255
Coupling with Batteries and Fuel Cells
current to the system duty cycle or bus voltage is used to demonstrate a reliable means of matching the system load power demands [4].
Another approach is to use algorithms derived from heuristics or through
a well-trained neural network implemented in the control of the HESS to provide load power. The latter is used by optimizing the set of currents required
of the HESS in various driving conditions while maintaining defined border conditions such as the supercapacitor SOC and operation of the battery
within safety limits.
Control strategies using buck–boost DC–DC converters are used for a
range of diverse topologies typically involving defined-by-system requirements. While systems may focus on a specific choice of power converter and
module, further optimization and/or compromise may be required to satisfy
system dynamics, cost and weight issues, and other factors. The advantages
of an indirect coupling and control strategy include operation of the battery
and supercapacitor at independent voltages, improved utilization of supercapacitor power capacity, and control of the battery current. The disadvantages
of converter power loss and increasing component count must, however,
be taken into account. In general, the improvements to a battery–ES HESS
cannot optimize both the energy efficiency and battery life simultaneously;
rather one property must be prioritized over the other.
6.5 Supercapacitor Integration with Fuel Cells
The fuel cell (FC) presents a clean power source alternative to current internal combustion engines. Among the many types of FCs characterized by
their electrolytes, the polymer electrolyte membrane fuel cell (PEMFC) is
lightweight and small, has a reasonably facile membrane fabrication, and
shows great promise. However, one key weak point that continues to draw
attention is the slow dynamic limitation demonstrated by PEMFCs during
experimental use and the negative consequences that can result.
Sizing a PEMFC to match the average current demanded by a system load
does not address high current pulses. Atypical or infrequent high currents
are thus met by a delayed response of the fuel supply system and a subsequent voltage drop to the region defining limited reactant transport operation (concentration polarization) occurs. Furthermore, the rate at which the
voltage drop occurs is increased by a reaction breakdown initiated by an
undersupply of reactants. Consequently, ensuing reactions will fail and reactant starvation takes place. Irreversible damage can then arise from the continuing current demand on the PEMFC.
Adding to the slow dynamics inherent to FCs, the hydrogen and oxygen
delivery systems (pumps, valves, hydrogen reformer, etc.) endure mechanical stress under high power demands, leading to mechanical failures. To
Coupling with Batteries and Fuel Cells
current to the system duty cycle or bus voltage is used to demonstrate a reliable means of matching the system load power demands [4].
Another approach is to use algorithms derived from heuristics or through
a well-trained neural network implemented in the control of the HESS to provide load power. The latter is used by optimizing the set of currents required
of the HESS in various driving conditions while maintaining defined border conditions such as the supercapacitor SOC and operation of the battery
within safety limits.
Control strategies using buck–boost DC–DC converters are used for a
range of diverse topologies typically involving defined-by-system requirements. While systems may focus on a specific choice of power converter and
module, further optimization and/or compromise may be required to satisfy
system dynamics, cost and weight issues, and other factors. The advantages
of an indirect coupling and control strategy include operation of the battery
and supercapacitor at independent voltages, improved utilization of supercapacitor power capacity, and control of the battery current. The disadvantages
of converter power loss and increasing component count must, however,
be taken into account. In general, the improvements to a battery–ES HESS
cannot optimize both the energy efficiency and battery life simultaneously;
rather one property must be prioritized over the other.
6.5 Supercapacitor Integration with Fuel Cells
The fuel cell (FC) presents a clean power source alternative to current internal combustion engines. Among the many types of FCs characterized by
their electrolytes, the polymer electrolyte membrane fuel cell (PEMFC) is
lightweight and small, has a reasonably facile membrane fabrication, and
shows great promise. However, one key weak point that continues to draw
attention is the slow dynamic limitation demonstrated by PEMFCs during
experimental use and the negative consequences that can result.
Sizing a PEMFC to match the average current demanded by a system load
does not address high current pulses. Atypical or infrequent high currents
are thus met by a delayed response of the fuel supply system and a subsequent voltage drop to the region defining limited reactant transport operation (concentration polarization) occurs. Furthermore, the rate at which the
voltage drop occurs is increased by a reaction breakdown initiated by an
undersupply of reactants. Consequently, ensuing reactions will fail and reactant starvation takes place. Irreversible damage can then arise from the continuing current demand on the PEMFC.
Adding to the slow dynamics inherent to FCs, the hydrogen and oxygen
delivery systems (pumps, valves, hydrogen reformer, etc.) endure mechanical stress under high power demands, leading to mechanical failures. To