2014-01-0219
Published 04/01/2014
Copyright © 2014 SAE International
doi:10.4271/2014-01-0219
saepcelec.saejournals.org
EMC Management in HEV/EV Applications
Rich Boyer
Delphi Automotive
ABSTRACT
Shielding of the high voltage cabling is a cost effective method for reducing unwanted EMI in hybrid and electric vehicles.
Ensuring the shielding effectiveness (SE) of the high voltage (HV) cabling and connectors is critical at the component and
subsystem level. The effectiveness of the shielding must also be proven for the useful life of the vehicle. This paper will
examine some of the critical aspects of ensuring good SE of HV cabling and connectors in hybrid and electric vehicles.
This paper will also review some of the test methods utilized to make these measurements.
CITATION: Boyer, R., "EMC Management in HEV/EV Applications," SAE Int. J. Passeng. Cars – Electron. Electr. Syst.
7(1):2014, doi:10.4271/2014-01-0219.
INTRODUCTION
Background
Suppliers are being requested to develop new products for
present and future hybrid electric vehicles (HEV) / plug-in
hybrid electric vehicles (PHEV), extended range electric
vehicles (EREV), and battery electric vehicles (BEV). One of
the technologies utilized in these vehicles is a combined unit of
an inverter and converter used to manage the power and
recharging circuits in these vehicles. These power inverters
and converters are used to invert HV battery pack direct
current (DC) to alternating current (AC) for motors that are
used to propel the vehicle down the road and to convert AC to
DC to charge the HV battery pack. Converters are also used to
convert HV DC down to lower DC voltages to power existing 12
V systems. Another technology implemented in these vehicles
makes use of inverting HV battery pack to 3 phase AC within
modules. These technologies utilize switching techniques to
invert and convert the necessary voltages. These switching
techniques generate unwanted electromagnetic interference
(EMI) specifically in the frequency range of 100.0 kHz to 200
MHz. In the past with 12 volt systems, unwanted EMI in the
frequency range of 100 kHz to 200 MHz has not been an issue
for the cabling and connectors. The unwanted EMI has been
suppressed to acceptable levels inside the specific electronic
components keeping EMI from coupling to the harness and
connectors. Reducing the EMI inside the electronic module is
the most cost effective way to reduce the unwanted EMI for the
low, 12 V, systems. However, due to the HV and large power of
the components generating the unwanted EMI in HEV/PHEV/
EREV/BEV, the most cost effective way to reduce unwanted
EMI is through use of shielded cabling and connectors.
Because the shielded cabling and connectors main function is
to reduce the unwanted EMI specifically in the frequency range
of 100 kHz to 200 MHz, a standard test method is required to
measure the effectiveness of the shielding. This measurement
is referred to as SE. Shielding effectiveness is reported in dB
and the higher the number the more the unwanted EMI is
reduced.
DESIGN ASPECTS OF HV CABLE
ASSEMBLIES
The HV cable assemblies consist of shielded HV cables and
HV connectors. Figure 1 is an example of a typical assembly.
Figure 1. Typical HV Cable Assembly
A typical HV cable has a braided shield made with tin plated
copper having a minimum coverage of 92 %. The cable is rated
for the intended application for environmental and electrical
requirements. The SE of the cable only is very good at greater
than 70 dB for the frequency range of interest and this is
because of the construction and minimum coverage of 92 %.
Because the cable is a uniform homogenous coaxial structure
the SE can be measured using standard test methods. Also
because of the structure, the SE can also be easily modeled
and calculated.
Boyer / SAE Int. J. Passeng. Cars – Electron. Electr. Syst. / Volume 7, Issue 1 (May 2014)
The HV connector must be shielded and designed to continue
the shield of cable into the next shielded structure. Therefore
the connection of shielded cable to the shielded connector
becomes one of the critical aspects of ensuring the
effectiveness of the shielding. The design of the connector
shield must maintain good coverage by minimizing openings,
gaps, and seams. This connector shield then becomes the next
critical piece in maintaining the effectiveness of assembly. The
connection of shielded connector to either the header
connector or connector in an in-line connection becomes the
third interface of importance. And finally the connection from
either header connector shield or the connector shield to
shielded cable in an in-line connection is the final critical link of
the shielded assembly. Figure 2 is a simplified block diagram
outlining the HV shielded assembly.
Figure 2. Simplified block diagram of assembly. Blue outlines indicate
shielded and the orange blocks are critical shielded connection paths.
As can be seen in figure 2, the interfaces are important to the
overall SE performance because of their need to continue the
shielding performance of components and connectors. These
interfaces can represent some of the greatest challenges in
maintaining good SE because of the automotive OEM
temperature, humidity, and vibration requirements. These
connectors and interfaces must maintain their SE performance
throughout their life cycle and therefore the SE must be
measured as the product is goes through accelerated life cycle
testing. These interfaces have to seamlessly continue the
shield of components to the next shielded component. These
components and interfaces must remain a cost effective
solution for reducing unwanted EMI. In order to optimize the
design of connectors and interfaces a test method that predicts
performance in vehicle must be utilized. This will allow the
designer to try out concepts for the intended frequency range
and then modify these concepts to ensure best performance at
reasonable cost.
without disturbing the interfaces that must be measured. This
becomes a challenge due to the various sizes of connectors in
use.
Although the author has researched and tried many different
test methods, this paper will only address a few of them.
One of the industry standard test methods that will
accommodate all of the sizes is IEC 61726 Reverberation
Chamber Method. According to IEC 61726 the smallest
dimension of reverb chamber must exceed 3 wavelengths at
the lowest test frequency. The lowest test frequency we are
interested in is 100 kHz. This would make the smallest
dimension of reverb chamber approximately 9 km!
Another industry standard test is IEC 62153-4-7 Tube in Tube
Method. The physical length of tubes is dictated by frequency
range. The commercially available systems can test in the
frequency range of 30 kHz - 3 GHz. The limiting factor in using
this method is that it allows for only devices less than the
diameter of tubes or use of test boxes attached to the tubes as
long as test box resonance does not affect the measurements
in selected frequency range. This is a feasible test but requires
time consuming construction of needed test boxes and varying
tube diameters for the various sizes of connectors. This
method usually requires additional preparation of the samples
used in the accelerated environmental testing that can disrupt
the interfaces.
Another test method is IEC 61196-1 Absorbing Clamp Method,
measurement with extension lines. This method utilizes
measuring the RF currents on the shield outside of the
connector and does not require placing the sample inside of
the absorber clamp. This will ensure that the interfaces are not
disrupted. This method also allows for all of the various sizes of
connectors to be measured. Figures 3 and 4 show the setup
diagram and the picture of setup.
AVAILABLE TEST METHODS TO MEASURE
SE
Having shown the block diagram of the cable assembly it is
obvious that a test method needs to be able to measure the
shield interfaces into and out of connector. There are a number
of industry standards for measuring SE Most of these were
developed for RF cabling and connectors. The test method
must give results that predict vehicle performance reliably. Also
when choosing an appropriate method one must account for
the ability to perform measurements on the samples
throughout their exposure to accelerated environmental testing
Figure 3. Absorbing Clamp Method, measurement with extension lines
diagram.
Boyer / SAE Int. J. Passeng. Cars – Electron. Electr. Syst. / Volume 7, Issue 1 (May 2014)
100 kHz to 200 MHz the induced RF current on shield for
each frequency step is recorded in dB on EMC analyzer
(a.k.a spectrum analyzer)
4. The center conductor short to shield is removed and steps 2
and 3 are repeated.
5. The data from step 4 is subtracted from step 3 and result is
SE in dB.
6. Steps 1 through 5 are repeated for each HV lead.
Figure 7 shows a typical data set for the sample shown in
figure 5. Each of the high voltage lines of the in-line connector
are measured and plotted in figure 7.
Figure 4. Absorbing Clamp Method, measurement with extension lines
picture.
Because of the frequency range of interest, sample preparation
is a relatively simple task that utilizes UHF connectors attached
to the HV coaxial cables. Figure 5 shows an in-line HV
shielded connector prepped for testing with UHF connectors.
Figure 5. Shielded in-line HV prepped for testing.
Figure 6 shows a small sampling of HV connectors that have
been tested to this method. This figure gives an idea of the
varying sizes encountered for this product.
Figure 7. Data from sample shown in figure 5.
This test method was selected for use because it provides the
the most advantages needed for testing this type of product.
The advantages are; covers frequency range, ease of
preparation, ability to measure without disturbing interfaces,
industry standard, allows for large range of sizes, uses low cost
RF connections for sample prep, short test time, and easily
implemented with standard equipment found in an EMC lab.
VALIDITY OF SELECTED TEST METHOD
In order for test method to be valid the results must predict
vehicle performance. To test the validity of the selected method
the following three steps were taken;
1. Compare test method to other test method on same sample.
Figure 6. Various HV connector samples prepped for testing.
The samples shown in figure 6 were tested before, during, and
after various accelerated environmental testing.
The procedure for running this test method is described in
detail in the IEC specification. Simplified description of this
method is as follows;
1. Sample is mounted into setup with the center conductor
short to shield as described by IEC specification.
2. RF signal generator output power is turned on.
3. While the frequency of RF signal generator is stepped from
2. Compare results of various connectors from selected test
method and then install connectors onto actual components
being tested to radiated emissions according to CISPR25.
3. Compare results of various connectors from selected test
method to the radiated emissions performance on vehicles.
The selected test method was used to test RG223 RF coaxial
cable. These results were compared to tube in tube method on
same samples. The tube in tube method was performed in the
frequency range 300 kHz to 300 MHz due to the limitations of
equipment being used. This showed very good correlation in
the frequency range of 300 kHz to 10 MHz. Above 10 MHz the
tube in tube reported much better shielding results. The reason
Boyer / SAE Int. J. Passeng. Cars – Electron. Electr. Syst. / Volume 7, Issue 1 (May 2014)
for the higher SE has to do with the measurement method
using RF current probes and measuring inner tube voltage.
This was noted when looking at the next 2 steps. A one meter
length of RG223 cable comparing the 2 test methods is shown
in figure 8.
Finally the selected test method was compared to vehicle level
RE performance. Due to the time and cost of vehicle level RE
testing only limited data was gathered for this step. Suffice to
say that with a limited number of runs there were favorable
results in that the selected test method predicted vehicle
performance in the same 3 bands in which the critical
interfaces were compromised.
SUMMARY
Figure 8. Comparison of selected test method and tube in tube method
on 1 Meter RG 223.
A set of connectors were tested on intended products at the
component level. These products were tested according to
CISPR25 radiated emissions. The connectors were then
modified in ways that compromised the critical interfaces. This
comparison showed correlation in the difference of shielding
between the 2 sets of data; i.e. when CISPR25 RE went up the
SE went down the same amount. The results for the LW band
(150 kHz - 280 kHz), AM band (500 kHz - 2.0 MHz), and FM
band (88 MHz - 108 MHz) are shown in table 1.
Table 1. Absorber clamp SE versus changes to components RE as
tested to CISPR25.
The HEV and EV utilize shielded cable and connectors to
reduce unwanted EMI. In order to produce best design to
reduce unwanted EMI an understanding of where the EMI
originates was shown. After identifying the source an
understanding of the critical aspects of the HV assemblies
were pointed out. Various test methods were examined and
one was selected as the preferred method for best measuring
these types of assemblies. This selected test method was then
shown to have correlation to intended use of the assemblies in
both component and limited vehicle testing. The selected test
method has been in use at Delphi since 2008 with very good
results.
REFERENCES
1. IEC 61726 Cable assemblies, cables, connectors and passive
microwave components - Screening attenuation measurement by
the reverberation chamber method, Second edition 1909-11.
2. IEC 62153-4-7 Metallic communication cables test methods Electromagnetic compatibility (EMC) - Test method for measuring
the transfer impedance and the screening - or the coupling
attenuation - Tube in tube method, First edition 2006-04.
3. IEC 1196-1 Radio-frequency cables - Part 1 Generic specification
- General, definitions, requirements and test methods, First edition
1995-05.
CONTACT INFORMATION
Rich Boyer
Rich.Boyer@Delphi.com) is EMC technical manager at Delphi
Packard's EMC lab in Warren, OH.
ACKNOWLEDGMENTS
I would like to acknowledge all of the technicians, test and
design engineers, and management for their support in
developing the test method and the materials contained within
this paper.
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