Title of Invention	METHOD FOR SAMPLINIG A CURRENT OR VOLTAGE PROFILE AND FOR FORMING SAMPLING VALUES, IN PARTICULAR FOR USE IN PROTECTION OR CONTROL DEVICES FOR ENERGY TRANSMISSION SYSTEMS
Abstract	The invention relates to a method for sampling a current or voltate profile (U(t) and for forming sampling values (U(n) having a temporal relationship with a predefined system clock (G). According to the invention, an auxiliary clock (H) which runs freely in relation to t the system clock is used to form auxiliary sampling values (U(n), the time offset of the sampling time of each auxiliary sampling value in each case in relation to the system clock is determined, time offset values (Δ t(n) specific to auxiliary sampling values are determined, and the auxiliary sampling values (U(n) are re-sampled using the time offset values (Δ t(n) specific to auxiliary sampling values, with the sampling values (U'(n), which have a temporal relationship with the system clock being formed in the re-sampling.

Title of Invention

METHOD FOR SAMPLINIG A CURRENT OR VOLTAGE PROFILE AND FOR FORMING SAMPLING VALUES, IN PARTICULAR FOR USE IN PROTECTION OR CONTROL DEVICES FOR ENERGY TRANSMISSION SYSTEMS

Abstract

The invention relates to a method for sampling a current or voltate profile (U(t) and for forming sampling values (U(n) having a temporal relationship with a predefined system clock (G). According to the invention, an auxiliary clock (H) which runs freely in relation to t the system clock is used to form auxiliary sampling values (U(n), the time offset of the sampling time of each auxiliary sampling value in each case in relation to the system clock is determined, time offset values (Δ t(n) specific to auxiliary sampling values are determined, and the auxiliary sampling values (U(n) are re-sampled using the time offset values (Δ t(n) specific to auxiliary sampling values, with the sampling values (U'(n), which have a temporal relationship with the system clock being formed in the re-sampling.

Full Text	Description Method for sampling a current or voltage profile and for forming sampling values, in particular for use in protection or control devices for energy transmission systems The invention relates to a method, in particular for use in protection or control devices for energy transmission systems, having the features according to the precharacterizing clause of claim 1. Such a method is disclosed in the German laid-open specification 199 33 684. In this method, a high-voltage or heavy-current signal is sampled using an internal clock which is synchronized with the globally available GPS (Global Positioning System) signal. The GPS signal thus predefines a system clock to which the sampling values are related. The sampling values are then evaluated for the purposes of protection, in particular for the purposes of differential protection. The invention is based on the object of specifying a method which can be used to form sampling values, which have little jitter and very little noise, with little outlay in terms of devices or hardware. On the basis of a method of the type specified at the outset, this object is achieved according to the invention by the characterizing features of claim 1. Advantageous refinements of the method according to the invention are specified in subclaims. Accordingly, the invention provides for an auxiliary clock or auxiliary clock signal which runs freely relative to the system clock to be used to form auxiliary sampling values, for the temporal offset of the sampling time of each auxiliary sampling value to be respectively determined relative to the system clock and temporal offset values which are specific to the auxiliary sampling values to be determined, and for the auxiliary sampling values to be subjected to resampling, in which the sampling values which are temporally related to the system clock are formed, using the temporal offset values which are specific to the auxiliary sampling values. A crucial advantage of the method according to the invention can be seen in the fact that less hardware than in previous sampling systems is needed overall to generate the sampling values since the auxiliary clock used for sampling runs freely and it is thus possible to completely dispense with phase tracking, for example on the basis of a PLL (Phase Locked Loop) circuit. Sampling is thus effected using a free-running clock and resampling is effected "only" arithmetically, for example, using the temporal offset values which have been determined. Another crucial advantage of the method according to the invention can be seen in the fact that the sampling values have very little jitter and noise. The inventors found that a sampling clock derived from a predefined system clock and phase-coupled to the latter may, under certain circumstances, have a relatively large amount of jitter and may result in a relatively large amount of noise in the sampling values. The invention begins at this point by dispensing with such phase coupling or phase tracking; instead of this, sampling is carried out independently of the system clock and an auxiliary clock which runs freely with respect to the system clock and is of high quality, in particular has little jitter, is used for upstream auxiliary sampling. The sampling times of the auxiliary sampling values are thus generally temporally offset or phase-shifted as desired with respect to the system clock; in order to nevertheless establish a temporal relationship with the system clock, the auxiliary sampling values are then subjected to resampling, to be precise using the temporal offset values which are specific to the auxiliary sampling values and have previously been recorded for each auxiliary sampling value during auxiliary sampling. The result is thus the formation of sampling values with the correct time base but with considerably less jitter and less noise because the system clock is used only during downstream resampling, which is only carried out numerically for example, but not for primary "physical" sampling. The GPS signal, the Galileo signal, a real-time SNTP signal, a system clock of an SDH network or a system clock signal derived using one or more of these signals is preferably used as the system clock. The output signal of a local free-running oscillator is preferably used as the auxiliary clock signal. The auxiliary clock signal can be generated, for example, using a central busbar protection device and can be fed into sampling devices which are connected to said central busbar protection device using the latter. The sampling devices may be integrated, for example, in measuring transducers which are connected to one or more energy transmission lines. Alternatively, the auxiliary clock signal may be derived from the signals of a real-time transmission network, in particular a real-time ETHERNET network. The temporal offset values are formed, for example, using a counter which counts the clock pulses of a predefined counting clock and is respectively reset by pulses of the system clock and the count, of which is respectively read out as the temporal offset value if the auxiliary clock is used to record an auxiliary sampling value. The count is clearly a measurement variable for the period of time which has passed between the last respective pulse of the system clock and the recording of the respective auxiliary sampling value. The sampling values formed using the method described are are processed further for the purposes of protection in protection or control devices. The invention also relates to an arrangement for sampling a current or voltage profile and for forming sampling values which are temporally related to a predefined system clock. With respect to such an arrangement, the invention is based on the object of ensuring that the sampling values have little jitter and have as little noise as possible. According to the invention, this object is achieved by means of an arrangement having an auxiliary sampling device and a resampling device: the system clock and an auxiliary clock, which runs freely relative to the system clock, are applied to the auxiliary sampling device and the latter uses the auxiliary clock to form auxiliary sampling values and temporal offset values which are specific to the auxiliary sampling values and each specify the temporal offset relative to the system clock for each sampling time. The resampling device is arranged downstream of the auxiliary sampling device and subjects the auxiliary sampling values of the auxiliary sampling device to resampling, in which the sampling values which are temporally related to the system clock are formed, using the temporal offset values which are specific to the auxiliary sampling values. With regard to the advantages of the arrangement according to the invention, reference is made to the above statements in connection with the method according to the invention. The auxiliary sampling device is preferably contained in a current or voltage converter if the intention is to form sampling values which relate to an energy transmission system. The resampling device may, for example, form part of a field device, in particular a protection device. The auxiliary sampling device and the resampling device are preferably connected to one another by means of a data transmission bus or a data transmission network. If a central busbar protection device is present in the energy transmission system, it is considered to be advantageous if the central busbar protection device forms the auxiliary clock and transmits it to the auxiliary sampling device. With a view to the formation of phasor measured values, it is considered to be advantageous if a phasor formation device which uses the sampling values to form current or voltage phasors is connected to the resampling device. The invention is explained in more detail below using exemplary embodiments; in this case, by way of example figure 1 shows a first exemplary embodiment of an arrangement for generating sampling values, which is also used to explain the method according to the invention by way of example, figure 2 shows, by way of example, a sampled voltage signal, figure 3 diagrammatically shows the reconstruction of a voltage signal, figure 4 shows a basic illustration of a resampling operation with an interpolation filter, figure 5 shows a comparison of different interpolation filters, figure 6 shows the amplitude response, which is associated with the pulse response, of an interpolation filter having a Blackman window, figure 7 shows the amplitude response of the interpolation filter shown in figure 6 in the passband, figure 8 shows, by way of example, sampling times, figure 9 shows a table containing relevant mathematical properties of the interpolation filter shown in figure 6, figure 10 shows a flowchart which summarizes the method for forming sampling values once again by way of example, and figure 11 shows another exemplary embodiment of an arrangement according to the invention. Figure 1 illustrates an arrangement 10 for sampling a current or voltage profile and for forming a corresponding current or voltage phasor. In this case, the arrangement is explained, by way of example, for the situation in which a voltage signal U(t) is intended to be sampled and a voltage phasor U is intended to be formed. The arrangement 10 has an auxiliary sampling device 20, at the input E20a of which the voltage signal U(t) to be sampled is fed in. A further input E2 0b of the auxiliary sampling device 20 is connected to an auxiliary clock generator 30 which generates a free-running auxiliary clock or auxiliary clock signal H on the output side and feeds it into the auxiliary sampling device 20. On the input side, the auxiliary sampling device 20 has an A/D converter 40 whose analog input is connected to the input E20a of the auxiliary device 20 and thus has the voltage signal U(t) applied to it. A measured value forming device 50 which transmits sampling values U(n) formed by the A/D converter 40 to a downstream measured value memory 60 is arranged downstream of the A/D converter 40. The measured value forming device 50 is also connected to a memory or latch module 70 which has a counter 80 connected upstream of it on the input side. The reset input R80 of the counter 80 is connected to a GPS receiving device 90 which generates a GPS signal as the system clock or system clock signal G and feeds it into the counter 80. The system clock G generates a respective short pulse for each second, for example. A clock input T80 of the counter 80 is connected to a signal generator 100 which feeds a clock signal or counting clock T into the clock input T80 of the counter 80. An output A20 of the auxiliary sampling device 20 is formed by an output A60 of the measured value memory 60; the latter is connected to a resampling device 200 which has a phasor formation device 210 connected downstream of it. The resampling device 200 subjects the auxiliary sampling values U(n) of the analog/digital converter 40 to resampling and generates, on the output side, resampled voltage values U'(n) which are then converted into the voltage phasor U by the phasor formation device 210; the voltage phasor U is thus related to the system clock G of the GPS receiving device 90 and forms a so-called synchronous phasor. The term synchronous phasor is used to mean that the phasor U is related to the system clock. The arrangement shown in figure 1 is operated, for example, as follows: The GPS receiving device 90 is used to generate, on the output side, the system clock G which is fed into the counter 80. At the same time, the signal generator 100 is used to feed the counting clock T into the counter 80 which then begins to count. The counter 80 is reset whenever the system clock G generates a pulse. The count Z of the counter 80 is respectively stored in the memory module 70 when it is triggered with the free-running auxiliary clock H. As soon as the auxiliary clock H thus generates its n-th clock pulse, both the A/D converter 40 is triggered and a sampling value U(n) is generated and the respective count Z(n) is simultaneously recorded in the memory module 70 and is transmitted to the measured value forming device 50 as a temporal offset value At(n) which is specific to the auxiliary sampling value. If the counting clock has a clock rate of fT = 1 GHz, the temporal offset value At(n) relative to the pulses of the system clock G can be determined with a temporal accuracy of 1 ns. The counter 80 and the memory module 70 thus together form a counting device which forms the temporal offset values At(n) by counting the clock pulses of the counting clock T, respectively resetting itself if a pulse of the system clock G is present and respectively outputting its count Z as a temporal offset value as soon as the auxiliary clock H is used to record an auxiliary sampling value U(n). The measured value forming device 50 transmits the respective auxiliary sampling value U(n) of the A/D converter 40, together with the associated temporal offset value At (n) which is specific to the auxiliary sampling value, to the measured value memory 60 which stores the auxiliary sampling value U(n), with the associated temporal offset value ?t(n) which is specific to the auxiliary sampling value, as a measured value pair (U(n); At(n)) . Although the auxiliary sampling value U(n) has not been sampled with the system clock G, it nevertheless has a known temporal phase angle with respect to the system clock G because the respective temporal relationship with the system clock G or with the respective preceding pulse of the system clock G has been defined, for each auxiliary sampling value U(n), by the temporal offset value At (n) which is specific to the auxiliary sampling value. In addition to the counter value Z, an absolute time statement TAS which states the time of the last pulse of the system clock in absolute terms may also be stored in the temporal offset value ?t(n) or with the temporal offset value ?t (n) ; this makes it possible to determine the sampling time TAH for each auxiliary sampling value in absolute terms according to: TAH = TAS + Z * 1/fT. The resampling device 200 reads the auxiliary sampling values U(n), together with the associated temporal offset values At (n) which are specific to the auxiliary sampling values, from the measured value memory 60 and carries out "arithmetic" resampling using the system clock G. Resampled sampling values U'(n) which are related to the system clock G are generated on the output side during this resampling operation; a resampling rate which corresponds to an integer multiple of the system clock G is preferably used for this purpose. The sampling values U' (n) can then be used in the phasor formation device 210 to form the voltage phasor U which forms a so-called synchronous phasor. As already explained, the term "synchronous phasor" should be understood in this context as meaning a phasor which is synchronized with the predefined system clock G. Figure 2 shows, by way of example, the voltage signal U(t) sampled by the free-running auxiliary clock H at a fixed sampling rate. In order to be able to calculate a phasor U which is as exact as possible for the purpose of characterizing the fundamental of the voltage signal U(t), the sampling frequency of the auxiliary clock H is preferably set in such a manner that it is an integer multiple of the frequency of the fundamental of the voltage signal U(t). In order to be able to meet this requirement, the frequency of the fundamental of the voltage signal U(t) is measured, for example. A multiple of the fundamental frequency determined in this manner is then used further as the auxiliary clock H. As already mentioned, a resampling method is used to adapt the sampling values U(n) to the system clock G. The resampling method is based on the theory of the Shannon sampling theorem. This theorem states that each ideally band-limited signal x can be interpolated using the si function: Figure 3 illustrates this situation using part of a sinusoidal function with the depicted si interpolation functions which make it possible to reconstruct sampled band-limited signals. An ideally band-limited function which is given at points 3, 4, 5, ... etc. can thus be calculated at any desired other location by solving the Shannon equation for these points. There are now two possible ways of interpreting this function for resampling use: The first option is to place the extreme value of the interpolation function through tne given sampling values, as shown in figure 3. However, this variant is not particularly practical for resampling use since an infinite sum of all si functions would have to be calculated in this case for each sampling value. According to a second variant, use is made of the fact that, apart from at the sampling value to be interpolated, the si function assumes the value 0 at the location of all other sampling values. That is to say, if the signal is interpolated with the si function at the locations of the new sampling values, only one si function must be considered. If the si function is now positioned at the location of the new sampling value with the period duration of the new sampling interval and is calculated at the locations of the given sampling values, the new sampling value can be determined. Figure 4 illustrates this situation using resampling by means of an interpolation filter. In practice, of course, this interpolation should not be carried out directly with the si function since this function does not only have a value that is not equal to zero in a finite interval of time. However, simply cropping the function at the fifth zero crossing on both sides of the extreme value does not provide a frequency response which differs considerably from the ideal low-pass in the frequency range. In this case, it is better to limit the si function to a finite range with a window function. The Blackman window function is used for this purpose in the present example. In this case, a stop-band attenuation ratio of at least 60 dB is achieved. Although better values could be achieved with the known Kaiser function, this is at the expense of the window size. Since 60 dB can be considered to be sufficient, a Kaiser window should preferably not be used. Figure 5 shows the interpolation function used in more detail. The curve denoted "xi" represents the Blackman window function which has been selected by way of example. The curve denoted "si" shows the si function which is not temporally limited. The curve denoted "hsi" is the interpolation function which has been temporally limited using the window function. Figure 6 shows the amplitude response associated with the illustrated pulse response using the example of a sampling rate reduction from 10 kHz to 5 kHz. As can be seen in figure 6, the interpolated signals are band-limited to the new half sampling frequency. The ripple in the passband is at most 0.2 10-4 . Figure 7 shows the characteristic curve in the passband. It can be seen in figure 7 that the ripple in the entire passband is on average considerably less than 10-4. This filter can thus be used to meet all the accuracy requirements even in the passband. As is not intended to be proven here any further, the This equation is the solution of a least-squares estimator which fits the interpolation function into the received sampling value stream at the desired location t0- The function w(t) is the Blackman window function. Figure 8 shows the implementation of resampling for the selected resampling method: a sampling value in the original sampling value stream on the basis of the auxiliary clock H is present at the times denoted with a cross. Resampling is intended to be carried out at the points denoted with a circle. A sampling rate which is synchronized with the system clock G and preferably corresponds to a multiple, for example an integer multiple, of the pulse rate of the system clock G is used for resampling. The designation "GPS sync pulse" marks, by way of example, one of the pulses of the GPS signal, one of which usually occurs each second. The ratio of the new sampling frequency to the old sampling frequency is 3/5 in this example. If the sampling value is intended to be calculated at the time t=0, an interpolation filter whose extreme value is precisely at the original sampling value 0 is used. In this case, the data window extends precisely w/2 sampling values into the past and w/2 sampling values into the future. In order to calculate the new sampling value at the point t=3, an interpolation filter whose extreme value has been shifted to the right by precisely 3/5 TA of the original sampling interval TA must be used. In total, five different sets of filter coefficients are thus needed to implement resampling in this example. The formulas in the table shown in figure 9 describe the proposed algorithm in detail. Figure 10 summarizes the exemplary method sequence once again in the form of a flowchart. The exact determination of the signal fundamental frequency f of the input signal U(t) is decisive for the accuracy of the synchronous phasor U determined. For this purpose, the frequency f is preferably determined from phasors of a plurality of successive data windows according to the following formula: The validity of the frequency measured value f can be derived from the development of the phase angle cp(t). The frequency measured value f determined is valid when the phase angle develops in a virtually linear manner. If sudden changes are determined in the profile of the measured phase angle, the data window must be repositioned for the frequency measurement. Resampling is carried out a second time in a second step with a frequency measured value f which is now valid. The phasor determined in this manner can then be used as a synchronous phasor. The method is continued in the recursion steps described. The specific technical implementation of the resampling method in the resampling device 200 can be effected, for example, in a manner as explained in "A flexible sampling-rate conversion method" (Smith, J.O. and Gosset, P.; 1984; Proceedings of the International Conference on Acoustic, Speech, and Signal Processing, San Diego, Volume 2, pages 19.4.1-19.4.2; New York. IEEE Press). Figure 11 illustrates another exemplary embodiment of an arrangement according to the invention which can also be used to carry out the method according to the invention. An energy transmission line 500 to which two measuring transducer units 510, 520 are connected is seen in figure 11. The two measuring transducer units 510 and 520 are each provided with an auxiliary sampling device 20 as has already been explained in connection with figure 1. The two measuring transducer units 510 and 520 are connected to a downstream protection device 530; the connection between the protection device 530 and the two measuring transducer units 510 and 520 is ensured by a data bus or a data transmission network (for example an Ethernet network) 540 which can be provided with a switch 550, for example. As can also be seen in figure 11, a system clock G which is predefined, for example, by the GPS signal is applied to the two measuring transducer units 510 and 520 and the protection device 530. The protection device 530 is provided with a resampling device 200 and a phasor formation device 210; the two components may correspond to the resampling device 200 and the phasor formation device 210 shown in figure 1. The arrangement shown in figure 11 can be operated as follows: Current and voltage measured values Ul(t) and II(t) and U2(t) and 12 (t) of the energy transmission line 500 are recorded using the measuring transducer units 510 and 520 and are subjected to analog/digital conversion. In this case, auxiliary sampling values II(n), 12(n), Ul(n) and U2(n) are formed on the output side according to an auxiliary clock H and are transmitted, together with the respective associated temporal offset values ?t(n) which are specific to the auxiliary sampling values, to the protection device 530 via the network 540. The auxiliary clock H can be individually generated in each of the measuring transducer units 510 and 520 or can be predefined from the outside for both measuring transducer units 510 and 520; for example, the auxiliary clock H is formed by a central busbar protection device 600 and is fed into the measuring transducer units 510 and 520. Alternatively, the auxiliary clock H can be derived from the data signals of the network 540 which is preferably a real-time transmission network, in particular a real-time ETHERNET network. The protection device 530 subjects the auxiliary sampling values Ul(n), U2(n), II(n) and 12(n) to resampling and generates, on the output side, sampling values Ul' (n) , U2' (n), I1'(n) and 12'(n) which are synchronized with the system clock G. The phasor formation device 210 of the protection device 530 uses these sampling values Ul'(n), U2'(n), II'(n) and 12'(n) to form synchronous phasors Il, I2, U1 and U2. The synchronous phasors Il, I2, U1 and U2 can be evaluated inside the protection device 530 or outside the protection device 530, for example in a downstream control system or the like, in order to determine whether a fault, in particular a short circuit, has occurred on the energy transmission line 500. The synchronous phasors Il, I2, Ul and U2 can thus be used to generate fault signals. Patent claims 1. A method for sampling a current or voltage profile (U(t)) and for forming sampling values (U' (n) ) which are temporally related to a predefined system clock (G), characterized in that an auxiliary clock (H) which runs freely relative to the system clock is used to form auxiliary sampling values (U(n) ) , the temporal offset of the sampling time of each auxiliary sampling value is respectively determined relative to the system clock and temporal offset values (At(n)) which are specific to the auxiliary sampling values are determined, and the auxiliary sampling values (U(n)) are subjected to resampling, in which the sampling values (U1(n)) which are temporally related to the system clock are formed, using the temporal offset values (At(n)) which are specific to the auxiliary sampling values. 2. The method as claimed in claim 1, characterized in that the GPS signal, the Galileo signal, a real-time SNTP signal, a system clock of an SDH network or a system clock signal derived using one or more of these signals is used as the system clock. 3. The method as claimed in one of the preceding claims, characterized in that a clock signal of a local free-running oscillator (30) is used as the auxiliary clock. 4. The method as claimed in one of the preceding claims 1-2, characterized in that the auxiliary clock is obtained from a clock signal of a real- time transmission network, in particular a real-time ETHERNET network. 5. The method as claimed in one of the preceding claims, characterized in that the temporal offset values (?t(n)) are formed using a counting device (70, 80) which counts the clock pulses of a predefined counting clock (T) and is respectively reset by pulses of the system clock (G) and the count (Z) of which is respectively read out as the temporal offset value (At(n)) if the auxiliary clock (H) is used to record an auxiliary sampling value (U(n)). 6. The method as claimed in one of the preceding claims, characterized in that current or voltage phasors (U) are formed using the sampling values. 7. An arrangement for sampling a current or voltage profile (U(t)) and for forming sampling values (U'(n)) which are temporally related to a predefined system clock (G), characterized by an auxiliary sampling device (20) to which the system clock (G) and an auxiliary clock (H) , which runs freely relative to the system clock, are applied and which is intended to form auxiliary sampling values (U(n)) and to form temporal offset values (At) which are specific to the auxiliary sampling values and each specify the temporal offset of the sampling time of the associated auxiliary sampling value relative to the system clock, and a resampling device (200) which is arranged downstream of the auxiliary sampling device (20) and subjects the auxiliary sampling values (U(n)) of the auxiliary sampling device (20) to resampling, in which the sampling values (U' (n) ) which are temporally related to the system clock (G) are formed, using the temporal offset values (At) which are specific to the auxiliary sampling values. 8. The arrangement as claimed in claim 7, characterized in that the auxiliary sampling device forms part of a current or voltage converter (510, 520) of an energy transmission system. 9. The arrangement as claimed in one of the preceding claims 7-8, characterized in that the resampling device (200) forms part of a field device (530), in particular a protection device, of an energy transmission system. 10. The arrangement as claimed in one of the preceding claims 7-9, characterized in that the auxiliary sampling device and the resampling device are connected to one another by means of a data transmission bus or a data transmission network (540). 11. The arrangement as claimed in one of the preceding claims 7-10, characterized in that the auxiliary sampling device has a counting device (70, 80) which forms the temporal offset values (At(n)) by counting the clock pulses of a predefined counting clock (T), resetting its count (Z) if a pulse of the system clock (G) is respectively present and outputting its respective count (Z) as the temporal offset value if the auxiliary clock (H) is used to record an auxiliary sampling value (U(n)). 12. The arrangement as claimed in one of the preceding claims 7-11, characterized in that a phasor formation device (210) which uses the sampling values (U'(n)) to form current or voltage phasors (U) is connected to the resampling device (200). The invention relates to a method for sampling a current or voltate profile (U(t) and for forming sampling values (U(n) having a temporal relationship with a predefined system clock (G). According to the invention, an auxiliary clock (H) which runs freely in relation to t the system clock is used to form auxiliary sampling values (U(n), the time offset of the sampling time of each auxiliary sampling value in each case in relation to the system clock is determined, time offset values (? t(n) specific to auxiliary sampling values are determined, and the auxiliary sampling values (U(n) are re-sampled using the time offset values ( ? t(n) specific to auxiliary sampling values, with the sampling values (U'(n), which have a temporal relationship with the system clock being formed in the re-sampling.

Full Text

Description
Method for sampling a current or voltage profile and for
forming sampling values, in particular for use in protection or
control devices for energy transmission systems
The invention relates to a method, in particular for use in
protection or control devices for energy transmission systems,
having the features according to the precharacterizing clause
of claim 1.
Such a method is disclosed in the German laid-open
specification 199 33 684. In this method, a high-voltage or
heavy-current signal is sampled using an internal clock which
is synchronized with the globally available GPS (Global
Positioning System) signal. The GPS signal thus predefines a
system clock to which the sampling values are related. The
sampling values are then evaluated for the purposes of
protection, in particular for the purposes of differential
protection.
The invention is based on the object of specifying a method
which can be used to form sampling values, which have little
jitter and very little noise, with little outlay in terms of
devices or hardware.
On the basis of a method of the type specified at the outset,
this object is achieved according to the invention by the
characterizing features of claim 1. Advantageous refinements of
the method according to the invention are specified in
subclaims.
Accordingly, the invention provides for an auxiliary clock or
auxiliary clock signal which runs freely relative to the system
clock to be used to form auxiliary sampling values, for the
temporal offset of the sampling time of each auxiliary sampling
value to be respectively determined relative to the system
clock and temporal offset values which are specific to the
auxiliary sampling values to be determined, and for the
auxiliary sampling values
to be subjected to resampling, in which the sampling values
which are temporally related to the system clock are formed,
using the temporal offset values which are specific to the
auxiliary sampling values.
A crucial advantage of the method according to the invention
can be seen in the fact that less hardware than in previous
sampling systems is needed overall to generate the sampling
values since the auxiliary clock used for sampling runs freely
and it is thus possible to completely dispense with phase
tracking, for example on the basis of a PLL (Phase Locked Loop)
circuit. Sampling is thus effected using a free-running clock
and resampling is effected "only" arithmetically, for example,
using the temporal offset values which have been determined.
Another crucial advantage of the method according to the
invention can be seen in the fact that the sampling values have
very little jitter and noise. The inventors found that a
sampling clock derived from a predefined system clock and
phase-coupled to the latter may, under certain circumstances,
have a relatively large amount of jitter and may result in a
relatively large amount of noise in the sampling values. The
invention begins at this point by dispensing with such phase
coupling or phase tracking; instead of this, sampling is
carried out independently of the system clock and an auxiliary
clock which runs freely with respect to the system clock and is
of high quality, in particular has little jitter, is used for
upstream auxiliary sampling. The sampling times of the
auxiliary sampling values are thus generally temporally offset
or phase-shifted as desired with respect to the system clock;
in order to nevertheless establish a temporal relationship with
the system clock, the auxiliary sampling values are then
subjected to resampling, to be precise using the temporal
offset values which are specific to the auxiliary sampling
values and have previously been recorded for each auxiliary
sampling value during auxiliary sampling. The result is thus
the formation of sampling values with the correct time base but
with considerably
less jitter and less noise because the system clock is used
only during downstream resampling, which is only carried out
numerically for example, but not for primary "physical"
sampling.
The GPS signal, the Galileo signal, a real-time SNTP signal, a
system clock of an SDH network or a system clock signal derived
using one or more of these signals is preferably used as the
system clock.
The output signal of a local free-running oscillator is
preferably used as the auxiliary clock signal. The auxiliary
clock signal can be generated, for example, using a central
busbar protection device and can be fed into sampling devices
which are connected to said central busbar protection device
using the latter. The sampling devices may be integrated, for
example, in measuring transducers which are connected to one or
more energy transmission lines.
Alternatively, the auxiliary clock signal may be derived from
the signals of a real-time transmission network, in particular
a real-time ETHERNET network.
The temporal offset values are formed, for example, using a
counter which counts the clock pulses of a predefined counting
clock and is respectively reset by pulses of the system clock
and the count, of which is respectively read out as the temporal
offset value if the auxiliary clock is used to record an
auxiliary sampling value. The count is clearly a measurement
variable for the period of time which has passed between the
last respective pulse of the system clock and the recording of
the respective auxiliary sampling value.
The sampling values formed using the method described are
are processed further for the purposes of protection in
protection or control devices.
The invention also relates to an arrangement for sampling a
current or voltage profile and for forming sampling values
which are temporally related to a predefined system clock.
With respect to such an arrangement, the invention is based on
the object of ensuring that the sampling values have little
jitter and have as little noise as possible.
According to the invention, this object is achieved by means of
an arrangement having an auxiliary sampling device and a
resampling device: the system clock and an auxiliary clock,
which runs freely relative to the system clock, are applied to
the auxiliary sampling device and the latter uses the auxiliary
clock to form auxiliary sampling values and temporal offset
values which are specific to the auxiliary sampling values and
each specify the temporal offset relative to the system clock
for each sampling time. The resampling device is arranged
downstream of the auxiliary sampling device and subjects the
auxiliary sampling values of the auxiliary sampling device to
resampling, in which the sampling values which are temporally
related to the system clock are formed, using the temporal
offset values which are specific to the auxiliary sampling
values.
With regard to the advantages of the arrangement according to
the invention, reference is made to the above statements in
connection with the method according to the invention.
The auxiliary sampling device is preferably contained in a
current or voltage converter if the intention is to form
sampling values which relate to an energy transmission system.
The resampling device may, for example, form part of a field
device, in particular a protection device.
The auxiliary sampling device and the resampling device are
preferably connected to one another by means of a data
transmission bus or a data transmission network.
If a central busbar protection device is present in the energy
transmission system, it is considered to be advantageous if the
central busbar protection device forms the auxiliary clock and
transmits it to the auxiliary sampling device.
With a view to the formation of phasor measured values, it is
considered to be advantageous if a phasor formation device
which uses the sampling values to form current or voltage
phasors is connected to the resampling device.
The invention is explained in more detail below using exemplary
embodiments; in this case, by way of example
figure 1 shows a first exemplary embodiment of an arrangement
for generating sampling values, which is also used to
explain the method according to the invention by way
of example,
figure 2 shows, by way of example, a sampled voltage signal,
figure 3 diagrammatically shows the reconstruction of a
voltage signal,
figure 4 shows a basic illustration of a resampling operation
with an interpolation filter,
figure 5 shows a comparison of different interpolation
filters,
figure 6 shows the amplitude response, which is associated
with the pulse response, of an interpolation filter
having a Blackman window,
figure 7 shows the amplitude response of the interpolation
filter shown in figure 6 in the passband,
figure 8 shows, by way of example, sampling times,
figure 9 shows a table containing relevant mathematical
properties of the interpolation filter shown in
figure 6,
figure 10 shows a flowchart which summarizes the method for
forming sampling values once again by way of example,
and
figure 11 shows another exemplary embodiment of an arrangement
according to the invention.
Figure 1 illustrates an arrangement 10 for sampling a current
or voltage profile and for forming a corresponding current or
voltage phasor. In this case, the arrangement is explained, by
way of example, for the situation in which a voltage signal
U(t) is intended to be sampled and a voltage phasor U is
intended to be formed.
The arrangement 10 has an auxiliary sampling device 20, at the
input E20a of which the voltage signal U(t) to be sampled is
fed in. A further input E2 0b of the auxiliary sampling device
20 is connected to an auxiliary clock generator 30 which
generates a free-running auxiliary clock or auxiliary clock
signal H on the output side and feeds it into the auxiliary
sampling device 20.
On the input side, the auxiliary sampling device 20 has an A/D
converter 40 whose analog input is connected to the input E20a
of the auxiliary device 20 and thus has the voltage signal U(t)
applied to it. A measured value forming device 50 which
transmits sampling values U(n) formed by the A/D converter 40
to a downstream measured value memory 60 is arranged downstream
of the A/D converter 40.
The measured value forming device 50 is also connected to a
memory or latch module 70 which has a counter 80 connected
upstream of it on the input side. The reset input R80 of the
counter 80 is connected to a GPS receiving device 90 which
generates a GPS signal as the system clock or system clock
signal G and feeds it into the counter 80. The system
clock G generates a respective short pulse for each second, for
example.
A clock input T80 of the counter 80 is connected to a signal
generator 100 which feeds a clock signal or counting clock T
into the clock input T80 of the counter 80.
An output A20 of the auxiliary sampling device 20 is formed by
an output A60 of the measured value memory 60; the latter is
connected to a resampling device 200 which has a phasor
formation device 210 connected downstream of it.
The resampling device 200 subjects the auxiliary sampling
values U(n) of the analog/digital converter 40 to resampling
and generates, on the output side, resampled voltage values
U'(n) which are then converted into the voltage phasor U by the
phasor formation device 210; the voltage phasor U is thus
related to the system clock G of the GPS receiving device 90
and forms a so-called synchronous phasor. The term synchronous
phasor is used to mean that the phasor U is related to the
system clock.
The arrangement shown in figure 1 is operated, for example, as
follows:
The GPS receiving device 90 is used to generate, on the output
side, the system clock G which is fed into the counter 80. At
the same time, the signal generator 100 is used to feed the
counting clock T into the counter 80 which then begins to
count. The counter 80 is reset whenever the system clock G
generates a pulse.
The count Z of the counter 80 is respectively stored in the
memory module 70 when it is triggered with the free-running
auxiliary clock H. As soon as the auxiliary clock H thus
generates its n-th clock pulse, both the A/D converter 40 is
triggered and a sampling value U(n) is generated
and the respective count Z(n) is simultaneously recorded in the
memory module 70 and is transmitted to the measured value
forming device 50 as a temporal offset value At(n) which is
specific to the auxiliary sampling value. If the counting clock
has a clock rate of fT = 1 GHz, the temporal offset value At(n)
relative to the pulses of the system clock G can be determined
with a temporal accuracy of 1 ns.
The counter 80 and the memory module 70 thus together form a
counting device which forms the temporal offset values At(n) by
counting the clock pulses of the counting clock T, respectively
resetting itself if a pulse of the system clock G is present
and respectively outputting its count Z as a temporal offset
value as soon as the auxiliary clock H is used to record an
auxiliary sampling value U(n).
The measured value forming device 50 transmits the respective
auxiliary sampling value U(n) of the A/D converter 40, together
with the associated temporal offset value At (n) which is
specific to the auxiliary sampling value, to the measured value
memory 60 which stores the auxiliary sampling value U(n), with
the associated temporal offset value ?t(n) which is specific to
the auxiliary sampling value, as a measured value pair (U(n);
At(n)) .
Although the auxiliary sampling value U(n) has not been sampled
with the system clock G, it nevertheless has a known temporal
phase angle with respect to the system clock G because the
respective temporal relationship with the system clock G or
with the respective preceding pulse of the system clock G has
been defined, for each auxiliary sampling value U(n), by the
temporal offset value At (n) which is specific to the auxiliary
sampling value. In addition to the counter value Z, an absolute
time statement TAS which states the time of the last pulse of
the system clock in absolute terms may also be stored in the
temporal offset value ?t(n) or with the temporal offset value
?t (n) ; this makes it possible to determine the sampling time
TAH for each auxiliary sampling value in absolute terms
according to:
TAH = TAS + Z * 1/fT.
The resampling device 200 reads the auxiliary sampling values
U(n), together with the associated temporal offset values At (n)
which are specific to the auxiliary sampling values, from the
measured value memory 60 and carries out "arithmetic"
resampling using the system clock G. Resampled sampling values
U'(n) which are related to the system clock G are generated on
the output side during this resampling operation; a resampling
rate which corresponds to an integer multiple of the system
clock G is preferably used for this purpose. The sampling
values U' (n) can then be used in the phasor formation device
210 to form the voltage phasor U which forms a so-called
synchronous phasor. As already explained, the term "synchronous
phasor" should be understood in this context as meaning a
phasor which is synchronized with the predefined system clock
G.
Figure 2 shows, by way of example, the voltage signal U(t)
sampled by the free-running auxiliary clock H at a fixed
sampling rate.
In order to be able to calculate a phasor U which is as exact
as possible for the purpose of characterizing the fundamental
of the voltage signal U(t), the sampling frequency of the
auxiliary clock H is preferably set in such a manner that it is
an integer multiple of the frequency of the fundamental of the
voltage signal U(t). In order to be able to meet this
requirement, the frequency of the fundamental of the voltage
signal U(t) is measured, for example. A multiple of the
fundamental frequency determined in this manner is then used
further as the auxiliary clock H.
As already mentioned, a resampling method is used to adapt the
sampling values U(n) to the system clock G. The resampling
method is based on the theory of the Shannon sampling theorem.
This theorem states that each ideally band-limited signal x can
be interpolated using the si function:
Figure 3 illustrates this situation using part of a sinusoidal
function with the depicted si interpolation functions which
make it possible to reconstruct sampled band-limited signals.
An ideally band-limited function which is given at points 3, 4,
5, ... etc. can thus be calculated at any desired other
location by solving the Shannon equation for these points.
There are now two possible ways of interpreting this function
for resampling use:
The first option is to place the extreme value of the
interpolation function through tne given sampling values, as
shown in figure 3. However, this variant is not particularly
practical for resampling use since an infinite sum of all si
functions would have to be calculated in this case for each
sampling value.
According to a second variant, use is made of the fact that,
apart from at the sampling value to be interpolated, the si
function assumes the value 0 at the location of all other
sampling values. That is to say, if the signal is interpolated
with the si function at the locations of the new sampling
values, only one si function must be considered.
If the si function is now positioned at the location of the new
sampling value with the period duration of the new sampling
interval and is calculated at the locations of the given
sampling values, the new sampling value can be determined.
Figure 4 illustrates this situation using resampling by means
of an interpolation filter.
In practice, of course, this interpolation should not be
carried out directly with the si function since this function
does not only have a value that is not equal to zero in a
finite interval of time. However, simply cropping the function
at the fifth zero crossing on both sides of the extreme value
does not provide a frequency response which differs
considerably from the ideal low-pass in the frequency range. In
this case, it is better to limit the si function to a finite
range with a window function. The Blackman window function is
used for this purpose in the present example. In this case, a
stop-band attenuation ratio of at least 60 dB is achieved.
Although better values could be achieved with the known Kaiser
function, this is at the expense of the window size. Since 60
dB can be considered to be sufficient, a Kaiser window should
preferably not be used.
Figure 5 shows the interpolation function used in more detail.
The curve denoted "xi" represents the Blackman window function
which has been selected by way of example. The curve denoted
"si" shows the si function which is not temporally limited. The
curve denoted "hsi" is the interpolation function which has
been temporally limited using the window function.
Figure 6 shows the amplitude response associated with the
illustrated pulse response using the example of a sampling rate
reduction from 10 kHz to 5 kHz. As can be seen in figure 6, the
interpolated signals are band-limited to the new half sampling
frequency. The ripple in the passband is at most 0.2 10-4 .
Figure 7 shows the characteristic curve in the passband. It can
be seen in figure 7 that the ripple in the entire passband is
on average considerably less than 10-4. This filter can thus be
used to meet all the accuracy requirements even in the
passband. As is not intended to be proven here any further, the
This equation is the solution of a least-squares estimator
which fits the interpolation function into the received
sampling value stream at the desired location t0- The function
w(t) is the Blackman window function.
Figure 8 shows the implementation of resampling for the
selected resampling method: a sampling value in the original
sampling value stream on the basis of the auxiliary clock H is
present at the times denoted with a cross. Resampling is
intended to be carried out at the points denoted with a circle.
A sampling rate which is synchronized with the system clock G
and preferably corresponds to a multiple, for example an
integer multiple, of the pulse rate of the system clock G is
used for resampling. The designation "GPS sync pulse" marks, by
way of example, one of the pulses of the GPS signal, one of
which usually occurs each second.
The ratio of the new sampling frequency to the old sampling
frequency is 3/5 in this example. If the sampling value is
intended to be calculated at the time t=0, an interpolation
filter whose extreme value is precisely at the original
sampling value 0 is used. In this case, the data window extends
precisely w/2 sampling values into the past and w/2 sampling
values into the future. In order to calculate the new sampling
value at the point t=3, an interpolation filter whose extreme
value has been shifted to the right by precisely 3/5 TA of the
original sampling interval TA must be used. In total, five
different sets of filter coefficients are thus needed to
implement resampling in this example.
The formulas in the table shown in figure 9 describe the
proposed algorithm in detail.
Figure 10 summarizes the exemplary method sequence once again
in the form of a flowchart.
The exact determination of the signal fundamental frequency f
of the input signal U(t) is decisive for the accuracy of the
synchronous phasor U determined. For this purpose, the
frequency f is preferably determined from phasors of a
plurality of successive data windows according to the following
formula:

The validity of the frequency measured value f can be derived
from the development of the phase angle cp(t). The frequency
measured value f determined is valid when the phase angle
develops in a virtually linear manner. If sudden changes are
determined in the profile of the measured phase angle, the data
window must be repositioned for the frequency measurement.
Resampling is carried out a second time in a second step with a
frequency measured value f which is now valid. The phasor
determined in this manner can then be used as a synchronous
phasor. The method is continued in the recursion steps
described.
The specific technical implementation of the resampling method
in the resampling device 200 can be effected, for example, in a
manner as explained in "A flexible sampling-rate conversion
method" (Smith, J.O. and Gosset, P.; 1984; Proceedings of the
International Conference on Acoustic, Speech, and Signal
Processing, San Diego, Volume 2, pages 19.4.1-19.4.2; New York.
IEEE Press).
Figure 11 illustrates another exemplary embodiment of an
arrangement according to the invention which can also be used
to carry out the method according to the invention.
An energy transmission line 500 to which two measuring
transducer units 510, 520 are connected is seen in figure 11.
The two measuring transducer units 510 and 520 are each
provided with an auxiliary sampling device 20 as has already
been explained in connection with figure 1.
The two measuring transducer units 510 and 520 are connected to
a downstream protection device 530; the connection between the
protection device 530 and the two measuring transducer units
510 and 520 is ensured by a data bus or a data transmission
network (for example an Ethernet network) 540 which can be
provided with a switch 550, for example.
As can also be seen in figure 11, a system clock G which is
predefined, for example, by the GPS signal is applied to the
two measuring transducer units 510 and 520 and the protection
device 530.
The protection device 530 is provided with a resampling device
200 and a phasor formation device 210; the two components may
correspond to the resampling device 200 and the phasor
formation device 210 shown in figure 1.
The arrangement shown in figure 11 can be operated as follows:
Current and voltage measured values Ul(t) and II(t) and U2(t)
and 12 (t) of the energy transmission line 500 are recorded
using the measuring transducer units 510 and 520 and are
subjected to analog/digital conversion. In this case, auxiliary
sampling values II(n), 12(n), Ul(n) and U2(n) are formed on the
output side according to an auxiliary clock H and are
transmitted, together with the respective associated temporal
offset values ?t(n) which are specific to the auxiliary
sampling values, to the protection device 530 via the network
540. The auxiliary clock H can be individually generated in
each of the measuring transducer units 510 and 520
or can be predefined from the outside for both measuring
transducer units 510 and 520; for example, the auxiliary clock
H is formed by a central busbar protection device 600 and is
fed into the measuring transducer units 510 and 520.
Alternatively, the auxiliary clock H can be derived from the
data signals of the network 540 which is preferably a real-time
transmission network, in particular a real-time ETHERNET
network.
The protection device 530 subjects the auxiliary sampling
values Ul(n), U2(n), II(n) and 12(n) to resampling and
generates, on the output side, sampling values Ul' (n) , U2' (n),
I1'(n) and 12'(n) which are synchronized with the system clock
G. The phasor formation device 210 of the protection device 530
uses these sampling values Ul'(n), U2'(n), II'(n) and 12'(n) to
form synchronous phasors Il, I2, U1 and U2.
The synchronous phasors Il, I2, U1 and U2 can be evaluated
inside the protection device 530 or outside the protection
device 530, for example in a downstream control system or the
like, in order to determine whether a fault, in particular a
short circuit, has occurred on the energy transmission line
500. The synchronous phasors Il, I2, Ul and U2 can thus be used
to generate fault signals.
Patent claims
1. A method for sampling a current or voltage profile (U(t))
and for forming sampling values (U' (n) ) which are temporally
related to a predefined system clock (G),
characterized in that
an auxiliary clock (H) which runs freely relative to the
system clock is used to form auxiliary sampling values
(U(n) ) ,
the temporal offset of the sampling time of each auxiliary
sampling value is respectively determined relative to the
system clock and temporal offset values (At(n)) which are
specific to the auxiliary sampling values are determined,
and
the auxiliary sampling values (U(n)) are subjected to
resampling, in which the sampling values (U1(n)) which are
temporally related to the system clock are formed, using
the temporal offset values (At(n)) which are specific to
the auxiliary sampling values.
2. The method as claimed in claim 1,
characterized in that
the GPS signal, the Galileo signal, a real-time SNTP signal, a
system clock of an SDH network or a system clock signal derived
using one or more of these signals is used as the system clock.
3. The method as claimed in one of the preceding claims,
characterized in that
a clock signal of a local free-running oscillator (30) is used
as the auxiliary clock.
4. The method as claimed in one of the preceding claims 1-2,
characterized in that
the auxiliary clock is obtained from a clock signal of a real-
time transmission network, in particular a real-time ETHERNET
network.
5. The method as claimed in one of the preceding claims,
characterized in that
the temporal offset values (?t(n)) are formed using a counting
device (70, 80) which counts the clock pulses of a predefined
counting clock (T) and is respectively reset by pulses of the
system clock (G) and the count (Z) of which is respectively
read out as the temporal offset value (At(n)) if the auxiliary
clock (H) is used to record an auxiliary sampling value (U(n)).
6. The method as claimed in one of the preceding claims,
characterized in that
current or voltage phasors (U) are formed using the sampling
values.
7. An arrangement for sampling a current or voltage profile
(U(t)) and for forming sampling values (U'(n)) which are
temporally related to a predefined system clock (G),
characterized by
an auxiliary sampling device (20) to which the system
clock (G) and an auxiliary clock (H) , which runs freely
relative to the system clock, are applied and which is
intended to form auxiliary sampling values (U(n)) and to
form temporal offset values (At) which are specific to the
auxiliary sampling values and each specify the temporal
offset of the sampling time of the associated auxiliary
sampling value relative to the system clock, and
a resampling device (200) which is arranged downstream of
the auxiliary sampling device (20) and subjects the
auxiliary sampling values (U(n)) of the auxiliary sampling
device (20) to resampling, in which the sampling values
(U' (n) ) which are temporally related to the system clock
(G) are formed, using the temporal offset values (At)
which are specific to the auxiliary sampling values.
8. The arrangement as claimed in claim 7,
characterized in that
the auxiliary sampling device forms part of a current or
voltage converter (510, 520) of an energy transmission system.
9. The arrangement as claimed in one of the preceding claims
7-8,
characterized in that
the resampling device (200) forms part of a field device (530),
in particular a protection device, of an energy transmission
system.
10. The arrangement as claimed in one of the preceding claims
7-9,
characterized in that
the auxiliary sampling device and the resampling device are
connected to one another by means of a data transmission bus or
a data transmission network (540).
11. The arrangement as claimed in one of the preceding claims
7-10,
characterized in that
the auxiliary sampling device has a counting device (70, 80)
which forms the temporal offset values (At(n)) by counting the
clock pulses of a predefined counting clock (T), resetting its
count (Z) if a pulse of the system clock (G) is respectively
present and outputting its respective count (Z) as the temporal
offset value if the auxiliary clock (H) is used to record an
auxiliary sampling value (U(n)).
12. The arrangement as claimed in one of the preceding claims
7-11,
characterized in that
a phasor formation device (210) which uses the sampling values
(U'(n)) to form current or voltage phasors (U) is connected to
the resampling device (200).

The invention relates to a method for sampling a current or voltate profile (U(t) and for forming sampling values (U(n) having a temporal relationship with a predefined system clock (G). According to the invention, an auxiliary clock (H) which runs freely in relation to t the system clock is used to form auxiliary sampling values (U(n), the time offset of the sampling time of each auxiliary sampling value in each case in relation to the system clock is determined, time offset values (? t(n) specific
to auxiliary sampling values are determined, and the auxiliary sampling values (U(n) are re-sampled using the time offset values ( ? t(n) specific to auxiliary sampling values, with the sampling values (U'(n), which have a temporal relationship with the system clock being formed in the re-sampling.

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Patent Number

268401

Indian Patent Application Number

431/KOLNP/2009

PG Journal Number

36/2015

Publication Date

04-Sep-2015

Grant Date

28-Aug-2015

Date of Filing

30-Jan-2009

Name of Patentee

SIEMENS AKTIENGESELLSCHAFT

Applicant Address

WITTELSBACHERPLATZ 2, 80333 MUNCHEN

Inventors:

#	Inventor's Name	Inventor's Address
1	ANDREAS JURISCH	EICHENWEG 11 16727 SCHWANTE
2	TORSTEN KERGER	KASTANIENALLEE 22 14621 SCHÖNWALDE-GLIEN

PCT International Classification Number

G01R 19/25

PCT International Application Number

PCT/DE2006/001414

PCT International Filing date

2006-08-07

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA