A SystemLevel Automotive EMC Expert System

1
A System-Level Automotive EMC Expert System
Sreeniwas Ranganathan UMR EMC Laboratory,
University of Missouri Rolla
2
Summary

• EMC issues in Automotive industry
• Expert system Application
• Architecture
• Preliminary Algorithms
• Bench-top Validation
• Conclusion and Future work

3
Introduction

• EMC in automotive industry
• Design for EMC increasingly critical
• Incomplete design information early in design
  cycle
• Lack of flexibility in placement/routing of
  modules
• EMC problems undetected until late in design
  cycle
• Fixes late in design cycle often expensive or
  impractical

4
Expert System

• Detect system-level EMC problems early in design
  cycle
• Use rules of thumb and simple formulae
• Work with incomplete information
• Run repeatedly throughout design cycle
• Complement not replace human expert and more
  sophisticated numerical modeling tools
• Expert System used to find problems that should
  be investigated further

5
Expert System Design

• Help with
• Wire harness routing
• Placement of antennas, modules
• Radiation and immunity issues
• Component grounding
• Test plan formation
• Easy to use
• Rapidly perform an analysis and return useful
  results even with incomplete information

6
Expert System Architecture
7
Input Stage

• Automatically gather information required for
  analysis
• Identify and classify circuits
• Circuit characteristics determined from design
  database or inferred from component
  characteristics or design defaults

8
Circuit classification algorithm

• Function classify_circuits
• Information about nets stored in an array
  net_info,
• net_info contains additional lists and variables

• power_signal
• analog_digital
• load
• VMAX
• IMAX
• VMIN
• tr_time

• high_freq
• digi_freq
• low_freq
• S_class
• R_class
• noise_margin
• returns

9
Circuit classification algorithm

• Check for information within module library
• Check if information is available from the
  object_id of the net
• Check if information available from mimic pins
• Check for information from similar input pins of
  module
• Check for defaults within module library

10
Circuit classification algorithm

• Assign confidence values to each variable
  assigned to a net
• CF-10 Information found within design
  database/module library
• CF-9 Information assigned based on default
  values assigned to a net
• (CF of mimic pin -1) Information assigned from
  mimic pins
• CF- 7 Information obtained from EMC Personality
  File
• CF-0 Information not found reliably from any
  database

11
Expert System Architecture Evaluation Stage
12
Power Bus Noise

• Power bus noise treated as a signal by expert
  
• system algorithms
• Power Bus Noise algorithm
• Calculates noise on power lines
• Passes noise as signal to cross-talk and
  field-to-harness coupling algorithms

13
Common Resistance Coupling

• Predicts coupling due to shared resistance along
  a common path
• Identifies common return path for
• circuit-pairs
• Approximates total resistance of
• common return path
• Noise calculated for transient
• and continuous signals

14
Inductive Coupling

• Predicts noise due to magnetic
• field coupling
• Calculate mutual inductance
• between two circuits
• intra-harness coupling
• harness-to-harness coupling
• Calculate noise voltage for transient
• and continuous signals

L1
ZL source
L2
ZS source
M
ZL victim
VS
ZS victim
M Mutual inductance between
circuits L1, 2 Self inductance of the
circuits ZS, L source Impedances of source
circuit ZS, L victim Impedances of victim
circuit VS Voltage of source circuit
15
Capacitive Coupling

• Predicts noise due to electric
• field coupling
• Calculate mutual capacitance
• between two circuits
• Calculate capacitance to ground
• Calculations differ for
• intra-harness coupling
• harness-to-harness coupling
• Calculate noise voltage for transient
• and continuous signals

16
Radiated Emissions and Field-To-Harness Coupling

• Predict radiated emissions from and coupling to
  circuits from an external field
• Gain of circuit estimated using transmission line
  theory
• Calculate coupling between circuit and external
  field.

17
Output Stage

• Processes results of evaluation stage
• Identifies potential problem areas and their
  cause
• Prioritizes problems
• Suggests possible design changes

18
Validation

• Preliminary algorithms were partially validated
  experimentally
• Common resistance coupling
• Inductive coupling
• harness-to-harness
• Intra-harness
• Validation performed on bench top

19
Common resistance coupling(Experimental setup)
Active probe to Port-2 of NA
Port-1 of NA
Source end
51 ohms
4.7 ohms
Load end
Grounding lug
The ground plane is 40 by 20, the wires are
82.5 cm long and 9.3 cm apart
20
Experiment 1 Large return resistance
Common resistance 1 ohm
Red algorithm Blue measurement
21
Accounting for self-inductance (1)Model
22
Transmission line theory model
RL1
RL2
RS1
L
L
Z0, tpd
Z0, tpd
LG
1M?
VS
RG
23
Transmission line theory result
24
Changes to Common resistance Algorithm

• Common-resistance algorithm changed to
  Common-impedance algorithm
• Uses self-inductance of circuits
• Uses self-inductance of common-return path

25
Inductive coupling

• Harness-to-harness algorithm was verified.
• Assumptions and approximations
• Formula based on a lumped element model
• Influence of other circuits on coupling was
• ignored
• Influence of body surface metal in addition
• to ground plane was ignored

26
Experimental setup
Source end
Port 1
Load end
Port 2
27
Lumped element model
A 90-ohm resistance was used for source and load.
28
Influence of other circuits
29
Influence of other circuits
When the additional circuit is shorted, the
coupling decreases 6 db.
30
Influence of additional BSM
Subtract about 6 dB for additional BSM.
31
Inductive coupling Intra-harness coupling
validation

• Intra-harness coupling algorithm was verified
• Both circuits use body surface metal return
• Victim circuit uses a return wire
• Both circuits use wire return within the harness
• Influence of other wires in the same harness

32
Experimental set up
33
Lumped Element Model
34
Equivalent Circuit Model including multiple
coupling
35
Multiple Coupling
36
Lumped Element Model -2
37
Influence of other circuits
38
Wire Return for Victim Circuit
39
Wire Return for Both Circuits
40
Changes to Inductive Coupling Algorithm

• Expert System calculates inductive coupling if
• Include the effect of additional circuits
• Include the effect of BSM
• Use transmission line theory to calculate
  coupling when wavelength lt 10 times length of
  culprit/victim circuit

41
Conclusions and Future Work

• Common impedance, and inductive coupling
  algorithm verified through bench top experiments
• Algorithms work well at low frequency (up to 10s
  of MHz)
• Experiments on actual vehicle are being performed
  by others
• Results of experiments will be used to form final
  algorithms