Optimization of PHEV/EV Battery Charging
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Optimization of PHEV/EV Battery Charging
Lawrence WangCURENT YSP PresentationsRM 52511:00-11:25
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Outline•Background and Introduction•Problem Statement and Technical
Approach•Battery charging system model and
simulation•Minimum loss algorithm formulation and
test•Conclusion and future work
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Background
• EV and PHEV will help solve energy dependency and environmental issues & are becoming popular
• All EV/PHEV rely on batteries
• One of challenges is battery charging – the success of the EV will depend on availability of charging infrastructure
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Battery Charger Systems
On-Board Charging System
Off-Board Charging SystemZhang et al “Research on energy efficiency of the vehicle's battery pack arch on energy efficiency of the vehicle's battery pack,” 2011 ICEICE
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Review of Previous Charging Schemes•Previous studies showed optimal charging
(complex function) was very close to the CC-CV method.
E. Inoa, Jin Wang, “PHEV Charging Strategies for Maximized Energy Saving,” IEEE Transactions on Vehicular Technology, 2011
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Problem Statement & Approach• Problem Statement
▫Given a certain maximum time to charge a battery from a starting SOC to a final SOC, find the optimal current and voltage to minimize energy loss
• Approach▫Model for both battery and charger▫Determine total loss and charging time relationship
with charging current, voltage and SOC▫Design an method for selection of current and
voltage.
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Battery Model & Verification
Min Chen, G.A. Rincon-Mora, “Accurate electrical battery model capable of predicting runtime and I-V performance,” IEEE Transactions on Energy Conversion
Battery model is modified to be consistent with the battery in the Nissan Leaf Electric Vehicle. Components are scaled by a factor of 96 cell units and a 66.2 Ah capacity. Verified to be consistent (16kWh)
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Charger & Loss Modeldcv
CAv ABvBCv
Laps bps cps
ans bns cns
C Battery
p
n
avbv
cv
0.92
0.93
0.94
0.95
0.96
0.97
0.98
0 50 100 150IDC (A)
Charging efficiency variation with current.
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For a given SOC
Vary maximum current and
voltage
Calculate battery and charger power
loss
Integrate for energy loss
Matlab Model
End
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Loss as Function of Current and SOC
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Time as Function of Current and SOC
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Voltage Relationship Loss vs. Current for 3 Maximum Voltages Time vs. Current for 3 Maximum Voltages
The loss and time approaches an asymptote for higher maximum voltages. (E.g. setting a maximum voltage of 450 will yield the same result as 412.8V, as it cannot reach that voltage within the allotted time.)
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Observation•Raising the maximum voltage allows charging
to be achieved faster, but also creates more loss at the same current. Ultimately, the decrease in time corresponds to a lower loss.
•There is a current that will lead to minimum loss. This current is consistent throughout all SOC.
•This means that for all currents below this minimum, it is better to use the threshold current.
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Minimum Loss Algorithm
Determine Imin from
Input treq
treq < tmin
YesNo
treq = tmin
Determine SOCinit
Imin < Icmin
I = Icmin
Yes
I = Imin
No
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iz{1,1}
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dotprod6
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dotprod5
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dotprod4
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dotprod3
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dotprod2
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Mux
Mux
Weights
IW{1,1}(9,:)'
Weights
IW{1,1}(8,:)'
Weights
IW{1,1}(7,:)'
Weights
IW{1,1}(6,:)'
Weights
IW{1,1}(5,:)'
Weights
IW{1,1}(4,:)'
Weights
IW{1,1}(3,:)'
Weights
IW{1,1}(2,:)'
Weights
IW{1,1}(10,:)'
Weights
IW{1,1}(1,:)'
pd{1,1}
Output
a{1}
Process Output 1
Process Input 1
Layer 2
Layer 1
a{1}
Input
Implementation•A neural network was developed as a
function 𝑡 = 𝑓ሺ𝑆𝑂𝐶𝑖𝑛𝑖𝑡 ,𝐼𝑐,𝑉maxሻ
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Test in Simulation
# SOCinit treq (hrs) Loss (MJ) DLoss
1 20% 0.5 5.10 15.7%
2 20% 1.0 3.53 41.7%
3 20% 8.0 2.98 50.7%
4 50% 0.5 2.13 35.8%
5 50% 1.0 1.74 47.6%
6 50% 8.0 1.72 48.2%
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Conclusion and Future Work•A simple voltage and current selection
criterion is developed in CC-CV charging mode that will result in minimal loss for a given charging time.
•Both battery and charger loss are considered. The algorithm tested in simulation benefits both slow and fast charging.
•Experimental verification will be performed in the future.
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Acknowledgement
•CURENT faculty, staff, and graduate students
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Questions