Chapter 7 - EMI.pdf

Advanced Power Electronics

1. Chapter 7 –Electromagnetic Interference of
Power Electronics
1
Advanced Power Electronics (EE4007A/B/D)
19/11/2019

2. Outline
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Chapter 7 –Electromagnetic Interference
•Electromagnetic interference (EMI) generation and transmission
•International standards about EMI
•EMI suppression methods
•EMI related power quality issues

3. 3
Chapter 6 –Electromagnetic Interference
Electromagnetic Interference (EMI)
•EMI-Electromagneticdisturbanceleadstodegradationoftheperformance
ofdevices,equipmentorsystems
•EMIisnotavaryingvoltageorcurrent.Itistheharmfuleffectcausedby
electromagneticwavesorfastchangingvoltage/current

4. 4
Chapter 7 –Electromagnetic Interference
Electromagnetic Interference (EMI)
•Inpowerelectronics,electromagneticinterference(EMI)isgenerated
internallyandexternally.EMIcanbetransmittedbyelectricalconduction,
electromagneticinductionandradiationtoandfromapowerelectroniccircuit.
❖Electricalconduction–EMItransmittedthroughelectricalcurrentin
physicalchannelsuchascable.
❖Electromagnetic induction –without physical contact
❖Radiation-emissionortransmissionof
energyintheformofwavesthroughspace

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Spectrum ofElectromagnetic Waves
•Electromagneticinterference(EMI)isalsocalledradio-frequencyinterference
(RFI).
Sunlight
Main focus of EMI in
power electronics
--Wikipedia
•ThischapterisabouthowtheEMIaffectstheelectricalcircuits,devices,andsystemsand
howtosuppressEMI

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Chapter 7–Electromagnetic Interference
Sources of Electromagnetic Interference
❑Natural sources
▪Lightningstrikingonconductor(eg.
overheadpowerline)
•Producing large surge
•Inducingelectricfieldinfrequencywith
50MHzto100MHz
▪Solar radiation
•Cosmic ray producing electromagnetic
wavesin frequency with 100MHz to
1000MHz

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Chapter 7 –Electromagnetic Interference
Sources of Electromagnetic Interference
❑Man-made Sources
▪Electrostatic discharges (ESD)
•Suddenflowofelectricitybetweentwoelectricallychargedobjects
causedbycontact
▪Electromagnetic Pulse (EMP)
•Fromnuclearexplosionsoranysystemsorweaponswiththis
function(eg.EMPBombs)
▪Variations in mains supply voltage
•From malfunction of power systems
•From tripping of circuit breakers
•Fromsuddenchangeofoutputofpowergenerators,criticalloads
andreactivepower(VAR)

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Chapter 7 –Electromagnetic Interference
Sources of Electromagnetic Interference
❑Man-made Sources
▪Electrical and electronic sub-systems producing noise from
•Systemsandpartsinautomotivesuchasignitionsystems,
alternatorsandelectricmachines
•Powerdistributionsystemsincludingpowerlines,staticVAR
compensators(SVC)andgeneratorstations
•Industrialequipmentsuchasweldingmachines,inductionheaters,
circuitbreakers,variablespeeddrivesandoscillators
•Radio transmitters including all mobile communication systems
•Emittedwavesgeneratedbyswitchingtransientofhighfrequency
systemssuchasSMPSandinverters
•HarmonicsofinputcurrentofappliancesfromSMPS,motordrives
andanyapplianceswithoutpowerfactorcorrection

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Chapter 7 –Electromagnetic Interference
❑Media of EMI transmission from power electronics
EMI from power electronics
❑Switching of transistors
▪Rapid changed of current (di/dt)
•Generating high transient voltage with parasitic inductor
▪Rapid change of voltage (dv/dt)
•Generatinghighleakagecurrentthroughstraycapacitance
(electrostaticcoupling)
▪EMIgeneratedinternallyinapowerelectroniccircuitmaybespreadto
thelineandtheloadbyelectricalconduction,andtothesurroundingby
electromagneticinduction,electrostaticcouplingandradiation.

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Chapter 7–Electromagnetic Interference
EMI from power electronics
❑Harmonics of input current
▪EMI transmitted by conduction
▪Degrading power quality
▪Generating EMI
▪Examples of power electronics
•Bridgerectifiers,StaticVARcompensators(SVC),controlled
rectifier,switchedmodeconverterswithoutgoodinputfiltering

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Chapter 7 –Electromagnetic Interference
EMI to power electronics
❑From power network by conduction
▪Poor power quality
•Harmonics
▪Sudden change of power generators and
appliance
•Voltage surge and sags (dv/dt)
▪Noise in power line
❑Noise through electromagnetic induction and radiation
▪Electricalmachine,transmitters,mobilephoneandremote
signaltransmissionequipment

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Chapter 7 –Electromagnetic Interference
Definition of Terms of EMI and Harmonics
❑Electromagnetic Interference (EMI)
▪Electromagneticdisturbancedegradingperformanceofdevices,
equipmentorsystem
▪LowEMIispreferred
❑Electromagnetic Compatibility (EMC)
▪Abilityofanequipmentorsystemtofunctionsatisfactorilyinits
electromagneticenvironmentwithoutintroducingintolerable
electromagneticdisturbancestoanything,inthatenvironment
▪High EMC is preferred

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Chapter 7 –Electromagnetic Interference
Definition of Terms of EMI and Harmonics
❑Emission
▪Phenomenonwhichwhichelectromagneticenergyemitsfromasource
▪Divided into conductive emission and radiated emission
❑Immunity (what is the difference to EMC?)
▪Abilityofadevice,anequipmentorasystemtoperformwithout
degradationinpresenceofanelectromagneticdisturbance.Inother
words,theabilitytowithstandtheEMI

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Chapter 7 –Electromagnetic Interference
Definition of Terms of EMI and Harmonics
❑Susceptibility (the inverse of immunity)
▪Inability of a device, an equipment or a system to perform without
degradation in the presence of an electromagnetic disturbance
❑Total Harmonic Distortion (THD)
▪RMS addition of all harmonics, except the fundamental, as compared to
fundamental component
▪THD can be higher than 100%
▪Good power quality if THD < 15%
Harmonics is one of the sources causing EMI

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Chapter 7 –Electromagnetic Interference
International Standards
❑The British Standards Institute (BSI) -UK
❑The Federal Communications Commission (FCC) -USA
❑Verband Deutscher Elektrotechniker (VDE) -Germany
❑The International Electrotechnical Commission (IEC) -EU
❑TheInternationalSpecialCommitteeonRadioInterference
(CISPR)-IEC
▪Subcommittee of IEC
▪Firstly proposing EMC standards
❑CE Mark -EU
❑Why are Standards needed?

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Chapter 7 –Electromagnetic Interference
International Standards
❑IEC standards for emission

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Chapter 7 –Electromagnetic Interference
International Standards
❑IEC standards for emission

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Chapter 7 –Electromagnetic Interference
International Standards
❑IEC standards for Immunity

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Chapter 7 –Electromagnetic Interference
IEC Standard -EN61000-3-2 (Emission)
❑Class A
▪3-phase equipment except the following classes
❑Class B
▪Portable tools
❑Class C
▪Lighting equipment including dimming devices
❑Class D
▪EquipmenthavinginputcurrentwithspecialwaveshapeandP<600W
▪Measured under test conditions given in EN61000-3-2-Annex C

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Chapter 7 –Electromagnetic Interference
IEC Standard -EN61000-3-2 (Emission)

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Chapter 7 –Electromagnetic Interference
IEC Standard -EN61000-3-2
❑Harmonic standard of Class A

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Chapter 7 –Electromagnetic Interference
IEC Standard -EN61000-3-2
❑Harmonic standard of Class C
*λ is the circuit power factor

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Chapter 7 –Electromagnetic Interference
IEC Standard -EN61000-3-2
❑Harmonic standard of Class D

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Chapter 7 –Electromagnetic Interference
Harmonics from Bridge Rectifiers
❑Bridge rectifier without an output filter capacitor
▪Input current is sinusoidal without harmonic, but the output voltage
presents large ripple

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Chapter 7 –Electromagnetic Interference
▪Higher output capacitance decreasing output ripple but increasing
input harmonic current
Harmonics from Bridge Rectifiers
❑Bridge rectifier with an output filter capacitor

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Chapter 7 –Electromagnetic Interference
▪Higher output capacitance decreasing output ripple but increasing
input harmonic current
Harmonics from Bridge Rectifiers
❑Bridge rectifier with an LC low-pass filter capacitor

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Chapter 7 –Electromagnetic Interference
Power Factor Correction Converters
❑Powerfactorcorrection(PFC)converterscanbeusedforvoltage
rectificationwithregulatedDCoutputvoltagetosolvetheaboveinput
harmoniccurrentandpowerfactorproblem.
❑AC/DC converter with very high PF and regulated output voltage
❑Closed-loop controlled for I/P current and O/P voltage
▪Shape of input current regulated to be half sinusoidal
▪Phase of input current regulated to be in phase with I/P voltage
❑Peak current mode control or average current mode control
❑SizeofoutputfilteringcapacitorNOTabletobereducedbyincreasing
switchingfrequency

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Chapter 7 –Electromagnetic Interference
Power Factor Correction Converters
❑Single phase PFC converter with boost topology
▪Shape and phase of iL regulated to be the same as vDC

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Chapter 7 –Electromagnetic Interference
Power Factor Correction Converters
❑3-phase full bridge PFCC

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Chapter 7 –Electromagnetic Interference
Active Harmonic Compensation
❑Harmonicactivefilterseliminatingarangeorwholerangeofharmonics
❑Compensating displacement VAR
❑Fast response
❑For shunt type, shunt connected to the line
▪Switched mode converter (Inverters)
▪Current mode closed-loop control
▪Similar to STATCOM
▪Series type active filter similar to SSSC

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Chapter 7 –Electromagnetic Interference
Active Harmonic Compensation
❑Constructedwithabidirectional3-phasefull-bridgeinverter
▪3-ph Inverter →6 boost converters sharing 3 input inductors
❑Large capacitor as energy storage device and power source
Diagram of a shunt active filter

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❑Whenthepowerlinecurrentishigherthanthereferencecurrent,thelargecapacitorprovides
powertotheinvertertogeneratetheamountofexceedingcurrenttotheloadthroughthe
powerlineinstantaneously.
❑Whenthepowerlinecurrentislowerthanthereferencecurrent,thebidirectionalinverteracts
asaboostconverter(similartopologyof3-phasepowerfactorcorrectionconverterwithboost
topology).Theactivepowerfilterinputstheamountofcurrentunderthereferencecurrent
instantaneouslytotheconvertertochargethecapacitor.
Active Harmonic Compensation
Control objective: grid current are sinusoidal currents
Operation principle: i_load (ila, ila, ila) = i_grid (ia, ib, ic) + i_filter (i1, i2, i3)
Grid current

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Chapter 7 –Electromagnetic Interference
Types of Electromagnetic Interference
❑Differential mode noise
❑Common mode noise
▪EMIconductingthroughconductorstoandfrominputlines
▪EMIconductingthroughstraycapacitorsbyelectrostaticcoupling
betweenpowerlinesandground
❑BothtypesofEMIinACcurrentorvoltagemanner
❑Suppressing EMI necessary for meeting standard
▪EMI suppression filters commonly used
▪Different types of filters for different types of EMI

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Chapter 7 –Electromagnetic Interference
Types of Electromagnetic Interference
Noise from converter
Noise to converter

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Chapter 7 –Electromagnetic Interference
Differential Mode Noise Suppression
❑Differential mode chokes
▪Using magnetic components (a pair of inductors)
❑Class X capacitors
▪Shunt connected capacitor at the input of the converter

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Chapter 7 –Electromagnetic Interference
❑Constructed with a pair of inductors
▪Connected to input of converter
▪Providing high reactance of noise (high frequencies)
▪AC current of noise reduced
Differential Mode Noise Suppression

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Chapter 7 –Electromagnetic Interference
❑Varistor, Also called voltage dependent resistor
❑Connected in the input of the whole converter circuit
❑Withnonlinearandvariableresistancecharacteristicwithdifferentvoltage
▪Very high resistance during normal operation
▪Resistance decreasing while increasing voltage
▪Resistance decreasing drastically while voltage beyond rated voltage
Differential Mode Noise Suppression

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Chapter 7 –Electromagnetic Interference
❑Resistance of varistor is very low during surge occurring
❑Current returning to the power lines
▪Circuit protected from differential mode voltage surge
▪Especially surge during switching on the converters
❑Selectingvaristorswithdifferentvaristorvoltage,maximumclamping
voltageandmaximumenergy(Joule,J)
Differential Mode Noise Suppression

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Chapter 7 –Electromagnetic Interference
Other Methods for Reducing EMI
❑Good design of transformers and inductors
▪Using toroid cores to reducing leakage magnetic flux
❑Electricalisolationofpowerconvertersisolatingdifferentialmode
noisebythetransformer
❑Applyingsnubbercircuitsfordecreasingdv/dtbutthisdecreasing
efficiencyoftheconverters
❑Applyingsoft-switchingtechniquestoreduceswitchingloss,di/dtand
ordv/dtoftransistors

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Chapter 7 –Electromagnetic Interference
Other Methods for Reducing EMI
❑Good PCB tracks and components arrangement
▪Decreasing inner area of PCB tracks of current loop ()
▪Decreasing length of tracks
❑Using double layer PCB with ground on the top layer
▪The ground on the top layer absorbing external and internal EMI
•Theroutineofcurrentformsacurrentloop.Decreasinginner
areaofthecurrentloopordecreasingthelengththetrackscan
reduceparasiticinductanceandEMI