The abstract wide band power line correspondence (BPLC) uses when the existing electric power network takes the high speed data transmission medium, the existence shielding property difference, the impedance do not match, the carrier frequency and the shortwave radio frequency band overlap and so on questions, from this initiates the electromagnetic interference into BPLC popularization and the promoted biggest barrier, simultaneously also gave the BPLC commercialization to set the higher electromagnetic compatibility request. This article has discussed the electromagnetic interference question which as well as the electromagnetic radiation measuring technique in the wide band power line correspondence possibly exists, and proposed improves the BPLC system electromagnetic compatibility measure.
1st, introduction
It is well known, the electric power network is in various networks has the user to be most now, the most essential network. Along with the networking and multimedia technologies’ development, use the ready-made electric power network to realize the broadband access and the data, the pronunciation, the video frequency and so on multimedia intelligence transmission into current research hot spot. In recent years, the wide band power line correspondence (BPLC) the technical related research and the application development were rapid, now already entered the preliminary application stage. The wide band power line correspondence uses the existing power line to take the communications channel, uses the power line digit wide frequency (SST) the technology or the orthogonal frequency division multiplexing (OFDM) the technology realizes data transmission [1]. Because what but on the power line simultaneously transmits is the strong electricity, moreover electrical network’s stability is much worse than the traditional communications network, causes the power line correspondence the electromagnetic environment to be extremely complex. The power line correspondence can give in the frequency band more importantly other wireless activities to create the latent electromagnetic interference, this also gave the wide band power line correspondence the popularization and the promotion set the higher electromagnetic compatibility request.
The electromagnetic compatibility (Electromagnetic Compatibility, EMC) is an emerging comprehensive discipline, it is refers to the electricity, the electronic installation or the system can under the identical electromagnetic environment the normal work, will not constitute the electromagnetic interference which cannot withstand, will achieve is mutually compatible, realizes respective function condition [2]. The electromagnetic compatibility the content controls two aspects including the antijamming and the electromagnetic radiation. Along with the electric power communication’s rapid development and the widespread application, take one kind “the last kilometer” the turning on technology wide band power line correspondence electromagnetic compatibility question appear more and more prominent. Specially the electric power communications system antijamming technology, electromagnetic radiation’s survey and the control, as well as questions and so on standard standard already aroused in the worldwide scale interest, the electromagnetic compatibility technology have also become realize one of wide band power line correspondence key technologies.
2nd, wide band power line correspondence
As one kind of new family networking and the broadband access technology, the wide band power line correspondence is the present domestic and foreign correspondences and the electrical engineering and so on overlapping domain attention hot spot. It is mainly refers to the 1~30MHz frequency range, realizes the Internet using the power line to turn on, the data and the voice feature high speed transmission. At present the world already had certain kind of BPLC system to carry on the field test, the majority systems can provide the highest data rate is above several Mbit/s. The wide band power line correspondence’s carrier frequency scope, in the US is 4~20MHz (HomePlug Specification V1.0), mainly uses in the indoors; Europe is 1.6~10MHz (Access) and 10~30MHz (In-House), this was the ETSI standard, the CENELECB standard threshold is 13MHz, the EU commission starts from 2002 to be coordinated unifies; China still did not have wide band PLC the standard.
The BPLC broadband access network covers generally from the transformer substation to the user housing public region (outdoor) and the user housing personal region (indoor) two parts. This is because the entire strip communication link’s attenuation is high, in satisfies in the situation which the electromagnetic compatibility (EMC) requests, only then about 10% users may by jump the link to serve only directly, must therefore divide into the low pressure distribution network outdoor PLC and the indoor PLC two parts. Outdoor part including from transformer substation to house junction point (HAP) the public region, the indoor part is refers to from the HAP proficient inside socket outlet. The communication signal pours into the transformer substation and branches out. Through the transformer substation in 1 head end HE (Head End), namely the ethernet (Ethernet) the point with the indoor electric power network connections, enables the insertion wall socket the equipment to turn on the wide band backbone network. Usually the outdoor PLC carrier frequency uses 1~10MHz to compare the low frequency, but indoor PLC uses 15~30MHz the high frequency band, provides the 2Mbit/s above data transfer rate, thus meets the requirements which the multimedia data transmissions as well as the Internet turn on. Figure 1 is the power line communication network structure drawing, the figure shows the PLC system is a central host/from the architecture, has the point-multipoint network analysis situs characteristic. On the one hand installs in the transformer substation the outdoor master controller provides the ethernet connection for the branch connection, the branch connection uses the optical fiber and the digital subscriber line generally (DSL). On the other hand, in each user’s housing some 1 independent indoor PLC part, (IC) controls by the indoor controller, in the IC control room the adapter (IA), provides the standard network for the end-user (ether network, UBS and simulation telephone line and so on) connection [3,4].
Figure 1 power line correspondence (PLC) network architecture
In recent years, along with the Internet technology and the digital modulation technology’s swift development, the wide band power line communication became the broadband access technology which the present prospects for development favored. The wide band PLC turning on remarkable merit is the use existing power line network, does not need the wiring, the network coverage area is again broad, the connection is convenient, may realize the broadband access fast. The shortcoming uses the mesolow power line channel transmission communication signal, will meet the ripple noise to questions and so on data harm as well as signal attenuation, in addition will have and between other wireless activity electromagnetic compatibility problem.
3rd, in BPLC electromagnetic compatibility question
In power line correspondence noise important source in with low pressure electrical network connected all loads as well as radio broadcasting disturbance and so on, therefore along power line transmission data time will bump into many unexpected questions. Generally to achieve counts the Mbit/s above data transfer rate, must use counts above MHz the frequency band. But under the current engineering factor, will possibly initiate the electromagnetic interference (EMI) the question. BPLC uses the 1~30MHz frequency band was already assigned by the National Radio Committee for other has applied radio, like fixed service, mobile service, radiolocation, radio navigation, Broadcasting station, ham radio service, satellite amateur service and radioastronomy and so on. Because the BPLC system’s intelligence signal energy possibly radiates to the periphery space, regarding this in the frequency band wireless activity has the influence, must therefore solve effectively by BPLC the system initiation EMI question, protects in this frequency band the wireless activity.
In 3.1 BPLC communications system’s electromagnetic compatibility
The power cable is defers to 50Hz or the 60Hz low loss electric transmission request design, when uses in them the high speed data transmission, means that must transmit between the 9kHz~30MHz frequency the signal. The signal which transmits in this HF frequency band, the power cable can have divulging, the part high frequency signal power will radiate by the electromagnetic wave form. This time a power line channel probably open wireless channel, while receives the noise, the multi-diameter decline and disturbing effect, also will form the disturbance to other signals. In order to realize the data high speed transmission, the signal attenuation to be smallest, at present develops the wide band power line correspondence uses 1.6~30.0MHz the optimum data transmission frequency band, has concentrated the shortwave radio broadcasting, the Coast station, fixed and the mobile communication shortwave frequency band and so on numerous users. When the power line modem works, the power line will produce the high divulging electric wave, will therefore create the electromagnetic interference to this frequency band wireless activity (EMI). The BPLC system other radio traffics will create the disturbance to the transmission band, mainly will be has the disturbance to the radio traffic frequency overlap sector, its size and the sending power, the distance and the wiring special details will be related. When BPLC system application scale expansion, the power line will form an antenna array, possibly has the radiation cumulative effect.
In addition, when the power line takes the high speed data transmission the medium, itself will meet many noise jammings. First, with the low pressure electrical network connected all load like switching power supply, the domestic electric appliances and so on, will cause on the power line the electric current fluctuation, will cause power line’s periphery to produce the electromagnetic radiation, when power line transmission data will have the unpredictable noise jamming; Next, because on the power line has turned on many electrical equipments, these load’s switch is stochastic, thus causes power line’s characteristic to change unceasingly along with the time, very difficult to carry on the impedance matching. Therefore the power line correspondence’s environment is extremely bad, to guarantee that the data transmission the quality, must use many related technologies to solve.
between 3.2 neighboring BPLC communications system’s electromagnetic compatibility
Along with the BPLC system’s widespread use, between the different BPLC local area network possibly presents the electromagnetic radiation the superimposed effect. Between the redundant use same frequency’s neighboring BPLC system will disturb (i.e. between mutually plot disturbance). In the outdoor PLC network, will have this kind of disturbance especially in the plot edge, this will mainly be by the electric cable terminal (located at roadside distributing box or link box) the remaining crosstalk will create. But actual, in outdoor very little has between the plot to disturb, because the radiation harassment’s electric-field intensity increases along with the distance the weaken is very big, gap distance according to the present building’s, the radiation harassment’s superimposition cannot be very obvious. Between the indoor neighboring PLC system’s disturbance is the subject matter. In the most situations, (IC) between the outdoor circuit’s loss is close or is smaller than in the neighboring indoor controller the indoor link loss, therefore carries on coordinated between the plot to the upward time slot and the downward time slot’s use, may drop to the IC between disturbance lowly. Actual to reduce between the plot to disturb, may be a group latent disturbs the IC definition IC the synchronized master controller, or meets the IC pair after the power distribution dial plate. But along with the BPLC turning on system’s expanded application, the communication network internal node number will increase massively in the future, between the plot will disturb will occur frequently, must therefore introduce a more effective disturbance to examine and to reduce the measure.
4th, in BPLC electromagnetic radiation survey
Whether does the BPLC electromagnetic interference obtain the effective survey, is whether BPLC to promote the application the necessary factor. At present did not have a unified standard to the BPLC electromagnetic radiation’s survey, but has a unified understanding is should take the BPLC system a noise source. Is mainly the survey has the antenna effect power line to the BPLC electromagnetic radiation’s survey, because the BPLC system’s equipment volume in 0.5m, (10~300m) is much smaller in the 1~30MHz frequency band internal phase regarding the electromagnetic wave length, according to the electromagnetic radiation theory, the radiation which the equipment produces is small, therefore the BPLC system’s electromagnetic interference mainly comes from power line’s conducted interference. May divide into the guided waves and the radiated wave two types in the power line nearby electromagnetic field, the guided waves is the main electromagnetic field, the radiation field is very small, along with leaves the wire distance increase, the guided waves declines rapidly, by radiation field primarily. Considered building’s influence, the radiation field actual weaken speed must be much quicker than (theory weaken speed).
Usually, electric-field intensity E is uses for to appraise and the description electromagnetic interference, but in the market the existing electric field sensor’s precision permits the survey vertical field quantity merely, therefore usually uses the magnetic field sensor to survey the BPLC system’s radiation, as shown in Figure 2, is multiplied by the wave impedance to transform the electric-field intensity. Pours into the signal in the low pressure distribution wire (in chart with interface resistance for 50Ω the potential source Us expression), because the low pressure distribution network the impedance characteristic change is very big under high frequency, not only therefore the distribution wire signal coupler must have passes high frequency, filters the low frequency function, by reduces as far as possible injects distribution network’s signal energy to weaken, but must be able to match auto-adapted line impedance Pin 50Ω. Is away from and the electromagnetic wave length according to the survey compares says, the electromagnetic environment may divide into the distant field and the near field, when survey electromagnetic radiation, to achieve the survey the authenticity, must shield the outside as far as possible to the BPLC system’s electromagnetic interference. According to electromagnetic theory, in the BPLC system is in the distant field in the situation is the electric field and the magnetic field direction orthogonal, radiation electric-field intensity EPLC may (Z=377Ω) calculates based on magnetic field strength H and the free space impedance:
EPLC=Z · H (V/m)
But as a result of actual survey electromagnetic screen space limit (, because 30 MHz following electromagnetic waves are long), the survey distance very possibly falls in the near field scope, but is unable to achieve the distant field the effect, therefore the present majority measurement results are only obtain in the near field situation. Surveys when the near field, the wave impedance is 377Ω 2~3 times, because the wave impedance change is big, actual often uses the mean value in the near field survey, means in the switching process possible to introduce the error because of the coefficient relations. Therefore, this kind of near field’s survey is unable to appraise the BPLC system distant field the disturbance effect. This kind of near field’s metrical data can only use for to appraise the work to be away from the disturbance which between near different equipment possibly produces, obtains the distant field very difficultly through the calculation the electromagnetism radiation value.
Figure 2 uses the magnetic field sensor to survey the BPLC radiation field
Has also caused the difficulty the entire BPLC system as the noise source for electromagnetic radiation’s survey. Because the electric-field intensity relies on the power line network many parameters, like geometry construction, load, power line physical property and so on, to define in the different network construction the electric-field intensity, must in the different region (indoor, outdoor) survey the magnetic field, these results because of the actual BPLC application environment, but will be infinitely varied. Therefore, is impossible in the standardization only to use one kind of electric-field intensity, must act according to the network architecture, the environment position, the power line parameter and so on definition different electric-field intensity.
5th, improves the BPLC system electromagnetic compatibility measure
What because in the BPLC system transmits is the high frequency signal, and the power line has not shielded the measure, from this produces the electromagnetic radiation will create the electromagnetic interference radio to this frequency band shortwave; Simultaneously the power line correspondence works under the complex electromagnetic environment, also will receive other noise harassment the influence. In order to speed up the BPLC technology the development speed and expands its application scope, must improve the BPLC system’s electromagnetic compatibility gradually. At present, the active control BPLC system electromagnetic radiation’s method is reduces the energy emission through the control intelligence signal power. Moreover, according to electromagnetic radiation mechanism, but may also take the following several measures to enhance the BPLC system’s electromagnetic compatibility:
(1) the full use or improves the BPLC system power line’s symmetry.
The BPLC system’s radiation intensity is decided by the PLC network or its electric cable’s symmetry. The symmetry is defines according to between the wire and the place impedance, speaking of two power lines, if between each wire and the place impedance is equal, then regards this line for the symmetry or balanced. In order to reduce the electromagnetic radiation, the signal should realize the ideal different mold transmission (i.e. in signal wire different mold electric current size to be equal as far as possible, but direction is opposite, does not have radiation), therefore the line must be symmetrical. On the contrary, the line is asymmetrical the syntype which will cause not to hope. Syntype electric current in two wires current flow, returns after the place. The syntype electric current will produce the radiation generally. The highly symmetric line’s characteristic is the different mold electric current and syntype electric current ratio is very big, therefore radiates is small.
The specific measures have three. First, installs the filter in the close neighbor transformer and in the close neighbor family user’s junction, or directly in power line modem interior introduction filter [5]. Like this both may maintain the PLC signal the different mold dissemination, and may prevent the PLC signal to enter the radiation efficiency high wire or other attaches meets the equipment, this method is very effective, but the cost is high. Second, choice symmetry good wire, for example 4 core electric cables, but this law is not suitable for the indoor network. Third, uses the transformer and the syntype impedance coil reduces the syntype noise, this technology may apply in the PLC modem; Meanwhile makes the improvement to the PLC system receiving and dispatching analogous circuit, decreases power line’s divulging electric field.
(2) reduces the BPLC system intermediate frequency signal the power spectral density.
Because the BPLC signal’s electromagnetic radiation is measures in the 30MHz limited band width, therefore reduces the BPLC signal the power spectral density (PSD) to be able to reduce the radiation level immediately, but does not affect the total sending power. Therefore, BPLC system being suitable uses the wideband modulation technology, but its wide frequency efficiency power line low pass characteristic limit.
(3) chooses the OFDM modulating technology reasonably the related parameter.
Regarding the BPLC application, must first consider that has not assigned in the 1~30MHz frequency band for other wireless activity frequency band. In order to adapt this kind of frequency band not continual situation, at present uses in the high speed data transmission the BPLC system using the Orthogonal Frequency Division Multiplexing most (OFDM) the technology, OFDM uses the multi-carrier modulation, may choose certain frequency bands which nimbly the sub-carrier frequency avoided already used, increased the emissive power spectral density in the frequency band gap, thus eliminated thoroughly to these frequency band disturbance. Meanwhile, when the BPLC communications system receives noise jammings and so on gate pulse, but suitably reduces in certain sub-carriers the data transfer rate, enhances overall system’s data transmission performance.
(4) introduces network technologies and so on network adjustment.
Because a typical BPLC turning on network possibly covers several hundred meters, thus we may think that the electromagnetic interference will have the varying degree influence regarding the different webpage. In this case, the BPLC network receives the so-called spot jamming the influence, for example in the network workstation because of will be in the network the different position to receive the different disturbance the influence. This time, may act according to the noise source the position, to different network part measures and so on power line implementation grid protection.
6th, conclusion
Along with distribution network’s expansion and communication’s development, the wide band power line communication is occupying in the high speed developing process, how to use the existing low pressure distribution network to realize the broadband access and the high speed data transmission has aroused the various countries Electricity company’s high interest. As one resources widespread communication network, the electric power network structure is complex, the power transmission line has not shielded the measure, easy to receive the interference noise the influence to be many moreover the BPLC system’s carrier frequency and the shortwave radio frequency band has overlaps, has the possibility to create the electromagnetism harassment, therefore the electromagnetic compatibility technology becomes one of development wide band power line correspondence important technical. Through the BPLC modulating technology and the electric power network network technology’s unceasing consummation, the BPLC system’s electromagnetic compatibility question is being improved gradually. Along with electromagnetic compatibility related research’s expansion as well as the related standard’s formulation, the BPLC technology’s application can have health fast prospects for development.
Reference
[1] Liang is bright, Liang Enming, Song Jinji and so on. High speed power line correspondence key technologies [J]. electrician technical journal, 2004,4:11-14.
[2] Wang Xiaohu. Electrical power system automatic equipment’s electromagnetic compatibility technology [J]. Guangxi water conservation water and electricity, 2006,3:76-79.
[3] Lin Yuju, Latchman A H, Lee Minkyu et a1. A Power Line Communication Network Infrastructure for the Smart Home[J].IEEE Wireless Communications:2002,9 (6): 104-111.
[4] Liu Weilin, Widmer Hanspeter, Raffin Philippe.Broadband PLC Access Systems and field Development in European Power Line Networks [J].IEEE Communications Magazine.2003,41 (5) 114-118.
[5] Ding Daoqi. Must face up to and study in the power line communication development the key question [J]. electrical power system correspondence, 2003,4:1-12.
