EMI Filter Design for an Isolated DC-DC Boost Converter

EMI Filter Design for an Isolated DC-DC
Boost Converter
Ishtiyaq Ahmed Makda (PhD Research Fellow)
Morten Nymand (Supervisor)
Maersk Mc-Kinney Moller Institute, University of Southern Denmark, Odense,
Denmark
Outline:
 Introduction
 DC-DC Converter in Electric Vehicles
 System Definition
 Common Mode EMI Filter Design and important
outcomes
 Differential Mode EMI Filter Design
2
 Conclusion
Introduction:
 One of the most critical issues for the environment today is pollution
generated by hydrocarbon combustion
 However, today it is one of the main sources for transportation
 But, hybrid electric vehicles (HEV) and full electric vehicles (EV) are
rapidly advancing as an alternative
 One of the key blocks inside HEV and EV is the DC–DC converter
 This converter has to be capable of handling the energy transfer
from the low voltage DC bus and the high voltage DC bus (used for
the electric traction)
3
EV Drive System:
Some design considerations are essential for automotive applications:
•
•
•
•
Reliable
Light weight
Small volume
High efficiency
• Low electromagnetic interference (EMI)
4
Ultra High Efficiency Converter:
Primary Parallel Isolated Full Bridge Boost Converter
(Invented by Morten Nymand)
5
Vital Features:
• Input voltage range= 30 to 60Vdc
• High Output Voltage > 360Vo
• Maximum efficiency is 98%
• Power ranges from 1.5 to 10kW
• Power loss reduced by factor 4 as
compared to the state-of-the-art
• Reduced
weight
6
converter
size
and
Electromagnetic Interference (EMI)
Conducted Emission
Differential
Mode (DM)
Noise
7
Common
Mode (CM)
Noise
Radiated Emission
Common Mode (CM) & Differential Mode (DM) Noise:
 Differential-Mode Noise
 Flows on Line and take
return path from Neutral
 Currents flowing around
loops
 Easy to understand
 Common-Mode Noise





Ref: http://www.hottconsultants.com/pdf_files/APEC2002.pdf
8
Flows on Line and Neutral
simultaneously and take return
path from chassis
Involves parasitic
Currents flow around loops
usually involving parasitic
capacitances
More difficult to understand
The noise source and current
path must first be visualized and
understood before a solutions
can be determined
Common Mode (CM) noise – Generation mechanism,
modelling and filter design
9
Motivation:
10
•
In high current applications, transformer needs extensive interleaving of primary and
secondary windings to reduce the proximity effect
•
Such a transformer exhibits large capacitive coupling between primary and secondary
windings
•
This large capacitive coupling is known to create large CM noise in the converter
•
Therefore we are analyzing the impact of large coupling capacitance on CM noise
•
However, surprisingly enough, this study shows that this inherently large
capacitive coupling has very little influence on the CM noise current propagation
in the converter
Major CM Noise Source (Transformer Coupling Capacitance):
Transformer Winding Arrangement
Transformer Coupling Capacitance (CSPS) as a
major CM noise source
How Big is the Transformer Coupling Capacitance?
CSPS of one transformer is 3.7nF
Two transformers in parallel, so CSPS is 7.4nF
11
CM Noise Voltage Generation Mechanism:
State 1: When all primary switches are ON and the energy is being stored in the inductor L1
Equivalent Circuit of Converter during State 1
•
Both transformer primary windings are clamped to primary return
•
Average primary winding voltages during this state is therefore zero
•
All secondary rectifier diodes are reverse biased and OFF – energy is supplied to the load by C1 capacitor
•
Potential of Secondary winding float – coupled to secondary return potential only through parasitic junction
capacitances of diodes and heat sink
•
12
Both transformer secondary windings have the same potential
CM Noise Voltage Generation Mechanism (Cont.):
State 2: When only two diagonal primary switches in each bridge are ON
Equivalent Circuit of Converter during State 2
•
Two series connected transformer secondary windings are connected to output voltage Vo
•
Average voltage of the two series connected secondary windings (at node ‘A’ w.r.t secondary return) is half of the
output voltage, i.e. Vo/2
•
Due to turns ratio of two transformers, the average potential on each of the two primary windings will be at half of
the reflected output voltage w.r.t. primary return, i.e. Vo/4n
13
CM Noise Model (Cont.):
Cpar,PS is the transformer coupling capacitance (in nF) which is in series with the
parasitic diode capacitances (in off-state)
NEWS: Total effective capacitance is a few hundred of pF and hence CSPS
has a very little influence on the CM noise propagation in the converter
14
CM Noise Suppression:

Two noise suppression measures has been taken:
CM noise model with 1st noise suppression measure
CM noise model with two noise suppression measure
Ceff = CSPS −1 + CSD −1
15
−1
= 358 pF (4)
Validity of the CM Noise Model:
16
Experimental Setup:
EMI Test Receiver
Digital Function Generator
Digital Oscilloscope
Input power source
LISN
Current Probe
17
Power Converter (DUT)
Experimental Results (Cont.):
(a)
(b)
(a) CM noise without capacitors Y1, Y2 and LCM
(b) CM noise with capacitors Y1 and Y2 only
(c) CM noise with Y1, Y2 and LCM
(c)
18
Conclusion for CM Noise Filter:
19
•
A CM noise model for an isolated full-bridge boost converter has been presented
•
Since the inherently large transformer coupling capacitance (in nF) is in series
with output rectifier diode parasitic capacitances (in pF), the effect of the large
transformer coupling capacitance is effectively eliminated
•
Large transformer turns ratio further reduces the magnitude of the injected CM
noise voltage in low input voltage high power isolated boost converters
•
Therefore, despite of a much larger transformer coupling capacitance, lowvoltage high-current converters have lower CM noise and thus requires less
common mode attenuation
Differential Mode (DM) noise filter design
20
Filter Design Process
1.
2.
3.
4.
5.
6.
7.
8.
21
Measurement of inductor ripple current and calculation of amplitude odd
harmonics
Calculation of attenuation requirement at worst case frequency
Cutoff frequency calculation and determination of filter order
Sizing of filter capacitor
Inductor calculation
Filter damping branch
Selection of components
Simulation and experimental results
Filter Order and Cut-off frequency
 Since 75dB of attenuation is required, 4th order LC filter
is employed
22
DM EMI Filter Hardware
23
Experimental Results
24
Thank you for your attention
25

Download Report