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Modeling and optimization of a hybrid power system comprising several
different power sources provides a tool to size the individual power system
components and to optimize the power system control variables. The hybrid
power system is required to meet the demanding requirements of long
duration mission of unmanned surface vehicles (USVs). These demands for
power may be met by a combination of renewable energy resources,
conventional fossil-fueled energy sources and energy storage options. The
hybrid power system being considered here comprises a solar array, an ocean
wave energy converter, a fuel cell system, a diesel generator and a lithium
ion battery pack. The approach gives high priority to natural energy
sources, i.e. solar and wave energy converter within the discrete time
domain followed by minimization of a cost/energy ratio associated with the
storage based energy elements, i.e., battery pack, fuel cell system (H"2
storage) and diesel generator (fuel storage). The results show that
optimization has been achieved with 19.6% contribution by solar power
during daylight hours and 5.53% contribution of the wave energy harvester
to meet the load demands. The battery bank contributes 39.7% which is 4.4%
above the fuel cell contribution. The diesel generator does not contribute
during the stealth mode of operation of the USV mission. The average
percentage energy contribution from each source confirmed the priorities
based on minimization of cost/energy ratio of hybrid power elements.
However, in the first case study the optimized result shows a constraint
violation when fuel cell performs slightly higher than the battery. Later,
in the second case study, it is corrected by increasing the size of the
battery bank.
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