268
Electrochemical Supercapacitors for Energy Storage and Delivery
reliable diode replaces the DC–DC converter implemented in Topology 2 to
connect the battery; both lead to the high voltage bus line.
With a supercapacitor directly connected to the high voltage bus, efficient
power is provided on demand, discharging to the extent that it matches the
battery–diode terminal voltage. Following this event, the battery and supercapacitor share the power demands according to their respective impedances (Topology 1). The location of the supercapacitor also suits its ability to
capture regenerative brake energy for recharging well beyond the voltage of
the given battery.
This configuration better utilizes the power capabilities of a supercapacitor
to efficiently discharge and charge the inverter and motor of the power train,
while conserving the use of the battery for infrequent demands beyond the
power capacity or voltage limit of the supercapacitor. The charging of the
battery takes place through a low power unidirectional boost converter for
operation in a high efficiency region and minimizes I 2 R power losses within
the battery [17].
6.6.5 Control and Optimization of ESS
Of the supercapacitor-battery-fuel cell (ES-B-FC) systems discussed,
Topology 5 was proposed as a superior means of enhancing the utilization
of each system through efficient power supply and distribution to complement their inherent operational discharging and recharging mechanics. The
control strategy, improvements, and optimizations are considered in relation
to their application in power train systems.
A unique aspect of Topology 5 is how power sharing is governed for
the simultaneous operation of the battery and supercapacitor. The size of
either system can be manipulated to affect power performance. A greater
capacitance for a supercapacitor will translate to reducing the rate of voltage decline and subsequently extend the point at which the battery begins
to provide supplementary power. In an alternative manner, a higher voltage battery begins to supply power earlier than a low voltage battery. Thus,
these two design parameters can be used to control the power split between
the battery and supercapacitor. Simulations involving various battery and
supercapacitor sizes were evaluated to determine optimal performance.
Figure 6.15 is a simplified diagram of the control strategy for Topology
5. The two variables for input control are (1) the fuel cell power command
provided to the high power DC–DC converter; and (2) the command from
the motor inverter to the inverter. In this manner, the power requested by
the load is partitioned into separate requests to the FC and the ESS (battery–
supercapacitor). To effectively split the power requirement, a low -pass filter
with time constant τ is used as a variable. In this manner the filter evaluates the power request made on the FC. Through its limiters, it blocks any
demands below a prescribed low efficiency level, rerouting them to the ESS.
Electrochemical Supercapacitors for Energy Storage and Delivery
reliable diode replaces the DC–DC converter implemented in Topology 2 to
connect the battery; both lead to the high voltage bus line.
With a supercapacitor directly connected to the high voltage bus, efficient
power is provided on demand, discharging to the extent that it matches the
battery–diode terminal voltage. Following this event, the battery and supercapacitor share the power demands according to their respective impedances (Topology 1). The location of the supercapacitor also suits its ability to
capture regenerative brake energy for recharging well beyond the voltage of
the given battery.
This configuration better utilizes the power capabilities of a supercapacitor
to efficiently discharge and charge the inverter and motor of the power train,
while conserving the use of the battery for infrequent demands beyond the
power capacity or voltage limit of the supercapacitor. The charging of the
battery takes place through a low power unidirectional boost converter for
operation in a high efficiency region and minimizes I 2 R power losses within
the battery [17].
6.6.5 Control and Optimization of ESS
Of the supercapacitor-battery-fuel cell (ES-B-FC) systems discussed,
Topology 5 was proposed as a superior means of enhancing the utilization
of each system through efficient power supply and distribution to complement their inherent operational discharging and recharging mechanics. The
control strategy, improvements, and optimizations are considered in relation
to their application in power train systems.
A unique aspect of Topology 5 is how power sharing is governed for
the simultaneous operation of the battery and supercapacitor. The size of
either system can be manipulated to affect power performance. A greater
capacitance for a supercapacitor will translate to reducing the rate of voltage decline and subsequently extend the point at which the battery begins
to provide supplementary power. In an alternative manner, a higher voltage battery begins to supply power earlier than a low voltage battery. Thus,
these two design parameters can be used to control the power split between
the battery and supercapacitor. Simulations involving various battery and
supercapacitor sizes were evaluated to determine optimal performance.
Figure 6.15 is a simplified diagram of the control strategy for Topology
5. The two variables for input control are (1) the fuel cell power command
provided to the high power DC–DC converter; and (2) the command from
the motor inverter to the inverter. In this manner, the power requested by
the load is partitioned into separate requests to the FC and the ESS (battery–
supercapacitor). To effectively split the power requirement, a low -pass filter
with time constant τ is used as a variable. In this manner the filter evaluates the power request made on the FC. Through its limiters, it blocks any
demands below a prescribed low efficiency level, rerouting them to the ESS.