EP3097426A1

EP3097426A1 - Grid detection module for a wind turbine, and method for determining the grid frequency

Info

Publication number: EP3097426A1
Application number: EP15700269.2A
Authority: EP
Inventors: Heinz-Hermann Letas; Jörg Gätjens
Original assignee: Senvion GmbH
Current assignee: Senvion GmbH
Priority date: 2014-01-22
Filing date: 2015-01-05
Publication date: 2016-11-30
Also published as: WO2015110276A1; DE102014201143A1

Abstract

The invention relates to a method for determining the grid frequency, in which a voltage curve (U1) of a first phase (281) of the grid (16) and a voltage curve (U2) of a second phase (282) of the grid (16) are measured. A linear combination (UXi) is formed from the voltage curve (U1) of the first phase (281) and the voltage curve (U2) of the second phase (282). The time interval between a first voltage value of the linear combination (UXi) and a second voltage value of the linear combination (UXi) is determined. The invention also relates to a grid detection module which is suitable for carrying out the method. By virtue of the invention, it is possible to determine the grid frequency with shorter cycles and/or with increased accuracy.

Description

Grid detection module for a wind turbine and method for determining the grid frequency

The invention relates to a network detection module for a wind energy plant and to a method for determining the network frequency.

If a wind power plant feeds electrical energy in a network, the feeding takes place in synchronism with the Netzfre ^acid sequence. For the operation of a wind turbine, it is consequently necessary to determine the grid frequency. In order to meet the increasing demands placed on the grid compatibility of wind turbines, it is desirable to measure the grid frequency with shorter clocking or with increased accuracy.

In today's frequency measurements, it is common to determine the frequency based on the time interval between two zero crossings of the voltage curve of a phase. In ei ^¬ ner mains frequency of 50 Hz, every 20 ms gives a measured value, if one uses a zero crossing per period for the determination of the power frequency, and there is every 10 ms, a measurement value when two zero crossings per cycle for the determination of uses the network frequency. The time interval between two measured values is shortened, if the zero crossings not only at one phase, but at uses a plurality of phases for determining the network frequency.

The invention has the object of providing a method and a network acquisition module for a wind power plant determine prior ^¬ with which the mains frequency can be measured with improved quality. Based on the above-mentioned prior art, the problem is solved with the Merk ^¬ paint the independent claims. Advantageous embodiments are specified in the subclaims.

In the method according to the invention, a first voltage profile of the network is measured, and a second voltage profile of the network is measured. There is formed a linear ^¬ combination of the first voltage gradient and the second voltage waveform. A time interval between a first voltage value of the linear combination and a second voltage value of the linear combination is determined. If the time interval between two voltage ^values (for example the zero crossings) is known, it is easy to deduce the period of the oscillation and thus the frequency of the oscillation. The time interval is another form of representation of the frequency. If necessary, the frequency can be determined explicitly as the reciprocal of the period. The determination of the time interval in the context of the invention corresponds to the determination of a measured value for the mains frequency.

Since the mains frequency is identical in all phases of the network, the sinusoidal oscillation of two voltage ^curves results in a sinusoidal oscillation again from the linear combination. The frequency of the linear combination is identical to the frequency in the individual phases, where the voltage curve is verscho ^¬ ben by a fixed phase angle. So just like a directly measured voltage ^¬ extending possible to infer the frequency of oscillation from the time interval between two voltage values of the linear combination.

For measuring the voltage curve, there are various possibilities that are equivalent in the sense of the invention. Thus, the voltage curve between one of the phases of the network and the star point can be measured. Alterna tively ^¬ the voltage curve between one of the phases of the network and the ground potential can be measured. It is also possible to measure a voltage curve between two phases of the net ^¬ zes.

The invention has recognized that there are advantages when the network frequency is determined based on such a linear combination. First, by averaging over several measurements, the line frequency can be determined with increased accuracy. Second, it becomes possible to determine the network frequency at arbitrary times. The distance between two times at which the mains frequency is determined is therefore no longer specified by the fact that predetermined voltage values occur in the measured voltage curve. In addition, the linear combination can be used for a plausibility check, for example to detect a phase jump.

If the amplitude is known, it can be concluded based belie- biger voltage values within a period of a sinus ^¬ shaped vibration to the period and consequently on the frequency in principle. There is therefore no fundamental restriction between which voltage values time interval is determined to close to the frequency.

If the phase angle between the two voltage values is not greater than 360 °, then it is ensured that both voltage values are recorded within the same period of the oscillation. With a larger phase angle between the two voltage values, a conversion to the individual period is required. Preferably, both voltage values, between which the time interval is determined, lie within one period of the oscillation. The time interval can be determined to twice per period ^¬. To determine the period of oscillation, and thus the frequency, it is advantageous if the time interval between two voltage values is determined, between which a half period or a multiple of a half Pe ^¬ Riode. After a half period, the amount of the voltage value is the same and only the sign or Stei ^¬ supply can be opposite. The grid frequency is then accessible without further conversion or scaling.

The determination of the network frequency is further simplified if the voltage values between which the time interval is determined are zero crossings of the Li near combination. It is then not necessary to consider the amplitude of the oscillation. In a preferred embodiment, the invention determines the network frequency using the linear combination is additionally made to a classic determination the grid frequency, which is based directly on a measured voltage curve. In the method according to the invention, therefore, additionally the time interval between two voltage values of the first voltage profile and / or between two voltage values of the second voltage profile can be determined.

The grid into which the wind turbine feeds electrical energy regularly includes three phases whose phase angles are each shifted by 120 °. The erfindungsge ^¬ Permitted process is preferably carried out such that three voltage profiles are measured whose phase angles are each ^¬ weils shifted by 120 °. Is determined with each zero crossing, a value for the grid frequency for all three clamping ^¬ voltage gradients, then six equally distributed over the period values for the mains frequency arise. Expressed in Pha ^¬ senwinkeln located every 60 ° before a new measured value for the mains frequency. At a mains frequency of 50 Hz, this corresponds to six measured values in 20 ms, ie a time-dependent distance of 3.33 ms between two successive measured values. In a preferred embodiment of the method according to the invention more than six times per Pe ^¬ Riode of the oscillation is determined, a measurement value for the mains frequency. The phase angle between two successive measured values for the mains frequency can be less than 60 °, preferably less than 30 °, more preferably less than 15 °, over the entire period of the oscillation. Given a suitable plurality of linear combinations and / or a plurality of measured voltage profiles, the time interval between two

Voltage values determined. The time interval preferably relates in each case to two voltage values of the same voltage curve or the same linear combination. The linear combination of the voltage profiles is selected in a preferred embodiment so that the zero crossing of the linear combination includes a phase angle of 30 ° with one of the measured voltage waveforms. The time interval to the previous measured value for the mains frequency is then halved. At a mains frequency of 50 Hz, it is thus possible to obtain a measured value every 1.67 ms. Can be achieved, the phase angle of 30 °, in which the linear combination is formed as the difference between the first measured voltage waveform and the second measured voltage waveform when the first voltage gradient and the second voltage waveform has a phase angle of 120 ° Zvi ^¬ rule lock themselves. The linear combination then closes with the first measured voltage waveform a phase angle of 30 ° and with the second measured voltage ^¬ extending a phase angle of 150 °.

If one forms a linear combination from each adjacent one of the measured voltage curves, then three linear combinations result, which are offset by 120 ° from each other. If one measured value for the mains frequency is determined at every zero crossing of one of the measured voltage profiles or one of the linear combinations, this results in twelve measured values which are uniformly distributed over the period. The phase angle between two successive measured values is 30 °, the time interval at a mains frequency of 50 Hz ^¬ is 1.67 ms. The term linear combination denotes the sum of a first measured voltage curve and a second measured voltage curve, wherein both voltage curves are multiplied by a constant factor not equal to zero. For example, the first voltage waveform to the Fak ^¬ gate 1 and the second voltage waveform can be multiplied by a factor Zvi ^¬ rule and -1. 1 In the example in which the linear combination is the simple difference between two measured voltage curves, the first voltage curve is multiplied by the factor 1 and the second voltage curve by the factor -1.

By selecting appropriate linear combinations of the phases senwinkel or the time interval between two aufei ^¬ nanderfolgenden measurements of the line frequency can be further reduced. The linear combinations can be selected such that the 60 ° -Phasenwinkel, which can be by direct from ^¬ evaluation of three voltage waveforms which include a phase angle of 120 ° with one another, reach, is divided into more than two partial angle. The partial angles can be the same or different.

If one describes the time-dependent voltage of a first voltage curve with Ul (t), the time-dependent voltage ei ^¬ nes second voltage waveform, which is shifted to the first voltage ^¬ course by a phase angle of 120 °, with U2 (t) and a linear combination of both UXi (t), a suitable number of factors Fi yields a multiple number of linear combinations UXi (t):

UXi (t) = Ul (t) + Fi * U2 (t).

For each factor Fi between 0 and 1, a new linear combination UXi results, which with Ul (t) includes a phase angle between 0 ° and 60 ° with Ul. The factors Fi can be chosen such that the 60 ° angle range is subdivided into a plurality of equally large partial angles. For example, five factors Fi can be ^so-¬ selects that adjacent linear combinations each of which includes a phase angle of 12 ° with each other.

The mathematical treatment is simplified if the phase angles between adjacent linear combinations do not have to be exactly the same, but if it is sufficient that they are approximately the same size. The linear ^¬ combinations can then be defined as follows:

UXi (t) = UI (t) + i / N * U2 (t) with i = 1 ... Nl With i = 0, there is no linear combination according to the invention before, but the voltage curve would Ul (t) entspre ^¬ chen , With i = N, there is likewise no linear combination in the sense of the invention, but the voltage curve would correspond to -U3 (t). These two voltage curves are accessible by direct measurement, so that the erfindungsge ^¬ MAESSEN linear combinations are not applied. The phase angles between two successive measured values of the mains frequency are in this example no greater than 15 °. If one forms corresponding linear combinations be- see all three measured voltage characteristics of the network, so is not exceeded over the entire period of the oscillation of these Pha ^¬ senwinkel between two successive measurements of the mains frequency. The 60 ° phase separations between two successive measurements of the line frequency are obtained by detecting the zero crossing twice per period in each of the three phases. The same result can be obtained by taking the Zero crossing detected only once per period, and for each ^¬ Weil additionally determined the zero crossing of the negative voltage waveform. The six different measurements per period then result from evaluation of Ul, -Ul, U2, -U2, U3 and -U3.

A wind power plant supplies the electric power re ^¬ regularly initially in a wind park internal connection network, a, from the forwarding in a public transmission network takes place. The generator of the wind energy plant is synchronized with the grid, so that the frequency in the electrical system of the wind turbine, in the wind farm internal connection network and in the public transmission network coincides. The voltage profiles according to the invention can be measured in the electrical system of a wind energy plant and / or in a wind farm internal access network and / or in a transmission network. In a preferred embodiment, the method according to the invention is carried out Wenig ^¬ least a wind turbine of a wind park and / or in a parking master of a wind farm. Carried the dung OF INVENTION ^¬ proper determination of the mains frequency preference ^¬ as on unfiltered measured values of the voltage profile.

The invention also relates to a network detection module suitable for carrying out the method. The net ^¬ metering module comprises a voltage sensor for measuring a first voltage waveform of the network and a second voltage waveform of the network. The power detection module to ^¬ also incorporates a computing module, which is adapted to form a linear combination of the first voltage gradient and the second voltage waveform as well as an evaluation module, which is adapted to the time interval between a first voltage value of the linear combination and to determine a second voltage value of the linear combination. The voltage sensor can be designed to measure voltage profiles in the electrical system of a wind energy plant and / or in a wind park-internal access network and / or in a transmission network.

The power detection module may be with other features fortge ^¬ forms, which are described in the context of the inventive method. In particular, the re chenmodul and / or the evaluation module can be configured to carry out further steps of the method according to the invention durchzu ^¬. In addition, the power detection module may further comprise Mo ^¬ modules that are designed for carrying out further steps of the inventive method.

The invention also relates to a wind turbine equipped with such a network detection module. The wind turbine comprises a rotor and a generator driven by the rotor. The wind turbine is designed to generate electricity generated by the generator

To feed energy into a network. In addition, the invention relates to a parkmaster for a wind turbine comprising several wind turbines. The parkmaster is designed to handle central control tasks for wind farm wind turbines. In particular, receives the

Parkmaster specifications from outside the wind farm, based on the de ^¬ rer Parkmaster specifications for the operation of the wind turbines of the wind farm determined. The invention will now be described by way of example with reference to the accompanying drawings, given by way of advantageous embodiments. Show it: a schematic representation of a wind farm; a schematic representation of a wind energy ^¬ plant with a network detection module according to the invention;

the voltage curve in the three phases of the Net ^¬ zes;

the view of Figure 3, in addition, three Li nearkombinationen are shown.

a vector representation of the voltage waveforms of Fig. 4;

the voltage curve in two phases of the network; a plurality of linear combinations of the voltage waveforms shown in FIG. 6; and

a vector representation of the voltage waveforms of Fig. 7.

In a wind farm in Fig. 1, a plurality of wind turbines 14, 15 connected to a wind park internal connection network 16. In the connection network 16 is a medium voltage of, for example, 20 kV. Before the transfer to a public transmission network 17, the voltage is transformed by a transformer 18 to a high voltage of, for example, 380 kV. To the transmission network 17, a plurality of consumers 20 is connected, which are indicated only schematically in Fig. 1.

In the schematic representation of the wind turbine 14 in Fig. 2, the rotation of a rotor 21 is translated by a gear 22 to a higher speed, with which a generator 23 is driven. The electric current generated by the generator 23 is transmitted via a connection with three phases 281, 282, 283 to a transformer 25. tet, which brings the voltage to the voltage applied in the connection network 16 medium voltage. It is a dop ^¬ pelt fed induction generator (DFIG), is connected to parallel to the generator 23 at a converter 24th The converter 24 comprises a machine-side converter 241 and a line-side converter 242, which are connected to one another via a DC link.

A voltage sensor 29 measures between the generator 23 and the transformer 25 in the three phases 281, 282, 283 of the three-phase system, the voltages Ul, U2, U3 relative to the neutral. The grid frequency, which is measured with the voltage sensor 29, coincides with the grid frequency in the wind farm internal access network 16 and the transmission network 17. Plotting the measured values of the voltage sensor 29 over time, so there are three sinusoidal clamping voltage gradients ^¬ Ul, U2, U3, which are each displaced by a phase angle of 120 ° relative to each other. The voltage profiles Ul, U2, U3 are shown in FIG.

An evaluation module 31, which is integrally joined ^¬ the voltage sensor 29, evaluates the voltage waveforms Ul, U2, U3, and identifies the zero crossings. In each phase 281, 282, 283 there are two zero crossings per full period. Substituting the full period with a ^¬ phase angle of 360 ° is equal to the two zero crossings are 180 degrees apart. If one considers the three voltage profiles Ul, U2, U3 together, there are six zero ^crossings per period. In phase angles, the next zero crossing follows after 60 °.

The evaluation module 31 also determines the time ^interval between two successive zero crossings same phase. From the reciprocal of the time interval can be easily close to the mains frequency. For the purposes of the invention, the time interval between two zero crossings therefore applies as another form of representation of the network frequency.

If the evaluation module 31 uses every zero crossing in one of the phases 281, 282, 283 in order to determine the network frequency, this results in six measured values for the network frequency per period. At a frequency of 50 Hz, the period lasts 20 ms. Thus, each time after 3.33 ms, a new measured value for the line frequency is obtained.

According to FIG. 2, the wind energy installation furthermore comprises a computing module 30 in order to form linear combinations of the voltage profiles U1, U2 and U3. The arithmetic module 30 is exactly like the evaluation module 31, the measured values of the tension ^¬ opening sensor 29 in unfiltered form. The linear combinations form sinusoidal voltage curves with the same frequency as the voltage profiles Ul, U2 and U3. From the computing module 30, the linear combinations are transmitted to the evaluation module 31. The evaluation modules 31 can determine the network frequency from the linear combinations in the same way as from the voltage profiles obtained directly from the voltage sensor 29.

4 shows in addition to the voltage curves from FIG. 3 in dashed lines three linear combinations which the calculation module 30 has formed by subtraction from the voltage profiles U1, U2 and U3. The linear combinatio ^¬ NEN U2-U1, U3 and U1-U2-U3 respectively corresponding to the clamping ^¬ voltage gradients, which is obtained when measuring the voltage in two of the three phases to each other. FIG. 5 shows a vector illustration of the three voltage profiles U1, U2 and U3 as well as the linear combinations U2-U1, U3-U2 and U1-U3. In the vector representation, the information about the time course is missing, but the information about the phase angle is more accessible. The voltage profiles Ul, U2 and U3 include a Phasenwin ^¬ angle of 120 ° each with each other. Vector subtraction with the adjacent phase results in the linear combinations U2-U1, U3-U2 and U1-U3, which are shown in dashed line according to FIG. The amplitude of the linear combinations is greater than the amplitude in the phases. This has no effect on the method according to the invention if the grid frequency is determined on the basis of the zero crossings.

The phase angle between the linear combination and the adjacent phase is 30 ° in each case. Since the zero crossings occur not only once per period but once per half-wave, a non-illustrated second zero crossing, which is shifted by a phase angle of 180 °, results for each of the vectors shown in FIG. 5. The zero crossings are thus equally distributed over the period, so that in each case after a phase angle of 30 °, the next zero crossing occurs. This can be seen in FIG. 4.

If one uses each of the zero crossings of the voltage profiles U1, U2 and U3 as well as the linear combinations for a renewed investigation of the network frequency, a new measured value results after phase angles of 30 ° each. On the time axis, the distance between two Benach ^¬ disclosed zero crossings halved. At a frequency of 50 Hz results Consequently, every 1.67 ms a new measured value for the grid frequency.

By suitable selection of the linear combinations, the phase angle or the time interval between two successive measurements of the mains frequency can be shortened even further. An example of this is shown in FIGS. 6 to 8. For the sake of clarity, FIG. 6 does not show all three phases of the network 16, but only the two phases Ul and U2. In Fig. 7, the phase Ul and four linear combinations of Ul and U2 are shown. In Fig. 8, the solid arrows extending from the center point correspond to the voltage waveforms shown in Fig. 7. In this embodiment, the 60 ° phase angle between Ul and -U3 is divided into five sections. The Un ^¬ division is accomplished by the following four linear combinations of Ul and U2: UXi (t) = UI (t) + i / 5 * U2 (t) with i = 1 ... 4 d.

The phase angle between two adjacent Linearkombina ^¬ functions UXi is approximately 12 °. Due to the linear gradation of the factors before U2, the phase angles between two adjacent linear combinations UXi are not completely identical but only approximately identical.

For the sake of clarity, the representation in FIGS. 7 and 8 is limited to the angular range between U1 and -U3. If one forms corresponding linear combinations UXi between U2 and U3 as well as between U3 and Ul and one uses each zero crossing of one of the phases or one of the linear combinations for the determination of the mains frequency, so you get after phase angles of each about 12 °, a new measured value for the grid frequency. At a mains frequency of 50 Hz, a new measured value for the mains frequency results every 0.67 ms. This opens up the possibility that the wind turbine can react very quickly to changes in the grid frequency. In addition, the network frequency can be determined with increased accuracy by averaging over a plurality of measured values.

Claims

claims

Method for determining the network frequency with the following steps:

a. Measuring a first voltage waveform (Ul) of the network (16);

b. Measuring a second voltage waveform (U2) of the network (16);

c. Forming a linear combination (UXi) from the first voltage waveform (Ul) and the second clamping ^¬ extending voltage (U2);

d. Determining the time interval between a first voltage value of the linear combination (UXi) and a second voltage value of the Linearkombi ^¬ nation (UXi).

A method according to claim 1, characterized in that the phase angle between the first voltage value and the second voltage value is not greater than 360 °.

A method according to claim 1 or 2, characterized in that the first voltage value and / or the second voltage value is a zero crossing.

Method according to one of claims 1 to 3, characterized in that in the linear combination (UXi), the time interval is determined twice per period.

Method according to one of claims 1 to 4, characterized in that in addition the time interval between two voltage values of the first voltage profile (U1) and / or between two voltage values of the second voltage profile (U2) is determined.

A method according to any one of claims 1 to 5, characterized in that more than six times per period of the time interval between two voltage values is ermit ^¬ telt.

Method according to one of claims 1 to 6, characterized in that the phase angle between two determinations of the time interval is not greater than 30 °, preferably not greater than 15 °.

Method according to one of claims 1 to 7, characterized in that the time interval is determined several times, so that over a period of Span ^¬ voltage curve (Ul, U2) considered the phase angle between two successive determinations is not greater than 30 °, preferably not greater than 15 °.

Method according to one of claims 1 to 8, characterized in that the linear combination of the dif ference from the voltage curve (U2) of the second phase

(282) and the voltage curve (Ul) of the first phase

(281).

10. The method according to any one of claims 1 to 9, characterized in that a plurality of Linearkombina ^¬ tions (UXi) from the voltage curve (Ul) of the first phase (281) and the voltage curve (U2) of the second phase (282) is formed , Method according to one of Claims 1 to 10, characterized in that the time interval is determined on the basis of un filtered measured values of the voltage profile (U1, U2).

Network detection module with a voltage sensor (29) for measuring a first voltage curve (U1) of the network

(16) and to measure a second voltage waveform

(U2) of the network (16), wherein the network detection module further comprises a computing module (30), which is designed to ^¬ a linear combination (UXi) from the first voltage waveform (Ul) and the second voltage waveform

(U2), and an evaluation module (31), which is adapted to the time interval between a first voltage value of the linear combination (UXi) and a second voltage value of the linear combination

(UXi) to determine.

Network detection module according to claim 12, characterized in that the first voltage value and / or the second voltage value are zero crossings of the Linearkombi nation (UXi). 14. Wind energy plant with a rotor and a by the rotor (21) driven generator (23), wherein the wind turbine is ^{adapted to} feed with the Genera ^¬ gate (23) generated electrical energy in a network (16), characterized in that the wind power plant comprises a grid detection module according to claim 12 or 13.