An electrolyzer is part of a renewable energy system and generates hydrogen from water electrolysis that is used in fuel cells. A dc-to-dc converter is required to couple the electrolyzer to the system dc bus. This paper presents the design of three soft-switched high-frequency transformer isolated dc-to-dc converters for this application based on the given specifications. It is shown that LCL-type series resonant converter (SRC) with capacitive output filter is suitable for this application. Detailed theoretical and simulation results are presented. Due to the wide variation in input voltage and load current, no converter can maintain zero-voltage switching (ZVS) for the complete operating range. Therefore, a two-stage converter (ZVT boost converter followed by LCL SRC with capacitive output filter) is found suitable for this application. Experimental results are presented for the two-stage approach which shows ZVS for the entire line and load range.

1. ELECTRICAL PROJECTS USING MATLAB/SIMULINK
Gmail: asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in
0-9347143789/9949240245
For Simulation Results of the project Contact Us
Gmail: asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in
0-9347143789/9949240245
A Comparison of Soft-Switched DC-to-DC Converters for
Electrolyzer Application
ABSTRACT:
An electrolyzer is part of a renewable energy system and generates hydrogen from water
electrolysis that is used in fuel cells. A dc-to-dc converter is required to couple the electrolyzer to
the system dc bus. This paper presents the design of three soft-switched high-frequency
transformer isolated dc-to-dc converters for this application based on the given specifications. It
is shown that LCL-type series resonant converter (SRC) with capacitive output filter is suitable
for this application. Detailed theoretical and simulation results are presented. Due to the wide
variation in input voltage and load current, no converter can maintain zero-voltage switching
(ZVS) for the complete operating range. Therefore, a two-stage converter (ZVT boost converter
followed by LCL SRC with capacitive output filter) is found suitable for this application.
Experimental results are presented for the two-stage approach which shows ZVS for the entire
line and load range.
KEYWORDS
1. DC-to-DC converters
2. Electrolyzer
3. Renewable energy system (RES)
4. Resonant converters
SOFTWARE: MATLAB/SIMULINK

2. ELECTRICAL PROJECTS USING MATLAB/SIMULINK
Gmail: asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in
0-9347143789/9949240245
For Simulation Results of the project Contact Us
Gmail: asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in
0-9347143789/9949240245
BLOCK DIAGRAM:
Fig.1.Two-stage boost-LCL SRC with capacitive output filter.
EXPECTED SIMULATION RESULTS:

3. ELECTRICAL PROJECTS USING MATLAB/SIMULINK
Gmail: asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in
0-9347143789/9949240245
For Simulation Results of the project Contact Us
Gmail: asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in
0-9347143789/9949240245
Fig.2. Simulation waveforms for LCL SRC with capacitive output filter at full-load (2.4 kW)
with Vin = 40V and Vo = 60V: inverter output voltage vab ; current through resonant tank inductor
iLr ; switch currents (iS1 –iS4 ); rectifier input voltage (vrectin ); voltage across and current through
output rectifier diode DR1 .
Fig.3. Simulation waveforms of Fig. 13 repeated for LCL SRC with capacitive output filter at
10% load with Vin = 40V and Vo = 60V.

4. ELECTRICAL PROJECTS USING MATLAB/SIMULINK
Gmail: asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in
0-9347143789/9949240245
For Simulation Results of the project Contact Us
Gmail: asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in
0-9347143789/9949240245
CONCLUSION:
A comparison of HF transformer isolated, soft-switched, dc to- dc converters for electrolyzer
application was presented. An interleaved approach with three cells (of 2.4kWeach) is suitable
for the implementation of a 7.2-kW converter. Three major configurations designed and
compared are as follows: 1) LCL SRC with capacitive output filter; 2) LCL SRC with inductive
output filter; and 3) phase-shifted ZVS PWM full-bridge converter. It has been shown that LCL
SRC with capacitive output filter has the desirable features for the present application.
Theoretical predictions of the selected configuration have been compared with the SPICE
simulation results for the given specifications. It has been shown that none of the converters
maintain ZVS for maximum input voltage. However, it is shown that LCL-type SRC with
capacitive output filter is the only converter that maintains soft-switching for complete load
range at the minimum input voltage while overcoming the drawbacks of inductive output filter.
But the converter requires low value of resonant inductor Lr for low input voltage design.
Therefore, it is better to boost the input voltage and then use the LCL SRC with capacitive output
filter as a second stage. When this converter is operated with almost fixed input voltage, duty
cycle variation required is the least among all the three converters while operating with ZVS for
the complete variations in input voltage and load. A ZVT boost converter with the specified
input voltage (40–60 V) will generate approximately 100V as the input to the resonant converter
for Vo = 60V. Therefore, we have investigated the performance of a ZVT boost converter
followed by the LCL SRC with capacitive output filter. It was shown experimentally that the
two-stage approach obtained ZVS for all the switches over the complete operating range and also
simplified the design of resonant converter.

5. ELECTRICAL PROJECTS USING MATLAB/SIMULINK
Gmail: asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in
0-9347143789/9949240245
For Simulation Results of the project Contact Us
Gmail: asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in
0-9347143789/9949240245
REFERENCES:
[1] A. P. Bergen, “Integration and dynamics of a renewable regenerative hydrogen fuel cell
system,” Ph.D. dissertation, Dept. Mechanical Eng., Univ. Victoria, Victoria, BC, Canada, 2008.
[2] D. Shapiro, J. Duffy, M. Kimble, and M. Pien, “Solar-powered regenerative PEM
electrolyzer/fuel cell system,” J. Solar Energy, vol. 79, pp. 544–550, 2005.
[3] F. Barbir, “PEM electrolysis for production of hydrogen from renewable energy sources,” J.
Solar Energy, vol. 78, pp. 661–669, 2005.
[4] R. L. Steigerwald, “High-frequency resonant transistor DC-DC converters,” IEEE Trans. Ind.
Electron., vol. 31, no. 2, pp. 181–191, May 1984.
[5] R. L. Steigerwald, “A Comparison of half-bridge resonant converter topologies,” IEEE
Trans. Power Electron., vol. 3, no. 2, pp. 174–182, Apr. 1988.