1. automotive and vehicles
2. electric vehicles

Centre for Green Energy and Vehicle
Innovations (GEVIC)
Component sizing optimization for an
active hybrid energy storage system
LI (ERIC) SUN
11/Mar/2015
Agenda
• Introduction
• Research problems and aims
• Simulation results for optimal solutions
• Conclusions and future work
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Introduction
Source: [1] gpahybrid.com.au/ Accessed on 31/July/2014
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Introduction
Source: http://cleantechnica.com/2014/07/01/nissan-leaf-replacement-battery-priced-5499/ Accessed on 31/July/2014
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Introduction
Standard
US-EPA
“LA92
driving
cycle”
Source: [3] Andreas A. Malikopoulos, Juan P. Aguilar, “An Optimization Framework for Driver
Feedback Systems,” IEEE Transactions on Intelligent Transportation Systems, Vol. 14, No.2, 2013
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Research Problems
• The energy consumption (hence the CO2 emission) of electric
vehicle (EV) and all-electric range (AER) of hybrid electric
vehicles (HEVs) are highly dependent on the onboard energystorage system (ESS) of the vehicle. Charging or discharging
onboard electrochemical batteries under high load has a
tendency to reduce their life cycle regardless of its material
composition.
• In order to increase the AER of vehicles by 15% the incremental cost of the ESS has to be doubled. This is due to the fact
that to meet the design criteria of vehicle performance the
ESS of HEVs has to be over-designed to provide higher peak
power whilst preserving sufficient energy density.
• Supercapacitors are the options with higher power densities
and life cycles in comparison with batteries. A hybrid ESS
(HESS) composed of batteries and supercapacitors creates a
power source with greater power and energy density than
either source can alone. Yet how much ratio each source
should be designed to achieve optimality is NOT certain yet. 6
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In analogy of a Power-split HEV
Source: http://www.toyota.com.au/prius Accessed on 31/July/2014
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General HESS configuration
the configuration of a general HESS equipped in an EV.
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General HESS configuration
battery semiactive topology
Source: J. Cao and A. Emadi, "A New Battery/UltraCapacitor Hybrid Energy Storage System for Electric, Hybrid,
and Plug-In Hybrid Electric Vehicles," Power Electronics, IEEE Transactions on, vol. 27, pp. 122-132, 2012.
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General HESS configuration
Supercapacitor semiactive topology
Source: S. Lu, K. A. Corzine, and M. Ferdowsi, "A New Battery/Ultracapacitor Energy Storage System Design and Its Motor
Drive Integration for Hybrid Electric Vehicles," Vehicular Technology, IEEE Transactions on, vol. 56, pp. 1516-1523, 2007
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Chosen HESS configuration
ZVS Interleaved buck-boost bi-directional converter
Source: Junhong Zhang; Jih-Sheng Lai; Rae-young Kim; Wensong Yu, "High-Power Density Design of a Soft-Switching HighPower Bidirectional dc–dc Converter," Power Electronics, IEEE Transactions on , vol.22, no.4, pp.1145,1153, July 2007
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Research Aims
• For any given (fixed) price target, one needs to first
know all possible combination(s) under a set of
constraints (so as to ensure ALL requirements are met),
and then pick up the most suitable (i.e. optimal)
candidate for the application.
• Power converter is a bulky but key element that is often
ignored in cost modelling thru literature survey, which is
wrong and needs to be included back into analysis.
• This study is to be served not only as a design tool, but
also an analytical framework whose important
parameters and concept can be generalized for a broad
range of applications.(e.g. from passenger cars, trucks,
city buses or any fields requiring energy storage).
These parameters include weight of the HESS, weight
of the rest of vehicle, specific power, energy and cost of
each hybridized source, as well as those of the power
converter.
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Specifications of known technology
Technology
Specific Energy Speci- Specific Power SpeciEnergy
fic Cost
Power
fic Cost
(wh/kg) () (AUD/kwh)
(kw/kg) ()
(AUD/kw)
Life Cycle by Specific
80%
Cost
discharge ($AUD/kg)
(cycles)
(C)
Power Converter
N/A
N/A
5
40
> 10^6
200
SuperCapacitor
5
20000
2
40
> 10^6
100
Lead-Acid Battery
30
170
0.05
100
3*10^2
5
NiMH Battery
44
800
0.4
90
4*10^3
35
Li-ion (LFP)
90
670
0.18
300
5*10^3
60
x 20!
x 6!
Optimization using exhaustive search method
Cost ratio = Cost of SC
pack (incl. cost of power
converter)/cost of the
overall HESS system
Design requirements
• Peak power of HESS should be greater than 100kw.
• The supercapacitor bank should be able to source/sink
75kw for more than continuous 10 seconds (i.e. >200wh).
• The rest of the 25kw under peak demand should be able
to be sourced from the battery pack.
• Weight of the overall system should be sized less than
400kg.
• The acceleration performance indicator power to weight
ratio is chosen to be equal or greater than 0.12 [4]
Source: [4] Fundamentals of vehicle dynamics, Thomas D. Gillespie, SAE press, 1992
Possible combinations
Hybridized Cost ratio
Possible combinations
Possible combinations
The rest of the 25kw under peak
demand should be able to be
sourced from the battery pack.
Weight of the
overall system
should be sized
less than 400kg.
Peak power of HESS should be greater than 100kw.
The supercapacitor bank should be able to source/sink
75kw for more than continuous 10 seconds (i.e. >200wh).
The acceleration
performance indicator
power to weight ratio is
chosen to be equal or
greater than 0.12
Hybridized Cost ratio
Optimized solutions
*Note the 1st index is
the exact capacity (Ah)
of battery cell for
400V battery pack;
The 2nd index is the
exact capacity (Farad)
of the supercapacitor
cell for 300V SC pack
*Note there’s no optimal solution for 15, 17, 19, 20, 22, 23, 24,
27, 28 kwh battery pack under the current constraints setup.
Optimal solution
Cost
Weight
Power
314.2
18850
112.8 112.8
56.5
5639
4511
56.4
22.6
Conclusions and future works
• Compared with other methods, this optimization framework
is simple, fast, and most importantly, effective to size a
hybridized systems with multiple sources.
• Not only local, but global optimal solutions can be logically
found and compared against a given set of input data and
constraints whose parameters are adjustable.
• Future work might include lifecycle analysis of battery to
show how much each solution will slow down the
depreciation process over entire lifespan of battery pack.
• As EVs are still fairly new in the market, it might be
worthwhile to include a “learning curve” analysis into the
existing framework to predict the total costing and design
trends of the HESS system functioning as a strategic
planner.
Thank you!
Q&A
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