modeling conducted emi in power electronic systems · 2019. 10. 17. · • commonode (and...

Modeling Conducted EMI in Power Electronic Systems

Aaron BrovontAssistant Professor

Electrical and Computer [email protected]

Distribution A. Approved for public release, distribution is unlimited. Approved, DCN# 43-5296-19

Contributors & Collaborators

Dr. Rob Cuzner

Dr. Seungdeog ChoiMr. Mark Didat

Dr. Steven Pekarek

Dr. Andy LemmonDr. Aaron Brovont

Dr. Mike MazzolaMr. Jim Gafford

2


Outline

• Background on electromagnetic compatibility (EMC)• Conducted emissions testing• Common-mode (and differential-mode) modeling tutorial• Application and validation in UA EMI testbed• Study of leakage current through multi-chip power module (MCPM)

baseplate

3


The paradigm shift in power systems due to power electronics makes EMC critical to design.

Ideal, 3-phase 60-Hz voltage supply Two-level, VSI phase-to-neutral output

4


Present trends in power electronics likely to worsen EMI.

• Maturation of wide-bandgap devices

• Drive for increased efficiency and/or power density

• Increased penetration of renewables and power electronics applications

• Results: higher edge rates (dv/dt), switching frequencies, and voltage levels

5


What is electromagnetic compatibility?

• Concerned with the generation, transmission, and reception of electromagnetic energy

• A system is electromagnetically compatible if1. It does not cause interference in surrounding systems;2. It does not allow interference from surrounding systems;3. It does not cause interference with itself

6

Emitter Transmission Path Receptor


Some basic EMC terminology

• Emissions, interference, and susceptibility• Conducted emissions vs. radiated emissions• Differential-mode vs. common-mode

• Electrical length: – f = 300 kHz, λ = 1 km– f = 3 MHz, λ = 100 m– f = 30 MHz, λ = 10 m– f = 300 MHz, λ = 1 m

• Antennae are poor radiators of signals for which

7


Spectra of Modern Power Electronics

102 103 104 105 106 107 108 109

300 MHz

3GHz

Si IGBTOperation

FrequencyRange

WBGOperation

FrequencyRange

Si IGBTExtendedDynamics

Range

WBGExtendedDynamics

Range

VHF UHF

Lumped Element Analysis Increasingly Valid

Lumped Element Analysis Increasingly Invalid

“Near RF”Domain

HF

3MHz

30 MHz

• Traditional IGBT-based systems: • Operation Frequencies to ~50 kHz• Easily-suppressed extended dynamics• Packaging impedances are not critically

important

• WBG-based systems: • Operation Frequencies to a few MHz• Extended dynamics to ~50 MHz• Packaging impedances are critically

important in “Near-RF” domain

A. N. Lemmon, R. Cuzner, J. Gafford, R. Hosseini, A. D. Brovont, and M. S. Mazzola, “Methodology for Characterization of Common-Mode Conducted Electromagnetic Emissions in Wide-Bandgap Converters for Ungrounded Shipboard Applications,” IEEE J. Emerg. Sel. Topics Power Electron., vol. 6, no. 1, pp. 300–314, Mar. 2018.


Approach to EMI challenges in PE systems

• PE emissions primarily in conducted band (~10 kHz–30 MHz)• Objective is to prevent emissions from reaching grid (large antenna)• Three options: reduce susceptibility, make transmission inefficient, or eliminate

source• Our Approach: Employ modeling to minimize conducted emissions

– Conducted emissions simpler and possible early in design– Reduces potential for radiated EMI

9

Conducted EMI predictable Radiated EMI predictable

Early-stage design Late-stage design

Architecture System fabrication

Component topologies

Component selection

System layout


How do you measure conducted emissions?• Line Impedance Stabilization

Network‡:– Provide a standard source impedance for

evaluating/measuring EUT emissions– Decouple source and EUT emissions– Typically modeled as 50 Ω to ground

• LISN only used on input side of EUT• Commercial LISNs are not available for

voltage levels > 1 kV• Custom LISNs designed and built at

UA

Fischer FCC-LISN-50-XXX LISN

‡ “DOD Interface Standard, Requirements for the control of electromagnetic interference characteristics of subsystems and equipment, Mil-Std-461G, 10 Mar. 2015.

LISNs

Vdc

Zheatsink

Rli

LlCliClo

Rlo

Zg

a

Cug

CpgClg

Cdc

Rli

LlCliClo

Rlo

Q1

Q4

Earth

System Ground

u

l

b

Cug

CpgClg

Q2

Q5c

Cug

CpgClg

Q3

Q6

Zwg

PMSM


Example: emissions from a machine-driveLISNs

Vdc

Zheatsink

Rli

LlCliClo

Rlo

Zg

a

Cug

CpgClg

Cdc

Rli

LlCliClo

Rlo

Q1

Q4

Earth

System Ground

u

l

b

Cug

CpgClg

Q2

Q5c

Cug

CpgClg

Q3

Q6

Zwg

PMSM

i1

i2v1Pv2P

P

– Differential mode (DM):

– Common mode (CM):

A. D. Brovont and A. N. Lemmon, “Utilization of Power Module Baseplate Capacitance for Common-Mode EMI Filter Reduction,” IEEE Electr. Ship Technol. Symp., 2019, submitted.


Fields from CM current are more likely to radiate and couple with nearby equipment

• Magnetic field accumulates

Fields fall off for long wires

• Magnetic field cancels

Fields fall off for long wires

12

i1i2 i12


The many faces of the “Common Mode”

• Bearing currents and shaft voltages– Cause premature bearing failure in electric machines with VFDs– Shock hazard and voltage stress on insulation

• Leakage currents– Unintended ground currents typically through capacitive couplings with chassis and heat

sinks– Interference with low-power electronics

• Circulating currents– Steady-state current flow between paralleled converters– Can be large and low-frequency, down to DC– Lossy, can cause instability, and unbalanced power sharing

13


DIFFERENTIAL-MODE AND COMMON-MODE EQUIVALENT CIRCUIT MODELING

14


Objectives of modeling conducted EMI

• Analytically predict parasitic/undesirable behavior of power electronic systems

• Inform/guide measurements to support modeling and analysis• Predict the impact of new technologies (e.g., WBG devices)• Evaluate methods to mitigate EMI and CM current through design

15


i1

i2v1Pv2PP

invnP

iNvNP

vPg

Modified definition for CM voltage enables rigorous & flexible model generation

Common Mode

Differential Mode

16

P is arbitrary

A. D. Brovont, "Generalized Differential-Common-Mode Decomposition for Modeling Conducted Emissions in Asymmetric Power Electronic Systems," IEEE Trans. Power Electron., vol. 33, no. 8, pp. 6461-6466, Aug. 2018.


DM and CM definitions can be viewed generally as a space transformation

17

i1

i2v1Pv2PP

invnP

iNvNP

vPg

P is arbitrary



Sourceeas Ls Rs

ebs

ecs

LfsLdc Rdc

eal

ebl

ecl

D1 D3 D5 S1 S2 S3

Ldc Rdc

Ls Rs Lfs

Ls Rs LfsD4 D6 D2 S4 S5 S6

Cwgs

LlRlLf l

LlRlLf l

LlRlLf l

Cwgl

DC Bus

Cdc1 Cdc2

Rectifier Inverter AC Load

Rb

Lb

Lb

Cgb

CgbDb

Sb

Buck Converter DC Load

Cwgs Cwgs Cwgl Cwgl

These specific definitions lay the foundation for CM equivalent circuit modeling.

Example microgrid

Reduced CM model

CM equivalent circuit theory

Rl /3Lf l /3iCM,lPvCM,lRs /3 Lfs /3 iCM,s

vCM,s Rdc /2Ldc /2 Pʹ

3Cwgs 3Cwgl

Lb /2iCM,bvCM,b

2Cgb

vCM,dc vʹCM,dc

A. D. Brovont & S. D. Pekarek, "Derivation and application of equivalent circuits to model common-mode current in microgrids," IEEE J. Emerg. Sel. Topics Power Electron., vol. 5, no. 1, pp.1-12, March 2017.

18


Why don’t we just simulate mixed-mode circuits?

• Wide range of time-constants• Often a large number of electrical components• Recipe for numerical heartache as number of components increase• Does not give any design insight unless run many simulations and

interpret a lot of data

19

OR, why do we need CM equivalent circuits?


Example: platform developed for in situ emissions characterization of intermediary conversion systems.

Output LISNsInput LISNsEUT

(half-bridge inverter)

Vdc

Rh

Rli

LlCliClo

Rlo

Zg

ACn

Cn

ClgCagCug

Cdc

Rli

LlCliClo

Rlo

NRlo

LlCloCli

Rli

Rlo

LlCloCli

Rli

vQ1

vQ2

Earth

Testbed Ground

iin,cm iout,cmU

L

• Architecture inspired by MIL-STD-461 CE-102

• Terminations at input and output representative of fielded applications

• Platform provides DM and CM model validation environment for EUT

• Employed to study leakage currents through module parasitics

20


An example application of the modeling approach

21

Half-bridge EMI testbed CM equivalent modelCM equivalent circuit theory

ioii

Vdc

Zh

Rli

Ll

CliCloRlo

Rg

A

Cn

Cn

kCpCpCp

Cdc

Rli

Ll

CliCloRlo

NRlo

LlCloCli

Rli

Rlo

LlCloCli

Rli

vQ1

vQ2

cmcm

Rli/2

Ll /2io

2Cli

iivovi

vp

vCp

Zh

(2+k)Cp

2Clo

Rli/2

Ll /2

2Cli2Clo

Rlo/2 Rlo/2

Rg

Acm cm

cm

cmcm

dmcm

Half-bridge configuration of UA EMI testbed

A. D. Brovont and A. N. Lemmon, "Common-mode/differential-mode interactions in asymmetric converter structures," in Proc. IEEE Electric Ship Technologies Symposium, Arlington, VA, 2017, pp. 84-90.


CM model development in four steps

1. Add important parasitics to MM component models2. Partition MM model around switches3. Transform components to CM equivalent circuits4. Connect component equivalent circuits using CM reference to form

system model

22


23

1) Create the mixed-mode model

Zh

Rli

LlCliClo

Rlo

Rg

P

kCpCpCp

Cdc

Rli

LlCliClo

Rlo

Rlo

LlCloCli

Rli

Rlo

LlCloCli

Rli

N

v 2P

L

U

1 2 3

A

Rh

P

kCpCpCp

v 1P

v3Pv 2

P

1 2 3

vCMp

vm

Rh

(2+k)Cp

P

Left multiply by T3vand sub in (T3i)-1iDCM

2) Partition model around switches

3) Decompose components into equivalents 4) Combine equivalents using CM reference

ioii

Vdc

Zh

Rli

Ll

CliCloRlo

Rg

A

Cn

Cn

kCpCpCp

Cdc

Rli

Ll

CliCloRlo

NRlo

LlCloCli

Rli

Rlo

LlCloCli

Rli

vQ1

vQ2

cmcm

Rli/2

Ll /2io

2Cli

iivovi

vp

vCp

Zh

(2+k)Cp

2Clo

Rli/2

Ll /2

2Cli2Clo

Rlo/2 Rlo/2

Rg

Acm cm

cm

cmcm

dmcm


Step 1: Create the mixed-mode model

• Add parasitics to the standard MM model (if desired or necessary)• Assuming symmetric parasitics for sake of demonstration

24

Vdc

Zh

Rli

Ll

CliCloRlo

Rg

A

Cn

Cn

CpCpCp

Cdc

Rli

Ll

CliCloRlo

NRlo

LlCloCli

Rli

Rlo

LlCloCli

Rli

vQ1

vQ2


Step 2: Partition MM model around switches

Focus on the non-power-electronic elements – partition into groups

25

Zh

Rli

LlCliClo

Rlo

Rg

P

CpCpCp

Cdc

Rli

LlCliClo

Rlo

Rlo

LlCloCli

Rli

Rlo

LlCloCli

Rli

N

v 2P

L

U

1 2 3

A

Vdc

Zh

Rli

Ll

CliCloRlo

Rg

A

Cn

Cn

CpCpCp

Cdc

Rli

Ll

CliCloRlo

NRlo

LlCloCli

Rli

Rlo

LlCloCli

Rli

vQ1

vQ2


Step 3: Symmetric lines transform following simple parallel addition rules in CM.

26

Mixed-mode Model CM Equivalent Circuit

i1

i2v1Pv2P

P

vPg

R

R

L

L

CC

i1 ʹ

ʹi2

R/ 2L/ 2icm

2C

PvPg

vcm icm ʹ

A. D. Brovont & S. D. Pekarek, "Derivation and application of equivalent circuits to model common-mode current in microgrids," IEEE J. Emerg. Sel. Topics Power Electron., vol. 5, no. 1, pp.1-12, March 2017.


Step 3(a) Detail

27

Mixed-mode Modeli1

i2v1Pv2P

P

vPg

R

R

L

L

CC

i1 ʹ

ʹi2


28


Step 3(b): three-line example

29

Parasitic baseplate capacitance

Rh

P

CpCpCp

v 2P

1 2 3


vcm

Rh

3Cp

PLeft multiply by T3vand sub in (T3i)-1idcm



Step 3(b) Detail

30

Rh

P

CpCpCp

v 2P

1 2 3

Mixed-mode Model


Step 4: Form system model by specifying reference point(s)

31

Rli/2

Ll /2io

2Cli

iivovi

vp

Zh

3Cp

2Clo

Rli/2

Ll /2

2Cli2Clo

Rlo/2 Rlo/2

Rg

A

cm

cm cm cm cm

Rh

Rli

LlCliClo

Rlo

Rg

A

CpCpCp

Cdc

Rli

LlCliClo

Rlo

Rlo

LlCloCli

Rli

Rlo

LlCloCli

Rli

N

v 2A

L

U

1 2 3


Step 4: Form system model by specifying reference point(s)

• Select shared reference point and connect CM equivalent circuits

• Phase node A is selected in this example

Intrinsic CM voltage sources

32

A

Cn

Cn

N

vQ1

vQ2

U

L

vCn1

vCn2

Q1

Q2

Rli/2

Ll /2io

2Cli

iivovi

vp

Zh

3Cp

2Clo

Rli/2

Ll /2

2Cli2Clo

Rlo/2 Rlo/2

Rg

A

cm

cm cm cm cm


Overall system model

33


Half-bridge configuration of EMI testbed

Rli/2

Ll /2io

2Cli

iivovi

vp

Zh

3Cp

2Clo

Rli/2

Ll /2

2Cli2Clo

Rlo/2 Rlo/2

Rg

A

cm

cm cm cm cm

ioii

Vdc

Zh

Rli

Ll

CliCloRlo

Rg

A

Cn

Cn

CpCpCp

Cdc

Rli

Ll

CliCloRlo

NRlo

LlCloCli

Rli

Rlo

LlCloCli

Rli

vQ1

vQ2

cm cm


ioii

Vdc

Zh

Rli

Ll

CliCloRlo

Rg

A

Cn

Cn

kCpCpCp

Cdc

Rli

Ll

CliCloRlo

NRlo

LlCloCli

Rli

Rlo

LlCloCli

Rli

vQ1

vQ2

cm cm

How to model effects of asymmetry?

• Asymmetry between lines of a CM path produces “mode conversion”

• Introduce an asymmetry factor k in module parasitics to investigate impact

34


Mixed-mode ModelDecomposition approach to asymmetric components

35


Rh

P

kCpCpCp

v 2P

1 2 3

Left multiply by T3iand sub in (T3v)-1vdcm



vp

vCp

Rh

(2+k)Cp

P

dmcm

vCpcm

Decomposition approach to asymmetric components

36


Rh

P

kCpCpCp

v 2P

1 2 3



Overall system model

37


ioii

Vdc

Zh

Rli

Ll

CliCloRlo

Rg

A

Cn

Cn

kCpCpCp

Cdc

Rli

Ll

CliCloRlo

NRlo

LlCloCli

Rli

Rlo

LlCloCli

Rli

vQ1

vQ2

cmcm

Rli/2

Ll /2io

2Cli

iivovi

vp

vCp

Zh

(2+k)Cp

2Clo

Rli/2

Ll /2

2Cli2Clo

Rlo/2 Rlo/2

Rg

Acm cm

cm

cmcm

dmcm

Half-bridge configuration of UA EMI testbed



Bonus: Analyze/approximate output CM voltage source

The second term is the CM voltage of the neutral-clamping capacitors. If Cn is large, this voltage is approximately constant:

38


A

Cn

Cn

N

vQ1

vQ2

U

L

vCn1

vCn2

Q1

Q2


Bonus: Analyze/approximate mode conversion source

The second term is the CM voltage of the neutral-clamping capacitors. If Cn is large, this voltage is approximately constant:

39


Zh

2

kCpCpCp

Cdc

vQ1

vQ2

1

3


Summary: CM equivalent model of the testbed

Rli/2

Ll /2io

2Cli

iivovi

vp

vCp

Zh

(2+k)Cp

2Clo

Rli/2

Ll /2

2Cli2Clo

Rlo/2 Rlo/2

Rg

Acm cm

cm

cmcm

dmcm

• CM voltage sources dominated by switching– dv/dt & switching frequency critical

parameters

• Voltage ripple at neutral point injected into CM– Self-resonant behavior of Cn must be

avoided (ESL critical)

• Voltage ripple at dc input injected due to mode conversion– Self-resonant behavior of Cdc must be

avoided (ESL critical)

40



APPLICATION AND VALIDATION OF CM MODELING APPROACH

41


UA SiC EMI Characterization Testbed Implementation

• Identical, characterized input and output termination impedances

• Natural convection cooling to avoid corruption from thermal management

• Diff. probes and current probes used for utility ground isolation

• Testbed and utility ground connected only through DC supply

• Testbed configured with half-bridge inverter EUT employing Cree CAS120 1.2-kV SiC half-bridge MCPM

42

A. Brovont, A. Lemmon, C. New, B. Nelson, B. DeBoi, "Cancellation of Leakage Currents through Power Module Baseplate Capacitance," in Proc. IEEE Appl. Power Electron. Conf., March 2019.


Leakage current through MCPM was measured in the EMI characterization testbed.

• Half-Bridge EUT with shorted load (only LISN impedance)†

– Measured displacement current through MCPM baseplate through LISNs on input and output.

– 100 kHz fixed-duty PWM, 300 ns dead time, 600 V DC bus

• Results were compared against nominal model with measured parasitic baseplate capacitances

43

†A. Lemmon, R. Cuzner, J. Gafford, R. Hosseini, A. Brovont, M. Mazzola, "Methodology for Characterization of Common-Mode Conducted Electromagnetic Emissions in Wide-Band-Gap Converters for Ungrounded Shipboard Applications," in IEEE Journal of Emerging and Selected Topics in Power Electronics, vol. 6, no. 1, pp. 300-314, March 2018.

LISNFilters

LISNInductors

Inverter Core

EMI Characterization Testbed at UA


Characterizing the MCPM Baseplate Capacitance• Baseplate capacitance was not

measured previously• Cannot be measured from the

terminals• A sample module (Cree

CAS120) from the EMI testbed was deconstructed to accurately quantify the capacitances

44


CM voltage noise source modeling

• The dominant component of the CM voltage is proportional to (vQ1-vQ2)

• This term is readily modeled from the nominal input voltage, duty cycle, and average rise and fall time of the switch voltage:

45


Equivalent model reduced and analyzed to predict baseplate current.• The expression for the equivalent CM source with respect

to the baseplate is approximately

• Model indicates strong influence of MCPM parasitic asymmetry and potential compensation†

46

Reduced CM Equivalent Model

Ll /4

4Clivbp,eq

(2+k)Cp

4Clo

Zlisn4

Rh

Rli4

Rlo4

cm



STUDY OF BASEPLATE CAPACITANCE IN MULTICHIP POWER MODULES

48


D1 (U) S1D2 (A)S2 (L)

Unbalanced baseplate capacitance is a critical factor affecting leakage current through baseplate.• DBC substrate geometry leads to

capacitive coupling between terminals and baseplate

• High dv/dt drives leakage current through the baseplate

• Low-side source terminal (S2) usually occupies much less substrate area than D1 and S1D2(which are similar)

• In general, D1, S1D2, and S2 substrate areas are all different leading to unequal Cug, Cag, and Clg

49

Cree CAS120 Module - Disassembled


Relaxed concept of CM voltage and flexible DM and CM definitions permit derivation of CM equivalent model.

50

iout,cmiin,cm

Rh

ibpCug+Clg

Cag

A

vdm→cm

vUL,cm vAN,cmU,L

Zin2

Zout2

iulg,cm

iag

A,N

ul

Output LISNsInput LISNsEUT

(half-bridge inverter)

Vdc

Rh

Rli

LlCliClo

Rlo

Zg

ACn

Cn

ClgCagCug

Cdc

Rli

LlCliClo

Rlo

NRlo

LlCloCli

Rli

Rlo

LlCloCli

Rli

vQ1

vQ2

Earth

Testbed Ground

iin,cm iout,cmU

L

Half-bridge EMI testbed CM equivalent modelCM equivalent circuit theoryA. Brovont, A. Lemmon, C. New, B. Nelson, B. DeBoi, "Cancellation of Leakage Currents through Power Module Baseplate Capacitance," in Proc. IEEE Appl. Power Electron. Conf., March 2019.


Analysis of leakage current through the MCPM baseplate

• The equivalent CM ac voltage driving BP current is given by

where

• In a typical module,

51

vcm,ac

Cbp

Zin2

vcm,dc

Zout2

Rhibp



Experimental setup was devised to validate the CM model predictions.

• Discrete capacitors were placed between the module terminals and the baseplate

• The qac parameter was swept across the range including the “critical” value of 1/4

• Total baseplate capacitance (Cbp) was held constant for all cases

52

External Caps Added for Sweep of qac



Results of the qac sweep experiments

53

• Model accurately predicts BP current RMS amplitude over full sweep

• Cancellation occurs at the qac = 1/4• Model accurately predicts the polarity

inversion and symmetry about the “critical” qac value of 1/4



Model accurately predicts all significant characteristics of the BP current including ringing frequency and amplitude.

54



Acknowledgment

This research was supported by the U.S. Office of Naval Research under award numbers N00014-18-1-2156, N00014-18-1-2601, and N00014-18-1-2260.

55


Modeling Conducted EMI in Power Electronic SystemsContributors & CollaboratorsOutlineThe paradigm shift in power systems due to power electronics makes EMC critical to design.Present trends in power electronics likely to worsen EMI.What is electromagnetic compatibility?Some basic EMC terminologySpectra of Modern Power ElectronicsApproach to EMI challenges in PE systemsHow do you measure conducted emissions?Example: emissions from a machine-driveFields from CM current are more likely to radiate and couple with nearby equipmentThe many faces of the “Common Mode”Differential-Mode and Common-mode Equivalent circuit modelingObjectives of modeling conducted EMIModified definition for CM voltage enables rigorous & flexible model generationDM and CM definitions can be viewed generally as a space transformationThese specific definitions lay the foundation for CM equivalent circuit modeling.Why don’t we just simulate mixed-mode circuits?Example: platform developed for in situ emissions characterization of intermediary conversion systems.An example application of the modeling approachCM model development in four stepsSlide Number 23Step 1: Create the mixed-mode modelStep 2: Partition MM model around switchesStep 3: Symmetric lines transform following simple parallel addition rules in CM.Step 3(a) DetailSlide Number 28Step 3(b): three-line exampleStep 3(b) DetailStep 4: Form system model by specifying reference point(s)Step 4: Form system model by specifying reference point(s)Overall system modelHow to model effects of asymmetry?Decomposition approach to asymmetric componentsDecomposition approach to asymmetric componentsOverall system modelBonus: Analyze/approximate output CM voltage sourceBonus: Analyze/approximate mode conversion sourceSummary: CM equivalent model of the testbedApplication and validation of CM modeling approachUA SiC EMI Characterization Testbed ImplementationLeakage current through MCPM was measured in the EMI characterization testbed.Characterizing the MCPM Baseplate CapacitanceCM voltage noise source modelingEquivalent model reduced and analyzed to predict baseplate current.Study of Baseplate capacitance in multichip power modulesUnbalanced baseplate capacitance is a critical factor affecting leakage current through baseplate.Relaxed concept of CM voltage and flexible DM and CM definitions permit derivation of CM equivalent model.Analysis of leakage current through the MCPM baseplateExperimental setup was devised to validate the CM model predictions.Results of the qac sweep experimentsModel accurately predicts all significant characteristics of the BP current including ringing frequency and amplitude.Acknowledgment

modeling conducted emi in power electronic systems · 2019. 10. 17. · • commonode (and...

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