Andersen, Michael A. E.

Nielsen, Dennis

Thomsen, Ole Cornelius

A conducted emission measurement contains a common and a differential mode component. Accurate separation of these two components is critical, when designing the input filter of a switch mode power supply. Many techniques exists for performing such separation. Some authors suggested the useof wideband transformers, while other prefer current probes. In this paper the use of commercial power splitters/combiners as noise separators are considered. The performance of the noise separators are analyzed and validated based on scattering parameters (S-parameters). Impedance and rejection ratios (common and differential mode) are shown. The results based on S-parameters are used to propose a complete noise separator design. This separator is verified through experimental measurements. Finally an example on how to use the separator, when measuring conducted noise is given

Online Research Database In Technology

                       General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.  • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal   If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.     Downloaded from orbit.dtu.dk on: Dec 20, 2017Separation of common and differential mode conducted emission: Powercombiner/splittersAndersen, Michael A. E.; Nielsen, Dennis; Thomsen, Ole Cornelius; Andersen, Michael A. E.Published in:Proceedings of the International Conference on Renewable Energies and Power QualityPublication date:2012Link back to DTU OrbitCitation (APA):Andersen, M. A. E., Nielsen, D., Thomsen, O. C., & Andersen, M. A. E. (2012). Separation of common anddifferential mode conducted emission: Power combiner/splitters. In Proceedings of the International Conferenceon Renewable Energies and Power QualitySeparation of common and differential modeconducted emission: Power combiner/splittersDennis NielsenTechnical University of DenmarkDepartment of Electrical EngineeringØrsteds Plads, Building 349, room 0082800 Kgs. Lyngby, DenmarkEmail: deni@elektro.dtu.dkOle Cornelius ThomsenTechnical University of DenmarkDepartment of Electrical EngineeringØrsteds Plads, Building 349, room 0242800 Kgs. Lyngby, DenmarkEmail: oct@elektro.dtu.dkMichael A. E. AndersenTechnical University of DenmarkDepartment of Electrical EngineeringØrsteds Plads, Building 349, room 0342800 Kgs. Lyngby, DenmarkEmail: ma@elektro.dtu.dkAbstract—A conducted emission measurement contains acommon and a differential mode component. Accurate separationof these two components is critical, when designing the inputfilter of a switch mode power supply. Many techniques existsfor performing such separation. Some authors suggested the useof wideband transformers, while other prefer current probes.In this paper the use of commercial power splitters/combinersas noise separators are considered. The performance of thenoise separators are analyzed and validated based on scatteringparameters (S-parameters). Impedance and rejection ratios(common and differential mode) are shown. The resultsbased on S-parameters are used to propose a complete noiseseparator design. This separator is verified through experimentalmeasurements. Finally an example on how to use the separator,when measuring conducted noise is given.Key words: EMI, Conducted emission, Power combin-ers/splitters, Differential and Common mode.I. INTRODUCTIONSeparation of conducted emission is a subject which hasintrigue authors within the area of power electronics formany years [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11].Conducted emission can be divided into the categories ofCM (Common Mode) and DM (Differential Mode). Each ofthese modes will in general refer to different parts of theEMI (Electromagnetic Interference) or input filter. In order tooptimizes the design of such filters, correct diagnosis of CMand DM is key.Figure 1: Measuring conducted emission [4].The literature reports of many different techniques forseparating conducted emission. Wide-band transformer arefound in [9], [2], [3], [4], [12], while a combination of purelyresistive networks and transformers are used in [6], [7], [8].Current probes is another alternative as suggested in [1] and[11], while a software approach is introduced in [10]. A finaloption is active separation using operational amplifiers. Suchconfigurations does however place significant demands on thebandwidth of the operational amplifiers.In this paper power splitters/combiners will be used asnoise separators. This idea was original proposed in [5] withan reported CMRR of around -50 dB and DMRR of -50dB in the frequency region of 10 kHz to 30 kHz. Howeverthe verification process used in [5] has been questioned by[2], as power combiners essential where used to validatepower combiners. Further more the issue of maintaining theimpedance requirements of the Line Impedance StabilizingNetwork (LISN) is not addressed in [5]. The purpose ofthe LISN is to isolate the measurement from unwantedinterference of the supply mains, and to define a impedanceacross the measuring point. This paper will cover the issue ofmaintaining the LISN impedance requirements, and validatethe proposed noise separator using appropriate techniques.A. LISNConducted emission on the mains port are measured usinga LISN. CISPR 16-1-2 defines the most common type ofLISN. Figure 2 shows a schematic of the network, whilethe impedance requirements are illustrated in figure 3 withthe tolerances of ±20% imposed [9]. Later in this paperan existing LISN will be modified in order to create thecomplete noise separator. The impedance of this LISN is alsoshown in figure 3 (before any modinification). Clearly, therequirements are fulfilled.When adding a noise separator to the LISN, one should beextreme careful not to violate the impedance requirements ofthe network. The LISN is expected to see at pure resistiveload of 50 Ω, corresponding to the load resistance of a1Figure 2: LISN [9].spectrum analyzer. As shown in figure 3, this will cause theCM emission to se 50Ω2 = 25Ω, while the DM emission sees50Ω+50Ω= 100Ω.101 102 103 104010203040506070f [kHz]Impedance [Ω]  50 Ohm TerminationEnvelope (Williams)Figure 3: Input impedance of LISN.B. Power combiners/splittersA power combiner can be considered as a three port device,which adds the signals of the two inputs ports and providesthe result at the output. On the contrary a power splittershift the phase between the two ports 180o, and effectivelyprovides the difference at the output port. By adding a powercombiner to the LISN receiver ports, the CM component willbe passed on, while the DM component is suppressed (inthe ideal case with infinity damping). A power splitter onthe other hand will let the DM component through, whilethe CM component is suppressed. Addition and subtractionof the conducted emission measurement can thus be used toform a noise separator.II. THEORYWhen designing a noise separator, the question naturallyarises as to which theoretical framework and evaluationmethod, is the most suitable one. The subject has beencovered in [2], concluding that S-parameters will present avery suitable framework. This is among others, due to thefull characterization obtained of the separator, as comparedto the only partial one, which is obtained by using just thetransmission coefficients. Accordingly, S-parameters will bethe choice of this paper. For a three port device as shown infigure 4, [2] defines:ZIn1 ≈ Z0 1+S111−S11 (1)andZIn2 ≈ Z0 1+S221−S22 (2)ZIn1 and ZIn2 are the input impedances, when the device isterminated by the load Z0.Figure 4: S-parameters of three port device [2].The rejection ratio1 of a differential mode separator aredefined as:DMRR =S311+S11 +S21Γs2S121−S22Γs2− S321+S22 +S21Γs1S121−S11Γs1(3)≈ S311+S11− S321+S22(4)CMRR =S311+S11 +S21Γs2S121−S22Γs2+S321+S22 +S21Γs1S121−S11Γs1(5)≈ S311+S11+S321+S22(6)For a common mode separator the rejection ratios are foundfrom:DMRR =S311+S11 +S21Γs2S121−S22Γs2− S321+S22 +S21Γs1S121−S11Γs1(7)≈ S311+S11− S321+S22(8)CMRR =S311+S11 +S21Γs2S121−S22Γs2− S321+S22 +S21Γs1S121−S11Γs1(9)≈ S311+S11+S321+S22(10)1Differential Mode Rejection Ratio (DMRR), Common Mode RejectionRatio (CMRR).2The simplified equations 1, 2, 4, 6, 8 and 10 assumes,that the reflection can be neglected. This is normally a validassumption [2]. The equations of this section will be usedin the design, analyze and verification process. Wheneverreference is made to any of these equations, the impedanceor rejection ratio is obtained by measuring the S-parametersand preforming the relevant calculation.III. ANALYSISThis section will analyze three commercial powercombiners/splitters. The purpose is to establish, which ofthe devices are suitable for designing a complete noiseseparator. All three devices are from Mini-Circuits: ZSCJ-2-2,ZFSCJ-2-1 and ZFSC-2-6. The impedance (magnitude andphase) of the devices are shown in figure 5, 6 and 7.An HP4195A Network/Spectrum Analyzer with associatedTransmission/Reflection test set are used to obtain theS-parameters, and the impedances are then calculated basedon equations 1 and 2. The devices were terminated by a 50Ωresistive load during the measurements.ZSCJ-2-2 and ZFSCJ-2-1 are both power splitters, whileZFSC-2-6 is a power combiner. [5] suggest to use ZFSCJ-2-1and ZFSC-2-6 to form a noise separator. However looking atfigure 5 and 7, it is clear, that ZSCJ-2-2 is a fare better choicefor the splitter than ZFSCJ-2-1. ZSCJ-2-2 and ZFSC-2-6reflects the 50Ω resistive load with very little change in phaseand magnitude over the targeted frequency range (150 kHz –30 MHz).Full S-parameter characterization of each device has beenpreformed. It can be shown, that the presented impedanceplots are obtained using equations 1 and 2. However, due tothe limited number of allowed pages for this conference, theindividual S-parameters will not be presented.IV. DESIGNIt is shown in section III, that ZSCJ-2-2 and ZFSC-2-6 isthe suitable choice for designing a complete noise separator.It is suggested to coupled ZSCJ-2-2 and ZFSC-2-6 in parallelallowing for CM and DM to be measured simultaneous. Inorder to fulfill the impedance requirements of the LISN a25 Ω resistance must be placed in series with the parallelconnected splitters/combiners. An schematic of the completeseparator and its interface with the LISN are shown in figure8, while a photo of the test bench is provided in figure 9.V. MEASUREMENTSThis section verifies the proposed noise separator throughmeasurements, and provides an example on how to used theseparator in a real life measuring setup.101 102 103 10451015202530354045505560f [kHz]Impedance [Ω]  Port 1Port 2(a) Magnitude.101 102 103 104−50−40−30−20−1001020304050f [kHz]Phase [o ]  Port 1Port 2(b) Phase.Figure 5: Impedance of ZFSCJ-2-1for each of the two inputports.A. S-parametersS-parameters and the equations of 4, 6, 8 and 10 are usedto find DMRR and CMRR of the proposed noise separator.The resulting rejection ratios are shown in figure 10. Fromfigure 10 it can be concluded, that the proposed noiseseparator guarantees a DMRR of -70 dB and a CMRR of-60 dB over the frequency range of 30 kHz–30 MHz. Ideallythe separators should provide infinity damping of either CMor DM, while letting the other one through without anydamping. However, in order to establish wether CM or DMare the dominate one, a relative comparison with respect tothe total noise spectrum is sufficient. The component which ismost compressed compared to the total noise spectrum, willbe the dominant one, and thus the one, which the designer ofthe input filter should pay close attention to.3101 102 103 10451015202530354045505560f [kHz]Impedance [Ω]  Port 1Port 2(a) Magnitude.101 102 103 104−50−40−30−20−1001020304050f [kHz]Phase [o ]  Port 1Port 2(b) Phase.Figure 6: Impedance of ZFSC-2-6 for each of the two inputports.B. LISN impedanceIt is verified that the combined LISN and noise separatordoes not violate the impedance requirements. The impedancemeasurement is performed using an AP300 FrequencyResponse Analyzer (by Ridley Engineering). Figure 11show the measured result together with the envelop ofthe impedance tolerance. Clearly the impedance is notviolated with the exceptions of the very high frequencyrange of 10-30 MHz. Extra attention to the layout of thenoise separator and its symmetry should be paid in order tocounteract this. This is however beyond the scope of the paper.C. SpectrumsIn order to illustrate how to use the complete separatorsetup, spectrum measurements are conducted on a commercialswitch mode power supply with is input filter removed. Themeasurements are conducted with a Rohde & Schwarz EMITest Receiver (20 kHz – 7GHz), and the separator setup101 102 103 10451015202530354045505560f [kHz]Impedance [Ω]  Port 1Port 2(a) Magnitude.101 102 103 104−50−40−30−20−1001020304050f [kHz]Phase [o ]  Port 1Port 2(b) Phase.Figure 7: Impedance of ZSCJ-2-2 for each of the two inputports.ZSCJ-2-2ZFSC-2-6Analyzer25Ω25ΩLISN50Ω50ΩFigure 8: Schematic of complete noise separator with LISN.described in figure 8.The resulting spectrums are shown in figure 12. Limits ofconducted emission according to EN55022 are imposed onthe plots. Figure 12(a) and 12(b) gives the line and neutral,respectively, with both outlets for the spectrum analyzerterminated by 50 Ω. The close similarity of the two plotsconfirms, that the noise separator does not violates thesymmetry of the LISN.4Figure 9: Complete separator with LISN.Figure 12(c) and 12(d) shows the output of the ZSCJ22and ZFSC26, respectively. CM is the component suppressedin figure 12(c), while DM is suppressed in figure 12(d).Traditionally the designer of a EMI filter will look at figure12(a) and/or 12(b). He will then assume, that DM emission areassociated with low frequency switching, while CM emissionare due to the higher frequency switching components [9].This leads to the conclusion, that the DM part of the inputfilter should provide about 45 dB of damping, while the CMpart must provide roughly 30 dB damping. However if thedesigner used the proposed separator, he will arrive to a bitdifferent conclusion. First most, it should be stressed, that thespectrums of 12(c) and 12(d) must be viewed with referenceto 12(a) and 12(b), as one essential wishes to comparedthe total noise with the suppressed noise. Figure 12(c)shows that the spectrum is damped over the entire frequencyrange, with the high frequencies being the most suppressedones. From figure 12(d) one sees, that the spectrum onlyis suppressed in the very low frequency range (below 400kHz). It can thus be concluded, that CM emission is thedominant one in the considered case. The CM part of theinput filter should thus be emphasized during the design phase.101 102 103 104−90−80−70−60−50−40−30−20−100f [kHz]Magnitude [dB]  DMRRCMRR(a) ZSCJ22.101 102 103 104−90−80−70−60−50−40−30−20−100f [kHz]Magnitude [dB]  DMRRCMRR(b) ZFSC26.Figure 10: Rejection ratios of the proposed noise separator.VI. CONCLUSIONThis paper presents a conducted emission noiseseparator based on commercial power combiners/splitters.Characterization are performed using S-parameters, andbased on these results a design for the noise separator isproposed. The noise separator is verified through experimentalmeasurements. An example is presented, where the separatoris used for measuring common and differential mode noise ofa commercial switch mode power supply with its input filterremoved.REFERENCES[1] J. Stahl, D. Kuebrich, and T. Duerbaum, “Characterisation of an effectiveemi noise separation including a standard lisn,” in Proc. URSI IntElectromagnetic Theory (EMTS) Symp, 2010, pp. 13–16.[2] S. Wang, F. C. Lee, and W. G. Odendaal, “Characterization, evaluation,and design of noise separator for conducted emi noise diagnosis,”vol. 20, no. 4, pp. 974–982, 2005.[3] M. C. Caponet and F. Profumo, “Devices for the separation of thecommon and differential mode noise: design and realization,” in Proc.Seventeenth Annual IEEE Applied Power Electronics Conf. and Exposi-tion APEC 2002, vol. 1, 2002, pp. 100–105.5101 102 103 104010203040506070f [kHz]Impedance [Ω]  RightLeftEnvelope (Williams)Figure 11: Input impedance of LISN.[4] M. C. Caponet, F. Profumo, L. Ferraris, A. Bertoz, and D. Marzella,“Common and differential mode noise separation: comparison of twodifferent approaches,” in Proc. PESC Power Electronics Specialists Conf.2001 IEEE 32nd Annual, vol. 3, 2001, pp. 1383–1388.[5] T. Guo, D. Y. Chen, and F. C. Lee, “Separation of the common-mode-and differential-mode-conducted emi noise,” vol. 11, no. 3, pp. 480–488,1996.[6] A. A. Ramesh, B. Subbarao, and R. Sivaramakrishnan, “Design of lowcost common and differential mode noise diagnostic circuit,” in Proc. 9thInt ElectroMagnetic Interference and Compatibility (INCEMIC) Conf,2006, pp. 343–348.[7] H.-L. Su and K.-H. Lin, “Computer-aided design of power line filterswith a low cost common and differential-mode noise diagnostic circuit,”in Proc. EMC Electromagnetic Compatibility 2001 IEEE Int. Symp,vol. 1, 2001, pp. 511–516.[8] M. J. Nave, “A novel differential mode rejection network for conductedemissions diagnostics,” in Proc. IEEE 1989 National Symp. Electromag-netic Compatibility, 1989, pp. 223–227.[9] T. Williams, EMC for Product Designers, Fourth, Ed. Elsevier Ltd,2007.[10] Y.-S. Lee and Y. Shu, “Line filter design of switching mode power supplyusing software approximation for conducted emission separation,” inProc. Fifth Int. Conf. Power Electronics and Drive Systems PEDS 2003,vol. 2, 2003, pp. 1339–1344.[11] J. Stahl, D. Kuebrich, and T. Duerbaum, “Modification and character-ization of a standard lisn for effective emi noise separation,” in Proc.Int Electromagnetics in Advanced Applications (ICEAA) Conf, 2010, pp.39–42.[12] C. R. Paul and K. B. Hardin, “Diagnosis and reduction of conductednoise emissions,” vol. 30, no. 4, pp. 553–560, 1988.10−1 100 1010102030405060708090100Frequency [MHz]Level [dBµV]  Quasi−peakAverageEN55022 Quasi−peak limitsEN55022 Average limits(a) Neutral.10−1 100 1010102030405060708090100Frequency [MHz]Level [dBµV]  Quasi−peakAverageEN55022 Quasi−peak limitsEN55022 Average limits(b) Line.10−1 100 1010102030405060708090100Frequency [MHz]Level [dBµV]  Quasi−peakAverageEN55022 Quasi−peak limitsEN55022 Average limits(c) ZSCJ22.10−1 100 1010102030405060708090100Frequency [MHz]Level [dBµV]  Quasi−peakAverageEN55022 Quasi−peak limitsEN55022 Average limits(d) ZFSC26.Figure 12: Spectrum measurements.6

Separation of common and differential mode conducted emission: Power combiner/splitters

http://orbit.dtu.dk/ws/files/10092505/440-nielsen.pdf

Separation of common and differential mode conducted emission: Power combiner/splitters

Abstract

Similar works

Full text

Available Versions

Online Research Database In Technology