Power line co need for signa s seen as carr ween power viously dumb mmunicate and rgy. The Smar. The down sid als is that t rference (EMI interfere with.
2014 18th IEEE International Symposium on Power Line Communications and Its Applications
C Contacctless Power P r-Linee Com mmunicationns A.S S. de Beer,
H.C. Ferreiira
A.J. Haan Vinck
Department D of Electrical annd Electronic Engineering E Sciennce Universitty of Johannessburg, P.O. Boox 524, Auckkland Park, 20006, South Afrrica
Institu ute for Experimental Matheematics Duisburg-Esssen Universityy Ellernnstr. 29, D-453 326, Essen, Geermany
Ab bstract – Poweer lines that caarry communiication signals tend to prroduce radiateed electromagnetic interfereence (EMI). In n this papeer it is shown how this, usu ually negative effect, is used for contactless signal transmission n. Commerccial PLC moodems a used and LAN operrating in the 150kHz – 30MHz band are signa als are contacttlessly transmittted and receivved up to 2m. ndex Terms – C Contactless, Poower-line Com mmunications, PLC, In EMII.
I. INTRO ODUCTION Power line coommunicationn is increasingg in importannce as the need n for signaal transmissionn increases. Not N only are power p liness seen as carriers of interneet informationn, but connecttivity betw ween power devices and systems are on the incrrease. Prevviously dumb power conveerters and loaads are requireed to com mmunicate andd arrange pow wer loading schedules to save enerrgy. The SmarrtGrid movem ment attests to this t [1]. The down sidde to power lines that carr rry communiccation signals is that tthe lines pro oduce radiatedd electromaggnetic interrference (EMII) [2]. This is usually an unnwanted effectt as it can interfere withh radio recepttion – especiaally in the 1500kHz to 300MHz high freequency (HF)) bandwidth. In this paper,, the radiationn effect is useed as an advanntage to establish e conttactless signaal transfer. Contactless C s signal transsfer can be used u whereverr there is a need n to physiically havee separation between the power linne and a deevice com mmunicating thhrough the linee. This may be useful: • Where maachinery or paarts are rotatinng and inform mation must be transferred across a a physically touch less barrier. • Where devices are sealeed for examplle where a parrt of a system is under pressurre. • In a buildding, where communicating c g devices muust be able to moove freely. Sim milarly to Wirreless systems.. In this papper the prinnciple of conntactless PLC C is illustrated by usinng two comm mercially availaable PLC mod dems that operate in thhe in the 150k kHz to 30MH Hz band usingg the Hom meplug standaard [3]. One modem is used u in a noormal fashion and conneected directlyy to the powerr line. The othher is nected to a looop antenna and a clean isolated sourcce of conn 220V VAC / 50H Hz. Meaninggful data transmission t was estab blished up to 22m.
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I MEASURE II. EMENT SET--UP F Fig.1. shows the measureement set-up for demonstrrating conttactless PLC. One modem is used in a normal n fashion n and connnected directly y to the poweer line and a PC P (PC 1 in Fig.1). F Thiss power line is i then laid in the proximityy of a loop anntenna that feeds inform mation through h a PLC modeem to a PC (P PC 2). For the purposes of this study, signal flow froom PC 1 to PC C 2 is deem med as uploadding and dow wnloading takees place from PC 2 to PC P 1.
Fig.11. Measurement seet-up for contactless transmission using u modems in the 150kkHz – 30MHz ran nge.
Fig.. 1 also showss that the moddem on the looop antenna side is connnected directlly to a clean power sourcce (in terms of o the signnal). This is done d to ensuree that the signnal travels thrrough spacce via the looop antenna annd not the poower networkk. The pow wer source on this t side consists of a 12V battery, b a 12V VDC / 220V VAC inverterr and a Line Im mpedance Staabilisation Nettwork (LIS SN). The LIS SN was addeed for its filltering effect.. The inveerter output is i a quasi-sq quare wave and a contains noise harm monics in the 150kHz to 30 0MHz band. T The output from m the LISN N is a clean 50Hz sine waave. At the innput to the modem m the signal from the loop anteenna and the clean powerr sine wavve are mixed. Since the looop antenna is connected dirrectly to thhe modem, it is subject to 220VAC. A 1.8µF capaciitor is placced in series with the looop to keep the antenna from shorrting the supply and effectivvely forms a coupling c circuuit. A
coup ple of pF’s w were used to tu une the loop to resonate in n the 150k kHz to 30MH Hz bandwidthh. Fig. 2 show ws a photo of o the pow wer line and looop antenna beetween whichh contactless signal s transsfer was estabblished. It alsoo shows the LIISN and modeem. III. MEASSUREMENTS Bit rate speeed measuremeents were donne for the seet-ups show wn in Fig. 1 and Fig. 2. 2 The data transfer rate was measured in the ddirection of thee cable to the antenna (uplo oad – o the Fig. 3) and antennna to cable (ddownload – Fig. 4). Each of a Fig. 4 waas measured using u data points shownn in Fig. 3 and mmercially avaailable LAN speed softwaare. A 20MB B file com was send from onne PC to anotther, the time measured and the transsfer rate calcuulated in Mbpss. Ten measurrements were done at eaach distance between the anntenna and pow wer line. For F a given distance betw ween power line and anteenna, measured data traansfer rates differed. This iss due to noisee that o on the poower line butt also coupples into the cchannel not only throu ugh the air bbetween the antenna a and power p line. Duuring testin ng it was obsserved that devvices switchinng on and offf onto the power p line chaanged the trannsfer speed as noise n was addded to the channel. c The T upload trransfer rate starts s at abouut 35Mbps for the anten nna and pow wer line touch hing (0cm – Fig. F 3). It fallls to arou und 4.5Mbps ffor separation at 2m. The downloadd transfer ratee starts at aboout 20Mbps foor the anten nna and pow wer line touch hing (0cm – Fig. F 4). It fallls to arou und 0.65Mbps for separation n at 2m. Looking L at Fiig. 3 and Figg. 4 one woulld expect the data transsfer rate to sm moothly fall off o with distannce. This doees not happpen and it can clearly be seeen that there iss a periodicity y with peak ks and valleyss. Although the t exact reasson for this is not know wn a couple of o factors shoould be taken into considerration when n analyzing Fiig.3 and Fig. 4. 4 These incluude: • The fact that the meassurements weere not done in i an anechoic chamber annd therefore were subjecct to reflections from nearbyy objects. Theese reflectionss can cause stannding waves annd the shape of o the results. • Contactless transfer of the data was w mainly taaking place in tthe near field d where the wave w impedannce is subject too change with h distance. This T can influ uence transfer raates. I DESIGN CONSIDERATION IV. O NS In I order to deetermine signnal strengths and a the maximum distaance over whhich contactleess transfer can c take placce, a num mber of factorss have to be taken into coonsideration. These T facto ors are summaarized in the block diagram of Fig. 5. Although A not analytically given it is meant to list the impo ortant aspects for future worrk in this regaard. The T diagram in Fig. 5 is set-up s with thhe assumptionn that conttactless data transfer t is taking place between a PC C and mod dem with antennna and a PC with modem on a power line l – similarly to that off Fig. 1 and Fiig. 2.
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Fig. 2. Measurementt set-up showingg the LISN, loopp antenna, modeem and poweer line (refer to Fiig. 1).
I the diagram In m of Fig. 5, thhe upload direcction is form left l to righht and downloaad from right to t left. A. Upload U S Starting with the modem on the poweer line (top leeft of Fig.5), the contacctless distancee is primarilyy influenced by b the l signnal level the modem outpputs. The modem output levels how wever are lim mited by EM MC regulatioons [4],[5]. EMC reguulations limit the radiation n levels from m power linees by limiiting the high frequency vooltage and/or current flowinng on the line. This is done d so that PLC P does nott interfere witth HF radio reception. The T signal leveel on the line also competess with RF noise n that is present on the line l – due to different d sourcces: • Radio signals thatt are received by the line (w where the liine act as anteenna) and; • Interrference from other connectted sources suuch as poweer converters. • Switcching on the line. T Differenttial Mode (DM The M) Line impeedance also pllays a role. The modem m is a voltage source that works w into thee line i drawn. The DM current varies v impedance and a DM current is D line impeddance propportionally to the line impeedance. The DM varies over orderss of magnitudee [6]. It is dependent on: • Traansmission linne effects; • Ch haracteristics of o the line andd; • Looads on the line.
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Fig. 3. Upload performance of the contactless PLC set-up (cable to antenna)
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Fig. 4. Download performance of the contactless PLC set-up (antenna to cable).
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Fig. 5. Bloock diagram show wing different facctors involved in influencing the ddistance over whicch contactless PL LC transmission can c take place.
Common C modde (CM) is thee main transm mission mode for a pow wer line [7]. D Due to unbalaance in the linne with respeect to earth h, DM to CM conversion taakes place. Thiis is determineed by a facctor known as the Transversse Conversionn Loss (TCL) of o the line [2]. A CM currrent flows on n the line and transmits t RF. The T length off the line andd geometry deetermines a power p line antenna gainn. Strictly speeaking, the anntenna gain iss just valid d if the distaance of comm munication iss far enough (and frequ uency high ennough) to radiiate in the farr field. If radiiation takes place in the near field onee should look at a coupling annd not n. For frequenccies up to 30M MHz and distannces up to 2m m (that gain was used for meaasurement in thhis paper) thee antenna is mainly m in th he near field annd electromaggnetic couplingg was taking place. p With h larger distannces it will bee appropriate to look at anttenna gain n. Depending D onn the radiatinng or couplingg field levelss, RF noisee enters the chhannel. The RF R noise enteriing the channeel can be frrom: • Intenntional (radio) transmitters • Transsient switchingg on lines closse by • Convverter operatioon on lines thhat radiate thrrough free space. s The T distance from the linee to antenna determines signal s stren ngth. Generallly die signal leevel falls with 1/d in the farr field and 1/d2 in the neaar field.
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O the receivver side (forr uploading) a loop antennna is On connnected to thhe modem. Depending D oon all the before b menntioned factorrs, a field off given strenggth falls in on the anteenna. The anntenna gain or coupling factor (depennding wheether it is in th he near or far field) f determinnes the signall level that will be an inp put to the receiving modem.. T The receiverr sensitivity is the finnal parameteer in deteermining signaal strength and d distance oveer which contaactless dataa transfer can take t place. B. Download D T downloadd path is a reversal of the uppload path. Staarting The withh the modem connected c to the t loop antennna (bottom rigght of the diagram d of Fig. 5), the dow wnload speed is i influenced by b the moddem transmisssion level. Th he signal is radiated from a loop anteenna and recep ption is greatlyy influenced by b the distancce and wheether far field radiation or near field couupling takes place. p RF noise enters the t channel. The T power linee act as an anntenna and current is gen nerated in CM M due to the eleectromagneticc field emissions. Unballance on the power line causes c CM too DM convversion to tak ke place. It is this t DM curreent that is the input to thhe receiving modem. m
V. CONCLUSION In this paper, it is shown that a signal can contactlessly be transmitted and received from a power line using off-the-shelf PLC modems. This was done between a modem connected to a power line and a modem connected to an antenna. It was shown to be practical to at least 2m. Uploading at 2m was at a rate of 4.5Mbps and downloading around 0.65Mbps. Design considerations were given qualitatively to help understand parameters affecting signal strengths and contactless transfer distance. This technique opens new avenues where PLC can be applied to situations where contactless signal transfer might be required, such as with rotating systems and “wireless” connectivity.
[3]
[4]
[5]
[6]
REFERENCES [1] Farhangi, H., "The path of the smart grid," Power and Energy Magazine, IEEE, vol.8, no.1, pp.18,28, January-February 2010. [2] .H. C. Ferreira, L. Lampe, J. Newbury and T. G. Swart, Power Line Communications: Theory and Applications for Narrowband
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and Broadband Communications over Power Lines, Chichester, England: John Wiley & Sons, 2010. Gardner, S. "The HomePlug standard for powerline home networking." ISPL2001 Proceedings of the 5th international Symposium on Power-Line Communications and its Applications, pp. 66-72, 2001. EN 50065-1: Signaling on low-voltage electrical installations in the frequency range 3 kHz to 148,5 kHz - Part 1: General requirements, frequency bands and electromagnetic disturbances. European Standard, CENELEC, Ref. No. EN 50065-1:2011 E, Brussels, April 2011. CISPR 16: Specification for radio disturbance and immunity methods, International measuring apparatus and Electrotechnical Commission (IEC). Canete, F.J.; Díez, L.; Cortes, J.A.; Entrambasaguas, J.T., "Broadband modelling of indoor power-line channels," Consumer Electronics, IEEE Transactions on , vol.48, no.1, pp.175,183, Feb 2002 C.R. Paul, Introduction to Electromagnetic Compatibility. 2nd Ed., New Jersey: John Wiley & Sons, 2006.
