l23: electromagnetic compatibilityemc).pdfelectromagnetic compatibility • electromagnetic...

L23: Electromagnetic compatibility

L23: 21-MAY-2019

Lund University / LTH / IEA / AR / EIEN25 / 2019-05-21 2

Outlook

• Electromagnetic energy– Emission and propagation

– Interference and disturbance

• Electromagnetic compatibility – Power electronics

– Electric drives

• Remedies and Regulations– Conducted emission limits


Electromagnetic compatibility

• Electromagnetic compatibility (EMC) is the branch of electrical engineering concerned with the unintentional generation, propagation and reception of electromagnetic energy which may cause unwanted effects such as electromagnetic interference (EMI)

• EMC issues– Emission (generation) – reduce unwanted emission

– Coupling – identify propagation mechanisms between transmitter and receiver

– Susceptibility – (receiver as victim) lack of immunity to electromagnetic disturbances


EMC is an equipment

characteristic or property

EMI is a phenomenon

Electromagnetic interference

• Electromagnetic interference (EMI) is en external disturbance that affects an electrical circuit by the coupling mechanisms

1. Radiative

2. Conductive

3. Electric Capacitive

4. Magnetic Inductive

transmitterreceiver

1

2

3

4


Conducted emission

• Electromagnetic energy propagation via a direct electric contact, capacitive and inductive paths in a power distribution network (cables, transmission line, frames, …)

ZdiffUdiffVcom

Vcom ZcomZcom

Idiff

Idiff

Icom

Icom

Coupled less than

a wavelength apart

compared to wave

propagation


Types of interference

• Continuous wave from DC to daylight– Audio frequency from low to 20 kHz

– Radio frequency 20kHz to 30MHz for conducted EMI

– Broadband noise

• Pulse or transient interference– Switched & pulsed supplies (repetitive)

– Power line surges & pulses

– Electrostatic discharge, lightning

– Geomagnetically induced currents


Switching states and output voltage

0

0ū

0-√1/ 2-√1/ 2

0+√1/ 2+√1/ 2

00

uβ

01/3-1/3

-2/3-1/31/32/30

ua

0+√1/ 6-√1/ 6

-√2/3-√1/ 6+√1/ 6+√2/3

0uα

010

-1-1010

uab

001

10-1-10

uac

0-1-1

01100

ubc

01/32/3

1/3-1/3-2/3-1/3

0uc

0-2/3-1/3

1/32/31/3-1/3

0ubvb vovc

+1/6+1/2-1/2+1/2101-1/6+1/2-1/2-1/2001

+1/6+1/2+1/2-1/2011-1/6-1/2+1/2-1/2010+1/6-1/2+1/2+1/2110

+1/2+1/2+1/2+1/2111

-1/6-1/2-1/2+1/2100-1/2-1/2-1/2-1/2000

vas[abc]

sa

Q1

+Udc/2

Udc

uabva

-Udc/2

sb scQ3 Q5

Q2 Q4 Q6

vb vcubc

uca

dcU3

2dcU

6

1

dcU2

1

100

011

110010

001 101

000111

cb

a

cc

bb

aa

cba

uuu

uu

vvu

vvu

vvu

vvvv

2

1

2

3

3

0

0

0

0

Udc x

2.7


Differential and common mode

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02-200

-100

0

100

200

line

time, t [s]

uab

uab

*

va-v

o

-100

-50

0

50

100

phas

e

va

va*

tri

-100

-50

0

50

100

refe

renc

e

triv

o

va*

vb*

vc*

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02-200

-100

0

100

200

line

time, t [s]

uab

uab

*

va-v

o

-100

-50

0

50

100

phas

e

va

va*

tri

-100

-50

0

50

100

refe

renc

e

triv

o

va*

vb*

vc*


Modulation spectra

• Modulation spectrum from low to high speed and back

– Fundamental carries out power amplification control action

– Common mode voltage excites capacitive insulation currents

– High frequency noise


Fast switching inverters

• dV/dt – short voltage rise time from –Udc/2 to +Udc/2

• Wave propagation time can be in the same order of magnitude as voltage switch on

– Wave reflection due to impedance mismatch as μmachine>μcable

– Critical cable length that causes full voltage wave reflection

– Voltage overshoot at motor winding terminal – voltage can be doubled

– Nonlinear voltage distribution causes E-field stress and discharge

''cablecablecable

cable

cablep CLl

v

lt


Trapezoidal waveform spectrum

• Time domain

• Frequency domain

T

d

tr

t

A

2A/(d/T)

1/πd

Log(f)

A

1/πtr

2A/(πTf)

2A/(π2Ttrf2)1/T


Electric drive system

• HF effects in inverter-fed machines– PWM→HF emission, high dV/dt+Ucom vs reflection & overshoot

• Grounding current, shaft voltage, bearing currents– Unbalanced magnetic field, axial rotor flux, electrostatic effect, …

– HF bearing currents: non circulating discharge and circulating


Insulation system response

• Electrical machine as a load– RC for electric insulation

system (EIS) & RL for windings

– Ringing at voltage switching– Voltage distribution

determined by distributed capacitances – local inception E field and discharges

• Leakage current measurement

– Ground, differential across winding, zero sequence, ..

–10

-110

010

110

210

310

410

5-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

indu

ctan

ce,

L [H

]

10-1

100

101

102

103

104

105

100

101

102

103

104

105

resi

stan

ce,

R [

Ohm

]

frequency, f [Hz]

HMOU12

HMRU12

HKRU12

HKRU-VW

FEO 1mA

FEO 1A

FER 1mA

FER 1A

A B C D

+

– +

+’

–

–’

RMF & LMF CMF1 CMF2

ZCM(f)

ZDM(f)f

Z(f)

fR1 fR2 fR3 fR4 fR5


d=2μm E=4.9kV/mm

d=12μm E=3.8kV/mm

d=7μmE=4.3kV/mm

d=4μm E=4.6kV/mm

B:32

A:17 A:32

B:17

43

Electric field intensity E, [kV/mm]

1

Insulation fatigue and failure

• Variable speed drive insulation system safety requirements – electric field distribution over the imperfect insulation system at possible thermal load conditions

• Electrical stresses vsdurability & dielectric insulation capability testing

– polarization index, high potential, C, tan δ, surge characterization and partial discharge recognition


Interference mitigation

• Electromagnetic compatibility by looking at – (quiet) sources of disturbances

– (inhibit) coupling paths

– (harden) potential victims (stresses, fatigue, failure)

• Mitigation techniques– Grounding and shielding – providing low impedance path for EMI

– Decoupling by introducing RF filters

– Transmission line techniques – differential signal and return path balancing, impedance matching


Procedure to achieve EMC

• Customer specification and applicable standards– Emissions– Immunity

• Calculation of generation of harmonic currents, filter design and selection of modulation strategy

• Design rules to improve immunity and to minimize EMI and magnetic fields

• Immunity and emission testing on apparatus or system level in laboratory/test room

• Final validation of EMI, magnetic fields and harmonic currents by measurements on site


Example

• LISN – line impedance stabilization network – LPF of known impedance and measurement point


Measurements, parameter identification

DM @ 0.5MHz

• Frequency response analysis, frequencies and excitation modes ofinterest, circuit and parameter identification, sensitivity analysis, …

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