Output Filter for the High-Voltage DC/DC Converter

160A
155A
I L
160
140
IL, A
Inductor Current
150A
120
145A
100
140A
80
135A
60
130A
125A
I out
40
Output Current, Iout
1 501 18 1001 36 1501 54 2001
72 t, ms
Output Current
160
IOUT, A
120A
12.0ms 12.4ms 12.8ms 13.2ms 13.6ms 14.0ms 14.4ms 14.8ms 15.2ms 15.6ms 16.0ms
I(L2) -I(RLoad)
Time
Fig. 7. Inductor current (I L ) and output current (I out )
waveforms with the minimum switch duty cycle
Fig. 8 demonstrates rectifier output voltage (U 3 ) and
converter output voltage (U out ) waveforms. The
peak-to-peak output voltage ripple is about 1.5%.
800V
700V
U 3
140
120
100
80
60
40
Output Voltage, Uout
1 501 18 1001 36 1501 54 72
2001 t, ms
Output Voltage
410
UOUT, V
390
370
600V
350
500V
400V
U out
330
310
300V
290
200V
270
1 501 18 1001 36 1501 54 72 t, ms
2001
100V
0V
Fig. 9. Simulated waveforms of the isolated halfbridge
DC/DC converter with proposed LC-filter
-100V
0s 2ms 4ms 6ms 8ms 10ms 12ms 14ms 16ms
V(RLoad:2) V(L2:1)
Time
Fig. 8. Rectifier output voltage (U 3 ) and converter
output voltage (U out ) with the minimum switch duty
cycle
3 Converter dynamic response
Above-presented simulations are demonstrating that
filter components were selected properly.
Corresponding voltage and current ripple values are
minimal. Thus, for the prototype it was decided to
implement the laminated iron-core inductor with
inductance value of 5 mH. Two electrolytic
capacitors (EPCOS B437 560 µF, 450 V) will be
connected in series with the total capacitance value
of 280 µF.
To test the converter dynamic response with the
selected output filter components the generalized
mathematical model of the converter was developed
by help of Simplorer® simulation software.
The converter model was tested with the maximal
input voltage conditions (4000 V) and during the
random load step change (see Fig. 9), when the
output current of the converter is changing instantly
from some intermediate value (70 A) to a maximal
value (143 A).
The maximum inductor current ripple is about 10%,
while the output current ripple is less than 2%. The
voltage ripple of unregulated output is about 1.5%.
The voltage overshoot during load step change is
14%, which can be fully compensated by the
appropriated control system algorithm.
Conclusion
Output filters play a very important role in DC/DC
converters. Important aspects of converters such as
dynamic response, size and cost are closely related
to the components of the filter. Small values for the
filter components improve the performance of the
converters and increase the power density, whereas
minimum values should be provided to guarantee the
filtering objective.
References
[1] D. Vinnikov, „Research, Design and
Implementation of Auxiliary Power Supplies
for the Light Rail Vehicles”, PhD Thesis,
Tallinn, 2005.
[2] Pressman, A.I., “Switching Power Supply
Design”, Second Edition, McGraw-Hill, 1998.
[3] Billings, K.H., “Switchmode Power Supply
Handbook”, McGraw-Hill, 1989.
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