EP1344366A2 - Method and device for transmitting data on at least one electrical power supply line - Google Patents

Abstract

The orthogonal frequency division multiplexing (OFDM) method is well-known for transmitting data on electrical power supply lines. According to this method, the items of information to be transmitted are distributed among numerous carriers, and the composite signal of the modulated carrier signals is transmitted in the form of an OFDM block. Standard OFDM methods are, however, highly sensitive to strong periodic pulse jammers. According to the invention, the method is thus devised such that the OFDM blocks to be transmitted have a length of approximately 85 % of the interval between two periodic disturbing pulses. The carrier interval accordingly results from the reciprocal duration of the OFDM blocks. The transmitted OFDM blocks are synchronized with pulse-shaped periodic jammers in such a manner that one block at a time is located between two disturbing pulses. The pulse-shaped jammers can be gated at the receiver. To this end, the inventive device comprises an appropriately designed transmitter (20) and an associated receiver (30).

Description

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Particularly in the case of direct current supplies, periodic interference signals in particular occur due to the generation of direct voltage with rectifiers. _R. Dj- ^{e are} briefly referred to below as "disturbers or generally as interference pulses". ^';

The periodic interference pulses are caused by the commutation of the current in the rectifier. The converter components or valves, usually diodes or thyristors, in a rectifier carry the direct current alternately. When the direct current changes from one valve to another valve, inductances between the valves create a voltage peak, which is associated with voltage increases of the order of magnitude of approximately 400 kV / s. Since the commutation times are determined by the frequency of the AC network, the interference pulses occur in a certain time grid, that is to say periodically.

The object of the invention is therefore to specify a suitable data transmission method, which can be used in particular in DC voltage power supplies, and to provide an associated device.

The object is achieved by the measures according to claim 1. Further developments are specified in the dependent method claims. A device for performing the method according to the invention is the subject of claim 9. Further developments of the device are specified in the dependent claims.

In the invention, the problem mentioned at the outset is solved in a simple manner by designing the OFDM method in such a way that the OFDM blocks to be transmitted have a length of approximately 85% of the distance between two periodic interference pulses. To ensure the orthogonality of the carriers, the frequency difference of two carriers must be in an integer ratio to the reciprocal length of the OFDM block. cυ ur KJ h- ¹ P ¹ cπ o cπ o cπ o Cπ

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Has faults. This generally applies to DC voltage networks and often also to AC voltage networks.

Further details and advantages of the invention result from the following description of the figures with reference to the drawing in conjunction with the patent claims. Show it

Figure 1 is a graphical representation of the time course of a DC voltage for a subway system, Figure 2 and the transmitter part

3 shows the receiver part of a suitable device for data transmission in the case of DC voltage curves according to FIG. 1.

In addition to energy supply, data should also be transmitted on the stioma supply lines of subways. The technology, also known as Powerline Communication (PLC), modulates the information to be transmitted on suitable carriers and superimposes the modulation products on the supply voltage of the subway system.

For example, subways are operated with a nominal DC voltage of 750 V. It is common practice to provide the DC voltage using 12-pulse rectifiers, which in turn are fed by a converter transformer. The 12-pulse rectifiers consist of two 6-pulse rectifiers, which in turn are fed by two windings of the converter transformer that are electrically offset by 30 ° from each other. The converter transformer is primarily connected to the general energy supply with a mains frequency of 50 Hz. The described method can also be used at other frequencies such as Can be used at 60 Hz.

Generally includes a subway system. several rectifiers installed at intervals of approx. 2 km along the route network. All rectifiers feed the subway System in common and are electrically connected to each other via the busbar of the subway system.

To further clarify the problem, FIG. 1 shows, by way of example, a measured time profile of the DC train voltage over a period of 20 ms. The voltage signal is denoted by 1. It can be seen that the DC voltage is not constant, but rather is subject to fluctuations of up to approximately 80 V.

Particularly when commutating the currents in the rectifiers, steep-edged voltage jumps with amplitudes of typically 50 V occur at intervals of 20 ms / 12 = 1.67 ms (with 50 Hz supply). The resulting broadband interference extends up to frequencies of a few 100 kHz and are therefore in the frequency range of powerline communication systems.

It can be seen from FIG. 1 that the interference caused by the steep-edged voltage jumps in the web tension can only be partially suppressed by filters, since part of the spectral interference energy can always pass the bandpass filter. Thus, even by means of complex filter circuits, the voltage jumps on the web tension are reduced to only 10% and are thus typically 5 V. After a filter, periodic pulse disturbers of considerable amplitude that are synchronous to the network are still present.

The useful signal of a PLC system arriving at the receiver depends on the transmission properties of the route and the distance of the transmitter and is only a few 10 mV to a maximum of about 1 V due to the limited permissible transmission power. The pulse-shaped interference signal is therefore always higher than the useful signal, which means that there is a very poor signal-to-noise ratio (SNR = signal-to-noise ratio). co ω w N>P> P ¹

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Ω P "O: P- v <! Cu α tr Ω tr X Hi P- ti Φ P ⁾ dd CU Φ d ti tn tr Φ Hi d O Ω F- H! P ⁾ φ Φ PJ er b- ^> ? C O Ω cn 13 ti P Φ vq d Hi cn F-

Φ ^• Hi P- H tr Φ o Φ cn P- φ TI tr rt t → P Hl d Cπ P ¹ o vq

P 1 φ 1 dd φ tn cn 1 1 ü cu: n Hi vq 1 Φ α F- ti d ü P- d φ ti 1 1 φ <! F- F- 1 1 tu 1 1 1 1 1 1 Φ 1

can be influenced, but only fixed to the glitch grid.

This is followed by a coupling unit ^" 24" for coupling to a rail system 25 of a subway. ^" Another power supply network for traffic facilities can also be used.

In the transmitter 20, the data signal is partitioned in such a way that a single data block with a certain safety distance fits between two interference pulses. The data signal is thus always transmitted in a fault-free time period, the precise temporal correlation with the interference pulse pattern being established with the combination of threshold switch 33a and subsequent phase-locked loop 33b described above.

In FIG. 3, a receiver 30 is formed from a coupling unit 31 for the rail system from FIG. 2, which is followed by a filter 32, an impedance 34 and a short-circuiter 35.

The short circuiter 35 is a unit for automatic gain control (AGC = Automatic Gain Control) according to the prior art. The data are sent to a processing unit 38 for OFDM signals via an A / D converter 37.

Here, too, the interference pulses are recorded with the aid of a threshold switch on the network side and fed to a phase locked loop (PLL) for the purpose of jitter suppression as a rectangular guide signal.

The stable synchronizing signal from the phase locked loop in the time grid of the interference pulses is then fed to a the ^'short closers 35 and the other processing unit 38 for OFDM signals. The short-circuiter thus suppresses the received signal for as long as an interference pulse lasts and releases the receiver input as soon as the interference-free period between the interference pulses begins. Due to the stable synchronization signal, the processing unit 38 for OFDM signals the exact ^'temporal position of the known data packets to be processed, can be carried out so that a proper data recovery.

Instead of the short-circuiting device 35 in the output line of the filter 32 with an upstream impedance 34, a switch in the parallel branch can also be used. The impedance 34 is not required in this case.

After decoupling via the impedance 34, the interference pulse is e.g. kept away from the OFDM processing unit in that the signal line via an analog switch, e.g. in

Form of a transistor that is short-circuited. As mentioned, it is also possible to mount an electronic switch in series and to separate the downstream signal processing from the filter output during the pulse disturbance.

The signal is fed to the amplifier 36 with automatic gain control (AGC), which amplifies it to a level optimally set for the A / D conversion. The partitioned signals are then combined in the subsequent processing units and decoded in accordance with the prior art.

It is essential in the method described above and the associated device that the OFDM method known per se is modified by a division, ie a so-called partitioning of the data, in such a way that a transmission takes place only in virtually trouble-free time segments .. For this purpose, the transmission process is synchronized with the periodic pulse interferer and it is sent exactly between the interference pulses. Accordingly, the detection and masking of the interference pulses takes place in the receiver. After OFDM signal processing, the partitioned data can be combined.

The invention has been described above ^' specifically for data transmission in a DC voltage supply for subways. The invention can also be used in other networks operated with DC voltage, for example in DC voltage networks for the self-supply of switchgear.

Claims

claims 1. A method for transmitting .y.on data on at least one electrical power supply line, wherein periodically I - pulse-shaped noise signals with intermediate virtually interference-free time intervals occur using the OFDM method ^'(Orthogonal Frequency Division Multiplexing), wherein the information to be transmitted to distributed several carriers and the sum signal of all modulated carriers is transmitted in the form of an OFDM block with the following features: the OFDM method is designed such that the OFDM blocks to be transmitted fill the majority of the period of the pulse-shaped interference signals and a pause of approximately the duration of an interference pulse is maintained between two successive OFDM blocks, - The position of the OFDM blocks sent is synchronized with the pulse-shaped, periodic interference pulses so that an OFDM block lies between two periodic interference pulses, and - the pulse-shaped interference signals at the receiver are masked out by a suitable circuit. 2. The method according to claim 1, so that the OFDM blocks fill a length of approximately 85% of the period of the pulse-shaped interference signals and maintain a pause of approximately 15% of the period of the interference signals between two successive OFDM blocks. 3. The method according to claim 1, so that the synchronization between the periodically recurring interference pulses and the transmitters and receivers is carried out via threshold switches for pulse detection. 4. The method according to claim 3, characterized in that in the transmitter after snapping the Phase locked loop on the pulse disturbance successes of the threshold switches is deactivated during the transmission of the data and a suitable time window is only opened at the times when an interference pulse is expected. 5. The method of claim 3, d a d u r c h g e k e n n z e i c h n e t that an analog or digital phase locked loop is used to suppress jitter during synchronization. 6. The method of claim 1 and claim 2, so that the OFDM signal can pass through the circuit for masking out interference pulses unhindered. 1 7. The method according to claim 1 and claim 2, so that an impedance is applied between the coupling unit and the receiver, and the interferers are hidden behind the impedance by short-circuiting the reception line. 8. The method of claim 1 and claim 2, that the interference pulses are masked out by the receiver by separating the coupling unit. 9. The method according to any one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that the periodically recurring interference pulses are used for a coarse synchronization of OFDM transmitters and OFDM-E receivers. 10. The method according to any one of the preceding claims, characterized in that the first OFDM block is used for fine synchronization of the receiver, and that training sequences are transmitted after the fine synchronization and that the OFDM blocks carrying the useful information are connected to this. 11. Device for performing the method according to claim 1 or one of claims 2 ^; to 10, with a transmitter and with a receiver, characterized in that the transmitter (-20) and the receiver (30) have processing units (21, 38) for the OFDM signal with associated coupling units (24, 31), wherein means ( 23, 33) for synchronizing the transmission signals with the periodic interference pulses. 12. The apparatus according to claim 11, characterized in that the means for synchronization threshold switches (23a, 33a) with a subsequent phase locked loop (23b, 33b) in the transmitter (20) and in the receiver (30), the threshold switch in the transmitter after the phase locked loop has engaged is only active in the periods in which an interference pulse is expected. 13. The apparatus of claim 11, d a d u r c h g e - k e n n z e i c h n e t that an amplifier (22) is connected downstream of the processing unit (21) for the OFDM signal in the transmitter (20). 14. The apparatus according to claim 11, so that the receiver (30) has a processing unit (38) for the OFDM signal and a coupling unit (31). 15. The apparatus according to claim 14, so that the coupling unit (31) is followed by a filter (32), an impedance (34) and a short-circuiter (35). 16. The apparatus according to claim 14, so that the coupling unit (31) is followed by a filter (32) and a switch in the series branch without impedance.