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304 Renewable Energy Devices and Systems with Simulations in MATLAB and ANSYS ®
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fuel flow and also a change in the rate of fuel flow. If the amount of hydrogen flow to
the stack is higher than that required by the electrical load, then energy is wasted in the
exhaust. If the fuel flow is less than that required by the electrical load, then the imped-
ance of the stack increases, thus overheating the stack. Hence, it is necessary to match the
amount of hydrogen flow to the stack to meet the desired electrical load at the output.
• The sequence of shutting off the entire system.
• Effect on the fuel input if the load is suddenly disconnected.
• Isolation of the fuel cell stack from the drive system.
• Connecting the battery and the fuel cell stack.
• Charging the capacitors of the inverter and the limitation of capacitor inrush current.
• Coordination of the battery charging simultaneously using regenerative energy and from
the fuel cell.
• Charging the battery from the fuel cell stack alone.
• Coordination of the power delivered for propulsion from the battery and from the fuel cell
stack.
• Limiting the battery current during regeneration and charging at the same time.
• Supplying the power to the accessory loads of the vehicle and to the accessory loads of the
fuel cell stack.
• Matching the fuel cell output characteristics with those of the battery and the drive system.
• Advanced sensors for fuel flow measurement, temperature/pressure regulation, and sensing
the various chemical reactions in the fuel cell unit.

12.5.2 Fuel Cell for APU and Plug-in-Fuel Cell Vehicles

Start–stop technology for automobiles based on 48 V DC is rapidly gaining momentum particularly
in Europe. This technology will automatically switch off the engine every time the vehicle stops
or when the engine is idling and restart it instantly as and when needed. However, instead of the
engine-driven alternator, a fuel cell can produce electricity when the engine is running as well as
not running and thus could eliminate the need for an alternator. Also, it has higher efficiency as
compared to an engine-driven generator. The fuel cell APU can be used in conventional or hybrid
vehicle systems and is not linked to a fully electric drivetrain [4, 22]. It could be used to generate
power at 42 or 48 V and meet the challenges of providing higher power to the increasing electrical
loads such as electrical air-conditioning, drive-by-wire, and steer-by-wire systems. Instead of the
PEMFC, high-temperature SOFC could also be used for automotive APU because of the potential
for internal reforming of more conventional petroleum fuels.
An electrical architecture with a typical fuel cell APU is shown in Figure 12.9. In this system,
the fuel cell unit generates 48 V and powers the 48 and 12 V vehicle loads [22, 23]. A 48 V/12 V
buck–boost converter is employed for charging the 12 V battery in the vehicle and for powering all
the 12 V accessories. The system is started by boosting the 12–48 V to power the accessories of the
fuel cell unit. The function of the power conditioner is to obtain controlled 48 V to power the loads.
The control system operation is similar to the systems in Figures 12.7 and 12.8.
The fuel cells could be used as range extenders instead of the ICE-driven generators in series
hybrid vehicles. A range extender–type fuel cell with a lower rating could be used only to charge the
batteries. The battery should be designed to supply the full propulsion power to the vehicle. For such
applications, it is possible to use the PEMFC or SOFC. The battery unit of this type of vehicle can
be charged at night similar to a plug-in hybrid electric vehicle. This plug-in hybrid fuel cell vehicle
(PFCV) consisting of a smaller fuel cell and a larger battery (battery dominant) may be the future
direction for automobiles [24]. The PEM technology is already available and combining this with
a compressed hydrogen cylinder for onboard charging would lead to a zero-emission vehicle with
a range greater than 500 miles (800 km). If SOFC is used as shown in Figure 12.10, it would also
provide electric power to the house as vehicle-to-grid operation and sustained heat. The hydrogen