiment of a frequency block 300 of this type can be inferred from FIG. 3.

[0069] The filter block 400 has as an input variable at least one or the potentially critical frequency fpi and a comparative value Ai.

[0070] By comparing the potentially critical frequency fpi with the comparative value Ai, the filter block 400 selects all those vibrations which represent a critical frequency fki and ascertains a correction value Bi for this.

[0071] The correction value Bi, which can also be understood as damping, is subsequently used as an input signal for the controller block 500.

[0072] One further embodiment of a filter block 400 of this type can be inferred from FIG. 4.

[0073] The controller block 500 has as an input variable at least the correction value Bi and a reference variable Ci from which the control variable Di is ascertained.

[0074] The control variable Di is subsequently used in order to control a generator and/or an inverter which is connected to the generator, in particular in order to counteract amplitudes which are too high at potentially critical frequencies within the electrical supply network.

[0075] One further embodiment of a controller block of this type can be inferred from FIG. 5.

[0076] The control system 200 thus creates at least one possibility for counteracting critical situations, in particular critical frequencies, within an electrical supply network by means of wind power installations.

[0077] In one particularly preferred embodiment, the control system is used to counteract subsynchronous resonance in the electrical supply network, in particular by means of reactive power control of the wind power installations and/or of the wind farm.

[0078] In particular, it is therefore proposed to modulate the reactive power in such a way that neighboring consumers draw a different active power due to the changed frequency in the electrical supply network, owing to the changed reactive power.

[0079] This dynamic reactive power setting actively intervenes in the active power draw of neighboring consumers and thus in the network oscillations.

[0080] FIG. 3 shows a schematic structure of a frequency block of a control unit 300, in particular as shown in FIG. 2.

[0081] The frequency block 300 has as an input variable at least one frequency fi, for example a frequency specification vector f.sub.GO or a lower limit value f.sub.Low and an upper limit value f.sub.High for a frequency band f.sub.High, f.sub.Low which is to be monitored.

[0082] The frequency specification vector f.sub.GO is preferably specified by the network operator and is between 0.1 Hz and 5 Hz, for example.

[0083] The frequency band is selected in such a way, for example, that it comprises a frequency range in which interferences can be expected or can be assumed to be sufficiently likely. The frequency bands are preferably determined depending on a prevailing network topology.

[0084] Within the frequency band which is to be monitored, the frequency block 300 therefore searches for conspicuous patterns and/or frequencies fcon, for example by means of an analysis block 310. This can take place by means of a spectral analysis SA or a (Fast) Fourier transform FFT, for example.

[0085] In this case, determining the conspicuous frequencies fcon further preferably results from measured voltages Vmeas and currents Imeas which are provided to the analysis block 310 via a measurement input.

[0086] In particular, it is therefore also proposed to ascertain critical frequencies from the spectra of voltages Vmeas and currents Imeas. This can take place, for example, by means of the amplitudes of the voltages Vmeas and currents Imeas, or via auxiliary variables calculated from these measurement values or by using historical level values of the frequencies. In this case, an amplitude at a certain frequency is preferably considered to be conspicuous if it has exceeded a certain threshold compared to a historical mean-level value. For example, for vibrations in the measured voltages and/or currents, a limit of 0.5% of the nominal value of the fundamental vibration, i.e., the nominal voltage or the nominal current of the fundamental vibration, can be specified, so that only clearly perceptible vibrations are identified as critical frequencies.

[0087] Depending on the operating mode MOD, the corresponding frequency f.sub.GO, f.sub.CON can be output or classified as a potentially critical frequency fpi via a mode circuit 320.

[0088] In particular, it is therefore proposed to determine a potentially critical frequency fpi from the frequency fi.

[0089] The output of the potentially critical frequency or frequencies fpi can take place by means of a vector, for example. This vector can also be referred to as a result vector of the frequency block 300.

[0090] The frequency block 300 is thus in particular set up to provide information regarding the electrical supply network in the form of a frequency fpi, preferably in the form of a vector comprising at least one frequency fpi, depending on a detected and/or determined frequency fi.

[0091] In addition, the potentially critical frequency fpi can be used as an input signal for a filter block 400, as shown in FIG. 2, for example.

[0092] FIG. 4 shows a schematic structure of a filter block 400 of a control unit, in particular as shown in FIG. 2.

[0093] The filter block 400 has as an input variable at least one or the potentially critical frequency fpi, as preferably generated in FIG. 3, and a comparative value Ai.

[0094] The comparative value Ai comprises a detected voltage Vmeas and/or a detected current Imeas as well as a minimum amplitude response threshold Lpi for each potentially critical frequency fpi, for example.

[0095] The detected voltage Vmeas is preferably the voltage Vpoc which can be detected at the network connection point of the wind farm or the voltage which can be detected at the low voltage terminals of the wind power installation.

[0096] The detected current Imeas is preferably the current Iline of a line between a wind power installation or wind farm and an electrical supply network.

[0097] The minimum amplitude response threshold Lpi corresponds to a minimum from which a response should take place. The minimum amplitude response threshold Lpi is preferably selected in such a way that a response only takes place if vibrations in the voltage, for example, are greater than a certain percentage of the nominal voltage of the fundamental vibration, for example 0.5%.

[0098] Unless the potentially critical frequencies are sufficiently known, the amplitude response threshold is defined as a continuous frequency spectrum. An applicable amplitude response threshold therefore exists for each amplitude.

[0099] The filter block 400 preferably determines a problem vector Xpi from the potentially critical frequency fpi and/or the detected voltage Vmeas and/or the detected current Imeas by means of a Kalman filter 410, for example in αβ coordinates.

[0100] In this case, the problem vector Xpi preferably comprises the amplitude and the phase position of the vibration component in the case of the frequency fpi. In particular, the vibration component is the component in the frequency spectrum of current or voltage (or an auxiliary variable) which is at a potentially critical frequency fpi.

[0101] Determining the problem vector Xpi preferably takes place in αβ coordinates.

[0102] In addition, the minimum amplitude response threshold Lpi is preferably transformed into αβ coordinates, for example by means of an αβ transformation 420.

[0103] The problem vector Xpi is subsequently compared with the minimum amplitude response threshold Lpi in a comparator 430.

[0104] Provided that the vector(s) have a plurality of elements, each element of the problem vector Xpi is compared with a respective amplitude response threshold Lpi.

[0105] Provided that elements of the problem vector Xpi exceed their respective amplitude response threshold Lpi, these elements are classified as an actual critical frequency.

[0106] The output of the comparator 430 is therefore preferably also a vector Xai, wherein it only comprises the actual critical frequencies.

[0107] A phase correction 440 is subsequently preferably carried out, i.e., the individual elements of the vector Xai are corrected in their phase position according to the measurements, i.e., current measurement and/or voltage measurement, such that a phase-corrected vector Xci emerges.

[0108] In this case, the correction preferably takes place using a correction factor Lx which is preferably such that even more corrections can be carried out, in particular with respect to the controlled system.

[0109] The phase-corrected vector Xci is subsequently multiplied by a proportionality factor ki, represented by block 450.

[0110] The result from this is a vector with voltage values and/or current values with vibration components at the actual critical frequencies.

[0111] The voltage values and/or current values obtained in this way can subsequently be used as control values Vcontrol, Icontrol. The control values Vcontrol, Icontrol can also be referred to as correction values Bi. A limitation is particularly preferably further provided which limits the control values Vcontrol, Icontrol to a maximum.

[0112] The filter block 400 therefore produces correction values Bi, in particular for voltage and/or current, from potentially critical frequencies fpi and comparative values Ai.

[0113] The control values Vcontrol, Icontrol can also be given as correction values Bi to a controller block, in particular as input signals to a controller block 500 as shown in FIG. 5, for example.

[0114] FIG. 5 shows a schematic structure of a controller block 500 of a control unit, in particular as shown in FIG. 2.

[0115] The controller block 500 has as an input variable the correction value Bi, in particular in the form of the control values Vcontrol, Icontrol, and a reference variable Ci, in particular a voltage set point Vset and/or a current set point Iset and a detected voltage Vpoc and/or a detected current Iline.

[0116] The detected voltage Vpoc can also be referred to as an actual voltage.

[0117] The input signals, voltage set point Vset or current set point Iset and detected voltage Vpoc or detected current Iline, are subtracted from one another, for example by means of a subtraction 510, in order to ascertain a voltage deviation ΔV or current deviation ΔI.

[0118] The voltage deviation ΔV or the current deviation ΔI thus forms a control deviation.

[0119] The control value Vcontrol or the control value Icontrol is added to this control deviation, i.e., the voltage deviation ΔV or the current deviation ΔI, for example by means of an adder 520, in order to ascertain a voltage control value Vc or a current control value Ic. The control values Vcontrol, Icontrol can be ascertained for this purpose as shown in FIG. 4, for example.

[0120] The voltage control value Vc or the current control value Ic is subsequently supplied to a controller 530 which is designed as a P controller or PI controller, for example.

[0121] The controller 530 then produces a reactive power set point Qset from the voltage control value Vc or the current control value Ic, which reactive power set point can be transferred to an inverter control system (controller) of the wind power installation, for example, in order to produce a correspondingly amplitude-modulated reactive power Qmod or Qpoc.

[0122] FIG. 6 shows an amplitude-modulated reactive power Qmod which has been produced by a converter which has a control unit which is described previously or hereinafter and/or performs a method which is described previously or hereinafter.

[0123] The amplitude-modulated reactive power Qmod has a fundamental wave Qbase which vibrates with a frequency of 50 Hz.

[0124] A harmonic is modulated on this fundamental wave Qbase, the amplitude of which vibrates with time by a magnitude ΔQ1 or ΔQ2, for example at 0.8 Hz.

[0125] In this case, this harmonic is in particular modulated in such a way that the detected network oscillations are counteracted.

[0126] The reactive power which is exchanged with the electrical supply network therefore has an additional modulation which is outside the fundamental frequency which is specified by the electrical supply network, for example at 50 Hz.

[0127] The amplitude of the reactive power is therefore modulated in such a way that the detected network oscillations are counteracted.

REFERENCE SYMBOLS

[0128] 100 wind power installation

[0129] 102 tower of the wind power installation

[0130] 104 nacelle of the wind power installation

[0131] 106 aerodynamic rotor of the wind power installation

[0132] 108 rotor blade of the wind power installation

[0133] 110 spinner of the wind power installation

[0134] 200 control unit

[0135] 300 frequency block

[0136] 310 measurement input of the frequency block

[0137] 400 filter block

[0138] 500 controller block

[0139] Ai comparative value

[0140] Bi correction value

[0141] Ci reference variable

[0142] Di control variable

[0143] fi frequency, in particular frequency set point

[0144] fCON conspicuous frequency

[0145] fGO frequency specification of a network operator

[0146] fHigh upper limit value of the frequency band

[0147] fLow lower limit value of the frequency band

[0148] fpi potential critical frequency

[0149] fki critical frequency

[0150] Imeas detected current, in particular of the electrical supply network

[0151] Iline detected current between wind power installation and electrical supply network

[0152] Mi measurement input, in particular in three phases

[0153] MOD control value (operating mode)

[0154] Vc voltage control value

[0155] Vcontrol control value

[0156] Vmeas detected voltage, in particular of the electrical supply network

[0157] Vpoc voltage at the network connection point

[0158] ΔV voltage deviation

[0159] Pmod amplitude-modulated active power

[0160] Qmod amplitude-modulated reactive power

[0161] ΔQ1, ΔQ2 magnitude of the amplitude vibration

[0162] The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.