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ELECTROMAGNETIC INTERFERENCE (EMI) SELF-LEARN KITS
BASED ON POWER ELECTRONICS APPROACH
Werachet Khan-ngern
Research Center for Communications and Information Technology,
Faculty of Engineering, King Mongkut’s Institute of Technology Ladkrabang
E-mail: [email protected].
Abstract: This paper presents a simplified toolkit on
conducted electromagnetic interference (EMI) based on
the basic circuits and concepts of power electronics. The
simulated and simplified results of the toolkit is to
introduce the effect of conducted EMI caused by selfresonant frequency (SRF) of the passive components,
switching characteristic of a switching device such as free
wheeling diode (FWD), gate drive control, snubber circuit
and parasitic of capacitors to ground. The simplified
prototype of line impedance stabilization network (LISN)
is also introduced. Those basic phenomena can lead
designing engineers can understand the EMC concept by
both of simulation and experiment.
The first one is noise disturbance or the initiation of EMI
source. This part consists of EMI generation: free
wheeling diode. The second category consists of EMI
controlling such as gate control for decreasing the rise
time and fall time of the switching device, di/dt and dv/dt
are the controlled parameters, and snubber circuit: RLD
and RCD snubber circuit. The third category is conducted
EMI measurement where LISN is focused to maintain the
function of stabilize the 50 ohm impedance during 150
kHz to 30 MHz while avoiding the EMI between the
source and the load.
The three main categories are shown as in figure 1.
and table 1.
Keywords: EMI self-learning, Conducted EMI emission,
Power electronics Noise, Gate control, Snubber circuit,
Self-resonant frequency, LISN.
EMI
measurement
I. Introduction
EMI is unfamiliar concept for most engineers in most
of universities in Thailand while many companies and
manufactories would like to have engineers who can
ready to serve in those electrical and electronics areas.
The EMI studies in terms of theory and practice are
developed and proposed with the simplified learning
toolkit. Self-learning on EMI studies can help those
engineers to understand the EMI phenomena [1]. Some
EMI issues may not suitable to demonstrate by
experiment such as the operation of without free wheeling
diode on inductive load. This issue can be done by
simulation. Most of learning toolkits are selected based on
the guideline the engineers to understand about the EMI.
The mechanism of LISN operation is necessary to
those engineers to understand. The EMI simulated result
included the LISN is needed due to lacking of LISN and
EMI analyzer for most small and medium companies.
II. The development of a simplified
learning toolkit of EMI issues
The simplified EMI studies focused on power
electronics [1] has been published. This paper is the
extended development of EMI self-learning kit. Key
issues of the toolkits are divided by three main categories.
EMI
disturbance
EMI
Control
Figure 1. Three main basic categories of EMI learning
kits
Table 1 EMI learning contents
EMI
EMI
disturbance
Control
1
Free wheeling Gate Control
diode
2
di/dt
RCD Snubber
circuit
3
dv/dt
RLD Snubber
circuit
4
Self-resonant
frequency
EMI
measurement
LISN
The basic concept in table 1 is to provide the EMI
phenomena and EMI effects from power converters such
as step down (buck) converter starting from EMI
disturbance, EMI control and following by home-made
EMI measurement: LISN.
III. Proposed of simplified EMI
learning toolkits
EMI disturbace
The free wheeling diode (FWD) should be clearly
understood about the switching operation with inductance
load [2]. The FWD mechanism and operation should be
introduced by simplified simulation shown in figure 2.
EMI control
Some of the gate control for MOSFET drives can be
controlled using RC time constant shown in figure 4. This
case includes the stray capacitance of the heatsink for
safety reason [3]. The measured results show in figure 5
where the operating conditions and equipment is given in
table 2. The upper trace shows EMI level at without RC
gate control where the lower trace shows the reduction of
EMI level at RC gate control for MOSFET operation. It is
clearly seen that from 2 MHz to 30 MHz, the EMI
reduction is a great achieved about 20 dB in average.
(a) PSPICE simulation
40
20
0
-20
580us
I(V4)
584us
V(M2:d,M2:s)
588us
592us
Figure 3 shows the FWD phenomena: dv/dt during
switch turn off and di/dt during switch turn on. This is one
of the prime mechanism of EMI noise in power
electronics. The EMI control can be done such as RCD
snubber circuit control shown in the simulated result in
figure 3. The achievement of reduce in spike voltage
during turn off also with the increasing of rise time. Both
reducing in spike voltage and increasing of rise time can
reduce the EMI effect.
One of EMI sources can be generated by impedance
response of inductors and capacitors. The self-resonant
frequency (SFR) of passive components can effect the
EMI phenomena depend upon the frequency response.
Higher SFR is preferred. The SFR effect is shown with
the LISN implementation.
596us
+Vcc
+Vcc
Cs
Cs
600us
Time
(b) Vds and id waveform
Figure 2. Without FWD operation
G
G
S
S
(a)
(b)
Figure 4 Common mode conducted EMI emission
between without and with RC gate control for the
MOSFET
(a) PSPICE simulation
40
20
0
-20
580us
V(M2:d,M2:s)
584us
I(V4)
588us
592us
596us
600us
Time
(b) Vds and id waveform
Figure 3. With snubber circuit operation
Figure 5 Measured conducted EMI emission between
without and with RC gate control for the MOSFET
Table 2 Operation condition and measuring equipment
The Snubber circuit: both of RCD and RLD is shown
in Figure 6 (a). where figure 6 (b) shows a slightly better
in term of EMI level compared to without snubber circuit.
Figure 6 (c) shows a better EMI reduction by the
combination of RCD and RLD snubber circuit.
EMI measurement
Line impedance stabilization network (LISN), which
is quite expensive in the market, is developed to use in the
laboratory for economic reason. LCR meter is needed for
modeling the parasitic parameter. EMI analyzer, which
can be related with EMI standard, is preferred. But normal
spectrum analyzer can be complied.
Prototype of LISN is built based on the commercial
LISN: EMCO model 3810/2 where the frequency range is
9 kHz to 30 MHz. The comparison of EMI performance
shows a closed agreement as shown in figure 7. LISN 1 is
the prototype or home-made LISD while LISN 2 is the
commercial LISN. It is shows that it is different by 10 dB
over the conducted EMI range.
Many parasitic components of inductor and
capacitor are involved. The details are not given in this
paper. But the basic material of higher SRF is required. A
lot of winding techniques for inductors are compared and
should be mentioned to reduce parasitic capacitance.
RLD Snubber
RLS
LS
DS1
RCD Snubber
ID
MOSFET
RS
VDS
AC
DS1
C
LISN
CS
L
D
C
Load
EMI Receiver
(a) LISN prototype
(a) EMI measurement for RCD and RLD snubber circuit
dB uV
100
90
80
70
E N 55 0 11 ; C la ss B C on ducted , G rou p 1 a nd 2 , Q ua si-P e ak
w itho ut s nu b be r
E N 5 5 011 ; C la ss B C on du cted, G rou p 1 a nd 2, A v era ge
60
50
40
30
20
w ith R C D sn ub b er
10
0
1
10
(b) RCD snubber effect
dBuV
100
90
80
70
E N 55 011; C lass B C onducted, G rou p 1 and 2, Q ua si-P e ak
E N 55011; C la ss B C on ducted, G roup 1 a nd 2, A v erage
w ithout snu bber
60
(b) LISN 1 is prototype compared to commercial
LISN
Figure 7. Conducted EMI measurement: LISN
50
40
30
20
10
0
w ith R C D + R LD s nubb er
(d) EMI reduction affected by RCD operation
1
10
(c). RCD and RLD combination
Figure 6. The RCD and RLD snubber circuit affect on
EMI reduction
Reference
IV. Conclusions
[1]
A simplified toolkit on conducted electromagnetic
interference (EMI) based on the basic circuits and
concepts of power electronics is introduced. Three main
categories are presented to understand the basic concept
of EMI phenomena and their effects. Some simulation and
measured results can guide the design engineers and
student to do self-learning based on home-made
equipment and free software such as OrCAD 9.1 student
version. Finally, the goals of EMI self–learning is
concluded and done by the process in table 3.
[2]
[3]
Table 3. the conclusion of EMI self-learning kits.
Title
Free wheeling
diode effect
High
frequency
magnetic
concepts
Process
PSPICE simulation
Goals
Principle operation
Modeling by
measured result
Power
electronics
simulation
PSPICE and
MATLAB
Snubber
circuit
PSPICE simulation
and measurement
Gate control
PSPICE simulation
and measurement
Stray parameters
effect and SRF of
Inductor and
capacitors
Modeling passive
components
PSPICE tools for
conducted EMI
simulation via Line
Impedance
Stabilization
Network (LISN)
RCD, RLD
operation to reduce
spike and reduce
di/dt and dv/dt
To Control rise time
and fall time of
switching device
(MOSFET)
W.
Khan-ngern,
“Electromagnetic
Compatibility Experimental Laboratory on
Power Electronics” Proceeding of 2002
International Conference on Electromagnetic
Compatibility, Bangkok, Thailand, July 24-27,
2002, pp. 406-411.
R. Valentine; “Motor Control Electronics
Handbook” .Mc Graw Hill, 1998, pp.418-424.
L. Tihanyi, “Electromagnetic Compatibility in
Power Electronics”, IEEE Press, 1995.