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Description:
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With the escalating number of vehicles on the road , great concerns are drawn to
the large amount of fossil fuels they use and the detrimental environmental impacts from
their emissions . A lot of research and development have been conducted to explore the
alternative energy sources . The fuel cell has been widely considered as one of the most
promising solutions in automobile applications due to its high energy density , zero
emissions and sustainable fuels it employs . However , the cost and low power density of
the fuel cell are the major obstacles for its commercialization .
This thesis designs a novel converter topology and proposes the control method
applied in the Fuel Cell Hybrid Vehicles (FCHVs ) to minimize the fuel cell's cost and
optimize the system's efficiency . Unlike the previous work , the converters presented in
the thesis greatly reduce the costs of hardware and energy losses during switching . They
need only three Metal -Oxide -Semiconductor Field -Effect Transistors (MOSFETs ) to
smoothly accomplish the energy management in the cold start , acceleration , steady state
and braking modes . In the converter design , a boost converter connects the fuel cell to the DC bus
because the fuel cell's voltage is usually lower than the rating voltage of the motor . In
this way , the fuel cell's size can be reduced . So is the cost . With the same reason , the
bidirectional converter connected to the ultracapacitor works at the buck pattern when
the power is delivered from the DC bus to the ultracapacitor , and the boost converter is
selected when the ultracapacitor provides the peaking power to the load . Therefore , the
two switches of the bi -directional converter don't work complementarily but in different
modes according to the power flow's direction .
Due to the converters' simple structure , the switches' duty cycles are
mathematically analyzed and the forward control method is described . The fuel cell is
designed to work in its most efficient range producing the average power , while the
ultracapacitor provides the peaking power and recaptures the braking power . The
simulation results are presented to verify the feasibility of the converter design and
control algorithm . |