TY - JOUR
T1 - Efficiency Improvement of a Cascaded Buck and Boost Converter for Fuel Cell Hybrid Vehicles with Overlapping Input and Output Voltages
AU - Kunstbergs, Noass
AU - Hinz, Hartmut
AU - Schofield, Nigel
AU - Roll, Dennis
N1 - Funding Information:
This work is supported by the Frankfurt University of Applied Sciences, Faculty of Computer Science and Engineering.
Publisher Copyright:
© 2022 by the authors.
PY - 2022/9/1
Y1 - 2022/9/1
N2 - Fuel cell hybrid vehicles represent an alternative to battery electric vehicles and will gain importance in the future as they do not need large battery capacities and thus require less critical raw materials. Depending on the electric architecture, the voltage of the fuel cell stack and traction battery may overlap. Accordingly, it is necessary to use a bidirectional DC–DC converter that connects the battery to the DC bus, which supports overlapping input and output voltages. Furthermore, these converters should be non-isolating in terms of compact design. Concerning complexity and controllability, the bidirectional cascaded buck and boost converter is preferable and is the subject of this study. Published literature presents the bidirectional cascaded buck and boost converter with high losses for overlapping input and output voltages, introducing two methods for this operation mode. The method selected for this study, namely buck + boost, uses two switches, whereby one switch has a fixed duty cycle. However, there is no appropriate investigation to determine the impact of this fixed duty cycle on converter efficiency to date. Furthermore, efficiency improvement is possible by switching frequency modulation, but current literature does not address this modulation method for overlapping input and output voltages. Therefore, this paper investigates a non-isolated hard-switched bidirectional cascaded buck and boost converter for fuel cell hybrid vehicles operating with up to 19.8 kW. The study focuses on determining the optimum fixed duty cycle and efficiency optimisation through a novel critical conduction mode with adapted switching frequency by utilising the load-dependent inductance of the inductor with powder cores. Measurements with an experimental setup validate the proposed modulation method with Si-IGBT half-bridge modules. The results demonstrate that a loss reduction of 39% is possible with switching frequency modulation and the optimum duty cycle compared to fixed switching frequency. As a result, the converter achieves high efficiencies of up to 99% and low device junction temperatures.
AB - Fuel cell hybrid vehicles represent an alternative to battery electric vehicles and will gain importance in the future as they do not need large battery capacities and thus require less critical raw materials. Depending on the electric architecture, the voltage of the fuel cell stack and traction battery may overlap. Accordingly, it is necessary to use a bidirectional DC–DC converter that connects the battery to the DC bus, which supports overlapping input and output voltages. Furthermore, these converters should be non-isolating in terms of compact design. Concerning complexity and controllability, the bidirectional cascaded buck and boost converter is preferable and is the subject of this study. Published literature presents the bidirectional cascaded buck and boost converter with high losses for overlapping input and output voltages, introducing two methods for this operation mode. The method selected for this study, namely buck + boost, uses two switches, whereby one switch has a fixed duty cycle. However, there is no appropriate investigation to determine the impact of this fixed duty cycle on converter efficiency to date. Furthermore, efficiency improvement is possible by switching frequency modulation, but current literature does not address this modulation method for overlapping input and output voltages. Therefore, this paper investigates a non-isolated hard-switched bidirectional cascaded buck and boost converter for fuel cell hybrid vehicles operating with up to 19.8 kW. The study focuses on determining the optimum fixed duty cycle and efficiency optimisation through a novel critical conduction mode with adapted switching frequency by utilising the load-dependent inductance of the inductor with powder cores. Measurements with an experimental setup validate the proposed modulation method with Si-IGBT half-bridge modules. The results demonstrate that a loss reduction of 39% is possible with switching frequency modulation and the optimum duty cycle compared to fixed switching frequency. As a result, the converter achieves high efficiencies of up to 99% and low device junction temperatures.
KW - buck + boost
KW - DC–DC converter
KW - fuel cell hybrid vehicles
KW - switching frequency modulation
UR - http://www.scopus.com/inward/record.url?scp=85138721092&partnerID=8YFLogxK
U2 - 10.3390/inventions7030074
DO - 10.3390/inventions7030074
M3 - Article
AN - SCOPUS:85138721092
VL - 7
JO - Inventions
JF - Inventions
SN - 2411-5134
IS - 3
M1 - 74
ER -
