Download EMC - CAS - Cern Accelerator School

EMC
WARRINGTON - Monday 17 May - Alain CHAROY
AEMC
POWER CONVERTERS FOR PARTICLE ACCELERATORS - [email protected]
Introduction
Differential Mode Immunity
Differential Mode Emissions
Common Mode Emissions
Electromagnetic Radiations
EMC terms and lab assessment conditions
Electromagnetic emission
Electromagnetic susceptibility
Standardized
test
Standardized
test
Given EM
disturbance
The best situation is
Given EM
disturbance
to undertake EMC tests
Defined
Disturbance
source
& to solve EMC problems
Standardized
Measuring
conditions
Defined
Measuring
equipment
Standardized
Measuring
conditions
Emission-test
level
before they appear in situ
Immunity-test
level
Emission-test
limit
Immunity-test
limit
Single emitter
Single victim
Deterministic situation
Deterministic situation
EMC best controlling conditions
Electromagnetic emission
Standardized
test
Electromagnetic susceptibility
Standardized
test
In situ test
Given EM
disturbance
Given EM
disturbance
Given EM
disturbance
Given EM
disturbance
Defined
Measuring
equipment
Defined
Measuring
equipment
Defined
Disturbance
source
Defined
Disturbance
source
Standardized
Measuring
conditions
Defined
Measuring
conditions
Defined
Measuring
conditions
Standardized
Measuring
conditions
Emission-test
level
Emission
level
Immunity
level
Immunity-test
level
Emission-test
limit
Emission
limit
Immunity
limit
Immunity-test
limit
An EMC Validation is
desirable to plan in situ
after system installation
before problems appear
Single emitter
Single victim
Deterministic situation
Deterministic situation
EMC troubleshooting
Electromagnetic emission
Standardized
test
Electromagnetic susceptibility
Standardized
test
In situ test
Given EM
disturbance
Given EM
disturbance
Given EM
disturbance
Given EM
disturbance
Given EM
disturbance
Given EM
disturbance
Defined
Measuring
equipment
Defined
Measuring
equipment
Defined
Measuring
equipment
Non-defined
Disturbance
sources
Defined
Disturbance
source
Defined
Disturbance
source
Standardized
Measuring
conditions
Defined
Measuring
conditions
Adapted
Measuring
conditions
Adapted
Measuring
conditions
Defined
Measuring
conditions
Standardized
Measuring
conditions
Emission-test
level
Emission
level
Disturbance
level
Interference
level
Immunity
level
Immunity-test
level
Emission-test
limit
Emission
limit
Disturbance
limit
Interference
limit
Immunity
limit
Immunity-test
limit
Single emitter
Probability situation
Single victim
Deterministic situation
Superposition of disturbance
Deterministic situation
Common Mode & Differential Mode
ICM
2
ICM
Equipment
2
VCM
Common Mode Path
Ground (chassis)
IDM
IDM
VDM
Differential Mode Path
Equipment
The 5 kinds of disturbances generated by a converter
5
INPUT
ZC2
ZC1
3 VDM
VDM
Z
Safety wire
1
Chassis ground
1
2
3
4
5
Input-to-Chassis Common Mode
Input-to-Output Common Mode
Input Differential Mode
Output Differential Mode
Electromagnetic radiations (E & H)
2
4 OUTPUT
How to measure CM & DM currents ?
ICM
2
Current probe (Clamp)
ICM
2
CM current
measurement
ICM
IDM
IDM
DM current
measurement
2.IDM
Typical input current of a 5 kVA filtered converter
RTCA DO160D Power lines category B
DIFFERENTIAL
MODE
COMMON MODE
Frequency
How to measure a disturbing voltage ?
50 µH
250 µH
EUT
Line
To Spectrum
Analyzer
or 50 load
220 nF
8 µF
Bleeder
100 k
1 µF
1 k
5
Ground
CISPR 50 // (50 µH + 5 ) L I S N
100 LISN impedance
LISN 50 µH
50 LISN 5 µH
10 6
10 kHz
100 kHz
1 MHz
10 MHz
30 MHz
A concealed key point: the switching dynamic impedance
k
k
=
1
10
Z
=
Z
Z
Z
=
=
1
10
0
M
100 kV
k
V
=
1
W
M
kW
kW
E field dominates, so:
Reduce parasitic capacitors
Limit high V/ t trace lengths
Choose low r materials (air !)
Use lower V circuits in series
1
0
10
=
=
P
P
1 kV
Circuits
in series
P
10
0
10
=
=
P
P
10 kV
kW
W
100 V
P
1
10
=
=
P
W
W
V diode
critical
=
1
Z
=
Z
Increasing
severity
0.
1
10
=
Z
Z
=
10
0
10 V
1V
10 mA
Increasing
severity
High
impedance
zone
100 mA
1A
10 A
100 A
1000 A
Circuits
in parallel
Any switching circuit should
be positioned in this plane…
I
Low
impedance
zone
H field dominates, so:
Reduce ESR and ESL
Limit high I/ t loop areas
Choose “sandwich” geometries
Use lower I circuits in parallel
Introduction
Differential Mode Immunity
Differential Mode Emissions
Common Mode Emissions
Electromagnetic Radiations
The voltage tolerance boundary
New Voltage-Tolerance Boundary
New parameters (bullets)
Old Voltage-Tolerance Boundary
Duration of Disturbance in
Cycles (c) and Seconds (s)
106
90
Voltage-Tolerance
Envelope
200 s
1 ms
3 ms
20 ms
0.5 s
10 s
Steady
State
Transient Turn-on Overvoltage
Self-pulsation : 0 =
1
L.C
L
Quality Factor : Q =
R
Vin
L.0
R
Vout
C
2
Time response
1.8
( Vin = 1 )
Q = 10
1.6
Q=5
1.4
Q=2
1.2
1
0.8
Q=1
0.6
Q = 0.7
0.4
Q = 0.5
0.2
0
0
1
2
3
0.t
4
5
6
7
Where to install a DM Voltage Transient Suppressor ?
Peak résidual voltage : kV
Overvoltage : kV
EMC
Filter
Power line
CONVERTER
Without TVS : serious risk of destruction
Peak résidual voltage 800 V !…
Clipped overvoltage 500 V
MOV
EMC
Filter
CONVERTER
(Ageing)
Varistor on line input : a risk remains
Overvoltage : kV
Power line
Peak résidual voltage 500 V
EMC
Filter
OK
Varistor at converter input : best results
CONVERTER
& Filter inductance prevents
TVS premature triggering
Where to add protection components ?
Overvoltage
protection Diode
No impedance on the DC side to limit
reverse overvoltage on rectifier bridge
NTC
L
AC Line
C
« PFC Boost »
No voltage
limitation
A Diode
avoids doubling
output voltage
doubling
No
inrush current
limitation
nothermistor
inrush
current
limitation
yet
ABut
NTC
limits
inrush current
Output
The problem of the negative impedance of a DC/DC converter
Zout
Output
EMC filter
Z cable
R + jL
Z1
Input
EMC filter
Z2
Zin
SOURCE
DC / DC
Negative
impedance
positive
Impedance
Zin
65 0
Phase
-180°
0.1 Hz
Risks :
1 Hz
10 Hz
100 Hz
1 kHz
10 kHz
Solutions :
- No Start Up
- Add a large capacitor at DC / DC input
- Output voltage instability
- Reduce cable inductance (several pairs in //)
- Destruction of DC / DC converter - Reduce the converter regulation bandwidth
Introduction
Differential Mode Immunity
Differential Mode Emissions
Common Mode Emissions
Electromagnetic Radiations
Some problems of converters harmonics
Harmonics are generated by non sinusoidal currents. For an electric network,
harmonics are a low frequency problem ( < 2 kHz and in Differential Mode only).
Usually, even harmonics are low (because + and – half-waves look the same).
Most of inverters and AC / DC converters without PFC exceed normalized levels.
Odd harmonics of converters can be severe ( > 50 % @ H3 ; > 30 % @ H5 ).
For most single – phase converters without PFC on a 3 phase network, the 3rd
harmonics (150 Hz) is an “homopolar” current. So, Ineutral can exceed Iphase.
Anti-harmonic or active filters are useful for a low power source (electric generator).
For a high power network, the problem of harmonics is not the voltage distortion
but the mastering of cabling protection scheme (cables & circuits breakers).
Differential Mode interferences
IDM
1
Power Line
V1
Z1
I1
I2
2
Z2 V2
Z Load
IDM
V1
V1
2
2
1 V1 Z1 . I1 ( If Z LISN >> Z1 - Generally, V1 = f ( F ) )
V1 is not applied to the secondary, so it does not disturb the load.
2 V2 Z2 . I2 ( If Z Load >> Z2 - Generally, V2 = f ( t ) )
V2 may be disturbing ( typically if peak-to-peak V2 1 V )
Differential Mode Emission Spectrum Without Filtering
Converter DM Equivalent Scheme
Switching frequency = F0
Transition time = r
I
1
F
dBµA
Z capacitor
C
ESR
I
LISN
100 Fc =
0.35
r
VDM
Switched
current
simplified
spectrum
1
F2
ESL
F0
Fc 0.5 to 5 MHz
log (F)
Convolution Result
Z
dB
Electrolytic capacitor impedance
dBµV
ESR
Fd =
2.ESL
1
C
VDM
ESL.
Rectifier bridge
wideband noise
(diode recovery for
AC/DC converter)
ESR
KHz
Fd 0.5 to 5 MHz
1
F
log (F)
F0
Fc Fd
log (F)
Insertion Loss of a Differential Mode EMC Filter
L1
L = L1 + L2
There wire
EMC Filter
Cx
L2
Back wire
C
Switched
current I
ESR
filter
VV11: :V Without
without filter
WithImpedance
EMC filter
V2:DM
LISN
100 DM
DMequivalent
equivalentscheme
schemeofofaaconverter
converterwith
without
an EMC
any filter
filter
+20
dB
+10
V2
V1
Resonance before cut-off
0
-10
-20
F0 =
-30
-40
0.1
0.2
1
2 L.Cx
0.3
0.5 0.7 1
F
F0
2
3
5
7
10
Traps of a Differential Mode EMI filter
3
4
LISN
L
L1
H
Cx L2
7
1
2
C’
Electrolytic
capacitors
6
Converter
5
1 - Choose the proper structure (to mismatch the impedances)
2 - Choose (L1+L2) x Cx value so that Fresonance < lowest frequency to filter
3 - Verify that no inductance saturates at max current (Max P & Min V)
4 - Limit H field coupling to leakage inductance (in air) of L1 & L2
5 - Safety margin necessary to compensate electrolytic caps ESR dispersion
6 - Add C’ as needed to reduce wideband recovery noise of rectifier bridge
7 - Limit H field-to-loop coupling to avoid parasitic voltage pick-up.
Take care of Differential Mode cabling…
Those cabling inductances
reduce filtering effectiveness
NO !
Take care of Differential Mode cabling…
NO !
Those areas
radiate if they
BETTER
carry high I / t
Take care of Differential Mode cabling…
NO !
BETTER
BEST !
How to reduce cabling parasitic impedances…
ZG
ZG
ZL
ZL
V
V
Parallel
Capacitance
Serial
Impedances
Improper
Routings
Z < 10 Z > 1 K
To reduce the cabling areas is necessary, but insufficient
V
V
To move
away
Minimal
length
Correct
Routings
How to measure Output Ripple…
C = 1 µF to measure HF ripple only
C = 100 µF to measure 100 Hz ripple
Input
Converter
Output
terminal
R
Nominal
Current
Very short connection
(Max length = 2 cm)
Oscilloscope
50 Coaxial Cable
50 input
How to analyse Output Ripple
C = 1 µF to measure HF ripple only
C = 100 µF to measure 100 Hz ripple
Input
Output
terminal
Converter
Nominal
Current
R
Very short connexion
(Max length = 2 cm)
Oscilloscope
50 Coaxial Cable
50 input
Voltage
60 mV
Usually CM - to - DM conversion
0
t
–60 mV
HF « NOISE »
« RIPPLE »
( @ > 3 MHz )
( @ Switching F )
10 mV : Excellent
—
« RIPPLE + NOISE »
100 mV : Average
—
1 V : Excessive
Introduction
Differential Mode Immunity
Differential Mode Emissions
Common Mode Emissions
Electromagnetic Radiations
Common Mode interferences
ICM
2
C2
ZDM
Load
Power Line
V
ICM
2
C1
ZCM
Safety wire
ICM
1
I1
2
I2
1 I1 = C1 . V / t
I1 doesn’t circulate through the load, so it is little disturbing.
2 I2 C2 . V / t (but possibly modified by ZCM)
I2 can circulate through the load, so it may be very disturbing.
Measured total CM current : ICM = I1 + I2
Common Mode Emission Spectrum Without Filtering
Converter CM Equivalent Scheme
Switching Frequency = F0
L
cable inductance
V
dBµV
1
F
r
Transition Time = r
V
1 µH
V
C
Switched
Voltage
Simplified
Spectrum
Fc = 0.35
30 pF to 3 nF
LISN
25 1
F2
VCM
C : Parasitic cap between “hot conductors” & ground
F0
Fc 1 to 10 MHz
log (F)
Convolution Result
1
Loop
Z
admittance
-1
dB
Resonance
VCM
dBµV
flat
1
F
F
Fr =
Resonance
1
F
1
2 LC
1
F3
log (F)
Fr 3 to 30 MHz
F0
Fc
Fr
log (F)
Insertion Loss of an EMC Common Mode Filter
M
2 wires
CCM = Cp + C'p + 2 x Cy
Switched
Voltage
“Hot Cap”
EMC Filter
V
C'p
2 x Cy
Cp
LISN
25 VV
1:1:VWithout
without filter
With
the filter
V2:CM
impedance
Ground
CM
CMequivalent
equivalentscheme
schemeofofananisolated
isolatedconverter
converterwithout
with a afilter
filter
+20
dB
+10
V2
V1
Resonance before cut-off
0
-10
-20
F0 =
-30
-40
0.1
1
2 M.CMC
0.2
0.3
0.5 0.7 1
F
F0
2
3
5
7
10
The 3 cases of Primary-to-Secondary Common Mode
Metallic chassis
Grounded
output
Filter
1
Converter
No CM noise in electronic circuits
Electronics
EMC filter easy to optimize
IMC
Not filtered
output
Filter
2
Converter
Electronics
C
IMC
IMC
Converter
Not
Filtered
output
No disturbance outside of the chassis
CM Noise through electronic circuits
EMC filter more difficult to optimize
EM radiations outside of the chassis
3
Filter
No disturbance outside of the chassis
Input filter impossible to optimize
IMC
The output cable must be shielded
or filtered
Load
To float or not to float the output, that’s the question…
CM inductance
can saturate
Primary
circuits
Ground
M
Connexion
to ground
I+
I–
Ig
Ig
I+ I–
I+
Primary
circuits
M
I–
C 100 nF
I+ = I–
A (nearly) universal solution
How to measure Primary - to - Secondary C. M. current ?
Nominal V
Converter
Nominal I
R
Time measurement
50 mV/mA sensitivity
100 MHz bandwidth
Oscilloscope
1 mA peak-peak = Excellent
Coaxial cable
10 mA peak-peak = Average
100 mA peak-peak = Excessive
50 Nominal V
Converter
Nominal I
R
Frequency measurement
9 or 10 kHz RBW, Peak detection
Short wire
Current
clamp
Spectrum Analyser
Span : 0.1 to 50 MHz (100 MHz)
10 dBµA = Excellent
30 dBµA = Average
50 dBµA = Excessive
This simple “ CM / DM SEPARATOR ” reduces by 10 +
the time and difficulty to optimize a single-phase EMC filter
From LISN
Line 1
To analyzer
2.N turns
N turns
Differential Mode
Output
50 Line 2
Common Mode
Output
Ferrite tore with µr 5000 & AL > 2000 nH/turn2
e.g. Philips 3E25 (orange), Diam. = 14 mm, N = 7
50 Practical realisation of a “ CM / DM SEPARATOR ”
Line 1
input
DM
output
AND
OR
CM
output
Line 2
input
CM / DM separator adaptation on a commercial LISN
Added BNC on the
non-measured output
(internal 50 suppressed)
2 coaxial cables
with same length
Introduction
Differential Mode Immunity
Differential Mode Emissions
Common Mode Emissions
Electromagnetic Radiations
Sources of Electromagnetic Radiations
1
H
I1
I2
IMC
E
2
1 Sources of H field :
Leakage fields of windings
Secondary loop areas
Primary loop area
2 Sources of E field :
High V/t conductive parts (Heat sink, ferrite core…)
HF insufficiently filtered cables (e.g. output cable)
HF solutions must be installed close to the sources
Noisy
converter
Noisy
converter
Ni - Zn
Ferrite tube
Load
Output
2 x 1 nF
Chassis metal sheet
“BLM”
Ferrite
bead
High
µr
bead
R
10 to
100 MOS
R
Clock
C
R 22 C 47 pF
HF Diode
Even small converters (few W) can be very noisy (I/O CM & radiation)
Ground Loop : Definition & Effects
Apparatus
Interconnect. cable
Apparatus
#2
#1
GROUND LOOP
Z
I
nearest ground conductor / structure
Ground loop cannot be avoided !
1 Common impedance coupling
Earth impedance
does not matter
2
Field - to - Loop coupling
Star Grounding : Principle & Reality
3
2
4
5
1
Voltage
reference
The
Thereal
Theory…
world !
Ground Grid : Definition & Effects
Apparatus
Apparatus
#1
#2
ground conductor / structure
GROUND GRID
Other ground wire or structure
How to improve immunity ?
Ground Grid : Definition & Effects
Reduction of Ground Loop =
Apparatus
#1
Better immunity against
radiated fields
Apparatus
#2
Improvement of Ground Grid =
Adding a Ground Strap =
Better immunity against
conducted disturbances
Further reduction of the
Ground Loop Area
A GROUND GRID is highly recommended !
Where to connect the shielded cables braid ?
Any power cable : At both ends, to chassis ground, without pigtail.
High frequency coax : At both ends, to chassis ground, without pigtail.
Digital link (except coaxial Ethernet): At both ends, to chassis ground…
High impedance source (> 10 k): At both ends, to chassis ground…
Any cable inside an equipment : At both ends, to chassis ground…
Any outer shield (not signal return): At both ends, to chassis ground…
Low voltage signal cable, with low frequencies to transmit,
with a low impedance source, in a noisy environment,
without balanced transmission (bad CMRR): At one end only
… But then good immunity will be hard to achieve !
Avoid aluminium foil with a drain wire (without braid).
Please, let us remember…
EMC is not black magic (Just simple physics…)
Some measurement equipments are required
Usually, only simple equipments are sufficient
It’s good to be experienced (& confident enough)
It’s important to understand how system works
It’s useful to methodically analyse what happens
It’s efficient to foresee and simplify EMC problems
It’s necessary to know the orders of magnitudes
It’s politically effective to be persuasive (& smiling)
It’s essential never to become discouraged !…
Questions ?