| Abstract |
Fuel Cell Electric Vehicles (FCEV) have higher
efficiency and lower emissions compared with the internal
combustion engine vehicles. But, the fuel cell has a slow
dynamic response; therefore, an auxiliary power source is
needed during start up and transient conditions. Batteries
and ultracapacitors can be used as auxiliary power sources.
Batteries have high energy density and ultracapacitors have
high power density. By using both the battery and
ultracapacitors as the auxiliary power sources of the FCEV,
the performance and efficiency of the overall system can be
improved. In this system, there is a boost converter, which
steps up the fuel cell voltage, and two bi-directional DC-DC
converters, that each of them couples the battery and
ultracapacitors to the bus. Each bi-directional converter has
two modes of operation. During the buck mode the battery/
ultracapacitors will charge through the fuel cell or
regenerative braking. During the boost mode they will
supply the load. These converters should be properly
controlled. Besides, a control strategy is needed to select the
most suitable power source for supplying the load at each
operating point, due to the efficiency of the system and
demanding power. In this paper the fuzzy control method
has been employed for controlling the whole system. Three
kinds of fuzzy controllers are needed for this system. One of
them is the main controller, which selects the switches that
should be activated at each moment. The second one is the
boost controller, which has 3 inputs and is needed for three
switches. The third one is the buck controller, which has 3
inputs and is used for two switches. The simulation has been
done in simulink/MATLAB, and the PLECS toolbox has
been employed to achieve more accurate results for power
electronics circuits. Moreover an accurate model has been
used for the fuel cell. The simulation results show that this
system has a good dynamic performance and high
reliability. |
