Fuel Cells
345
the 12 V or 42 V auxiliaries, and about 140 V or 300 V for other loads such
as pumps, air-conditioning, and power-steering applications. It is important,
at the same time, to maintain high levels of efficiency, low-electromagneticinterference, low-acoustic disturbances, and most importantly, low costs. It
is critical for fuel-cell based automotive power electronic systems to last
approximately 10–15 years. In addition, an alternative automotive application involves providing power for auxiliary loads, where the peak-to-average
power ratio may be more suitable for fuel-cell operation.
A simple DC/AC inverter system is suitable only if the fuel cell stack can
produce a voltage suitable for the inverter to operate without any additional
converter requirements. Mostly, this is not the case and, hence, an additional DC/DC booster is required between the fuel cell stack and the DC/AC
inverter. Another possible arrangement involves the usage of a higher current
output inverter and a 60 Hz output transformer, when the DC link voltage is
below the required inverter operation voltage, typically about 400 V.
The schematic for the power system of a fuel-cell based drivetrain for a FCV
is shown in Figure 11.4. The arrangement shown in Figure 11.4 also includes
a battery pack and has regenerative braking (Williamson and Emadi 2002).
The secondary battery provides an input DC voltage to the DC/AC inverter
during warm-up time of the fuel-cell. Once the fuel-cell warms-up, the battery is removed from service and the system is run on the fuel-cell and the
dual power conversion circuitry. The battery system also provides voltage
during transient conditions. The traction controller basically sends control
signals to the fuel cell, DC/DC converter, and DC/AC inverter depending on
the feedback speed and torque signals as well as drive commands. Thus, the
speed and torque of the traction motor is controlled at all times, which, in
turn is coupled to the vehicle transmission system.
A typical hybridized power system with a lead–acid or nickel/cadmium
battery pack connected in parallel with the fuel-cell in order to meet the
peak power demand to also take advantage of regenerative braking is shown
in Figure 11.5. The DC/DC converter raises the level of the voltage from the
fuel cell stack to the level of the main DC bus voltage. The initial peak power
during transients, such as start-up and acceleration, is supplied by the battery pack. Varying DC and AC loads are fed from the main DC-bus through
appropriate DC/DC converters and DC/AC inverters. Furthermore, the electric motor is controlled by a motor controller system, which, in turn, drives
the wheels of the bus. On changing the speeding and braking commands, a
suitable signal is fed back to the controller, which accordingly controls the
speed and torque delivered by the motor.
Another configuration for fuel-cell buses includes a nonhybridized topology. In this case, direct hydrogen fuel cells are used to provide the entire
power to the propulsion system. XCELLSiS Fuel Cell Engines, jointly owned
by Daimler-Chrysler, Ford Motor Company, and Ballard Power Systems,
are involved in the development of such fuel cell engines for automotive
applications.
345
the 12 V or 42 V auxiliaries, and about 140 V or 300 V for other loads such
as pumps, air-conditioning, and power-steering applications. It is important,
at the same time, to maintain high levels of efficiency, low-electromagneticinterference, low-acoustic disturbances, and most importantly, low costs. It
is critical for fuel-cell based automotive power electronic systems to last
approximately 10–15 years. In addition, an alternative automotive application involves providing power for auxiliary loads, where the peak-to-average
power ratio may be more suitable for fuel-cell operation.
A simple DC/AC inverter system is suitable only if the fuel cell stack can
produce a voltage suitable for the inverter to operate without any additional
converter requirements. Mostly, this is not the case and, hence, an additional DC/DC booster is required between the fuel cell stack and the DC/AC
inverter. Another possible arrangement involves the usage of a higher current
output inverter and a 60 Hz output transformer, when the DC link voltage is
below the required inverter operation voltage, typically about 400 V.
The schematic for the power system of a fuel-cell based drivetrain for a FCV
is shown in Figure 11.4. The arrangement shown in Figure 11.4 also includes
a battery pack and has regenerative braking (Williamson and Emadi 2002).
The secondary battery provides an input DC voltage to the DC/AC inverter
during warm-up time of the fuel-cell. Once the fuel-cell warms-up, the battery is removed from service and the system is run on the fuel-cell and the
dual power conversion circuitry. The battery system also provides voltage
during transient conditions. The traction controller basically sends control
signals to the fuel cell, DC/DC converter, and DC/AC inverter depending on
the feedback speed and torque signals as well as drive commands. Thus, the
speed and torque of the traction motor is controlled at all times, which, in
turn is coupled to the vehicle transmission system.
A typical hybridized power system with a lead–acid or nickel/cadmium
battery pack connected in parallel with the fuel-cell in order to meet the
peak power demand to also take advantage of regenerative braking is shown
in Figure 11.5. The DC/DC converter raises the level of the voltage from the
fuel cell stack to the level of the main DC bus voltage. The initial peak power
during transients, such as start-up and acceleration, is supplied by the battery pack. Varying DC and AC loads are fed from the main DC-bus through
appropriate DC/DC converters and DC/AC inverters. Furthermore, the electric motor is controlled by a motor controller system, which, in turn, drives
the wheels of the bus. On changing the speeding and braking commands, a
suitable signal is fed back to the controller, which accordingly controls the
speed and torque delivered by the motor.
Another configuration for fuel-cell buses includes a nonhybridized topology. In this case, direct hydrogen fuel cells are used to provide the entire
power to the propulsion system. XCELLSiS Fuel Cell Engines, jointly owned
by Daimler-Chrysler, Ford Motor Company, and Ballard Power Systems,
are involved in the development of such fuel cell engines for automotive
applications.