A New Battery/Ultra Capacitor Hybrid Energy Storage System for Electric, Hybrid, and Plug-In Hybrid Electric Vehicles

2. Introduction
• ENERGY storage systems (ESSs) are of critical importance in
hybrid electric vehicles
• Batteries are one of the most widely used among energy storage
systems
• In battery-based ESSs, power density of the battery needs to be high
enough to meet the peak power demand
• Applications of instantaneous power input and output -- batteries
suffering from frequent charge and discharge operations
• which have an adverse effect on battery life
• To solve the problems hybrid energy storage systems (HESS) have
been proposed

3. • The basic idea of an HESS is to combine ultracapacitors (UCs) and
batteries to achieve a better overall performance
• UCs have a high power density, but a lower energy density. This
combination inherently offers better performance in comparison to
the use of either of them alone
• Based on the use of power electronic converters in the configurations
Several configurations for HESS designs have been proposed.

4. The topologies of hybrid energy storage systems (HESS)
Basic passive parallel hybrid configuration UC/battery configuration.
Battery/UC configuration

5. DESIGN CONSIDERATIONS
of Hybrid energy storage systems
• Voltage Strategy of the Two Energy Sources
i) VBatt < Vuc = Vdc ii) VBatt = Vuc = Vdc iii) VBatt = Vuc = Vdc
• Effective Utilization of UC Stored Energy
• Protection of the Battery From Overcurrent
• HESS Total Cost
i) UC cost is a major component of the overall HESS system cost
ii) Power handling capacity of the converter is another important
factor

6. PROPOSED
Hybrid energy storage systems
• Conventional HESS connects the UC via a dc/dc converter to satisfy the
real-time peak power demands of the powertrain controller
• This will require the dc/dc converter to have the same power capability as
the UC bank or at least higher than the maximum possible demand value
• The proposed HESS achieves this in a different way, which can be
considered an application of the averaging concept
• Different from the conventional HESS designs, the high-voltage dc link is
allowed to vary in a predefined ratio.

7. Modes of Operation
Vehicle Low Constant Speed
Operation
If Pdmd is equal to or
smaller than Pconv , we call this
operating condition the low
constant speed mode
Vehicle High Constant
Speed Operation
In the high constant speed
operating mode, Pdmd > Pconv ,
(Condition: VUC < VBatt )
Therefore, the main power diode
is forward biased.

8. Energy flow of the
Acceleration mode phase I
•At the beginning of the
acceleration mode,
assume VUC >VBatt .
•Since Pconv < Pdmd, VUC will
keep decreasing
•Energies from the UC and the
dc/dc converter are both
supporting the vehicle
acceleration.
Energy flow of the
Acceleration mode phase II
In the high constant speed
operating mode, if Pdmd <Pconv ,
the power difference between
Pconv and Pdmd will be used to
charge the
UC.

9. Energy flow of Regenerative
braking phase I when VUC< VUC _tgt
In phase I, the regenerative
power will be injected into the UC only
When depending VUC < target UC
Boost Operation
Energy flow of Regenerative
braking phase I when VUC>=VUC _tgt
voltage VUC_tgt >= to the target VUC
No Operation
Energy flow Regenerative braking
phase II
The dc/dc converter will work in
buck mode to convey the energy from the
UC to the battery

10. Conclusion
• The new design is able to fully utilize the power capability of
the UCs without requiring a matching power dc/dc converter.
• Smoother load profile is created for the battery pack – results
power requirement of the battery pack reduced
• Drivability of the vehicle at low temperatures can be improved
as well
• proposed HESS requires a smaller size dc/dc converter to
convey energy to charge the UC bank, while still utilizing up to
75% of the UC energy
• A relatively constant load profile is created for the battery
• by using the topology which is good for the life of the battery

11. Thank You